Ibogaine effects on sweet preference and amphetamine induced locomotion: implications for drug addiction

The Nonclassic Psychedelic Ibogaine Disrupts Cognitive Maps

Background

The ability of psychedelic compounds to profoundly alter mental function has been long known, but the underlying changes in cellular-level information encoding remain poorly understood.

Methods

We used two-photon microscopy to record from the retrosplenial cortex in head-fixed mice running on a treadmill before and after injection of the nonclassic psychedelic ibogaine (40 mg/kg intraperitoneally).

Results

We found that the cognitive map, formed by the representation of position encoded by ensembles of individual neurons in the retrosplenial cortex, was destabilized by ibogaine when mice had to infer position between tactile landmarks. This corresponded with increased neural activity rates, loss of correlation structure, and increased responses to cues. Ibogaine had surprisingly little effect on the size-frequency distribution of network activity events, suggesting that signal propagation within the retrosplenial cortex was largely unaffected.

Conclusions

Taken together, these data support proposals that compounds with psychedelic properties disrupt representations that are important for constraining neocortical activity, thereby increasing the entropy of neural signaling. Furthermore, the loss of expected position encoding between landmarks recapitulated effects of hippocampal impairment, suggesting that disruption of cognitive maps or other hippocampal processing may be a contributing mechanism of discoordinated neocortical activity in psychedelic states.

Tropane-Based Ibogaine Analog Rescues Folding-Deficient Serotonin and Dopamine Transporters

Missense mutations that give rise to protein misfolding are rare, but collectively, defective protein folding diseases are consequential. Folding deficiencies are amenable to pharmacological correction (pharmacochaperoning), but the underlying mechanisms remain enigmatic. Ibogaine and its active metabolite noribogaine correct folding defects in the dopamine transporter (DAT), but they rescue only a very limited number of folding-deficient DAT mutant proteins, which give rise to infantile Parkinsonism and dystonia. Herein, a series of analogs was generated by reconfiguring the complex ibogaine ring system and exploring the structural requirements for binding to wild-type transporters, as well as for rescuing two equivalent synthetic folding-deficient mutants, SERT-PG^601,602AA and DAT-PG^584,585AA. The most active tropane-based analog (9b) was also an effective pharmacochaperone in vivo in Drosophila harboring the DAT-PG^584,585AA mutation and rescued 6 out of 13 disease-associated human DAT mutant proteins in vitro. Hence, a novel lead pharmacochaperone has been identified that demonstrates medication development potential for patients harboring DAT mutations.

Quantitative trait locus analysis identifies rat genomic regions related to amphetamine-induced locomotion and Galpha(i3) levels in nucleus accumbens

Identification of the genetic factors that underlie stimulant responsiveness in animal models has significant implications for better understanding and treating stimulant addiction in humans. F(2) progeny derived from parental rat strains F344/NHsd and LEW/NHsd, which differ in responses to drugs of abuse, were used in quantitative trait locus (QTL) analyses to identify genomic regions associated with amphetamine-induced locomotion (AIL) and G-protein levels in the nucleus accumbens (NAc). The most robust QTLs were observed on chromosome 3 (maximal log ratio statistic score (LRS(max))=21.3) for AIL and on chromosome 2 (LRS(max)=22.0) for Galpha(i3). A 'suggestive' QTL (LRS(max)=12.5) was observed for AIL in a region of chromosome 2 that overlaps with the Galpha(i3) QTL. Novelty-induced locomotion (NIL) showed different QTL patterns from AIL, with the most robust QTL on chromosome 13 (LRS(max)=12.2). Specific unique and overlapping genomic regions influence AIL, NIL, and inhibitory G-protein levels in the NAc. These findings suggest that common genetic mechanisms influence certain biochemical and behavioral aspects of stimulant responsiveness.

Glial cell line-derived neurotrophic factor mediates the desirable actions of the anti-addiction drug ibogaine against alcohol consumption

Alcohol addiction manifests as uncontrolled drinking despite negative consequences. Few medications are available to treat the disorder. Anecdotal reports suggest that ibogaine, a natural alkaloid, reverses behaviors associated with addiction including alcoholism; however, because of side effects, ibogaine is not used clinically. In this study, we first characterized the actions of ibogaine on ethanol self-administration in rodents. Ibogaine decreased ethanol intake by rats in two-bottle choice and operant self-administration paradigms. Ibogaine also reduced operant self-administration of ethanol in a relapse model. Next, we identified a molecular mechanism that mediates the desirable activities of ibogaine on ethanol intake. Microinjection of ibogaine into the ventral tegmental area (VTA), but not the substantia nigra, reduced self-administration of ethanol, and systemic administration of ibogaine increased the expression of glial cell line-derived neurotrophic factor (GDNF) in a midbrain region that includes the VTA. In dopaminergic neuron-like SHSY5Y cells, ibogaine treatment upregulated the GDNF pathway as indicated by increases in phosphorylation of the GDNF receptor, Ret, and the downstream kinase, ERK1 (extracellular signal-regulated kinase 1). Finally, the ibogaine-mediated decrease in ethanol self-administration was mimicked by intra-VTA microinjection of GDNF and was reduced by intra-VTA delivery of anti-GDNF neutralizing antibodies. Together, these results suggest that GDNF in the VTA mediates the action of ibogaine on ethanol consumption. These findings highlight the importance of GDNF as a new target for drug development for alcoholism that may mimic the effect of ibogaine against alcohol consumption but avoid the negative side effects.

