Activation of subfornical organ efferents stimulates oxytocin secretion in the rat

The effects of activation of subfornical organ (SFO) efferents on plasma oxytocin concentrations were examined in conscious freely moving male Sprague-Dawley rats. Blood samples were obtained through chronically implanted atrial catheters and SFO efferents were activated electrically using chronically implanted bipolar stimulating electrodes. Hormone concentrations were measured by radioimmunoassay, and experimental animals were assigned to one of 3 experimental groups according to histologically verified anatomical locations of stimulating electrodes in either the SFO, the hippocampal commissure (HC), or the medial septum (MS). Electrical stimulation in the SFO resulted in increased plasma concentrations of oxytocin from control values of 2.54 +/- 0.9 pg/ml, to a post-stimulation level of 65.6 +/- 27.0 pg/ml. In contrast, stimulation in immediately adjacent structures including HC and MS was found to be without effect on plasma concentrations of oxytocin. These studies provide the first definitive evidence that SFO efferents may play a significant role in controlling the secretion of oxytocin from the posterior pituitary.