Charles O. Rutledge

Selectivity of release of norepinephrine, dopamine and 5-hydroxytryptamine by amphetamine in various regions of rat brain☆

Abstract Tissues from various regions of rat brain were incubated with [ 3 H]norepinephrine, [ 3 H]dopamine or [ 3 H]5-hydroxytryptamine; excess amine was washed from the tissues and the [ 3 H]amines present in the incubation medium and tissues were measured. The release of the accumulated [ 3 H]amine by amphetamine was related to the nature of the neurons in the several regions and the release of each of the [ 3 H]amines was quite selective for neurons which contain the corresponding endogenous amine. The release of [ 3 H]norepinephrine from norepinephrine neurons is most sensitive to amphetamine, while the release of [ 3 H]dopamine from dopamine neurons requires higher concentrations of amphetamine. Release of [ 3 H]5-hydroxytryptamine from 5-hydroxytryptamine neurons appears to be least sensitive to amphetamine. This selective effect of amphetamine on neurons containing biogenic amines may help to explain the behavioral changes which occur at different doses of amphetamine. The selectivity of release of the [ 3 H]-amines was also examined by observing the accumulation and release of [ 3 H]norepinephrine and [ 3 H]5-hydroxytryptamine in the presence of five-fold higher concentrations of the unlabeled amines. There was relatively little effect of unlabeled norepinephrine on the accumulation and release of [ 3 H]5-hydroxytryptamine or of unlabeled 5-hydroxytryptamine on [ 3 H]norepinephrine accumulation and release. Unlabeled dopamine reduced the accumulation and altered the release of [ 3 H]norepinephrine and [ 3 H]5-hydroxytryptamine, but this was much less marked than the effect of the unlabeled analogues of the [ 3 H]amines. The release of each of the [ 3 H]amines by its unlabeled analogue occurred with concentrations as low as, or lower than, the release produced by amphetamine or the other unlabeled amines. The release of the [ 3 H]amines by a five-fold higher concentration of the unlabeled analogues was so high that it was not increased further by very high concentrations of amphetamine (10 −3 M). These results suggest that, under the conditions of this study, the [ 3 H]amines are accumulated within specific neurons of brain tissue and that they are selectively released by amphetamine.

Effects of the d- and l-isomers of amphetamine on uptake, release and catabolism of norepinephrine, dopamine and 5-hydroxytryptamine in several regions of rat brain.

Abstract The stereoselectivity of d - and l -amphetamine for uptake, release and catabolism of biogenic amines was studied in vitro in three regions of rat brain. The ( d -isomer was about two times more potent than the l -isomer in inhibiting uptake and releasing biogenic amines from chopped cerebral cortex labeled with norepinephrine and midbrain labeled with 5-hydroxytryptamine. On the other hand, the d -isomer was five times more potent than the l -isomer in inhibiting the uptake and releasing [ 3 H]dopaminc from nerve terminals of corpus striatum. When the relative potencies of amphetamine on uptake and release were compared, it was found that approximately 11-fold higher concentrations of both isomers were required to release dopamine compared to their ability to inhibit neuronal uptake. Only 4-fold higher concentrations of both isomers of amphetamine were required to release [ 3 H]nore-pinephrine compared to their ability to inhibit neuronal uptake. Approximately equal concentrations of the two isomers released and inhibited neuronal uptake of 5-hydroxytryptamine. With high concentrations (10 −3 M). the d -isomer of amphetamine was more effective than the l -isomer in inhibiting monoamine oxidase activity in synaptosome-free homogenates of cerebral cortex tissue. These results indicate that the dopamine nerve terminals of the corpus striatum possess greater stereoselectivity toward amphetamine than either the norepinephrine nerve terminals of cerebral cortex or 5-hydroxytryptaminc neurons of midbrain.

Dopamine correlates of neurological and psychological status in untreated Parkinsonism.

Thirty-seven untreated Parkinsonism patients showed significant positive correlations among decreased excretion of free dopamine, MMPI scores indicative of schizophrenic-like looseness of thinking, and the severity of all Parkinsonism signs except tremor. The data could indicate that abnormalities of dopamine metabolism may underlie both the motor and mental abnormalities of Parkinsonism.

