Morphine differentially alters synthesis and turnover of dopamine in central neuronal systems

On the basis of biochemical indices of dopamine (DA) nerve activity (decline of DA after inhibition of tyrosine hydroxylase, accumulation of DOPA after inhibition of DOPA decarboxylase) it was revealed that morphine increases the activity of nigrostriatal and mesolimbic DA nerves which terminate in the striatum, nucleus accumbens and olfactory tubercle, but reduce the activity of tuberoinfundibular DA nerves which terminate in the median eminence. Morphine had no effect on tuberohypophyseal DA nerves which project to the posterior pituitary. Naloxone was without effect per se, but blocked the effects of morphine on DOPA accumulation. Thus, morphine differentially alters the diverse DA neuronal systems in the rat brain.