Ibogaine modulates cocaine responses which are altered due to environmental habituation: in vivo microvoltammetric and behavioral studies

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.

IUPHAR - invited review - Ibogaine - A legacy within the current renaissance of psychedelic therapy

Ibogaine is a powerful psychoactive substance that not only alters perception, mood and affect, but also stops addictive behaviors. Ibogaine has a very long history of ethnobotanical use in low doses to combat fatigue, hunger and thirst and, in high doses as a sacrament in African ritual contexts. In the 1960's, American and European self-help groups provided public testimonials that a single dose of ibogaine alleviated drug craving, opioid withdrawal symptoms, and prevented relapse for weeks, months and sometimes years. Ibogaine is rapidly demethylated by first-pass metabolism to a long-acting metabolite noribogaine. Ibogaine and its metabolite interact with two or more CNS targets simultaneously and both drugs have demonstrated predictive validity in animal models of addiction. Online forums endorse the benefits of ibogaine as an "addiction interrupter" and present-day estimates suggest that more than ten thousand people have sought treatment in countries where the drug is unregulated. Open label pilot studies of ibogaine-assisted drug detoxification have shown positive benefit in treating addiction. Ibogaine, granted regulatory approval for human testing in a Phase 1/2a clinical trial, joins the current landscape of psychedelic medicines in clinical development.

A Single Administration of the Atypical Psychedelic Ibogaine or Its Metabolite Noribogaine Induces an Antidepressant-Like Effect in Rats

Anecdotal reports and open-label case studies in humans indicated that the psychedelic alkaloid ibogaine exerts profound antiaddictive effects. Ample preclinical evidence demonstrated the efficacy of ibogaine, and its main metabolite, noribogaine, in substance-use-disorder rodent models. In contrast to addiction research, depression-relevant effects of ibogaine or noribogaine in rodents have not been previously examined. We have recently reported that the acute ibogaine administration induced a long-term increase of brain-derived neurotrophic factor mRNA levels in the rat prefrontal cortex, which led us to hypothesize that ibogaine may elicit antidepressant-like effects in rats. Accordingly, we characterized behavioral effects (dose- and time-dependence) induced by the acute ibogaine and noribogaine administration in rats using the forced swim test (FST, 20 and 40 mg/kg i.p., single injection for each dose). We also examined the correlation between plasma and brain concentrations of ibogaine and noribogaine and the elicited behavioral response. We found that ibogaine and noribogaine induced a dose- and time-dependent antidepressant-like effect without significant changes of animal locomotor activity. Noribogaine's FST effect was short-lived (30 min) and correlated with high brain concentrations (estimated >8 μM of free drug), while the ibogaine's antidepressant-like effect was significant at 3 h. At this time point, both ibogaine and noribogaine were present in rat brain at concentrations that cannot produce the same behavioral outcome on their own (ibogaine ∼0.5 μM, noribogaine ∼2.5 μM). Our data suggests a polypharmacological mechanism underpinning the antidepressant-like effects of ibogaine and noribogaine.

A case report SPECT study and theoretical rationale for the sequential administration of ibogaine and 5-MeO-DMT in the treatment of alcohol use disorder

Ibogaine is a plant-derived alkaloid and dissociative psychedelic that demonstrates anti-addictive properties with several substances of abuse, including alcohol. 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a naturally occurring psychedelic known to occasion potent mystical-type experiences and also demonstrates anti-addictive properties. The potential therapeutic effects of both compounds in treating alcohol use disorder require further investigation and there are no published human neuroimaging findings of either treatment to date. We present the case of a 31-year-old male military veteran with moderate alcohol use disorder who sought treatment at an inpatient clinic in Mexico that utilized a sequential protocol with ibogaine hydrochloride (1550mg, 17.9mg/kg) on day 1, followed by vaporized 5-MeO-DMT (bufotoxin source 50mg, estimated 5-MeO-DMT content, 5-7mg) on day 3. The patient received SPECT neuroimaging that included a resting-state protocol before, and 3 days after completion of the program. During the patient's ibogaine treatment, he experienced dream-like visions that included content pertaining to his alcohol use and resolution of past developmental traumas. He described his treatment with 5-MeO-DMT as a peak transformational and spiritual breakthrough. On post-treatment SPECT neuroimaging, increases in brain perfusion were noted in bilateral caudate nuclei, left putamen, right insula, as well as temporal, occipital, and cerebellar regions compared to the patient's baseline scan. The patient reported improvement in mood, cessation of alcohol use, and reduced cravings at 5 days post-treatment, effects which were sustained at 1 month, with a partial return to mild alcohol use at 2 months. In this case, serial administration of ibogaine and 5-MeO-DMT resulted in increased perfusion in multiple brain regions broadly associated with alcohol use disorders and known pharmacology of both compounds, which coincided with a short-term therapeutic outcome. We present theoretical considerations regarding the potential of both psychedelic medicines in treating alcohol use disorders in the context of these isolated findings, and areas for future investigation.

