Influence of Perinatal Androgen on the Sexually Dimorphic Distribution of Tyrosine Hydroxylase-Immunoreactive Cells and Fibers in the Anteroventral Periventricular Nucleus of the Rat

Abstract

Recently we reported that the anteroventral periventricular nucleus (AVPv) of the preoptic region contains a dramatic sexual dimorphism in the distribution of tyrosine hydroxylase- (TH-)immunoreactive cells and fibers in the rat. This sexual dimorphism appears to be due to a greater density of dopaminergic fibers, and a larger number of dopaminergic cell bodies, in the AVPv of the female. In the present study we used an indirect immunohistochemical method to evaluate the distribution of TH-immunoreactive cell bodies and fibers, and of dopamine-β-hydroxylase-(DBH-)stained fibers, in the AVPv of female rats that were treated with testosterone propionate (TP) perinatally or postnatally, or were left untreated. All of the postnatally TP-treated animals failed to show a phasic pattern of luteinizing hormone (LH) secretion in response to estrogen and progesterone injections. Both the perinatally and postnatally TP-treated females had polyfollicular ovaries that lacked corpora lutea at the time of gonadectomy. Perinatal TP exposure resulted in what appears to be a complete masculinization of both the number of TH-stained cells and the density of TH-stained fibers in the AVPv. The number of TH-stained cells in the postnatally TP-treated females was also completely masculinized, although the density of TH-stained fibers did not appear to be altered significantly. Gonadectomy resulted in a moderate increase in the density of TH-stained fibers in adult males, and did not significantly affect the fiber density in females, or the number of TH-stained cells in either sex. The distribution of DBH-stained fibers in the AVPv did not appear to be altered in any of the treatment groups. These results suggest that the distribution of dopaminergic fibers in the AVPv may be sensitive to testosterone levels in the adult male, and that although the critical period for the development of this fiber distribution may begin in the prenatal period, the number of dopaminergic cells in the AVPv can be completely sex reversed by a single postnatal dose of TP that appears to correlate with a permanent disruption of the normal pattern of gonadotropin secretion.

Deletion of Bax eliminates sex differences in the mouse forebrain

“…A small subset of AVPV neurons is dopaminergic, as identified by the presence of TH, the rate-limiting enzyme for catecholamine synthesis, and absence of dopamine-␤-hydroxylase, the enzyme required for conversion of dopamine to norepinephrine (6). In confirmation of previous reports (25,28), the number of TH-ir neurons in AVPV was much greater in female mice than in males (P Ͻ 0.0005; Fig.…”

Role for estradiol in female-typical brain and behavioral sexual differentiation

“…The sexually dimorphic expression of tyrosine hydroxylase (TH) and vasopressin (VP) were used as indices of brain sexual differentiation. The number of TH-expressing neurons in the anteroventral preoptic area (AVPv) is sexually dimorphic with females having greater numbers than males [91,92,96]. The AVPv plays a critical role in female reproductive function by transducing hormonal feedback controlling hypothalamic GnRH release and consequent pituitary luteinizing hormone secretion, as well as that it is needed for hormonally induced ovulation [115].…”

Evidence for the existence of an estrogen-responsive sexually dimorphic group of cells in the medial preoptic area of the 129SvEv mouse strain

“…[6][7][8] These sexually dimorphisms appear to be steroid responsive in most cases. [6][7][8][9][10][11][12][13] Sexual dimorphisms also exist in relation to aromatase expression, with wild-type (WT) neonatal male mice showing significantly higher levels of aromatase activity in whole brain extracts when compared with female mice, and in addition, adult male mice show higher aromatase activity following testosterone treatment than their female counterparts. 14 These data suggest a role for steroid hormones such as testosterone or estrogen in the sexual differentiation of specific regions within the hypothalamus including the preoptic region.…”