Circadian rhythm of suprachiasmatic nucleus neurons and its control to feeding centers in the rat hypothalamus

Circadian rhythm of suprachiasmatic nucleus (SCN) was studies using brain slice, and relations between optic nerve, ventromedial hypothalamic nucleus (VMH), lateral hypothalamic area (LHA), and SCN were studied in brain slice and anesthetized rat. Spontaneous SCN neural activity, measured as unit discharge rate, fluctuated in circadian cycles. Unit discharge rates in animals maintained in normal light-dark (L-D) schedules peaked during the day and neaped at night. In reversed L-D schedule, SCN activity also reversed so that peak still occurred during light phase of L-D cycle. Optic nerve stimulation facilitated SCN activity which in turn facilitated VMH neurons and inhibited LHA neurons. Neuronal effects on circadian rhythm of rat feeding behavior is discussed in the context of above results.