The key neurotransmitter involved in Alzheimer's disease is acetylcholine (ACh). In the CNS ACh acts as a neuromodulator and forms the cholinergic system. Alzheimer's disease is caused by a loss of neurons in the cortex and hippocampus primarily due to the toxic effects of the accumulation of beta amyloid and/or tau protein aggregates. This cell loss causes a marked decrease in the level of ACh leading to memory and cognitive impairment . Current approved therapies focus on cholinesterase inhibition so levels of ACh remain a high as possible. This approach offers limited benefits and does not address the underlying cause of the disease.

I see that Steve Runnels mentions "the toxic effects of the accumulation of beta amyloid and/or tau protein aggregates." While I believe there is no doubt that tau protein aggregates are intimately involved with the advance of dementia, the relationship between beta amyloid aggregates and dementia has enough exceptions to warrant a serious review of current research priorities. For instance, why do some people with high beta amyloid aggregates show no signs of dementia and why, in highly advanced cases of dementia, do pathologists often find a surprisingly modest beta amyloid accumulation more in line with that found in earlier stages of dementia? In science, while the general effect may help establish an association, it is usually the anomalies that provide the key.

The important role of acetylcholinesterase inhibitors in the management of Alzheimer's disease is well established. All these drugs (donepezil, galantamine & rivastigmine) block the cholinesterase enzyme from breaking down acetylcholine, an important neurotransmitter. This allows for stabilization of synaptic transmission for a short period of time until additional neuronal death overcomes the ability of this temporary solution. The only other approved treatment for Alzheimer's disease (memantine) does indeed play a role in modulating the glutaminergic system of neurotransmission and is recommended for later stages of the disease only. Like the acetylcholinesterase inhibitors, it does not treat the underlying disorder itself.

Thank you, Stephen Hurt, as well as Steve Runnels and Eva Zerovnik, for sharing your knowledge regarding the nature of neurotransmitters -- I certainly appreciate it. In a paper published in the Journal of Medical Hypotheses last July, I proposed that the underlying cause of Alzheimer's is a premature collapse of the microglial support system, which I suggest is a delayed effect of dental X-rays damaging microglia telemores. If this is the case, while the above-mentioned drug approaches may provide modest, if temporary, assistance to people exhibiting Alzheimer's symptoms, the best intervention would be supporting or supplementing microglia populations.

I would not argue with the need to advance our understanding of Alzheimer's disease beyond the twin roles of amyloid deposition and neurofibrillary tangles. Moreover, as you note Caroline, there is indeed evidence for microglial involvement in the disease process itself. Microglia are phagocytic, and so help to clear disabled neurons, but also appear to disrupt adjacent neurons by neuroinflammatory means. Recently, it has been suggested that microglial fragments rather than active, well-functioning microglia may be the neuroinflammatory culprit, perhaps rehabilitating microglia's generally neuroprotective role as part of the innate immune system. In any case, our understanding of Alzheimer's disease is currently incomplete in a number of respects. Finally, Caroline, although I find your hypothesis intriguing, do you know of any epidemiological investigation supporting your hypothesis? With a dramatic increase in the incidence of AD expected in several countries in the next 2 to 3 decades where few people receive dental x-rays, it would make an interesting epidemiological study for someone so inclined.

@Caroline, your hypothesis is really blasting, which I completely agree with Stephen about collecting the epidemiological records of the case. but I have one doubt (may be I could not fully grasp the idea by Caroline) that, the effect may be due to the X-ray of teeth? or can we also relate with the X-ray of Nose? I work in the Neurology section of one of Hospitals in China. Keenly interested in your idea and thanks for the sharing.

@ Avinash Chandra

I would include all x-rays of the head / neck. China is one of those countries which will experience a dramatic increase in the incidence of AD in the next 2-3 decades, as will India and other parts of SE Asia. It would be fascinating to know if the increase is larger in urban as opposed to rural areas since the prevalence of head / neck x-rays would be greater in urban areas I would guess. It is likely that other factors related to urban life would impact the incidence as well so this would be a difficult study to do.

A group of the Lomonosov Moscow State University scientists, together with their colleagues from the Institute of Molecular Biology, Russian Academy of Sciences and the King's College London, succeeded in sorting out the mechanism of Alzheimer's disease development and possibly distinguished its key trigger.

New mouse model reveals how Alzheimer's causes dementia 

Using a novel, newly developed mouse model that mimics the development of Alzheimer's disease in humans, Johns Hopkins researchers say they have been able to determine that a one-two punch of major biological "insults" must occur in the brain to cause the dementia that is the hallmark of the disease.

A new classification system for biomarkers of Alzheimer's disease that includes measures of amyloid (A), tau (T), and neurodegeneration (N) has been proposed.

The system, described in a paper published online July 1 in Neurology, includes different ways of measuring all three

Edible and medicinal mushrooms show potential to mitigate neurodegenerative diseasesEdible and medicinal mushrooms show potential to mitigate neurodegenerative diseases

Certain edible and medicinal mushrooms contain bioactive compounds that may enhance nerve growth in the brain and protect against neurotoxic stimuli such as inflammation that contribute to neurodegenerative diseases like dementia and Alzheimer's disease.