Neuropharmacological characterization of local ibogaine effects on dopamine release

Local perfusion with ibogaine (10(-6) M-10(-3) M) via microdialysis probes in the nucleus accumbens or striatum of rats produced a biphasic dose-response effect on extracellular dopamine levels. Lower doses (10(-6) M-10(-4) M) produced a decrease while higher doses (5 x 10(-4) M-10(-3) M) produced an increase in dopamine levels. Dihydroxyphenylacetic acid (DOPAC) levels were not effected. Naloxone (10(-6) M) and norbinaltorphimine (10(-6) M-10(-5) M) did not affect dopamine levels, but when co-administered with ibogaine (10(-4) M) blocked the decrease in dopamine levels produced by ibogaine. Ibogaine (10(-3) M) stimulation of dopamine levels in the striatum was calcium independent and not blocked by tetrodotoxin (10(-5) M). Pretreatment with cocaine (15 mg/kg), reserpine (5 mg/kg) or alpha-methyl-para-tyrosine (250 mg/kg) given intraperitoneally significantly reduced ibogaine (10(-3)M) stimulation of striatal dopamine levels. In striatal synaptosomes, both ibogaine and harmaline (10(-7)-10(-4) M) produced dose-dependent inhibition of [3H]-dopamine uptake. These findings suggest that ibogaine has both inhibitory and stimulatory effects on dopamine release at the level of the nerve terminal. It is suggested that the inhibitory effect is mediated by kappa opiate receptors while the stimulatory effect is mediated by interaction with the dopamine uptake transporter.

Application of electrophysiological method to study interactions between ibogaine and cocaine

The psychoactive indole alkaloid, ibogaine (IBO), has been investigated for over a decade concerning its reported anti-addictive properties for opioids as well as psychomotor stimulants. The mechanism for the anti-addictive action of IBO is still unclear. IBO interactions with opioid, NMDA, nicotinic, adrenergic, and serotonergic receptor sites have been suggested. The involvement of the dopaminergic system in IBO action is well documented. Increased or decreased levels of dopamine (DA) in specific brain regions following IBO pretreatment have been seen concomitantly with increased or decreased motor activity after subsequent amphetamine or cocaine administration. In this report, in vivo electrophysiological measures were monitored in awake adult male rats in order to investigate alterations of the electrocorticogram (ECoG) resulting from interactions between IBO and cocaine (COC). Rats were implanted bilaterally with bipolar ECoG electrodes. They were either injected with saline, COC alone (20 mg/kg, i.p.) or IBO (50 mg/kg, i.p.) and COC 1 hr later. The concentrations of DA, 5-HT, and their metabolites DOPAC, HVA, and 5-HIAA were assessed in the caudate nucleus in separate groups of saline-, COC-, and IBO/COC-treated rats. An alpha1 power increase was observed within 10 min after COC injection, which lasted for less than 20 min. A desynchronization over alpha2 and both beta power bands was observed throughout the recording. In IBO/COC-treated rats, a significant increase in delta, theta, and alpha1 power occurred within 20 min after COC injection (p <0.05). This effect lasted for up to an hour. DA levels significantly increased after COC only and decreased after IBO administration. A further decrease in levels of DA was observed in IBO/COC-treated rats. DA turnover increased significantly after IBO alone but was not observed after IBO/COC treatment. The alterations in ECoG and neurotransmitter levels suggest a decreased response to COC following IBO pretreatment.

