Effects of the d- and l-isomers of amphetamine on uptake, release and catabolism of norepinephrine, dopamine and 5-hydroxytryptamine in several regions of rat brain

m-CF3-substituted diphenyl diselenide attenuates all phases of morphine-induced behavioral locomotor sensitization in mice

BACKGROUND

Behavioral sensitization, thought to underlie some aspects of drug dependence, is typically measured as increased locomotion in response to repeated administration of a drug. The study aimed to investigate the (m-CF3-PhSe)₂ effects on the acquisition, withdrawal, and re-exposure phases of morphine-induced behavioral locomotor sensitization.

METHODS

Swiss male mice were treated with saline or morphine at 10 mg/kg twice a day for 3 days; those of the morphine group were kept in the morphine withdrawal period (5 days). On day 9, mice were re-exposed to morphine. (m-CF3-PhSe)₂ (10 mg/kg) or vehicle was administered at all phases of morphine protocol, and mice performed locomotor activity test. Oxidative stress markers and the levels of opioid, dopamine, and glutamate receptors were determined in samples of the cerebral cortex. (m-CF3-PhSe)₂ administered at all phases of protocol attenuated morphine-induced locomotor sensitization.

RESULTS

Mice exposed to morphine showed reduced weight gain and increased locomotor activity, but (m-CF₃-PhSe)₂ treatment attenuates the weight gain and behavioral hyperlocomotion effects. (m-CF3-PhSe)₂, independent of the administration phase, modulated the increase of opioidergic (MOR, DOR, KOR) and glutamatergic (NMDA 2A and 2B) protein contents and attenuated redox imbalance in the cerebral cortex of mice exposed to morphine. However, (m-CF3-PhSe)₂ did not modulate cortical protein levels of dopaminergic (D1 and D2) receptors in the acquisition phase of morphine-induced locomotor sensitization protocol.

CONCLUSION

(m-CF₃-PhSe)₂ was effective against the behavioral and molecular alterations caused by morphine at all phases of locomotor sensitization.

Enhancing the efficacy of 5-HT uptake inhibitors in the treatment of attention deficit hyperactivity disorder

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common childhood behavioural disorders, the frontline treatments for which are drugs with abuse potential. As a consequence, there is an urgent need to develop non addictive drug treatments with equivalent efficacy. Preclinical evidence suggests that selective serotonin uptake inhibitors (SSRIs) are likely to be effective in ADHD, however clinical reports suggest that SSRIs are of limited therapeutic value for the treatment of ADHD. We propose that this disconnect can be explained by the pattern of drug administration in existing clinical trials (administration for short periods of time, or intermittently) leading to inadequate control of the autoregulatory processes which control 5-HT release, most notably at the level of inhibitory 5-HT_1A somatodendritic autoreceptors. These autoreceptors reduce the firing rate of 5-HT neurons (limiting release) unless they are desensitised by a long term, frequent pattern of drug administration. As such, we argue that the participants in earlier trials were not administered SSRIs in a manner which realises any potential benefits of targeting 5-HT in the pharmacotherapy of ADHD. In light of this, we hypothesise that there may be under-researched potential to exploit 5-HT transmission therapeutically in ADHD, either through changing the administration regime, or by pharmacological means. Recent pharmacological research has successfully potentiated the effects of SSRIs in acute animal preparations by antagonising inhibitory 5-HT_1A autoreceptors prior to the administration of the SSRI fluoxetine. We suggest that combination therapies linking SSRIs and 5-HT_1A antagonists are a potential way forward in the development of efficacious non-addictive pharmacotherapies for ADHD.

Differential effects of d-amphetamine and atomoxetine on risk-based decision making of Lewis and Fischer 344 rats

Individuals with attention-deficit/hyperactivity disorder tend to make risker choices during probabilistic-discounting procedures. Thus, how common attention-deficit/hyperactivity disorder medications affect probabilistic discounting is of interest. In general, d-amphetamine increases risk-taking while atomoxetine has produced mixed effects in rats. Results from previous studies may result from genetic factors. Lewis and F344 rats have neurochemical differences that may be relevant to probabilistic discounting and how drugs affect such behavior. In this study, we evaluated dose-dependent effects of d-amphetamine and atomoxetine on probabilistic discounting of Lewis and F344. Male Lewis and F344 chose between one food pellet delivered 100% of the time and three food pellets delivered following decreasing probabilities of delivery (i.e. 100%, 66.7%, 33.3%, 16.5%, and 8.25%). Saline, d-amphetamine (0.1-1.8 mg/kg), and atomoxetine (0.1-7.8 mg/kg) were tested acutely. Lewis and F344 did not differ in choice at baseline. d-Amphetamine increased risky choice for both rat strains at low-to-moderate doses, although it did so at a lower dose (0.1 and 0.3 mg/kg) for F344 as compared to Lewis (0.3 mg/kg only). At high doses (1.0 and 1.8 mg/kg), d-amphetamine disrupted choice, increased frequencies of omitted trials, and reduced reinforcer sensitivity. Although atomoxetine increased frequencies of omitted trials at high doses (5.6 and 7.8 mg/kg), it had no effect on probabilistic discounting for either rat strain. Although Lewis and F344 differ in various types of impulsivity (i.e. motor, choice), with Lewis being the more impulsive of the two, the present results suggest that Lewis and F344 do not differ in risk-based decision-making. Effects of d-amphetamine on probabilistic discounting may be biology-dependent and differ from effects of atomoxetine.

Emission of categorized 50-kHz ultrasonic vocalizations in rats repeatedly treated with amphetamine or apomorphine: Possible relevance to drug-induced modifications in the emotional state

The emission of 50-kHz ultrasonic vocalizations (USVs) is increasingly emerging as a potential behavioral marker of the subjective effects that psychoactive drugs elicit in rats. However, multiple categories of 50-kHz USVs have been identified, which are thought to possess different behavioral significance. Besides, limited information is available on how psychoactive drugs affect the emission of categorized 50-kHz USVs. To further elucidate this issue, we evaluated the numbers of multiple categories of 50-kHz USVs emitted by rats repeatedly treated with amphetamine (1 or 2 mg/kg, i.p.) or apomorphine (2 or 4 mg/kg, i.p.), two drugs that elicit similar and dissimilar subjective effects. Amphetamine- and apomorphine-treated rats emitted patterns of categorized 50-kHz USVs that varied according to the drug administered, drug dose, and number of drug administrations. Nevertheless, the numbers of several categories of 50-kHz USVs were positively correlated with the number of total calls emitted (i.e., the sum of categorized 50-kHz USVs). Moreover, a marked interindividual variability in the emission of categorized 50-kHz USVs was observed. Taken together, the present results may be relevant to further elucidating the interplay between calling of the 50-kHz USVs group and psychopharmacological profile of drugs.

Effect fingerprinting of new psychoactive substances (NPS): What can we learn from in vitro data?

