Phase I metabolites of mephedrone display biological activity as substrates at monoamine transporters.

BACKGROUND AND PURPOSE: 4-Methyl-N-methylcathinone (mephedrone) is a synthetic stimulant that acts as a substrate-type releaser at transporters for dopamine (DAT), noradrenaline (NET) and 5-HT (SERT). Upon systemic administration, mephedrone is metabolized to several phase I compounds: the N-demethylated metabolite, 4-methylcathinone (nor-mephedrone); the ring-hydroxylated metabolite, 4-hydroxytolylmephedrone (4-OH-mephedrone); and the reduced keto-metabolite, dihydromephedrone. EXPERIMENTAL APPROACH: We used in vitro assays to compare the effects of mephedrone and synthetically prepared metabolites on transporter-mediated uptake and release in HEK293 cells expressing human monoamine transporters and in rat brain synaptosomes. In vivo microdialysis was employed to examine the effects of i.v. metabolite injection (1 and 3 mg·kg(-1) ) on extracellular dopamine and 5-HT levels in rat nucleus accumbens. KEY RESULTS: In cells expressing transporters, mephedrone and its metabolites inhibited uptake, although dihydromephedrone was weak overall. In cells and synaptosomes, nor-mephedrone and 4-OH-mephedrone served as transportable substrates, inducing release via monoamine transporters. When administered to rats, mephedrone and nor-mephedrone produced elevations in extracellular dopamine and 5-HT, whereas 4-OH-mephedrone did not. Mephedrone and nor-mephedrone, but not 4-OH-mephedrone, induced locomotor activity. CONCLUSIONS AND IMPLICATIONS: Our results demonstrate that phase I metabolites of mephedrone are transporter substrates (i.e. releasers) at DAT, NET and SERT, but dihydromephedrone is weak in this regard. When administered in vivo, nor-mephedrone increases extracellular dopamine and 5-HT in the brain whereas 4-OH-mephedrone does not, suggesting the latter metabolite does not penetrate the blood-brain barrier. Future studies should examine the pharmacokinetics of nor-mephedrone to determine its possible contribution to the in vivo effects produced by mephedrone.

Structural Modification of the Designer Stimulant α-Pyrrolidinovalerophenone (α-PVP) Influences Potency at Dopamine Transporters.

α-Pyrrolidinovalerophenone (α-PVP, 7) is an illegal synthetic stimulant that is being sold on the clandestine market as "flakka" and "gravel". The potent pharmacological effects of α-PVP are presumably mediated by inhibition of dopamine uptake at the dopamine transporter (DAT). However, little is known about how structural modification of α-PVP influences activity at DAT. Eleven analogs of α-PVP were synthesized and examined for their ability to inhibit uptake of [(3)H]dopamine and [(3)H]serotonin in rat brain synaptosomes. None of the analogs significantly inhibited [(3)H]serotonin uptake when tested at 10 µM at the serotonin transporter (SERT). All of the analogs behaved as DAT reuptake inhibitors, but potencies varied over a >1500-fold range. Potency was primarily associated with the nature of the α-substituent, with the more bulky substituents imparting the highest potency. Expansion of the pyrrolidine ring to a piperidine reduced potency up to 10-fold, whereas conformational constraint in the form of an aminotetralone resulted in the least potent compound. Our study provides the first systematic and comparative structure-activity investigation on the ability of α-PVP analogs to act as inhibitors of DAT.

Raphe serotonin neuron-specific oxytocin receptor knockout reduces aggression without affecting anxiety-like behavior in male mice only.

Serotonin and oxytocin influence aggressive and anxiety-like behaviors, though it is unclear how the two may interact. That the oxytocin receptor is expressed in the serotonergic raphe nuclei suggests a mechanism by which the two neurotransmitters may cooperatively influence behavior. We hypothesized that oxytocin acts on raphe neurons to influence serotonergically mediated anxiety-like, aggressive and parental care behaviors. We eliminated expression of the oxytocin receptor in raphe neurons by crossing mice expressing Cre recombinase under control of the serotonin transporter promoter (Slc6a4) with our conditional oxytocin receptor knockout line. The knockout mice generated by this cross are normal across a range of behavioral measures: there are no effects for either sex on locomotion in an open-field, olfactory habituation/dishabituation or, surprisingly, anxiety-like behaviors in the elevated O and plus mazes. There was a profound deficit in male aggression: only one of 11 raphe oxytocin receptor knockouts showed any aggressive behavior, compared to 8 of 11 wildtypes. In contrast, female knockouts displayed no deficits in maternal behavior or aggression. Our results show that oxytocin, via its effects on raphe neurons, is a key regulator of resident-intruder aggression in males but not maternal aggression. Furthermore, this reduction in male aggression is quite different from the effects reported previously after forebrain or total elimination of oxytocin receptors. Finally, we conclude that when constitutively eliminated, oxytocin receptors expressed by serotonin cells do not contribute to baseline anxiety-like behaviors or maternal care.

