Expression of vasopressin receptors in hamster hypothalamus is sexually dimorphic and dependent upon photoperiod.

Abstract

The distribution of vasopressin receptors was studied in the brain of a photoperiodic animal, the Siberian In photoperiodic species, the activity of the gonads is modulated by the length of the daily light phase and by its chronicity over weeks. Thus, in spring and summertimeduring the long photoperiod (LP)-the Siberian hamster is sexually active, whereas in the short photoperiod (SP)-autumn and winter-its gonads atrophy, and the animals become sexually inactive. At the end of winter, the process is reversed and the gonads increase again in weight (1-3). Circulating gonadal steroids follow a parallel course: their level is lowered following shortening of the photoperiod, and this effect is reversed when the photoperiod increases again (4-8). These physiological modifications may be artificially induced in controlling the length of the photoperiod in animal husbandry (9). In the Siberian hamster, gonadal regression is directly under photoperiodic control: it is not dependent on the temperature or the amount offood available (1,2,10,11).In both male and female rats, oxytocin-binding sites in the hypothalamic ventromedial nucleus are down-regulated by castration, and they can be restored to precastration level by injections of sexual steroids (12-16). We investigated the distribution of vasopressin-and oxytocin-binding sites in the brain of male and female Siberian hamsters either in LP or SP conditions, using a newly developed gaseous detector of 13-particles (17) and film autoradiography. We discovered that in Siberian hamsters, vasopressin receptors rather than oxytocin receptors are present in the ventromedial hypothalamic nucleus and that they are expressed differentially in the male and in the female. Furthermore, the density of the binding was found to be dependent on photoperiod.MATERIAL AND METHODS Animals. Young adult Siberian hamsters (Phodopus sungorus) were maintained under either a LP (16/8-hr light/dark cycle) or a SP (8/16-hr light/dark cycle) for 10 weeks. Temperature was set at 20 ±+ 1C and humidity at 60-70o. The animals received tap water and food pellets ad libitum.Fourteen males (9 in LP, 5 in SP) and 11 females (7 in LP, 4 in SP) were used for the autoradiographic localization of vasopressin-and oxytocin-binding sites in the brain. Animals, 5 months old with a body weight of 30-50 g, were decapitated, and the testes were removed and weighed, or the uterus was inspected, to assess the activity of the gonads (2, 18). The brain was frozen in isopentane at -250C, and 15-I.m-thick coronal sections were cut in a cryostat, laid on gelatin/chromalum-coated slides, air-dried, and processed for light microscopic autoradiography.Autoradiography. Autoradiography of vasopressin-binding sites was performed as described (19) tTo whom reprint requests should be addressed. 11163The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Vasopressin in the brain of a desert hibernator, the jerboa (Jaculus orientalis): Presence of sexual dimorphism and seasonal variation

“…In contrast with observations in the Siberian hamster (Dubois-Dauphin et al, 1991, we observed neither a sexually dimorphic expression nor a seasonal variation in the distribution of VP receptors in the jerboa. This situation is reminiscent of previous observations in the golden hamster (Dubois-Dauphin et al, 1990), whicn suggests that the seasonal variation of the vasopressin content of certain neurons is sufficient to control seasonal functions such as hibernation (Hermes et al, 1989).…”

Species, sex and individual differences in the vasotocin/vasopressin system: Relationship to neurochemical signaling in the social behavior neural network

“…In Siberian hamsters, the density of V1a binding is lower in females than in males in the VMH and ventrolateral (VLH) (i.e., medial tuberal nucleus) and in the premammillary nuclei of the hypothalamus(Dubois-Dauphin and others, 1991; Dubois-Dauphin and others, 1994). In Syrian hamsters, the density of V1a receptor binding is also found to be lower in the VLH in females than in males(Delville and Ferris, 1995; Delville and others, 1996).…”

An acetylcholine receptor alpha subunit promoter confers intrathymic expression in transgenic mice. Implications for tolerance of a transgenic self-antigen and for autoreactivity in myasthenia gravis.

“…Finally, sections were rinsed in water and dehydrated in 96% ethanol. Radioactivity in thymus sections was measured using a ␤ -imaging apparatus, followed by quantification and location with an RIHR device adapted from Dr. Charpak's first apparatus (20,21).…”