NO-ergic neurons of the cervical nucleus of the rat brain in normal conditions and after administration of opiates.

Histochemical reactions for NADPH-diaphorase (NADPH-d) were used to study the dynamics of NO synthesis activity in the cervical nuclei of the rat brain after i.v. administration of morphine hydrochloride. In normal conditions, NADPH-d activity was found in neurons in all the cervical nuclei. Acute and chronic administration of morphine at different doses (0.5 and 5 mg/kg) suppressed the NO-ergic activity of most cervical neurons. Decreases in the level of NADPH-d activity were different in different nuclei. NO-ergic changes were due to activation of opiate receptors, as they were dependent on the dose of morphine used, and treatment with the opiate antagonist naloxone restored the NO-ergic function of cervical neurons. Formation of tolerance to the analgesic effect of opiates was accompanied by significant but short-lived increases in NO synthesis activity. It is suggested that changes in the NO-ergic functions of cervical neurons may affect the balance of serotonin in the brain during opiate treatment.

[NO-ergic rat brain commissural neurons in the norm and during opiate administration]. / NO-ergicheskie neirony iader shva mozga krysy v norme i pri vvedenii opiatov.

Using histochemical reaction demonstrating NADPH-diaphorase (NADPH-d), the dynamics of NO synthesis was studied in the rat brain raphe nuclei following intravenous injection of morphine hydrochloride. In normal conditions NADPH-d activity was demonstrated in neurons of all raphe nuclei. Acute and chronic administration of morphine in different doses (0.5 mg/kg and 5 mg/kg) was found to inhibit NO-ergic activity of the major part of raphe nuclei neurons. The depression of NADPH-d activity was unequal in different nuclei. The NO-ergic changes are caused by an activation of opiate receptors, as they depend on morphine dose, while the application of opiate antagonist naloxone restores the NO-ergic function of raphe neurons. Formation of tolerance to opiate analgetic effect is accompanied by a significant, though short-lasting increase of NO synthesis activity. It is suggested that the changes in NO-ergic function of raphe neurons may influence brain serotonin balance after opiate administration.

Dynamics of NADPH diaphorase activity in raphe neurons during chronic treatment with opiates.

Systemic administration of diacetylmorphine considerably reduced the number of NADPH diaphorase-positive (NO-synthesizing) neurons in rat brain raphe nuclei. This effect was blocked by naloxone. In animals with the withdrawal syndrome NO-ergic activity in raphe neurons increased and surpassed the normal.