Journal of Neurophysiology, Vol 65, Issue 3 639-647, Copyright © 1991 by APS
Long-term potentiation of nicotinic transmission by a heterosynaptic mechanism in the stellate ganglion of the cat
M. Bachoo and C. Polosa
Department of Physiology, McGill University, Montreal, Quebec, Canada.
1. In the anesthetized, scopolamine-treated cat, the compound action
potential (CAP) evoked by a single supramaximal shock to the third thoracic
white ramus (T3WR) was recorded in the inferior cardiac nerve (ICN). The
CAP was depressed in a dose-dependent manner by the intravenous
administration of the nicotinic antagonist hexamethonium (C6). 2. During
steady intravenous infusion of C6, which reduced the amplitude of the CAP
by 80-90%, a short train of stimuli (few seconds, 10-40 Hz) to the
sympathetic trunk just below T4WR potentiated the CAP for periods of tens
of minutes to 1-2 h (heterosynaptic long-term potentiation, LTP). An LTP of
similar time course was obtained when both train and single shock were
applied to T3WR (homosynaptic LTP). Magnitude and duration of the
heterosynaptic LTP were dependent on number, frequency, and intensity of
the stimuli. No LTP was produced by a train to the ICN. Heterosynaptic LTP
was also observed in the absence of C6. Because of the limited subliminal
fringe of the test input under this condition, the LTP was of small
magnitude. Heterosynaptic LTP also of the heart rate (HR) response to a
test stimulus was observed after a conditioning train. 3. The conditioning
train produced a displacement to the right of the dose-response curve for
C6. The intravenous dose of C6 required for 50% attenuation of the test CAP
increased from 0.84 +/- 0.15 (SE) mg/kg pretrain to 2.56 +/- 0.46 mg/kg
posttrain (n = 5, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
