Differential ability of two adult molluscan neurons to regenerate electrical synapses.

The ability of two electrical synapses (neuron L4-R4 and neuron L19-R19) to regenerate in the adult Helisoma nervous system was examined. The L4-R4 electrical connection exhibited rapid restoration to 50% of normal strength, whereas L19-R19 reconnection was weak or absent. This disparity is attributable to the inability of neuron 19 to sprout effectively across a crush site in the buccal commissure, although peripheral sprouting was pronounced. The factors which underlie the inability of neuron 19 (but not neuron 4) to sprout into a central environment are unknown, but dictate differential synapse restoration in this adult nervous system.