Journal of Neuroscience, Vol 7, 473-481, Copyright © 1987 by Society for Neuroscience
Structure and physiology of developing neuromuscular synapses in culture
T Takahashi, Y Nakajima, K Hirosawa, S Nakajima and K Onodera
The structure and function of developing neuromuscular synapses in culture
have been investigated. We used neuromuscular junctions formed by
coculturing dissociated muscle cells and dissociated neurons obtained from
Xenopus embryos. After recording nerve-evoked endplate potentials (e.p.p.s)
and spontaneously occurring miniature endplate potentials (m.e.p.p.s) from
a given junction, the same specimen was investigated for
electron-microscopic histology. We surveyed almost the total area of the
junctional region by making serial sections. Even in preparations
cocultured for only a short time (4-11 hr), both e.p.p.s and m.e.p.p.s
could be obtained. The junctional region of these early synapses revealed a
simple structure. The presynaptic terminals contained smooth-surfaced clear
vesicles, but there were no presynaptic specializations such as active
zones. The width of the synaptic cleft was variable, with predominance of
narrow regions (10-30 nm), and there was no basal lamina inside the cleft.
When the coculture time was 1 d or longer, the junctional area started to
show structural features resembling a mature neuromuscular synapse. In the
presynaptic terminal there were active zones, consisting of the presynaptic
density and an accumulation of vesicles near the density. In many
junctions, the postsynaptic membrane showed densities and thickenings, with
a widened synaptic cleft, that contained basal lamina. It is known that
growth cones, prior to making neuromuscular junctions, can release the
transmitter substance with a very long latency if stimulated repetitively.
In contrast, e.p.p.s with short latencies can be evoked by single stimuli
soon after the growth cones attach to muscle cells. However, our data did
not reveal any structural changes to account for such functional
changes.(ABSTRACT TRUNCATED AT 250 WORDS)
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