Postural changes alter synaptic interactions between nonspiking interneurons and motor neurons of the locust.

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Abstract
In the locust, metathoracic ganglion nonspiking interneurons were depolarized or hyperpolarized with injected current steps to effect changes in the membrane potentials of postsynaptic tibial or tarsal motor neurons. The femoral-tibial joint of the ipsilateral hindleg was set at an angle of 0, 90 or 140.degree.. For some interneurons, the postsynaptic effects varied in amplitude according to the resting angle of the joint, and were largest at one extreme angle and smallest at the other. At the intermediate angle of 90.degree., the postsynaptic effects differed in size according to the previous set angle of the joint. Resistance and compensatory reflexes of tibial and tarsal motor neurons were elicited by varying sinusoidally the angle of the femoral-tibial joint. The strength of these reflexes could be changed by depolarizing nonspiking interneurons with small long-lasting current steps. The effects of nonspiking interneurons on motor neurons are flexible and can differ according to the context in which they occur.