ELECTROPHYSIOLOGIC AND CYCLIC-AMP CHANGES IN AXON-TRANSECTED FROG SPINAL ROOTS

Transection of a lumbar spinal nerve in the frog produces a disruption of spinal reflexes, a decrease in spinal nerve conduction velocity proximal to the lesion, and alterations in axonal cyclic AMP concentration. Conduction velocity decreases to 85% of control within 7 days of axon transection, and reaches a value 65% of control by 21 days. Monosynaptic spinal reflexes, initiated by either the descending lateral column (LC) pathway or intact lumbar dorsal roots (DRs), show a progressive increase in latency and a decrease in amplitude beginning 17 days postaxotomy. The disruption of reflex pathways continues in nonregenerating systems, but reflexes are restored to normal if regeneration occurs. The predominantly somatic terminations of the LC recover earlier than the predominantly axodendritic synapses of the DR. The signal(s) which initiates these axotomy-induced alterations in neuronal function remains to be identified. The cyclic AMP concentrations of normal and axon-transected spinal roots were measured to determine if cyclic nucleotides could play a role in this communication system. Cyclic AMP increased transiently in spinal roots 6 to 7 days after spinal nerve transection, then returned to control values and eventually began to decline 21 days postaxotomy. With the onset of regeneration, ventral root cyclic AMP concentration returned to control levels, but dorsal root concentration remained depressed. This disassociation between dorsal and ventral roots may reflect a preferential distribution of axonally transported materials into the peripheral process of the sensory axon. © 1979.