[Neurochemical mechanisms of morphine action on the function of neurons in the midbrain reticular formation].

The effect of microiontophoretically applied morphine and its interactions with the effect of microiontophoretic applications of either acetylcholine (ACh) or 5-hydroxytryptamine (5-HT) were studied in single neurons of the midbrain RF in immobilized rats. Morphine altered the firing rate of the majority of neurons: 39% neurons were excited, 16%-inhibited. Morphine reduced or blocked reactions of most (67%) neurons to 5-HT but had no effect on their reactions to ACh (86% of neurons). The findings suggest that interaction between morphine and sezotoninergic structures of the brain plays a more important role in mechanism of morphine central action than the interaction between morphine and cholinergic systems.