A veterinary neuroscientist has led a team of researchers from the University of Wisconsin-Madison in discovering that the myelin of cats suffering from neurological disorders can actually repair itself leading to substantial recovering of functions.
The study, Extensive remyelination of the CNS leads to functional recovery, was published in the March 30 issue of Proceedings of the National Academy of Sciences.
Lead author, Dr Ian Duncan is professor of medical sciences at the UW-Madison School of Veterinary Medicine and an authority on demyelinating diseases. He has been investigating the neurological dysfunction of cats which had been fed irradiated food. While the myelin sheaths appeared to have broken down, the nerves themselves remained intact.
The new study arose from a the neurological dysfunction that developed in pregnant cats used in testing cat food. A company testing the effects on growth and development in pregnant cats of diets that had been irradiated, reported that some cats developed severe neurological dysfunction, including movement disorders, vision loss and paralysis.
“After being on the diet for three to four months, the pregnant cats started to develop progressive neurological disease,” Dr Duncan said. The affected cats developed ataxia and paresis of the hindlimbs, worsening until two cats became paraplegic. In some cats, vision, as tested by the menace reflex was reduced or lost.
The cats were shown to have severe and widely distributed demyelination of the central nervous system. “The neurological examination, in summary, suggested that these abnormalities were primarily because of spinal cord disease with optic nerve involvement,” Dr Duncan said in his paper.
Once taken off the food their recovery was slow, but all of the previously demyelinated axons became remyelinated. The restored myelin sheaths, however, were not as thick as healthy myelin, he said.
“It’s not normal, but from a physiological standpoint, the thin myelin membrane restores function,” he says. “It’s doing what it is supposed to do.”
The foetuses of the affected pregnant cats were not studied, but their offspring appeared to have been unaffected.
The result has implications for people suffering from demyelination disorders such as multiple sclerosis, Dr Duncan said. “It indicates the profound ability of the central nervous system to repair itself.”
“Despite the severe myelin degeneration, axons remained essentially intact. There was a prompt endogenous response by cells of the oligodendrocyte lineage to the demyelination, with remyelination occurring simultaneously,” he reported.
“Histological examination of the CNS at this point showed extensive remyelination that was especially notable in the optic nerve where almost the entire nerve was remyelinated.”
However, biochemical analysis of the diet and tissues from affected cats showed no dietary deficiencies or toxic accumulations.
“Thus, although the etiology of this remarkable disease remains unknown, it shows unequivocally that where axons are preserved remyelination is the default pathway in the CNS in nonimmune-mediated demyelinating disease.
“Most importantly, it confirms the clinical relevance of remyelination and its ability to restore function.
Dr Duncan was not involved in the original study of diet, but noted the cats had been fed the irradiated food for several months. He said the disease his team reported on appeared to have a different pathology from that reported in the Irish cats, (in the 2007 paper in the Journal of The American Association For Laboratory Animal Sciences, ‘Effects Of Gamma Irradiation And Pasteurization On The Nutritive Composition Of Commercially Available Animal Diets’). He also considered it to be different from the Australian cases.
He said that while the neurological symptoms exhibited by the cats are similar to those experienced by humans with demyelination disorders, the disease did not seem to be like any of the known myelin-related diseases of humans.
Dr Duncan said he would like to hear from any Australian veterinary researchers who have investigated the irradiated food-related neurodegeneration, especially in regard to the pathology of the disease.
© Sue Cartledge