Neuroanatomical and biochemical evidence for the involvement of the area postrema in the regulation of vasopressin release in rats.

Studies were carried out in the rat to determine if the area postrema (AP), a medullary circumventricular organ, might be involved in the control of vasopressin (VP) release. The data from this study demonstrate the existence of direct neural connections between the AP and the hypothalamic VPergic neurons of the supraoptic nucleus (SON) as showed by the retrograde tracer horseradish peroxidase (HRP). Labeled neurons were observed in the AP following HRP injections into the SON. In addition, rats with AP lesions showed an impaired ability to conserve water and concentrate their urine in response to an hypertonic NaCl load. They, also, failed to maintain sodium retention and showed an attenuation of VP release during intracellular dehydration. These findings indicate that AP plays an important role in the regulation of VP release during changes in osmotic environment and suggest that this medullary circumventricular organ is a part of central circuitry subserving salt-water balance.