Influence of sex, estrous cycle and motherhood on dendritic spine density in the rat medial amygdala revealed by the Golgi method.

The medial nucleus of the amygdala (MeA), a sexually dimorphic area, contains estrogen and androgen receptors and has an integrative role in behavioral, vegetative and endocrine activities of rats. The density of dendritic spines along the first 40 microm of dendritic length was studied in neurons from the anterodorsal (MeAD), posterodorsal (MePD) and posteroventral (MePV) aspects of the MeA in males, in virgin females during the four phases of the estrous cycle and in multiparous females in diestrus. The single-section Golgi method was employed (N=48 observations per experimental group). In the three MeA subnuclei males showed more dendritic spines than virgin females (P<0.001), with the only exception being the MePD data of females in diestrus (P>0.05). In virgin females, whereas more dendritic spines were found in diestrus, a decline in these values was found during the proestrus, estrus and metaestrus in the MePD and MePV (P<0.05) but not in the MeAD (P>0.05). Compared with virgin females in diestrus, postpartum rats showed more spines in the MeAD (P<0.001) and fewer in the MePD (P<0.001) but no difference was found in the MePV (P>0.05). These data suggest that there are subregion-specific differences in the density of dendritic spines within the MeA and that they appear to be affected by sex, cyclic fluctuations in the levels of ovarian steroids and following pregnancy in rats. These findings may add to the understanding of the MeA neuronal plastic changes that affect the ongoing processing of sensory information and the organization of the neuroendocrine and behavioral basis of reproduction.