Innervation of dipteran eclosion muscles: ultrastructure, immunohistochemistry, physiology and death.

The thoracic eclosion muscles of flies die by cytotoxic attack under neural control. We have investigated the innervation, ultrastructure and immunohistochemistry of the ventral eclosion muscle of Glossina. Two neurons located in the thoracic ganglion innervate this muscle. One of these is immunoreactive for serotonin and does not provide motor innervation. It appears to terminate near the attachment of an immunocyte involved in the dismantling of the muscle. The neuromuscular junction has features that distinguish it from any other chemical junction. A narrow, 3 nm gap separates pre- and post-synaptic membranes and this apparently acts to limit diffusion into and out of the junction. The immunocyte may use neuromuscular innervation as a path-finder to all muscle fibres and may even receive direct input from this source. Neuromuscular transmission is probably chemical as decreasing temperature results in decreasing amplitude of the (graded) muscle potential.