CHARACTERIZATION OF NEURONAL REGENERATION IN THE ABDOMINAL-GANGLION OF APLYSIA-CALIFORNICA

The ability of neurons in the abdominal ganglion of Aplysia to regener ate their axons following brachial nerve crush was studied using retro grade straining and intracellular dye injection, The duration of the g ill withdrawal reflex (GWR) was measured prior to and following nerve crush. Three days after crushing the nerve, the duration of the gill w ithdrawal reflex was reduced to 20% of control levels. There was rapid recovery 19 days after crushing the branchial nerve. The GWR duration returned to control levels by postlesion days 25-27. Same of the beha vioral recovery can be attributed to axonal regeneration. Regeneration , as evidenced by retrograde staining, was first observed by postlesio n day 15. The number of stained neurons in ganglia with crushes increa sed until postlesion day 33. The number of stained neurons in experime ntal animals was always less than that of controls (67 +/- 9% at postl esion day 56). More axonal regeneration was seen in the hemiganglion i psilateral to the branchial nerve. Regeneration after 32 days postlesi on was 60 +/- 5% of controls in the ipsilateral hemiganglion, as oppos ed to 29 +/- 6% in the contralateral hemiganglion. Regeneration of ind ividual neurons was also demonstrated. Identified neuron R2 was shown by intracellular dye injection and electrical stimulation of antidromi c action potentials to have an axon in the branchial nerve in all gang lia allowed to regenerate for longer than 32 days. These results indic ate that in Aplysia, despite behavioral recovery, complete axonal rege neration does not occur in a large segment of the neurons in the adult central nervous system. (C) 1998 John Wiley & Sons, Inc.