Age difference in endogenous opiate modulation of short photoperiod-induced testicular regression in golden hamsters

Abstract

Effects of age and naloxone on testicular function were studied in golden hamsters exposed to short photoperiods. Subjection of hamsters to short photoperiods of 6 h light: 18 h darkness for 6 weeks led to testicular regression in young adult (5-6 months) or middle-aged (11-12 months) golden hamsters but not in prepubertal hamsters of 1-2 months of age. The middle-aged hamsters had decreased testis width by week 4 of treatment and the young hamsters by week 5. Daily injection of naloxone at the time of 'lights on' partially prevented testicular regression in young and middle-aged hamsters but the extent of regression was significantly greater in the middle-aged animals. Plasma LH and FSH concentrations were significantly reduced in hamsters placed in short photoperiods regardless of age or testicular weight, while naloxone treatment significantly increased the LH concentrations in all age groups. Plasma beta-endorphin-like immunoreactivity was significantly increased by short photoperiod or older age. These results indicated that (a) the sensitivity of the testicular suppression to short photoperiod increases as a function of age, (b) naloxone, a specific opiate receptor blocker, can partially prevent short photoperiod-induced testicular regression and (c) ageing and short photoperiods increase beta-endorphin-like immunoreactivity. It is concluded that the opiate system may be involved in ageing and photoperiod regulation of reproductive function.

Differential Interaction of Estrogen Receptor and Thyroid Hormone Receptor Isoforms on the Rat Oxytocin Receptor Promoter Leads to Differences in Transcriptional Regulation

“…Such crosstalk can lead to different consequences in OTR gene transcription, which in turn, can lead to behavioral differences. Thyroid hormone elevation has been documented to lead to suboptimal reproduction in birds [24, 25], sheep [26, 27, 28, 29, 30]and rodents [31, 32]. Injection of thyroid hormone to ovariectomized female rats leads to a decrease in the levels of an estrogen-induced gene, OT, in the PVN in the brain [34].…”

“…Such high levels of thyroid hormone inhibit reproduction in many species including sheep [26, 27, 28, 29, 30], birds [24, 25]and rodents [31, 32]. Estrogen-controlled lordosis is decreased in the presence of high circulating levels of thyroid hormone in both rats [32]and mice [31].…”

“…Thyroid hormone elevation has been shown to have an adverse effect on reproduction in several species, such as starlings [24, 25], sheep [26, 27, 28, 29, 30]and rodents [31, 32]. Evidence from other studies suggests that this effect on reproduction could be due to reduction in the levels of estrogen-induced genes, such as OT and OTR, which facilitate reproduction [33].…”

Thyroid Hormone Coadministration Inhibits the Estrogen-Stimulated Elevation of Preproenkephalin mRNA in Female Rat Hypothalamic Neurons

“…In both mice and rats, hyperthyroid females showed decreased levels of sexual behavior, while hypothyroid animals demonstrated increased lordosis behavior in response to EB treatment [13, 14]. Elevations in circulating concentrations of thyroid hormones are also known to negatively affect female reproduction in sheep and birds [15, 16, 17, 18, 19, 20, 21, 22]. …”

“…For example, thyroid hormones can reduce estrogen-stimulated lordosis behavior in both rats [13]and mice [14]. In addition, high levels of thyroid hormones reduce female reproductive functions in animals that breed seasonally, such as sheep [15, 16, 17, 18, 19]and birds [20, 21, 22]. To begin searching for genes whose altered expression could participate in the mechanisms of thyroid/estrogenic interactions in female rodents, we recently used in situ hybridization histochemistry for oxytocin mRNA and found hormonal interactions which were isomorphic with lordosis behavior results [23].…”