The use of new psychoactive substances (NPS) is increasing and currently >600 NPS have been reported. However, limited information on neuropharmacological and toxicological effects of NPS is available, hampering risk characterization. We reviewed the literature on the in vitro neuronal modes of action to obtain effect fingerprints of different classes of illicit drugs and NPS. The most frequently reported NPS were selected for review: cathinones (MDPV, α-PVP, mephedrone, 4-MEC, pentedrone, methylone), cannabinoids (JWH-018), (hallucinogenic) phenethylamines (4-fluoroamphetamine, benzofurans (5-APB, 6-APB), 2C-B, NBOMes (25B-NBOMe, 25C-NBOMe, 25I-NBOMe)), arylcyclohexylamines (methoxetamine) and piperazine derivatives (mCPP, TFMPP, BZP). Our effect fingerprints highlight the main modes of action for the different NPS studied, including inhibition and/or reversal of monoamine reuptake transporters (cathinones and non-hallucinogenic phenethylamines), activation of 5-HT₂receptors (hallucinogenic phenethylamines and piperazines), activation of cannabinoid receptors (cannabinoids) and inhibition of NDMA receptors (arylcyclohexylamines). Importantly, we identified additional targets by relating reported effect concentrations to the estimated human brain concentrations during recreational use. These additional targets include dopamine receptors, α- and β-adrenergic receptors, GABA_Areceptors and acetylcholine receptors, which may all contribute to the observed clinical symptoms following exposure. Additional data is needed as the number of NPS continues to increase. Also, the effect fingerprints we have obtained are still incomplete and suffer from a large variation in the reported effects and effect sizes. Dedicated in vitro screening batteries will aid in complementing specific effect fingerprints of NPS. These fingerprints can be implemented in the risk assessments of NPS that are necessary for eventual control measures to reduce Public Health risks.

Effect of methylphenidate on visual responses in the superior colliculus in the anaesthetised rat: Role of cortical activation

The mechanism of action of psychostimulant drugs in the treatment of Attention Deficit Hyperactivity Disorder is still largely unknown, although recent evidence suggests one possibility is that the drugs affect the superior colliculus (SC). We have previously demonstrated that systemically administered d-amphetamine attenuates/abolishes visual responses to wholefield light flashes in the superficial layers of the SC in anaesthetised rats, and the present study sought to extend this work to methylphenidate (MPH). Anaesthetised rats were administered MPH at a range of doses (or saline) and subjected to monocular wholefield light flashes at two intensities, juxta-threshold and super-threshold. In contrast to d-amphetamine, systemic MPH produced an enhancement of visual activity at both intensities. Methylphenidate was also found to produce activation of the cortical EEG in anaesthetised rats. Furthermore, cortical activation induced by electrical stimulation of the pons was found to enhance visual responses in superficial layers of the SC, and when MPH was paired with pontine-induced cortical activation, the response-enhancing effects of MPH were substantially attenuated. Taken together, the results suggest that the enhancement of visual responses in the superficial layers of the SC by MPH in the anaesthetised rat is an artefact of the drug's interaction with cortical arousal.

Electrophysiological Actions of Synthetic Cathinones on Monoamine Transporters

Products containing psychoactive synthetic cathinones, such as mephedrone and 3,4-methylenedioxypyrovalerone (MDPV) are prevalent in our society. Synthetic cathinones are structurally similar to methamphetamine, and numerous synthetics have biological activity at dopamine, serotonin, and norepinephrine transporters. Importantly, monoamine transporters co-transport sodium ions along with their substrate, and movement of substrates and ions through the transporter can generate measurable ionic currents. Here we review how electrophysiological information has enabled us to determine how synthetic cathinones affect transporter-mediated currents in cells that express these transporters. Specifically, drugs that act as transporter substrates induce inward depolarizing currents when cells are held near their resting membrane potential, whereas drugs that act as transporter blockers induce apparent outward currents by blocking an inherent inward leak current. We have employed the two-electrode voltage-clamp technique in Xenopus laevis oocytes overexpressing monoamine transporters to determine whether synthetic cathinones found in the so-called bath salts products behave as blockers or substrates. We also examined the structure-activity relationships for synthetic cathinone analogs related to the widely abused compound MDPV, a common constituent in "bath salts" possessing potent actions at the dopamine transporter.

m-Trifluoromethyl-diphenyldiselenide as a pharmacological tool to treat preference symptoms related to AMPH-induced dependence in rats

Amphetamine (AMPH) abuse is a world concern and a serious public health problem. Repeated administration of high doses of AMPH induces neuropsychiatric consequences, including addiction, reward and psychosis, whose pharmacological treatment has shown limited effectiveness. The m-trifluoromethyl-diphenyldiselenide [(m-CF3-PhSe)2] has been documented as a promising pharmacological agent in different animal models related to oxidative damage. In this study, we examined the influence of (m-CF3-PhSe)2 on withdrawal following re-exposure to AMPH. Wistar rats received d,l-AMPH or saline in the conditioned place preference (CPP) paradigm for 8days. Then, half of each initial (AMPH or saline) experimental group was treated with (m-CF3-PhSe)2 or vehicle, resulting in four final groups: i) Saline/vehicle; ii) (m-CF3-PhSe)2/saline; iii) AMPH/vehicle; and iv) AMPH/(m-CF3-PhSe)2. After fourteen days of (m-CF3-PhSe)2 treatment, animals were re-exposed to AMPH or vehicle in the CPP paradigm for three more days in order to assess drug re-conditioning and memory/locomotor activity, performed 24h after AMPH re-exposure in the CPP and the Y maze, respectively. Subsequently, ex-vivo assays were carried out in samples of the prefrontal cortex (PFC) of the animals. The (m-CF3-PhSe)2 treatment was able to prevent AMPH-induced re-conditioning symptoms in rats. Behavioral observations in the Y maze task showed no significant changes. AMPH exposure was able to increase 5-HT uptake as well as oxidative damage in the PFC, whereas (m-CF3-PhSe)2 treatment exerted a preventative effect against these alterations. The current findings suggest that (m-CF3-PhSe)2 might be considered a promising therapeutic tool for AMPH-induced addiction.

Khat use and appetite: an overview and comparison of amphetamine, khat and cathinone

ETHNOPHARMACOLOGICAL RELEVANCE

To understand the role of khat (Catha edulis) use on the aberrations in appetite and weight which are common comorbidities for khat and other amphetamine users.

MATERIALS AND METHODS

We provide a comprehensive overview and conceptual summary of the historical cultural use of khat as a natural stimulant and describe the similarities and differences between cathinone (the main psychoactive constituent of khat) and amphetamine highlighting the limited literature on the neurophysiology of appetite and subsequent weight effects of khat.

RESULTS

Animal and some human studies indicate that khat produces appetite suppression, although little is known about mechanisms of this effect. Both direct and indirect effects of khat stem from multiple factors including behavioral, chemical and neurophysiological effects on appetite and metabolism. Classic and newly identified appetite hormones have not been explored sufficiently in the study of appetite and khat use. Unique methodological challenges and opportunities are encountered when examining effects of khat and cathinone including khat-specific medical comorbidities, unique route of administration, differential patterns of behavioral effects relative to amphetamines and the nascent state of our understanding of the neurobiology of this drug.

