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:

  • Dopamine
  • Norepinephrine
  • Serotonin.

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 HuntingtonÕs disease and ParkinsonÕs 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 brainÕs 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.

Resources

Alexopoulos, G., et al. (1997). “Vascular depression hypothesis.” Archives of General Psychiatry, 54(10):915-22.

McGill University Staff. (n.d.). The brain from top to bottom: Synapses. Retrieved May 10, 2010, from the McGill University website: thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.html.

Meltzer, C., et al. (2001). “Brain aging research at the close of the 20th century: from bench to bedside.” Dialogues in Clinical Neuroscience, 3(3), 167-180.

Merck Pharmaceuticals Staff. (n.d.). Changes in the brain. Retrieved May 17, 2010, from the Merck website: www.merck.com/mkgr/mmg/sec6/ch42/ch42a.jsp.

National Institute of Mental Health Staff. (2008). New theories show promise for vascular depression; heart, metabolic, risks of some antipsychotic medications flagged. Retrieved May 17, 2010, from the National Institute of Mental Health website: www.nimh.nih.gov/science-news/2008/new-therapies-show-promise-for-vascular-depression-heart-metabolic-risks-of-some-antipsychotic-medications-flagged.shtml.

 Posted on : June 26, 2014