Mf. Klemm, NEUROMUSCULAR-JUNCTIONS MADE BY NERVE-FIBERS SUPPLYING THE LONGITUDINAL MUSCLE OF THE GUINEA-PIG ILEUM, Journal of the autonomic nervous system, 55(3), 1995, pp. 155-164
This study reports on the ultrastructure of the projections to the lon
gitudinal muscle of the guinea-pig ileum from nerves of the tertiary p
lexus. Reconstructions of serial electron micrographs through axons in
bundles of the tertiary plexus showed that the majority of vesicle co
ntaining profiles which became exposed through a gap in the Schwann ce
ll formed specialized neuromuscular junctions. At these junctions, the
exposed profile and the muscle cell were separated by less than 100 n
m and the intervening-cleft was filled with a single layer of basal la
mina. Small synaptic vesicles were aggregated towards the area of clos
e contact, In this tissue two different types of neuromuscular junctio
n were found. Two-thirds of junctions were similar to those found in o
ther tissues. They had many small vesicles aggregated towards the area
of junctional contact: some 20% of these junctions had pre-junctional
membrane specializations. The remaining junctions were smaller than t
hose usually found in autonomic end organs. These junctions covered a
small area of membrane and contained only a few small synaptic vesicle
s: pre-junctional membrane specializations were not found on these jun
ctions. Results of physiological experiments have shown that neurally
released transmitters activate a different subset of receptors to exte
rnally applied transmitters. The morphological data presented here sug
gest that specialized neuromuscular junctions exist where these recept
ors may be localised.