Wednesday, 17 April 2013

Cortisol, AVP, Oxytocin - Part II Stress Reactivity Model

I think today's post is going to be one of my better efforts.  We are continuing with the theme of Cortisol, depression and stress; but we are going to add two further chemicals, both "social neuropeptides".

The reason than today's post is worth reading is that it will bridge neurobiology and neuropsychology.   For me at least, psychology is light reading whereas biology needs more thought and understanding.  A social neuropeptide is a nice term not invented by me; it seems to come from Dr Stein from the University of Cape Town.

Rather than understand everything about human hormones, we are just trying to understand stress and coping mechanisms, so that we can reduce or  just better manage autistic behaviours. 


Cortisol is a hormone that is very easy to measure; saliva samples will do just fine.  Cortisol levels, or changes in cortisol levels, tell us about how the body is coping with emotion stress.  We are not talking about oxidative stress, but clearly there is direct linkage between the two.

We know that cortisol is a hormonal body clock (it maintains diurnal rhythms), cortisol levels should peak 30 minutes after waking, decline rapidly in the morning and then reach its lowest level in the evening.  This is well illustrated in the figure below, from an excellent study by Vahdettin Bayazit from Turkey.  He was studying the effect of exercise and stress on cortisol levels.


Children with ASD are known to have atypical response to stress and some have dysregulation of diurnal rhythms and abnormally high evening cortisol levels.  Among children with ASD there are significant individual differences, so the level of dysregulation is variable.  Note that many children with ASD have sleeping disorders; not surprising really if their body clock is malfunctioning.

In Bayazit's study he comments:-
"The more unexpected finding was that the evening values (of cortisol) for the children with autism tended to be consistently elevated in comparison with the neurotypical group."
I do not find this result surprising; in fact I would expect it.
He goes on to tell us that it is known that older children with depression have altered hormone levels, including hypersecretion of cortisol in the evening.
Now back to a stressful event.  In Turkey, a group of high functioning children with ASD were given a public speaking task; their heart rates and saliva cortisol were measured, before, after and during this "stressful event".
All we need to note is that the stress tended to cause a spike in cortisol level.

Stress Reactivity Model

Now we combine biology with psychology.  I took an existing model from an excellent book called "The neuropsychology of Autism".  Chapter 22 has a paper by Suma Jacob et al; she provided the biology and I just added the psychology (the opposite of what you might have expected)

This model shows how the equilibrium in managing stress is hopefully maintained.

The two little interlopers on the chart above, oxytocin and AVP are social neuropeptides.  Oxytocin is seen as beneficial; it reduces stress levels and gives a feeling of wellbeing.  AVP (Arginine Vasopressin) works in conjunction with CRH (Cortisol Releasing Hormone) to control the release of cortisol.  AVP seems to work in a "bad" way, in that it exaggerates/magnifies natural changes in cortisol.  So if you have a lot of AVP, a small spike in cortisol would become a big spike in cortisol.

Both AVP and cortisol have numerous other functions in the body. For example AVP is also known as the antidiuretic hormone (ADH) and a version of it is used in therapy in extreme cases of bedwetting by children. Whoever designed the human body was either short of chemicals, or likes to play practical jokes.

We already learned in Part I, that you can reduce your own level of cortisol just by singing.  It is reassuring to know that you do not always need drugs.  There are in fact other ways that you can maintain your own homeostatis and reduce cortisol.

A clever clinical psychologist from the University of Zurich, called Markus Heinrichs,  has provided us with an excellent study that compares the effect of social support vs oxytocin as regulators of stress.  What he did was to create two groups of people, in one group each subject brought along their best friend; the other group all came alone.  Then each subject was put through this stressful process:-

"During the introduction to the TSST (Trier Social Stress Test) they were then told that they would be required to give a 5-min mock job interview to an unknown panel (consisting of one man and one woman) on personal suitability for a job and to enumerate their strengths and qualifications in an unstructured manner, followed by 5 min of mental arithmetic performed out loud. To increase task engagement, the job description was matched to each participant, taking into consideration his own individual goals and aspirations. The panel of evaluators were presented as experts in the evaluation of nonverbal behavior."

The subjects were typical males in their early 20s.  Half the subjects had social support of a friend being present, and then each group had either a placebo or had a dose of oxytocin.  Here are the results:-

The base case is the "No social support + placebo".  This shows the highest increase in cortisol (i.e. stress).  The calmest group had "social support + oxytocin".  Of great interest is that the "social support + placebo" ended up less stressed than the "no social support + oxytocin".

This experiment showed the clear positive effect of both social support and oxytocin.

So in the stress reactivity model (the blue one up top) I decided to add social support and singing.  Clearly there are plenty of other social/psychological strategies that would likely have a similar cortisol reducing effect. 

Another dose of cortisol will come shortly in Part III.


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