Summary: Researchers have found that the brains of three types of captive dolphins have classic biomarkers associated with Alzheimer’s disease in humans. The findings add to the “sick leader” concept, where a group of healthy dolphins show disorientation after following a group leader in dangerously shallow water.

Source: University of Glasgow

According to the most extensive study of dementia in odontocetes (toothed whales), the brains of three types of captive dolphins show signs of Alzheimer’s disease in humans.

The new pan-Scottish research, a collaboration between the University of Glasgow, the Universities of St Andrews and Edinburgh and Morden Research Institute, studied the brains of 22 odontocetes, all caught in Scottish coastal waters.

The study published in European Journal of NeuroscienceIt included five different species—Risso’s dolphins, long-finned pilot whales, white-beaked dolphins, harbor porpoises, and bottlenose dolphins—and four animals from different dolphin species were found to have some of the brain changes associated with Alzheimer’s disease in humans.

The findings may provide answers to unexplained live transmission events in some odontocete species. The study authors found that the results support the “sick leader” theory, where healthy animal pods find themselves in dangerously shallow water after following a group leader who may become confused or lost.

Whales, dolphins and porpoises are regularly caught around the English coast, often in groups or pods, in shallow water and sometimes stranded on beaches. While some animals can be taken to safe and deep water by a team of experts, others are not so lucky and perish as a result. The root causes of live streaming events are not always clear, and research is ongoing to gain better insights.

For this study, researchers looked at the presence of brain pathology that is part of the symptoms of Alzheimer’s disease, the formation of amyloid-beta plaques, the accumulation of phospho-tau and gliosis (changing cell numbers in response to damage to the central nervous system). The results showed that the brains of all the aged animals studied had amyloid-beta plaques.

Three animals in particular—each from a different odontotete species—had amyloid-beta plaques in their brains as well as multiple brain lesions, suggesting that some odontotete species develop Alzheimer’s-like neuropathology. However, the study was unable to confirm whether any of the animals experienced the same cognitive deficits associated with clinical Alzheimer’s disease in humans.

Lead researcher Dr Mark Daglish, from the University of Glasgow, said: “These significant findings show for the first time that brain pathology in odontocetes is similar to the brains of people with clinical Alzheimer’s disease.

This shows a picture of a dolphin
The findings may provide answers to unexplained live transmission events in some odontocete species. Image is in public domain.

“At this point, the presence of these brain lesions in odontotes suggests that humans may suffer from the cognitive deficits associated with Alzheimer’s disease, but more research is needed to understand what is happening in these animals.”

Co-author Professor Frank Gunn Moore, from the University of St Andrews, said: “I have always been interested in answering the question: do only humans have dementia? Our findings answer this question because dementia-related pathology is not only seen in human patients. This research is a great example for both different research institutions, but also different branches of the life sciences, to work together.

Professor Tara Spiers-Jones of the University of Edinburgh said: “We were fascinated to see brain changes from aging dolphins that are seen in human aging and Alzheimer’s disease. Whether these pathological changes contribute to the bending of these animals is an interesting and important question for future work.

All animals in this research were studied after the stuttering event. Marine Scotland and Defra carry out post-mortem investigations, through the Scottish Marine Animal Stranding Scheme (SMASS), of cetaceans (including odontocetes), pinnipeds and sea turtles that drown in Scottish coastal waters.

So animal neuroscience and Alzheimer’s disease research news

Author: Press office
Source: University of Glasgow
Contact: Press Office – University of Glasgow
Image: The image is in the public domain.

Preliminary study: Open Access.
Alzheimer’s disease-like neuropathology in three oceanic dolphin species” by Marissa C. Vacher et al European Journal of Neuroscience

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This shows the olfactory neurons

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Alzheimer’s disease-like neuropathology in three oceanic dolphin species

Alzheimer’s disease (AD) is the most common neurodegenerative disease and the leading cause of disability and dependency in the elderly worldwide. AD is thought to be a disease specific to humans, although many other animals develop some aspects of AD-like pathology. Odontocetes (toothed whales) share characteristics with humans that suggest they may be susceptible to AD.

AD In order to investigate the presence and absence of neuropathological signs, the brains of 22 arrested odontocetes of five different species were examined using immunohistochemistry: amyloid-beta plaques, phospho-tau accumulation and glycation.

Immunohistochemistry revealed that all aged animals accumulated amyloid plaque pathology. Amyloid-beta plaques, intraneuronal accumulation of hyperphosphorylated tau, neuropil filaments and neuritic plaques co-occurred in three animals of three different odontocete species.

One animal showed well-developed neuropil filaments, phospho-tau accumulation and neuritic plaques, but no amyloid plaques. Microglia and astrocytes were present in all brain samples as expected, but we observed differences in cell morphology and numbers between individual animals.

The simultaneous occurrence of amyloid-beta plaques and hyperphosphorylated tau pathology in the brains of odontocetes suggests that these three species spontaneously develop AD-like neuropathology. It remains to be determined how important this pathology is in relation to the health and ultimately the death of the animal.

However, it may contribute to an unknown cause(s) of live transmission in some odontocete species and supports the ‘sick leader’ hypothesis of healthy conspecifics in the pod mass strand due to high social connectivity.

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