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Thursday, 18 September 2014

GABA A Receptors in Autism – How and Why to Modulate Them


This post will get complicated, since it will look at many aspects of the GABA A receptor, rather than just a small fraction that usually appear in the individual pieces of the scientific literature. 

It was prompted by comments I have received from regular readers, regarding Bumetanide, Clonazepam, epilepsy and whether there might be alternatives with the same effect.  So it is really intended to answer some complex issues. 

There are some new interesting facts/observations that may be of wider interest, just skip the parts that too involved.

Regarding today’s picture, most readers of this blog are female and by the way, while the US is the most common location by far,  a surprisingly high number of page views come from France, Hong Kong, South Africa and Poland.


GABA

We have seen that GABA is one of the brain's most important neurotransmitters and we know that various forms of GABA dysfunction are associated with autism, epilepsy and indeed schizophrenia.

One recurring aspect in the research is the so-called excitatory-inhibitory balance of GABA.

The way the brain is understood to function assumes that GABA should be inhibitory and NMDA should be excitatory.

What makes GABA inhibitory is the level of the electrolyte chloride within the cells.  If the level is “wrong”, then GABA may be excitatory and the fine balance required with the NMDA receptor is lost.  The brain then cannot function as intended.




Source: Sage Therapeutics, a company that is developing new drugs that target GABAA and NMDA receptors

To understand what is going wrong in autism and how to treat it we need to take a detailed look at the GABAA receptor and all the anion transport mechanism associated with it.  Most research looks at either the receptor OR the transporters and exchangers.


Anion Transport Mechanisms of the GABAA receptor

You will either need to be a doctor, scientist or very committed to keep reading here.

We know that level of chloride within the cells is critical to whether GABA behaves as excitatory or inhibitory.  This has all been established in the laboratory.

The usual target in autism is the NKCC1 transporter that lets chloride INTO cells, but as you can see in the two figures below, there are other ways to affect the concentration of chloride.  

·        The KCC2 transporter lets chloride out of the cells

·        The sodium dependent anion exchanger (NDAE) lets chloride out of the cells

·        The sodium independent anion exchanger 3 (AE3), lets chloride in.  It extrudes intracellular HCO3- in exchange for extracellular Cl-.

All this does actually matter since we will be able to link it back to a known genetic dysfunction and it would suggest alternative therapeutic avenues.  We can also see how epilepsy fits into the picture.












NKCC1 in Autism

Without doubt, the transporter that controls the flow of chloride into the brain is the expert field of Ben Ari.

His recent summary paper is below:-


He showed that by reducing the level of chloride in the autistic brain using the common diuretic Bumetanide, a marked improvement in many peoples’ autism could be achieved


This post is really about expanding more on what he does not tell us.


KCC2 in Autism

In typical people, very early in life the KCC2 transporter develops and as a result level of chloride falls inside the cells, since the purpose of the transporter is to extrude chloride.

It appears that in autism this mechanism has been disrupted.  The existing science can show us what has gone wrong.

The following study shows that KCC2 is itself regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses.

It gets more interesting because the scientists looking for genetic causes of autism have already identified the gene that encodes NL2, which they call NLGN2 (neuroligin 2) as being associated with autism and schizophrenia (adult onset autism).





  

Abstract

Background

GABAA receptors are ligand-gated Cl- channels, and the intracellular Cl- concentration governs whether GABA function is excitatory or inhibitory. During early brain development, GABA undergoes functional switch from excitation to inhibition: GABA depolarizes immature neurons but hyperpolarizes mature neurons due to a developmental decrease of intracellular Cl- concentration. This GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl- outside neurons. However, the upstream factor that regulates KCC2 expression is unclear.

Results

We report here that KCC2 is unexpectedly regulated by neuroligin-2 (NL2), a cell adhesion molecule specifically localized at GABAergic synapses. The expression of NL2 precedes that of KCC2 in early postnatal development. Upon knockdown of NL2, the expression level of KCC2 is significantly decreased, and GABA functional switch is significantly delayed during early development. Overexpression of shRNA-proof NL2 rescues both KCC2 reduction and delayed GABA functional switch induced by NL2 shRNAs. Moreover, NL2 appears to be required to maintain GABA inhibitory function even in mature neurons, because knockdown NL2 reverses GABA action to excitatory. Gramicidin-perforated patch clamp recordings confirm that NL2 directly regulates the GABA equilibrium potential. We further demonstrate that knockdown of NL2 decreases dendritic spines through down-regulating KCC2.

Conclusions

Our data suggest that in addition to its conventional role as a cell adhesion molecule to regulate GABAergic synaptogenesis, NL2 also regulates KCC2 to modulate GABA functional switch and even glutamatergic synapses. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.



KCC2 in Peripheral nerve injury (PNI)

Autism is not the only diagnosis associated with reduced function of the KCC2 transporter; Peripheral nerve injury (PNI) is another.

In this condition researchers sought to counter the failure of KCC2 to remove chloride from within the cell by increasing the flow chloride through the Cl-/HCO3- anion exchanger known as AE3.