Stereoselective Actions of Methylenedioxypyrovalerone (MDPV) To Inhibit Dopamine and Norepinephrine Transporters and Facilitate Intracranial Self-Stimulation in Rats.

The designer stimulant methylenedioxypyrovalerone (MDPV) is a potent reuptake inhibitor at transporters for dopamine (DAT) and norepinephrine (NET) that produces a constellation of abuse-related behavioral effects. MDPV possesses a chiral center, and the abused formulation of the drug is a racemic mixture, but no data are available on the pharmacology of its isomers. Here, the individual optical isomers of MDPV were prepared and examined with respect to their neurochemical actions on neurotransmitter reuptake and behavioral effects in an assay of intracranial self-stimulation (ICSS) in rats. In assays of DAT uptake inhibition, S(+)MDPV (EC50 = 2.13 nM) was more potent than either (±)MDPV (EC50 = 4.85 nM) or R(-)MDPV (EC50 = 382.80 nM); the three drugs were less potent at NET uptake inhibition, with the same rank order of potency. Neither racemic MDPV nor its optical isomers inhibited the reuptake of serotonin at concentrations up to 10 µM. S(+)MDPV produced an abuse-related and dose-dependent facilitation of ICSS, and the potency of S(+)MDPV (significant facilitation at doses ≥ 0.1 mg/kg) was greater than that of the racemate (significant facilitation at doses ≥ 0.32 mg/kg). R(-)MDPV failed to alter ICSS at doses up to 100 times greater than the lowest effective dose of S(+)MDPV. The results indicate that abuse-related neurochemical and behavioral effects of racemic MDPV reside primarily with its S(+) isomer.

Quantitative structure-activity relationship analysis of the pharmacology of para-substituted methcathinone analogues.

BACKGROUND AND PURPOSE: Methcathinone (MCAT) is a potent monoamine releaser and parent compound to emerging drugs of abuse including mephedrone (4-CH3 MCAT), the para-methyl analogue of MCAT. This study examined quantitative structure-activity relationships (QSAR) for MCAT and six para-substituted MCAT analogues on (a) in vitro potency to promote monoamine release via dopamine and serotonin transporters (DAT and SERT, respectively), and (b) in vivo modulation of intracranial self-stimulation (ICSS), a behavioural procedure used to evaluate abuse potential. Neurochemical and behavioural effects were correlated with steric (Es ), electronic (σp ) and lipophilic (πp ) parameters of the para substituents. EXPERIMENTAL APPROACH: For neurochemical studies, drug effects on monoamine release through DAT and SERT were evaluated in rat brain synaptosomes. For behavioural studies, drug effects were tested in male Sprague-Dawley rats implanted with electrodes targeting the medial forebrain bundle and trained to lever-press for electrical brain stimulation. KEY RESULTS: MCAT and all six para-substituted analogues increased monoamine release via DAT and SERT and dose- and time-dependently modulated ICSS. In vitro selectivity for DAT versus SERT correlated with in vivo efficacy to produce abuse-related ICSS facilitation. In addition, the Es values of the para substituents correlated with both selectivity for DAT versus SERT and magnitude of ICSS facilitation. CONCLUSIONS AND IMPLICATIONS: Selectivity for DAT versus SERT in vitro is a key determinant of abuse-related ICSS facilitation by these MCAT analogues, and steric aspects of the para substituent of the MCAT scaffold (indicated by Es ) are key determinants of this selectivity.

Steric parameters, molecular modeling and hydropathic interaction analysis of the pharmacology of para-substituted methcathinone analogues.

