N-type calcium channels are involved in the dopamine releasing effect of nicotine

Effect of ractopamine on the release of dopamine from the striatum dissected from mice

In the past two decades, ractopamine has been used as a feed additive to increase protein synthesis in farmed animals (swine, cattle, and turkeys) and to produce high-quality meat. However, the excessive feeding of animals with ractopamine may result in its accumulation in animal and human tissues after consuming the meat. Ractopamine is a trace amine-associated receptor1 and β-adrenoceptor agonist banned in the EU but approved in the USA, and it may pose a potential risk to human health. In this paper, the authors, for the first time, provide neurochemical evidence that ractopamine leads to the release of dopamine from nerve terminals of the nigrostriatal pathway in the striatum.

Domain III regulates N-type (CaV2.2) calcium channel closing kinetics

Ca(V)2.2 (N-type) and Ca(V)1.2 (L-type) calcium channels gate differently in response to membrane depolarization, which is critical to the unique physiological functions mediated by these channels. We wondered if the source for these differences could be identified. As a first step, we examined the effect of domain exchange between N-type and L-type channels on activation-deactivation kinetics, which were significantly different between these channels. Kinetic analysis of chimeric channels revealed N-channel-like deactivation for all chimeric channels containing N-channel domain III, while activation appeared to be a more distributed function across domains. This led us to hypothesize that domain III was an important regulator of N-channel closing. This idea was further examined with R-roscovitine, which is a trisubstituted purine that slows N-channel deactivation by exclusively binding to activated N-channels. L-channels lack this response to roscovitine, which allowed us to use N-L chimeras to test the role of domain III in roscovitine modulation of N-channel deactivation. In support of our hypothesis, all chimeric channels containing the N-channel domain III responded to roscovitine with slowed deactivation, while those chimeric channels with L-channel domain III did not. Thus a combination of kinetic and pharmacological evidence supports the hypothesis that domain III is an important regulator of N-channel closing. Our results support specialization of gating functions among calcium channel domains.

Role of tissue plasminogen activator in the sensitization of methamphetamine-induced dopamine release in the nucleus accumbens

We have previously demonstrated that repeated, but not acute, methamphetamine (METH) treatment increases tissue plasminogen activator (tPA) activity in the brain, which is associated with the development of behavioral sensitization to METH. In this study, we investigated whether the tPA-plasmin system is involved in the development of sensitization in METH-induced dopamine release in the nucleus accumbens (NAc). There was no difference in acute METH-induced increase in extracellular dopamine levels in the NAc between wild-type and tPA-deficient (tPA-/-) mice. Repeated METH treatment resulted in a significant enhancement of METH- induced dopamine release in wild-type mice, but not tPA-/- mice. Microinjection of exogenous tPA or plasmin into the NAc of wild-type mice significantly potentiated acute METH- induced dopamine release. Degradation of laminin was evident in brain tissues incubated with tPA plus plasminogen or plasmin in vitro although tPA or plasminogen alone had no effect. Immunohistochemical analysis revealed that microinjection of plasmin into the NAc reduced laminin immunoreactivity without neuronal damage. Our findings suggest that the tPA-plasmin system participates in the development of behavioral sensitization induced by repeated METH treatment, by regulating the processes underlying the sensitization of METH-induced dopamine release in the NAc, in which degradation of laminin by plasmin may play a role.

Effects of alpha-scorpion toxin, tityustoxin on the release of [3H] dopamine of rat brain prefrontal cortical slices

