Suppression of the cell body response in axotomized frog spinal neurons does not prevent initiation of nerve regeneration.

Frog spinal neurons, in animals maintained at environmental temperatures above 20 degree C, show the classic features of the cell body response following peripheral axotomy. In contrast, axotomized spinal neurons in frogs held at an ambient temperature of 15 degree C showed no apparent cell body response. The 15 degree C neurons retained normal morphology, continued to synthesize and transport normal levels of acetylcholinesterase activity, and sustained normal reflex connections. Despite the apparent absence of a cell body response, the proximal nerve stump began to regenerate. The apparent latency to the initiation of axonal growth was increased at 15 degree C; regeneration began 3.8 days after axotomy at 25 degree C, but 4.5 days following nerve section at 15 degree C. The rate of axon regeneration was also considerably slower at 15 degree C: 0.6 mm/day compared to 2.4 mm/day at 25 degree C. Nonetheless, these data imply that initiation of axonal sprouting and regeneration may not depend on alterations in the cell body. Additional data indicated that the appearance of the cell body response may not be linked to the elimination of a normal, peripherally-derived, constituent of the retrograde transport system. Injured motor axons at 15 degree C were able to acquire and transport horseradish peroxidase from the point of transection to the cell body. Material normally in transit to the cell body should also be drained from the injured axons over time. Yet, the elimination of this "trophic' supply did not induce the appearance of the cell body response.