BACKGROUND AND PURPOSE: There is growing concern over the abuse of certain psychostimulant methcathinone (MCAT) analogues. This study extends an initial quantitative structure-activity relationship (QSAR) investigation that demonstrated important steric considerations of seven 4- (or para-)substituted analogues of MCAT. Specifically, the steric character (Taft's steric ES ) of the 4-position substituent affected in vitro potency to induce monoamine release via dopamine and 5-HT transporters (DAT and SERT) and in vivo modulation of intracranial self-stimulation (ICSS). Here, we have assessed the effects of other steric properties of the 4-position substituents. EXPERIMENTAL APPROACH: Definitive steric parameters that more explicitly focus on the volume, width and length of the MCAT 4-position substituents were assessed. In addition, homology models of human DAT and human SERT based upon the crystallized Drosophila DAT were constructed and docking studies were performed, followed by hydropathic interaction (HINT) analysis of the docking results. KEY RESULTS: The potency of seven MCAT analogues at DAT was negatively correlated with the volume and maximal width of their 4-position substituents, whereas potency at SERT increased as substituent volume and length increased. SERT/DAT selectivity, as well as abuse-related drug effects in the ICSS procedure, also correlated with the same parameters. Docking solutions offered a means of visualizing these findings. CONCLUSIONS AND IMPLICATIONS: These results suggest that steric aspects of the 4-position substituents of MCAT analogues are key determinants of their action and selectivity, and that the hydrophobic nature of these substituents is involved in their potency at SERT.

Selective suppression of cocaine- versus food-maintained responding by monoamine releasers in rhesus monkeys: benzylpiperazine, (+)phenmetrazine, and 4-benzylpiperidine.

Monoamine releasers constitute one class of drugs currently under investigation as potential agonist medications for the treatment of cocaine dependence. The efficacy and safety of monoamine releasers as candidate medications may be influenced in part by their relative potency to release dopamine and serotonin, and we reported previously that releasers with approximately 30-fold selectivity for dopamine versus serotonin release may be especially promising. The present study examined the effects of the releasers benzylpiperazine, (+)phenmetrazine, and 4-benzylpiperidine, which have 20- to 48-fold selectivity in vitro for releasing dopamine versus serotonin. In an assay of cocaine discrimination, rhesus monkeys were trained to discriminate 0.4 mg/kg i.m. cocaine from saline in a two-key, food-reinforced procedure. Each of the releasers produced a dose- and time-dependent substitution for cocaine. 4-Benzylpiperidine had the most rapid onset and shortest duration of action. Phenmetrazine and benzylpiperazine had slower onsets and longer durations of action. In an assay of cocaine self-administration, rhesus monkeys were trained to respond for cocaine injections and food pellets under a second order schedule. Treatment for 7 days with each of the releasers produced a dose-dependent and selective reduction in self-administration of cocaine (0.01 mg/kg/injection). The most selective effects were produced by phenmetrazine. Phenmetrazine also produced a downward shift in the cocaine self-administration dose effect curve, virtually eliminating responding maintained by a 30-fold range of cocaine doses (0.0032-0.1 mg/kg/injection) while having only small and transient effects on food-maintained responding. These findings support the potential utility of dopamine-selective releasers as candidate treatments for cocaine dependence.

Tolerance to 3,4-methylenedioxymethamphetamine in rats exposed to single high-dose binges.

3,4-Methylenedioxymethamphetamine (MDMA or ecstasy) stimulates the transporter-mediated release of monoamines, including 5-HT. High-dose exposure to MDMA causes persistent 5-HT deficits (e.g. depletion of brain 5-HT) in animals, yet the functional and clinical relevance of such deficits are poorly defined. Here we examine functional consequences of MDMA-induced 5-HT depletions in rats. Male rats received binges of three i.p. injections of MDMA or saline, one injection every 2 h; MDMA was given at a threshold pharmacological dose (1.5 mg/kgx3, low dose) or at a fivefold higher amount (7.5 mg/kgx3, high dose). One week later, jugular catheters and intracerebral guide cannulae were implanted. Two weeks after binges, rats received acute i.v. challenge injections of 1 and 3 mg/kg MDMA. Neuroendocrine effects evoked by i.v. MDMA (prolactin and corticosterone secretion) were assessed via serial blood sampling, while neurochemical effects (5-HT and dopamine release) were assessed via microdialysis in brain. MDMA binges elevated core temperatures only in the high-dose group, with these same rats exhibiting approximately 50% loss of forebrain 5-HT 2 weeks later. Prior exposure to MDMA did not alter baseline plasma hormones or dialysate monoamines, and effects of i.v. MDMA were similar in saline and low-dose groups. By contrast, rats pretreated with high-dose MDMA displayed significant reductions in evoked hormone secretion and 5-HT release when challenged with i.v. MDMA. As tolerance developed only in rats exposed to high-dose binges, hyperthermia and 5-HT depletion are implicated in this phenomenon. Our results suggest that MDMA tolerance in humans may reflect 5-HT deficits which could contribute to further dose escalation.

