The presence of active systems of protein synthesis in axons and nerve endings has raised the question of the cellular origin of the local RNAs which were attributed to the neuronal soma almost by default. In experiments with squid preparations axoplasmic and presynaptic RNAs were shown to originate respectively in periaxonal glial cells and nearby cells.

Comparable experiments have been recently performed with slices from rat brain incubated with [3H]uridine. Under these conditions radiolabeled RNA accumulates in the incubated slices in approximately linear fashion for several hours. The process is markedly inhibited by actinomycin D, which indicates its prevalent origin from nuclear transcription processes. The distribution of newly synthesized RNA in the subcellular fractions prepared from incubated slices shows that a considerable amount is present in the synaptosomal fraction in a form which is largely released by hypo-osmotic treatment of the slices. The data provide preliminary support to the hypothesis of a local synthesis of presynaptic RNA in rat brain, and to the existence of synaptic systems of local gene expression.

This novel perspective might reveal unexpected insights into the mechanisms underlying brain plasticity.