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

Abstract

<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

Functional connectivity of intercalated nucleus with medial amygdala: A circuit relevant for chemosignal processing

“…We have evidence for a modulation of medial amygdala activity by mICNc during chemosensory investigation ( Biggs and Meredith, 2020 , Meredith and Westberry, 2004 ). When male hamsters investigate social-signal-odors of (unfamiliar) male or female hamsters (conspecifics), both MeA and MeP are activated (increased immediate early gene (IEG) expression), including GABA-Receptor-ir cells ( Westberry and Meredith, 2016 ).…”

“…Ad libitum food and water was provided. Because our data implicating the proposed circuit in social chemosensory responses of the medial amygdala are from males ( Biggs and Meredith, 2020 , Meredith and Westberry, 2004 , Westberry and Meredith, 2016 ), we used only males in this study of the circuit connections.…”

“…1 shows horizontal slices as described here, with calbindin and/or calretinin immunoreactive (ir) cells stained and mounted in DAPI-mounting medium which stains cell nuclei. The immunohistochemical methods used are described in detail in Biggs and Meredith (2020) . Briefly, animals were deeply anesthetized, perfused with PBS and 4% paraformaldehyde.…”

Hypothalamic cellular and molecular plasticity linked to sexual experience in male rats and mice

“…BNST does not appear to be affected by sexual experience, as the number of cells expressing c-Fos remains unchanged (Parfitt and Newmann, 1998). In hamsters MeA, different subpopulations are activated between naive and sexually experienced animals (Biggs and Meredith, 2020). For the rat, a conversion of MeA dendritic spines (in the posterodosal part) toward a mushroom phenotype was described with sexual experience (Zancan et al, 2018) and oxytocin participates in this spine remodeling (Becker et al, 2017).…”