Restoration of 3,4-methylenedioxymethamphetamine-induced 5-HT depletion by the administration of L-5-hydroxytryptophan.

BACKGROUND: 3,4-Methylenedioxymethamphetamine (MDMA) causes persistent decreases in brain 5-HT content and 5-HT transporter (SERT) binding, with no detectable changes in SERT protein. Such data suggest that MDMA impairs 5-HT transmission but leaves 5-HT nerve terminals intact. To further test this hypothesis, we carried out two types of experiments in rats exposed to high-dose MDMA. First, we examined the effects of MDMA on SERT binding and function using different in vitro assay conditions. Next, we treated rats with the 5-HT precursor, l-5-hydroxytryptophan (5-HTP), in an attempt to restore MDMA-induced depletions of 5-HT. METHODS: Rats received three i.p. injections of saline or MDMA (7.5 mg/kg), one injection every 2 h. Rats in one group were decapitated, and brain tissue was assayed for SERT binding and [(3)H]5-HT uptake under conditions of normal (100 or 126 mM) and low (20 mM) NaCl concentration. Rats from another group received saline or 5-hydroxytryptophan/benserazide (5-HTP-B), each drug at 50 mg/kg i.p., and were killed 2 h later. RESULTS: MDMA reduced SERT binding to 10% of control when assayed in 100 mM NaCl, but this reduction was only 55% of control in 20 mM NaCl. MDMA decreased immunoreactive 5-HT in caudate and hippocampus to about 35% of control. Administration of 5-HTP-B to MDMA-pretreated rats significantly increased the 5-HT signal toward normal levels in caudate (85% of control) and hippocampus (66% of control). CONCLUSION: 1) Following high-dose MDMA treatment sufficient to reduce SERT binding by 90%, a significant number of functionally intact 5-HT nerve terminals survive. 2) The degree of MDMA-induced decreases in SERT binding depends on the in vitro assay conditions. 3) 5-HTP-B restores brain 5-HT depleted by MDMA, suggesting that this approach might be clinically useful in abstinent MDMA users.

Monoamine releasers with varying selectivity for dopamine/norepinephrine versus serotonin release as candidate "agonist" medications for cocaine dependence: studies in assays of cocaine discrimination and cocaine self-administration in rhesus monkeys.

Monoamine releasers constitute one class of drugs under investigation as candidate medications for the treatment of cocaine abuse. Promising preclinical and clinical results have been obtained with amphetamine, which has high selectivity for releasing dopamine/norepinephrine versus serotonin. However, use of amphetamine as a pharmacotherapy is complicated by its high abuse potential. Recent preclinical studies suggest that nonselective monoamine releasers or serotonin-selective releasers have lower abuse liability and may warrant evaluation as alternatives to amphetamine. To address this issue, the present study evaluated the effects of five monoamine releasers in assays of cocaine discrimination and cocaine self-administration in rhesus monkeys. The releasers varied along a continuum from dopamine/norepinephrine-selective to serotonin-selective [m-fluoroamphetamine (PAL-353), methamphetamine, m-methylamphetamine (PAL-314), 1-napthyl-2-aminopropane (PAL-287), fenfluramine]. In drug discrimination studies, rhesus monkeys were trained to discriminate saline from cocaine (0.4 mg/kg i.m.) in a two-key, food-reinforced drug discrimination procedure. Substitution for cocaine was positively associated with selectivity for dopamine/norepinephrine versus serotonin release. In drug self-administration studies, rhesus monkeys responded for cocaine (0.01 and 0.032 mg/kg/injection) and food (1-g pellets) under a second-order fixed-ratio 2 (variable-ratio 16:S) schedule. In general, monoamine releasers produced dose-dependent and sustained decreases in cocaine self-administration. However, the dopamine/norepinephrine-selective releasers decreased cocaine self-administration with minimal effects on food-maintained responding, whereas the more serotonin-selective releasers produced nonselective reductions in both cocaine- and food-maintained responding. These results are consistent with the conclusion that dopamine/norepinephrine-selective releasers retain cocaine-like abuse-related effects but may also be capable of producing relatively selective reductions in the reinforcing effects of cocaine.

