A single allatostatin-immunoreactive neuron innervates skeletal muscles of several segments in the locust

Abstract

In the nervous system of embryos and adult Locusta migratoria, somata, neurites within the ganglia, and axons leaving the thoracic ganglia show allatostatin immunoreactivity. The immunoreactive efferent axons divide to follow different nerve branches and form varicose terminals on skeletal muscles. In the adult locust, one pair of motor neurons is particularly prominent among the allatostatin-immunoreactive neurons. The somata are located symmetrically in a lateral position in the first abdominal neuromere of the fused metathoracic ganglion. Each neuron gives rise to five axon branches projecting into ipsilateral nerves. Three axons project posteriorly and exit through the dorsal nerves of the abdominal neuromeres A1, A2, and A3. One axon extends into the metathoracic neuromere and exits through metathoracic nerve 1 (N1). The fifth axon extends anteriorly through the connective into the mesothoracic ganglion, where it leaves through the mesothoracic N1. The targets of this neuron, among them the mesothoracic and metathoracic muscles M87, M88, M116 and the dorsal longitudinal muscles M81 and M112, are located in five different segments. In addition to supplying skeletal muscles, the neuron forms neurohaemal-like structures in the sheath of nerve branches. The authors call this neuron the common lateral neuron (CLN). The innervation of several muscles by Diploptera allatostatin 7-immunoreactive axon branches with a common cellular origin and the anatomy of one of the corresponding motor neurons in adults, the CLN, suggest that allatostatin acts as a modulator of neuromuscular parameters in insects by multisegmental direct innervation of skeletal muscles.