Influence of sex and estrous cycle, but not laterality, on the neuronal somatic volume of the posterodorsal medial amygdala of rats

The aim of the present study was to measure the cell body volume of neurons from the posterodorsal subnucleus of the medial amygdala (MePD) of adult male (n = 5) and diestrus, proestrus and estrus female (n = 4-5 in each group) rats to reveal a possible sexual dimorphism, estrous cycle variations and laterality in this morphological parameter. The brains of adult Wistar rats were sectioned (1 μm), stained with 1% toluidine blue and the stereological estimation of neuronal soma volume of both sides of MePD was realized using the Cavalieri method and the technique of point counting. Data were compared by a two-way ANOVA for repeated measures and the least significance difference post hoc test. In the MePD, mean neuronal somatic volume showed a statistical difference among groups (p = 0.005), but neither an effect of laterality (p = 0.33) nor interactions between groups and laterality (p = 0.78) were found. Post hoc test showed that males (mean ± S.E.M., 2075.67 ± 135.79 μm3) have larger mean neuronal somatic volume compared to females in proestrus (1503.30 ± 44.46 μm3) and in estrus (1616.69 ± 71.49 μm3, p < 0.05 in both cases), but not in diestrus (1940.78 ± 129.68 μm3, p > 0.05). Moreover, diestrus females displayed larger mean neuronal somatic volume than proestrus female rats (p < 0.05). It is suggested that neuronal somatic volume is another sexually dimorphic finding in the MePD, for which it is relevant to set apart the different phases of the estrous cycle to reveal the presence of gonadal hormones effects in the rat MePD neurons.