Optogenetic stimulation of the infralimbic to nucleus accumbens shell projection in hedonics: Sex differences in rats

Current research into treatment for affective disorders like depression and addiction is focused on understanding pathways in the brain that participate in hedonic processing, the regulation of pain and pleasure. One of these key pathways is the glutamatergic projection from the infralimbic cortex to the nucleus accumbens shell of the rat brain (IL-NAcSh). The IL has been shown to be a homologue of the ventromedial prefrontal cortex in humans, an area known to be implicated in the regulation of affective states. Previous studies have shown the IL-NAcSh to be involved in the regulation of negative affect and have demonstrated that stimulation of the pathway during behavioral testing can suppress the expression of learned negative affect in male rats. The same effect has not been observed in female rats, suggesting sex differences in structure and possibly function. We sought to achieve a similar suppression of negative affect in female rats by testing a different stimulation frequency. Optogenetics was used to stimulate the IL-NAcSh projections, and a conditioned taste aversion (CTA) behavioral methodology was used to model the development of negative affect. We found that CTA was suppressed in male but not female rats at a stimulation frequency of 20 Hz, as previous studies had shown. Stimulation at 80 Hz also proved to be ineffective in female rats, providing evidence for the possibility that the IL-NAcSh has different functions in each sex and is not similarly involved in the regulation of learned negative affect in females as it is in males.Bachelor of Scienc