Neurons innervating both the central amygdala and the ventral tegmental area encode different emotional valences.

Mammals are frequently exposed to various environmental stimuli, and to determine whether to approach or avoid these stimuli, the brain must assign emotional valence to them. Therefore, it is crucial to investigate the neural circuitry mechanisms involved in the mammalian brain's processing of emotional valence. Although the central amygdala (CeA) and the ventral tegmental area (VTA) individually encode different or even opposing emotional valences, it is unclear whether there are common upstream input neurons that innervate and control both these regions, and it is interesting to know what emotional valences of these common upstream neurons. In this study, we identify three major brain regions containing neurons that project to both the CeA and the VTA, including the posterior bed nucleus of the stria terminalis (pBNST), the pedunculopontine tegmental nucleus (PPTg), and the anterior part of the basomedial amygdala (BMA). We discover that these neural populations encode distinct emotional valences. Activating neurons in the pBNST produces positive valence, enabling mice to overcome their innate avoidance behavior. Conversely, activating neurons in the PPTg produces negative valence and induces anxiety-like behaviors in mice. Neuronal activity in the BMA, on the other hand, does not influence valence processing. Thus, our study has discovered three neural populations that project to both the CeA and the VTA and has revealed the distinct emotional valences these populations encode. These results provide new insights into the neurological mechanisms involved in emotional regulation.

Sex differences in oxytocin receptor binding in forebrain regions: correlations with social interest in brain region- and sex- specific ways.

Social interest reflects the motivation to approach a conspecific for the assessment of social cues and is measured in rats by the amount of time spent investigating conspecifics. Virgin female rats show lower social interest towards unfamiliar juvenile conspecifics than virgin male rats. We hypothesized that the neuropeptide oxytocin (OT) may modulate sex differences in social interest because of the involvement of OT in pro-social behaviors. We determined whether there are sex differences in OT system parameters in the brain and whether these parameters would correlate with social interest. We also determined whether estrus phase or maternal experience would alter low social interest and whether this would correlate with changes in OT system parameters. Our results show that regardless of estrus phase, females have significantly lower OT receptor (OTR) binding densities than males in the majority of forebrain regions analyzed, including the nucleus accumbens, caudate putamen, lateral septum, bed nucleus of the stria terminalis, medial amygdala, and ventromedial hypothalamus. Interestingly, male social interest correlated positively with OTR binding densities in the medial amygdala, while female social interest correlated negatively with OTR binding densities in the central amygdala. Proestrus/estrus females showed similar social interest to non-estrus females despite increased OTR binding densities in several forebrain areas. Maternal experience had no immediate or long-lasting effects on social interest or OT brain parameters except for higher OTR binding in the medial amygdala in primiparous females. Together, these findings demonstrate that there are robust sex differences in OTR binding densities in multiple forebrain regions of rats and that OTR binding densities correlate with social interest in brain region- and sex-specific ways.