Sex difference and response to testosterone in gabaergic cells of the medial preoptic nucleus and ventral bed nuclei of the stria terminalis in gerbils

Abstract

The medial preoptic nucleus (MPN) and ventral bed nuclei of the stria terminalis (BST) are needed to maintain mating in sexually experienced male gerbils and rats. The gerbil ventral BST is also activated with mating, as assessed by Fos expression, as is the medial MPN (MPNm) of both species. In gerbils, many of those mating-activated cells contain glutamic acid decarboxylase (GAD), the enzyme that synthesizes γ-aminobutyric acid (GABA). Some of those cells are projection neurons, but others may release GABA locally. Through actions in the medial preoptic area, GABA inhibits and testosterone (T) promotes male sex behavior. Thus, T may promote mating, in part, by decreasing GAD in MPNm or ventral BST cells. In rats, T increases GAD mRNA in the central MPN (MPNc), where MPN GABAergic cells are densest, but mating behavior does not change in sexually experienced males when the MPNc is ablated. Therefore, this study focused on the MPNm and ventral BST to ask whether their GABAergic cells respond to T or are sexually dimorphic. This was done by visualizing cells immunoreactive (IR) for GAD(67), an isoform found primarily in cell bodies, in male and female gerbils and in castrated males with and without T. At both sites, males had more GAD(67)-IR cells than females, and T decreased GAD(67)-IR cell numbers in males. Thus, the MPNm and ventral BST have GABAergic cells that are sexually dimorphic and in which T decreases GAD, consistent with local effects of T and GABA on mating.

Fig. 1

Sex differences and effects of testosterone (T) on cells immunoreactive (IR) for glutamic acid decarboxlyase₆₇ (GAD₆₇) in the medial part of the medial preoptic nucleus (MPNm) and ventral bed nuclei of the stria terminalis (ventral BST) of gerbils. Data are shown as group means ± SEM. The N is given at the bottom of each bar. Cell counts are for areas of 0.024 mm² for the MPNm and 0.029 mm² for the ventral BST. Cast = castrated male.

Fig. 2

Montage of photomicrographs of a coronal section through the medial preoptic nucleus (MPN) of a castrated male gerbil showing cells IR for GAD₆₇. Arrows point to the corners of a cell-count area in the medial MPN. Bar = 0.1 mm. MPNc = central MPN.