GLUTAMATE STIMULATION OF ARCUATE NUCLEUS INHIBITS RESPONSES OF SUBFORNICAL ORGAN NEURONS TO PLASMA HYPERNATREMIA AND ANGIOTENSIN-II

Experiments were done in urethane anesthetized rats to investigate the effect of glutamate (Glu) stimulation of arcuate nucleus of the hypot halamus (Are) on the discharge rate of subfornical organ (SFO) neurons during changes in plasma sodium concentration and angiotensin II (ANG II) levels. Extracellular recordings were made from 67 histologically verified single neurons within SFO. Of these, 17 (25.4%) were excited by intracarotid infusion of hypertonic NaCl and 21 (31.3%) by intraca rotid ANG II infusion. Five (29.4%) of the units excited by hypertonic NaCl were also excited by Glu stimulation of Are. Similarly, seven (3 3.3%) of the units excited by ANG II were also excited by Are stimulat ion. Additionally, four (19.0%) of the units excited by ANG II were in hibited by Glu stimulation of Are. The remaining SFO units did not alt er their discharge rate to activation of Are neurons. The response of units to hyper tonic NaCl or to ANG II was attenuated during simultane ous activation of Are. These data suggest that Are may be involved in modulating the activity of SFO neurons that function in the detection of blood-borne signals from the depletion of intra- and extracellular fluid volumes.