Alterations in alcohol consumption, withdrawal seizures, and monoamine transmission in rats treated with phentermine and 5-hydroxy-L-tryptophan.

We have previously shown that coadministration of the dopamine (DA) agonist phentermine plus the serotonergic agonist fenfluramine suppresses alcohol intake and withdrawal seizures in rats. In the present study, phentermine and the serotonin (5-HT) precursor, 5-hydroxy-L-tryptophan (5-HTP), were administered alone, or in combination, to rats fed on a 6% alcohol-containing diet or an isocaloric control diet. Following a 9-h withdrawal period from the alcohol-containing diet, phentermine enhanced the effects of 5-HTP on both reduction of alcohol withdrawal seizures as well as changes in striatal serotonin. Food intake was monitored for 24 h after drug treatment, and neurochemical measures were examined at various time points. Phentermine alone reduced food intake in all diet conditions, but this anorectic effect was followed by hyperphagia in control rats. Phentermine plus 5-HTP reduced the consumption of the alcohol-containing diet, while its effects on consumption of control diets were mixed. In vivo microdialysis in rat nucleus accumbens revealed that phentermine increased extracellular DA, whereas 5-HTP caused marked elevations in extracellular 5-HT. Coadministration of phentermine and 5-HTP evoked simultaneous elevations in extracellular DA and 5-HT that mirrored the effects of each drug alone. Collectively, these findings show that coadministered phentermine plus 5-HTP is effective in reducing alcohol intake and suppressing alcohol withdrawal seizures. These therapeutic actions may be related to elevations in synaptic DA and 5-HT in critical brain regions.

Relationship between the serotonergic activity and reinforcing effects of a series of amphetamine analogs.

It has been reported that among drugs with mixed actions on central nervous system monoamine systems, increased serotonergic activity is associated with decreased potency as a reinforcer. The present experiment was designed to examine this relationship for amphetamine analogs that varied in serotonin releasing potency and to evaluate whether serotonergic actions can affect reinforcing efficacy. Compounds PAL 313 and 314 are para- and meta-methylamphetamine, respectively. PAL 303 and 353 are para- and meta-fluoroamphetamine, respectively. All compounds had similar potencies as in vitro releasers of dopamine (DA) and norepinephrine (NE) but differed in potency for 5-hydroxytryptamine (serotonin) (5-HT) release [EC(50) (nanomolar) PAL 313 = 53.4; PAL 314 = 218; PAL 303 = 939; PAL 353 = 1937]. When made available to rhesus monkeys (Macaca mulatta)(n = 4) for self-administration under a fixed-ratio 25 schedule, all were positive reinforcers with biphasic dose-response functions (0.003-1.0 mg/kg) and were equipotent. PAL 313 was self-administered at a lower rate than the other compounds, which were indistinguishable. Under a progressive-ratio schedule (n = 5), all drugs were positive reinforcers. Dose-response functions increased to a maximum or were biphasic (0.01-1.0 mg/kg), and drugs were equipotent. At maximum, PAL 313 maintained less responding than other PAL drugs, which maintained similar maxima. Thus, all compounds were positive reinforcers under both schedules, consistent with their potent DA actions. Responding was lower when 5-HT potency was higher and comparable with DA and NE potency. The results suggest that the mechanism for this effect involves a decrease in reinforcing potency and efficacy among monoamine releasing agents when 5-HT releasing potency is increased relative to DA.

Evidence for alterations in alpha2-adrenergic receptor sensitivity in rats exposed to repeated cocaine administration.

