CARDIOVASCULAR AND SINGLE-UNIT RESPONSES TO SUBFORNICAL ORGAN STIMULATION ARE ABOLISHED BY PENTOBARBITAL-ANESTHESIA

The nature of reflex cardiovascular responses to electrical stimulatio n in the central nervous system has been suggested to be influenced by anesthetic. We report here that presser responses to subfornical orga n stimulation observed in urethane-anesthetized rats (n = 4) are absen t, or reversed in animals under pentobarbital anesthesia (n = 5; Stude nt's t test, p < 0.01, compared with urethane anesthesia. Single-unit recordings from identified hypothalamic neurons (n = 60) showed that t he activation of these cells, by subfornical organ efferents, with sys temic angiotensin observed in urethane-anesthetized animals (29 of 39 cells tested), was not observed under pentobarbital anesthesia (2 of 2 1 cells tested). Bicuculline treatment of pentobarbital-anesthetized r ats (n = 5) restores small presser responses to subfornical organ stim ulation (t test, p < 0.05), suggesting that potentiated GABA inhibitio n underlies this modified state under pentobarbital anesthesia.