Intrasegmental inhibition of the displacement-sensitive pathway in the crayfish (Procambarus clarkii)

Abstract

1. Inhibition across the body median ofProcambarus was investigated using fluid movement as stimulus. The medially cut tailfan with connected isolated ventral cord was mounted in two compartments of the dissection dish in order to stimulate selectively each side of the fan (Fig. 1). 2. Higher order interneurons (as inferred by latency of response to electrical root stimulation and response behavior) of the fluid-movementmonitoring pathway are subject to much stronger inhibitory influences than are lower order interneurons. 3. Among the interneurons strongly inhibited by contralateral stimuli two groups are established: fibers that receive unilateral input and others that receive excitatory input from both sides of the body. The group of ‘bilaterals’ receives stronger inhibition than do fibers with unilateral excitation. 4. Inhibitory circuits crossing the median line of the body are functionally subdivided so as to convey inhibition only between interneurons of the same vector polarity. 5. The strong inhibitory influence (in the average 80% reduction of a response to an exclusively ipsilateral stimulus of comparable strength) observed in fibers with bilateral input suggests that the function of such interneurons in this system of orientation to the signal source is the indication of fluid movement parallel to the long axis of the body using a method comparable to the balancing of a bridge circuit.