Castration reversibly alters levels of cholecystokinin immunoreactivity within cells of three interconnected sexually dimorphic forebrain nuclei in the rat.

Abstract

Three sexually dimorphic cell groups in the forebrain of the rat-the central part of the medial preoptic nucleus, the encapsulated part of the bed nucleus of the stria terminalis, and the posterodorsal part of the medial nucleus of the amygdala-are larger in males, contain a high density of gonadal-steroid-concentrating cells, and are thought to play important roles in the control of reproductive behavior and physiology. Since each of these regions contains a large number of cholecystokinin-immunoreactive cells, we used an indirect immunohistochemical method to examine the possibility that levels of this peptide are modulated by circulating gonadal steroids in adult male rats. Rats were castrated at 60 days of age, and one group each was pretreated with colchicine and then killed 3, 7, and 14 days after gonadectomy. Castration clearly decreased CCK immunoreactivity within cells of each region, with the most dramatic effects occurring 7 and 14 days after gonadectomy, and these effects were reversed by treatment with testosterone over a 14-day period. The results suggest that CCK levels within individual cells in each of the interconnected sexually dimorphic nuclei examined here are regulated by circulating gonadal steroids and may be related to the hormonal modulation of reproductive functions thought to be mediated by these cell groups.An important role for gonadal steroid hormones in the control of reproductive behavior is well-established, although mechanisms underlying their influence on neural circuits mediating such functions remain unclear. Gonadal steroids have been shown to markedly affect biochemical indices of neurotransmitter function (see ref. 1 for review), and steroid-induced changes in the levels of putative neurotransmitters within individual neurons have been demonstrated immunohistochemically. For example, 15 weeks after gonadectomy, the density of vasopressin-immunoreactive fibers in the lateral septum is markedly reduced in the adult male rat, and vasopressin-stained cell bodies are no longer demonstrable in the bed nucleus of the stria terminalis and medial nucleus of the amygdala (2). Similarly, the density of substance Pimmunoreactive fibers decreases within 14 days after gonadectomy (3). In contrast, the distribution of serotoninimmunoreactive fibers in the medial preoptic nucleus (MPN) and the density of tyrosine hydroxylase-immunoreactive (presumably dopaminergic) cells in the anteroventral periventricular nucleus do not appear to be sensitive to the influences of circulating gonadal steroids in the adult but can be dramatically altered by manipulation of the perinatal steroid environment (4, 5).The sexual differentiation of neural structures in the mammalian brain has been documented for a number of cytological features of individual neurons, the synaptology of specific brain regions, and the volume and cytoarchitecture of several nuclei (see refs. 6 and 7 for reviews). Three such nuclei, the medial preoptic nucleus (especially its central subdivision, MPNc; ref. 8), the encaps...

Tyrosine hydroxylase-synthesizing cells in the hypothalamus of prairie voles (Microtus ochrogaster): Sex differences in the anteroventral periventricular preoptic area and effects of adult gonadectomy or neonatal gonadal hormones

“…However, it was unexpected that this sex difference was found only after gonadectomy. Examples can be found of sex differences in the rat brain that are due to and only exist in the presence of adult circulating gonadal hormones in males (Cooke et al, 1999;Simerly and Swanson, 1987), but our finding may be the first example of a neural sex difference that exists only because of the absence of gonadal hormones in males. We can only speculate why a sex difference in the prairie vole AVPV is absent in gonadally intact voles.…”

Effects of Estrogen in the Male Rat Medial Amygdala: Infusion of an Aromatase Inhibitor Lowers Mating and Bovine Serum Albumin-Conjugated Estradiol Implants Do Not Promote Mating

“…For example, E 2 induces changes in levels of cholecystokinin (CCK) in brain areas that mediate female rat sexual behavior [53,54,55]. Moreover, T modulation of CCK has been reported to occur in areas of the male rat brain that are important for the display of copulatory behavior, and it is possible that these changes result from the aromatization of T to E 2 [56]. These studies raise the possibility that E 2 acts as a ‘chemical switch’ [53] regulating differential levels of neurotransmitters in behaviorally-relevant neurons.…”

Neuroanatomical Projections of the Species-Specific Tyrosine Hydroxylase-Immunoreactive Cells of the Male Prairie Vole Bed Nucleus of the Stria Terminalis and Medial Amygdala

“…This was not due to the complete absence of input from the BSTpr to the MEApd, because many cells of unknown phenotype projected in that direction. Given these results, the BSTpr must communicate with the MEApd primarily through other neurochemicals, including GABA given that it is synthesized in the majority of BSTpr neurons in other rodents [Stefanova, 1998;Simmons and Yahr, 2003], but numerous other neurotransmitters found in the BSTpr are also possibilities [De Vries et al, 1984Muganini and Oertel, 1985;Simerly and Swanson, 1987;Malsbury and McKay, 1989;Swann and Newman, 1992;Miller et al, 1993;Simmons and Yahr, 2003;Poulin et al, 2009].…”