CONCLUSION

A considerable amount of work remains in the study of the appetite effects of khat chewing and outline a program of research that could inform our understanding of this natural amphetamine׳s appetite effects and help prepare health care workers for the unique health effects of this drug.

Exercise modifies amphetamine relapse: behavioral and oxidative markers in rats

Exercise has been reported to attenuate rewarding symptoms related to addictive drugs mainly by affecting the brain neuroplasticity and neurotransmission. In this study, we investigated the influence of physical exercise on the behavioral and enzymatic status related to drug relapse in rats. Animals were primarily treated with amphetamine (AMPH; 4.0 mg/kg, i.p.) or vehicle (C; NaCl 0.9% solution) in the conditioned place preference (CPP) paradigm for 14 days. Half of each experimental group was then submitted to swimming sessions (60 min/day, 5 days/week) for 5 weeks. Animals were re-exposed to AMPH- or vehicle-CPP paradigm for another 3 days, in order to observe drug relapse and anxiety-like symptoms, which were observed 24h after AMPH reconditioning in CPP, and elevated plus maze (EPM), respectively, and brain biochemical evaluations were carried out subsequently. While AMPH was related to place preference and anxiety, indicating drug addiction and abstinence symptoms, respectively, physical activity was able to prevent relapse symptoms after AMPH reconditioning, as observed through consecutive decreased CPP and anxiety-like symptoms. In addition, AMPH exposure increased reactive species (RS) generation and protein carbonyl (PC) levels together with decreased activity of catalase- and Na(+)K(+)-ATPase in hippocampus. On the other hand, while all AMPH-induced effects were prevented by physical activity, there was a negative correlation between PC levels (r=0.65; p<0.003) and CAT activity, and a positive correlation between RS generation and PC levels (r=0.54; r=0.52, p<0.05) with AMPH-CPP after exercise. These results indicate that exercise has a clear beneficial influence on the prevention of psychostimulant drug relapse.

Enantiomeric separations of illicit drugs and controlled substances using cyclofructan-based (LARIHC) and cyclobond I 2000 RSP HPLC chiral stationary phases

Recently a novel class of chiral stationary phases (CSPs) based on cyclofructan (CF) has been developed. Cyclofructans are cyclic oligosaccharides that possess a crown ether core and pendent fructofuranose moieties. Herein, we evaluate the applicability of these novel CSPs for the enantiomeric separation of chiral illicit drugs and controlled substances directly without any derivatization. A set of 20 racemic compounds were used to evaluate these columns including 8 primary amines, 5 secondary amines, and 7 tertiary amines. Of the new cyclofructan-based LARIHC columns, 14 enantiomeric separations were obtained including 7 baseline and 7 partial separations. The LARIHC CF6-P column proved to be the most useful in separating illicit drugs and controlled substances accounting for 11 of the 14 optimized separations. The polar organic mode containing small amounts of methanol in acetonitrile was the most useful solvent system for the LARIHC CF6-P CSP. Furthermore, the LARIHC CF7-DMP CSP proved to be valuable for the separation of the tested chiral drugs resulting in four of the optimized enantiomeric separations, whereas the CF6-RN did not yield any optimum separations. The broad selectivity of the LARIHC CF7-DMP CSP is evident as it separated primary, secondary and tertiary amine containing chiral drugs. The compounds that were partially or un-separated using the cyclofructan based columns were screened with a Cyclobond I 2000 RSP column. This CSP provided three baseline and six partial separations.

Amphetamine, past and present--a pharmacological and clinical perspective

Amphetamine was discovered over 100 years ago. Since then, it has transformed from a drug that was freely available without prescription as a panacea for a broad range of disorders into a highly restricted Controlled Drug with therapeutic applications restricted to attention deficit hyperactivity disorder (ADHD) and narcolepsy. This review describes the relationship between chemical structure and pharmacology of amphetamine and its congeners. Amphetamine's diverse pharmacological actions translate not only into therapeutic efficacy, but also into the production of adverse events and liability for recreational abuse. Accordingly, the balance of benefit/risk is the key challenge for its clinical use. The review charts advances in pharmaceutical development from the introduction of once-daily formulations of amphetamine through to lisdexamfetamine, which is the first d-amphetamine prodrug approved for the management of ADHD in children, adolescents and adults. The unusual metabolic route for lisdexamfetamine to deliver d-amphetamine makes an important contribution to its pharmacology. How lisdexamfetamine's distinctive pharmacokinetic/pharmacodynamic profile translates into sustained efficacy as a treatment for ADHD and its reduced potential for recreational abuse is also discussed.

Sub-optimal performance in the 5-choice serial reaction time task in rats was sensitive to methylphenidate, atomoxetine and d-amphetamine, but unaffected by the COMT inhibitor tolcapone

Prefrontal cortical dopamine (DA) and norepinephrine (NE) are implicated in multiple aspects of cognitive function assessed via the 5-choice serial reaction time task (5-CSRTT) in rodents. The present studies assessed the effects of the NE reuptake inhibitor atomoxetine (0.5-2.0 mg/kg), the mixed DA/NE reuptake inhibitor methylphenidate (0.1-2.0 mg/kg), the catecholamine releaser D-amphetamine (0.1-1.0 mg/kg) and the catecholamine-o-methyl-transferase (COMT) inhibitor tolcapone (3.0-30.0 mg/kg) in rats that exhibited sub-optimal performance (reduced accuracy: <70% correct) in the 5-CSRTT. Increased ITI durations were associated with increased premature responding. Decreased ITI durations resulted in increased percent omissions, increased perseverative responses and increased response latencies, but had no effects on magazine latencies or percent correct. Atomoxetine decreased premature responding at prolonged ITI durations and methylphenidate decreased percent omissions at low doses (0.1 and 0.5 mg/kg). By contrast, D-amphetamine increased premature and perseverative responding in a dose-dependent manner (0.3-1.0 mg/kg). Finally, tolcapone had no effects on sub-optimal performance in the variable ITI 5-CSRTT. These results suggest minimal potential of tolcapone as a therapeutic agent for ADHD and implicate cortical NE, not DA, in impulsive action.

Withdrawal from chronic amphetamine produces persistent anxiety-like behavior but temporally-limited reductions in monoamines and neurogenesis in the adult rat dentate gyrus

Acute amphetamine administration activates monoaminergic pathways and increases systemic corticosterone, both of which influence anxiety states and adult dentate gyrus neurogenesis. Chronic amphetamine increases anxiety states in rats when measured at 24 h and at 2 weeks of withdrawal. However, the effects of chronic amphetamine exposure and withdrawal on long term anxiety-like behavior and adult neurogenesis in the dentate gyrus are unknown. Adult male rats were administered amphetamine (2.5 mg/kg, ip.) daily for two weeks. Anxiety-like behaviors were increased markedly in amphetamine-treated rats following four weeks of withdrawal from amphetamine. Plasma corticosterone level was unaltered by amphetamine treatment or withdrawal. However, norepinephrine and serotonin concentrations were selectively reduced in the dentate gyrus 20 h following amphetamine treatment. This effect did not persist through the four week withdrawal period. In separate experiments, rats received bromodeoxyuridine to label cells in S-phase, prior to or immediately following amphetamine treatment. Newly generated cells were quantified to measure extent of progenitor cell proliferation and neurogenesis following treatment or withdrawal. Progenitor cell proliferation and neurogenesis were not significantly affected by amphetamine exposure when measured 20 h following the last amphetamine treatment. However, neurogenesis in the dentate gyrus was reduced after four weeks of withdrawal when compared to saline-pretreated rats. Overall, our findings indicate that withdrawal from chronic amphetamine leads to persistent anxiety-like behavior which may be maintained by reduced neurogenesis in the dentate gyrus at this protracted withdrawal time point. However, neurogenesis is unaffected at earlier withdrawal time points where anxiety states emerge, suggesting different mechanisms may underlie the emergence of anxiety states during amphetamine withdrawal.

