Oxytocin and Vasopressin Neuronal Activity In Response to Novel Versus Familiar Object Exposure In Mice

Abstract

Oxytocin (OT) and vasopressin (AVP), peptides synthesised in the hypothalamic supraoptic and paraventricular nuclei, are released during the introduction to a familiar or novel stimulus in low-stress social and environmental scenarios. Importantly, it is unknown whether the activity of neurons synthesising OT and AVP differs when animals are exposed to novel versus familiar objects. Therefore, mice were subjected to a short-term presence of a novel or familiar, small and distinctively shaped plastic object in a pre-exposed arena. Immunohistochemical analysis following exposure to a novel versus familiar object showed significantly greater activation of OT and AVP neurons in the paraventricular nucleus of the hypothalamus when exposed to a familiar stimulus versus a novel stimulus. Furthermore, immunohistochemical analysis showed an increasing, but not significant, trend in the number of active OT and AVP neurons in the supraoptic nucleus in response to a novel stimulus versus a familiar stimulus. Mice who received intraperitoneal injections of OT receptor antagonist L-368,899 prior to being exposed to a familiar versus a novel object showed a significant increase in the amount of time spent with a familiar object and a decrease of time spent with a novel object. We conclude that introduction to novelty results in a decrease in OT neuronal activity as well as changes in AVP neuronal activity in the paraventricular nucleus of the hypothalamus.