Alterations in Neuroendocrine Function During Photoperiod Induced Testicular Atrophy and

Transfer of golden (Syrian) hamsters from a 14L: 1OD (light:dark) to a 5L: 19D photoperiod causes profound changes in the reproductive axis. Testicular weight fell within 7 weeks of short photoperiod exposure and remained low until 19 weeks, at which time spontaneous recrudescence began. Plasma LH, FSH and PrI levels were undetectable at 7.5 weeks of exposure, but LH and FSH returned to basal levels by 15 weeks and PrI by 20.5 weeks. Hypothalamic LHRH levels increased concurrently with the fall in LH and FSH, suggesting that LHRH release was decreased. Increasing plasma gonadotropin levels and testicular recrudescence were associated with decreases in hypothalamic LHRH content. Hypothalamic norepinephrine (NE) turnover was low at 10 weeks, suggesting that decreased LH and FSH levels were ultimately due to decreased adrenergic activity. At 15 weeks, plasma LH levels and hypothalamic NE turnover were both increased over values seen at 10 weeks. Hypothalamic dopamine turnover, possibly reflecting decreased PrI feedback, was decreased between 0 and 10 weeks, but returned to control levels by 15 weeks. It, therefore, appears that the endocrine changes associated with photoperiod induced testicular regression and recrudescence are secondary to changes in hypothalamic function