Iboga compounds reverse the behavioural disinhibiting and corticosterone effects of acute methamphetamine: Implications for their antiaddictive properties

This study investigated the effects of pretreatment with the putative antiaddictive compound, ibogaine (IBO), and its synthetic derivative, 18-methoxycoronaridine (18-MC), on the changes in behaviour in an elevated plus maze and the changes in corticosterone (CORT) produced by a low dose of methamphetamine (METH). In the elevated plus maze, the acute administration of METH (0.1 mg/kg ip, -20 min) produced an increase in both the number and the duration of open arm entries relative to saline (SAL)-treated controls. No effect of METH administration was observed on the total number of arm entries. These data indicated that METH alone produced either anxiolysis or behavioural disinhibition in this paradigm. More consistent with the latter possibility, the open arm behaviour of METH controls was associated with an increase in plasma levels of CORT, supporting a facilitatory role for CORT in this METH-induced effect. Pretreatment with both IBO and 18-MC (40 mg/kg ip, 19 h earlier) antagonized the behavioural disinhibiting effects of acute METH without altering locomotor activity. In addition, both iboga agents antagonized the increase in CORT produced by METH. These data provide insight into yet another potential mechanism through which iboga compounds may exert their antiaddictive effects, a reversal of the behavioural disinhibiting properties of stimulant drugs. Furthermore, these data indicate that this reversal is related to effects of iboga compounds on the stimulation of neuroendocrine systems by stimulant drugs.

Iboga interactions with psychomotor stimulants: panacea in the paradox?

Currently, no effective therapy has been approved for the treatment of addiction to stimulant drugs (e.g., cocaine, amphetamine and its methylated derivatives). However, preclinical studies indicate that the naturally-occurring indole alkaloid, ibogaine, and a synthetic iboga alkaloid congener, 18-methoxycoronaridine (18-MC), attenuate stimulant self-administration in laboratory animals. The in vivo pharmacological interactions between iboga agents and stimulant drugs are unclear. Ibogaine enhances the increase in accumbal dopamine produced by the acute administration of stimulant drugs. Consistent with these data, both ibogaine and 18-MC potentiate the expression of stimulant-induced motor behaviors in acute and chronic stimulant-treated animals. To account for the paradox between their effects on self-administration and motor behavior, we proposed that iboga agents interfere with stimulant self-administration by increasing sensitivity to their psychomotor-activating effects. However, this interpretation is contradicted by very recent observations that 18-MC is without effect on the dopamine response to acute cocaine and that both ibogaine and 18-MC block the expression of sensitized levels of dopamine in the nucleus accumbens produced by chronic cocaine administration. Thus, a positive relationship exists between the effects of iboga pretreatment on stimulant-induced dopamine sensitization and stimulant self-administration behavior. These data indicate that iboga agents might attenuate stimulant self-administration by reversing the neuroadaptations theoretically implicated in drug craving and compulsive drug-seeking behavior.

18-Methoxycoronaridine (18-MC) and ibogaine: comparison of antiaddictive efficacy, toxicity, and mechanisms of action

18-MC, a novel iboga alkaloid congener, is being developed as a potential treatment for multiple forms of drug abuse. Like ibogaine (40 mg/kg), 18-MC (40 mg/kg) decreases the intravenous self-administration of morphine and cocaine and the oral self-administration of ethanol and nicotine in rats; unlike ibogaine, 18-MC does not affect responding for a nondrug reinforcer (water). Both ibogaine and 18-MC ameliorate opioid withdrawal signs. Both ibogaine and 18-MC decrease extracellular levels of dopamine in the nucleus accumbens, but only ibogaine increases extracellular levels of serotonin in the nucleus accumbens. Both ibogaine and 18-MC block morphine-induced and nicotine-induced dopamine release in the nucleus accumbens; only ibogaine enhances cocaine-induced increases in accumbal dopamine. Both ibogaine and 18-MC enhance the locomotor and/or stereotypic effects of stimulants. Ibogaine attenuates, but 18-MC potentiates, the acute locomotor effects of morphine; both compounds attenuate morphine-induced locomotion in morphine-experienced rats. Ibogaine produces whole body tremors and, at high doses (> or = 100 mg/kg), cerebellar damage; 18-MC does not produce these effects. Ibogaine, but not 18-MC, decreases heart rate at high doses. While 18-MC and ibogaine have similar affinities for kappa opioid and possibly nicotinic receptors, 18-MC has much lower affinities than ibogaine for NMDA and sigma-2 receptors, sodium channels, and the 5-HT transporter. Both 18-MC and ibogaine are sequestered in fat and, like ibogaine, 18-MC probably has an active metabolite. The data suggest that 18-MC has a narrower spectrum of actions and will have a substantially greater therapeutic index than ibogaine.

