Cell number deficiencies in the nervous system of dwarf mice

Abstract
A quantitative histologic investigation has been performed on the nervous system and striated muscle of the dwarf mouse (Snell's Strain).The number of nerve cells in the spinal cord of the dwarf mouse is half of that seen in the normal mouse. These data are fully confirmed by separate counts of efferent and afferent fibers of the spinal roots. Spinal root fiber diameters are similar in both normal and dwarf mice. The number of muscle fibers in the peroneus longus muscle is about the same in both the normal and in the dwarf mouse; the diameter of each muscle fiber, however, is reduced in the dwarf.At the muscular level the deficiency manifests itself as a volumetric reduction in the muscle fibers; whereas, at the level of the spinal cord there is a reduced number of nerve cells. It follows from these observations that in the dwarf mouse the ratio of nerve fibers to muscle fibers within a motor unit is altered so that each motor neuron innervates more muscle fibers than in the normal mouse. This fact could explain the peculiar movements of the dwarf mouse.