Synapse formation in the absence of cell bodies requires protein synthesis.

Protein synthesis at distal synaptic sites is thought to play a critical role in long-term synaptic plasticity at preexisting connections. We tested whether protein synthesis in distal neuritic processes contributes to the formation of new synaptic connections by Aplysia neurons regenerating in cell culture after removing their cell bodies. Removal of either the sensory neuron (SN) or motor cell L7 cell body did not affect the formation of synaptic connections during the next 48--72 hr period. Increases in synaptic efficacy after removal of the SN cell body was accompanied by neurite growth and an increase in the number of SN varicosities contacting L7. The increases in synaptic efficacy and the number of SN varicosities were blocked by anisomycin, a protein synthesis inhibitor. The initial formation of synaptic connections was not affected by the absence of the L7 cell body. In the absence of cell bodies from both presynaptic and postsynaptic cells, synaptic efficacy increased for 48 hr and was blocked reversibly by anisomycin. These results support the idea that distal neuritic processes contain stable mRNAs and the macromolecular machinery for protein synthesis that are required for the formation of new synaptic connections.