Tabernanthine

Mechanisms of action of ibogaine and harmaline congeners based on radioligand binding studies.[Pubmed:1377086]

Brain Res. 1992 Feb 7;571(2):242-7.

Assays using radioligands were used to assess the actions of ibogaine and harmaline on various receptor types. Ibogaine congeners showed affinity for opiate receptors whereas harmaline and harmine did not. The Ki for coronaridine was 2.0 microM at mu-opiate receptors. The Kis for coronaridine and Tabernanthine at the delta-opiate receptors were 8.1 and 3.1 microM, respectively. Ibogaine, ibogamine, coronaridine and Tabernanthine had Ki values of 2.08, 2.6, 4.3 and 0.15 microM, respectively, for kappa-opiate receptors. Long-lasting, dose-dependent behavioral effects of ibogaine have been reported. The possibility that these effects were due to irreversible binding properties of ibogaine at kappa-receptors was considered; however, radioligand wash experiments showed a rapid recovery of radioligand binding after one wash. A voltage-dependent sodium channel radioligand demonstrated Ki values in the microM range for all drugs tested. Using radioligand binding assays and/or 36Cl- uptake studies, no interaction of ibogaine or harmaline with the GABA receptor-ionophore was found. The kappa-activity of ibogaine (or an active metabolite) may be responsible for its putative anti-addictive properties whereas the tremorigenic properties of ibogaine and harmaline may be due to their effects on sodium channels.

Benzodiazepine receptors are involved in tabernanthine-induced tremor: in vitro and in vivo evidence.[Pubmed:2820763]

Eur J Pharmacol. 1987 Aug 21;140(3):303-9.

Tabernanthine, an indol alkaloid, is structurally related to carbolines (harmane, harmaline) which, in vitro, displace specific flunitrazepam binding to brain benzodiazepine receptors. In vivo, both Tabernanthine and carbolines cause a fine general tremor, suggesting that a possible interaction with benzodiazepine receptors could be involved in the activity of Tabernanthine. This hypothesis was validated by the in vitro and in vivo antagonism of benzodiazepine by Tabernanthine. In vitro, Tabernanthine inhibited specific flunitrazepam binding in a competitive manner with an affinity (IC50 150 microM) in the same range as harmane. Tabernanthine appeared as a benzodiazepine receptor inverse agonist in a discriminant in vitro binding assay. In vivo, the time course of tremorigenic activity was related to the Tabernanthine concentration in brain (half-life = 2 h). Moreover, Tabernanthine-induced tremor was inhibited reversibly by flunitrazepam or by Ro-15 1788 (an antagonist of benzodiazepine-receptors). These results suggest that part of the action of Tabernanthine may be mediated by an interaction at the benzodiazepine receptor level.

Peripheral cardiovascular effects of tabernanthine tartrate in anaesthetized rats.[Pubmed:4051640]

Arch Int Pharmacodyn Ther. 1985 Jul;276(1):60-72.

The peripheral cardiovascular effects of Tabernanthine tartrate have been studied in anaesthetized rats. Our results confirm that the bradycardic effect of Tabernanthine is not inhibited by vagotomy, atropine or propranolol. On the contrary, bivagotomy, atropine treatment, as well as carotid artery occlusion, potentiate the bradycardic effect of Tabernanthine. The same is true for its hypotensive action and can be explained by the suppression of a compensatory mechanism involving the central nervous system, the parasympathetic system and/or a baroreflex mechanism. In addition, domperidone and sulpiride, two dopaminolytic drugs, are able to potentiate the decrease in heart rate produced by Tabernanthine. In pithed rat, Tabernanthine 1 mg/kg, potentiates the increases in systolic blood pressure produced either by norepinephrine or serotonine; conversely the systolic blood pressure responses to angiotensin II are significantly inhibited by Tabernanthine 1 mg/kg. Thus, Tabernanthine appears to possess a complex cardiovascular mechanism of action, depending probably on a simultaneous stimulation of beta 2-vascular adrenoceptors and alteration of cellular movements of calcium. Part of the direct bradycardic effect, as well as the inhibition of the pressor responses of angiotensin II could be explained by a calcium antagonist action of the alcaloid.

Effects of iboga alkaloids on morphine and cocaine self-administration in rats: relationship to tremorigenic effects and to effects on dopamine release in nucleus accumbens and striatum.[Pubmed:7820611]

Brain Res. 1994 Sep 19;657(1-2):14-22.

Ibogaine, a naturally occurring alkaloid, has been claimed to be effective in treating addiction to opioid and stimulant drugs and has been reported to decrease morphine and cocaine self-administration in rats. The present study sought to determine if other iboga alkaloids, as well as the chemically related harmala alkaloid harmaline, would also reduce the intravenous self-administration of morphine and cocaine in rats. Because both ibogaine and harmaline induce tremors, an effect that may be causally related to neurotoxicity in the cerebellar vermis, the temorigenic activities of the other iboga alkaloids were assessed. Lastly, in view of the involvement of the dopaminergic mesolimbic system in the actions of drugs of abuse, the effects of some of the iboga alkaloids on extracellular levels of dopamine and its metabolites in the nucleus accumbens and striatum were determined. All of the tested alkaloids (i.e., ibogaine, Tabernanthine, R- and S-coronaridine, R- and S-ibogamine, desethylcoronaridine, and harmaline) dose-dependently (2.5-80 mg/kg) decreased morphine and cocaine intake in the hour after treatment; decreases in morphine and cocaine intake intake were also apparent the day after administration of some but not all of these alkaloids (i.e., ibogaine, Tabernanthine, desethylcoronaridine, and the R-isomers of coronaridine and ibogamine). In some rats, there were persistent decreases in morphine or cocaine intake for several days after a single injection or after two or three weekly injections of one or another of these alkaloids; R-ibogamine produced such effects more consistently than any of the other alkaloids.(ABSTRACT TRUNCATED AT 250 WORDS)