[Parasympathetic discharges of the pelvic nerve during stimulation of different hypothalamic structures]

The characteristics of evoked responses in pelvic nerve elicited with electrical stimulation of posterior, tuberal, anterior hypothalamus and preoptic area were studied in anesthetized and immobilized cats. The complex response in pelvic nerve consisted of waves I, II, III with latencies from 13 to 28, 52 to 96, 113 to 256 msec, resp. The evoked responses of lowest thresholds and shortest latencies were obtained from the posterior hypothalamus. These data suggest that hypothalamic parasympathoactivating neurons are localized mostly in the posterior hypothalamus. After high frequency (100/sec, 10-sec. period) stimulation of posterior and anterior hypothalamus which produced blood pressure increase, the mean component of pelvic discharge--wave III was depressed during the whole period of the pressure reaction, the inhibition being of baroreflex origin. Early components of the discharges after tetanic stimulation of hypothalamus were facilitated. Paired stimulation of the hypothalamus demonstrated that nearly 2.5 sec were required for complete recovery of the evoked test-responses in pelvic nerve.