Cross-species assessments of motor and exploratory behavior related to bipolar disorder

Alterations in exploratory behavior are a fundamental feature of bipolar mania, typically characterized as motor hyperactivity and increased goal-directed behavior in response to environmental cues. In contrast, abnormal exploration associated with schizophrenia and depression can manifest as prominent withdrawal, limited motor activity, and inattention to the environment. While motor abnormalities are cited frequently as clinical manifestations of these disorders, relatively few empirical studies have quantified human exploratory behavior. This article reviews the literature characterizing motor and exploratory behavior associated with bipolar disorder and genetic and pharmacological animal models of the illness. Despite sophisticated assessment of exploratory behavior in rodents, objective quantification of human motor activity has been limited primarily to actigraphy studies with poor cross-species translational value. Furthermore, symptoms that reflect the cardinal features of bipolar disorder have proven difficult to establish in putative animal models of this illness. Recently, however, novel tools such as the human behavioral pattern monitor provide multivariate translational measures of motor and exploratory activity, enabling improved understanding of the neurobiology underlying psychiatric disorders.

GBR 12909 administration as a mouse model of bipolar disorder mania: mimicking quantitative assessment of manic behavior

RATIONALE

Mania is a core feature of bipolar disorder (BD) that traditionally is assessed using rating scales. Studies using a new human behavioral pattern monitor (BPM) recently demonstrated that manic BD patients exhibit a specific profile of behavior that differs from schizophrenia and is characterized by increased motor activity, increased specific exploration, and perseverative locomotor patterns as assessed by spatial d.

OBJECTIVES

It was hypothesized that disrupting dopaminergic homeostasis by inhibiting dopamine transporter (DAT) function would produce a BD mania-like phenotype in mice as assessed by the mouse BPM.

METHODS

We compared the spontaneous locomotor and exploratory behavior of C57BL/6J mice treated with the catecholamine transporter inhibitor amphetamine or the selective DAT inhibitor GBR 12909 in the mouse BPM. We also assessed the duration of the effect of GBR 12909 by testing mice in the BPM for 3 h and its potential strain dependency by testing 129/SvJ mice.

RESULTS

Amphetamine produced hyperactivity and increased perseverative patterns of locomotion as reflected in reduced spatial d values but reduced exploratory activity in contrast to the increased exploration observed in BD patients. GBR 12909 increased activity and reduced spatial d in combination with increased exploratory behavior, irrespective of inbred strain. These effects persisted for at least 3 h.

CONCLUSIONS

Thus, selectively inhibiting the DAT produced a long-lasting cross-strain behavioral profile in mice that was consistent with that observed in manic BD patients. These findings support the use of selective DAT inhibition in animal models of the impaired dopaminergic homeostasis putatively involved in the pathophysiology of BD mania.

Drug therapies for attentional disorders alter the signal-to-noise ratio in the superior colliculus

Despite high levels of use, the mechanism of action of effective pharmacotherapies in attention deficit hyperactivity disorder (ADHD) is unknown. It has recently been hypothesized that one site of therapeutic action is the midbrain superior colliculus, a structure traditionally associated with visual processing, but also strongly implicated in distractibility, a core symptom of ADHD. We used male juvenile Wistar rats to examine the effects of therapeutically relevant doses of methylphenidate and d-amphetamine on collicular activity in vitro. Here we report a novel shared mechanism of the two drugs whereby they enhance the signal-to-noise ratio in the superior colliculus. The effects on the signal-to-noise ratio were mediated by serotonin (5-HT) via a pre-synaptic mechanism. This modulatory action would bias the system towards salient events and lead to an overall decrease in distractibility.

Effect of N-acetylcysteine and/or deferoxamine on oxidative stress and hyperactivity in an animal model of mania

Studies have consistently reported the participation of free radicals in Bipolar Disorder. Administration of d-amphetamine (d-AMPH) is a relevant animal model of mania and it increases oxidative stress in rat brain. Evidences indicate that the antioxidants N-acetylcysteine (NAC) and Deferoxamine (DFX) exert protective effects in the brain. The present study was designed to evaluate the effects of NAC, DFX or their combination on AMPH-induced hyperactivity. The protein oxidation levels were analyzed in prefrontal cortex and hippocampus. In the first animal model (reversal treatment), adult male Wistar rats received saline or d-AMPH for 14 days, and from the 8th to the 14th day, they were treated with saline, NAC, DFX, or NAC plus DFX. In the second animal model (prevention treatment), rats were pretreated with saline or antioxidant regime, and from the 8th to the 14th day, they also received saline or d-AMPH. In the prefrontal cortex, the protein carbonyls were not affected by the treatment with antioxidants alone but it was increased by treatment with NAC plus DFX. At the same model, NAC plus DFX reversed the protein damage in the hippocampus, but NAC alone increased this damage. In the prevention treatment, it was observed that the protein damage in the prefrontal cortex was prevented by DFX or NAC plus DFX. In the hippocampus, the pretreatment with all antioxidant regime prevented protein damage induced by d-AMPH. At both treatments (reversal or prevention) the antioxidants did not present any effect against d-AMPH-induced hyperactivity. In conclusion, NAC or DFX and the combination of NAC plus DFX reverse and protect against d-AMPH-induced oxidative protein damage. Using these protocols we could not observe affects on locomotion, however this effect varies depending on the brain region and the treatment regime.

Inhibition by oxytocin of methamphetamine-induced hyperactivity related to dopamine turnover in the mesolimbic region in mice

Accumulated data have shown the neuroactive properties of oxytocin (OT), a neurohypophyseal neuropeptide, and its capability of reducing the abuse potential of drugs. The present study investigated the effect of OT on methamphetamine (MAP)-induced hyperactivity in mice and its possible mechanism of action. Locomotor activity was measured after administered with MAP using an infrared sensor. High-performance liquid chromatography with electrochemical detection (HPLC-ECD) was used to detect the content of monoamines and their metabolites in the striatum and accumbens and prefrontal cortex in mice after the behavioral test. OT (0.1, 0.5, and 2.5 microg/mouse, i.c.v.) had no effect on locomotor activity in naïve mice, but inhibited, in a dose-dependent manner, the hyperactivity induced by acute administration of MAP. Atosiban (Ato) (2.0 microg/mouse, i.c.v.), the selective inhibitor of OT receptor, attenuated the inhibitory effect of OT on MAP. A marked reduction of the ratios of 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) to dopamine (DA) was observed in the striatum and accumbens of mice after acute administration of MAP. OT (2.5 microg, i.c.v.) significantly inhibited the reduction of DOPAC/DA and HVA/DA ratios. However, Ato decreased the ratio of DOPAC/DA significantly in mice compared with OT (2.5 microg) in combination with MAP. There was no significant change in serotonin (5-HT) metabolism in mice after a single administration of MAP. These results suggested that OT inhibited the MAP-induced hyperactivity by altering the DA turnover in the mesolimbic region of mice.

