Neural mechanisms underlying behavior in the locust Schistocerca gregaria I. Physiology of identified motorneurons in the metathoracic ganglion

Abstract

A preparation of the desert locust, Schistocera gregaria, has been developed, in which it was possible to work with identified neurons while still allowing some behavior. A total of 26 motorneurons to the hind leg were studied singly, and in various pairs, both by direct stimulation, and by recording during spontaneous activity and various reflex actions. Motorneurons were identified by passing current into their somata and correlating the evoked somata spikes with extracellularly or intracellularly recorded events in the muscles. Tension of the muscle was also recorded and motor axons were stimulated to evoke antidromic spikes in the somata. Both epsp's and ipsp's can be seen clearly in recordings from the somata; spikes appear as electrotonically conducted remnants only. Somata exhibited little or no electrogenesis. It is inferred that impulses are initiated in a zone tentatively identified with the region of emergence of the motor axon from the neuropil. Integration occurs in the neuropilar segment, with the soma serving as a parallel RC element. Data was obtained on the central mechanisms of coordination of synergistic and antagonistic motorneurons and on the modes of excitation of slow and fast neurons to the same muscles.