Abstract

Peripheral nerve injury (PNI) negatively influences spinal gamma-aminobutyric acid (GABA)ergic networks via a reduction in the neuron-specific potassium-chloride (K(+)-Cl(-)) cotransporter (KCC2). This process has been linked to the emergence of neuropathic allodynia. In vivo pharmacologic and modeling studies show that a loss of KCC2 function results in a decrease in the efficacy of GABAA-mediated spinal inhibition. One potential strategy to mitigate this effect entails inhibition of carbonic anhydrase activity to reduce HCO3(-)-dependent depolarization via GABAA receptors when KCC2 function is compromised. We have tested this hypothesis here. Our results show that, similarly to when KCC2 is pharmacologically blocked, PNI causes a loss of analgesic effect for neurosteroid GABAA allosteric modulators at maximally effective doses in naïve mice in the tail-flick test. Remarkably, inhibition of carbonic anhydrase activity with intrathecal acetazolamide rapidly restores an analgesic effect for these compounds, suggesting an important role of carbonic anhydrase activity in regulating GABAA-mediated analgesia after PNI. Moreover, spinal acetazolamide administration leads to a profound reduction in the mouse formalin pain test, indicating that spinal carbonic anhydrase inhibition produces analgesia when primary afferent activity is driven by chemical mediators. Finally, we demonstrate that systemic administration of acetazolamide to rats with PNI produces an antiallodynic effect by itself and an enhancement of the peak analgesic effect with a change in the shape of the dose-response curve of the α1-sparing benzodiazepine L-838,417. Thus, carbonic anhydrase inhibition mitigates the negative effects of loss of KCC2 function after nerve injury in multiple species and through multiple administration routes resulting in an enhancement of analgesic effects for several GABAA allosteric modulators. We suggest that carbonic anhydrase inhibitors, many of which are clinically available, might be advantageously employed for the treatment of pathologic pain states.

PERSPECTIVE:

Using behavioral pharmacology techniques, we show that spinal GABAA-mediated analgesia can be augmented, especially following nerve injury, via inhibition of carbonic anhydrases. Carbonic anhydrase inhibition alone also produces analgesia, suggesting these enzymes might be targeted for the treatment of pain




Treatment of neuropathic pain is a major clinical challenge that has been met with minimal success. After peripheral nerve injury, a decrease in the expression of the K–Cl cotransporter KCC2, a major neuronal Cl extruder, leads to pathologic alterations in GABAA and glycine receptor function in the spinal cord. The down-regulation of KCC2 is expected to cause a reduction in Cl extrusion capacity in dorsal horn neurons, which, together with the depolarizing efflux of HCO−3 anions via GABAA channels, would result in a decrease in the efficacy of GABAA-mediated inhibition. Carbonic anhydrases (CA) facilitate intracellular HCO−3 generation and hence, we hypothesized that inhibition of CAs would enhance the efficacy of GABAergic inhibition in the context of neuropathic pain. Despite the decrease in KCC2 expression, spinal administration of benzodiazepines has been shown to be anti-allodynic in neuropathic conditions. Thus, we also hypothesized that spinal inhibition of CAs might enhance the anti-allodynic effects of spinally administered benzodiazepines. Here, we show that inhibition of spinal CA activity with acetazolamide (ACT) reduces neuropathic allodynia. Moreover, we demonstrate that spinal co-administration of ACT and midazolam (MZL) act synergistically to reduce neuropathic allodynia after peripheral nerve injury. These findings indicate that the combined use of CA inhibitors and benzodiazepines may be effective in the clinical management of neuropathic pain in humans.

In conclusion, the major finding of the present work is that ACT and MZL act synergistically to inhibit neuropathic allodynia. In light of the available in vitro data reviewed above, a parsimonious way to explain this synergism is that CA inhibition blocks an HCO−3 -dependent positive shift in the Er of GABA and/or glycine-mediated currents and the consequent tonic excitatory drive mediated by extrasynaptic GABAA receptors, while preserving shunting inhibition that is augmented by benzodiazepine actions at postsynaptic GABAA receptors. Obviously, further work is needed at the in vitro level in order to directly examine the cellular and synaptic basis of the ACT-MZL synergism and clinical studies are required to determine the safety of intrathecally applied CA inhibitors in humans. Since MZL and ACT, as well as several other inhibitors of CA [37], are clinically approved, we propose that their use in combination opens up a novel approach for the treatment of chronic neuropathic pain


Midazolam and Acetazolamide

The therapeutic as well as adverse effects of midazolam are due to its effects on the GABAA receptors; midazolam does not activate GABAA receptors directly but, as with other benzodiazepines, it enhances the effect of the neurotransmitter GABA on the GABAA receptors (↑ frequency of Cl− channel opening) resulting in neural inhibition. Almost all of the properties can be explained by the actions of benzodiazepines on GABAA receptors. This results in the following pharmacological properties being produced: sedation, hypnotic, anxiolytic, anterograde amnesia, muscle relaxation and anti-convulsant.


Acetazolamide, usually sold under the trade name Diamox in some countries.  Acetazolamide is a diuretic, and it is available as a (cheap) generic drug.


In epilepsy, the main use of acetazolamide is in menstrual-related epilepsy and as an adjunct in refractory epilepsy.

Acetazolamide is not an immediate cure for acute mountain sickness; rather, it speeds up part of the acclimatization process which in turn helps to relieve symptoms.  I am pretty sure, many years ago, it was Diamox that I took with me when crossing the Himalayas from Nepal into Tibet.  We did not have any problems with mountain sickness.

If periodic paralysis above rings some bells it should.  Two forms already mentioned in this blog are Hypokalemic periodic paralysis and Andersen Tawil syndrome.  We even referred to a paper suggesting the use of Bumetanide.



Acetazolamide is a carbonic anhydrase inhibitor, hence causing the accumulation of carbonic acid Carbonic anhydrase is an enzyme found in red blood cells that catalyses the following reaction:


hence lowering blood pH, by means of the following reaction that carbonic acid undergoes






Anion exchanger 3 (AE3) in autism

Anion exchange protein 3 is a membrane transport protein that in humans is encoded by the SLC4A3 gene. It exchanges chloride for bicarbonate ions.  It increases chloride concentration within the cell.  AE3 is an anion exchanger that is primarily expressed in the brain and heart

Its activity is sensitive to pH. AE3 mutations have been linked to seizures


Bicarbonate (HCO3-) transport mechanisms are the principal regulators of pH in animal cells. Such transport also plays a vital role in acid-base movements in the stomach, pancreas, intestine, kidney, reproductive organs and the central nervous system.



