As the body ages, so do all the major organs, including the brain. Some changes may reduce "brain power." An accumulation of beta amyloid, a protein that is toxic to neurons (active brain cells), creates "plaques," which are believed to diminish cognitive function.
With aging, neurotransmitters - the brain's chemical messengers - don't function as well. Dopamine, one of the most important neurotransmitters, is less effective in dogs with cognitive dysfunction. This is one area where treatment can help. In the early 1990s, researchers studying the similarities between aging dogs' and humans' brains discovered that a drug used to treat Parkinson's disease in humans improved the memory of some geriatric dogs. The drug l-deprenyl (also called selegiline) is now offered to veterinarians under the trade name Anipryl, manufactured and marketed by Pfizer Inc. It works by inhibiting the enzyme that breaks down dopamine. As a result, the transmission of chemical messages required for cognitive function is enhanced.
The FDA approved use of l-deprenyl for treating CDS in the United States in December 1998; it has been used in Canada since 1996. L-deprenyl was first approved in the United States in 1997, but only for treating a form of Cushing's disease in dogs. Until the availability of Anipryl, veterinarians could offer owners of CDS-affected dogs little more than sympathy. " Owners and their dogs often just lived with the problem," said Gary Landsberg, DVM, diplomate of the American College of Veterinary Behaviorists, of Doncaster Animal Clinic in Thornhill, Ontario. "Many dogs were probably put to sleep earlier, not because of medical problems but because of the behavior changes." Anipryl doesn't cure CDS, but it can help improve quality of life and even extend the life of many dogs.
Letha Melton of Bend, Ore., thinks her 15-year-old Australian Cattle Dog mix, Ashes, may have cognitive dysfunction. "For the last few months, she has stood in the kitchen, staring at nothing, or she has whined for no apparent reason," Melton said. Ashes has trouble recognizing familiar people: "She has even growled at my parents, who she thinks the world of." She has to encourage Ashes to eat by tapping on the food dish, reminding her to take another bite. Melton plans to take Ashes to her veterinarian to confirm the diagnosis.
Veterinarians can't tell by looking at a dog if it has cognitive dysfunction, nor can they order a "cognitive dysfunction test." Older dogs often have more than one body system showing signs of wear that mimic CDS. Housetraining accidents may be related to kidney disease, diabetes or hormone imbalances, for example. A dog that paces restlessly, unable to lie down comfortably, may suffer from arthritis. Loss of interest in food may be a sign of a dental or metabolic disease, or cancer. A dog that seems to ignore its owner's commands may be losing its hearing.
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