The main aims of the proposed work are to specify the neural and endocrine bases for seasonal rhythms in physiology, behavior and structure of mammals. The model species to be studied is the Siberian hamster, Phodopus sungorus. A model system has been developed in which a single long day stimulates reproductive development in hamsters housed in short photoperiods. This renders feasible a new set of experiments with specific aims that include; 1) determining whether the time of weaning constitutes a special sensitive period for induction of reproductive development by light; 2) assessing whether puberty is associated with a permanent reduction in responsiveness to light; 3) establishing the roles of the pineal hormone melatonin and the suprachiasmatic nuclei in sustaining reproductive development once a long-day signal has been received by the neuroendocrine axis; 4) determining the duration of the daily photosensitive phase and how it is affected by prior photoperiodic history; 5) describing the postnatal development of responsiveness to melatonin in the neuroendocrine-gonadal axis; 6) determining the long-term behavioral consequences of a single long day given at weaning, and 7) describing the role of the circadian system and prior photoperiodic history in neurochemical mediation of seasonal cycles. Many human dysfunctions occur only at certain seasons. By specifying the role of the neuroendocrine system and day length in seasonality, we may establish principles that will permit better understanding and control of human behavior.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
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Biopsychology Study Section (BPO)
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University of California Berkeley
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Kauffman, A S; Cabrera, A; Zucker, I (2001) Energy intake and fur in summer- and winter-acclimated Siberian hamsters (Phodopus sungorus). Am J Physiol Regul Integr Comp Physiol 281:R519-27
Prendergast, B J; Flynn, A K; Zucker, I (2000) Triggering of neuroendocrine refractoriness to short-day patterns of melatonin in Siberian hamsters. J Neuroendocrinol 12:303-10
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Prendergast, B J; Gorman, M R; Zucker, I (2000) Establishment and persistence of photoperiodic memory in hamsters. Proc Natl Acad Sci U S A 97:5586-91
Prendergast, B J; Hugenberger, J L (1999) Frequency coding of melatonin signals sufficient to induce testicular growth in photoregressed Siberian hamsters. J Neuroendocrinol 11:237-41
Dark, J; Lewis, D A; Zucker, I (1999) Hypoglycemia and torpor in Siberian hamsters. Am J Physiol 276:R776-81
Prendergast, B J; Freeman, D A (1999) Pineal-independent regulation of photo-nonresponsiveness in the Siberian hamster (Phodopus sungorus). J Biol Rhythms 14:62-71
Bae, H H; Mangels, R A; Cho, B S et al. (1999) Ventromedial hypothalamic mediation of photoperiodic gonadal responses in male Syrian hamsters. J Biol Rhythms 14:391-401
Stamper, J L; Dark, J; Zucker, I (1999) Photoperiod modulates torpor and food intake in Siberian hamsters challenged with metabolic inhibitors. Physiol Behav 66:113-8
Prendergast, B J; Zucker, I; Yellon, S M et al. (1998) Melatonin chimeras alter reproductive development and photorefractoriness in Siberian hamsters. J Biol Rhythms 13:518-31

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