It is well established that cocaine stimulates monoamine transmission by blocking reuptake of norepinephrine (NE), dopamine and serotonin into nerve cells, yet few investigations have addressed the effects of chronic cocaine on NE function. In the present study, we examined the effects of repeated cocaine injections on neuroendocrine responses evoked by the alpha2-adrenergic receptor agonist, clonidine. Previous findings show that clonidine increases pituitary growth hormone (GH) secretion by a central mechanism involving postsynaptic alpha2-adrenergic receptors. Male rats previously fitted with indwelling jugular catheters received two daily injections of cocaine (15 mg/kg, i.p.) or saline for 7 days. At 42 h and 8 days after treatment, rats were challenged with clonidine (25 microg/kg, i.v.) or saline, and serial blood samples were withdrawn. Plasma GH and corticosterone levels were measured by radioimmunoassay. Prior cocaine exposure did not affect basal levels of either hormone. However, cocaine-pretreated rats displayed a significant reduction in clonidine-evoked GH secretion at 42 h, and this blunted response was still apparent 8 days later. Corticosterone responses produced by clonidine were similar regardless of pretreatment. The present data suggest that withdrawal from repeated cocaine injections may be accompanied by desensitization of postsynaptic alpha2-adrenoreceptors coupled to GH secretion. Since human patients with depression often exhibit blunted GH responses to clonidine, our findings provide evidence that cocaine withdrawal might produce depressive-like symptoms via dysregulation of NE mechanisms.

Amphoterin includes a sequence motif which is homologous to the Alzheimer's beta-amyloid peptide (Abeta), forms amyloid fibrils in vitro, and binds avidly to Abeta.

Many of the proteins associated with amyloidoses have been found to share structural and sequence similarities, which are believed to be responsible for their capability to form amyloid fibrils. Interestingly, some proteins seem to be able to form amyloid-like fibrils although they are not associated with amyloidoses. This indicates that the ability to form amyloid fibrils may be a general property of a greater number of proteins not associated with these diseases. In the present work, we have searched for amyloidogenic consensus sequences in two current protein/peptide databases and show that many proteins share structures which can be predicted to form amyloid. One of these potentially amyloidogenic proteins is amphoterin (also known as HMG-1), involved in neuronal development and a ligand for the receptor for advanced glycation end products (RAGE). It contains an amyloidogenic peptide fragment which is highly homologous to the Alzheimer's amyloid beta-peptide. If enzymatically released from the native protein, it forms amyloid-like fibrils which are visible in electron microscopy, exhibit apple green birefringence under polarized light after Congo red staining, and increases thioflavin T fluorescence. This fragment also shows high affinity to Abeta as a free peptide or while part of the native protein. Our results support the hypothesis that the potential to form amyloid is a common characteristic of a number of proteins, independent of their relation to amyloidoses, and that this potential can be predicted based on the physicochemical properties of these proteins.

1-(m-chlorophenyl)piperazine (mCPP) dissociates in vivo serotonin release from long-term serotonin depletion in rat brain.

Serotonin (5-HT) releasing agents such as d-fenfluramine are known to cause long-term depletion of forebrain 5-HT in animals, but the mechanism of this effect is unknown. In the present study, we examined the relationship between drug-induced 5-HT release and long-term 5-HT depletion in rat brain. The 5-HT-releasing actions of d-fenfluramine and a non-amphetamine 5-HT drug, 1-(m-chlorophenyl)piperazine (mCPP), were compared using in vivo microdialysis in the nucleus accumbens. The ability of d-fenfluramine and mCPP to interact with 5-HT transporters was tested using in vitro assays for [3H]5-HT uptake and radioligand binding. Local infusion of d-fenfluramine or mCPP (1-100 microM) increased extracellular 5-HT, with elevations in dopamine occurring at high doses. Intravenous injection of either drug (1-10 micromol/kg) produced dose-related increases in 5-HT without affecting dopamine. d-Fenfluramine and mCPP exhibited similar potency in their ability to stimulate 5-HT efflux in vivo and interact with 5-HT transporters in vitro. When rats received high-dose d-fenfluramine or mCPP (10 or 30 micromol/kg, i.p., every 2 h, 4 doses), only d-fenfluramine-treated rats displayed long-term 5-HT depletions. Thus, mCPP is a 5-HT releaser that does not appear to cause 5-HT depletion. Our data support the notion that 5-HT release per se may not be sufficient to produce the long-term 5-HT deficits associated with d-fenfluramine and other amphetamines.

In vivo neurobiological effects of ibogaine and its O-desmethyl metabolite, 12-hydroxyibogamine (noribogaine), in rats.

