Electrical stimulation of the dorsal periaqueductal gray matter (DPAG), an aversive area of the rat brain, increased the mean blood pressure of awake rats as well as of animals anesthetized with urethane. 2. In the anesthetized rats, increases in heart rate and in breath rate were also induced by DPAG stimulation. 3. Chlordiazepoxide, a benzodiazepine, decreased the blood pressure rise caused by aversive stimulation of the brain in the awake rat. 4. Chlordiazepoxide elicited the same effect in urethane-anesthetized rats. In addition, the hyperpnea induced by electrical stimulation of the dorsal periaqueductal gray matter was also decreased by the drug. 5. The pressor response to intravenous noradrenaline was not affected by chlordiazepoxide. 6. These results suggest that benzodiazepines attenuate the neurovegetative changes accompanying emotion by depressing brain systems that integrate emotional behavior.