Abstract

Chloride influx through GABA-gated Cl channels, the principal mechanism for inhibiting neural activity in the brain, requires a Cl gradient established in part by K+–Cl cotransporters (KCCs). We screened for Caenorhabditis elegans mutants defective for inhibitory neurotransmission and identified mutations in ABTS-1, a Na+-driven Cl–HCO3 exchanger that extrudes chloride from cells, like KCC-2, but also alkalinizes them. While animals lacking ABTS-1 or the K+–Cl cotransporter KCC-2 display only mild behavioural defects, animals lacking both Cl extruders are paralyzed. This is apparently due to severe disruption of the cellular Cl gradient such that Cl flow through GABA-gated channels is reversed and excites rather than inhibits cells. Neuronal expression of both transporters is upregulated during synapse development, and ABTS-1 expression further increases in KCC-2 mutants, suggesting regulation of these transporters is coordinated to control the cellular Cl gradient. Our results show that Na+-driven Cl–HCO3 exchangers function with KCCs in generating the cellular chloride gradient and suggest a mechanism for the close tie between pH and excitability in the brain.




Abstract

During early development, γ-aminobutyric acid (GABA) depolarizes and excites neurons, contrary to its typical function in the mature nervous system. As a result, developing networks are hyperexcitable and experience a spontaneous network activity that is important for several aspects of development. GABA is depolarizing because chloride is accumulated beyond its passive distribution in these developing cells. Identifying all of the transporters that accumulate chloride in immature neurons has been elusive and it is unknown whether chloride levels are different at synaptic and extrasynaptic locations. We have therefore assessed intracellular chloride levels specifically at synaptic locations in embryonic motoneurons by measuring the GABAergic reversal potential (EGABA) for GABAA miniature postsynaptic currents. When whole cell patch solutions contained 17–52 mM chloride, we found that synaptic EGABA was around −30 mV. Because of the low HCO3 permeability of the GABAA receptor, this value of EGABA corresponds to approximately 50 mM intracellular chloride. It is likely that synaptic chloride is maintained at levels higher than the patch solution by chloride accumulators. We show that the Na+-K+-2Cl cotransporter, NKCC1, is clearly involved in the accumulation of chloride in motoneurons because blocking this transporter hyperpolarized EGABA and reduced nerve potentials evoked by local application of a GABAA agonist. However, chloride accumulation following NKCC1 block was still clearly present. We find physiological evidence of chloride accumulation that is dependent on HCO3 and sensitive to an anion exchanger blocker. These results suggest that the anion exchanger, AE3, is also likely to contribute to chloride accumulation in embryonic motoneurons.



Sodium dependent anion exchanger (NDAE)

Not much has been written about these exchangers, outside of very technical literature.



Sodium-coupled anion exchange is activated by intracellular acidification (Schwiening and Boron, 1994), suggesting that regulation of the chloride gradient by NDAEs may be closely linked to the regulation of cellular pH. As prolonged neuronal activity can cause neuronal acidification by efflux of bicarbonate through GABAA receptors (Kaila and Voipio, 1987), sodium-coupled anion exchange may help to maintain a hyperpolarizing chloride reversal potential and thus promote the inhibitory action of GABA. Thus activation of sodium-coupled anion exchange by acidosis may also contribute to seizure termination by promoting a more negative chloride reversal potential and thus promoting the inhibitory effects of GABA.



The GABAA receptor  (background is cut and paste from Wikipedia)

In order for GABAA receptors to be sensitive to the action of benzodiazepines they need to contain an α and a γ subunit, between which the benzodiazepine binds. Once bound, the benzodiazepine locks the GABAA receptor into a conformation where the neurotransmitter GABA has much higher affinity for the GABAA receptor, increasing the frequency of opening of the associated chloride ion channel and hyperpolarizing the membrane. This potentiates the inhibitory effect of the available GABA leading to sedative and anxiolytic effects.


Structure and function





Schematic diagram of a GABAA receptor protein ((α1)2(β2)2(γ2)) which illustrates the five combined subunits that form the protein, the chloride (Cl-) ion channel pore, the two GABA active binding sites at the α1 and β2 interfaces, and the benzodiazepine (BDZ) allosteric binding site

The receptor is a pentameric transmembrane receptor that consists of five subunits arranged around a central pore. Each subunit comprises four transmembrane domains with both the N- and C-terminus located extracellularly. The receptor sits in the membrane of its neuron, usually localized at a synapse, postsynaptically. However, some isoforms may be found extrasynaptically. The ligand GABA is the endogenous compound that causes this receptor to open; once bound to GABA, the protein receptor changes conformation within the membrane, opening the pore in order to allow chloride anions (Cl) to pass down an electrochemical gradient. Because the reversal potential for chloride in most neurons is close to or more negative than the resting membrane potential, activation of GABAA receptors tends to stabilize or hyperpolarise the resting potential, and can make it more difficult for excitatory neurotransmitters to depolarize the neuron and generate an action potential. The net effect is typically inhibitory, reducing the activity of the neuron. The GABAA channel opens quickly and thus contributes to the early part of the inhibitory post-synaptic potential (IPSP).

Subunits

GABAA receptors are members of the large "Cys-loop" super-family of evolutionarily related and structurally similar ligand-gated ion channels that also includes nicotinic acetylcholine receptors, glycine receptors, and the 5HT3 receptor. There are numerous subunit isoforms for the GABAA receptor, which determine the receptor's agonist affinity, chance of opening, conductance, and other properties.
In humans, the units are as follows:
There are three ρ units (GABRR1, GABRR2, GABRR3), however these do not coassemble with the classical GABAA units listed above,[18] but rather homooligomerize to form GABAA-ρ receptors (formerly classified as GABAC receptors but now this nomenclature has been deprecated[19] ).
Five subunits can combine in different ways to form GABAA channels. The minimal requirement to produce a GABA-gated ion channel is the inclusion of both α and β subunits, but the most common type in the brain is a pentamer comprising two α's, two β's, and a γ (α2β2γ)
The receptor binds two GABA molecules, at the interface between an α and a β subunit



The important subunits for this post are:-
GABRA2,
Very little is written about this subunit.

