Activation of Calcium Binding Protein-ir Neurons in Medial Amygdala during Chemosignal Processing

The medial amygdala receives sensory input from chemical signals important in mammalian social communication. As measured by immediate-early gene expression, its responses to different chemosignals differ in the spatial patterns of neuronal activation and in the types of cells activated. Medial amygdala projections to basal forebrain contribute to generation of appropriate behavioral responses and GABA neurons are important for these functions, both as interneurons and as projection neurons. Here we investigate responses of male golden-hamster medial amygdala neurons expressing immunoreactivity (ir) for calbindin (CB), calretinin (CR) and parvalbumin (PV), calcium binding proteins (CBPs), which can distinguish different GABAergic neuron types. CB-ir and CR-ir cells had significant responses to female hamster chemosignals and showed different spatial patterns across medial amygdala. Responses to chemosignals from unfamiliar females were significantly reduced in males with sexual experience, compared with naive males. Medial amygdala did not express PV-ir cells and the adjacent intercalated nucleus, which has been implicated in medial amygdala chemosensory responses did not express any of the CBPs investigated here. This additional evidence for chemosensory specificity in the response of medial amygdala to social chemical signals, in cells characterized by CBP expression, suggests multiple GABA circuit elements may be involved in information processing for behavioral response.