Response of rat superior salivatory units to chorda tympani stimulation

Unit responses to chorda tympani stimulation in urethane anesthetized rats were characterized by response latency and frequency following ability. One hundred and fifty one units responded with constant latencies, mean: 16.9 msec, S.D.: 7.8 msec. Responses recorded from within the superior salivatory nucleus (SSN) had significantly longer latencies (18.8 +/- 6.8, n = 94) than those from surrounding areas (13.5 +/- 8.3, n = 50) (p less than 0.001). This difference was due to the higher incidence of responses with latencies between 2.7 and 10 msec outside of the SSN (44%) compared to SSN responses (8%). Ability to follow high frequency stimulation ranged from 2-550 Hz, and was the same for SSN neurons and those outside the nucleus. The population of responses localized to the SSN, with latencies greater than 10 msec and with high (greater than 100 Hz) frequency following, had a mean latency of 20.5 msec. The estimated conduction velocity for these presumed preganglionic, parasympathetic neurons is 0.85 M/sec +/- 0.25, significantly slower than that reported for similar responses in cats. The antidromic nature of these responses requires confirmation.