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Interactions of methylenedioxymethamphetamine with monoamine transmitter release mechanisms in rat brain slices
1Department of Pharmacology, University of Melbourne, Victoria, Australia.
Abstract:
This study investigates the effects of methylenedioxymethamphetamine (MDMA) and amphetamine on monoamine release from rat superfused brain slices in both the presence and absence of vesicular stores of transmitter. MDMA caused the release of radioactivity from slices incubated with [3H]5-hydroxytryptamine, [3H]noradrenaline or [3H]dopamine with EC50 values of 1.9 mumol/l (95% confidence limits 1.5-2.3 mumol/l), 4.5 mumol/l (2.3-8.7 mumol/l), and greater than 30 mumol/l, respectively. In contrast, amphetamine (0.1-300 mumol/l) was more effective in releasing radioactivity from slices incubated with [3H]dopamine than [3H]noradrenaline or [3H]5-hydroxytryptamine. When Ca2+ was excluded from the superfusion fluid, the MDMA-induced release of radioactivity from slices incubated with [3H]dopamine was unaltered, but that from slices incubated with [3H]noradrenaline or [3H]5-hydroxytryptamine was enhanced. MDMA (10 mumol/l) facilitated the stimulation-induced (5 Hz, 1 min) outflow of radioactivity from slices incubated with [3H]noradrenaline or [3H]5-hydroxytryptamine to 7.5-fold and 2.1-fold of control values, respectively, but had no effect on that from slices incubated with [3H]dopamine. Amphetamine (1 mumol/l) increased the stimulation-induced outflow from slices incubated with [3H]noradrenaline, but not that from slices incubated with [3H]5-hydroxytryptamine or [3H]dopamine. Inhibition of monoamine oxidase by a 30-min incubation with pargyline (100 mumol/l) enhanced the releasing action of MDMA on all three monoamines. Pargyline (100 mumol/l) also enhanced the facilitation caused by MDMA, of the stimulation-induced outflow of radioactivity from slices incubated with [3H]noradrenaline, [3H]5-hydroxytryptamine or [3H]dopamine. In some experiments, slices were obtained from reserpinised rats (2.5 mg/kg s.c. 24 h prior) and pre-exposed for 30 min to the monoamine oxidase inhibitor parglyine (100 mumol/l). Under these conditions, electrical stimulation evoked a small residual stimulation-induced outflow of radioactivity from slices incubated with [3H]noradrenaline, and failed to evoke an outflow of radioactivity from slices incubated with [3H]5-hydroxytryptamine or [3H]dopamine. However, a Ca(2+)-dependent stimulation-induced outflow of radioactivity was evoked in the presence of either MDMA (10 mumol/l) or amphetamine (1 mumol/l) from slices incubated with either [3H]dopamine or [3H]noradrenaline, but not from slices incubated with [3H]5-hydroxytryptamine. The stimulation-induced outflow of radioactivity from slices incubated with [3H]noradrenaline was enhanced in the presence of desipramine (1 mumol/l), however this enhancement was less than that caused by 10 mumol/l MDMA or 1 mumol/l amphetamine. The Ca(2+)-dependent response to electrical stimulation in the presence of MDMA from slices incubated with [3H]noradrenaline was greatly reduced when rats were pretreated with a higher dose of reserpine (10 mg/kg s.c.).(ABSTRACT TRUNCATED AT 400 WORDS)
Insights
Methylenedioxymethamphetamine (MDMA) and amphetamine differentially affect monoamine release from rat brain slices. MDMA primarily releases serotonin and norepinephrine, while amphetamine favors dopamine release, with distinct mechanisms observed under varying conditions.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- Monoamine transporters play a crucial role in regulating neurotransmitter levels.
- Methylenedioxymethamphetamine (MDMA) and amphetamine are psychostimulant drugs with known effects on monoamine systems.
- Understanding their precise mechanisms of action, particularly concerning vesicular storage, is essential for elucidating their neurobiological impact.
Purpose of the Study:
- To investigate the differential effects of MDMA and amphetamine on the release of [3H]5-hydroxytryptamine, [3H]noradrenaline, and [3H]dopamine from rat brain slices.
- To explore the role of vesicular stores and calcium (Ca2+) in mediating the release of these monoamines induced by MDMA and amphetamine.
- To examine the influence of monoamine oxidase inhibition and reserpine pretreatment on the drug-induced monoamine release.
Main Methods:
- Superfusion of rat brain slices pre-incubated with radiolabeled monoamines ([3H]5-HT, [3H]NE, [3H]DA).
- Administration of MDMA and amphetamine at various concentrations to assess dose-dependent release.
- Manipulation of extracellular Ca2+ levels and use of reserpine to deplete vesicular stores.
- Inhibition of monoamine oxidase (MAO) using pargyline.
- Electrical stimulation to evoke neurotransmitter release in the presence and absence of drugs and inhibitors.
Main Results:
- MDMA induced concentration-dependent release of all three monoamines, with higher potency for [3H]5-HT and [3H]NE compared to [3H]DA.
- Amphetamine showed greater efficacy in releasing [3H]DA compared to [3H]NE and [3H]5-HT.
- In Ca2+-free medium, MDMA-induced [3H]DA release was unaffected, while [3H]NE and [3H]5-HT release was enhanced.
- MDMA facilitated stimulation-induced [3H]NE and [3H]5-HT outflow, but not [3H]DA outflow.
- Pargyline pretreatment enhanced MDMA's releasing action and facilitation of stimulation-induced outflow for all three monoamines.
- In reserpinized rats, MDMA and amphetamine evoked Ca2+-dependent [3H]DA and [3H]NE release, but not [3H]5-HT release.
Conclusions:
- MDMA and amphetamine exhibit distinct substrate specificities and mechanisms for inducing monoamine release.
- Vesicular stores play a differential role in the release of monoamines mediated by MDMA and amphetamine.
- MDMA's effects on norepinephrine and serotonin release appear to be primarily non-exocytotic, while amphetamine's effects on dopamine and norepinephrine involve Ca2+-dependent mechanisms, potentially including exocytosis, especially after vesicular depletion.