ANGIOTENSIN-II AND GLUTAMATE INFLUENCE AREA POSTREMA NEURONS IN RAT-BRAIN SLICES

The area postrema (AP) has been repeatedly implicated in cardiovascula r regulation. Microinjection and single unit recording studies in vivo have suggested specific actions for angiotensin II (ANG) and glutamat e (GLU) in controlling the excitability of AP neurons. The present stu dy was therefore designed to examine the responsiveness of AP neurons to bath administration of these substances. Of the 133 AP neurons test ed with ANG (10(-8)-10(-6) M) 40% were excited, 13% inhibited and the remainder unresponsive. The excitatory effects of ANG on AP neurons we re dose-dependent. Following blockade of synaptic transmission with a low calcium high magnesium solution excitatory responses were maintain ed in 12 of 15 cells tested. Pretreatment of slices with the AT(1) rec eptor antagonist losartan blocked the excitatory effects of ANG in all cells (5/5) tested. The effects of GLU on AP neurons were also examin ed. Of the 71 AP cells tested, 40% were excited, 10% inhibited, 8% sho wed excitatory responses followed by periods of inhibition while the r emaining cells were unaffected. Excitatory effects of GLU were maintai ned in all AP neurons (7/7) tested during perfusion with low calcium, high magnesium solutions. Similar responses to NMDA were observed in f our of four cells tested, suggesting these GLU actions are mediated th rough NMDA receptors. These data demonstrate direct excitatory actions of ANG and GLU on AP neurons which are likely mediated through the AT (1) and NMDA receptors, respectively.