Formation of C/EBP transcription factors and possible pathways for controlling their activity during learning in Helix.

Formation of a conditioned defensive reflex in the common snail is accompanied by activation of DNA-binding transcription factors of the C/EBP family. Incubation of the CNS with serotonin, which imitates the effects of conditioning, and stimulation of adenylate cyclase with forskolin also increase the efficiency with which these transcription complexes are formed. Induction of protein kinase C with phorbol ester had no stimulating effect on the formation of C/EBP factors. However, simultaneous treatment with phorbol ester and serotonin produced some increase in the cAMP-inducible effects on the activation of C/EBP transcription factors. Larger increases in the DNA-binding activity of transcription factors of the C/EBP family in response to stimulation of the cAMP-dependent pathway were seen in conditions of elevated intracellular Ca2+ concentrations (by incubation of the CNS with the calcium ionophore A23187 and forskolin). Thus, it is possible that the Ca2+ and cAMP-dependent regulatory systems converge, leading to increases in the efficiency of the formation of C/EBP transcription complexes, which may reflect the interaction of stimuli of different modalities during learning.