Structural changes in the denervated neuromuscular junction in coxal muscles of the cockroach Periplaneta americana

Abstract

1. 1. Structural changes at neuromuscular junctions of the cockroach, Periplaneta americana following denervation have been studied using the electron microscope. 2. 2. The first sign of structural change correlated with the total disappearance of the miniature potentials together with the response to nerve stimulation was an increase in electron density of the terminal cytoplasm and the presence of clamped synaptic vesicles. Up to 48 hr, the glial cell had not proliferated in the synaptic cleft. 3. 3. By 5 days following denervation, proliferation of the glial cells, which were eventually in close contact with the muscle fibre, took place. At this stage agglutination of the synaptic vesicles in the nerve terminal and lamellar body within the glial cell were apparent. 4. 4. By 18 days following nerve crush, three cellular layers of the nerve terminal had been observed, although the nerve terminals were lower in number per section of the regenerating preparations and the glial cell seemed to take up much more space in the synaptic cleft. 5. 5. From our electron microscopy it is concluded that the resumed spontaneous release of transmitter in the insect muscle might be derived from the regenerative nerve terminals, not from the glial cell which once engulfed the nerve terminal.