Noribogaine (12-hydroxyibogamine): a biologically active metabolite of the antiaddictive drug ibogaine

Ibogaine (IBO) is a plant-derived alkaloid that is being evaluated as a possible medication for substance use disorders. When administered peripherally to monkeys and humans, IBO is rapidly converted to an o-demethylated metabolite, 12-hydroxyibogamine (NORIBO). We have found in rats that peak blood levels of NORIBO can exceed those of the parent compound, and NORIBO persists in the bloodstream for at least 24 h. Surprisingly few studies have examined the in vivo biological activity of NORIBO. In the present series of experiments, we compared the effects of intravenous (i.v.) administration of IBO and NORIBO (1 and 10 mg/kg) on unconditioned behaviors, circulating stress hormones, and extracellular levels of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of male rats. IBO caused dose-related increases in tremors and forepaw treading, whereas NORIBO did not. Both IBO and NORIBO produced significant elevations in plasma corticosterone and prolactin, but IBO was more potent as a stimulator of corticosterone secretion. Neither drug affected extracellular DA levels in the nucleus accumbens. However, both IBO and NORIBO increased extracellular 5-HT levels, and NORIBO was more potent in this regard. The present data demonstrate that NORIBO is biologically active and undoubtedly contributes to the in vivo pharmacological profile of IBO in rats. Most importantly, NORIBO appears less likely to produce the adverse effects associated with IBO (i.e., tremors and stress-axis activation), suggesting that the metabolite may be a safer alternative for medication development.

Comparative neurobiological effects of ibogaine and MK-801 in rats

Ibogaine is a plant-derived alkaloid with putative 'anti-addictive' properties. Although ibogaine binds to multiple targets in the brain, recent evidence suggests the drug acts as an N-methyl-D-aspartate (NMDA) antagonist similar to MK-801. The purpose of the present study was to compare neurochemical and neuroendocrine effects of ibogaine and MK-801 in vivo. Male rats received either i.p. saline, ibogaine (10 and 100 mg/kg), or MK-801 (0.1 and 1 mg/kg). Groups of rats (N=6-8/group) were decapitated 30 or 60 min after injection. Brains were harvested for analysis of dopamine (DA) and its metabolites, while trunk blood was collected for analysis of plasma corticosterone and prolactin. Ibogaine produced marked dose-dependent reductions in tissue DA with concurrent increases in the metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This profile of ibogaine-induced effects on DA metabolism was consistently observed in the cortex, striatum, olfactory tubercle, and hypothalamus. MK-801, on the other hand, did not reduce DA levels in any brain region but did cause modest region-specific elevations in DA metabolites. Ibogaine and MK-801 caused comparable elevations in circulating corticosterone, but only ibogaine increased prolactin. The present findings show that the effects of ibogaine on DA neurotransmission and neuroendocrine secretion are not fully mimicked by MK-801. Thus, the wide spectrum of in vivo actions of ibogaine can probably not be explained simply on the basis of antagonism at NMDA receptors.

NMDA receptor antagonist-induced dopamine release in the ventral pallidum does not correlate with motor activation

The ventral pallidum is the output structure of the nucleus accumbens in the ventral corticostriato-thalamocortical loop. Information processing in this loop is critically involved in motor behavior and reinforcement. The ventral pallidum receives a direct dopaminergic input from the ventral tegmental area, but also glutamatergic input from cortical and limbic areas. It has been assumed that dopamine release in the VP is indeed modulated by glutamate. The present study investigated the effects of NMDA receptor blockade on motor behavior and dopamine release in the ventral pallidum. In a first experiment, rats were implanted with microdialysis probes in the ventral pallidum and were systemically injected or locally perfused via the microdialysis probe with dizocilpine (0.32 mg/kg, 10 and 100 microM, respectively). Effects on dopamine and on locomotion were simultaneously monitored. In a second experiment, ventral pallidum was lesioned by quinolinic acid and the effects of systemic dizocilpine (0.08 and 0.16 mg/kg) on locomotion and stereotyped sniffing behavior were determined. It was found that systemic and local dizocilpine administration increased dopamine release in the ventral pallidum to a similar extent whereas only systemic treatment was accompanied by locomotor stimulation. Lesion of the ventral pallidum did not affect locomotion and stereotyped sniffing behavior induced by systemic dizocilpine treatment. Thus, DA release in the ventral pallidum that is elevated by blockade of NMDA receptors is not relevant for activation of motor behavior.

