Journal of Neurophysiology, Vol 67, Issue 2 470-476, Copyright © 1992 by APS
Use-dependent fade and slow recovery of long-term potentiation in superior cervical ganglion of the cat
M. Bachoo, M. A. Morales and C. Polosa
Department of Physiology, McGill University, Montreal, Quebec, Canada.
1. In anesthetized cats under partial block of nicotinic ganglionic
transmission by hexamethonium and in which the cervical sympathetic trunk
(CST) was split into two bundles of approximately equal size, a 40-Hz 5-s
conditioning stimulus train to one bundle produced prolonged potentiation
of the postganglionic compound action potential evoked by a test stimulus
to the same or to the other bundle [homosynaptic and heterosynaptic,
respectively, long-term potentiation (LTP)]. The LTP was detected also by
recording the nictitating membrane (NM) contraction in response to a test
preganglionic train. 2. The homosynaptic or heterosynaptic LTP produced by
applying the conditioning 40-Hz 5-s train to one bundle was markedly
depressed in amplitude and duration after stimulation of that bundle at 40
Hz for 20 min, whereas the homosynaptic or heterosynaptic LTP produced by
applying the conditioning 40-Hz 5-s train to the other bundle was
unchanged. The latter evidence suggests that all superior cervical ganglion
(SCG) synapses can still express LTP during the depression that follows the
40-Hz 20-min train. 3. In 4 h there was no appreciable recovery of LTP from
the depression produced by a 40-Hz 20-min train (n = 5). However, after 3
days (n = 3) and 5 days (n = 3), LTP recovered to 53 and 90% of control,
respectively. 4. When colchicine was applied to the CST bilaterally, at a
concentration sufficient to block fast axonal transport, and one CST only
was stimulated for 20 min at 40 Hz, the LTP recorded 4 days later was
significantly smaller on the stimulated than on the contralateral, control,
side.(ABSTRACT TRUNCATED AT 250 WORDS)
