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The action of (+/-)-MDMA on medial prefrontal cortical neurons is mediated through the serotonergic system
1Department of Psychiatry and Behavioral Science, State University of New York, Stony Brook 11794.
Abstract:
The mechanism of action of systemically administered (+/-)-MDMA (3,4-methylenedioxymethamphetamine) on spontaneously active neurons in the medial prefrontal cortex (mPFc) of chloral hydrate anesthetized rats was examined using standard single unit extracellular recording techniques. Intravenously administered MDMA dose-dependently decreased the firing rates of the majority of mPFc neurons in control rats. In contrast, in rats that were pretreated with p-chlorophenylalanine (PCPA), which depletes the brain serotonin (5-hydroxytryptamine, 5-HT) content by inhibiting tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of 5-HT, MDMA was largely ineffective in inhibiting the firing of mPFc cells. In PCPA-treated animals, the administration of 5-hydroxytryptophan (5-HTP), which presumably restored the brain 5-HT content, but not L-DOPA, reinstated MDMA's inhibitory action in PCPA-treated rats. In rats that were pretreated with alpha-methyl-p-tyrosine (AMPT), which depletes the brain dopamine (DA) content by inhibiting tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of DA, MDMA inhibited the firing of all of the mPFc cells. MDMA's effect on mPFc neurons was reversed by 5-HT receptor antagonists such as granisetron and metergoline. These results strongly suggest that MDMA exerts its action on mPFc cells indirectly by releasing endogenous 5-HT.
Insights
Systemic administration of 3,4-methylenedioxymethamphetamine (MDMA) inhibits medial prefrontal cortex (mPFc) neuron firing by releasing serotonin (5-HT). This effect is dependent on serotonin levels, not dopamine, and can be blocked by 5-HT receptor antagonists.
Area of Science:
- Neuroscience
- Pharmacology
Background:
- The medial prefrontal cortex (mPFc) plays a crucial role in cognitive functions.
- Understanding the neurochemical mechanisms of psychoactive substances like MDMA is essential for their therapeutic and toxicological assessment.
Purpose of the Study:
- To investigate the mechanism of action of systemically administered MDMA on mPFc neurons.
- To determine the role of serotonin (5-HT) and dopamine (DA) in mediating MDMA's effects on mPFc neuronal activity.
Main Methods:
- Single unit extracellular recording techniques in chloral hydrate anesthetized rats.
- Systemic administration of MDMA, p-chlorophenylalanine (PCPA), 5-hydroxytryptophan (5-HTP), alpha-methyl-p-tyrosine (AMPT), and 5-HT receptor antagonists (granisetron, metergoline).
Main Results:
- MDMA dose-dependently decreased mPFc neuronal firing rates in control rats.
- MDMA's inhibitory effect was significantly reduced in PCPA-treated rats (serotonin depletion) but restored by 5-HTP administration.
- MDMA inhibited mPFc neurons in AMPT-treated rats (dopamine depletion), and its effects were reversed by 5-HT receptor antagonists.
Conclusions:
- MDMA exerts its inhibitory action on mPFc neurons indirectly through the release of endogenous serotonin (5-HT).
- The findings highlight the critical role of the serotonergic system in mediating MDMA's neurophysiological effects in the mPFc.