GABRA3
While the effect of editing on protein function is unknown, the developmental increase in editing does correspond to changes in function of the GABAA receptor. GABA binding leads to chloride channel activation, resulting in rapid increase in concentration of the ion. Initially, the receptor is an excitatory receptor, mediating depolarisation (efflux of Cl- ions) in immature neurons before changing to an inhibitory receptor, mediating hyperpolarization(influx of Cl- ions) later on. GABAA converts to an inhibitory receptor from an excitatory receptor by the upregulation of KCC2 cotransporter. This decreases the concentration of Cl- ion within cells. Therefore, the GABAA subunits are involved in determining the nature of the receptor in response to GABA ligand. These changes suggest that editing of the subunit is important in the developing brain by regulating the Cl- permeability of the channel during development. The unedited receptor is activated faster and deactivates slower than the edited receptor.


Editing of the I/M site is developmentally regulated

A switch in the GABA response from excitatory to inhibitory post-synaptic potentials occurs during early development where an efflux of chloride ions takes place in immature neurons, while there is an influx of chloride ions in mature neurons (Ben-Ari 2002). GABA switches from being excitatory to inhibitory by an up-regulation of the cotransporter KCC2 that decreases the chloride concentration in the cell. However, if GABA itself promotes the expression of KCC2 is still under debate (Ganguly et al. 2001; Ludwig et al. 2003; Titz et al. 2003). Further, the α subunits are critical elements in determining the nature of the GABAA receptor response to GABA (Böhme et al. 2004). The α3 mRNA (Gabra-3) is present at high levels in several forebrain regions at birth with a major decline after post-natal day 12 (P12), when the expression of α1 is going up (Laurie et al. 1992). The change from α3 to α1 may cause the switch in GABA behavior from excitatory to inhibitory post-synaptic potentials during development.
GABAA receptors respond to anxiolytic drugs such as benzodiazepines and are thus important drug targets. The benzodiazepine binding site is located at the interface of the α and γ2 subunits (Cromer et al. 2002). Antagonists that bind to this site enhance the effect of GABA by increasing the frequency of GABA-induced channel opening events. Post-transcriptional modifications of the α3 subunit, such as the I/M editing described here, could be important in determining the mechanistic features that are responsible for the diversity of GABAA receptors and the variability in sensitivity to drugs

Ligands

A number of ligands have been found to bind to various sites on the GABAA receptor complex and modulate it besides GABA itself.

Types

  • Agonists: bind to the main receptor site (the site where GABA normally binds, also referred to as the "active" or "orthosteric" site) and activate it, resulting in increased Cl conductance.
  • Antagonists: bind to the main receptor site but do not activate it. Though they have no effect on their own, antagonists compete with GABA for binding and thereby inhibit its action, resulting in decreased Cl conductance.
  • Positive allosteric modulators: bind to allosteric sites on the receptor complex and affect it in a positive manner, causing increased efficiency of the main site and therefore an indirect increase in Cl conductance.
  • Negative allosteric modulators: bind to an allosteric site on the receptor complex and affect it in a negative manner, causing decreased efficiency of the main site and therefore an indirect decrease in Cl conductance.
  • Open channel blockers: prolong ligand-receptor occupancy, activation kinetics and Cl ion flux in a subunit configuration-dependent and sensitization-state dependent manner.
  • Non-competitive channel blockers: bind to or near the central pore of the receptor complex and directly block Cl- conductance through the ion channel.

The GABAA receptor include a site where benzodiazepine can bind.  These are drugs that include like valium. Binding at this site increase the effect of GABA.  Since this receptor is meant to be inhibitory, giving valium should make it strong inhibitory, ie calming. 

It was noted that in autism the effect of valium was often the reversed, instead of calming it further increased anxiety.

The Valium is working just fine, it is magnifying the effect the effect of GABA, the problem is that the receptor is functioning as excitatory, the Valium is making it over-excitatory.  Now we come to the reason why.

We know that the excitatory-inhibitory balance is set by the chloride concentration within the cells.  We also know that exact mechanism that determines this level.


 Highlights

BTBR mice have reduced spontaneous GABAergic inhibitory transmission
Nonsedating doses of benzodiazepines improved autism-related deficits in BTBR mice
Impairment of GABAergic transmission reduced social interaction in wild-type mice
Behavioral rescue by low-dose benzodiazepine is GABAA receptor α2,3-subunit specific

Summary

Autism spectrum disorder (ASD) may arise from increased ratio of excitatory to inhibitory neurotransmission in the brain. Many pharmacological treatments have been tested in ASD, but only limited success has been achieved. Here we report that BTBR T+ Itpr3tf/J (BTBR) mice, a model of idiopathic autism, have reduced spontaneous GABAergic neurotransmission. Treatment with low nonsedating/nonanxiolytic doses of benzodiazepines, which increase inhibitory neurotransmission through positive allosteric modulation of postsynaptic GABAA receptors, improved deficits in social interaction, repetitive behavior, and spatial learning. Moreover, negative allosteric modulation of GABAA receptors impaired social behavior in C57BL/6J and 129SvJ wild-type mice, suggesting that reduced inhibitory neurotransmission may contribute to social and cognitive deficits. The dramatic behavioral improvement after low-dose benzodiazepine treatment was subunit specific—the α2,3-subunit-selective positive allosteric modulator L-838,417 was effective, but the α1-subunit-selective drug zolpidem exacerbated social deficits. Impaired GABAergic neurotransmission may contribute to ASD, and α2,3-subunit-selective positive GABAA receptor modulation may be an effective treatment.
  
These results indicate that different subtypes of GABAA receptors may have opposite roles in social behavior, with activation of GABAA receptors containing α2,3 subunits favoring and of GABAA receptors with α1  subunits reducing social interaction, respectively.

