review paper: role of nitric oxide on dopamine release and morphine-dependency

the catastrophic effects of opioids use on public health and the economy are documented clearly in numerous studies. repeated morphine administration can lead to either a decrease (tolerance) or an increase (sensitization) in its behavioral and rewarding effects. morphine-induced sensitization is a major problem and plays an important role in abuse of the opioid drugs. studies reported that morphine may exert its effects by the release of nitric oxide (no). no is a potent neuromodulator, which is produced by nitric oxide synthase (nos). however, the exact role of no in the opioid-induced sensitization is unknown. in this study, we reviewed the role of no on opioid-induced sensitization in 2 important, rewarding regions of the brain: nucleus accumbens and ventral tegmentum. in addition, we focused on the contribution of no on opioid-induced sensitization in the limbic system.