Decremental conduction in a mammalian peripheral nerve.

Conduction velocities of the A-beta, A-delta and C-fibers in isolated vagal nerves were measured before, during, and after the nerve was exposed to sodium-deficient hypotonic solutions. The solution was kept at 23 degrees C. Recorded at a conduction distance of 18 mm and with the nerve in a 0.25% NaCl solution, the conduction velocity of the A-beta component in the response was found to decrease at an average rate of 1.07 m/s per min; of the A-delta, 0.35 m/s per min and of the C-fibers, 0.020 m/s per min. Thus, the A-delta component in the response would disappear in about 29 min; the C-component, in 49 min; and the A-beta component, in 54 min. Recorded at a distance of 36 mm, the decrease in conduction velocity of the A-beta was 1.40 m/s per min, of the A-delta, 0.43 m/s per min, and of the C-fibers, 0.023 m/s per min. Thus, recorded at this conduction distance, the A-delta would disappear in 20 min; the C-component, in 36 min; and the A-beta component, in 42 min. These findings indicate that when decremental conduction occurs in a mammalian peripheral nerve exposed to these solutions, the decrement is most apparent in the A-delta component, then the C-fiber component, and finally the A-beta component in the nerve. Similar observations were obtained in nerves exposed to 0.5% NaCl solution except that the rate of decrement was slower.