Biochemistry and pharmacology of tryptamines and beta-carbolines. A minireview

Human psychopharmacology of hoasca, a plant hallucinogen used in ritual context in Brazil

A multinational, collaborative, biomedical investigation of the effects of hoasca (ayahuasca), a potent concoction of plant hallucinogens, was conducted in the Brazilian Amazon during the summer of 1993. This report describes the psychological assessment of 15 long-term members of a syncretic church that utilizes hoasca as a legal, psychoactive sacrament as well as 15 matched controls with no prior history of hoasca ingestion. Measures administered to both groups included structured psychiatric diagnostic interviews, personality testing, and neuropsychological evaluation. Phenomenological assessment of the altered state experience as well as semistructured and open-ended life story interviews were conducted with the long-term use hoasca group, but not the hoasca-naive control group. Salient findings included the remission of psychopathology following the initiation of hoasca use along with no evidence of personality or cognitive deterioration. Overall assessment revealed high functional status. Implications of this unusual phenomenon and need for further investigation are discussed.

Plant hallucinogens: springboards for psychotherapeutic drug discovery

Medicinal chemists have traditionally looked to the biosynthetic diversity found in nature to provide structural templates for the development of novel therapeutic agents, and the field of hallucinogen chemistry is similar to other fields in this respect. Even LSD, for many psychopharmacologists the prototype hallucinogen, is not itself a natural compound but rather is a semisynthetic analogue of alkaloids found in plants and fungi. A similar statement could be made about the other major structural classes of hallucinogenic agents: the phenylethylamine derivatives, the tryptamine derivatives, and the beta-carboline derivatives. In each case, compounds occurring naturally in some plant, usually associated with a long tradition of ethnomedical or ceremonial use, have been the starting point for the synthesis of numerous analogues. Some of these, such as the methoxylated amphetamine derivatives, display a pharmacological profile that differs in important respects from their natural product templates. In some instances the analogues have proven to be useful tools in the hands of neurobiologists characterizing the structure and function of brain neurotransmitter systems; in other cases, they have led to the development of new psychopharmacological agents with realized or potential clinical utility. This paper gives a brief historical overview of the role of natural products in the history and development of medicinal chemistry and experimental pharmacology, particularly with respect to the development of psychopharmacology and the discovery of CNS-active agents. It discusses the potential for the discovery of new medications with psychotherapeutic and/or research applications though the investigation of plants and natural compounds with serotonergic activities. Finally, consideration is given to some lesser known plant hallucinogens which may provide further useful leads for psychotherapeutic drug discovery.

Differential interactions of indolealkylamines with 5-hydroxytryptamine receptor subtypes

Affinities of drugs for 21 indolealkylamine derivatives, some with putative hallucinogenic activity, were determined at 5-HT1A, 5-HT2A and 5-HT2B recognition sites, using radioligand competition studies. Nearly all of the derivatives displayed greatest potency for the 5-HT2A receptor, labelled by [125I]R-(-)DOI in the cortex of the rat. Most derivatives displayed 2-10 times lower affinity at the HT2B receptor labelled by [3H]ketanserin in bovine cortex. Derivatives lacking ring substituents displayed lower affinities for all of the recognition sites, compared to derivatives substituted in the 4- or 5-position of the indole ring. The 4-hydroxylated derivatives displayed 25-380-fold selectivity for the 5-HT2A site, vs the 5-HT1A site, while the 5-substituted derivatives displayed approximately equal potency at the 5-HT1A and 5-HT2A sites. Affinity of all the compounds at the 5-HT2B site was greater than 300 nM. The 6-substituted derivatives displayed greater than micromolar affinities for all of the 5-HT recognition sites examined. The size of the N,N-dialkyl substituent was a secondary determinant of affinity, with groups larger than N,N-diisopropyl resulting in a marked reduction in affinity at both the 5-HT2A and 5-HT1A recognition sites. This study demonstrated that hallucinogenic 4-hydroxy-indolealkylamines, like psychotomimetic phenylisopropylamines, bind potently and selectively to the 5-HT2A recognition site, labelled by [125I]R-(-)DOI. This provides further evidence indicating that this recently described subtype of the 5-HT2 receptor may partially mediate the action of hallucinogenic agents.

A proposed mechanism for the visions of dream sleep

The visions of dream sleep are suggested to occur through a dream mechanism which implicates tryptamine derivatives as endogenous paychedelics. The hallucinations that occur in some schizophrenic syndromes are also proposed to occur through a similar, though desynchronized, mechanism. These compounds occur in the human pineal gland and are regarded as neurotransmitters or neuroregulators. A protocol for experimental verification is suggested.