In an earlier post, I discussed the structural changes caused by Alzheimer’s disease, that make AD brains different than normal brain. But the plaques and tangles that appear in AD brain only tell part of the story. There are also changes occurring in the biochemistry of AD brains.
Neurotransmitters are reduced
Chemical messenger molecules (neurotransmitters) are reduced in the AD brain. These neurotransmitters carry information (signals) from one neuron to the next. There are many different neurotransmitters. Some transmit basic information. Others either amplify of decrease the strength of the signal sent. Most brain regions use several different neurotransmitters. Like the physical changes which occur in AD, decreases in neurotransmitters occur first in brain areas associated with learning and memory, such as the hippocampus and cortex.
Changes in the cholinergic system
The first neurotransmitter found to be reduced in AD was Acetylcholine (a-see’-til-ko’-leen). Brain neurons releasing the neurotransmitter acetylcholine are called cholinergic (ko’-lin-er’-jik) neurons. Together they make up the cholinergic system, which is the earliest and arguably the most severely affected neurotransmitter system in AD.
Although acetylcholine is not the only neurotransmitter used in the hippocampus and cortex, it plays a crucial role in learning and memory processes in those areas.
The role of cholinergic neurons
Cholinergic neurons encourage other neurons in the hippocampus and cortex to transmit messages. When the cholinergic system is not functioning properly, the other neurons are less likely to pass messages on. This interferes with both learning and remembering.
Other biochemical changes
Other biochemical molecules are also affected by Alzheimer’s disease.
Some researchers find that growth-promoting molecules which would normally support the health of neurons are either decreased or ineffective in the Alzheimer brain. This may partly explain the large number of neurons and neuron connections (synapses) that are lost.
Other scientists have found a lack of growth-inhibiting molecules in the AD brain, and think a lack of appropriate inhibition may help explain the growth of abnormal neuronal fibers inside cell bodies and the growth of neuronal processes that curl randomly about instead of making proper synaptic contacts.
The ultimate significance of changes in growth-promoting and growth-inhibiting molecules is not yet clear.
The role of Alzheimer’s Research
Many researchers are involved in the fight against AD, but progress has been slow. The disease has been identified since 1904 when it was first described by Dr. Alois Alzheimer. Following the publication of Dr. Alzheimer’s initial description, the physical changes this disease caused in the brain were quickly and thoroughly catalogued. However, it took nearly 70 years, and the development of new research techniques, before a way to do more than just describe the symptoms was found.
In the years from 1986 to now, the pace of research in AD has increased. Still, because AD is probably the result of an accumulation of contributing factors, we may never identify a single simple cause for it.
More than just scientists
Biomedical research is more than just a job, and the biomedical researchers studying Alzheimer’s disease, are more than just scientists.
These men and women have chosen, from the whole world of medical research, to tackle problems affecting the most complex of all systems, the human brain. Driven not only by the desire to understand, but also by the desire to help, biomedical researchers share a need to have their work impact the lives of people. They want to make a difference. They are people with a mission.
Occasionally I will discuss new findings in scientific research. But I also want to give you the opportunity to recognize the people behind the work—people who, although you may never meet them or even know their names, are standing shoulder to shoulder with you in the fight against this debilitating disease. I hope that when you read about the work these men and women do, you will see more than just the advancement of science. I hope you will realize you are not alone.
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