Identification of neurons contributing to presynaptic inhibition in Aplysia californica.

Electrical stimulation of the connectives presynaptically inhibits the PSP from cell L10 to the left upper quadrant cells (LUQC). The present report describes the properties of some of the individual neurons contributing to this response. Action potentials produced in a cluster of cells in the abdominal ganglion reduce the amplitude of the L10-LUQC PSP for periods greater than 30 sec. At least some of their inhibitory action is mediated by a slow hyperpolarization of L10 which results in a decreased transmitter release. In other cases, however, the inhibition is produced with no significant alteration of L10 membrane potential, indicating that additional mechanisms may also be present. The neurons producing these effects are approximately 75 microns in diameter and are located on the left ventral surface of the ganglion. They have axons in the connectives and are thus activated by stimuli previously utilized to produce presynaptic inhibition. They appear to be some of the same cells that produce a slow inhibition of ink motoneuron L14; one of these has been identified as L32. The identification of these cells allows for the further biochemical, biophysical and morphological analysis of the events underlying presynaptic inhibition.