Differential effects of the D- and L- isomers of amphetamine on pharmacological MRI BOLD contrast in the rat

RATIONALE

The D - and L-amphetamine sulphate isomers are used in the formulation of Adderall XR(R), which is effective in the treatment of attention-deficit hyperactivity disorder (ADHD). The effects of these isomers on brain activity has not been examined using neuroimaging.

OBJECTIVES

This study determines the pharmacological magnetic resonance imaging blood-oxygenation-level-dependent (BOLD) response in rat brain regions after administration of each isomer.

MATERIALS AND METHODS

Rats were individually placed into a 2.35 T Bruker magnet for 60 min to achieve basal recording of variation in signal intensity. Either saline (n = 9), D-amphetamine sulphate (2 mg/kg, i.p.; n = 9) or L: -amphetamine sulphate (4 mg/kg, i.p.; n = 9) were administered, and recording continued for a further 90 min. Data were analysed for BOLD effects using statistical parametric maps. Blood pressure, blood gases and respiratory rate were monitored during scanning.

RESULTS

The isomers show overlapping effects on the BOLD responses in areas including nucleus accumbens, medial entorhinal cortex, colliculi, field CA1 of hippocampus and thalamic nuclei. The L-isomer produced greater global changes in the positive BOLD response than the D-isomer, including the somatosensory and motor cortices and frontal brain regions such as the orbitofrontal cortices, prelimbic and infralimbic cortex which were not observed with the D-isomer.

CONCLUSIONS

The amphetamine isomers produce different BOLD responses in brain areas related to cognition, pleasure, pain processing and motor control probably because of variations on brain amine systems such as dopamine and noradrenaline. The isomers may, therefore, have distinct actions on brain regions affected in ADHD patients.

Effects of amphetamine isomers, methylphenidate and atomoxetine on synaptosomal and synaptic vesicle accumulation and release of dopamine and noradrenaline in vitro in the rat brain

D- and L-amphetamine sulphate isomers, methylphenidate and atomoxetine, are effective treatments for attention-deficit hyperactivity disorder (ADHD). This study provides a detailed comparison of their effects on the synaptosomal and vesicular accumulation of dopamine (DA) and noradrenaline (NA) and release in vitro in rat prefrontal cortex and striatum. D-amphetamine was more potent than L-amphetamine at inhibiting accumulation of DA or NA in synaptosomes and vesicles. All drugs were weaker at inhibiting the accumulation of vesicular DA and NA compared to synaptosomal accumulation and more potently inhibited NA accumulation than DA. Methylphenidate was weak at inhibiting vesicular accumulation of DA and NA compared to its potent synaptosomal effects. The D-isomer had greater potency than the L-isomer on basal and electrically stimulated striatal DA release; however the L-isomer was 2-fold more potent than the D-isomer on basal fronto-cortical NA release. The selective DA reuptake inhibitor, GBR-12909 and NA reuptake inhibitors, maprotiline and atomoxetine, had different release profiles both on the potency and magnitude of basal and stimulated DA and NA release compared to the amphetamine isomers. These results identify distinct pharmacological action by the amphetamine isomers on dopaminergic and noradrenergic neurotransmission, which may impact on their therapeutic effects in the treatment of ADHD.

NAN-190, a possible specific antagonist for methamphetamine

Effect of NAN-190, a selective 5-HT(1A) receptor antagonist, on methamphetamine-induced locomotor activity, anorexia, analgesia, and hyperthermia was investigated in male mice. Methamphetamine (1.5 mg/kg, i.p) produced a significant increase in locomotor activity, which was significantly antagonized by NAN-190 at a dose of 4 mg/kg, i.p. NAN-190 did not alter the antinociceptive activity of mice when it was administered alone. Methamphetamine (2 mg/kg, i.p) produced a significant decrease in food intake of mice, which were deprived of food during the previous 24h. This anorectic activity of methamphetamine was significantly antagonized by NAN-190 at a dose of 2 mg/kg, i.p. NAN-190 did not alter the food intake of mice when it was administered alone. Methamphetamine (2 mg/kg, i.p) also produced a significant increase in body temperature of mice, which was significantly antagonized by NAN-190 at a dose of 0.5 mg/kg, i.p. NAN-190 did not alter the body temperature of mice when it was administered alone. In the writhing test, methamphetamine (1 mg/kg, i.p) produced a significant antinociceptive effect in mice. This was significantly antagonized by NAN-190 at a dose of 1 mg/kg, i.p. NAN-190 did not alter the antinociceptive activity of mice when it was administered alone. The results of the present study indicate a possible role for serotonergic mechanisms, in addition to the catecholaminergic systems, in the above-studied activities of methamphetamine in mice. This role is possibly mediated through direct stimulation of the 5-HT(1A) receptor subtype. All of the above-studied activities of methamphetamine were antagonized by NAN-190, which may indicate that NAN-190 is a possible antagonist for methamphetamine.

Lithium attenuates the activation-euphoria but not the psychosis induced by d-amphetamine in schizophrenia

d-Amphetamine (20 mg) was administered intravenously in a double-blind design to 17 schizophrenic patients with and without concurrent 3-week lithium carbonate pretreatment to evaluate the lithium attenuation of d-amphetamine effects which we had observed in affective disorder patients. Lithium significantly attenuated the acute d-amphetamine-induced changes in an activation-euphoria cluster and in the mannerisms and posturing item of the Brief Psychiatric Rating Scale. Because the psychosis-increasing effects of d-amphetamine were not significantly decreased, it is conceivable that the d-amphetamine-induced changes in activation and euphoria and in psychosis are regulated by different dopamine mechanisms. The small clinical effects seen at 3 weeks of lithium treatment in schizophrenic patients could be mediated by dopamine.

