Sexual dimorphism, estrous cycle and laterality determine intrinsic and synaptic properties of medial amygdala neurons

Abstract

The posterodorsal medial amygdala (MePD) is a sex-steroid-sensitive area that modulates different social behavior by relaying chemosensorial information to hypothalamic nuclei. However, little is known about cell type diversity and their functional connectivity. Here, we have characterized neurons and synaptic inputs in the right and left MePD of adult male and cycling female (in diestrus, proestrus or estrus) rats. Based on their electrophysiological properties and morphology, we found two coexisting subpopulations of spiny neurons that are sexually dimorphic. They were classified as Class I (predominantly bitufted-shaped neurons showing irregular spikes with frequency adaptation) or Class II (predominantly stellate-shaped neurons showing full spike-frequency adaptation). Furthermore, excitatory and inhibitory inputs onto MePD cells were modulated by sex, estrous cycle, and hemispheric lateralization. In the left MePD, there was an overall increase in the excitatory input onto neurons of males compared to cycling females. On the other hand, in proestrus, the MePD neurons received mainly inhibitory inputs. Therefore, our findings indicate the existence of hemispheric lateralization, estrous cycle and sexual dimorphism influences at cellular and synaptic level in the adult rat MePD.