Intermediate BA-NAc neuronal population engagement during interactions with the social reward stimulus
Using bulk Ca2+-activity fibre photometry it was possible to measure the in vivo peri-event activity of int-BA-NAc neurons during distal or proximal interactions with SR. Evidence for engagement would constitute an important complement to the c-Fos based evidence that a substantial proportion of int-BA-NAc neurons are responsive to SR. Of course, there was the caveat that both putative SR- or SA-engaged sub-populations of monovalent neurons were recorded from, and it has been demonstrated that BA-NAc aversion neurons are inhibited by reward . Despite this, in both distal and proximal phases of the SR test, there were consistent and transient increases in BA-NAc neuron Ca2+ activity coincident with episodes of socio-sexual behaviour. In the distal-SR phase, the activity increase occurred at 3-4 sec after social episode onset even though episodes were typically of 1-2 sec duration, perhaps reflecting post-contact processing of sensory (e.g. olfactory) stimuli. In the proximal-SR phase, the activity increase occurred at 2 sec after social episode onset, perhaps reflecting engagement during socio-sexual behavioural events including mounting and copulation . Integrating the findings with those from electrophysiological studies of local field potentials, the extent to which groups of BA glutamate neurons fire in a synchronized manner during interactions with emotional stimuli is positively associated with gamma oscillations; such synchronicity might explain how relatively small populations of neurons, such as BA-NAc neurons, can make marked contributions to circuitries underlying the processing of emotional stimuli and related behavior .