Biological aspects of the link between smoking and depression

A link between smoking and depressive symptoms has been described in the li terature for over a decade. The neurotransmitter systems affected by cigare tte smoke mirror the neurotransmitter pathways thought to be involved in th e biological mechanisms of depression. Cigarette smoke contains several psy choactive chemicals; nicotine is the best studied among these and is widely accepted to be the addictive substance in tobacco. Nicotine binds to nicot inic receptors in the brain, augmenting the release of numerous neurotransm itters, including dopamine, serotonin, norepinephrine, acetylcholine, gamma -aminobutyric acid, and glutamate. Cigarette smoke has other psychoactive p roperties apart from nicotinic receptor stimulation. For example, it inhibi ts monoamine oxidase (the enzyme responsible for breaking down the biogenic amine neurotransmitters norepinephrine, serotonin, and dopamine) in the br ain. Various antidepressants act through modulation of the biogenic amine n eurotransmitter pathways. That the neural substrates modified by both smoki ng and antidepressant drugs overlap has relevance to smoking cessation. The use of antidepressants as adjuvants to smoking-cessation treatment can enh ance cessation success rates. Understanding the neurobiological mechanisms underlying the association between smoking and depression may improve physi cians' ability to assist smokers in their efforts to quit and will contribu te to a more thorough comprehension of both the biology of addiction and th e etiology of depression.