Neurobiology of Mammalian Photoperiodism

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Light affects daily (circadian) and seasonal cycles in physiology and behavior. Dr. Nunez will examine the neural and endocrine systems that mediate these effects of light on these biological rhythms. The suprachiasmatic nucleus of the hypothalamus is believed to be the neural substrate for the biological clock. Therefore, Dr. Nunez will concentrate on identifying the outputs of the nucleus to determine how circadian signals reach the rest of the central nervous system. Both the circadian system and the suprachiasmatic nucleus are involved in the generation of seasonal reproductive cycles but the projection or output from this neural structure involved in seasonal cycles appears to be different than the projections responsible for daily cycles. It appears that seasonal cycles may also involve the paraventricular nucleus of the hypothalamus. Dr. Nunez will also investigate the pathways that originate in this brain structure. In addition, he will elucidate the endocrine changes that are produced by neural damage that abolishes seasonal cyclicity. Information about the anatomy and physiology of this biological clock provides the basic science for a more comprehensive understanding of certain psychiatric disorders at the extreme and fluctuations in mood and productivity in the more normal range. An additional value of knowledge of controls of photoperiodism may lie in an increased efficiency in animal husbandry.