RABBIT SCIATIC NERVE FASCICLE AND‘ENDONEURIAL’PREPARATIONS FOR IN VITRO STUDIES OF PERIPHERAL NERVE GLUCOSE METABOLISM

Abstract

Abstract— Suitable preparations for in vitro studies of the composite glucose and energy metabolism of peripheral nerve axons and Schwann cells have not been available. Methods are described for the preparation and incubation of a defined segment of a rabbit sciatic nerve fascicle, free of epineurial contamination, but with an intact perineurial membrane; removing the perineurium provides in addition an‘endoneurial’preparation. Conditions were selected for incubating each preparation with glucose that maintained stable P‐creatine and ATP concentrations and a stable rate of O2 uptake; under these conditions the preparations retained an unaltered EM appearance during a 2‐h incubation. Glucose diffusion into the endoneurial compartment of the fascicle is restricted, possibly by the perineurial membrane, and a higher medium glucose concentration (20 mM) was required to maintain a steady state of energy metabolism in this preparation than in the‘endoneurial’preparation, which was incubated with 5 mwglucose. The‘endoneurial’preparation required 0.50 mm‐myoinositol in the medium to prevent a decrease in tissue free myoinositol and a slow decrease in O2 uptake, which occurred when it was omitted. Under the incubation conditions selected the glucose concentrations in the‘endoneurial’preparation and in the endoneurial compartment of the fascicle were reasonably similar, and the preparations had similar rates of respiration, similar estimated rates of glucose utilization, and similar relative rates of respiration and lactate production. The preparations derive the major fraction of their energy requirements from respiration. Their rates of O2 uptake are 60% higher than the previous indirect estimate of O2 uptake in whole rabbit tibial nerve in situ. Constant rates of incorporation of 14C from [U‐14C]glucose into CO2 and total lipid were observed in the‘endoneurial’preparation after a 15‐min equilibration period. The preparations reported provide suitable tools for in vitro studies of peripheral nerve metabolism not previously available.