Converging projections of hydromineral imbalances and hormonal co-action upon neurons surrounding the anterior wall of the third ventricle.

Various structures have been found in the anterior third periventricular area (A3pV) which seem to be concerned with hydromineral imbalances, since they contain neurons which can sense changes in osmolality, blood volume, blood pressure, angiotensin II [Ang II] levels and temperature. These neurons also seem to be concerned with the setting in action of corrective responses at an autonomic or behavioural level. The discovery of neurons in this area that respond to more than one signal (for example osmotic and volaemic, or blood pressure and Ang II levels) suggested that this area has an integrative role. More recent findings from stimulation and lesion experiments have shown that the broadly inter-connected A3pV structures which extend from the region of the suprachiasmatic nucleus to the subfornical organ (SFO), are targets for many stimuli. Our recent electrophysiological data have strengthened the idea of an integrative role for A3pV structures. Iontophoretic application of various substances has shown that a single baro-sensitive neuron can have its firing modulated by Ang II. In the present paper we report the discovery of A3pV neurons which respond to both Ang II and vasopressin (VP). Furthermore the co-action of these two hormones may be subtractive, additive or even potentiating depending on conditions. It appears that, in addition to detecting hydromineral imbalances, the A3pV neurons can sense the presence of at least two sister hormones which can co-modulate their responsiveness.