Ontogeny of the gonadal response of golden hamsters to short photoperiod, blinding, and melatonin.

The age dependency of the time delay preceding a gonadal response to short photoperiod, blinding, and daily evening melatonin injection in young male and female hamsters has been examined to determine why the reproductive system of prepubertal golden hamsters is apparently unaffected by short-day treatment. Anestrous occurred in 50% of the female hamsters during the 10th week after blinding whether or not blinding occurred at 3, 5, 7, or 9 weeks of age. A similar latency was found following initiation of melatonin injections although the variance was greater (50% became anestrous during the 8th, 11th, 9th, and 8th week after initiation at ages of 3, 5, 7, and 9 weeks, respectively). After transfer to short days, however, females were 18 to 22 weeks old before 50% had become anestrous and the latency intervals were 19, 13, 11, and 10 weeks for transfer at 3, 5, 7, and 9 weeks of age, respectively. In males, mean testicular weights decreased to 50% of control values during the 9th and 10th week following blinding regardless of the age at which blinding occurred; the latency following initiation of melatonin injection or transfer to short days ranged between 8 and 11 weeks. These data support the conclusion that prepubertal male and female golden hamsters 3 weeks of age and older respond to light deprivation and melatonin treatment in the same manner as adults, but that the latency of the response is such that sexual maturity is attained before regression occurs. The response of 3-week-old female hamsters to short photoperiods, however, is apparently confounded by factors not governed by the pineal gland.