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Am J Physiol Regul Integr Comp Physiol 282: R744-R752, 2002; doi:10.1152/ajpregu.00299.2001
0363-6119/02 $5.00
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Vol. 282, Issue 3, R744-R752, March 2002

Temperature dependence of gonadal regression in Syrian hamsters exposed to short day lengths

Jennie E. Larkin1, Jennifer Jones2, and Irving Zucker1,2

Departments of 1 Psychology and 2 Integrative Biology, University of California, Berkeley, California 94270-1650

We sought to determine whether ambient temperature (Ta) affects gonadal function by altering the rate at which circadian rhythms entrain to short day lengths. Syrian hamsters were housed in cages where they received 14 h of light per day ("long days," 14L) at 22°C. Hamsters were then transferred to cages to receive 10 h of light per day ("short days," 10L) and kept at 5, 22, or 28°C or were maintained in 14L at 22°C. Body mass and estimated testis volume as well as duration of nocturnal locomotor activity (alpha ), previously established as a reliable indicator of the duration of nocturnal melatonin secretion, were determined over the course of 24 wk. Testicular regression in short days was accelerated by 4 wk at 5°C and delayed by 3 wk at 28°C relative to 22°C. The interval between alpha -expansion and initiation of testicular regression was markedly affected by Ta with delays of 0, 3, and 6 wk at 5, 22, and 28°C, respectively. All hamsters held at 5 and 22°C underwent testicular regression, but 25% of those maintained at 28°C failed to do so. We suggest that Ta modulates testicular regression primarily by affecting responsiveness of neuroendocrine target tissues to long melatonin signals.

melatonin; hibernation; body mass; refractoriness; photoperiodism; food hoarding


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