Research led by an academic from the University of Surrey’s School of Veterinary Medicine casts doubts on the long-held view that animals always lose neurons as they age.

The review, published in the International Review of Molecular and Cell Biology, saw Augusto Coppi, teaching fellow in veterinary anatomy, delve into six decades of research on the peripheral nervous system of animals.

It concluded that elderly animals do not always suffer from a reduction in neurons in the autonomic nervous system. In some species, the number of neurons can actually increase.

Better understanding of the autonomic nervous system could prove vital in improving early diagnosis and treatment of neurological disorders, including stroke, epilepsy and the peripheral form of Huntington’s and Parkinson’s disease. It could also have an impact on our understanding of how ageing affects other parts of the body.

Dr Coppi said: “Although our studies focused on the peripheral nervous system, we may be able to draw a parallel with the central nervous system (including the brain), which comprises the same main type of cells.

“This could be an example of where the concept of One-Health medicine (which links animal and human health) could directly translate this research into improving quality of life for elderly people – if ageing does not necessarily lead to neuron loss, then we could have the potential to learn and retain new knowledge, even in old age.”

The review examined 14 of Dr Coppi’s group papers on this subject (published from 2004 to 2013), which used a revolutionary way of sampling and counting particles including cells, bacteria and viruses in 3-D, a method called stereology.

Papers studied a broad range of animal species including mice, guinea pigs, cats, dogs, sheep, horses and South American wild rodents. They revealed elderly guinea pigs were the only animal species to display a reduction in the total number of neurons.

They also confirmed the existence of neurogenesis (production of new neurons) even in elderly animals, something that, until a few years ago, was considered impossible according to the medical literature on the topic. In dogs, for example, the number of neurons in aged animals was found to increase by 1,700%.

Dr Coppi said: “We can attribute the misleading conclusion that there was always neuron loss during ageing to the morphometric 2-D techniques previously used to quantify cells. Stereology is a state-of-the-art and more accurate and precise approach, which elicits more robust and reliable results.”

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