Posttetanic long-term potentiation in the dentate gyrus of freely moving rats is accompanied by an increase in protein synthesis.

In rats, the incorporation of L-[U-14C]leucine into proteins of cytosolic (soluble proteins) and of the 100,000 x g pellet fraction from ipsilateral hippocampus subregions (CA1, CA3 and CA4/area dentata) and visual cortex was studied from 5 min to 65 min after electrical tetanization of the right perforant path. The rates of protein synthesis were estimated calculating the relative specific radioactivity of proteins (RSA). The stimulation parameters used were identical to those of previous experiments inducing post-tetanic long-term potentiation (LTP) of both the amplitude of population spike and the slope function of the excitatory post-synaptic potential (EPSP) in the area dentata. Under these conditions, RSA-values of both fractions evaluated in the CA4/area dentata were found to be about two times higher in tetanized rats compared to either stimulated or passive controls (p less than 0.05). In all the other brain regions studied, no differences between tetanized and control animals were observed. These results provided evidence for an LTP-induced augmentation of protein synthesis in the ipsilateral dentate area which might be an essential prerequisite for those structural changes realizing the long-lasting enhanced efficacy of synaptic transmission at the perforant path-granular cell connections within this hippocampus subfield.