CIRCADIAN AND ULTRADIAN RHYTHMS OF SEROTONIN REGIONALLY IN CAT BRAIN

¹ Department of Neurology, Cornell University Medical College, New York, New York

There is a 24-hr (circadian) cycle in the concentration of serotonin in certain regions of the upper brainstem and telencephalon of the cat brain, including parts of the mesencephalon, the medial hypothalamus and most deep nuclei of the telencephalon. In the neocortex, serotonin rhythms are regionally specific. A biphasic or ultradian serotonin rhythm occurs in the substantia nigra-lateral tegmentum region and anterior hypothalamus. A rhythm in serotonin was not found in the cat pineal gland. No sex difference in regional serotonin was found in cat. The regional serotonin rhythms in cat brain are asynchronous and have different forms. Comparison with previous data on regional cycles of norepinephrine indicates that most regions of cat brain have a rhythm of one or the other amine, thereby assuring alteration in the ratios of the concentration of each amine in different brain regions. However, only the substantia nigra-lateral tegmentum region, the anterior hypothalamus and the tuber cinereum share rhythms of both norepinephrine and serotonin, which are generally 180° out of phase. We conclude that the regional rhythms of serotonin and norepinephrine concentrations are independently regulated in cat brain.

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