The aging brain experiences changes, including:
- Changes in hormones and neurotransmitters
- Loss of nerve cells, or atrophy
- Reduction in processing speed.
Neurotransmitter changes can contribute to the development of depression in the aging population. The neurobiology of aging, along with environmental and emotional effects that accompany old age, can lead to depression symptoms.
Biology of Depression
Depression and biology are connected; the development of depression is influenced by the function of neurotransmitters in the aging brain. Neurotransmitters are chemicals that transmit messages in the brain from neuron to neuron. The space between neurons is known as the synaptic cleft. The biology of depression involves an imbalance of several neurotransmitters, including:
Antidepressant drugs work to facilitate function of these neurotransmitters. The biology of depression treatment focuses on allowing neurotransmitters to remain in the synaptic cleft. This allows them a greater chance of binding to a receptor, rather than being re-absorbed before they can transmit their messages (called reuptake).
Neurobiology of Aging People
Brain changes associated with aging can cause neurotransmitter imbalances associated with depression. The aging brain may experience damage to the dopamine pathways. Since dopamine affects mood and sleep regulation, damage to these pathways may contribute to depression.
Damaged 5-HT receptors in the aging brain (part of the serotonin processing system) may also lead to depression, as serotonin also regulates mood and sleep. Increased monoamine oxidase activity in aging people may also occur. This enzyme prevents the actions of monoamine neurotransmitters, including several of those involved in the biology of depression.
Disrupted neurobiology of aging brains can cause other degenerative diseases such as HuntingtonÃ•s disease and ParkinsonÃ•s disease. Neurotransmitter pathway damage can cause both emotional and physical symptoms in these diseases as well as depression.
Vascular Depression and Biology
Cerebrovascular disease, affecting the blood vessels in the brain, has been connected to depression in some older individuals. This has been termed vascular depression. Vascular depression affects older individuals, and has been defined in terms of comorbidity of depressive symptoms with vascular problems in the brain, including ischemic lesions (blockages). These conditions lead to loss of blood supply in the brain, as well as abnormalities in the brainÃ•s white matter, particularly the frontal lobes. Treatments for this recently-defined type of depression are still under investigation.
Research on Neurobiology of Aging
The biology of depression in aging populations is not yet fully understood. Continued research into the neurobiology of aging is necessary to determine the effects of aging on neurotransmitter activity. The ability to evaluate neurotransmitter function in living individuals, using imaging techniques, can help to give a more accurate picture of the function of neurotransmitters in the aging brain.
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