Responses of the extrapyramidal and limbic substance P systems to ibogaine and cocaine treatments

Ibogaine is an indolamine found in the West Africa shrub, Tabernanthe iboga, and has been proposed for the treatment of addiction to central nervous system (CNS) stimulants such as cocaine and amphetamine. The mechanism of ibogaine action and its suitability as a treatment for drug addiction still remains unclear. Since previous studies demonstrated differential effects of stimulants of abuse (amphetamines) on neuropeptide systems such as substance P, we examined the impact of ibogaine and cocaine on extrapyramidal (striatum and substantia nigra) and limbic (nucleus accumbens and frontal cortex) substance P-like immunoreactivity. Ibogaine and cocaine treatments altered substance P systems by increasing striatal and nigral substance P-like immunoreactivity concentration 12 h after the last drug treatment. However, substance P-like immunoreactivity content was not significantly increased in nucleus accumbens after treatment with either drug. The ibogaine- and cocaine-induced increases in substance P-like immunoreactivity in striatum and substantia nigra were blocked by coadministration of selective dopamine D(1) receptor antagonist (SCH 23390; R(+)-7-Chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine hydrochloride) or dopamine D(2) receptor antagonist (eticlopride; S(-)-3-Chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2- methoxy-benzamide hydrochloride). Most of the responses by substance P systems to ibogaine administration resembled those caused by cocaine, except in cortical tissue where multiple administration of cocaine, but not ibogaine increased substance P-like immunoreactivity. These data suggest that substance P systems may contribute to the effects of ibogaine and cocaine treatment.

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.

The effects of ibogaine on dopamine and serotonin transport in rat brain synaptosomes

Ibogaine has been shown to affect biogenic amine levels in selected brain regions. Because of the involvement of these neurotransmitters in drug addiction, the effects of ibogaine on biogenic amine transport may contribute to the potential anti-addictive properties of ibogaine in vivo. With rat brain synaptosomes as our experimental system, we measured the effects of ibogaine on the uptake and release of dopamine (DA) and serotonin (5-HT). Ibogaine competitively blocked both DA and 5-HT uptake with IC50 values of 20 microM at 75 nM 3H-DA and 2.6 microM at 10 nM 3H-5-HT. Ibogaine had no effect on K+-induced release of 3H-DA from preloaded synaptosomes, but 20 microM and 50 microM ibogaine inhibited roughly 40% and 60%, respectively, of the K(+)-induced release of 3H-5-HT from preloaded synaptosomes. In the absence of a depolarizing stimulus, ibogaine evoked a small release of 3H-DA but not 3H-5-HT. These relatively low-potency effects of ibogaine on DA and 5-HT uptake in synaptosomes are consistent with the low binding affinity of ibogaine that has been previously reported for DA and 5-HT transporters. Our results show that if ibogaine modulates DA and 5-HT levels in the brain by directly blocking their uptake, then a concentration of ibogaine in the micromolar range is required. Furthermore, if the anti-addictive effects of ibogaine require this concentration, then ibogaine likely exerts these effects through a combination of neurotransmitter pathways, because binding affinities and functional potencies of ibogaine in the micromolar range have been reported for a variety of neuronal receptors and transporters.

Differential responses by neurotensin systems in extrapyramidal and limbic structures to ibogaine and cocaine

Ibogaine (Endabuse) is a psychoactive indole alkaloid found in the West African shrub, Tabernanthe iboga. This drug interrupts cocaine and amphetamine abuse and has been proposed for treatment of addiction to these stimulants. However, the mechanism of action that explains its pharmacological properties is unclear. Since previous studies demonstrated differential effects of psychotomimetic drugs (cocaine and methamphetamine) on neuropeptides such as neurotensin (NT), the present study was designed to determine: (1) the effects of ibogaine on striatal, nigral, cortical, and accumbens neurotensin-like immunoreactivity (NTLI); (2) the effects of selective dopamine antagonists on ibogaine-induced changes in NT concentrations in these brain areas; and (3) the effects of ibogaine pretreatment on cocaine-induced changes in striatal, nigral, cortical and accumbens NTLI content. Ibogaine treatments profoundly affected NT systems by increasing striatal, nigral, and accumbens NTLI content 12 h after the last drug administration. In contrast, NTLI concentrations were not significantly increased in the frontal cortex after ibogaine treatment. The ibogaine-induced increases in NTLI in striatum, nucleus accumbens and substantia nigra were blocked by coadministration of the selective D1 receptor antagonist, SCH 23390. The D2 receptor antagonist, eticlopride, blocked the ibogaine-induced increase in nigral NTLI, but not in striatum and nucleus accumbens. Ibogaine pretreatment significantly blocked the striatal and nigral increases of NTLI resulting from a single cocaine administration. Whereas many of the responses by NT systems to ibogaine resembled those which occur after cocaine, there were also some important differences. These data suggest that NT may contribute to an interaction between ibogaine and the DA system and may participate in the pharmacological actions of this drug.

