Influence of Photoinhibition, Photostimulation and Prolactin on Pituitary and Hypothalamic Nuclear Androgen Receptors in the Male Hamster

Abstract

Testosterone (T) feedback sensitivity is markedly altered in adult male golden hamsters following exposure to short photoperiods (SD). Using a technique which measures total androgen receptors within the cell nucleus, the present study examined pituitary and hypothalamic nuclear androgen receptor levels in animals exposed to (1) long days (LD) or SD in the presence and absence of a constant T level supplied via a Silastic implant, (2) photostimulation following SD-induced testicular regression and (3) short-term prolactin injections following SD-induced testicular regression. Short photoperiods were associated with a drop in nuclear androgen receptor levels which was correlated with a decline in circulating T. When constant T was supplied to gonadectomized hamsters, those exposed to SD possessed higher pituitary and similar hypothalamic nuclear androgen receptor levels than those exposed to LD. As expected, plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were greatly reduced in SD-exposed, castrated, T-treated hamsters as compared to LD-exposed, castrated, T-treated animals. Photostimulation of intact SD-exposed hamsters for 5 or 10 days was associated with a decline in pituitary nuclear androgen receptors. Prolactin treatment caused no noticeable change in pituitary or hypothalamic androgen receptors even though plasma LH and FSH levels were significantly increased. These results support the hypothesis that altered T feedback mechanisms controlling LH and FSH release following chronic exposure to SD may be related to an alteration in the amount of androgen receptors present in the anterior pituitary.

Seasonal changes in the expression of the androgen receptor in the testes of the domestic goose (Anser anser f. domestica)

“…Our findings corroborate the results of previous studies focused on central AR seasonal protein expression in songbirds [9,10,21,39]. Moreover, there is growing evidence that photoperiod induces changes in AR protein levels in various organisms and tissues, including the testes of bank vole [4,43] and brushtail possum (Trichosurus vulpecula) [26], the brain of Syrian hamster (Mesocricetus auratus) and electric fish (Brachyhypopomus gauderio) [34,35]. The up-regulation of AR in the breeding season suggests tissue sensitization to hormonal action, whereas the down-regulation of AR in the non-breeding season points to the limitation of undesirable androgenic influence during that phase of the cycle [5].…”

Distribution and hormonal regulation of androgen receptor immunoreactivity in the forebrain of the male European ferret

“…Therefore, we believe that the increase in AR-ir profile density and staining intensity observed in many brain regions after prolonged androgen treatment (i.e., over days) is the result of an initial, relatively rapid, concentration of AR in the nucleus and a more protracted androgen-induced increase in AR protein. This presumed upregulation of receptor protein is corroborated by androgen binding experiments, in which nuclear AR concentration is increased by treatment with androgen at time points later than that required for saturation of the AR (Bittman and Krey, 1988;Krey and McGinnis, 1990;Prins et al, 1990).…”

Seasonal changes in androgen receptor mRNA in the brain of the white-crowned sparrow

“…Thus, the increase in levels of androgen receptor mRNA in HVC and the lateral division of the bed nucleus of the stria terminalis could be attributed to changes in either or both of these factors. Prins et al (1990) reported a T-independent effect of photoperiod on nuclear androgen receptor protein levels in the pituitary (but not hypothalamus) of golden hamsters. However, we would argue that the observed changes in levels of androgen receptor mRNA primarily reflect changes in circulating levels of T. In previous studies we have found that photoperiod alone has only minor effects on the plasticity of the song nuclei compared with the isolated effects of testosterone (Singh et al, 2003; Smith et al, 1997; Wissman and Brenowitz, 2009).…”