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 disease have not yet been fully identified. But one of the hypotheses to explain the causes is acetylcholine deficiency, among others, and a brain structure known as the Meynert’s basal nucleus and the temporal lobes are the most deficient regions in this regard.
This clear biochemical abnormality has been studied and associated with the disease. And not only with Alzheimer’s disease, but also with Parkinson’s disease where the basal nucleus suffers from degeneration.
In this article, we will take a look at what Meynert’s basal nucleus is and what we know about this part of the nervous system and its involvement in disease.
What is Meynert’s basal nucleus?
Meynert’s basal nucleus is defined as a group of nerve cells located in the unnamed substance with large projections towards the neocortex, rich in acetylcholine and o-acetyltransferase hill. Its name is in homage to psychiatrist, neuropathologist and anatomist Theodor Meynert, who believed that alterations in brain development could be a predisposition to psychiatric illness. In addition, he argued that some psychoses are reversible.
Meynert’s basal nucleus fulfills an essential function thanks to its axons directed throughout the cortex, making the latter the greatest contribution of acetylcholine.
The release of acetylcholine in sensory areas triggers a succession of cellular events that they cause a series of synaptic changes. Papez’s circuit (structures which James Papez said were linked to affective aspects of memory) and Meynert’s basal nucleus appear to be involved in a feedback process intended to consolidate memory and sustain it.
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 or Medicine in 1936. Otto Loewi began his research from a hypothesis by Elliot, who argued that the nerve impulse was transmitted by a chemical. 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, such as cortical activation, sleep-wake transition, memory and association processes.
Acetylcholine is synthesized in neurons by the enzyme cholinacetyltransferase, from hill and acetyl-CoA in the synaptic cleft.
Its link to Alzheimer’s disease
People with mild cognitive impairment have obvious atrophies of the basal nucleus of Meynert, including the brain structure 80% of cholinergic neurons share that facilitate a wide range of cognitive functions such as memory. It has been observed that lesions in this area of the brain are clearer in patients with greater memory loss. Early neuroimaging markers can determine early brain changes in people at high risk for Alzheimer’s.
A study estimated that 0.4% of the population was affected by Alzheimer’s disease in 2006 and that it would triple by 2050. Alzheimer’s disease is currently incurable and terminal. However, there are pharmacological and non-pharmacological treatments that show signs of effectiveness, such as anticholinesterase drugs with cholinesterase inhibitory action, The enzyme responsible for the breakdown of acetylcholine. The first to be marketed was tacrine, which ceased to be used due to its hepatotoxicity.
The available anticholinesterase drugs are donepezil (Aricept), rivastigmine (Exelon or Prometax) and galantamine (Reminyl). None of these four drugs are indicated to slow down or stop the progression of the disease. However, it has been noted that these drugs have some effectiveness in mild to moderate stages of the disease, but no effect in advanced stages.