Effect of morphine on catecholamine - stimulated cyclic AMP production in cortex slices from rats and mice

Morphine (10 micro M) blocked noradrenaline-stimulated cyclic AMP production in slices of cerebral cortex from normal rats but not in slices from rats pretreated with 6-hydroxydopamine (6-OHDA). In contrast, morphine failed to prevent noradrenaline-stimulated cyclic AMP production in mouse cortex slices. Levorphanol weakly antagonized the rise in cyclic AMP produced by noradrenaline in both normal and 6-OHDA-treated mouse cortex. Morphine had no effect on the adrenaline-stimulated cyclic AMP accumulation in mouse cortex but it entirely prevented the rise in cyclic AMP produced by isoprenaline. This effect was no observed in brain slices from 6-OHDA-treated mice. It is concluded that in slices of rat cortex, morphine stimulates postulated presynaptic, 6-OHDA-sensitive, opiate receptors associated with noradrenergic nerve terminals. These opiate receptors alter postsynaptic alpha - and beta - adrenoceptor activity. In the mouse, morphine appears to stimulate presynaptic opiate receptors that modify exclusively beta - adrenoceptor-mediated cyclic AMP production.