Nerve cells that release the neurotransmitter
Nerve cells that release the neurotransmitter acetylcholine form the cholinergic system in the brain, which is divided into two parts: muscarinic (main focus of attention in memory) and nicotinic. The muscarinic projections are outlined in Figure 3, which represents a midline slice through the whole brain. Specific masses of nerve cells, or nuclei, in the deep part of the brain form the center of the muscarinic cholinergic system, and they use acetylcholine as their neurotransmitter.
Degeneration of these cholinergic nerve cells deep in the brain leads to damage to the areas to which they project and are connected, namely, the hippocampus and frontal cortex. Naturally, memory loss is the result.
Role of Acetylcholine in Cognition
Increase in acetylcholine leads to improved attention, mental arousal, and memory.
From age forty to ninety, the nucleus basalis of Meynert gradually and progressively loses up to half its cholinergic nerve cells.
This loss of cholinergic nerve cells causes a delay in the brain’s ability to process information quickly and accurately, which is why aging leads to slower reactions as well as to mild memory loss.
In Alzheimer’s disease, the nucleus basalis is nearly wiped out within a few years after clinical onset of the illness, causing severe memory loss.
Cholinergic nerve cells release acetylcholine into a narrow cleft or space called the synapse. This acetylcholine molecule races across the synapse and latches onto a receptor in the next neuron, called the postsynaptic neuron. The postsynaptic receptor is specially configured for the acetylcholine molecule, the way a keyhole receives a key. Attachment to this receptor triggers a series of biochemical and physiologic events in the postsynaptic or receiving neuron, leading to a change in brain function that involves improved mental arousal and memory. Once acetylcholine completes its job, it is either sucked back by the nerve cell that released it, ready to fight another day, or it is
broken down by the enzyme acetylcholinesterase in the synaptic cleft.
Different Ways to Boost Acetylcholine
Cholinesterase inhibitors are compounds that inhibit the action of this enzyme, acetylcholinesterase. Treatment with cholinesterase inhibitors indirectly raises the level of acetylcholine by preventing its breakdown, thereby leading to improved attention, mental arousal, learning, and memory. In fact, cholinesterase inhibitors have now reached the forefront of treatment in Alzheimer’s disease, and memory loss more broadly.
If you step back for a moment and think about the issue, this indirect approach does seem a bit odd. Why not directly increase the amount of acetylcholine by pouring it directly into the synapse, or administer a substance (precursor) that is converted to acetylcholine in the brain? Well, these strategies have been tried with compounds like choline and lecithin.
Taken From: The Memory Program How to Prevent Memory Loss
and Enhance Memory Power
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