[Anxiety level during morphine abstinence correlates with the status of nitrergic system in the rat hippocampus].

Opiate addiction is accompanied by long-term structural and functional changes in brain regions persisting during abstinence, this status being an experimental model of the aberrant neuroplasticity. Nitric oxide is known to be involved in mechanisms of psychopathological events during opiate abstinence. In this study, indices of a nitregic system (nitric synthase activity--NOS, nitrites and nitrates concentration--NOx-) were measured in the rat brain region during morphine abstinence. Prior to this, the rats were tested for anxiety in an elevated plus maze. NOS activity increased in hippocampus 3 days after morphine withdrawal, while NOx--6 days after withdrawal. No changes of the nitrergic system could be revealed in other brain regions under study. Six days (but not 3 days) after morphine withdrawal, rats visited the open arms of the plus maze more frequently and spent more time in these arms as compared with respective controls. The data suggest that nitrergic system changes in the hippocampus may be involved in molecular mechanisms of behavioural alteration during morphine abstinence in rats.