Electrolytic lesions in the depressor area of the ventrolateral medulla of the rat abolish depressor responses to the aortic nerve stimulation.

The pressor (VLPA) and the depressor (VLDA) areas in the ventrolateral medulla were identified with the microinjections of L-glutamate (1.77 nmol/site) in artificially ventilated, pentobarbital-anesthetized male Wistar rats. Electrical stimulation of the left or right aortic nerve (1-6 V, 10-40 pulses/s, 3 ms) produced usual depressor responses. Electrolytic lesions (2.5 mA for 30 s) were placed bilaterally in the VLDA. Lack of responses to subsequent microinjections of glutamate into the VLDA indicated that the lesions were complete. The function of the VLPA was not compromised because it continued to respond to microinjections of glutamate. Subsequent stimulation of the aortic nerves failed to elicit the usual depressor responses. These results confirm our earlier reports indicating that the VLDA is important in mediating the depressor component of the aortic baroreflex.