AMPA, kainate, and NMDA receptor densities in the hippocampus of untreated male rats and females in estrus and diestrus.

Steroid hormones systematically affect numerous neuronal targets, thus influencing, in a permanent or a transitory manner, the way the brain reacts to external and internal stimuli. The hippocampus is an important brain region for learning and memory and the glutamatergic intrahippocampal pathway plays a major role in performing such functions. We applied quantitative in vitro receptor autoradiography to examine how the in vivo hormone milieu affects the densities of AMPA, kainate, and NMDA receptors in the hippocampus of adult male rats and females in estrus and diestrus. All three examined receptor types presented significant gender-specific differences in their densities. The hippocampus of male rats contains significantly more AMPA, kainate, and NMDA receptors than that of female rats. Female rats in diestrus have significantly higher AMPA receptor densities than female rats in estrus. AMPA changes occurred to the same extent in CA1-3 and in the dentate gyrus. Significant differences in the densities of NMDA receptors were observed in the CA1-3 regions, whereas kainate receptor differences were restricted to the CA1 region. These results further support that steroid hormones, through their modulation of AMPA and NMDA receptors, may be involved in the control of synaptic efficacy and, therefore, influence learning and memory.