The brains of stranded dolphins show common signs of Alzheimer’s disease

The brains of stranded dolphins show common signs of Alzheimer’s disease

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Summary: Researchers found that the brains of three species of stranded dolphins had classic biomarkers associated with Alzheimer’s disease in humans. The findings add weight to the “sick leader” theory, in which a group of healthy dolphins find themselves in dangerously shallow water after following a group leader showing signs of confusion.

source: University of Glasgow

The brains of three species of stranded dolphins show classic markers of Alzheimer’s disease in humans, according to the largest-ever study of dementia in odontocetes (toothed whales).

The new Scotland-wide study, a collaboration between the University of Glasgow, the Universities of St Andrews and Edinburgh and the Moredon Research Institute, examined the brains of 22 odontocetes, all of which were stranded in Scottish coastal waters.

The study, which was published in European Journal of Neuroscienceinvolved five different species—Riso’s dolphins, long-finned pilot whales, white-beaked dolphins, harbor porpoises, and bottlenose dolphins—and found that four animals from different dolphin species had some of the brain changes associated with Alzheimer’s disease in humans.

The findings may provide a possible answer to unexplained live coiling events in some species of odontocetes. The study’s authors confirm that the results could support the “sick leader” theory, in which an otherwise healthy group of animals find themselves in dangerously shallow water after following a group leader who may have become confused or lost.

Whales, dolphins and porpoises regularly strand around the UK coast. They are often found stranded in groups or pods in shallow water and sometimes on beaches. While some animals can be moved to safer, deeper waters by teams of experts, other animals are not so lucky and die as a result. The root causes of live event blocking are not always clear, and research is ongoing to gain better insights.

For this study, the researchers examined blocked animals for the presence of brain pathology that is part of the hallmarks of Alzheimer’s disease, including the formation of amyloid-beta plaques, the accumulation of phospho-tau, and gliosis (a change in the number of cells in response to damage of the central nervous system). The results showed that the brains of all the adult animals examined had amyloid-beta plaques.

Three animals in particular—each from a different odontocete species—had amyloid-beta plaques as well as a number of other dementia-related pathologies in their brains, indicating that some species of odontocetes develop Alzheimer’s-like neuropathology. However, the study could not confirm whether any of the animals would suffer from the same cognitive deficits associated with clinical Alzheimer’s disease in humans.

Lead researcher Dr Mark Daglish of the University of Glasgow said: “These are significant findings which show for the first time that brain pathology in twisted odontocetes is similar to the brains of humans affected by clinical Alzheimer’s disease.

The findings may provide a possible answer to unexplained live coiling events in some species of odontocetes. Image is in the public domain

“Although it is tempting at this point to speculate that the presence of these brain lesions in odontocetes indicates that they may also suffer from the cognitive deficits associated with Alzheimer’s disease in humans, more research needs to be done to better understand what happens to these animals. “

Co-author Professor Frank Gunn-Moore of the University of St Andrews said: “I’ve always been interested in answering the question: do only humans get dementia? Our findings answer this question, as they show that the potential pathology associated with dementia is indeed not only seen in humans. This study is also a great example of both different research institutes and different branches of the life sciences working together.

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

All animals in this study were examined after entrapment. Marine Scotland and Defra fund automorphological examinations through the Scottish Marine Animal Margin Scheme (SMASS) of cetaceans (including odontocetes), pinnipeds and sea turtles that land and die in Scottish coastal waters.

About this news about animal neuroscience research and Alzheimer’s disease

Author: Press office
source: University of Glasgow
Contact: Press Office – University of Glasgow
Image: Image is in the public domain

Original Research: Free access.
Alzheimer’s disease-like neuropathology in three species of oceanic dolphins” by Marissa C. Vacher et al. European Journal of Neuroscience

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Alzheimer’s disease-like neuropathology in three species of oceanic dolphins

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

The brains of 22 twisted odontocetes from five different species were examined using immunohistochemistry to examine the presence or absence of neuropathological hallmarks of AD: amyloid-beta plaques, phospho-tau accumulation, and gliosis.

Immunohistochemistry revealed that all adult animals had accumulated amyloid plaque pathology. In three animals from three different species of odontocetes, there was a co-occurrence of amyloid-beta plaques, intraneuronal accumulation of hyperphosphorylated tau, neuropil filaments and neuritic plaques.

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

The simultaneous appearance of amyloid-beta plaques and hyperphosphorylated tau pathology in odontocete brains indicates that these three species develop AD-like neuropathology spontaneously. The significance of this pathology in terms of animal health and ultimately death remains to be determined.

However, it may contribute to the cause(s) of unexplained coiling of living strands in some species of odontocetes and supports the ‘sick leader’ theory that robust conspecifics in the pod mass strand are due to high social cohesion.

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