Varela, J. | Search bioRxiv

bioRxiv2019

Insular cortex projections to nucleus accumbens core mediate social approach to stressed juvenile rats

Social interactions are shaped by features of the interactants including age, emotion, sex and familiarity. Age-specific responses to social affect are evident when an adult male rat is presented with a pair of unfamiliar male conspecifics, one of which is stressed via 2 footshocks and the other naive to treatment. Adult test rats prefer to interact with stressed juvenile (PN30) conspecifics, but avoid stressed adult (PN50) conspecifics. This pattern depends upon the insular cortex (IC) which is anatomically connected to the nucleus accumbens core (NAc). The goal of this work was to test the necessity of IC projections to NAc during social affective behavior. Here, bilateral pharmacological inhibition of the NAc with tetrodotoxin (1{micro}M; 0.5ul/side) abolished the preference for stressed PN30, but did not alter interactions with PN50 conspecifics. Using a combination of retrograding tracing and c-Fos immunohistochemistry, we report that social interactions with stressed PN30 conspecifics elicit greater Fos immunoreactivity in IC [->] NAc neurons than interactions with naive PN30 conspecifics. Chemogenetic stimulation of IC terminals in the NAc increased social exploration with juvenile, but not adult, conspecifics, while chemogenetic inhibition of this tract blocked the preference to investigate stressed PN30 conspecifics, which expands upon our previous finding that optogenetic inhibition of IC projection neurons mediated approach and avoidance. These new findings suggest that outputs of IC to the NAc modulate social approach, which provides new insight to the neural circuitry underlying social decision-making. Significance StatementSocial decision-making underlies an animals behavioral response to others in a range of social contexts. Previous findings indicate the insular cortex (IC) and the nucleus accumbens (NAc) play important roles in a range of social behaviors, and human neuroimaging implicates both IC and NAc in autism and other psychiatric disorders characterized by aberrant social cognition. To test whether IC projections to the NAc are involved in social decision making, circuit-specific chemogenetic manipulations demonstrated that the IC [->] NAc pathway mediates social approach toward distressed juvenile, but not adult, conspecifics. This finding is the first to implicate this circuit in rodent socioemotional behaviors and may be a neuroanatomical substrate for integration of emotion with social reward.

neuroscience↗

bioRxiv2017

Insular Cortex Mediates Approach And Avoidance Responses To Social Affective Stimuli

Social animals detect the affective states of others and utilize this information to orchestrate appropriate social interactions. Social affective behaviors include cooperation, reproductive acts and avoiding sick individuals. In a social affective behavioral test in which experimental adult male rats were given the choice to interact with either naive or stressed conspecifics, the experimental rats demonstrated both approach and avoidant behaviors towards the conspecific, depending upon the age of the conspecific; experimental adult rats approached the stressed juvenile but avoided the stressed adult. Optogenetic inhibition of the insular cortex, a region anatomically positioned to contribute to social cognition, disrupted these behaviors. Receptors for the social nonapeptide oxytocin (OT) are found in high density within the insular cortex and here oxytocin increased intrinsic excitability and synaptic efficacy in acute insular cortex slices. Blockade of oxytocin receptors (OTRs) in the insula eliminated the effect of conspecific stress on approach behavior, while insular administration of OT recapitulated the behaviors typically observed in response to stressed conspecifics. Network analysis using Fos immunoreactivity identified functional connectivity between the insular cortex and the network of regions involved in social decision making. These results implicate insular cortex as a novel target of OT and suggest that insula is a key component in the circuit underlying age-dependent social responses to stressed conspecifics.

neuroscience↗