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How Alzheimer’s Medicines Work

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Updated: November 18, 2005

How Alzheimer’s Medicines Work

Feb 16 2004

New research helps explain how Alzheimers medications work. Similar to antidepressants, these medications act on neurotransmitters - the chemicals that conduct nerve signals between neurons (nerve cells). These neurotransmitters move from one neuron to another, locking onto a "receptor" on the surface of the new neuron. When scientists chemically blocked receptors for the neurotransmitter called acetylcholine, even healthy young people found it harder to learn and remember.

This finding may shed light on how cholinesterase inhibitors, drugs that slow the breakdown of acetylcholine in Alzheimer’s patients, help alleviate dementia symptoms.

The study proved that acetylcholine helps keep old information from interfering with our ability to learn and remember new information. The findings may also help to explain why conditions associated with decreased acetylcholine in the brain cause problems with memory function. Decreased acetylcholine has been found in Alzheimer’s disease, Parkinson’s disease, dementia due to multiple strokes, multiple sclerosis and schizophrenia.

The study also helps us understand how higher acetylcholine levels modestly improve attention, memory, activities of daily living, and behavioral symptoms. Cholinesterase inhibitors increase acetylcholine by reducing the enzyme that breaks it down. The current study may help scientists develop more targeted and effective drugs - and help them avoid medications that may be impair memory.

A total of 28 healthy adults participated in the study. Researchers injected 12 of the study participants with scopolamine, an “anticholinergic” drug used for decades to treat motion sickness and intestinal spasms. Scopolamine also blocks acetylcholine receptors in the brain and impairs certain types of learning and memory. Researchers measured how well participants learned new pairs of words, a common memory test. Two other groups of eight participants each served as controls that were tested on learning but were given either no drugs or a medication that mimics the dry mouth produced when scopolamine is given.

Memory for word-pairs learned after scopolamine administration suffered significantly but memory for word-pairs learned immediately before injection was spared. Scopolamine made it harder to learn when stimuli overlapped, a condition more closely resembling everyday life.

The researchers suggest that anticholinergics might serve as a kind of cognitive ‘stress test’ for elderly patients who have early dementia, unmasking symptoms that would be hard to detect otherwise. They also suggest that elderly patients should not take medications with anticholinergic effects on a regular basis.

Reference: “Blockade of Central Cholinergic Receptors Impairs New Learning and Increases Proactive Interference in a Word Paired-Associate Memory Task,” Behavioral Neuroscience, Vol. 118, No. 1.

Last updated 11/17/05

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