Regeneration of an interneuronal network in Helisoma: re-establishment of synaptic contacts

We have identified a network of three interneurons located in the central ring ganglia of Helisoma. Two of these interneurons, designated Left Pedal Dorsal 1 (LPeD1) and Right Pedal Dorsal 1 (RPeD1), are the largest neurons of the pedal ganglia and appear to contain dopamine and serotonin, respectively. A third interneuron, identified as Visceral Dorsal 4 (VD4), is a small FMRFamide immunoreactive cell located on the dorsal surface of the visceral ganglion. Monosynaptic chemical connections exist between all these interneurons. For instance, a reciprocal inhibitory connection exists between LPeD1 and RPeD1, whereas VD4 has inhibitory effects on both LPeD1 and RPeD1. Furthermore, LPeD1, but not RPeD1, has an excitatory connection with VD4. We demonstrate that following axotomy these interneurons not only regenerate their axons but re-establish their appropriate synaptic connections.