The effect of tityustoxin (TsTX) on the release of [3H] dopamine in rat brain prefrontal cortical slices was investigated. The stimulatory effect of TsTX was dependent on incubation time and TsTX concentration with an EC50 of 0.05 microM. The release of [3H] dopamine stimulated by TsTX is dependent of Na+ channels and thus, was completely, inhibited by tetrodotoxin. Tityustoxin-induced release of [3H] dopamine was not blocked by ethylene glycol-bis(beta-aminoethyl) ether (EGTA) and thus was independent of extracellular calcium. However, [3H] dopamine release induced by TsTX was inhibited by 52% by BAPTA, a calcium chelator. Moreover, dantrolene (100 microM) and tetracaine (500 microM) partially inhibited by 38 and 29%, respectively, the tityustoxin-induced release of [3H] dopamine from prefrontal cortical slices suggesting a role from intracellular calcium increase. In conclusion, part of the TsTX-induced release [3H] dopamine may be due to an effect of the toxin on the reversal of the dopamine transporter (DAT), but the majority of the toxin stimulated release of [3H] dopamine involves the mobilization of intracellular calcium stores.

Mechanism of nicotine-evoked release of 3H-noradrenaline in human cerebral cortex slices

1. The mechanism of stimulation of noradrenaline (NA) release by nicotine (NIC) was investigated in human cerebral cortex slices preloaded with 3H-noradrenaline. 2 NIC (10-1000 micro M) increased 3H-NA release in a concentration-dependent manner. 3. NIC (100 micro M)-evoked 3H-NA release was largely dependent on external Ca2+, and was attenuated by omega-conotoxin GVIA (0.1 micro M) but not by nitrendipine (1 micro M). 4. Tetrodotoxin (1 micro M) and nisoxetine (0.1 micro M) attenuated the NIC (100 micro M)-evoked release of 3H-NA. 5. Mecamylamine (10 micro M), dihydro-beta-erythroidine (10 micro M) and d-tubocurarine (30 micro M), but not alpha-bungarotoxin (alpha-BTX, 0.1 micro M), attenuated the NIC (100 micro M)-evoked release of 3H-NA. 6. NIC (100 micro M)-evoked release of 3H-NA was not affected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 30 micro M) and D(-)-2-amino-5-phosphonopentanoic acid (D-AP5, 100 micro M), but attenuated by MK-801 (10 micro M). MK-801 (0.1-1000 micro M) displaced the specific binding of 3H-nisoxetine with K(i) values of 91.2 micro M. NIC (100, 300 and 1000 micro M) did not induce 3H-D-aspartate release in human cerebral cortex slices. 7. NIC (100 micro M)-evoked release of 3H-NA was attenuated by 7-nitroindazole (10 micro M), N(G)-nitro-L-arginine methyl ester HCl (L-NAME, 30 micro M), N(G)-monomethyl-L-arginine acetate (L-NMMA, 300 micro M). [(3)H]-NA release induced by NIC (100 micro M) was attenuated by methylene blue (3 micro M) and 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ, 10 micro M), and enhanced by zaprinast (30 micro M). 8. In conclusion, NIC stimulates the release of 3H-NA through activation of alpha-BTX-insensitive nicotinic acetylcholine receptors in the human cerebral cortex slices and this action of NIC is associated with modulation of the NO/cGMP pathway.

Effects of voltage-sensitive calcium channel blockers on extracellular dopamine levels in rat striatum

Various subtypes of voltage-sensitive calcium channels (VSCCs) support the release of dopamine (DA) in the central nervous system. Using in vivo microdialysis, we investigate the influence of these subtypes of calcium channels on dopaminergic terminals in the rat striatum. L-type (nifedipine-sensitive), N-type (omega-conotoxin GVIA-sensitive), or N- and P/Q-type (omega-conotoxin MVIIC-sensitive) Ca2+ channels were blocked using selective antagonists injected locally, and K+-evoked DA release was measured in freely moving animals. K+ (100 mM) induced a massive increase of basal DA extracellular levels (930%) and was without significant effect on extracellular levels of DA metabolites DOPAC and HVA, and on the serotonin metabolite 5HIAA. Omega-conotoxin GVIA (1 microM) and omega-conotoxin MVIIC (1 microM) significantly reduced the K+-evoked DA release by 55 and 62%, respectively. The simultaneous application of the two conotoxins at the same concentration reduced K+-evoked DA release by 66%. Nifedipine (10 microM) had no significant effect on K-evoked DA release, while neomycin, a nonspecific VSCC blocker, produced a highly significant decrease when applied at 250 and 500 microM (56 and 75%, respectively). The compounds. however, had no effect on basal DA release and on the levels of extracellular DOPAC, HVA, and 5HIAA. These results suggest that under high and persistent conditions of membrane depolarization (15 min, 10 mM K+), striatal DA release is mainly mediated by N-type VSCCs.

