Inhibition of synaptosomal neurotransmitter uptake by hallucinogens

Administration of N,N-dimethyltryptamine (DMT) in psychedelic therapeutics and research and the study of endogenous DMT

As with all drugs, the route, form, and/or dose of a substance administered or applied can play a defining role in its overall pharmacology and use as a therapeutic. This review will focus on these factors as they relate to the psychedelic N,N-dimethyltryptamine (DMT). It will examine the positive and negative aspects of different formulations and routes of administration of DMT and the observed effects from such administrations in the form of ayahuasca teas; oral "pharmahuasca"; injections by intravenous (IV) and intramuscular (IM) routes; inhalation, insufflation; and other routes; and high-dose, low-dose, and "micro-dose" effects. The review will consider possible oral route of administration alternatives that would not require concomitant use of a monoamine oxidase inhibitor. The review will then address the current research findings for DMT from in vivo and in vitro studies as well as the possibility that these findings may be revealing the role of endogenous DMT in normal brain function.

N, N-Dimethyltryptamine (DMT), an Endogenous Hallucinogen: Past, Present, and Future Research to Determine Its Role and Function

This report provides a historical overview of research concerning the endogenous hallucinogen N, N-dimethyltryptamine (DMT), focusing on data regarding its biosynthesis and metabolism in the brain and peripheral tissues, methods and results for DMT detection in body fluids and brain, new sites of action for DMT, and new data regarding its possible physiological and therapeutic roles. Research that further elaborates its consideration as a putative neurotransmitter is also addressed. Taking these studies together, the report proposes several new directions and experiments to ascertain the role of DMT in the brain, including brain mapping of enzymes responsible for the biosynthesis of DMT, further studies to elaborate its presence and role in the pineal gland, a reconsideration of binding site data, and new administration and imaging studies. The need to resolve the "natural" role of an endogenous hallucinogen from the effects observed from peripheral administration are also emphasized.

Neuropharmacology of N,N-dimethyltryptamine

N,N-dimethyltryptamine (DMT) is an indole alkaloid widely found in plants and animals. It is best known for producing brief and intense psychedelic effects when ingested. Increasing evidence suggests that endogenous DMT plays important roles for a number of processes in the periphery and central nervous system, and may act as a neurotransmitter. This paper reviews the current literature of both the recreational use of DMT and its potential roles as an endogenous neurotransmitter. Pharmacokinetics, mechanisms of action in the periphery and central nervous system, clinical uses and adverse effects are also reviewed. DMT appears to have limited neurotoxicity and other adverse effects except for intense cardiovascular effects when administered intravenously in large doses. Because of its role in nervous system signaling, DMT may be a useful experimental tool in exploring how the brain works, and may also be a useful clinical tool for treatment of anxiety and psychosis.

Dimethyltryptamine and other hallucinogenic tryptamines exhibit substrate behavior at the serotonin uptake transporter and the vesicle monoamine transporter

N,N-dimethyltryptamine (DMT) is a potent plant hallucinogen that has also been found in human tissues. When ingested, DMT and related N,N-dialkyltryptamines produce an intense hallucinogenic state. Behavioral effects are mediated through various neurochemical mechanisms including activity at sigma-1 and serotonin receptors, modification of monoamine uptake and release, and competition for metabolic enzymes. To further clarify the pharmacology of hallucinogenic tryptamines, we synthesized DMT, N-methyl-N-isopropyltryptamine (MIPT), N,N-dipropyltryptamine (DPT), and N,N-diisopropyltryptamine. We then tested the abilities of these N,N-dialkyltryptamines to inhibit [(3)H]5-HT uptake via the plasma membrane serotonin transporter (SERT) in human platelets and via the vesicle monoamine transporter (VMAT2) in Sf9 cells expressing the rat VMAT2. The tryptamines were also tested as inhibitors of [(3)H]paroxetine binding to the SERT and [(3)H]dihydrotetrabenazine binding to VMAT2. Our results show that DMT, MIPT, DPT, and DIPT inhibit [(3)H]5-HT transport at the SERT with K ( I ) values of 4.00 +/- 0.70, 8.88 +/- 4.7, 0.594 +/- 0.12, and 2.32 +/- 0.46 microM, respectively. At VMAT2, the tryptamines inhibited [(3)H]5-HT transport with K ( I ) values of 93 +/- 6.8, 20 +/- 4.3, 19 +/- 2.3, and 19 +/- 3.1 muM, respectively. On the other hand, the tryptamines were very poor inhibitors of [(3)H]paroxetine binding to SERT and of [(3)H]dihydrotetrabenazine binding to VMAT2, resulting in high binding-to-uptake ratios. High binding-to-uptake ratios support the hypothesis that the tryptamines are transporter substrates, not uptake blockers, at both SERT and VMAT2, and also indicate that there are separate substrate and inhibitor binding sites within these transporters. The transporters may allow the accumulation of tryptamines within neurons to reach relatively high levels for sigma-1 receptor activation and to function as releasable transmitters.

