Spontaneously Occurring Posterior Paralysis: Further Studies to Determine the age of Onset and Progression of the Syndrome

Nodular deposits were observed in the vertebral canal of a few male F₁ rats that died with paralysis. By studying the lesions in rats that had severe paresis or paralysis at the time of death, it was possible to determine several features of this syndrome. The different incidences in the various strains and sexes was determined. The age-associated incidence in male F₁ rats was established. The lesions that were present in the spinal cords, spinal nerve roots, vertebrae, intervertebral disks, and skeletal muscle were described. In contrast to the finding in the paralyzed rats, lesions, when present, were mild, and several findings in the aging animals were not seen in those killed at younger ages. Nerve root and peripheral nerve degeneration occurred in both male and female F₁ rats. The earliest lesions began in rats between 18 to 22 months old and, surprisingly, these seemed to be more frequent in females than in the males.