Rostral-caudal differences in effects of nucleus accumbens amphetamine on VTA ICSS

The effects of amphetamine along the rostrocaudal axis of the nucleus accumbens (NAcc) on ventral tegmental area (VTA) intracranial self-stimulation (ICSS) were studied. Eighteen rats were trained to lever press for ICSS in the VTA. Rate-frequency functions were determined by logarithmically decreasing the frequency of cathodal pulses in a stimulation train from a value that induced maximal responding to one that induced no responding (thresholds). After ICSS thresholds stabilized, (+)-amphetamine (20.0 micrograms/0.5 microliter) or its vehicle, distilled H2O (0.5 microliter), were injected directly into the rostral NAcc (n = 6) or the caudal NAcc (n = 8) or the caudate-putamen (CP) (n = 5) just dorsal to the caudal NAcc. Results showed that amphetamine in the caudal NAcc significantly decreased ICSS thresholds without affecting asymptomatic rates of responding, indicating a potentiation of the rewarding efficacy of VTA stimulation. Amphetamine in the rostral NAcc or CP produced smaller, non-significant, decreases in ICSS thresholds. Further analyses revealed a significant positive correlation (r13 = 0.51, P < 0.05) between the site of injection along the rostrocaudal axis of the NAcc and the size of the amphetamine-produced potentiation of VTA stimulation reward. Others have reported topographical differences, including dopamine terminal density and D1 receptor density, in the NAcc. The present results indicate that these anatomical and neurochemical differences appear to be correlated with behavioural differences.

Effect of ethanol on ascorbate release in the nucleus accumbens and striatum of freely moving rats

An in vivo voltammetry technique was used to monitor the extracellular ascorbate (AA) concentration in the nucleus accumbens and striatum of unanesthetized, freely moving rats. A single injection of ethanol, 1.0 g/kg intraperitoneally (IP), induced a significant increase in extracellular AA concentration in both the nucleus accumbens and striatum. This effect was dose dependent within a dose range from 0.5-2.0 g/kg. 4-Methylpyrazole (50 mg/kg, IP), which inhibits alcoholdehydrogenase, could not prevent the increase in AA concentration, evoked by ethanol. Furthermore, systemic administration of acetaldehyde (20 mg/kg, IP), the main metabolite of ethanol, did not have any effect on the level of AA in the nucleus accumbens or striatum. These results show that ethanol can alter the brain extracellular AA levels and that this effect seems to be attributed to ethanol itself and not to acetaldehyde. Consequently, these results indicate that a role for AA in the action of ethanol in the brain should be considered.

Morphometric and neurosecretory changes in supraoptic neurons after D-amphetamine treatment

Several morphological and immunochemical characteristics of the neurosecretory neurons of the supraoptic nucleus (SON) have been studied of rats treated for 1 month with D-amphetamine sulfate (AMP) (8 mg/kg weight, daily). An increase of SON volume (11%) has been observed as a consequence of the growth of the dorsoventral axis. Neurosecretory neurons increased their nucleolar area (11.4%), their nuclear area (8.3%), and their cytoplasmatic area (18.3%). Vasopressin immunoreaction did not show any differences between treated and control animals, but oxytocin immunostaining displayed an important increase (23.7%) in the neuronal cytoplasm of the treated rats. The SON hypertrophy of the AMP-treated rats corresponded to the hypertrophy/hyperfunction of its oxytocinergic neurons, and could be considered as a new mechanism of the action of the AMP. The results are discussed in relation to the plastic features of the SON and its central (neuronal) and peripheral (hormonal) function.

Circling induced by intra-accumbens amphetamine injections

Microinjections of d-amphetamine (5.0, 10.0 and 20.0 micrograms/0.5 microliters) into the nucleus accumbens caused reliable dose-dependent circling away from the side of injection. Injections of l-amphetamine were not effective, ruling out non-specific effects of pH, osmolarity and the like and also ruling out noradrenergic actions as explanations of the behavioral effects. Injections of d-amphetamine into the ventral caudate were less potent than those into the nucleus accumbens, suggesting nucleus accumbens rather than more dorsal tissue as the site of this behavioral effect. These data suggest that asymmetrical activation of the nucleus accumbens is a sufficient condition to induce circling behavior and raise questions for the commonly accepted view that asymmetrical activation of the caudate is a necessary condition for dopamine dependent circling behavior.

Procedures affecting maintenance and loss of tolerance to amphetamine-induced anorexia and cross-tolerance to haloperidol-induced catalepsy

Procedures affecting the maintenance and loss of tolerance to amphetamine anorexia were investigated. Following a period in which rats acquired tolerance to amphetamine-induced anorexia via the contingent- tolerance procedure, a variety of manipulations were investigated to determine which effected a loss of tolerance. The procedures included: continued milk availability or its absence, saline injections or no injections and a switch to non-contingent amphetamine injections. These procedures were each investigated while animals continued to be food-deprived or were maintained at their ad libitum weights. The animals maintained at 100% ad lib. lost tolerance whereas tolerance was maintained by the 85% groups, regardless of what other manipulations were given. Subsequently all animals were tested for catalepsy induced by 1.25 mg/kg haloperidol. Animals that had maintained tolerance to amphetamine anorexia (85% groups) were significantly less cataleptic than the animals that had lost tolerance to amphetamine anorexia (100% groups). The finding that tolerance to amphetamine anorexia is lost in animals that have ad lib. access to food indicates that a homeostatic imbalance caused by food-deprivation is perhaps the most important factor in the maintenance of tolerance to amphetamine anorexia.

Stimulation of both D1 and D2 dopamine receptors increases behavioral activation and ascorbate release in the neostriatum of freely moving rats

Electrochemically modified carbon-fiber electrodes were used to assess the effects of indirect (amphetamine and GBR-12909) as well as direct D1 (SKF-38393) and D2 (quinpirole) dopamine agonists on extracellular ascorbate in the neostriatum of awake, behaving rats. Relative to controls, 2.5 mg/kg d-amphetamine and 20.0 mg/kg GBR-12909 produced marked behavioral activation concomitant with a significant increase in ascorbate. Comparable effects were observed following the combined administration of 10.0 mg/kg SKF-38393 and 1.0 mg/kg quinpirole, but not after either of these drugs alone. Thus, behavioral activation and release of neostriatal ascorbate were closely related to the concurrent stimulation of both D1 and D2 dopamine receptors.

Enhancement of apomorphine and l-amphetamine-induced behaviors by magnesium

The behavioral effects of magnesium suggest that this divalent cation has psychomotor stimulant-like properties. Because deficiencies of this cation lead to reductions in drug-induced behaviors dependent on the levels of norepinephrine and dopamine, and numerous in vitro studies have demonstrated a relationship between magnesium and catecholamine activity, the present experiments investigate whether administration of magnesium will lead to increases in stereotyped and locomotor behaviors induced by apomorphine and l-amphetamine. Such changes would suggest that magnesium is increasing the activity of catecholamines in vivo. The results demonstrate that magnesium dose dependently increases the potency of these drugs by producing greater behavioral effects at certain drug doses, by producing shifts to the left in dose-response functions, and by producing decreases in the ED50 as dose of magnesium increases.

Amphetamine- and morphine-induced feeding: evidence for involvement of reward mechanisms

The present study examined the possibility that the increased feeding found following central and peripheral administrations of low doses of d-amphetamine (AMP) and morphine (MOR) may involve central reward mechanisms. In order to examine this possibility, the effects of these drugs on food selection and intake of foods that varied in palatability and nutritive content were determined. In addition, the importance of the nucleus accumbens (ACB), a critical structure for AMP and MOR reward, in these effects was determined. Results indicated that MOR increased the intake of preferred food regardless of nutritive content. In contrast, AMP was most effective at increasing the intake of preferred foods which contained carbohydrates. These effects were observed following systematic or intra-ACB administration of low doses of MOR and AMP. Together these findings implicate reward mechanisms in the expression of MOR- and AMP-induced feeding. It is further suggested that the feeding effects of MOR and AMP can be differentiated in paradigms where animals have a choice of several foods which may vary in palatability and/or nutritive content. The relevance of the present findings for our understanding of which elements of food and feeding behavior are coupled with ACB reward signals is also discussed.

