Degenerative Myelopathy in Three Strains of Aging Rats

Abstract

Absrracr. Spontaneous paresis and paralysis associated with degenerative spinal cord and spinal nerve root lesions occurred in three strains of rats used in studies of aging. Focal or segmental spinal cord lesions had mild to severe dernyelination, loss of nerve axons, and lipid-filled gitter cells. The lesions were limited to the white matter and were most severe in the lateral and ventral funiculi. The nerve roots had cholesterol clefts, focal hemorrhage, and demyelination. Atrophy of the skeletal muscle probably was secondary to the cord lesions. Vertebral lesions that involved the spinal canal and vascular blood flow were found, which may explain pathogenesis.Spontaneous posterior paralysis with associated spinal cord and spinal nerve root lesions occurs in several rat strains [3, 5, 131. The syndrome is usually associated with aging since the paralysis has been seen only in rats more than 2 years old. Along with paralysis, severe atrophy of skeletal muscle in the posterior part of the body also has been seen. The condition is progressive and eventually results in death. The cause and pathogenesis are unknown. Some rats had tumors in the spinal cord or canal that could have caused paralysis whilst others had large pituitary tumors. However, in most rats, no specific cause could be found.Three different strains of rats were kept for aging studies at the Institute for Experimental Gerontology. Sporadic cases of paralysis occurred in two strains, but the incidence was very low. We have noticed that the third strain (F, hybrid of the other two strains) has a much higher incidence of posterior paresis and paralysis. Preliminary studies on these rats are presented and the pathologic features are compared to those in other reports [3, 5, 9, 131.

Effects of aging and axotomy on the expression of neurotrophin receptors in primary sensory neurons

“…This finding indicates a positive correlation between the degree of trk-receptor deficit and clinical symptoms, because the hind limbs show the most severe behavioral deficits in the aged rat. This is also consistent with morphologic findings, revealing that aging-induced lesions are most prominent in nerves supplying the hindlimbs and tail (Berg et al, 1962;Van Steenis and Kroes, 1971;Burek et al, 1976;Thomas et al, 1980). When comparing the results from DRG and TG, one should be aware of the fact that the major proportion of the trigeminal proprioceptors have their cell bodies in the mesencephalic trigeminal nucleus (Waite and Tracey, 1995), leading to differences in the size distribution of the neuronal profiles.…”

“…We have defined aged as the time point that coincides with the median survival age of the litter members. As described elsewhere (Berg et al, 1962;Van Steenis and Kroes, 1971;Burek et al, 1976;Mitsumori et al, 1981;Krinke, 1983;Johnson et al, 1995;Bergman and Ulfhake, 1998), rats show a progressive deterioration of motor behavior with advancing age, the symptoms usually starting during the third year of life and mainly affecting the hindlimbs (''posterior paralysis''). All aged rats used in this study disclosed clinical signs of behavioral sensory-motor dysfunction, defined according to a previously described staging protocol (Johnson et al, 1995).…”

“…However, peripheral nerves and dorsal roots of aged animals show abundant morphologic changes, including axonal dystrophy, demyelination, axonal degeneration, as well as loss of fibers (Berg et al, 1962;Gilmore, 1972;Burek et al, 1976;Sharma et al, 1980;Thomas et al, 1980;CotardBartley et al, 1981;Mitsumori et al, 1981;Krinke, 1983;Knox et al, 1989). Furthermore, a considerable and selective loss of cutaneous sensory nerve endings and receptor organs (Cauna, 1965;Fundin et al, 1997) have been observed with advancing age, with a more profound effect found on mechanoreceptive than nociceptive fibers (Fundin et al, 1997).…”

Stress-effects in Microcebus murinus

“…Because the frequency of cardiac lesions is constant throughout captiv ity, we can exclude the hypothesis of cardiac disease being a result of aging in the captive population, as is the case for laboratory animals [Ayers and Jones, 1978;Burek, 1978], In mouse Lemurs, evolution of hypothyroidism is not parallel to cardiac lesions since thyroid activity decreases with time. Therefore, hypothyroidism would act on heart disease through 2 mecha nisms; (1) water retention promotes cardiac insufficiency aggravated by reduced myocardial activity; and (2) theoretically, a hypothyroid state represents some protection for the myocardium by reducing the cardiac sensitivity to catecholamines.…”

Granular cell myoblastoma in the tongue of a dog: A case report

“…Eleven equine cases have been documented, all occurring in the lungs (2,9,16,19,20,25). Granular cell tumours have also been described in laboratory rodents, four cases occurring in mice (6, 17) and 22 cases in rats (4,22,24). In aging rats it was the most common of primary brain tumours (4).…”