PERIPHERAL-NERVE AND MUSCLE FUNCTION IN THE AGING FISCHER-344 BROWN-NORWAY RAT

This study was designed to define the age-related changes that occur i n the F1 cross of the male Fischer 344 and brown Norway rats and to de termine if these findings were associated with electrophysiologic abno rmalities indicative of motor neuron loss. Contractility, morphologic, and histochemical studies were performed on the tibialis anterior mus cles (TA) from 25 male rats at ages 6, 18 and 30-32 months. Tibialis a nterior weight was 17% greater in the 18-mo vs 6-mo-old animals, but a t age 32 months mean TA weight was 20% less than at 18 months. Other c hanges at 32 months included a 12% decrease in specific tension and re duced contractile/relaxation velocities of isometric twitches and maxi mal tetanic tension; findings associated with a 40% decrease in type I Ib fiber cross-sectional area. Electrophysiologic studies on 15 rats r evealed prolonged H-reflex latencies at 18 and 32 months. Needle elect romyography demonstrated abnormal spontaneous activity consistent with peripheral axonal, not motor neuron loss. These findings demonstrate age-related changes in muscle mass and strength that are associated wi th changes in the peripheral nervous system. These findings are consis tent with previous work in homozygous, inbred strains and help to esta blish the F1 cross of the Fischer 344 and brown Norway strains as a po tentially useful rodent model in gerontologic studies of the neuromusc ular system.