Protein kinase C regulation of dopamine transporter initiated by nicotinic receptor activation in slices of rat prefrontal cortex

We previously reported that activation of nicotinic receptors causes an enhancement in amphetamine-stimulated release of dopamine via its transporter from slices of prefrontal cortex, but no such enhancement of release from slices of nucleus accumbens or striatum. The nicotinic receptors mediating the enhancement most likely contain alpha4 and beta2 subunits based upon pharmacological characterization. In this study, we sought to characterize the second messenger systems associated with the nicotine-mediated response. Sodium channel involvement was confirmed by the observation that tetrodotoxin blocked nicotine-mediated enhancement, whereas veratridine or elevated K(+) mimicked the enhancement seen with nicotine. Inclusion of EGTA blocked nicotine-mediated enhancement, suggesting that, even though no exogenous Ca(2+) was added, endogenous stores were required for the enhancement. The enhancement by nicotine was also abolished by the L-type voltage-dependent calcium channel (VDCC) antagonist nitrendipine, but not by the N-type VDCC antagonist omega-conotoxin GVIA. Finally, inhibition of protein kinase C also abolished the nicotine-mediated enhancement of amphetamine-stimulated dopamine release, whereas inhibitors of Ca(2+)/calmodulin kinase II did not. These findings establish that nicotine can exert selective effects on dopamine transporter activity in prefrontal cortex, an area involved in cognition and learning.

Possible involvement of L-type voltage-gated calcium channels in release of dopamine in the striatum of irradiated rats

The object of this study was to determine the effect of exposure to gamma radiation on potassium chloride (KCl)-stimulated release of dopamine (DA) in the striatum of the rat. In addition, the effect of some calcium channel blockers [nicardipine, a blocker of the L-type voltage-gated N-type VGCC; Omega-agatoxin TK, a selective blocker of P-type VGCC; and nickel chloride (NiCl(2)), which preferentially blocks the T-type VGCC] on KCl-stimulated release of DA in the striatum in sham-irradiated and irradiated rats was determined. Exposure of rats to 1-10 Gy (60)Co gamma rays had no significant effect on KCl-stimulated release of DA in the striatum in comparison to sham-irradiated animals. Administering 100, 300 and 500 nM of Omega-agatoxin TK or 50, 100 and 200 nM of Omega-conotoxin GVIA significantly decreased the release of DA stimulated by KCl in both irradiated and sham-irradiated animals in a dose-dependent manner. However, 10, 30 and 50 microM of nicardipine decreased the release of DA in irradiated animals but not in sham-irradiated animals. It is unknown why doses of 5-20 microM NiCl(2) had no effect on the release of DA in sham-irradiated and irradiated animals. The results demonstrate that the doses of radiation used in this study had no effect on release of DA in the striatum. Multiple calcium channel types coexist to regulate release of DA. P- and N-type VGCCs are involved in release of DA in sham-irradiated and irradiated animals, whereas only L-type VGCCs are involved in release of DA in irradiated animals.

N-type calcium channel blockers - tools for modulation of cerebral functional units?

