Time-related effects of apomorphine on noradrenaline metabolism and their regional differences in rat brain.

In the whole brain of rats, apomorphine in doses of 5-10 mg/kg elevated noradrenaline (NA) level 10-20 min after s.c. injection , but reduced NA level 60-90 min after injection in doses of 2-10 mg/kg associated with increased level of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPGSO4). With 5 mg/kg of apomorphine, NA content in the pons+medulla oblongata and midbrain showed biphasic changes as seen in the whole brain , whereas NA content increased in the cerebral cortex and hippocampus after 10-20 min, and decreased in the hypothalamus and amygdala after 60 min . Apomorphine in 0.1-0.2 mg/kg did not cause marked changes in brain NA metabolism. These results show that high doses of apomorphine which stimulate postsynaptic dopamine receptors have variable effects on noradrenergic neurons depending upon the time after injection and the brain region under investigation.