Conjugation of l-DOPA and its metabolites after oral and intravenous administration to Parkinsonian patients

Abstract Tracer quantities of 3 H- l -dopa were given either orally or intravenously to patients with Parkinsons disease. The metabolism of 3 H- l -dopa was estimated by measurement of 3 H- l -dopa and some of its metabolites in urine samples collected during the first 24 hr. The decarboxylation of 3 H- l -dopa to 3 H-dopamine was approximately the same when 3 H- l -dopa was given by the two routes. The subsequent metabolism of the newly formed 3 H-dopamine was markedly dependent upon the route of administration. Conjugation was the major metabolic route of 3 H-dopamine derived from 3 H- l -dopa given orally, while O -methylation and deamination of 3 H-dopamine to 3 H-homovanillic acid predominated when 3 H- l -dopa was given intravenously. In contrast to the metabolism of tracer quantities of oral 3 H- l -dopa, large oral doses of l -dopa 3·0 g/day) resulted in a smaller proportion of conjugated dopamine and a greater proportion of homovanillic acid. The conjugation of 3 H-dopamine after tracer quantities of intravenous 3 H- l -dopa was only slightly decreased by the concomitant administration of 3·0 g/day of oral l -dopa. There is evidence that conjugation occurs primarily in the gastrointestinal-hepatic system after oral administration of l -dopa. When conjugation is either suppressed by large quantities of oral l -dopa or avoided by intravenous l -dopa, the amounts of free dopamine as well as homovanillic acid are increased. Thus, under these conditions, more free dopamine is available to produce the peripheral side effects of l -dopa therapy.

Dissociation of amphetamine-induced release of norepinephrine from inhibition of neuronal uptake in isolated brain tissue

Publisher Summary This chapter reviews the dissociation of amphetamine-induced release of norepinephrine (NE) from inhibition of neuronal uptake in isolated brain tissue. Neuronal uptake of 3H-norepinephrine into chopped rat brain tissue was measured by a method involving a 10 min incubation of chopped rat brain tissue with 10−7 M 3H-norepinephrine, and measuring total radioactivity in the incubation medium, and tissue. Drugs were added to the incubation medium 10 min before, and during the incubation with 3H-norepinephrine. Experimental samples were incubated at 37°C, and compared to control samples incubated at 0°C. It is found that because there is relatively little metabolism of 3H-norepinephrine in this 10 min exposure, 3H-norepinephrine was not separated from the deaminated metabolites. Results were expressed as tissue to medium ratios. This ratio approaches 1.0 at 0°C which indicates a lack of specific uptake at this temperature. The ratio was 7.1 ± 0.4 at 37°C in the absence of drugs, and this reflects approximately a sevenfold increase in uptake, and accumulation of 3H-norepinephrine into the tissue.

DISSOCIATION OF AMPHETAMINE-INDUCED RELEASE OF NOREPINEPHRINE FROM INHIBITION OF NEURONAL UPTAKE IN ISOLATED BRAIN TISSUE*

Publisher Summary This chapter reviews the dissociation of amphetamine-induced release of norepinephrine (NE) from inhibition of neuronal uptake in isolated brain tissue. Neuronal uptake of 3H-norepinephrine into chopped rat brain tissue was measured by a method involving a 10 min incubation of chopped rat brain tissue with 10−7 M 3H-norepinephrine, and measuring total radioactivity in the incubation medium, and tissue. Drugs were added to the incubation medium 10 min before, and during the incubation with 3H-norepinephrine. Experimental samples were incubated at 37°C, and compared to control samples incubated at 0°C. It is found that because there is relatively little metabolism of 3H-norepinephrine in this 10 min exposure, 3H-norepinephrine was not separated from the deaminated metabolites. Results were expressed as tissue to medium ratios. This ratio approaches 1.0 at 0°C which indicates a lack of specific uptake at this temperature. The ratio was 7.1 ± 0.4 at 37°C in the absence of drugs, and this reflects approximately a sevenfold increase in uptake, and accumulation of 3H-norepinephrine into the tissue.

Inhibition of aldehyde dehydrogenase by 2-chloroacetophenone and the resultant effects on the catabolism of norepinephrine in brain.

Abstract Rabbit brain cortex slices were incubated with 14 C-norepinephrine and the amounts of 14 C-phenolic acids and 14 C-phenolic glycols formed were measured. Pretreatment of rabbits with 2-chloroacetophenone, 300 mg/kg, results in an inhibition of the formation of phenolic acids (especially dihydroxymandelic acid) and a corresponding stimulation of the formation of phenolic glycols. Similar results were observed when the 2-chloroacetophenone was incubated in vitro with brain tissue slices. The concentrations of 2-chloroacetophenone required to inhibit an isolated enzyme preparation of aldehyde dehydrogenase and to inhibit the production of dihydroxymandelic acid in brain tissue slices are similar, which suggests that the effect of 2-chloroacetophenone on norepinephrine metabolism is due to inhibition of aldehyde dehydrogenase. The decrease in aldehyde dehydrogenase activity leads to an increase in substrate available for reduction to phenolic glycols and probably accounts for the observed stimulation of phenolic glycol formation. The effect of 2-chloroacetophenone on norepinephrine metabolism or on isolated aldehyde dehydrogenase could be prevented with glutathione. In addition, the effect on aldehyde dehydrogenase could be reversed with sulfhydryl reagents. This suggests that the interaction of 2-chloroacephenone with sulfhydryl groups may be important in the inhibition of aldehyde dehydrogenase.