The proposed work seeks to identify neural and endocrine mechanisms underlying the generation and entrainment of circannual rhythms of reproduction, body weight, food intake and hibernation. The species to be studied are the golden-mantled ground squirrel and the European hamster. Specific projects include: (1) Elaboration of the relation between circadian and circannual rhythms, in particular the role of frequency demultiplication of circadian rhythms as a mechanism for measuring circannual intervals (2) Assessment of the role of postnatal sexual differentiation for the development of seasonal sex differences in body weight and plasma luteinizing hormone levels (3) Determining the phase-shifting effects of estradiol on the circannual body weight cycle and specifying the sites within the hypothalamus at which estradiol influences circannual time-keeping processes (4) Establishing the role of lipids as synchronizers of circannual cycles in reproduction, hibernation and body weight. The effects of lipids on feedback regulation of food intake will be assessed at several phases of the circannual body weight cycle (5) comparison of the role of the suprachiasmatic nuclei as oscillators for circannual rhythms entrained by photoperiod versus those synchronized by non-photo-periodic zeitgebers (6) Evaluation of the role of adrenal steroids in the generation of circannual rhythms of plasma luteinizing hormone (7) Determination of hormone secretory patterns during homothermic and heterothermic phases of hibernation (8) Assessment of the role of the paraventricular nuclei in the generation of circannual rhythms. Parameters to be measured include body weight, food intake, locomotor activity, luteinzing hormone and testesterone levels in plasma, body temperature and several morphological and physiological indices of reproductive status. The proposed research will develop concepts and data relevant to understanding and manipulating human circannual rhythms presumed to underlie seasonal cycles in affective disorders.
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