FUNCTIONAL-CHANGES OF THE PERIPHERAL NERVOUS-SYSTEM WITH AGING IN THEMOUSE

The influence of aging on peripheral nerve and target organ function w as investigated in six groups of mice aged 2, 6, 9, 12, 18, and 24 mon ths. Sudomotor, motor, and sensory functions mediated by the sciatic n erve were evaluated by silicone imprints, electrophysiological recordi ngs and pinprick test from the distal hindpaw. Nerve conduction was al so studied in the caudal nerves. The results showed that the number of sweat glands reactive to pilocarpine does;lot change significantly wi th aging, but the size of the sweat droplets is smaller in aged mice t han in young mice. The amplitude of muscle and nerve action potentials evoked by stimulation of sciatic and caudal nerves decreased progress ively from 2 to.:24;months, while the latencies decreased from 2 to 6 months, remained unchanged until 12 months and increased thereafter. A il the animals of the six groups studied showed positive, indistinguis hable responses to pinprick. These results indicate that neurophysiolo gical responses mediated by large diameter nerve fibers deteriorated w ith age, while those dependent of small fibers were preserved.