Acute iboga alkaloid effects on extracellular serotonin (5-HT) levels in nucleus accumbens and striatum in rats

The iboga alkaloid, ibogaine, its metabolite, noribogaine, and the congener, 18-methoxycoronaridine (18-MC) have all been claimed to have anti-addictive properties in animal models, but the mechanisms underlying these effects are unclear. Ibogaine and noribogaine were shown to have affinity for the serotonin transporter, and inhibition of serotonin reuptake has been proposed to be involved in their anti-addictive actions. It is not known yet if 18-MC also has this property. In vivo microdialysis and HPLC (microbore) were used to determine acute changes in extracellular serotonin levels in nucleus accumbens (NAC) and striatum (STR) after both i.p. (40 mg/kg for all drugs) and i.v. (1-10 mg/kg for ibogaine and noribogaine) drug administration in awake freely moving female Sprague-Dawley rats (250-275 g). After i.p. administration, ibogaine, noribogaine and 18-MC had very different effects on extracellular serotonin levels in both NAC and STR: ibogaine elicited large increases (up to 25-fold in NAC and 10- fold in STR), noribogaine produced moderate increases (up to 8-fold in NAC and 5-fold in STR), and 18-MC had no effect in either brain region. These and other data suggest that (1) the serotonergic system may not be an essential factor in the anti-addictive actions of these drugs; (2) ibogaine (or an unidentified metabolite) may release serotonin as well as inhibit its reuptake; (3) stimulation of the ascending serotonergic system may mediate ibogaine's hallucinogenic effect; and (4) 18-MC probably has no affinity for the serotonin transporter, and is unlikely to be a hallucinogen.

Time-dependent interactions between iboga agents and cocaine

The purpose of this study was to clarify the effects of iboga agents on cocaine-induced hyperactivity. Both inhibition and enhancement of cocaine-induced activity by ibogaine have been reported. In the present study, rats were treated with either ibogaine (40 mg/kg, i.p.), noribogaine (40 mg/kg, i.p.), 18-methoxycoronaridine (40 mg/kg, i.p.), or saline, 1 or 19 h prior to the administration of cocaine (20 mg/kg, i.p.) or saline. Motor activity was monitored thereafter for 3 h. All three iboga agents had acute inhibitory effects and delayed potentiating effects on cocaine-induced hyperactivity. These time-dependent effects, which could not be attributed to the motor activity induced by the iboga agents alone, account for divergent results reported in the literature.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. Basis for 5-HT--DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

Ibogaine and cocaine abuse: pharmacological interactions at dopamine and serotonin receptors

Ibogaine is an indole alkaloid that has been of interest in recent years due to its putative efficacy in the treatment of drug dependence. For the most part, animal data have shown attenuation of some of the effects of stimulant drugs, for example, motor stimulation and self-administration. The mechanism of this inhibition of drug-induced behavior seems to suggest the action of the dopamine, serotonin, NMDA, kappa, and/or sigma receptor sites, as indicated by the affinity of ibogaine to receptor selective ligands in binding competition studies. However, affinity for receptors does not in itself indicate their involvement. In vitro perfusion studies have proven a useful model to study the effect of ibogaine on neurotransmitter systems and the functional effects of such interactions. This review summarizes these data and the support of multiple effects of ibogaine, and the potential importance of its action on serotonergic modulation of dopamine release.

Neuroendocrine and neurochemical effects of acute ibogaine administration: a time course evaluation

Ibogaine (IBO) is an indole alkaloid that is reported to facilitate drug abstinence in substance abusers. Despite considerable investigation, the mechanism of IBO action in vivo and its suitability as a treatment for drug addiction remains unclear. The present study was designed to evaluate the time-course effects of acute IBO on neuroendocrine and neurochemical indices. Adult male rats were treated with i.p. saline or 50 mg/kg IBO and sacrificed 15, 30, 60, 120 min and 24 h later. Trunk blood was collected for hormone measures and brains were dissected for neurochemical analyses. IBO produced a rapid elevation in plasma prolactin that declined to control levels by 60 min. Corticosterone levels increased 15 min after drug administration, continued to increase for 120 min, but returned to control levels 24 h after dosing. IBO decreased dopamine (DA) concentrations in the striatum and frontal cortex at 30, 60 and 120 min after injection while DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were elevated over the same time period. 24 h after IBO, DOPAC concentrations in striatum and HVA levels in the frontal cortex were below control values. Serotonin (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA) were decreased at 60 min after IBO administration only in the striatum. These data indicate that a single injection of IBO produces a spectrum of effects that includes: (1) elevation of plasma prolactin and corticosterone, (2) short- and long-term effects on DA neurotransmission, and (3) modest, transient effects of 5-HT neurotransmission. The effects of IBO reported herein may have relevance to the anti-addictive properties of this drug, and this proposal warrants further investigation.

