Re: How does Serotonin help control sleep?

Dear Maz:

As I don't know your grade level, I will try the following answer first. I hope it will answer your question with satisfaction.

As you may know, our circadian rhythms are generated by the suprachiasmatic nuclei(SCN) of the hypothalamus in our brain. That is, the SCN generates electrophysical and metabolic cycles which repeat about 24 hours. This rhythm is synchronized to the environmental photoperiod (light cycle), which is also about 24 hrs. Light(photons) can induce phase-shifts in the SCN, which then controls our sleep-wake cycle. Photic information can also indirectly access the SCN through the intergeniculate leaflet(IGL).

The SCN, as well as IGL, receive very dense serotonergic innervation from midbrain raphe nuclei, where serotonin is produced. This means serotonin produced by raphe nuclei is released at the SCN and IGL and functions there. In fact, serotonin is a kind of inhibitory neurotransmitter that can modulate the effects of light on the SCN and IGL and thus the sleep-wake cycle. Serotonin functions by binding to its receptors in the SCN and IGL thus initiating signal transduction to inhibit the excitory effect of light on SCN.

The following observation is interestiing. When serotonin is directly applied to the SCN, it blocks light-induced phase-shift during subjective night but causes phase advance during subjective day!

Maz, do you get some sense about serotonin? If you have more questions, let me know, please.

Zong-Ping XIA