Comparison of the effects of three indirect dopamine agonists, GK 13, GBR 12783 and dexamphetamine on behavioural tests involving central catecholaminergic transmissions

GK 13 (N-[1-(2-benzo (b) thiophenyl)-cyclohexyl] piperidine), GBR 12783 (1-[2-(diphenylmethoxy)-ethyl] 4-(3-phenyl propenyl)-piperazine and dexamphetamine are three indirect catecholaminergic agonists, acting via different neurochemical mechanisms. We have compared their effects in rodents, in several behavioral tests. All three drugs increased locomotion. The stimulant locomotor effect of dexamphetamine was more easily antagonized by haloperidol than that of GBR 12783 and GK 13. Only dexamphetamine reversed reserpine-induced akinesia. This reversal was prevented by pretreatment with either GK 13 or GBR 12783. The three drugs reduced pentobarbital sleeping time in mice. They induced rotation ipsilateral to a unilateral 6-OHDA lesion of the nigrostriatal dopaminergic pathway. The stereotypies induced by GK 13 and GBR 12783 were essentially limited to sniffing. Haloperidol-induced catalepsy was apparently more easily antagonized by dexamphetamine than by GK 13 or GBR 12783. GK 13 and GBR 12783 had no significant effects on body temperature. The three drugs displayed an anti-immobility effect in the "despair test". Dexamphetamine and GK 13 reversed the hypothermia induced by apomorphine (16 mg/kg), as well as reserpine-induced hypothermia and reserpine-induced ptosis. Dexamphetamine induced a dose-dependent anorectic effect, whereas GK 13 and GBR 12783 induced only a brief and partial anorexia. Similar observations were made on water intake. Pretreatment with either GBR 12783 or GK 13 did not affect the dexamphetamine-induced anorexia. Effects of the three drugs are discussed by reference to their known neurochemical properties on catecholaminergic transmission.

Amphetamine enantiomers and rat consummatory behavior: a new perspective

The anorectic actions of amphetamine have been known for over forty years, yet the precise relationship(s) between the enantiomeric forms of the drug and anorexia is not clearly understood. Previous studies have utilized primarily racemic amphetamine or its d-isomer in the analysis of feeding behavior. In the present investigation, a detailed examination of the effects of single and repeated equiactive doses of d- and l-amphetamine on food consumption by adult male rats was undertaken with emphasis on aspects of tolerance development. Weight loss and pattern of daily food intake differed depending upon the isomer, dose, and degree of tolerance. Two types of tolerance were seen with both isomers, an initial tolerance with a decrease in efficacy between days 1 and 2, and a later gradual decrease in efficacy over 12 days of repeated dosage. Rats tolerant to the anorectic effects of d-amphetamine were only minimally affected when challenged with an equiactive anorectic dose of l-amphetamine, while rats tolerant to the anorectic effects of l-amphetamine showed a significantly depressed food intake and modified eating pattern when challenged with an equiactive dose of d-amphetamine. Therefore two-way cross tolerance, as previously assumed, does not completely exist between low equiactive doses of d- and l-amphetamine.

Facilitation of feeding by nucleus accumbens amphetamine injections: latency and speed measures

Food-deprived rats were offered food in small meal segments, and latency to initiate feeding and time to complete it were recorded for each segment. Bilateral microinjections of d-amphetamine into nucleus accumbens dramatically increased the mean speed with which meal segments were eaten, but had no reliable effect on mean latency to initiate eating of new segments; l-amphetamine had similar but weaker effects. While mean eating speed was increased, this increase resulted from a decrease in the frequency of slow trials and not from an increase in the absolute speed of the fastest trials. These data suggest that amphetamine facilitates feeding by some other means than simple improvement of the motoric capacity of the animal, and they indicate that nucleus accumbens is an important site for amphetamine's established but not widely appreciated facilitory effects on feeding.

Effects of nucleus accumbens amphetamine on lateral hypothalamic brain stimulation reward

The effects of amphetamine were examined in a brain stimulation reward paradigm in which response rate was measured across a range of stimulation frequencies. Both low (0.0625 and 0.125 mg/kg) and high (1.0, 2.0 and 4.0 mg/kg) doses of systemic amphetamine decreased the stimulation frequency needed to sustain low rates of responding; high doses decreased the maximal response rates that were sustained by the highest stimulation frequencies. Ipsilateral microinjections (2.5, 5.0 and 10.0 micrograms/0.5 microliter) of D-amphetamine sulfate into the nucleus accumbens also caused shifts to the left of the rate-frequency function; no central dose caused a change in the asymptotic response rate associated with high stimulation frequencies. Contralateral injections of D-amphetamine (10.0 micrograms) also shifted the rate-frequency functions to the left, but were much less potent. Ipsilateral injections of D-amphetamine into the caudate were also less potent, suggesting nucleus accumbens rather than more dorsal tissue as the site of this behavioral action. Also less potent were the effects of L-amphetamine, ruling out non-specific effects of pH, osmolarity and the like and also ruling out noradrenergic actions as explanations of the behavioral effects of the injections. These data suggest that nucleus accumbens is a site of amphetamine's reward-enhancing and threshold-lowering effects on brain stimulation reward.

[Pharmacological and molecular aspects of the regulation of eating behavior. With special reference to the role of catecholamines and effects of amphetamine]

Among the numerous endogenous substances involved in the regulation of feeding behaviours, the catecholamines are in the front rank. The numerous studies devoted to this aspect of catecholamines emphasize the importance and complexity of their intervention. Depending on the cerebral structures on which they act and on whether noradrenaline or dopamine are concerned, orexigenic or anorexigenic effects have been described. Alpha-2 and beta adrenergic receptors as well as D1 and D2 dopaminergic receptors participate in these effects. Amphetamine, which is an indirect catecholaminergic agonist, mobilizes neuronal catecholamines and fosters their various effects. Moreover, it exercises direct effects by its association with sites borne by glycaemia-sensitive neurons. This target seems to be common to a wide variety of anorectic agents. They are thought to reproduce on this hypothalamic "glucostat" the effect of a high blood glucose level, thus triggering off signals of satiety. In this unifying hypothesis, the diverse pharmacological profiles these agents are known to possess would result from associated properties.

