LONG-TERM ENHANCEMENT BUT NOT SHORT-TERM IN HERMISSENDA IS DEPENDENT UPON MESSENGER-RNA SYNTHESIS

The reversible transcription inhibitor 5,6-dichloro-1-beta-n-ribobenzi midazole (DRB) was used to examine the contribution of mRNA synthesis to long-term enhancement (LTE) following one-trial conditioning of Her missenda. Inhibition of mRNA synthesis by DRB or inhibition of protein synthesis by anisomycin did not significantly affect the induction an d maintenance of short-term enhancement (STE) examined 1 h after one-t rial conditioning. In contrast to the absence of an effect of the inhi bitors on STE, LTE was blocked by DRB or anisomycin applied shortly be fore and during the presentation of the conditioning trial. Consistent with previous reports, animals that received an unpaired CS and US di d not exhibit LTE. In addition, a control group that received a concen tration of DRB (10(-7) M) that does not significantly affect mRNA synt hesis exhibited typical LTE when tested 24 h postconditioning. These r esults demonstrate that the induction of LTE produced by one-trial con ditioning is dependent upon transcription and the regulation of gene e xpression. (C) 1997 Academic Press.