Interactions between 18-methoxycoronaridine (18-MC) and cocaine: dissociation of behavioural and neurochemical sensitization

The phenomenon of sensitization has been implicated in various aspects of drug addiction. As such, the present study determined the effects of a potential anti-addictive agent, 18-methoxycoronaridine (18-MC; 40 mg/kg, IP, 19 h earlier), on the expression of sensitization following the repeated administration of cocaine (COC; five once daily injections of 15 mg/kg, IP) or saline. The effects of 18-MC on COC metabolism were also assessed. Compared to vehicle controls, 18-MC significantly enhanced the expression of COC-induced locomotion (0, 10, 20 and 40 mg/kg, IP) in chronic COC treated rats only. In both acute and chronic COC rats, 18-MC potentiated the stereotypy induced by higher COC doses (20 and 40 mg/kg, IP). In contrast, 18-MC abolished the sensitized dopamine (DA) response in the nucleus accumbens (NAC) to COC (20 mg/kg), without altering the DA response of acute COC rats. None of the interactions between 18-MC and COC appear to be related to alterations in COC metabolism as no effect of 18-MC pretreatment was observed on extracellular levels of COC or two of its metabolites, benzoylecogonine and norcocaine. From the present findings, it is concluded that the enhancement of COC-induced behaviour produced by 18-MC pretreatment is independent of effects on either COC pharmacokinetics or COC-induced alterations in DA transmission. However, given that 18-MC decreases the self-administration of COC in laboratory animals, it is proposed that the anti-addictive efficacy of 18-MC might be related to an ability to selectively block the expression of sensitized extracellular levels of DA in the NAC in rats with previous COC experience.

The potential anti-addictive agent, 18-methoxycoronaridine, blocks the sensitized locomotor and dopamine responses produced by repeated morphine treatment

18-Methoxycoronaridine (18-MC), a novel synthetic iboga congener, attenuates the reinforcing efficacy of morphine, disrupts some signs of morphine withdrawal in physically dependent rats and attenuates the dopamine response in the nucleus accumbens to acute morphine. The present study further investigated the interactions between 18-MC and morphine by examining the effects of 18-MC (40 mg/kg, i.p., 19 h earlier) on the expression of dopamine sensitization in the nucleus accumbens in response to morphine (20 mg/kg, i.p.) and on the dose-effect curves for morphine-induced locomotion (0-30 mg/kg, i.p.) in rats treated either acutely or repeatedly (five, once daily, injections of 20 mg/kg, i.p.) with morphine. Compared to vehicle pretreated controls, 18-MC increased the potency of morphine, shifting the dose-response curve to the left, in acute morphine treated rats; however, 18-MC did not alter the potency of morphine in rats treated repeatedly with morphine. Repeated morphine administration induced locomotor sensitization in approximately 50% of the rats tested; in vehicle pretreated rats, the morphine dose-response curve was shifted to the left in sensitized as compared to non-sensitized rats. In 18-MC pretreated rats, sensitized and non-sensitized rats responded similarly to morphine, revealing a blockade of sensitization by 18-MC. Consistent with this behavioural finding, 18-MC pretreatment completely abolished the sensitized dopamine response in the nucleus accumbens expressed by rats repeatedly treated with morphine. It is suggested that the potential anti-addictive efficacy of 18-MC might be related to an ability to restore normal functioning to a hypersensitive mesolimbic dopamine system produced by previous repeated morphine administration.

Ibogaine enhances the expression of locomotor sensitization in rats chronically treated with cocaine

Pretreatment (19 h) with the putative antiaddictive agent, ibogaine, has been shown previously to potentiate cocaine-induced locomotion in rats. The present study demonstrates that the magnitude of this effect of ibogaine is dependent on the previous cocaine history of the animal, on the time following ibogaine treatment, and on the number of ibogaine treatments. Compared to rats with no previous cocaine experience, ibogaine pretreatment (40 mg/kg, IP, 19 h earlier) markedly enhanced the expression of locomotor sensitization in response to a cocaine challenge injection (7.5 mg/kg) in rats that were chronically treated with cocaine (15 mg/ kg, IP, daily for 5 days). Tolerance to cocaine-induced locomotor sensitization appeared to occur in vehicle-pretreated chronic cocaine controls. Following a second series of identical treatments (beginning 3-4 days after the initial treatment series), locomotor responding to the cocaine challenge was further enhanced by a second ibogaine injection in chronically cocaine-treated animals. Twenty-four hours later, when animals were challenged again with cocaine in the absence of any further ibogaine pretreatment, the effect of ibogaine had dissipated. Consistent with previous studies from this laboratory, these data demonstrate that ibogaine can enhance sensitivity to the psychomotor stimulant effect of cocaine. The results of the present study further indicate that the extent of this effect depends on the animal's history of exposure to both ibogaine and cocaine.