Because of their broad availability and safety, benzodiazepines and other positive allosteric modulators of GABAA receptors administered at low nonsedating, nonanxiolytic doses that do not induce tolerance deserve consideration as a near-term strategy to improve the core social interaction deficits and repetitive behaviors in ASD.

These results are most consistent with the hypotheses that reduced inhibitory neurotransmission is sufficient to induce autistic-like behaviors in mice and that enhanced inhibitory neurotransmission can reverse autistic-like behaviors.



Epilepsy

I have received various comments about epilepsy.  Epilepsy has many variants, just like autism.  Epilepsy is often comorbid with autism.  GABA dysfunction is known to be closely involved in some types of autism and some types of epilepsy.

It is known that Bumetanide has very different effects in different types of epilepsy.
The question that naturally arises is whether you can give Bumetanide to someone who has autism and epilepsy and if you cannot, is there an alternative with the same desired effect?

Well it appears that any method that changes chloride levels is likely to affect epilepsy.  It appears that all three methods (NKCC1, KCC2 and AE3) would likely have the same impact on epilepsy.

But would it be a good effect or a bad effect?

Would it interact with any existing anti-epilepsy drugs?

I suspect that Bumetanide might be an effective anti-epileptic in people with autism and that other GABA related drugs might no longer be needed.  Quite likely the effect of Bumetanide and the anti-epileptic targeting GABA might be too much.  So the blog reader that pointed out that the bumetanide clinical trial excluded children with epilepsy has highlighted an important point.

While epilepsy is not fully understood and there are various variants, it would seem plausible that the epilepsy common in core classic autism and early regressive autism is the same type and that it is linked to the same excitatory/inhibitory dysfunction.

You may be wonder if other diuretics have anti-epileptic properties. Here is a paper by a Neurologist from Denver on the subject:-




Why is there an excitatory/inhibitory dysfunction in Autism?

People are writing entire books on the GABA excitatory/inhibitory balance.  I was curious as to why this dysfunction exists at all in autism. 

We learnt from Ben-Ari in earlier posts all about this switch from excitatory to inhibitory that is supposed to occur very early on in life, we now have two reasons why this may fail to happen in autism:-

1.     Editing modifies the GABAA receptor subunit α3.  The change from α3 to α1 may cause the switch in GABA behavior from excitatory to inhibitory post-synaptic potentials during development.  This change appears not to occur in some types of autism.  We see from the Clonazepam research that α3 and  α1 have opposite effects in autism.   In autism, activation of GABAA receptors containing α2,3 subunits favours social interaction  and activation of α1  subunits reduces social interaction.

And/Or

2.     The GABA functional switch is mainly mediated by the up-regulation of KCC2, a potassium-chloride cotransporter that pumps Cl- outside neurons.  NL2 also regulates KCC2 to modulate GABA functional switch. Therefore, NL2 may serve as a master regulator in balancing excitation and inhibition in the brain.  The gene that encodes NL2 is called NLGN2 (neuroligin 2).  Dysfunction in gene NLGN2 is known to occur in both autism and schizophrenia (adult onset autism).


Conclusion

We came full circle back to Bumetanide and Clonazepam as most likely the safest and most effective therapy to adjust the E/I (excitatory/inhibitory) balance in autism. KCCI agonists do not seem to exist.  The bicarbonate exchanger agonist Acetazolamide/Diamox is another common diuretic and I see no reason why it would not also be effective, but we would then affect bicarbonate levels.  Since these ions play a role in controlling pH levels, I think we might risk seeing some unintended effects.  We know that Bumetanide is safe in long term use.  We know that all diuretics that change chloride level within the cell and will affect epilepsy; so it is a case of “better the devil you know”. 

I finally understood exactly why tiny dose of Clonazepam are effective and how this fits in with the changes the Bumetanide has produced.  Thankfully, such tiny doses are free of the typical side effects expected from benzodiazepines.  One tablet lasts 10 days.

It also answers somebody else’s question about starting with Clonazepam before the Bumetanide.  If you did that you might well make things much worse, you would magnify the unwanted excess brain cell firing.  Once you added bumetanide things would then reverse and brain cell firing would be inhibited.

I rather like the parallel with neuropathic pain, the other condition we looked at with reduced KCC2 transporter function, the researchers there proposed the combination of a diuretic (Acetazolamide) to lower cellular chloride (via exchanger AE3) and a benzodiazepine (Midazolam) as a positive allosteric modulator.  This is extremely similar to Ben Ari’s bumetanide (diuretic affecting transporter NKCC1) plus Catterall’s tiny doses of clonazepam (benzodiazepine) as a positive allosteric modulator.

As for epilepsy and bumetanide, we know that bumetanide has different effects on different types of autism. It seems plausible that people with autism might tend to have the same type of epilepsy.  In any case Monty, aged 11 with ASD, does not have epilepsy/seizures and I suspect taking bumetanide has decreased the chance he ever will.  Of course I cannot prove this, it is just conjecture.






28 comments:

  1. Thank you for this remarkable in-depth review. I have personally tried Bumetanide for 4 months, with discernible cognitive effects. However, the side-effects of hypotension and Raynauds are difficult to deal with. Do you know of any medications to counter these effects, and would you elaborate on why changing to clonazepam would be unadvisable?

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    Replies
    1. Perhaps you are not drinking enough water. Drinking more fluids will increase the volume of your blood, which will raise your blood pressure. Perhaps by taking Bumetanide you have become dehydrated and your problems stem from this. You should expect to drink much more fluids if you take bumetanide; for autism the diuresis effect is just the side effect of the drug. You need to replace the lost fluids.

      Clonazepam in tiny doses is worth a try with or without the Bumetanide. But it seems possible that without the Bumetanide, it may just magnify the existing excitatory/inhibitory inbalance. In this case it would make the symptoms worse. The research done was on two mouse models, not humans. It is not clear that these mice have the genuine excitatory/inhibitory inbalance of humans with autism.

