Effects on protein synthesis produced by pairing depolarization with serotonin, an analogue of associative learning in Aplysia.

A form of associative plasticity in Aplysia, activity-dependent neuromodulation, involves the convergence of neuronal activity and the effects of a modulatory transmitter. To investigate the role of protein synthesis in associative plasticity, we examined the effects of a biochemical analogue of activity-dependent neuromodulation on the level of incorporation of labeled amino acid into proteins. To mimic associative training, abdominal ganglia were exposed to paired treatments of a depolarizing agent, elevated potassium, and a modulatory transmitter, serotonin. The effects of elevated potassium and serotonin applied alone were also examined. At least two proteins (nos. 9 and 17) were affected in a nonadditive way by the paired procedure. Incorporation of label into protein 9 was increased by the paired procedure but was not affected by either elevated potassium or serotonin. Incorporation of label into protein 17 was significantly affected by elevated potassium or serotonin, but the effect of the paired procedure was significantly less than the summed effects of elevated potassium and serotonin applied alone. These results indicate that changes in protein synthesis may be important in the induction of associative plasticities. Amino acid sequences of two peptides derived from protein 9 were obtained. Then, a partial cDNA clone for protein 9 was obtained by performing PCR with degenerate primers corresponding to portions of the sequences of the two peptides. The sequence of protein 9 is related to sequences previously reported for a family of genes comprising the stringent starvation protein of Escherichia coli, auxin-induced proteins of plants, and glutathione S-transferases of a number of organisms.