EARLY MALNUTRITION FOLLOWED BY NUTRITIONAL RESTORATION LOWERS THE CONDUCTION-VELOCITY AND EXCITABILITY OF THE CORTICOSPINAL TRACT

The physiological sequelae of undernutrition were investigated in rats that were undernourished from day 1-21 and subsequently free-fed to 7 5 days of age. Population responses were recorded in the corticospinal tract following surface stimulation of the motor cortex, which activa tes corticospinal cells directly, and also indirectly via cortical syn apses. The conduction velocity of the fastest corticospinal fibers in 15 malnourished rats was 16.9 m/s, significantly slower (P < 0.001) th an the 20.0 m/s observed in 26 controls. In addition, the excitability of corticospinal neurons to direct stimulation was reduced as much as 67% in malnourished rats, while no effect on synaptic activation was observed. Our findings suggest that early malnutrition reduces the num ber of large fibers in the adult corticospinal tract. These results ar e discussed with respect to known morphological and behavioral effects of malnutrition in rats and their relevance to humans.