INCREMENTAL REDISTRIBUTION OF PROTEIN-KINASE-C UNDERLIES THE ACQUISITION CURVE DURING IN-VITRO ASSOCIATIVE CONDITIONING IN HERMISSENDA

An incremental increase in the excitability (i.e., input resistance, e voked spike frequency) of B photoreceptors in Hermissenda accompanied successive pairings of light and presynaptic stimulation of vestibular hair cells (simulating light-rotation pairings in an intact animal). Analysis of protein kinase C (PKC) in the Hermissenda's photoreceptors indicated a training-induced incremental reduction of PKC in cytosoli c compartments, a tendency toward an increase in membrane compartments , and a small decrease in total enzyme activity (possibly owing to a d ownregulation or conversion of PKC to a calcium-independent state). Ne ither the biophysical or biochemical effects were observed in Hermisse nda exposed to unpaired light and rotation or in those trained in the presence of the selective PKC inhibitor NPC-15437 (which had no effect on synaptic interactions or light-induced generator potentials). Thes e results suggest that the intracellular redistribution of a protein k inase contributes critically to the kinetics of new learning.