Neurochemical Anatomy

The primary neurotransmitters for circadian rhythm generators are as follows. SCN neurons are mostly GABAergic. The neurotransmitter released from the RHT is glutamate, which affects both n-methyl-D-aspartate (NMDA) and non-NMDA receptors in the SCN. The putative neurotransmitters of the indirect pathway, GHT, are GABA and neuropeptide Y. Cholinergic agonists like carbachol also have an effect on activity of the SCN, and their administration shifts the activity of the SCN in a manner similar to that of light exposure. Less pronounced effects on SCN activity have been described following clonidine, an alpha-2 receptor agonist. The SCN also receives nonentrainment afferents from serotonergic projections of the median and dorsal raphe nucleus of the midbrain and histaminergic projections from the posterior hypothalamic tuberomammillary neurons. Vasopressin, neurophysin, and vasoactive intestinal polypeptide are important neurotransmitters in some of these efferent pathways from the SCN. The neurotransmitter from the SCN to the pineal is norepinephrine. y

The neurochemical constituents involved in the generation and maintenance of REM and NREM are listed in TabJe.,2,-1 . Neurochemically, REM sleep is associated with an increase in cholinergic activity and a reduction in noradrenergic and serotonergic activity. In contrast, SWS is associated with increased serotonergic activity .[ ] [ ] [ ]

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