Innervation and neural excitation of ventral muscle fibres of the larva of the waxmoth, Galleria mellonella

Abstract

The ventral muscle fibres may be classified anatomically as oblique, segmental, and intersegmental. All have a very dense innervation on at least one surface. Synaptic areas were found in all sections examined under the electron microscope. The largest segmental fibre has, at a conservative estimate, at least 1000 synaptic areas. Terminating axons run beneath the muscle fibre basement membrane and tracheoblasts while still wrapped in glial cells. Sections of axons showing synapses are either entirely surrounded by muscle cytoplasm and an elaborate subsynaptic reticulum or perhaps are still in contact with glial cells over part of their surface. Apart from this, synaptic areas resemble those previously described in other insects. All fibres examined were innervated by one fast axon and the five segmental fibres used in locomotion are evidently a single motor unit supplied by the same axon. The electrical response to nerve stimulation is similar to that described previously in other lepidopterous larvae but slower than that recorded from muscle fibres of adults. The responses are graded and not propagated. This nerve-muscle preparation has advantages over most others described for electrophysiological study of herbivorous Lepidoptera.