[Nitric oxide synthase activity and nitrates/nitrites level in brain regions during the spontaneous morphine...

Nitric oxide synthase (NOS) activity and nitrate/nitrites (NO(x)-) concentrations were measured in brain regions of rats during the spontaneous morphine withdrawal. Male Wistar rats were injected intraperotoneally with morphine hydrochloride at increasing doses (10-100 mg/kg) during 6 days twice a day. Thirty six hours after the last injection the severity of the spontaneous morphine withdrawal syndrome was determined by specific autonomic and locomotor indices. Both NOS activity and NO(x)- levels increased in the midbrain and the hippocampus, decreased in the striatum and the hypothalamus, and did not change in the cerebral cortex and the brain stem. NO(x)- concentrations in the cerebellum did not change, while NOS activity decreased. Both NOS activities and NO(x)- concentrations in the cerebral cortex, striatum, midbrain, and cerebellum correlated with withdrawal syndrome severity on the whole, and with the specific signs of abstinence.