The effects of noribogaine and harmaline in rats trained with ibogaine as a discriminative stimulus

EEG Gamma Band Alterations and REM-like Traits Underpin the Acute Effect of the Atypical Psychedelic Ibogaine in the Rat

Ibogaine is a psychedelic alkaloid that has attracted large scientific interest because of its antiaddictive properties in observational studies in humans as well as in animal models. Its subjective effect has been described as intense, vivid dream-like experiences occurring while awake; hence, ibogaine is often referred to as an oneirogenic psychedelic. While this unique dream-like profile has been hypothesized to aid the antiaddictive effects, the electrophysiological signatures of this psychedelic state remain unknown. We previously showed in rats that ibogaine promotes a waking state with abnormal motor behavior along with a decrease in NREM and REM sleep. Here, we performed an in-depth analysis of the intracranial electroencephalogram during "ibogaine wakefulness". We found that ibogaine induces gamma oscillations that, despite having larger power than control levels, are less coherent and less complex. Further analysis revealed that this profile of gamma activity compares to that of natural REM sleep. Thus, our results provide novel biological evidence for the association between the psychedelic state and REM sleep, contributing to the understanding of the brain mechanisms associated with the oneirogenic psychedelic effect of ibogaine.

Stimulus control by 5-methoxy-N,N-dimethyltryptamine in wild-type and CYP2D6-humanized mice

In previous studies we have observed that, in comparison with wild type mice, Tg-CYP2D6 mice have increased serum levels of bufotenine [5-hydroxy-N,N-dimethyltryptamine] following the administration of 5-MeO-DMT. Furthermore, following the injection of 5-MeO-DMT, harmaline was observed to increase serum levels of bufotenine and 5-MeO-DMT in both wild-type and Tg-CYP2D6 mice. In the present investigation, 5-MeO-DMT-induced stimulus control was established in wild-type and Tg-CYP2D6 mice. The two groups did not differ in their rate of acquisition of stimulus control. When tested with bufotenine, no 5-MeO-DMT-appropriate responding was observed. In contrast, the more lipid soluble analog of bufotenine, acetylbufotenine, was followed by an intermediate level of responding. The combination of harmaline with 5-MeO-DMT yielded a statistically significant increase in 5-MeO-DMT-appropriate responding in Tg-CYP2D6 mice; a comparable increase occurred in wild-type mice. In addition, it was noted that harmaline alone was followed by a significant degree of 5-MeO-DMT-appropriate responding in Tg-CYP2D6 mice. It is concluded that wild-type and Tg-CYPD2D6 mice do not differ in terms of acquisition of stimulus control by 5-MeO-DMT or in their response to bufotenine and acetylbufotenine. In both groups of mice, harmaline was found to enhance the stimulus effects of 5-MeO-DMT.

Drug discrimination studies with ibogaine

The results of the studies described here support the hypothesis that ibogaine produces its effects via selective interactions with multiple receptors. It appears that 5-HT2A, 5-HT2C, and sigma 2 receptors are involved in mediating the stimulus effects of ibogaine. In addition, opiate receptors may also be involved. In contrast, sigma 1, PCP/MK-801, 5-HT3, and 5-HT1A receptors do not appear to play a major role. Ibogaine's hallucinogenic effects may be explained by its interactions with 5-HT2A and 5-HT2C receptors, while its putative antiaddictive properties may result from its interactions with sigma 2 and opiate receptors. Alternatively, the possibility that ibogaine's hallucinogenic properties underlie its antiaddictive effects, as previously suggested (34), would support a role for 5-HT2 receptors in mediating the reported therapeutic effects of ibogaine. Certainly many questions remain regarding ibogaine's mechanism of action. Although drug discrimination will be useful for answering some of those questions, the true potential of this technique is realized whin it is combined with other techniques. The next few years promise to be fruitful with respect to our understanding of this agent. Reasons supporting this belief include advances in the study of sigma receptors, interest in ibogaine's effects on second messenger systems, and the development of ibogaine congeners such as 18-methoxycoronaridine (35). In conclusion, the aforementioned studies should serve to guide further endeavors. Pertinent questions have been generated: What is the role of sigma receptors in the effects of ibogaine, especially with regard to addiction? How does ibogaine affect opiate neurotransmission? What effects, if any, do the Harmala alkaloids have on addiction phenomena? What is the mechanism of action of harmaline? Can 10-hydroxyibogamine serve as a discriminative stimulus and, if so, what receptor interactions mediate its stimulus effects? Does the ibogaine-trained stimulus generalize to novel agents, including 18-methoxycoronaridine?

Further investigations of the serotonergic properties of the ibogaine-induced discriminative stimulus

1. 5-HT3, 5-HT2C, and 5-HT1A receptor ligands were assessed in rats trained to discriminate ibogaine from water. 2. Significant ibogaine-appropriate responding was observed following treatment with the 5-HT2C agonists MK-212 (79.6%) and mCPP (76.4%). This substitution was completely antagonized by metergoline, an agent with 5-HT2C antagonist properties. However, metergoline was ineffective against ibogaine itself. This suggests that although ibogaine may act as an agonist at 5-HT2C receptors, this interaction is not essential to its discriminative cue. 3. Neither the 5-HT3 agonist, mCPBG (44.3%), nor the 5-HT3 antagonist, ondansetron (48.9%) substituted for ibogaine. Likewise, the 5-HT1A agonist 8-OH-DPAT (34.7%) and the 5-HT1A antagonist WAY-100635 (30.1%) failed to substitute. Furthermore, WAY-100635 failed to antagonize the ibogaine cue. 4. Unlike 5-HT2C receptors, 5-HT1A and 5-HT3 receptors do not appear to be involved in the ibogaine stimulus.

The effects of beta-carbolines in rats trained with ibogaine as a discriminative stimulus

The structural features and hallucinogenic properties shared by ibogaine and certain beta-carbolines prompted the evaluation of several representative beta-carbolines in rats trained with ibogaine as a discriminative stimulus. In a previous report from our laboratory harmaline completely substituted for ibogaine (83.5%). In the present study, only 6-methoxyharmalan completely substituted (86.3%). However, partial substitution was observed with harmine, harmane, harmalol, and tetrahydro-beta-carboline (THBC). Norharmane and 6,7-dimethoxy-4-ethyl-carboline-3-carboxylate (DMCM) failed to produce appreciable substitution. These results provide evidence for an ibogaine-like ether this extends to the previously reported anti-addictive effects of ibogaine remains to be established.

Effects of chronic ibogaine treatment on cerebellar Purkinje cells in the rat

The present investigation assessed the chronic toxicity of ibogaine on cerebellar Purkinje cells in male Fischer 344 rats. A behaviorally active dose of ibogaine (10 mg/kg, i.p.) was administered to a group of six subjects every other day for 60 days while the control group received an equivalent volume of saline (1 ml/kg). Estimates of Purkinje cell number were determined using the optical dissector/fractionator technique. No significant differences in Purkinje cell number were observed between the ibogaine (243764[+/-32766]) and control groups (230813[+/-16670]).