      Lemmonier's experience was that in some autistic people drugs of this type (benzodiazepines) often worked in reverse. So valium was not calming, rather it caused agitation

      The dose of Clonazepam is extremely low. I think the only way to find out for sure would be to try it.

      Large doses of Clonazepam are often given to people with autism with seizures. It does not work in reverse for them.

      The mechanism behind the micro dose and the large dose may indeed be different.

      Delete
  2. Peter, I’ve read this post several times and I think your analysis is outstanding.

    If I have understood correctly, when inhibitory function of GABA is restored with bumetanide, then activating GABA A receptor might be beneficial, at least with a correct, low dose of benzodiazepines. I wonder if that is relevant also to drugs that increase the synaptic availability of GABA (e.g. valproate). When we decided to give our son bumetanide, he was still on a very low dose of valproate, which was then withdrawn within few days. In just hours from the first bumetanide tablet his mood changed radically for the better and he surprised us with social behaviors in the next week. Unfortunately he got a cold later and became generally unwell. The good effects of bumetanide continue, but what I saw at the beginning was striking. Maybe it’s just typical effect of bumetanide?

    I am about to decide: back to low dose valproate or try clonazepam. I have one question and would be grateful for practical help: how do you dissolve clonazepam? Can you make a transparent, homogeneous liquid with the tablets you use? Are they soluble? Ours is more like a cloudy suspension and when left overnight some “sediments” can be seen… I can’t describe it well in English, but I am not sure how to prepare this solution to be sure about the dose.

    By chance I found something intriguing, while trying to understand my son’s recent EEG: “Concomitantly with the inflammation, changes in expression of NKCC1 and KCC2 co-transporters have been observed that resemble the immature brain”: http://www.epilepsybehavior.com/article/S1525-5050(10)00695-5/fulltext
    However, the paper referenced for this statement is about epilepsy and is quite unreadable for me.

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    1. Agnieszka, I think trying a small dose of valproate is a very interesting idea. The effect of bumetanide on my son was not immediate, it took a few days. When there is an effect within hours, something interesting must be going on.

      When I introduced Clonazepam, Monty was taking bumetanide once a day in the morning. It was in the afternoons that I first noticed the behavioral change. I think they are complementary and because the clonazepam dose is so tiny I see no reason to stop it.

      In terms of impact, the broccoli/sulforaphane effect is greater than clonazepam. That too was a near instant change. So far almost everyone I have feedback from, has found the broccoli powder works and from the first dose.

      Clonazepam is not soluble in water. I have a small electric mixer, which in some countries is used to mix instant coffee to make it frothy. It fits inside a 100ml medicine bottle, so I "dissolve" the pill in water and then mix well with my mixer. Then each time I give use the bottle I give it a good shake and then use a syringe to withdraw say 4ml from near the bottom. The very last part of the bottle I through away, since it is over-concentrated.

      In pharmacies they have a special "syrup" that holds such powders in suspension.

      I do not know about any other effects of valproate. If a tiny dose makes the bumetanide effect greater, that would be great. It also has a sound basis behind it.

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    2. Having read all that once more, I gave Mateusz valproate in the lowest dose he took before. I saw the same type of social behavior as previously, although this time it did not happen immediately, but after 3 days of valproate: he became much more social e.g. spontaneously giving hugs and kisses (the last one is something that never happened before in his life). The change was distinct, visible to people other than family and it was not seen with bumetanide alone. This was accompanied by quite euphoric mood, but then also some anxiety. I lowered the valproate dose, currently it’s less about a twentieth of a dose recommended him a year ago for mood stabilisation. The “hugging effect” continues. He wakes up at night more often though - have you experienced such effect with clonazepam?

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    3. For the first few days clonazepam also produced euphoria, it no longer does. Sulforaphane/broccoli also did the same. What dose of valproate are you now giving? It will be very interesting to see if the positive effects continue.

      The broccoli also increased anxiety slightly and made him more interested in talking than sleeping. I think it will take time to reach a new equilibrium.

      I think it is inevitable that at the start sleep will be affected by these interventions. You will just need to experiment and find the best combination. I suspect in different people the combination will vary. The good thing is that we are talking about tiny doses, so side effects and tolerance are less likely to be a problem.

      Having "re-purposed" GABA, to increase it does make sense. I read recently that a significant number of the newly identified autism genes are related to GABA. So doing whatever possible to correct these dysfunctions does seem a good focus to have.

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    4. Thank you for reply. In fact, the sleep issues seem to decrease.

      At the moment I use valproate 1 mg/kg body weight daily, but will try to lower this dose further. My son took 20 mg/kg for mood stabilisation previously, however always tested below levels considered therapeutic. Fortunately he doesn’t mind blood drawing (provided he gets some extra jelly beans afterwards of course), so I am also going to check this.

      In my son, his unstable mast cell activation/allergic condition as well as other treatments influence his behaviors, but this ‘social effect’ seem to be associated with the concurrent use of bumetanide and low dose valproate. Few months ago, when he was still on high dose valproate I tried bumetanide for ten days, but I did not see anything like that.

      I will let you know when I am able to say more about these valproate and bumetanide effects also with regard to EEG, which I think it would be better to have without epileptiform sleep activity...

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    5. It will be very interesting to see the longer term effect of bumetanide plus the low dose of valproate. Perhaps valproate, in low doses, is a positive allosteric modulator of the GABA receptor? Or perhaps it has another unknown effect?

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  3. Valproate has a “black box warning” for adverse events, clonazepam does not. Valproate has not been studied in this context even on mice. These are the main cons, hopefully they are not that bad for tiny doses.

    Sprouts have been already on the way and perhaps addressing oxidative stress and inflammation may be the best step to decrease hyperexcitability, but in the sulforaphane study two participants had unprovoked seizure and they “cannot rule out the possibility of seizures as an adverse effect of sulforaphane in ASD”. To be on the safe side I will try the idea of potentiating “GABA-ergic” effect of bumetanide first. My son has strange EEG.

