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.