Submitted on October 31, 2005
Accepted on January 17, 2006
Oxytocin actions within the supraoptic and paraventricular nuclei: differential effects on peripheral and intranuclear vasopressin release
Inga D Neumann1*, Luz Torner1, Nicola Toschi2, and Alexa H Veenema1
1 Institute of Zoology, Department of Behavioural Neuroendocrinology, University of Regensburg, Regensburg, Germany
2 Max-Planck-Institute of Psychiatry, Munich, Germany
* To whom correspondence should be addressed. E-mail: inga.neumann{at}biologie.uni-regensburg.de.
In response to forced swimming (FS), vasopressin (AVP) is released somato-dendritically within the supraoptic (SON) and paraventricular (PVN) nuclei, but not from neurohypophysial terminals into blood. Together with AVP, oxytocin (OXT) is released within the SON and PVN. Here, we studied the role of intra-SON and intra-PVN OXT in the regulation of local AVP release and into blood in male rats. Within the SON, bilateral retrodialysis of an OXT receptor antagonist (OXT-A) increased local AVP release in response to FS (60 s, 21°C, vehicle 2-fold, n.s.; OXT-A: 15-fold increase, p<0.05) without significantly affecting basal AVP release. In addition, local OXT-A elevated plasma AVP secretion under basal conditions (2-fold increase, p<0.05) without further elevation after FS. Within the PVN, exposure to FS elevated local AVP release, reaching significance only in the OXT-A group (vehicle: 1.4-fold, n.s.; OXT-A: 1.6-fold increase, p=0.050). Bilateral OXT-A into the PVN did not affect peripheral AVP secretion either under basal or stress conditions. Basal ACTH concentrations tended to be elevated by local OXT-A within the PVN (1.7-fold increase, p=0.076). In contrast, the swim-induced ACTH secretion was attenuated after retrodialysis of OXT-A within both the SON (at 5 min) and PVN (at 15 min) (p<0.05 both) compared to vehicle. The results demonstrate a receptor-mediated effect of OXT within the SON and PVN on local and neurohypophysial AVP release, which depend upon the activity conditions. Further, while exerting an inhibitory effect on HPA axis activity under basal conditions, hypothalamic OXT is essential for an adequate acute ACTH response.
