Secondary late components of the muscarinic postsynaptic potentials, in rabbit superior cervical ganglion.
The well known muscarinic slow excitatory polysynaptic potential (s-EPSP) of rabbit superior cervical ganglion (SCG) peaking at about 1-2 s and lasting 5-10 s, is immediately followed by an abrupt change in slope to a longer, lower depolarizing phase. A brief dip in the level of depolarization (DP) often separates the two depolarizing phases. The secondary phase of s-EPSP rises to its own peak at about 25 s; total duration 60-120 s. With repetition of orthodromic volleys secondary s-EPSP builds up more gradually than initial s-EPSP, but more rapidly than slow-slow (ss-) EPSP. The later 'secondary' depolarizing phase along with the antecedent 'dip in DP' are, like the 'initial' s-EPSP, eliminated by a muscarinic antagonist, quinuclinidyl benzilate hydrochloride (QNB). This distinguishes secondary s-EPSP from the even slower rising non-cholinergic ss-EPSP. The ss-EPSP, although relatively small in the responses to the usual 3-pulse test stimuli, rises to an extraordinary amplitude (equal to the compound action potential) during a 10 s-120 s train of pulses. Gallamine blocked most of the slow IPSP component in test responses but not initial or secondary s-EPSP. A preganglionic conditioning train (10/s for 2 min) induced a long-term-enhancement (LTE) of secondary s-EPSP lasting greater than 3 h, with maximum postconditioning percentage increases greater than for initial s-EPSP. Also enhanced was the dip in DP, now forming a deeper notch between initial and secondary s-EPSPs; this attains a maximum at about 30 min postconditioning but thereafter progressively loses the enhancement by about 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)
Mochida
S
S
Department of Physiology, School of Medicine, University of California, San Francisco 94143.
Libet
B
B
D000818:Animals; D003213:Conditioning, Psychological; D004558:Electric Stimulation; D004594:Electrophysiology; D005728:Ganglia, Sympathetic / Q000502:physiology*; D009116:Muscarine / Q000037:antagonists & inhibitors / Q000502:physiology*; D011813:Quinuclidinyl Benzilate / Q000494:pharmacology; D011817:Rabbits; D013569:Synapses / Q000502:physiology*
D011813:Quinuclidinyl Benzilate; D009116:Muscarine