The density of Golgi-impregnated dendritic spines from adult rat posterodorsal medial amygdala neurons displays no evidence of hemispheric or dorsal/ventral differences.

The posterodorsal medial amygdaloid nucleus (MePD) is a sexually dimorphic area in the rat brain and dendritic spines are specialized postsynaptic sites involved with local neural plasticity. Previous electrophysiological data showed that prepubertal males have more excitatory synapses than females in the left MePD. Besides, dorsal and ventral MePD neurons have a heterogeneous expression of estrogen receptors alpha or beta in mating-responsive neurons in females. Based on these findings, the "single-section" Golgi method was employed in adult rats (n=6 in each group) to reveal: (1) the effect of hemispheric laterality in the density of dendritic spines in the MePD of males and diestrus females, and (2) the density of dendritic spines in the MePD dorsal and ventral subregions in proestrus females (mean values from n=48 neurons for each experimental variable). There were no statistically significant differences for sex, laterality or the interaction of these factors in the dendritic spine density between males and diestrus females (p>0.2), nor for the dorsal and the ventral MePD dendritic spine density in proestrus females (p>0.1). These findings complement current knowledge about the rat MePD and suggest that the number of proximal dendritic spines is not lateralized at adulthood. Furthermore, the differential expression of estradiol receptors in the dorsal and ventral MePD did not lead to distinct spine number in these subregions when circulating ovarian steroids peak in proestrus.