Role of the glutamatergic system in nicotine dependence dependence - Implications for the discovery and development of new pharmacological smoking cessation therapies

Preclinical research findings in laboratory animals indicate that the glutamatergic system is critically involved in nicotine dependence. In animals, compounds that decrease glutamatergic neurotransmission, such as antagonists at postsynaptic NMDA receptors, antagonists at excitatory postsynaptic metabotropic glutamate (mGlu) 5 receptors, or agonists at inhibitory presynaptic mGlu2 and mGlu3 receptors, decreased nicotine self-administration or reinstatement of nicotine-seeking behaviour. These findings suggest that medications that decrease glutamatergic transmission overall may reduce the reinforcing effects of tobacco smoking and prevent relapse to tobacco smoking in humans. Furthermore, compounds that increase glutamate release, such as antagonists at mGlu2 and mGlu3 receptors, ameliorated reward deficits associated with nicotine withdrawal in animals, and thus may alleviate the depression-like symptoms associated with nicotine withdrawal in humans. Animal studies also showed that alpha-amino-3-ydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors did not appear to be involved in mediating the primary reinforcing effects of nicotine but that they may be involved in the development of nicotine dependence and withdrawal. Taken together, the preclinical data indicate that different glutamatergic receptors are involved in the mediation of different aspects of nicotine dependence. These findings have implications for the discovery and development of new pharmacotherapies that target the glutamatergic system to aid in smoking cessation. At present, very few clinical studies have addressed the effects of glutamatergic compounds on cigarette smoking. Clinical studies involving compounds that have actions at ionotropic glutamate receptors are briefly discussed in this review and suggest the potential of glutamatergic compounds as pharmacotherapies to aid in smoking cessation. Medications that target mGlu receptors have recently been tested in human phase II trials for various indications; however, the potential of these mGlu compounds as medications for nicotine dependence remains to be evaluated in humans. The preclinical data evaluated in this review indicate that such clinical trials for smoking cessation with mGlu compounds are clearly warranted and may reveal novel treatments for nicotine dependence.