Transmitter release from normal and degenerating locust motor nerve terminals.

Abstract

1. An analysis has been made of spontaneous and evoked transmitter release from terminals of 'fast' excitatory motor axons on locust muscle fibres using intra‐ and extracellular recording together with a Ca‐electrode technique for activating transmitter release from single nerve terminals on multiterminally innervated muscle fibres. 2. Spontaneous intracellular miniature excitatory junction potentials (m.e.j.p.s), recorded at active spots on these muscle fibres, occurred non‐randomly with frequent bursts of m.e.j.p.s. 3. M.e.j.p.s of subnormal amplitude were also seen but contributed only a small fraction of the minature discharge. 4. The amplitude distribution of intracellularly recorded excitatory junction potentials (e.j.p.s) evoked during ionophoretic application of Ca onto single nerve terminals was adequately predicted by Poisson statistics. 5. During the course of nerve terminal degeneration m.e.j.p.s of subnormal amplitude became more frequent and eventually formed the major part of the miniature discharge. Transmitter quanta responsible for 'small' m.e.j.p.s did not contribute to evoked release either at normal or degenerating terminals. Evoked transmitter release from degenerating axon terminals before excitation‐secretion coupling failure conformed to Poisson statistics. 6. It is concluded that more than one release mechanism operates on the transmitter pool or pools in locust motor nerve terminals.

Properties of miniature excitatory junctional currents at the locust nerve‐muscle junction

“…2A (see also Fig. 1 A) a population of small m.e.j.c.s is sometimes detectable (Hodgkiss & Usherwood, 1978) similar to that found at vertebrate end-plates (Kriebel & Gross, 1974;Bevan, 1976). In normal bathing medium the mean m.e.j.c.…”

Evidence for a presynaptic action of chlordimeform at the insect neuromuscular junction

“…That the mechanism of evoked transmitter release is distinct from spontaneous transmitter release is suggested by the presence of "small" mepsps at normal and denervated neuromuscular junctions of locust [26] and frog [27,281. The "small" mepsps apparently represent transmitter quanta not released by nerve impulses.…”

“…An alternative explanation for the lack of correspondence between the spontaneous and evoked release of transmitter is that the two processes of transmitter release might depend on different mechanisms. That the mechanism of evoked transmitter release is distinct from spontaneous transmitter release is suggested by the presence of "small" mepsps at normal and denervated neuromuscular junctions of locust [26] and frog [27, 281. The "small" mepsps apparently represent transmitter quanta not released by nerve impulses. Small miniature potentials have also been described at vertebrate neuromuscular junctions poisoned by botulinum toxin 1291.…”

OsK2, a New Selective Inhibitor of Kv1.2 Potassium Channels Purified from the Venom of the Scorpion Orthochirus scrobiculosus

“…The experiments were made on the muscle fibres of metathoracic extensor tibiae nerve-muscle preparation of the locust Schistocerca gregaria (11). Miniature membrane potentials (MMP) of the nerve-muscle junction were recorded intracellularly from muscle fibre of the retractor unguis muscle using simplified technique (12). Nerve-muscle preparation was exposed and equilibrated for 1 h in locust saline standard composition (in mM): 170 NaCl, 10 KCl, 2 CaCl 2 , 10 Hepes, pH 6.8.…”