According to in vitro and in vivo studies, the direct application of N-type calcium channel blockers as for instance omega-conotoxin GVIA (omega-ctx) potently inhibits the release of neurotransmitters like dopamine. To find out whether this effect could be used for modulation of neurological functions, omega-ctx was used for continuous infusion into the functionally well characterized rat striatum. Over the 2-week time course of intrastriatal application, rats developed a decrease in spontaneous motor activity, spontaneous rotational asymmetry towards the side of application, and behavioral supersensitivity to apomorphine. After the end of infusion period, all functional deficits showed reversibility. The pattern of spontaneous neurological deficits - in particular supersensitivity to apomorphine - points to a substantial unilateral alteration of dopaminergic transmission due to omega-ctx, which is suggested also by an increase in dopamine receptor protein expression within the ipsilateral striatum. Time course and reversibility of neurological deficits caused by omega-ctx, as well as a lack of dopamine depletion contrast findings after selective destruction of dopaminergic neurons and support a functional modulation of dopaminergic transmission. The present study suggests that omega-ctx is an effective potent tool for the unilateral and reversible intracerebral modulation of neuronal circuits. Intracerebral application of omega-ctx could possibly open the way to therapeutic interventions.

Effect of calcium channel blockers on cerebral ischemia-induced hyperactivity in Mongolian gerbils

When both common carotid arteries of Mongolian gerbils were occluded for 5 min to produce ischemic insult, locomotor activity was increased the following day. The effect of calcium channel blockers on this ischemia-induced hyperactivity was investigated. Nimodipine, at doses of 5, 10, and 20 mg/kg, dose dependently and significantly decreased ischemia-induced hyperactivity. Nicardipine significantly decreased ischemia-induced hyperactivity and doses of 10 and 20 mg/kg. Nifedipine and flunaridine also significantly decreased ischemia-induced hyperactivity at doses of 20 mg/kg. Verapamil had no effect on ischemia-induced hyperactivity at a dose of 20 mg/kg. These findings suggest that ischemia-induced hyperactivity is related to calcium channels. These relationship between calcium channels and dopaminergic function is discussed.

Contribution of CNS nicotine metabolites to the neuropharmacological effects of nicotine and tobacco smoking

Nicotine, the principal alkaloid in tobacco products, is generally accepted to be the active pharmacological agent responsible for CNS effects resulting from tobacco use. Arguments are presented in this commentary which take issue with this popular dogma, by providing evidence that nicotine metabolites may also be responsible for the CNS effects commonly attributed to nicotine. CNS effects attributed to nicotine include reinforcing effects, mood elevation, arousal, locomotor stimulant effects, and learning and memory enhancement. The reinforcing and locomotor stimulant effects of nicotine have been suggested to be the result of activation of CNS dopaminergic systems, and nicotine-induced modulation of dopaminergic neurotransmission has been studied in detail. Nicotine acts at a family of nicotinic receptor subtypes composed of multiple subunits; however, the exact composition of the subunits in native nicotinic receptors and the functional significance of the receptor subtype diversity are currently unknown. This nicotinic subtype diversity increases the complexity of the potential mechanisms of action of nicotine and its metabolites. Although peripheral metabolism of nicotine has been studied extensively, metabolism in the CNS has not been investigated to any great extent. Recently, studies from our laboratory have demonstrated that several nicotine metabolites are present in the CNS after acute nicotine administration. Moreover, nicotine metabolites are pharmacologically active in neurochemical and behavioral assays. Thus, CNS effects resulting from nicotine exposure may not be due solely to nicotine, but may result, at least in part, from the actions of nicotine metabolites.

Involvement of N- and P/Q- but not L- or T-type voltage-gated calcium channels in ischaemia-induced striatal dopamine release in vitro

