Substrates supporting activity in immature nerve fibers

¹ Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire

The ‘A’ fibers within mixed nerve trunks from immature chicks (16–21 days incubation) become inexcitable after 2 hours in nutrient-free Ringer's solution. Conduction in the ‘C’ fibers persists up to 8 hours under the same conditions. In contrast, nerves from adult chickens or rats are capable of transmitting impulses up to 14 hours in the same media. Addition of 5 mm/l. glucose or pyruvate rapidly restores conduction; however, there is no restoration when a variety of carbohydrate intermediates are present for 5 hours. Anaerobic survival of conduction with paired nerves is longer in 5 mm/l. glucose than in 10 mm/l. pyruvate and is inversely proportional to the frequency of stimulation. Our findings suggest that: a) a glycolytic energy source in immature axons is available for activity during anaerobiasis; b) the axon membrane is relatively impermeable to certain carbohydrate intermediates; c) in developing nerve the fraction of the total metabolism that is essential for the maintenance of the excitatory state is relatively small.

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