Oxytocin in the CeA on OT and AVP mRNA expression and hormonal responses induced by BVE

Abstract

We investigated the effects of oxytocin (OT) and the oxytocinergic antagonist vasotocin (OVT) injection in the central amygdala (CeA) in the regulation of vasopressin (VP) and OT mRNA expression in the hypothalamus. We also assessed VP and OT plasma levels in response to isotonic volume expansion (BVE). Male Wistar rats with cannulas unilaterally in the CeA were subjected to BVE (2 ml/100 g bw). OT (1μg), OVT (1μg) or vehicle was injected into the CeA 20 min before the BVE. 5 min after BVE rats were decapitated and the blood was collected for OT and VP plasma determination. Another group was submitted to the same protocol and perfused 40 min after BVE. Brain sections of the paraventricular (Pa) and the supraoptic (SON) nuclei were processed for in situ hybridization using a 35S‐labeled VP or OT probe. In rats treated with vehicle in the CeA, BVE increased plasma OT levels. OT injection in the CeA reduced VP mRNA expression in the SON, but did not alter plasma VP. Also, OT in the CeA enhanced the effects of BVE on plasma OT while OVT reduced this effect. OVT in the CeA enhanced the effects of BVE on plasma VP but did not change VP mRNA expression. Our data suggest that OT in the CeA inhibits the central neural network that controls the VP mRNA expression in the SON neurons. In parallel, OT in the CeA may modulate the physiological mechanisms involved in plasma OT release but does not affect OT gene expression in the Pa and SON following isotonic BVE.