    A year ago I wouldn’t believe that a frappe mixer and an oxygen tank might be necessary to deal with my son’s autism issues ;-) Also I wouldn’t believe he can ever get mainstreamed. Thank you for all help.

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  4. HI Peter,
    I am reading one of your posts about the GABAA receptor. As I trying to find a way to discover what to try for my son's facial grimacing, jaw tensing/contraction, and vocalizations, I have thought GABA was an issue.
    When I give him small doses of valium (5 mg for blood draws) it definitely has a calming effect on his otherwise often physically agitated body.
    Does that help one deduce that the GABA receptors are, in fact, acting properly and I should be considering that some other dysfunction might be largely responsible for his motor and vocalization issues?Thanks
    Nancy

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    1. Hi Nancy, your discovery is very interesting.
      It appears that the active substance is something called Thujone.
      It affects both GABA and 5-HT3 receptors in the brain. It is found in essentials oils, perfume and even the drink Absinthe. It is found in wormwood and some species of mint.
      As a GABAa antagonist it should shift the excitatory/inhibitory balance towards excitatory and thus can cause convulsions at high doses.
      It is the opposite of valium, and can be used to counter its effects.
      The other effects are not surprisingly sleeplessness and anxiety.
      The fact that valium works as it should does not rule out a GABA dysfunction, since there are different types. There is no way of knowing for sure what will help, but there are certainly things well worth trying.
      I would try the GABAa drugs Bumetanide and low dose Clonazepam. This would mainly affect cognition and, by consequence, other behavior. These have both proved effective by readers of this blog and have a sound scientific basis for their use.
      I would also try the GABAb drugs like Baclofen. Baclofen is often used for spasticity and so it could well help with jaw tensing/contraction etc which may just be symptoms of the underlying dysfunction. Baclofen does seem to help people with Asperger’s for anxiety, and a smaller number of people with classic autism and Fragile X.
      GABAb has a connection to growth hormones and I think that in people whose growth patterns are unusual this may be a pointer as to why. In autism you often have extremes, so you have big heads, small heads, large stature, small stature and also people who start out big for their age and end up small for their age.

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  5. Nancy, I don't pretend to know but my son's facial grimacing was tied to strep. Does he have high titers for Group A strep (and waxing and waning, etc).

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  6. Hi, my son also has facial grimacing tied to group A strep,he almost always has sore trhorat and low white t cells.valentina

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  7. Peter, one striking and very personal memory just hit me. If you'd be kind and elaborate (speculate) for me, if possible?
    Here goes:
    While we were waiting for our daughters diagnose, I typically fell into some kind of anxiety/depression state.
    My doctor first prescribed a mild benzodiazepine for me (oxazepam, 5-10 mg) to relieve the stress. Unfortunately this had a rather bad effect and I felt nervous, confused and "unreal". This would be rather surprising, not only because the effect should be calming but also since the dosage was so low.
    Of course I stopped taking it after a week or so.

    My question is: What could be the cause for this? Can I have excitatory GABA without being autistic?
    If so, what would the implication be for that "feat" being acquired at birth vs acquired later in life (due to stress and somee genetical predisposition)?

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    1. It looks like excitatory GABA can be a feature of various conditions, including autism. So it does not define autism, but it is a step towards it. I would guess that this is something people are born with.

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    2. Seems that around 1-2 % of all people have this type of adverse effects to benzodiazepines, some even get aggressive, impulsive or psychotic. There could of course be some other explanation to this than excitatory GABA, though the other theories I've seen doesn't sound as plausible.
      I just find it very interesting that this might be a more common condition than previously known.
      One question is if it always is a handicap (brain fog) or if it under some conditions is beneficial?
      Another one is if it's a condition that can be acquired anytime in life and also reversed permanently. And a third one, could you have different severity of this condition, so that some people have mixed GABA?
      Hmm.

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    3. Interesting and good to hear I am not the only one. Long ago I was given diazepam post-surgery, supposedly to help me with calm sleep. It kept me awake then for two days. My thoughts were racing and very far from calm.

      Actually that's why I hoped for Bumetanide effect in my child.

      I don't think I am aggressive or psychotic or brain-fogged.

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    4. This paper do suggest that the GABAA inhibitory strength (and even direction if I understand it correctly) can be tuned up and down:
      Neuronal chloride transport tuning.(Lancet 2015)
      "KCC2 transport strength varied considerably in magnitude depending on the combination of alanine mutations present on the protein. KCC2 transport strength determined the direction and magnitude of GABAA receptor-mediated current amplitudes and was observed to have a linear correlation with the reversal potential of GABAergic currents."

      I am not aggressive nor psychotic either, and not brain-fogged enough to be unable to follow this blog. Maybe this is just wishful thinking, but could it be possible that a little bit of excitatory GABAA makes you slightly more intelligent (and more prone to cognitive overload)??
      (Anonymous nr 1 here)

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    5. Anonymous (whats the plural),

      Well, since both of you had an abnormal reaction to benzodiazepine, how did your trial of bumetanide on your children turn out, if you happened to carry it out.

      Alprax (alprazolam) kept me wired for two days, similar reaction to yours, so it seems I finally belong somewhere. Me? Agressive? No. Psychotic? Not sure. Brain fogged...maybe a little as I could not make out whether these traits were manifested as a side effect of the drug or defined a personality type who react atypically to benzodiazepines.

      Did either of you try bumetanide on your kid?

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    6. Many traits of autism can have benefits. Lack of sensory gating = great situational awareness, for example.

      It may well be that a little shift in the E/I balance towards E does increase IQ. Some autism is known to be associated with high IQ, just look at all the very clever profesors etc who end up with a child with classic autism.

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    7. Anonymous nr 1 here again.
      I actually am a Mensa member... And there are a lot of Aspberger people in that community, though I am not one of them.
      Kritika: Neiher me or my kid has tried bumetanide yet.
      Thinking of how eventually excitatory GABA can give some advances, it is a worrysam thought that by using bumetanide your childs brain will be rewired to a state where GABA is solely inhibitory. And, if someone comes up with another treatment one day (like suramin or whatever), that there might not be a way back to a life without bumetanide (where GABAA is partially excitatory).
      This is highly speculative of course, but without facts we are left to imagination.

