Synaptosomal fractions from rat brain have long been used to determine rate and main features of synaptic protein synthesis. Using these fractions we have previously shown that in adult rats trained for a two-way active avoidance task, the local synthesis of two synaptic proteins of 66.5 kDa and 87.6 kDa is selectively enhanced.

To verify if the effect is age-dependent, we examined synaptosomal protein synthesis in brain macroregions of two years old rats trained for the same task. In comparison with control rats kept in their home cage, trained old rats exhibited a marked increase in synthesis of the 66.5 kDa protein in cerebral cortex, brainstem and cerebellum. A somewhat lesser increment occurred for the 87.6 kDa protein. In addition, the newly synthesized 87.6 kDa protein correlated with avoidances and escapes and inversely correlated with freezings in cerebral cortex and brainstem while correlations of the newly synthesized 66.5 kDa protein remained below significance. These correlative patterns are sharply at variance with those observed in trained adult rats. The data confirm that the local system of synaptic protein synthesis is selectively modulated by training, and show that the synaptic response of old rats differs from that of adult rats due to significant differences in behavioral responses.