We sought to determine by using kainic acid (KA), an agent stimulating neuronal cell bodies but not fibers, whether the elevations in arterial pressure (AP) and heart rate (HR) elicited by electrical stimulation of the cerebellar fastigial nucleus (FN) are due to excitation of local neurons in FN or fibers passing through the area. Rats were anesthetized (chloralose 40 mg/kg), paralyzed (tubocurarine) and artificially ventilated. Electrical stimulation of FN (50 Hz, 10-100 microA) increased AP and HR. In contrast restricted microinjections of KA (0.05-5 nmol/100 nl) in FN elicited a sustained, dose-dependent decrease in AP and HR. The response is not due to diffusion of KA to adjacent sites. Excitation by KA of neurons intrinsic to FN elicits a heretofore unrecognized vasodepressor response, the fastigial depressor response.