Changes occur in central adrenoreceptor function following long-term morphine treatment and during morphine...

Radioligand binding techniques were used in combination with in vivo electrophysiological recording to characterize changes in beta adrenoreceptor activity in various brain areas in rats treated chronically with morphine. Following chronic morphine treatment, the maximum number of specific binding sites for 3H-dihydroalprenolol (3H-DHA) in parietal cortex and hippocampus showed a biphasic change, indicating an initial increase and decrease (relative to controls) in beta adrenoreceptors in these regions with time during withdrawal. No appreciable changes were observed in the dissociation constants for 3H-DHA binding. The changes in cortical beta adrenoreceptor density found in early (8 hr) and later phases (32 hr) of withdrawal were paralleled by a selective increase and decrease, respectively, in cortical neuron sensitivity to noradrenergic stimulation. These results suggest a possible linkage between changes in central adrenoreceptor function and the formation and/or expression of opiate dependence.