Formation of deaminated metabolites of dopamine in noradrenaline neurons

The deaminated monoamine metabolites 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined electrochemically following organic solvent extraction and reverse-phase, high performance, liquid chromatography in four regions of the mouse brain. In the noradrenaline (NA)-predominant regions (hemispheres, brain stem), the ratio of the concentrations of DOPAC plus HVA to NA plus dopamine (DA) was approximately the same as in the DA-predominant regions (corpus striatum, limbic system). Yohimbine and reserpine elevated the concentrations of DOPAC and HVA both in the NA- and the DA-predominant regions. The effect of yohimbine was somewhat enhanced by the alpha 1-receptor blocking agent prazosin in the NA-predominant regions. The concentration of MOPEG was increased by yohimbine and decreased by reserpine. The concentrations of DOPAC and HVA were lowered by clonidine, but not by apomorphine in the NA-predominant regions of reserpine-treated mice. In the DA-predominant regions, apomorphine, but not clonidine, reduced the concentrations of DOPAC and HVA. The effects of clonidine and apomorphine were reversed by yohimbine and haloperidol, respectively. The results indicate that the concentrations of the acid DA metabolites DOPAC and HVA in the NA-predominant regions reflect the rate of synthesis of DA in the NA neurons.