Activation of Infralimbic to Nucleus Accumbens Shell Pathway Suppresses Conditioned Aversion in Male But Not Female Rats.

Abstract

Hedonic processing plays an integral role in directing appropriate behavior, but disrupted hedonic processing is associated with psychiatric disorders such as depression. The infralimbic cortex (IL) is a key structure in affective processing in rodents and activation of its human homolog, the ventromedial prefrontal cortex, has been implicated in suppressing aversive states. Here, we tested whether optogenetic activation of glutamatergic projections from the IL to the nucleus accumbens shell (NAcSh) suppresses the aversive impact of sucrose devalued using the conditioned taste aversion paradigm in males and female rats. In naive rats, no significant differences in appetitive or aversive taste reactivity (TR) to sucrose was observed indicating that initial sucrose palatability was equivalent across sex. However, we found that optical activation of the IL-NAcSh pathway during intraoral infusion of devalued sucrose inhibited aversive TR in male but not female rats. Interestingly, when allowed to freely ingest water and sucrose in a two-bottle test both males and females with a history of IL-NAcSh stimulation exhibited greater preference for sucrose. Optical pathway activation failed to alter TR to innately bitter quinine in either sex. Finally, both sexes lever pressed to self-stimulate the IL-NAcSh pathway. These results indicate that the IL-NAcSh pathway plays an important role in suppressing learned aversive states selectively in males but spares hedonic processing of innately aversive tastants. Further, pathway activation is reinforcing in both sexes, indicating that suppression of conditioned aversive TR can be dissociable from the effects of unconditioned rewarding properties of IL-NAcSh pathway activation.SIGNIFICANCE STATEMENT Negative emotional states contribute to psychiatric disorders including depression and substance use disorders. In this study, we examined whether brain circuitry previously implicated in suppressing negative emotional states in humans can inhibit learned aversion in male and female rats. We found that optical activation of the infralimbic to nucleus accumbens shell pathway attenuates learned aversive responses in male but not female rats, indicating an important sex difference in the function of this brain pathway. Furthermore, we found that pathway stimulation was reinforcing in both sexes. Collectively, these findings support the role of the infralimbic cortex and its projection to the nucleus accumbens shell in suppressing learned negative emotional states and highlight an important sex-specific function of this pathway.