Effects of food restriction on motoneuronal loss with advancing age in the rat.

The effects of life-long food restriction on motoneuronal cell death with advancing age was studied in male Fischer rats, which had access to food only 3 days a week after weaning (FR rats). Motoneurons innervating the medial gastrocnemius muscle were labeled with retrogradely transported HRP. The number of labeled motoneurons in FR rats and rats fed ad libitum (AL rats) was similar at the age of 16 months (131.8 +/- 1.7 for FR rats vs. 133.8 +/- 4.5 for AL rats). However, at 28 months of age, AL rats had less labeled motoneurons compared to FR rats (117.0 +/- 2.4 for FR rats vs. 124.3 +/- 7.0 for FR rats). The number of type I muscle fibers in the medial gastrocnemius muscle increased significantly in AL rats during the period from 16 to 28 months of age, which might reflect motor unit reorganization following retraction of axons and/or death of innervating motoneurons. FR rats did not show statistically significant alteration. These findings were also true for the data compiled from several different experiments including those conducted for primarily different purposes in our laboratory. The results suggest that life-long food restriction retards motoneuronal cell death occurring with advancing age.