Methadone's effect on nAChRs--a link between methadone use and smoking?

Methadone is a long-acting opioid agonist that is frequently prescribed as a treatment for opioid addiction. Almost all methadone maintenance patients are smokers, and there is a correlation between smoking habit and use of methadone. Methadone administration increases tobacco smoking, and heavy smokers use higher doses of methadone.

Methadone is a non-competitive antagonist at the α4β2 and α3* nicotinic acetylcholine receptors and an agonist at the α7 nicotinic acetylcholine receptor.

Nicotine-methadone interactions have been studied in human beings and in various experimental settings regarding addiction, reward and pain. Most methadone maintenance treatment patients are smokers, and methadone administration has been shown to increase cigarette smoking. Previous in vitro studies have shown that methadone is a non-competitive antagonist at rat α3β4 nicotinic acetylcholine receptors (nAChR) and an agonist at human α7 nAChRs.

Nicotine-morphine interactions at α4β2, α7 and α3(⁎) nicotinic acetylcholine receptors.

Nicotine and opioids share several behavioral and rewarding properties. Although both opioids and nicotine have their own specific mechanism of action, there is empirical and experimental evidence of interactions between these drugs. We studied receptor-level interactions of nicotine and morphine at α4β2, α7 and α3(⁎) nicotinic acetylcholine receptors.

Nicotine exposure throughout early development promotes nicotine self-administration in adolescent mice and induces long-lasting behavioural changes.

Maternal cigarette smoking during pregnancy can result in behavioural problems of the offspring. Although the causative agent in tobacco smoke that leads to these aberrations is not known, some studies using animal models have supported the hypothesis that nicotine may cause impairments in fatal and neonatal development. However, in many of the animal studies nicotine has been administered by subcutaneous injections, which could lead to significant fetal hypoxia; some routes of drug administration included stressful procedures to pregnant dams that could create unfavorable fetal environment.