Posture and history of movement determine membrane potential and synaptic events in nonspiking interneurons and motor neurons of the locust.

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Abstract
In the locust, passively imposed changes in the rest angle of the femoral-tibial joint of a hindleg resulted in long-lasting changes in the membrane potential and synaptic inputs of ipsilateral motor neurons, and premotor nonspiking interneurons within the metathoracic ganglion. The angle of the femoral-tibial joint was changed at intervals of 15 s to 6 min, being held either at 0 (fully flexed), 90, or 140.degree. (nearly maximum extension). When the angle of the joint was changed from 90-0.degree., the maintained central changes were opposite to those occurring when the angle was changed from 90-140.degree.. Interneurons that were tonically depolarized when the joint was set at 0.degree. were tonically hyperpolarized when the joint was set at 140.degree.. The magnitudes of these changes differed from neuron to neuron. In 1 nonspiking interneuron the membrane potential differed some 15 mV between the 2 extremes of femoral-tibial joint angle; in another the difference was less than 1 mV. Approximately 80% of the nonspiking neurons that affected hindleg motor neurons responded tonically to changes in resting joint angle. The tonic responses of motor neurons and interneurons showed hysteresis. The steady membrane potential, pattern of synaptic inputs, and spike frequency (for tonic motor neurons) at a femoral-tibial angle of 90.degree. were different when that angle was approached from 0.degree. than from 140.degree.. There are widely distributed tonic changes in the activity of nonspiking interneurons and motor neurons according to the animals'' posture and its history of movement.

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