Calcium influx and transmitter efflux are central events in the neuropathological cascade that occurs during and following cerebral ischaemia. This study explored the role of voltage-gated calcium channels (VGCCs) in ischaemia-induced striatal dopamine (DA) release in vitro. Slices (350 microm thickness) of rat neostriatum were superfused (400 ml/h) with an artificial cerebrospinal fluid (aCSF) at 34 degrees C and subjected to episodes of 'ischaemia' by reduction of the glucose concentration from 4 to 2 mM and gassing with 95% N2/5% CO2. DA release was monitored with fast cyclic voltammetry at implanted carbon fibre microelectrodes. The time to onset, time to peak, rate and magnitude of DA release were measured. Non-selective blockade of VGCCs with a high concentration of Ni2+ (2.5 mM), markedly delayed (P < 0.01) and slowed (P < 0.05) DA release but preferential blockade of T-type VGCCs with a lower concentration (200 microM) had no effect. DA release was also unaffected by selective antagonism of L-type VGCCs with nimodipine and nicardipine (10 microM each). Selective blockade of N-type VGCCs with omega-conotoxin GVIA (100 nM) delayed DA release (P < 0.05) but did not affect its rate or magnitude. Blockade of P- and possibly Q-type VGCCs with omega-agatoxin IVA (up to 200 nM) both delayed (P < 0.05) and slowed (P < 0.05) DA release. Preferential blockade of P- type VGCCs with neomycin (500 microM) also delayed (P < 0.05) and slowed (P < 0.05) DA release. These findings suggest that N-, P- and possibly Q- but not L- or T-type VGCCs mediate ischaemia-induced DA release. Although it is not possible to say, on the basis of these results, that the effects are directly upon the dopamine terminals, these calcium channels nevertheless constitute promising targets for therapeutic intervention.

Modulation of nicotine-evoked [3H]dopamine release from rat striatal synaptosomes by voltage-sensitive calcium channel ligands

The calcium channel subtypes mediating nicotine-evoked [3H]dopamine release from rat striatal synaptosomes were probed with L-, N-, and P-type calcium channel ligands. Responses to nicotine were blocked by the peptides omega-conotoxin GVIA and omega-agatoxin IVA. The affinity constants for these compounds were consistent with their actions at N- and P-type channels, respectively. Together, these channels mediate at least 90% of the calcium-dependent response to nicotine. The L-type antagonists nifedipine, verapamil, and nicardipine were also effective blockers of nicotine-evoked release with maximal effects of 80-100% inhibition. However, these effects occurred at concentrations 2-3 orders of magnitude higher than those necessary to block L-type channels. Moreover, Bay K8644, an L-type agonist, also blocked nicotine-evoked release. Together, these findings argue strongly against the involvement of L-type channels.

Differential mechanisms involved in the effect of nicotinic agonists DMPP and lobeline to release [3H]5-HT from rat hippocampal slices

In the present study we investigated the effect of different nicotinic agonists (dimethylphenyl-piperazinium-iodide (DMPP), (-)nicotine, cytisine, (-)-lobeline, and (-)epibatidine) and antagonists (mecamylamine and dihydro-beta-erythroidine) on the release of [3H]5-HT from hippocampal slices. The nicotinic agonists DMPP and lobeline and electrical field stimulation, released [3H]5-HT from the hippocampus; other nicotinic agonists, such as (-)-nicotine, cytisine, and (-)-epibatidine had no effect. Unlike lobeline-induced release of [3H]5-HT, the effect of DMPP (10 and 40 microM) was antagonized by mecamylamine (20 and 10 microM). The effect of DMPP was [Ca2+]o-independent. In experiments carried out at 7 degrees C, i.e. the membrane carrier proteins are inhibited and the release by lobeline was abolished while the DMPP-induced release of 5-HT was rather potentiated. It is proposed that the effect of DMPP and lobeline, to enhance the release of [3H]5-HT from the hippocampus, was mediated by two different mechanisms. While DMPP-induced 5-HT release can be linked to a non-classical nAChR activation ([Ca2+]o-independence), the effect of lobeline was likely mediated by uptake carriers.

