Specific high molecular weight mRNAs induced by associative learning in Hermissenda

Associative conditioning of Hermissenda crassicornis has been demonstrated to result in long-term changes in the potassium currents IA and ICa2(+)-K+ in photoreceptor neurons in the eye and to increase mRNA levels in the eye 2- to 3-fold. mRNA isolated from Hermissenda trained with paired light and rotation stimuli was labeled with [3H]acetic anhydride, while mRNA from naive animals or from animals subjected to random light and rotation stimuli was labeled with [14C]acetic anhydride. The labeled RNA was combined and separated by agarose gel electrophoresis. The overall size distribution of labeled mRNA was shifted to longer chain lengths in the paired group. In addition, the 3H/14C ratios were markedly increased for 21 distinct size bands, indicating increased mRNA of specific chain lengths in the paired group. Increases in the same size bands were also observed with mRNA labeled in vivo with 32Pi. This indicates that associative learning in Hermissenda results in a specific induction of a distinct set of at least 21 mRNAs, rather than in a generalized increase in synthesis of all mRNA, thus resembling in some respects a differentiation-like response.