Effects of the d- and l-isomers of amphetamine on the levels of 3-methoxy-4-hydroxyphenylglycol sulfate in whole rat brain and rat brain regions

Determination of the course of brainstem catecholamine fibers mediating amphetamine anorexia

Previous studies suggest that brainstem catecholamine (CA) fibers which mediate amphetamine (AMPH)-induced anorexia ascend through the midlateral medical forebrain bundle and perifornical region and terminate in the perifornical hypothalamic region (PFH) at the level of the hypothalamic ventromedial nucleus. Through studies of wire-knife cuts (KCs) placed in the lower brainstem, the present paper further delineates the course of fibers mediating AMPH feeding suppression, as they ascend through the medullary, pontine and midbrain tegmentum. The results indicate that the crucial CA fibers ascend through the ventrolateral medulla just dorsal to the nucleus of the seventh cranial nerve, 1.1-1.9 mm lateral to midline. In their rostral course, these fibers apparently maintain a relatively straight position in the ventral pons and then enter the ventrolateral midbrain just dorsal to the medial lemniscus, between 0.7 and 1.1 mm lateral to midline. These medullary fibers, possibly originating from the norepinephrine/epinephrine-containing ventrolateral cell group (A1/C1), then appear to join additional fibers from the scattered dopamine-containing neurons positioned in the caudal midbrain (A8 CA cell group). Together, these dopamine, epinephrine and norepinephrine systems are believed to ascend into the medial aspect of the medial forebrain bundle on their way to the PFH at the level of the ventromedial nucleus.

Conversion of 3, 4-dihydroxyphenylalanine and deuterated 3, 4-dihydroxyphenylalanine to alcoholic metabolites of catecholamines in rat brain

We have investigated the effects of 3, 4-dihydroxyphenylalanine (L-DOPA) and its deuterated analogue on the concentrations of alcoholic metabolites of catecholamines in rat brain by means of gas chromatography/mass spectrometry with selected-ion monitoring. Whole brain concentrations of the two neutral norepinephrine metabolites, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3, 4-dihydroxyphenylethyleneglycol (DHPG), were significantly increased in a dose-dependent manner by a single intraperitoneal injection of L-DOPA. Both MHPG and DHPG, as well as the corresponding dopamine metabolites, reached a maximum 1 h after injection. Brain MHPG and DHPG concentrations were elevated by 78 and 134%, respectively, 1 h after injection of 150 mg/kg L-DOPA. Analyses of discrete brain regions revealed that concentrations of the norepinephrine metabolites were elevated uniformly in all regions, except that MHPG showed a greater increase in the cerebellum than in other regions. The latter result appeared to be explained by the finding that 52% of the total MHPG in the cerebellum was unconjugated (compared to 15% in the whole brain). L-DOPA caused a proportionately greater increase in free MHPG than in total MHPG in the cerebellum and brain stem. By using deuterated L-DOPA in place of L-DOPA and measuring both the deuterated and nondeuterated norepinephrine metabolites, we demonstrated that virtually all of the increases in MHPG and DHPG were due to the conversion of the exogenous L-DOPA to norepinephrine. Thus, the effects of norepinephrine metabolism need to be considered in attempts to understand clinical and behavioral effects of L-DOPA.

Regional distribution and production rate of 3-methoxy-4-hydroxyphenylethyleneglycol sulphate (MHPG-SO4) in rat brain

The levels of noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulphate (MHPG-SO4) in 15 brain regions showed a parallel distribution in male Wistar rats. The differences in regional distribution of MHPG-SO4 were similar to those in the rate of NA turnover reported by other investigators. The accumulation rates of MHPG-SO4 during 45 and 90 min after probenecid injection significantly correlated to the steady state levels of MHPG-SO4 in nine regions studied. With the results, the regional levels of MHPG-SO4 either in untreated or in probenecid-treated rats, are considered to be a useful index of NA turnover.