The role of various calcium and potassium channels in the regulation of somatodendritic serotonin release

We prepared slices from midbrain containing the raphe nuclei and from hippocampus of rats. The brain slices were loaded with [3H]serotonin and superfused in order to measure the release of radioactivity at rest and in response to electrical stimulation. No difference was observed in the resting and stimulated fractional release of tritium in the somatodendritic and axon terminal parts of serotonergic neurons. The selective 5-HT1A receptor agonist 8-OH-DPAT decreased the electrically induced tritium efflux from raphe nuclei slices preloaded with [3H]serotonin, and this inhibition was reversed by the 5-HT1A receptor antagonist (+)WAY-100135. The 5-HT1B receptor agonist CGS-12066B but not 8-OH-DPAT, inhibited the stimulation-evoked tritium efflux from hippocampal slices after labeling with [3H]serotonin. The electrical stimulation-evoked tritium efflux in raphe nuclei slices incubated with [3H]serotonin was completely external Ca(2+)-dependent, and omega-conotoxin GVIA and Cd2+, but not diltiazem, inhibited the tritium overflow. In raphe nuclei slices 4-aminopyridine enhanced the electrical stimulation-induced tritium release in a concentration-dependent manner. The inhibition of tritium efflux by 8-OH-DPAT was abolished with 4-aminopyridine. Glibenclamide or tolbutamide proved to be ineffective. These data indicate that (1) different 5-HT receptor subtypes (5-HT1A and 5-HT1B) regulate dendritic and axon terminal 5-HT release; (2) serotonin release from the dendrites may be regulated by the voltage-sensitive N-type Ca2+ channels; (3) the 5-HT1A receptor-mediated inhibition of serotonin release may be due to opening of voltage-sensitive K+ channels.

The apomorphine test in heroin addicts

Chronic administration of opiates to laboratory animals induces supersensitivity of the dopamine receptors in the cerebral areas innervated by the mesotelencephalic dopamine pathways. In humans, the in vivo study of the sensitivity of the dopamine neurotransmitter system in Parkinson's patients can be done by means of the apomorphine test, which consists of measuring the number of yawns induced by the subcutaneous administration of low doses of apomorphine (0.005 mg/kg). If chronic opiate use in humans, as in experimental animals, results in supersensitivity of the dopamine systems, the apomorphine test could differentiate between heroin addicts and healthy volunteers, with the former showing greater number of yawns. In order to test this hypothesis we carried out the apomorphine test in two groups of subjects: a group of male heroin addicts attending our Addiction Treatment Centre for detoxification and the other group consisting of healthy volunteer male university students. Results showed that subcutaneous apomorphine administration induced a greater number of yawns (p < 0.05) in the group of heroin addicts as compared with the group of healthy volunteers, suggesting that heroin addicts present an enhanced sensitivity of the dopamine nuerotransmitter system.

omega-Conotoxin GVIA blocks nicotine-induced catecholamine secretion by blocking the nicotinic receptor-activated inward currents in bovine chromaffin cells

We have studied the contribution of N-type voltage-dependent Ca2+ channels to both norepinephrine and epinephrine secretion from bovine chromaffin cells induced by high K+ or nicotine using omega-conotoxin GVIA, a selective blocker of N-type voltage-dependent Ca2+ channels. We found that high K+ (75 mM) induced catecholamine secretion was not affected by exposure of bovine chromaffin cells to omega-conotoxin GVIA (1 microM). However, nicotine-induced both norepinephrine and epinephrine secretion were similarly blocked (about 25%) by omega-conotoxin GVIA (1 microM). This effect could be explained by a potent (about 80%) and reversible blockade of the inward current induced by nicotine receptor activation in bovine chromaffin cells. The results indicate that besides the blockade of N-type voltage-dependent channels, omega-conotoxin GVIA is a potent and reversible blocker of the nicotinic receptor-induced currents in chromaffin cells.

Isradipine, a calcium channel blocker, attenuates the ischemia-induced release of dopamine but not glutamate in rats

This study was designed to investigate the role of the L-type voltage sensitive calcium channel blocker, isradipine, in the ischemia-induced release of neurotransmitters. Male spontaneously hypertensive rats were subjected to cerebral ischemia for 60 min by bilateral carotid artery occlusion, and recirculated for 120 min. Isradipine (0.25 mg/kg n = 6) or vehicle (n = 6) was administered subcutaneously at 20 min before ischemia. In the striatum, cerebral blood flow was determined by the hydrogen clearance method and concentrations of extracellular dopamine and glutamate were measured by in vivo brain dialysis technique. Extracellular dopamine in the vehicle-treated group increased by 180-fold from the basal level, and glutamate by 24-fold during cerebral ischemia. Isradipine significantly attenuated the ischemic release of dopamine to 33-34% (P < 0.05) of the vehicle group, while it did not affect glutamate release. It is suggested that the release mechanism of dopamine and glutamate during cerebral ischemia may be different, especially in the dependence on the L-type calcium channels.

