1) Male prairie voles given low and medium doses of chronic intranasal oxytocin (OT) had significantly fewer cells containing OT in the paraventricular nucleus (PVN) of the hypothalamus compared to those given saline. 2) This decrease in OT-producing cells in the PVN likely contributed to the abnormal social behaviors previously observed in voles given these doses. 3) In contrast, OT cell numbers in the supraoptic nucleus (SON) were not significantly changed by any dose, suggesting the behavioral effects were mediated by PVN rather than SON projections.