Evidence for 5-HT2 involvement in the mechanism of action of hallucinogenic agents

Background The psychostimulant khat (Catha edulis Forsk), is a herbal drug cultivated and chewed as a recreational and socializing drug in East Africa and the Arabian Peninsula for centuries. Due to increasing air transportation and the loosening of customs restrictions, it is now readily available in the Western Countries mainly used by immigrants from khat growing areas causing a concern to policy-makers. Objective We conducted this review to further gain an insight to the neuropharmacological effects of khat. Methodology PubMed search engine with key terms ‘khat’ or ‘qat’ or ‘mirra’ or’qaad/jaad’ or ‘cathinone’ was used to obtain articles relevant to khat chewing. In total 284 English written articles published from 1959 to 2007 were screened. Results Most of the studies focused on cathinone, the postulated active psychostimulant alkaloid in khat. There were few studies which investigated the entire plant extract in either in vitro or animal studies. In the majority of the studies it was reported that both cathinone and cathine, another psychoactive constituent, have actions that are similar to those of amphetamine. Conclusions It seems that the well investigated khat alkaloids have many features similar to amphetamines; however there is a need for a more thorough examination of khat itself in well designed in vitro, animal and human studies with a range of comparator drugs before confirming the claim that khat is a “natural amphetamine”.

A review of the neuropharmacological properties of khat

The neural basis of psychedelic action

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.

/pdf/n-n-dimethyltryptamine-dmt-an-endogenous-hallucinogen-past-20yx6ezqau.pdf

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

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 [3H]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 [3H]paroxetine binding to the SERT and [3H]dihydrotetrabenazine binding to VMAT2. Our results show that DMT, MIPT, DPT, and DIPT inhibit [3H]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 μM, respectively. At VMAT2, the tryptamines inhibited [3H]5-HT transport with K
 I
 values of 93 ± 6.8, 20 ± 4.3, 19 ± 2.3, and 19 ± 3.1 μM, respectively. On the other hand, the tryptamines were very poor inhibitors of [3H]paroxetine binding to SERT and of [3H]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.

http://www.neurophys.wisc.edu/~cozzi/Hallucinogenic%20tryptamines%20as%20SERT%20and%20VMAT2%20substrates.%20%20Cozzi.%20%20J.%20Neural%20Transm.,%20116,%201591-1599%20(2009).pdf

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

A series of cathinone (alpha-aminopropiophenone) analogues was examined using the isolated rat fundus preparation. (S)-(-)-Cathinone possesses twice the serotonin receptor affinity of (+/-)-cathinone and four times the affinity of racemic amphetamine. Several derivatives of cathinone were found to either possess a lower affinity than the parent compound or did not interact with the receptors in a competitive manner. Several novel analogues, 1-(aminomethyl)-3,4-dihydronaphthalene hydrochloride (3), 4-(aminomethyl)-3-chromene hydrochloride (4b), as well as its 6-methoxy derivative, a, interact with serotonin receptors but in a fashion which is, most likely, dissimilar to the interaction of the substituted cathinone analogues.

Serotonin receptor affinity of cathinone and related analogues.

Hallucinogenic phenylalkylamine and N,N-dimethyltryptamine analogues are known to affect serotonergic systems both in vivo and in vitro. Using a rat stomach fundus model, the 5-HT receptor binding affinities of several of these analogues were determined and compared. The most behaviorally potent analogues examined, DOB, DOM, and 5-methoxy-N,N-dimethyltryptamine, were found to possess rather high affirmities (pA2 = 7.35, 7.12, and 7.08, respectively) for the 5-HT receptors of the model system.

Serotonin receptor binding affinities of several hallucinogenic phenylalkylamine and N,N-dimethyltryptamine analogues.

Chemical investigations leading to the construction of bis(bioreductive) alkylating agents having both conformationally restricted and mobile spacer regions are described. Two targets having the conformationally mobile ethylene spacer group, namely, 2,2'-ethylenebis[6-(hydroxymethyl)-p-benzoquinone] diacetate (3b) and 2,2'-ethylenebis[6-(bromomethyl)-p-benzoquinone] (3c), were studied in vivo and in vitro using an established epithelial/Burkitt lymphoma hybrid cell line (D98/HR1) previously shown to induce carcinomas in nude mice. Inactivity of both test compounds in vitro, the relative resistance of these cells to test drugs in vitro, and the selective antitumor properties of the bis(bromomethyl) analogue in vivo lead to the proposal that this compound undergoes bioreduction to an alkylating species in the hypoxic core of the tumor, thereby exerting its action.

Bis(bioreductive) alkylating agents: synthesis and biological activity in a nude mouse human carcinoma model.

Bis(bioreductive) alkylating agents: synthesis and biological activity in a nude mouse human carcinoma model

Mono-O-demethylation of several 2,5-dimethoxyphenalkylamines increases their affinity for the serotonin receptors of the isolated rat fundus preparation. In several instances, demethylation of methoxyphenalkylamines results in compounds which produce an antagonism which is not of a competitive nature. With respect to 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), demethylation of the 2-methoxy group alters affinity in a manner which parallels that observed upon demethylation of 5-methoxy-N,N-dimethyltryptamine. Using a discriminative stimulus paradigm, behavioral studies with rats reveal that the 2-hydroxy analogue, but not the 5-hydroxy analogue, of DOM produces effects (interoceptive cues) similar to those produced by 5-methoxy-N,N-dimethyltryptamine.

Demethyl analogues of psychoactive methoxyphenalkylamines: synthesis and serotonin receptor affinities.

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