Evidence that ibogaine releases dopamine from the cytoplasmic pool in isolated mouse striatum

We measured the effect of ibogaine on the tritium efflux from isolated mouse striatum preloaded with [3H]dopamine ([3H]DA). Ibogaine increased the basal tritium outflow in a concentration-dependent manner, but it was without effect on electrical stimulation-induced tritium overflow. Separation of the released radioactivity after ibogaine administration showed that this drug increased the release of [3H]DA and [3H]-dihydroxyphenylacetic acid ([3H]DOPAC), but the efflux of O-methylated-deaminated metabolites was not changed. The dopamine (DA)-releasing effect of ibogaine was reduced by the DA uptake inhibitors cocaine and nomifensine. The tritium efflux evoked by ibogaine was not altered by omission of Ca2+ from the perfusion buffer or by inhibition of the voltage-sensitive Na+ channels with tetrodotoxin. Ibogaine maintained its effect on release from superfused striatum prepared from reserpine-pretreated mice. The ibogaine-induced tritium release measured from mouse striatum that was preloaded with [3H]DA was not affected by the D-2 DA receptor ligands (-)-quinpirole and (+/-)-sulpiride, indicating that the ibogaine-induced release is not subject to presynaptic autoreceptor regulation. Ibogaine failed to affect [3H]DA uptake and retention in mouse striatum. These data indicate that at the nerve terminal level ibogaine releases DA, and the primary source for the release is probably the cytoplasmic pool. The DA-releasing effect of ibogaine may have importance in mediation of its hallucinogenic action, as seen in a frequent practice in African cults.

Ibogaine reduces amphetamine-induced locomotor stimulation in C57BL/6By mice, but stimulates locomotor activity in rats

The effect of ibogaine hydrochloride on locomotor stimulation induced by d-amphetamine sulfate was tested in male C57BL/6By mice and in female Sprague-Dawley rats. In mice, locomotor stimulation induced by d-amphetamine at 1 or 5 mg/kg s.c. was reduced by prior administration of one or two injections of ibogaine (40 mg/kg), given 2 or 18 hours earlier. This reduction in locomotor activity persisted for two days. Locomotor stimulation induced by a higher dose (10 mg/kg) of d-amphetamine was not reduced by such prior administration of ibogaine. A lower dose of ibogaine (20 mg/kg) did not reduce the subsequent locomotor activity induced by d-amphetamine. Ibogaine decreased striatal dopamine levels, while d-amphetamine increased them. Ibogaine treatment (2 x 40 mg/kg, 18 hours apart) induced a decrease by 30% in the level of striatal dopamine and its metabolites measured in tissue extracts 3 hours after the second ibogaine injection. One hour after d-amphetamine (5 mg/kg) administration, the level of striatal dopamine increased by 26%. Although the level of striatal dopamine was initially lower in the ibogaine-pretreated mice, d-amphetamine (5 mg/kg) administration induced an increase in striatal dopamine and its metabolites. The effect of ibogaine seems to be species specific, since in rats pretreated with ibogaine 18 hours before d-amphetamine, locomotor stimulation induced by d-amphetamine was further increased. In addition, the in vitro electrical-evoked release of [3H]dopamine from striatal tissue was either unchanged or inhibited in the presence of d-amphetamine, and after ibogaine pretreatment in vivo, the release of tritium in the presence of d-amphetamine was inhibited or stimulated in mice and rats, respectively.