Mechanism of heterosynaptic facilitation in the giant cell of the abdominal ganglion of Aplysia depilans.

In certain cells in the right upper quadrant of the abdominal ganglion of Aplysia depilans, a small excitatory post-synaptic potential (EPSP), produced by a weak stimulus to one pathway (test stimulus), underwent a prolonged facilitation when it was paired several times with a very strong stimulus to a second pathway (priming stimulus). In some cells this heterosynaptic facilitation was dependent upon the concomitant pairing of the two stimuli; in the right upper-quadrant giant cell the facilitation was independent of pairing (Kandel & Tauc, 1965). The stimulus parameters for optimal heterosynaptic facilitation in the giant cell were analysed in the preceding paper (Kandel & Tauc, 1965). The analysis of the mechanism underlying this facilitation is presented in this paper. This analysis was facilitated by the reliable identification of the right upperquadrant giant cell, as well as its large size (300-800 ,u). A preliminary note on this work has already been published (Kandel & Tauc, 1964).