Listening to the news on the BBC radio 4 this morning (6 December) I heard an item about a condition similar to Alzheimer’s disease being found in cats. This story would probably not surprise anyone who has lived with an aging pet, even though the range of cognitive tasks required of the domestic cat does not extend too much beyond sleeping and eating. The news item stated that the condition was caused by deposits of a protein within the nerve cell of the brain. As the details were fairly sparse I decided to check the CAB Abstracts Database to see if I could find out any more about dementia in cats.
It seems that the news item was sparked by a paper published some months ago in the Journal of feline Medicine & Surgery (2006, Vol 8, (4) 234-242). The researchers from the universities of Edinburgh, St Andrews, Bristol, and Irvine California assessed brain material from 19 cats, aged from 16 weeks to 14 years; 17 of which had clinical signs of neurological dysfunction. Immunohistochemical methods were used to detect A beta and its intracellular precursor protein (amyloid precursor protein (APP)) and hyperphosphorylated-tau. Their findings showed that APP was constitutively expressed, with diffuse staining of neurons and blood vessels being detected in all cats. More intense staining and diffuse extracellular A beta staining deposits were found within the deep cortical areas of the anterior- and occasionally mid-cerebrum of seven cats, all of which were over 10 years of age. Neurons staining intensely positive for AT8-immunoreactivity were seen in two cats, aged 11 and 13 years. However, no mature neurofibrillary tangles were detected. They concluded that extracellular A beta accumulation and AT8-immunoreactivity within neurons are age-related phenomena in cats, and that they can occur concurrently.
These findings showed similarities between these changes and those observed in the brains of aged people and other old mammals. As the life expectancy of domestic pet cats is increasing we can expect an increase in the occurrence of geriatric-onset behavioural problems, such as cognitive dysfunction syndrome (CDS). While the cause of CDS is unclear, it has been suggested that it may result from age-related neurodegeneration. In aged and in particular senile human beings, histopathological changes may include the extracellular accumulation of plaque-like deposits of beta -amyloid (A beta ) protein and the intracellular accumulation of an abnormally hyperphosphorylated form of the microtubule-associated protein, tau. In severe cases, the latter may form into neurofibrillary tangles. Similar findings have been found in the brains of aging dogs and there are several references in the literature on this.
What is the significance of this finding? As there is no cure for human dementia it is unlikely that one will soon be found for cats. The aged cat could be a useful laboratory model for the human disease and could help find the cure for this terrible condition.