Effects of d- and l-amphetamine on food intake: evidence for a dopaminergic substrate

The present experiment examined the effects of d- and l-amphetamine on the intake of sugar, sweetened rat chow and unsweetened rat chow in free feeding rats. Rats were injected IP with 4 doses of d- or l-amphetamine (0.0, 0.125, 0.50 and 2.00 mg/kg). Regardless of drug condition, animals were found to prefer sugar over sweetened or unsweetened chow. d-Amphetamine significantly increased food intake at 0.125 and 0.50 mg/kg doses but not at 2.00 mg/kg. l-Amphetamine had no significant effects at any dose. Further, d-amphetamine significantly increased sugar intake but not sweetened or unsweetened chow. Since d- and l-amphetamine are equipotent at releasing noradrenaline, while d-amphetamine is 2 to 5 times more potent at releasing dopamine, the results suggest that d-amphetamine-induced feeding is associated with activation of a dopaminergic substrate.

Stereochemical effects of 3,4-methylenedioxymethamphetamine (MDMA) and related amphetamine derivatives on inhibition of uptake of [3H]monoamines into synaptosomes from different regions of rat brain

3,4-Methylenedioxymethamphetamine (MDMA) is a recently popularized recreational drug, although some have advocated its psychotherapeutic potential. Since the pharmacology of MDMA is largely uncharacterized, the stereochemical profiles of MDMA and some of its homologs were derived on inhibition of synaptosomal uptake of [3H]monoamines and compared to those of amphetamine and the hallucinogenic phenylisopropylamine 2,5-dimethoxy-4-methylamphetamine (DOM). In contrast to the 5-fold stereoselectivity observed with amphetamine, only the S-(+) enantiomer of MDMA and 3,4-methylenedioxyamphetamine (MDA) inhibited [3H]dopamine uptake into striatal synaptosomes. Neither stereoisomer of the alpha-ethyl homolog of MDMA, N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine (MBDB), inhibited [3H]dopamine uptake. The two stereoisomers of amphetamine and the MDMA-related compounds were equipotent in inhibiting [3H]norepinephrine uptake into hypothalamic synaptosomes. Both stereoisomers of MDMA, MDA and MBDB were potent inhibitors of [3H]serotonin uptake into hippocampal synaptosomes, but only S-(+)-amphetamine produced an appreciable inhibition of [3H]serotonin uptake. Neither stereoisomer of DOM inhibited synaptosomal uptake of any [3H]monoamine. These results suggest that MDMA and its homologs may be more closely related to amphetamine rather than to DOM in their biochemical mode of action. The pronounced effects of the methylenedioxy-substituted compounds on [3H]serotonin and [3H]norepinephrine uptake implicate these neurotransmitters in the pharmacological effects of these drugs.

Temporal distribution of [3H]-imipramine binding in rat brain regions is not changed by chronic methamphetamine

Specific binding of [3H]-imipramine in the rat suprachiasmatic nuclei, occipital cortex and caudate putamen underwent significant and replicable changes throughout 24 hr under a light-dark cycle or under constant conditions. Daily variations were also found in the medial and dorsal raphe nuclei and the lateral hypothalamus. Methamphetamine, a psychoactive drug with marked effect on circadian rhythms in physiological and hormonal parameters and adrenergic receptors, did not have any significant effect on imipramine binding rhythms in eight discrete brain regions. Thus a drug known to reduce serotoninergic neurotransmission did not change characteristics of the modulatory binding site related to serotonin uptake.

Systemic and nigral application of amphetamine both cause an increase in extracellular concentration of ascorbate in the caudate nucleus of the rat

Unmodified microvoltammetric electrodes and electrochemically modified cylindrical electrodes, both constructed from carbon fibers, were used to determine changes in ascorbate concentration in the caudate nucleus of the anesthetized rat following administration of amphetamine. The increased ascorbate levels with systemic amphetamine originate from a CNS source, since the response is not eliminated in adrenalectomized animals, and does not occur when p-hydroxyamphetamine, an agent with peripheral actions similar to amphetamine, is used as a stimulus. Local application of amphetamine in the caudate nucleus results in an increase in catechols. However, this procedure results in a decrease of the extracellular concentration of ascorbate. Unilateral nigral infusion of dopamine or amphetamine leads to a significant increase in the concentrations of ascorbate detected bilaterally in the caudate nuclei with in vivo electrochemistry. In contrast, the paradigm causes a decrease in extracellular catechols on the ipsilateral side and an increase on the contralateral side. These experiments demonstrate that the extracellular level of ascorbate is not correlated with dopamine secretion. Furthermore, the data show that the action of amphetamine on ascorbate concentration in the caudate nucleus is in part mediated by the nigral actions of amphetamine.

Effects of D- and L-amphetamine on dopamine metabolism and ascorbic acid levels in nucleus accumbens and olfactory tubercle as studied by in vivo differential pulse voltammetry

Differential pulse voltammetry used together with electrochemically pretreated carbon fibre microelectrodes allowed us to detect in vivo two well-separated peaks in nucleus accumbens and olfactory tubercle. The two peaks situated at -50 mV (peak 1) and + 100 mV (peak 2) correspond, respectively, to the oxidation current of the ascorbic acid and to the oxidation current of the 3,4-dihydroxyphenylacetic acid (DOPAC). The experiments were carried out on anesthetized rats. Voltammograms were recorded in nucleus accumbens and olfactory tubercle every minute alternately in each structure. In control conditions, peak 1 height was greater in olfactory tubercle than in nucleus accumbens and peak 2 height was greater in nucleus accumbens than in olfactory tubercle. Both isomers of amphetamine induced a decrease of the peak 2 height in the two structures. The decrease was greater in olfactory tubercle. Higher doses of L-amphetamine were required to induce peak 2 height decrease of the same extent. Both isomers induced a marked increase of the peak 1 height in nucleus accumbens whereas peak 1 height in olfactory tubercle was slightly augmented. D-amphetamine was more effective than L-amphetamine in increasing peak 1 height.

Differential effects of neuroleptic and serotonergic drugs on amphetamine-induced hypothermia in mice

Intraventricular administration of amphetamine in mice produced hypothermia. Pretreatment with the dopaminergic (DA) receptor antagonist haloperidol reduced this response, whereas pretreatment with pimozide, sulpiride or cis-flupentixol did not. The direct DA agonist apomorphine strongly potentiated the hypothermia. Pretreatment with the serotonergic (5-HT) receptor blocker cyproheptadine also potentiated the hypothermia. Depletion of 5-HT in brain by p-chlorophenylalanine and accumulation of 5-HT induced by fluoxetine had no effect. In contrast, stimulation of 5-HT receptors by quipazine reduced the hypothermic effect of amphetamine. The inhibitor of catecholamine synthesis alpha-methyl-p-tyrosine, the alpha-adrenergic blocker phentolamine and the muscarinic antagonist atropine failed to alter the hypothermia. It was concluded that DA and 5-HT mechanisms are involved in amphetamine-induced hypothermia in mice and that these two systems display a functional antagonism.

Extracellular ascorbic acid increases in striatum following systemic amphetamine

Push-pull perfusion of the anterior striatum was performed in freely moving rats which were administered 4 mg/kg d-amphetamine sulfate. Ascorbic acid was measured in the perfusate using high performance liquid chromatography with electrochemical detection. Increased extracellular ascorbic acid resulted from the amphetamine, lasting over a period of two hours. The time course of the increase corresponded to the increased oxidation current measured by intrastriatal chonoamperometry under equivalent conditions.