Long-term potentiation induced changes in protein synthesis of hippocampal subfields of freely moving rats: time-course.

The incorporation of L-[U-14C]leucine into proteins of cytosolic (soluble proteins) and of the 100,000 x g pellet fraction from ipsilateral hippocampal subfields (CA1, CA3, CA4/area dentata) of rats was studied during and at various times after electrical tetanisation of the right perforant pathway using topical precursor applications and 1 h incorporation periods. Rates of protein synthesis were estimated calculating the relative specific radioactivity of proteins (RSA). The RSA-values of both protein fractions estimated in the ipsilateral CA4/area dentata were found to be about two times higher in tetanised rats compared to either passive or stimulated controls (p less than 0.05) when leucine was administered 5 min after tetanisation. Under these conditions, no differences between tetanised and control animals were observed in all other hippocampal subfields studied. No differences in RSA-values evaluated in CA4/area dentata between tetanised and passive controls were detected when leucine was administered immediately prior to tetanisation. From 2 h to 8 h after induction of LTP, protein synthesis in CA4/area dentata of tetanised rats appeared to be decreased (p less than 0.05) compared to passive controls. These results provide evidence for a transient LTP-induced augmentation of protein synthesis in the targets which might be an essential prerequisite for those structural changes realising the long-lasting enhanced efficacy of synaptic transmission at perforant path/granular cells connections.