      This excitatory GABAA thing - it seems very related to hypothyroidism. See for example: https://www.ncbi.nlm.nih.gov/m/pubmed/19087168/ "Hypothyroidism impairs chloride homeostasis and onset of inhibitory neurotransmission in developing auditory brainstem and hippocampal neurons."
      Perhaps this is true not only in the child, but also in the mother. I do have hypothyroidism, my kid not. How about you?

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    8. #1, use of bumetanide gives an effect that is reversible. We also need to note that excitatory and inhibitory are two ends of a spectrum. Bumetanide shifts the effect of GABA towards inhibitory, but not far enough in many cases. So many responders to bumetanide may benefit from further intervention.

      After a few days with no bumetanide the E/I (im)balance returns to where it was. There appears to be no lasting effect.

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    9. Hello anonymous 1,

      In fact, yes, I did develop subclinical hypothyroidism during my first trimester (actually that was the first time I got it tested). Now, I am not sure how that is linked to excitatory gaba which you say might be linked to some positives (not using the term intellect here) but I sure have read how even minor hypothyroidism in a pregnant woman can cause a whole lot of developmental problems in the child.

      Well, I liked how you evoked a post suramin or post bumetanide scenario but as of now I feel we realy could use some help in getting the gaba to start becoming a little inhibited, if that is what my son has issues with. Dis'abilities' do have 'abilities' but I need to get to a point where my son can use them. I am fond of myself, quirks and all, but I am worried if my son will ever have the freedom to choose what he wants to be and to be fond of it.

      A few days back I was joking with my biotechnologist sister about how I must be a smart woman as I birthed a child with autism . She replied she is certainly smarter as she birthed none (she is childless). Intellect, reproductive health, health of progeny. Dangerous terrain!

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    10. Bumetanide increased cognitive abilities in my son. In a reversible way: few days without bumetanide makes him can't find basic words.

      I haven't tried bumetanide myself, but appreciate some other interventions from this blog.

      Well, I was diagnosed with subclinical hypothyroidism, but only in my second pregnancy and it is my older child who developed severe autism. The younger is the most social person in my family. Nothing seems simple actually.

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    11. Hypothyroidism often gets "worse" the longer you are pregnant. If you already have it, you need to be monitored regularly during pregnancy and often up your medicines gradually until birth. At birth you stop all extra medicine. Of course you can start without hypothyroidism and develop it halfways through pregnancy too.

      I found an interesting paper eventually explaining the link between hypo/hyperthyroidism and GABA. It's from 2006 and deals mostly with mice, so there is probably more recent findings:

      "Thyroid hormone and gamma-aminobutyric acid (GABA) interactions in neuroendocrine systems."

      "Thyroid hormones have effects on multiple components of the GABA system. These include effects on enzyme activities responsible for synthesis and degradation of GABA, levels of glutamate and GABA, GABA release and reuptake, and GABA(A) receptor expression and function. In developing brain, hypothyroidism generally decreases enzyme activities and GABA levels whereas in adult brain, hypothyroidism generally increases enzyme activities and GABA levels. Hyperthyroidism does not always have the opposite effect (..) There is substantial evidence that THs also have an extranuclear effect to inhibit GABA-stimulated Cl(-) currents by a non-competitive mechanism in vitro. (..) In (..) humans, GABA inhibits thyroid stimulating hormone (TSH) release from the pituitary (..) strong support for the hypothesis that there is reciprocal regulation of the thyroid and GABA systems in vertebrates."
      https://www.ncbi.nlm.nih.gov/pubmed/16527506

      Kritika, I can see that you have a certain touch of humour running in the family! *smiling*

      /Ling

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  8. Peter, I think apple juice before bedtime may help with late onset sleep.
    One reason I could come up with is that fruit juices can act as OATPs and as a result there may be accumulation of the melatonin I supplement (3mg orally, plus 1mg spray).
    Of course I can't be sure about that because apple juice may also reduce the bioavailability of melatonin. We don't know what happens with different kinds of juice and drugs.
    I looked into apple juice research and found out lots of relevant to autism interesting facts.

    Apple juice concentrate maintains acetylcholine levels following dietary compromise.

    Chan A1, Graves V, Shea TB.

    Supplementation with apple juice can compensate for folate deficiency in a mouse model deficient in methylene tetrahydrofolate reductase activity.

    Chan A1, Ortiz D, Rogers E, Shea TB.

    I have no idea if acetylcholine or methylfolate deficiencies have anything to do with sleep, though.

    There are people on the internet claiming that apple juice helps with sleep and makes them have vivid dreams, without explaining the scientific basis.

    Peter, I'd like to ask you if melatonin plus apple juice seems a bad idea to you.
    Speaking of fruit juice I wanted to know the precautions you take concerning the possible interactions with drugs, particularly with Bumetanide. In order to make up for the loss of fluids and potassium it's inevitable to give juice and I am confused about adverse or favourable side effects.

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    1. Petra, apple juice is not going to do any harm. Another juice you might want to try is pomegranate, which is very common in Greece. It may have all kinds of beneficial effects, including anti-inflammatory (reduces IL6) and antioxidant.

      To compensate for loss of fluids, water is best. At low doses drug interactions are much less of an issue, most interactions either increase or reduce the effect of the drug, but this effect stays the same. Some interactions can indeed be beneficial, eg diamox plus bumetanide.

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  9. Anomymous, For me, as a mother/caregiver of a young adult Asperger's with High IQ and savant traits, this is also the case: intelligence leading to cognitive overload and anxiety. Pathology is like the two sides of the same coin and I am trying to keep cognition and at the same time help with overload and consequences.
    I still don't know how/if this could be achieved.

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