Biochemical resistance to development of morphine-dependence in rats: biogenic amines, its receptors and antibodies.

The level of norepinephrine (NE), epinephrine (E) and dopamine (DA) in hypothalamus and blood plasma along with antibodies to NE, DA and serotonin (5-HT) and characteristics of alpha 1-, alpha 2-adrenergic, D2-dopaminergic and S2-serotoninergic receptors in synaptic brain membranes were studied in two groups of rats predisposed or resistant to the formation of physical morphine dependence. The resistant animals were characterized by a significant elevation of DA levels in blood plasma, elevation of antibodies to NE, and by higher concentration of alpha 2-adrenergic receptors in the brain cortex and of D2-receptors in striatum. The affinity of D2-receptors to dopamine in resistant rats also was higher than in predisposed animals. The other parameters studied did not differ significantly between the two groups. These findings suggest that the increased activity of DA and NE neurotransmitter systems can be a cause for the genetic resistance of some individuals among Wistar rats to the formation of physical dependence on morphine.