Journal of Neuroscience, Vol 5, 9-15, Copyright © 1985 by Society for Neuroscience
Reciprocal inhibition in the motor nervous system of the nematode Ascaris: direct control of ventral inhibitory motoneurons by dorsal excitatory motoneurons
JP Walrond and AO Stretton
In previous physiological experiments (Stretton, A. O. W., R. M. Fishpool,
E. Southgate, J. E. Donmoyer, J. P. Walrond, J. E. R. Moses, and I. S. Kass
(1978) Proc. Natl. Acad. Sci. U. S. A. 75: 3493-3497), we have shown that
the dorsal cord of the nematode Ascaris lumbricoides includes the processes
of three types of dorsal excitatory (DE) motoneurons and one type of
ventral inhibitory (VI) motoneuron. Ultrastructural studies have revealed
that the axons of the DE motoneurons make monosynaptic contacts with the
dorsal processes of VI motoneurons. In this paper, we describe a
physiological preparation with which to investigate the properties of these
synapses. We show that activation of a DE neuron can excite a VI neuron
producing inhibition in ventral muscle cells shortly after dorsal muscle
cells are excited, thus mediating reciprocity between dorsal and ventral
muscles. Each VI dendrite receives input from four or five DE neurons;
activation of any one of these DE neurons is sufficient to activate the VI
neuron.