Pharmacological screen for activities of 12-hydroxyibogamine: a primary metabolite of the indole alkaloid ibogaine

The purported efficacy of ibogaine for the treatment of drug dependence may be due in part to an active metabolite. Ibogaine undergoes first pass metabolism and is O-demethylated to 12-hydroxyibogamine (12-OH ibogamine). Radioligand binding assays were conducted to identify the potency and selectivity profiles for ibogaine and 12-OH ibogamine. A comparison of 12-OH ibogamine to the primary molecular targets identified previously for ibogaine demonstrates that the metabolite has a binding profile that is similar, but not identical to the parent drug. Both ibogaine and 12-OH ibogamine demonstrated the highest potency values at the cocaine recognition site on the 5-HT transporter. The same rank order (12-OH ibogamine > ibogaine), but lower potencies were observed for the [3H]paroxetine binding sites on the 5-HT transporter. Ibogaine and 12-OH ibogamine were equipotent at vesicular monoamine and dopamine transporters. The metabolite demonstrated higher affinity at the kappa-1 receptor and lower affinity at the NMDA receptor complex compared to the parent drug. Quantitation of the regional brain levels of ibogaine and 12-OH ibogamine demonstrated micromolar concentrations of both the parent drug and metabolite in rat brain. Drug dependence results from distinct, but inter-related neurochemical adaptations, which underlie tolerance, sensitization and withdrawal. Ibogaine's ability to alter drug-seeking behavior may be due to combined actions of the parent drug and metabolite at key pharmacological targets that modulate the activity of drug reward circuits.

Effects of ibogaine, and cocaine and morphine after ibogaine, on ventral tegmental dopamine neurons

Ibogaine, an indole containing alkaloid, has been shown to reduce the rate of injection of morphine and cocaine in self-administration protocols. Since morphine- and cocaine-induced modulation of dopamine release is impulse dependent and essential for their reinforcing effects, disruption of dopamine neuronal activity by ibogaine could explain its purported 'antiaddictive' properties. Therefore, the present study was designed to determine: (1) the acute effects of ibogaine on the activity of VTA dopamine neurons, and (2) whether ibogaine pretreatment causes a persistent modification of the dopamine neuronal response to morphine and cocaine. Extracellular recordings in anesthetized animals found that intravenous ibogaine markedly excited VTA dopamine neuronal firing. However, ibogaine pretreatment (6-8 hr and 19 hr before) failed to alter either the spontaneous activity of VTA neurons, or the response of these dopamine neurons to morphine or cocaine. Thus, ibogaine's excitatory effect on VTA neurons is not long-lasting nor does it persistently alter cocaine- or morphine-induced changes in dopamine neuron impulse activity. Therefore, other mechanisms must be explored to account for the proposed antiaddictive properties of ibogaine.

Identification of a primary metabolite of ibogaine that targets serotonin transporters and elevates serotonin

Ibogaine is a hallucinogenic indole with putative efficacy for the treatment of cocaine, stimulant and opiate abuse. The purported efficacy of ibogaine following single dose administrations has led to the suggestion that a long-acting metabolite of ibogaine may explain in part how the drug reduces craving for psychostimulants and opiates. We report here that 12-hydroxyibogamine, a primary metabolite of ibogaine, displays high affinity for the 5-HT transporter and elevates extracellular 5-HT. In radioligand binding assays, 12-hydroxyibogamine was 50-fold more potent at displacing radioligand binding at the 5-HT transporter than at the DA transporter. Ibogaine and 12-hydroxyibogamine were equipotent at the dopamine transporter. In vivo microdialysis was used to evaluate the acute actions of ibogaine and 12-hydroxyibogamine on the levels of DA and 5-HT. Administration of 12-hydroxyibogamine produced a marked dose-related elevation of extracellular 5-HT. Ibogaine and 12-hydroxyibogamine failed to elevate DA levels in the nucleus accumbens over the dose range tested. The elevation in synaptic levels of 5-HT by 12-hydroxyibogamine may heighten mood and attenuate drug craving. The effects of the active metabolite on 5-HT transmission may account in part for the potential of ibogaine to interrupt drug-seeking behavior in humans.