Abstract 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.

The neuropeptide oxytocin (OXT) modulates social behaviors across species and may play a developmental role for these behaviors and their mediating neural pathways. Despite having high, stable levels of OXT receptor (OXTR) ligand binding from birth, endopiriform nucleus (EPN) remains understudied. EPN integrates olfactory and gustatory input and has reciprocal connections with several limbic areas. Because the role of OXTR signaling in EPN is unknown, we sought to provide anatomical and electrophysiological information about OXTR signaling in mouse EPN neurons. Using in situ hybridization, we found that most EPN neurons co-express Oxtr mRNA and the marker for VGLUT1, a marker for glutamatergic cells. Based on high levels of OXTR ligand binding in EPN, we hypothesized that oxytocin application would modulate activity in these cells as measured by whole-cell patch-clamp electrophysiology. Bath application of OXT and an OXTR specific ligand (TGOT) increased the excitability of EPN neurons in wild-type, but not in OXTR-knockout (KO) tissue. These results show an effect of OXT on a mainly VGLUT1+ cell population within EPN. Given the robust, relatively stable OXTR expression in EPN throughout life, OXTR in this multi-sensory and limbic integration area may be important for modulating activity in response to an array of social or other salient stimuli throughout the lifespan and warrants further study.

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The neuropeptide oxytocin (OXT) modulates social behaviors across species and may play a developmental role for these behaviors and their mediating neural pathways. Despite having high, stable levels of OXT receptor (OXTR) ligand binding from birth, endopiriform nucleus (EPN) remains understudied. EPN integrates olfactory and gustatory input and has bilateral connections with several limbic areas. Because the role of OXTR signaling in EPN is unknown, we sought to provide anatomical and electrophysiological information about OXTR signaling in mouse EPN neurons. Using in situ hybridization, we found that most EPN neurons co-express Oxtr mRNA and the marker for VGLUT1 and are thus glutamatergic cells. Based on high levels of OXTR ligand binding in EPN, we hypothesized that oxytocin application would modulate activity in these cells as measured by whole-cell patch-clamp electrophysiology. Bath application of OXT and an OXTR specific ligand (TGOT) increased the excitability of EPN neurons in wild-type, but not in OXTR-knockout tissue. These results show an effect of OXT on a presumably glutamatergic cell population within EPN. Given the robust, relatively stable OXTR expression in EPN throughout life, OXTR in this multi-sensory and limbic integration area may be important for modulating activity in response to an array of social or other salient stimuli throughout the lifespan and warrants further study.