Cytoarchitectonic sexual dimorphisms of the medial preoptic and anterior hypothalamic areas in guinea pig, rat, hamster, and mouse

Abstract

A cytoarchitectonic analysis is presented of a configuration of cells which extends through the medial preoptic and rostral part of the anterior hypothalamus of the guinea pig, rat, hamster, and mouse. Within that configuration, called here the sexually dimorphic nuclear complex of the medial preoptic-anterior hypothalamic area (SDNC-MPAH), there is nearly continuous variation in cellular distribution or packing density as one proceeds rostrocaudally, as well as variations between females and males at corresponding levels. The major cell groups comprising SDNC-MPAH are the medial preoptic nucleus (MP) and the preventricular portion of the periventricular nucleus (Pep) rostrally, and the anterior hypothalamic nucleus (AH), anterior portion of periventricular nucleus, (Pea), and bed nucleus of stria terminalis (ST) caudally. The most striking cytoarchitectonic dimorphisms usually involve MP and AH. In all four species examined, MP is larger and, except for the mouse, appears to be more densely cellular in the female than in the male. Most prominently in the rat and guinea pig, AH is densely cellular throughout in the female, including the subependymal zone, whereas in the male AH lies at a distance from the third ventricle, separated from the ependyma by a cell-poor zone. The significance of these findings may lie in the fact that the region exhibiting the sexual dimorphisms has been shown to be involved in the regulation of reproductive functions which are sexually differentiated and developmentally influenced by the fetal or perinatal hormonal milieu in some species.

Topography in the preoptic region: Differential regulation of appetitive and consummatory male sexual behaviors

“…Homologies between sexually dimorphic nuclei in various animal species including rats, hamsters, guinea pig, gerbils or quail and the dimorphic structures of the preoptic area in humans and monkeys [8,40,[45][46][47]133] remain unclear at present and information coming from different species is still likely to improve our understanding of the neural bases of behavior in primates including humans.…”

Developmental programming and endocrine disruptor effects on reproductive neuroendocrine systems

“…There are numerous sexually dimorphic brain nuclei [18] and here I have selected to discuss two representative regions that are strongly implicated as being neonatally imprinted and subsequently controlling sex-typical physiology and behaviors in the rat model. These two brain regions, the anteroventral periventricular nucleus (AVPV), and the sexually dimorphic nucleus of the preoptic area (SDN-POA), undergo sexually dimorphic development due to the influence of endogenous hormones, and can be manipulated in size (and presumably function) by castration or administration of exogenous hormones.…”

“…The AVPV of rats is larger in female than male rodents [18,43,150], due to influences of both estradiol and testosterone during the early postnatal (and possibly prenatal) periods [43,150,142]. The AVPV is essential to the control of preovulatory GnRH/LH release in female rats [167].…”

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.…”