The effects of lesions on cockroach giant interneurones (GIs) were studied to investigate the transient, Ca-dependent, action potentials which have been reported to appear near the tips of regenerating GIs (Meiri, Spira & Parnas, 1981). We were unable to repeat these observations. Ligation of connectives, before cutting, delayed the degenerative changes in segments of GIs that were separated from their cell bodies. The short-term injury response (which was normally observed on cutting while recording close to the site of lesion) was not recorded when the axon was ligated. The effect of cutting GIs at different distances from their cell bodies was also investigated. There was no apparent relation between the response of GIs to a lesion and the site of the lesion. Sprouting of GIs was observed both at the tip of the axon and also at sites some distance from the lesion. No changes of the cell body or its dendritic tree in the terminal ganglion were seen but sprouting was observed in other ganglia.

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