Interaction of synthetic opioid metenkephalin peptide analogs, Lilly 127623 and FK 33-824 with indole hallucinogens: antagonism of N,N-dimethyltryptamine- and LSD-induced disruption of food-rewarded bar pressing behavior in the rat

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.

Dark Classics in Chemical Neuroscience: N, N-Dimethyltryptamine (DMT)

Though relatively obscure, N, N-dimethyltryptamine (DMT) is an important molecule in psychopharmacology as it is the archetype for all indole-containing serotonergic psychedelics. Its structure can be found embedded within those of better-known molecules such as lysergic acid diethylamide (LSD) and psilocybin. Unlike the latter two compounds, DMT is ubiquitous, being produced by a wide variety of plant and animal species. It is one of the principal psychoactive components of ayahuasca, a tisane made from various plant sources that has been used for centuries. Furthermore, DMT is one of the few psychedelic compounds produced endogenously by mammals, and its biological function in human physiology remains a mystery. In this review, we cover the synthesis of DMT as well as its pharmacology, metabolism, adverse effects, and potential use in medicine. Finally, we discuss the history of DMT in chemical neuroscience and why this underappreciated molecule is so important to the field of psychedelic science.

Comparison of the discriminative stimulus effects of dimethyltryptamine with different classes of psychoactive compounds in rats

RATIONALE

There has been increased recreational use of dimethyltryptamine (DMT), but little is known of its discriminative stimulus effects.

OBJECTIVES

The present study assessed the similarity of the discriminative stimulus effects of DMT to other types of hallucinogens and to psychostimulants.

METHODS

Rats were trained to discriminate DMT from saline. To test the similarity of DMT to known hallucinogens, the ability of (+)-lysergic acid diethylamide (LSD), (-)-2,5-dimethoxy-4-methylamphetamine (DOM), (+)-methamphetamine, or (+/-)3,4-methylenedioxymethyl amphetamine (MDMA) to substitute in DMT-trained rats was tested. The ability of DMT to substitute in rats trained to discriminate each of these compounds was also tested. To assess the degree of similarity in discriminative stimulus effects, each of the compounds was tested for substitution in all of the other training groups.

RESULTS

LSD, DOM, and MDMA all fully substituted in DMT-trained rats, whereas DMT fully substituted only in DOM-trained rats. Full cross-substitution occurred between DMT and DOM, LSD and DOM, and (+)-methamphetamine and MDMA. MDMA fully substituted for (+)-methamphetamine, DOM, and DMT, but only partially for LSD. In MDMA-trained rats, LSD and (+)-methamphetamine fully substituted, whereas DMT and DOM did not fully substitute. No cross-substitution was evident between (+)-methamphetamine and DMT, LSD, or DOM.

CONCLUSIONS

DMT produces discriminative stimulus effects most similar to those of DOM, with some similarity to the discriminative stimulus effects of LSD and MDMA. Like DOM and LSD, DMT seems to produce predominately hallucinogenic-like discriminative stimulus effects and minimal psychostimulant effects, in contrast to MDMA which produced hallucinogen- and psychostimulant-like effects.

Opioid-hallucinogen interactions

Before the advent of neuroleptics, opioids such as morphine were used occasionally in the treatment of schizophrenia and other mental disorders. Recent interest in the possible therapeutic role of endogenous opioid peptides in various mental states has prompted a new look at the opioids. The present paper summarizes the research to date in the author's laboratory on opioid-hallucinogen interactions. A model behavioral state was induced in rats with N,N-dimethyltryptamine (DMT) or lysergic acid diethylamide-25 (LSD). Several mu opioid agonists, antagonists, and synthetic enkephalin analogs interacted with DMT and LSD. Adult male Holtzman rats trained on a positive reinforcement fixed ratio four (FR4) behavioral schedule (i.e., a reward of 0.01 ml sugar-sweetened milk was earned on every fourth bar press) were used in these studies. DMT (3.2 and 10.0 mg/kg) given with a 0.9% NaCl pretreatment IP, disrupted established food rewarded FR4 bar pressing behavior in a dose related fashion. Pre-determined behaviorally ineffective doses of mu opioid agonists showed selective biphasic effects against DMT and LSD. Low doses antagonized the effects of both hallucinogens, whereas larger doses enhanced their effects. In contrast to the antagonistic effects of low doses of mu opioid agonists, the mu-kappa opioid antagonist (-)-naloxone enhanced the effects of DMT and LS. (-)-Naloxone enhanced the effects of DMT and LSD. Potentiation of DMT-induced behavioral disruption was attributed to a stereospecific opioid antagonist effect of (-)-naloxone in that the (+)-naloxone enantiomer failed to potentiate the effects of DMT. Further studies are indicated to determine hallucinogen-opioid interactions in various species, including man.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone alters the effects of LSD, DOM and quipazine on operant behavior of rats

Administration of the indolealkylamine hallucinogen d-lysergic acid diethylamide (LSD), the phenethylamine hallucinogen 2,5-dimethoxy-4-methylamphetamine (DOM) and the putative 5-hydroxytryptamine (5-HT) agonist quipazine all produced a dose-dependent decrease in fixed ratio (FR-40) response rates and a concomitant increase in the number of 10-second pause intervals. Although naloxone (4.0 mg/kg) had no effect on FR-40 responding per se, the pause-producing effects of LSD and, to a lesser extent, DOM were potentiated by pretreatment with naloxone. The action of quipazine on reinforcers was unaffected by combination with naloxone, while the effect on pause intervals was slightly attenuated by naloxone pretreatment. These data and previous studies suggest that the pause-producing effects of indolealkylamine and phenethylamine hallucinogens reflect their activation of a selective portion of brain 5-HT receptors. The potentiation of these effects by naloxone may relate to a modulation of central 5-HT systems by endogenous opioid mechanisms tending to restore an imbalance in various 5-HT pathways caused by the hallucinogenic 5-HT agonists. The more generalized disruptive effects of quipazine on brain 5-HT systems may be less susceptible to the endogenous opioid modulation or may actually combine with it to induce a greater disruption.