Ibogaine is a naturally occurring compound with purported antiaddictive properties. When administered to primates, ibogaine is rapidly o-demethylated to form the metabolite 12-hydroxyibogamine (noribogaine). Peak blood levels of noribogaine exceed those of ibogaine, and noribogaine persists in the bloodstream for at least 1 day. Very few studies have systematically evaluated the neurobiological effects of noribogaine in vivo. In the present series of experiments, we compared the effects of i.v. administration of ibogaine and noribogaine (1 and 10 mg/kg) on motor behaviors, stress hormones, and extracellular levels of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of male rats. Ibogaine caused dose-related increases in tremors, whereas noribogaine did not. Both ibogaine and noribogaine produced significant elevations in plasma corticosterone and prolactin, but ibogaine was a more potent stimulator of corticosterone secretion. Neither drug altered extracellular DA levels in the nucleus accumbens. However, both drugs increased extracellular 5-HT levels, and noribogaine was more potent in this respect. Results from in vitro experiments indicated that ibogaine and noribogaine interact with 5-HT transporters to inhibit 5-HT uptake. The present findings demonstrate that noribogaine is biologically active and undoubtedly contributes to the in vivo pharmacological profile of ibogaine in rats. Noribogaine is approximately 10 times more potent than ibogaine as an indirect 5-HT agonist. More importantly, noribogaine appears less apt to produce the adverse effects associated with ibogaine, indicating the metabolite may be a safer alternative for medication development.

Inhibition of MAO-A fails to alter cocaine-induced increases in extracellular dopamine and norepinephrine in rat nucleus accumbens.

Monoamine oxidase (MAO) inhibitors are being investigated as possible medications for cocaine dependence, but there are potential problems with this approach. In the present study, we tested the hypothesis that inhibition of catecholamine metabolism with the MAO-A inhibitor, clorgyline, might enhance cocaine-induced increases in extracellular dopamine and norepinephrine in rat nucleus accumbens. Male rats were pretreated with clorgyline (1 mg/kg, s.c.) or its saline vehicle (1 ml/kg, s.c.), and microdialysis probes were inserted into previously implanted guide cannulae. After overnight perfusion of the probes in situ, rats received an acute challenge injection of either cocaine (1 mg/kg, i.v.) or its saline vehicle (1 ml/kg, i.v.). Clorgyline pretreatment alone caused significant elevations in basal levels of dialysate norepinephrine but not dopamine. Cocaine administration elicited significant increases in extracellular dopamine and norepinephrine in all groups of rats, and this effect was not altered by clorgyline pretreatment. The 1 mg/kg dose of clorgyline decreased dopamine metabolites in postmortem brain tissue by more than 80%. Our data are consistent with clinical studies that demonstrate pretreatment with the MAO-B selective inhibitor, selegeline, fails to alter cocaine-induced subjective effects in human drug users. Moreover, these findings suggest that adverse consequences related to altered catecholamine transmission would not occur if patients taking phenelzine, a non-selective MAO inhibitor, relapsed and used cocaine.

Management of spontaneous pneumothorax: an American College of Chest Physicians Delphi consensus statement.

OBJECTIVE: Provide explicit expert-based consensus recommendations for the management of adults with primary and secondary spontaneous pneumothoraces in an emergency department and inpatient hospital setting. The use of opinion was made explicit by employing a structured questionnaire, appropriateness scores, and consensus scores with a Delphi technique. The guideline was designed to be relevant to physicians who make management decisions for the care of patients with pneumothorax. OPTIONS: Decisions for observation, chest tube placement, surgical interventions, and radiographic imaging. OUTCOMES: Effectiveness of pneumothorax resolution, duration of and patient tolerance of care, and pneumothorax recurrence. EVIDENCE: Literature review from 1967 to January 1999 and Delphi questionnaire submitted in three iterations to a multidisciplinary physician panel. VALUES: The guideline development group determined by consensus the relevant outcomes to be considered in developing the Delphi questionnaire. BENEFITS, HARMS, AND COSTS: The type and magnitude of benefits, harms, and costs expected for patients from guideline implementation. RECOMMENDATIONS: Management decisions vary between patients with primary or secondary pneumothoraces, with observation of small pneumothoraces being appropriate only for primary pneumothoraces. The level of consensus varies regarding the specific interventions indicated, but agreement exists for the general principles of care. VALIDATION: Recommendations were peer reviewed by physician experts and were reviewed by the American College of Chest Physicians (ACCP) Health and Science Policy Committee. IMPLEMENTATION: The guideline recommendations will be published in printed and electronic form with distribution of synopses for patients and health care providers. Contents of the guideline will be incorporated into continuing medical education programs. SPONSORS: The ACCP.