Oxytocin neurons in the anterior and posterior paraventricular nucleus have distinct behavioral functions and electrophysiological profiles.

Oxytocin is a neuropeptide that can either promote or inhibit affiliative social behaviors. Recent evidence suggests that these diverse effects are mediated by distinct oxytocin receptor-expressing neuron. An outstanding question is whether these behavioral effects are also driven by distinct or overlapping populations of oxytocin-producing neurons. The paraventricular nucleus (PVN) of the hypothalamus is a major source of oxytocin and sends projections to the mesolimbic dopamine system and the extended amygdala. Previous work found that social defeat increased oxytocin neuron activity in the anterior PVN (aPVN) but not posterior PVN (pPVN). We reduced oxytocin synthesis with antisense morpholino oligonucleotides in either anterior or posterior PVN in California mice (Peromyscus californicus), a strong model system for studying effects of social stress on brain function and behavior. Antisense morpholinos in aPVN had no effect on behavior in unstressed females but increased social approach and reduced social vigilance in females exposed to social defeat stress. In pPVN, antisense morpholinos reduced social approach in unstressed male and female California mice. We then used Oxt (Cre) mice to compare electrophysiological profiles of oxytocin in aPVN and pPVN with a population of oxytocin neurons in the bed nucleus of the stria terminalis (BNST). Oxytocin neurons in aPVN and BNST oxytocin neurons had higher post-synaptic potentials and responded more strongly to current injections versus oxytocin neurons in pPVN. These findings shed light onto functional and physiological heterogeneity of PVN oxytocin neurons. Our results suggest that context dependent effects of oxytocin are mediated by different populations of oxytocin neurons.