Cardiovascular and single-unit responses to subfornical organ stimulation are abolished by pentobarbital anesthesia

The nature of reflex cardiovascular responses to electrical stimulation in the central nervous system has been suggested to be influenced by anesthetic. We report here that pressor responses to subfornical organ stimulation observed in urethane-anesthetized rats (n = 4) are absent, or reversed in animals under pentobarbital anesthesia (n = 5; Student's t test, p < 0.01, compared with urethane anesthesia. Single-unit recordings from identified hypothalamic neurons (n = 60) showed that the activation of these cells, by subfornical organ efferents, with systemic angiotensin observed in urethane-anesthetized animals (29 of 39 cells tested), was not observed under pentobarbital anesthesia (2 of 21 cells tested). Bicuculline treatment of pentobarbital-anesthetized rats (n = 5) restores small pressor responses to subfornical organ stimulation (t test, p < 0.05), suggesting that potentiated GABA inhibition underlies this modified state under pentobarbital anesthesia.