Cryogenic blockade of the central nucleus of the amygdala attenuates aversively conditioned blood pressure and respiratory responses.

The central nucleus of the amygdala (ACE) was reversibly blocked during extinction of an aversively conditioned cardiorespiratory response in unanesthetized, freely moving cats. Cryoprobes were positioned bilaterally in the ACE of 4 cats and in the nucleus entopeduncularis of 1 cat. Blood pressure typically showed biphasic changes in response to the conditioned stimulus (CS) during non-cooling trials. Blood pressure initially dropped and then rose. Heart rate consistently dropped, and respiratory rate increased in response to the CS. ACE cooling did not alter the pre-CS baseline blood pressure, heart rate or respiratory timing, but changed the cardiorespiratory response to the CS. During ACE cooling, blood pressure and respiratory responses were greatly attenuated or abolished. No significant effect on the heart rate response was observed during ACE cooling. Cooling of a nearby structure, the nucleus entopeduncularis, did not affect blood pressure, heart rate or respiratory responses to the CS. These results support the hypothesis that the ACE plays a role in both cardiovascular and respiratory regulation during conditioned aversive responses. The study also suggests that, in cats, the predominant influence of the ACE on cardiovascular control is on blood pressure rather than on heart rate regulation.