Nitric oxide and substance dependence.

The free-radical gas nitric oxide (NO) plays an important role in a diverse range of physiological processes. It is synthesized from the precursor L-arginine by the enzyme NO synthase (NOS), which transforms L-arginine into NO and citrulline. This synthetic pathway exists in the central nervous system (CNS), and NO appears to be a messenger molecule in the CNS, fulfilling most of the criteria of a neurotransmitter. Recent studies indicate that NO may play an important role in dependence on drugs of abuse. The purpose of this review is to address the role of NO in dependence on substances such as opioids, ethanol, psychostimulants and nicotine. Inhibitors of NOS modulate withdrawal from opioids and ethanol, diminishing many signs of withdrawal. In addition, NOS inhibitors suppress signs of withdrawal from nicotine. These data suggest that NO may be involved in the expression of withdrawal signs, and they leave open the possibility that NO may mediate the development of many of these signs. Although preliminary, data to date suggest that glutamate neurotransmission may be related to these beneficial effects of NOS inhibitors on signs of withdrawal. Emerging data further suggest that NO may have a general role in the dependence potential of various classes of drugs of abuse. Thus, modulation of NO systems may be a potential therapeutic target for treatment of substance abuse.