Thyronamines inhibit plasma membrane and vesicular monoamine transport

Thyroid hormone has long been known to have important transcriptional regulatory activities. Recently, however, the presence of endogenous derivatives of thyroid hormone, thyronamines, has been reported in various mammalian tissues. These derivatives have potent in vitro activity with a class of orphan G-protein-coupled receptors, the trace amine-associated receptors, and profound in vivo effects when administered to mice. We report here a novel neuromodulatory role for thyronamines. In synaptosomal preparations and heterologous expression systems, thyronamines act as specific dopamine and norepinephrine reuptake inhibitors. Thyronamines also inhibit the transport of monoamines into synaptic vesicles. These observations expand the nontranscriptional role of thyroid hormone derivatives and may help to explain the pharmacological effects of thyronamines in vivo.

5-Methoxy-N,N-diisopropyltryptamine (Foxy), a selective and high affinity inhibitor of serotonin transporter

5-Methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT) is a synthetic orally active hallucinogenic tryptamine derivative, known also as Foxy or Foxy methoxy. However, few studies have examined its effects in vitro. In the present study, we investigated the actions of 5-MeO-DIPT against monoamine neurotransmitter transporters, including the transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT), using COS-7 cells heterologously expressing these transporters and rat brain synaptosomes. 5-MeO-DIPT specifically inhibited the uptake of [3H]serotonin (5-HT) by the SERT-expressing COS-7 cells and rat striatal synaptosomes in a high affinity manner at concentrations similar to those for cocaine. The effect was reversible and competitive. 5-MeO-DIPT failed to stimulate reverse transport of [3H]5-HT through SERT, while it prevented the releasing action of methamphetamine. 5-MeO-DIPT induced cell toxicity at high concentrations in COS-7 cells, and it was not influenced by the expression of SERT. These results demonstrated that 5-MeO-DIPT acts as a competitive SERT inhibitor and has an inability to cause reverse transport, underlying its serotonergic actions.

Bufo toads and bufotenine: fact and fiction surrounding an alleged psychedelic

This paper investigates the supposedly psychedelic Bufo toad and the allegedly psychedelic drug bufotenine, which is contained in the skin and glands of this toad. The bufo toad has held a place in human mythologies and medicines worldwide since archaic times. Used by ancient peoples for a variety of purposes, its most spectacular effects, according to lore, involve magical and shamanic or occult uses for casting spells and for divination. In the Middle Ages, the Bufo toad was celebrated as a panacea and persecuted as a powerful poison. More recently, in the 1960s the Bufo toad was resurrected as a countercultural icon, with people purportedly licking or smoking the secretions to get high. Bufotenine has been at the center of a scientific debate since its discovery in 1893. This paper examines the extensive literature surrounding the Bufo toad and bufotenine, and untangles many of the myths and the misinformation that continue to vex both science and popular reporting. Finally, to promote further investigation, a comprehensive bibliography is provided that charts the history of the Bufo toad and bufotenine.

Structure-activity relationships of serotonin transport: relevance to nontricyclic antidepressant interactions

A transfectant cell model was used to examine the structure-activity relationships of serotonin (5-hydroxytryptamine, 5-HT) transport. The findings suggest that 5-HT interacts largely with nonpolar and sterically-confining environments on the transport system, and that a particular spatial coordination of the amino and phenyl groups (separated by an alkyl backbone) is important for transport interaction. Molecular modelling analyses revealed that this motif is also present in the structures of several nontricyclic antidepressants and specific inhibitors of 5-HT transport, as well as adrenergic agents which also possess 5-HT transport-inhibitory activities. While this amino-phenyl coordination motif seems to be a necessary structural requisite for transport interaction, and therefore likely to be part of the transport pharmacophore, additional phenyl rings present in some of the nontricyclic antidepressants may help to account for their relatively higher affinities in 5-HT transport interaction.

Stereochemical effects of 3,4-methylenedioxymethamphetamine (MDMA) and related amphetamine derivatives on inhibition of uptake of [3H]monoamines into synaptosomes from different regions of rat brain

3,4-Methylenedioxymethamphetamine (MDMA) is a recently popularized recreational drug, although some have advocated its psychotherapeutic potential. Since the pharmacology of MDMA is largely uncharacterized, the stereochemical profiles of MDMA and some of its homologs were derived on inhibition of synaptosomal uptake of [3H]monoamines and compared to those of amphetamine and the hallucinogenic phenylisopropylamine 2,5-dimethoxy-4-methylamphetamine (DOM). In contrast to the 5-fold stereoselectivity observed with amphetamine, only the S-(+) enantiomer of MDMA and 3,4-methylenedioxyamphetamine (MDA) inhibited [3H]dopamine uptake into striatal synaptosomes. Neither stereoisomer of the alpha-ethyl homolog of MDMA, N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine (MBDB), inhibited [3H]dopamine uptake. The two stereoisomers of amphetamine and the MDMA-related compounds were equipotent in inhibiting [3H]norepinephrine uptake into hypothalamic synaptosomes. Both stereoisomers of MDMA, MDA and MBDB were potent inhibitors of [3H]serotonin uptake into hippocampal synaptosomes, but only S-(+)-amphetamine produced an appreciable inhibition of [3H]serotonin uptake. Neither stereoisomer of DOM inhibited synaptosomal uptake of any [3H]monoamine. These results suggest that MDMA and its homologs may be more closely related to amphetamine rather than to DOM in their biochemical mode of action. The pronounced effects of the methylenedioxy-substituted compounds on [3H]serotonin and [3H]norepinephrine uptake implicate these neurotransmitters in the pharmacological effects of these drugs.