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Ventromedial Hypothalamic Mediation of Photoperiodic Gonadal Responses in Male Syrian Hamsters

Group in Endocrinology in the Department of Integrative Biology; University of California at Berkeley, Berkeley, CA 94720, USA,

Robert A. Mangels

Institute for Neuroscience; Northwestern University, Chicago, IL 60611, USA

Betty S. Cho

Department of Psychology; University of California at Berkeley, Berkeley, CA 94720, USA

John Dark

Department of Psychology; University of California at Berkeley, Berkeley, CA 94720, USA

Steven M. Yellon

Center for Perinatal Biology, Department of Physiology; Loma Linda University School of Medicine, Loma Linda, CA 92350, USA.

Irving Zucker

Psychology Department; University of California, Berkeley, CA94720, USA.

Short day lengths induce testicular regression in seasonally breeding Syrian hamsters. To test whether the ventromedial hypothalamus is necessary to maintain reproductive quiescence once testicular regression has been achieved, photoregressed male hamsters were subjected to lesions of the ventromedial hypothalamus (VMHx), pinealectomy (Pinx), or sham operation (Sham). VMHx hamsters underwent accelerated gonadal recrudescence compared to Pinx and Sham hamsters. Recovery of prolactin concentrations (PRL) to values characteristic of long-day hamsters was hastened in the VMHx animals compared to Sham hamsters. Concentrations of follicle stimulating hormone (FSH) increased prematurely in both the VMHx and Pinx animals, beginning a few weeks after surgery.By the time the gonads had undergone recrudescence and the hamsters were refractory to melatonin, PRL and FSH concentrations had returned to baseline long-day values in all groups; there was no evidence of hypersecretion of either hormone in any of the animals with lesions. Melatonin concentrations of VMHx hamsters did not differ from those of sham-operated animals, but because only a single determination was made, it remains possible that VMH damage altered the duration of nightly melatonin secretion. An intact VMH appears to be essential for the continued maintenance of reproductive suppression induced by exposure to short day lengths; these and earlier findings suggest that the VMH-dorsomedial hypothalamic complex mediates regression of the reproductive apparatus during decreasing day lengths of late summer and early autumn and also is necessary to sustain regression during the winter months.

Key Words: ventromedial hypothalamic lesions • gonadal recrudescence • melatonin • follicle stimulating hormone • prolactin

Journal of Biological Rhythms, Vol. 14, No. 5, 391-401 (1999)
DOI: 10.1177/074873099129000795


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