Got this link from Bill, it suggests that sleep onset is mediated by an increased sensitivity to GABA in certain area's of the brain. The reason I found this so interesting was because of the idea that a particular cell/tissue can rapidly change its sensitivity to a hormonal signal and that this in-turn controls the behavior of the cell/whole organism.
This phenomenon seems to exist in other area's of physiology aswell. For example, in tanning. with UV exposure, the MC1R is upregulated in the skin, this in-turn increases the production of eumelanin which is a darker pigment and gives your skin a darker appearance or "tan" .
Another situation that this seems to exist is in exercise and muscle hypertrophy, it seems resistance training increases androgen receptor's ONLY in the exercised muscle, and its thought this increased sensitivity to androgens is what mediates muscle hypertrophy.
In the last post we saw a similar thing with brain melanocortin signalling and insulin sensitivity , I.E. an injection of MT-ii into the brain potently increased skeletal muscle GLUT4.
Anyway, its worth remembering that considering cell sensitivity is just as important if not more important than considering the generalized changes in concentrations of hormones in the blood/cerebral-spinal fluid.
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