ABSTRACT
This chapter aims to summarize our knowledge of the functions of major neurochemical systems projecting to the suprachiasmatic nuclei (SCN), and of intrinsic SCN neurochemicals in intercellular communication required for the generation of daily rhythms and their synchronization by external events. Neurophysiological studies both in vivo and in vitro have shown that light, optic nerve stimulation, and glutamate application activate most SCN cells in nocturnal rodents, and these effects can be blocked by local applications of glutamate receptor antagonists. The SCN receive a substantial innervation from the median raphe nucleus, bringing high levels of serotonin primarily to the ventral and medial SCN. The SCN receive a modest innervation from neurons in the basal forebrain and brainstem which contain acetylcholine. Circadian rhythms in electrical activity of the SCN have been demonstrated using both single- and multi-unit recordings from hamster and rat SCN neurons in hypothalamic slice preparations, and from the SCN of several species in vivo.
