One fascinating (and very useful) aspect of the nervous systems and its units, the neuronal cells (known as neurons), is that structurally and functionally there is virtually no significant difference between those operating in worms, insects, fish or humans. In fact throughout the animal kingdom the nervous system basically functions on identical principles. And that explains why research on diseases like Parkinson’s and Alzheimer’s can resort to using fish and fruit flies as models. As the global human population ages, we can expect to have more and more cases of people suffering from these diseases, which are classified as “neuro-degenerative ”. This means that they lead to a gradual loss of neuronal function, to the degeneration and ultimate death of nerve cells in the brain.
In Parkinson’s Disease the most visible symptom is the tremor and that was also the diagnostic feature when the English surgeon James Parkinson in 1817 described the disease as “shaking palsy”. It was the renamed “Parkinson’s Disease” by the Scottish physician William Sanders in 1865. It is known that the movement disturbances are caused by the loss of the neurotransmitter “dopamine”, a substance vital for signal transfer from one neuron to another via contacts between nerve cells known as “synapses”. For Alzheimer’s Disease, named after the German psychiatrist Alois Alzheimer, who published his observations in 1906, neuronal dysfunction is also characteristic, but here a build-up of toxic protein deposits known as amyloids cause the neurons to malfunction and slowly die, which then leads to cognitive problems like loss of memory, delusions, hallucinations, etc.
What the diseases have in common apart from being neurodegenerative is that there is certainly a genetic component, but that environmental triggers are also important. Especially in connection with Parkinson’s Disease a link to metabolic disorders like diabetes mellitus, cardiovascular problems, high blood pressure, a fat-rich diet, obesity, etc. have been established and a sufficient amount of insulin available to the brain to maintain essential glucose levels for meeting the brain’s energy requirements, has been identified to be critically important. Insulin resistance in the brain affects turnover processes of dopamine in the synapses and causes the characteristic movement disorders in sufferers of Parkinson’s Disease. But how can fruit flies help? Since fruit flies can be bred in large numbers, have short life spans, possess neurons that function like those in humans and exhibit motor behaviours like crawling, climbing, grooming, flying, etc. they can serve as models for the disease and its underlying genetics. One distinguishes between the familial Parkinson’s Disease and an expression of the disease that’s caused by environmental stimuli like toxic compounds. To identify the underlying susceptible genes is one goal in which fruit flies help. After all they and humans share 61% of their genes including those that control the molecular mechanism of neurotransmitters. Paraquat (a pesticide) and rotenone (a poisonous plant substance) have been identified to disrupt the fruit flies’ metabolism in ways that resemble Parkinson’s Disease. There is, thus, hope that the fruit fly results can lead to treatments not just of the symptoms of the disease but the genetic causes as well.
Treating sufferers from Alzheimer’s Disease may one day benefit from research on the brain of the zebra fish, a small tropical aquarium fish that just like the fruit fly has become a “work horse” for genetic research of all sorts. In the past, the main approach to treat Alzheimer’s Disease was to try to prevent or slow down the degeneration of the affected neurons. But the research on the zebra fish has shown that there exist in this species’ brain some cells that can be induced to replace lost neurons. Hope is that such neurons in the human brain can be identified and induced to restore or replace neurons lost to Alzheimer’s. Progress often comes from unconventional approaches and as David Horrobin wrote “If a hypothesis which most people think is probably true does turn out to be true (or rather is not falsified by crucial and valid experimental tests) then little progress has been made. If a hypothesis which most think is improbable turns out to be true, then a scientific revolution occurs and progress is dramatic”. I love this comment on research!
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