Neuronal responses to iontophoretically applied angiotensin II, losartan and aldosterone, as well as gustatory stimuli, in non-anesthetized control and desoxycorticosterone acetate-pretreated rats.

The neuronal mechanism of the sodium appetite initiated in rats by priming with a mineralocorticoid (desoxycorticosterone acetate (DOCA)) treatment and subsequent central angiotensin II (Ang II) was investigated using electrophysiological-iontophoretic techniques and sapid salt stimulation of the tongue in non-anesthetized restrained, DOCA-pretreated (0.5 mg/day s.c. for 3 days) or non-pretreated male Wistar rats. The rats were trained to drink water and a 1.6% NaCl solution while their heads were painlessly held in a stereotaxic apparatus with an attachment fixed to the skull. A total of 634 neurons (375 in non-pretreated and 259 in DOCA-pretreated rats) were recorded in the medial septum and median preoptic area during iontophoretic application of Ang II, aldosterone or losartan, or tongue application of the salty solution or water. Of the 151 neurons recorded in control rats during the application of the solutions on the tongue, one (0.7%) was found specifically excited and 16 (10.6%) inhibited by the sapid sodium. Similarly, of the 110 neurons tested in the DOCA-pretreated rats, 5 (4.5%) were found specifically excited and 8 (7.3%) inhibited by the sapid sodium. The number of neurons responding to the iontophoretically applied agents was not significantly changed by the DOCA pretreatment. Thus, the DOCA pretreatment significantly increased the number of preoptic neurons that were specifically excited by a salty solution applied on the tongue. These results suggest that hormonally induced changes in the gustatory responsiveness of ventral forebrain neurons may be part of the sequence that alters the hedonic valence of NaCl during sodium appetite.