In vivo development of cholinesterase at a neuromuscular junction in the absence of motor activity in Xenopus laevis.

Abstract

SUMMARY1. Embryos of Xenopus laevis were selected prior to the onset of innervation and were raised for 2 days in the anaesthetic tricaine methanesulphonate (200 ,ug/ml). The gross development of these tricaine-reared animals appeared normal despite the absence of spontaneous motor activity and the lack of motor responses to prodding with a pin. Motor activity quickly appeared when the anaesthetic was withdrawn.2. Intracellular recording from the myotomes of intact, tricaine-maintained animals failed to reveal any spontaneous muscle action potentials. Synaptic potentials increased in frequency and amplitude upon withdrawing tricaine, but resting potentials remained unchanged.3. Cholinesterase activity, detected histochemically, was observed at the ends of the myotomes, the main site of innervation. The intensity of the histochemical reaction product at these sites appeared to be about as great in the myotomes of tricaine-reared animals as in control myotomes.4. Miniature end-plate currents (m.e.p.c.s), examined by focal external recording, declined with a time constant of 2-9 + 0-2 ms (mean+ S.E. of mean) in the myotomes of tricaine-reared animals (stages 40-41). The time constants in the myotomes of control animals were 1'8 + 0-1 ms at stages 40-41 and 8-7 + 0-7 ms at stages 24-26 (shortly after the onset of innervation).5. The anticholinesterase neostigmine doubled m.e.p.c. time constants in the myotomes of tricaine-reared animals as well as in control myotomes at stages 40-41.6. It is concluded that motor activity is not required for the in vivo development of physiological levels of synaptic cholinesterase in Xenopus myotomal muscle.

Effects of long‐term conduction block on membrane properties of reinnervated and normally innervated rat skeletal muscle.

“…The importance of muscle activity is indeed already well known for synaptic AChE accumulation in mammals and chicks L0mo & Slater, 1980;Rubin et al 1980) but an impulse-independent factor also appears to contribute significantly. This is indicated by the findings that: (1) nerve terminals clearly possess the ability to instruct the myofibre on where to accumulate the AChE (see in particular L0mo & Slater, 1980); (2) in some species such as Xenopus, apparently normal amounts of synaptic AChE can form in complete absence of evoked action potential activity (Cohen, Greschner & Tucci, 1984); and (3) even in mammals some AChE accumulation does occur during synaptogenesis under the major conduction block of the present experiments, even though muscle fibrillatory activity could also be playing a role. Partial denervation of blocked muscle Partial denervation of blocked muscle would alone be sufficient to account for an equal magnitude of the changes of TTX-blocked and denervated muscles, by boosting the extrajunctional changes in innervated ITX-blocked myofibres (see Introduction and Cangiano et al 1984).…”

Development of synaptic currents in immobilized muscle of Xenopus laevis.

“…Sohal & Wrenn (1984) also reports that the high molecular weight form of AChE developed in both paralysed and aneural extraocular muscle of duck embryos. In developing Xenopus muscle, Cohen et al (1984) demonstrated that AChE activity increased despite immobilization by tricaine, a local anaesthetic. However, m.e.p.c.…”

Localization of acetylcholine receptors and cholinesterase on nerve- contacted and noncontacted muscle cells grown in the presence of agents that block action potentials

“…Correspondence should be addressed to Dr. D. F. Davey Rubin et al, 1980;Steinbach, 1974). This is also the case for the nerve-induced changes in ChE localization that occur in Xenopus myotomal muscle (Cohen et al, 1984;. By contrast, muscle impulse activity is important for the localization of ChE in rat (Cangiano et al, 1980;Lamo and Slater, 1980b;Weinberg and Hall, 1979) and avian muscles (Betz et al, 1980;Gordon et al, 1974;Rubin et al, 1980; but see Sohal and Wrenn, 1984).…”