Nucleus basalis of Meynert: what is it and what are its functions

The Alzheimer's disease (AD), which is the most common form of dementia, accounts for between 60% and 70% of cases. The causes of Alzheimer's have not yet been fully found. But one of the hypotheses to explain the causes is the deficiency of acetylcholine, among others, and a brain structure known as the nucleus basalis of Meynert and the temporal lobes are the regions with the greatest deficit in this regard.

This clear biochemical abnormality was studied and associated with the disease. And not only with Alzheimer's disease, but also with Parkinson's disease where the nucleus basalis degenerates.

In this article we will see what the nucleus basalis of Meynert is and what we know about this part of the nervous system and its implication in the disease.

• Related article: "Parts of the human brain (and functions)"

What is the nucleus basalis of Meynert?

The nucleus basalis of Meynert is defined as a group of nerve cells located in the innominate substance with wide projections to the neocortex

, rich in acetylcholine and choline o-acetyltransferase. Its name is in homage to the psychiatrist, neuropathologist and anatomist Theodor Meynert, who believed that the alterations in brain development could be a predisposition to diseases psychiatric. In addition, he argued that certain psychoses are reversible.

The nucleus basalis of Meynert plays an essential role through its axons Targeted to the entire cortex, it provides the latter with the highest supply of acetylcholine.

The release of acetylcholine in sensory areas triggers a succession of cellular events that lead to a series of synaptic modifications. The Papez circuit (structures that according to James Papez were related to the affective aspects of memory) and the nucleus basalis of Meynert seem to be involved in a feedback process aimed at consolidating the memory and making it long lasting.

• You may be interested: "Acetylcholine (neurotransmitter): functions and characteristics"

The importance of acetylcholine

The importance of acetylcholine was discovered thanks to Henry Hallet Dale and Otto Loewi, who shared the Nobel Prize in physiology and medicine in 1936. Otto Loewi began his research on the basis of a hypothesis by Elliot, who argued that the nerve impulse was transmitted through a chemical substance. Loewi was able to show that in the parasympathetic nervous system this substance was mainly acetylcholine, a substance that Henry Hallet Dale had previously isolated.

Acetylcholine was the first neurotransmitter characterized in both the peripheral nervous system and the central nervous system of mammals. It intervenes in the regulation of various functions, as in cortical activation, transition from sleep to wakefulness, memory and association processes.

Acetylcholine is synthesized in neurons by the enzyme choline acetyltransferase, from choline and acetyl-CoA in the synaptic cleft.

Its link to Alzheimer's

People with mild cognitive impairment show obvious atrophies of the nucleus basalis of Meynert, the brain structure of which part 80% of cholinergic neurons that facilitate a wide range of cognitive functions such as memory. It has been observed that the lesions in this area of ​​the brain are clearer in those patients whose memory losses were more significant. Using neuroimaging markers, early changes in the brain of people at high risk of Alzheimer's can be determined.

A study estimated that in 2006 0.4% of the population was affected by Alzheimer's and that it would triple by 2050. Currently Alzheimer's disease is incurable and terminal. However, there are pharmacological and non-pharmacological treatments that show signs of efficacy, such as anticholinesterase drugs that have a cholinesterase inhibitory action, the enzyme responsible for breaking down acetylcholine. The first to be marketed was tacrine, which has been discontinued due to its hepatotoxicity.

The anticholinesterase drugs available are donepezil (Aricept), rivastigmine (Exelon or Prometax), and galantamine (Reminyl). None of these four medications are indicated to slow or stop the progress of the disease. However, these drugs have been found to have some efficacy in the mild and moderate stages of the condition, but no effect in the advanced stages.