Many intermediate BA-NAc neurons are monovalent with respect to social reward and social aversion
Using physical reward and aversion stimuli, the evidence from single neuron recording is that most responsive intermediate BA-NAc neurons were engaged by one emotional valence specifically, with more neurons responding to reward than aversion . Here we used Fos-TRAP methodology combined with c-Fos immunostaining to investigate whether int-BA-NAc neurons that respond to SR also do so to SA, and vice versa . Relative to control-social mice in which about 50% of neurons that responded once to SR or to SA did so again at SR or SA re-exposure, a substantially lower proportion of BA-NAc neurons that responded to SR responded subsequently to SA, and vice versa . The number of neurons responding exclusively to SR or to SA was equable. Therefore, we conclude that the majority of int-BA-NAc neurons are monovalent with respect to SR and SA and the number of neurons making up these two monovalent populations are similar. A previous study that used nicotine as reward and foot shock as aversion reported that the BA (not BA-NAc pathway specifically) contains intermingled populations of monovalent reward and aversion neurons, with activation also measured using c-Fos. Furthermore, Fos -dependent photo-stimulation of these neurons induced valence-specific and -relevant physiological and behavioral responses . The mice that we exposed twice to the same stimulus type provided essential control groups, and they also yielded important additional data on BA-NAc neuron engagement: firstly, more neurons were engaged by two exposures to SR or SA than were engaged by one exposure; second, the average intensity of neuronal c-Fos activation was lower at the second exposure. These findings are consistent with: weakly responsive (sub-threshold c-Fos activation) neurons nonetheless forming a memory of the stimulus that sensitizes their activation at stimulus re-exposure; previously activated neurons forming a memory of the stimulus that habituates their activation at stimulus re-exposure.