Body temperature, hormone production and other biological functions fluctuate according to a regular pattern over a 24-hour cycle. Such circadian rhythms control many aspects of human metabolism, including the sleep/wake cycles and attentiveness. It is also becoming more evident that humans, like other mammals, display annual cycles in many kinds of behavior. Among these seasonally fluctuating human traits are rates of suicide, violent crimes, and emotional levels as well as changes in hormone levels and conception. Dr. Herndon will use a primate model to understand the mechanisms underling the control of annual cycles. He proposes that reproductive success is regulated by daylength which is transduced by the nocturnal secretion of melatonin, a hormone of the pineal gland. To test this hypothesis, Dr. Herndon will determine the effects of altering daily photoperiod and melatonin levels on the pattern of luteinizing hormone, follicle stimulating hormone, and testosterone secretion. In addition, he will determine the effects of these manipulations on behavior. These results will provide important insight into the nature and neuroendocrine mechanisms underlying annual cycles in all primates, including humans.
