Differential effects of methamphetamine and cocaine on behavior and extracellular levels of dopamine and 3,4-dihydroxyphenylalanine in the nucleus accumbens of conscious rats

Enhancement of Haloperidol-Induced Catalepsy by GPR143, an L-Dopa Receptor, in Striatal Cholinergic Interneurons

Dopamine neurons play crucial roles in pleasure, reward, memory, learning, and fine motor skills and their dysfunction is associated with various neuropsychiatric diseases. Dopamine receptors are the main target of treatment for neurologic and psychiatric disorders. Antipsychotics that antagonize the dopamine D2 receptor (DRD2) are used to alleviate the symptoms of these disorders but may also sometimes cause disabling side effects such as parkinsonism (catalepsy in rodents). Here we show that GPR143, a G-protein-coupled receptor for L-3,4-dihydroxyphenylalanine (L-DOPA), expressed in striatal cholinergic interneurons enhances the DRD2-mediated side effects of haloperidol, an antipsychotic agent. Haloperidol-induced catalepsy was attenuated in male Gpr143 gene-deficient (Gpr143-/y ) mice compared with wild-type (Wt) mice. Reducing the endogenous release of L-DOPA and preventing interactions between GPR143 and DRD2 suppressed the haloperidol-induced catalepsy in Wt mice but not Gpr143-/y mice. The phenotypic defect in Gpr143-/y mice was mimicked in cholinergic interneuron-specific Gpr143-/y (Chat-cre;Gpr143flox/y ) mice. Administration of haloperidol increased the phosphorylation of ribosomal protein S6 at Ser240/244 in the dorsolateral striatum of Wt mice but not Chat-cre;Gpr143flox/y mice. In Chinese hamster ovary cells stably expressing DRD2, co-expression of GPR143 increased cell surface expression level of DRD2, and L-DOPA application further enhanced the DRD2 surface expression. Shorter pauses in cholinergic interneuron firing activity were observed after intrastriatal stimulation in striatal slice preparations from Chat-cre;Gpr143flox/y mice compared with those from Wt mice. Together, these findings provide evidence that GPR143 regulates DRD2 function in cholinergic interneurons and may be involved in parkinsonism induced by antipsychotic drugs.

Rho kinase inhibitors ameliorate cognitive impairment in a male mouse model of methamphetamine-induced schizophrenia

Schizophrenia (SCZ) is a severe psychiatric disorder characterized by positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic treatment in SCZ improves positive symptoms but has major side effects and little impact on negative symptoms and cognitive impairment. The pathoetiology of SCZ remains unclear, but is known to involve small GTPase signaling. Rho kinase, an effector of small GTPase Rho, is highly expressed in the brain and plays a major role in neurite elongation and neuronal architecture. This study used a touchscreen-based visual discrimination (VD) task to investigate the effects of Rho kinase inhibitors on cognitive impairment in a methamphetamine (METH)-treated male mouse model of SCZ. Systemic injection of the Rho kinase inhibitor fasudil dose-dependently ameliorated METH-induced VD impairment. Fasudil also significantly suppressed the increase in the number of c-Fos-positive cells in the infralimbic medial prefrontal cortex (infralimbic mPFC) and dorsomedial striatum (DMS) following METH treatment. Bilateral microinjections of Y-27632, another Rho kinase inhibitor, into the infralimbic mPFC or DMS significantly ameliorated METH-induced VD impairment. Two proteins downstream of Rho kinase, myosin phosphatase-targeting subunit 1 (MYPT1; Thr696) and myosin light chain kinase 2 (MLC2; Thr18/Ser19), exhibited increased phosphorylation in the infralimbic mPFC and DMS, respectively, after METH treatment, and fasudil inhibited these increases. Oral administration of haloperidol and fasudil ameliorated METH-induced VD impairment, while clozapine had little effect. Oral administration of haloperidol and clozapine suppressed METH-induced hyperactivity, but fasudil had no effect. These results suggest that METH activates Rho kinase in the infralimbic mPFC and DMS, which leads to cognitive impairment in male mice. Rho kinase inhibitors ameliorate METH-induced cognitive impairment, perhaps via the cortico-striatal circuit.

Methamphetamine enhances neural activation during anticipation of loss in the monetary incentive delay task

Stimulants like methamphetamine (MA) affect motivated behaviors via actions on circuits mediating mood, attention, and reward. Few studies examined the effects of single doses of stimulants on reward circuits during anticipation and receipt of rewards and losses. Here, we examined the effects of MA (20 mg) or placebo in a within-subject, double-blind study with healthy adults (n = 43). During 2 fMRI sessions, participants completed the monetary incentive delay task. Primary outcome measures were BOLD activation in selected regions of interest during anticipation and receipt of monetary rewards and losses. Secondary analyses included behavioral measures, whole brain analysis, and arterial spin labeling. MA produced its expected behavioral effects and increased neural activation in the ventral striatum and anterior insula during anticipation of monetary loss versus non-loss. MA did not affect activation during anticipation of gains, or during receipt of wins or losses. MA significantly reduced cerebral blood flow in the striatum and insula. The present finding that a stimulant enhances the responses of striatal and insular regions to upcoming loss suggests that this system may be sensitive to the salience of upcoming events. The finding adds to a complex body of evidence regarding the effects of stimulant drugs on neural processes during motivated behaviors.

Involvement of the L-DOPA receptor GPR143 in acute and chronic actions of methylphenidate

Methylphenidate (MPH) and methamphetamine (METH) are the current treatments of choice for attention deficit/hyperactivity disorder. We previously reported that METH induces the release of dopamine (DA) and of the neurotransmitter candidate L-3,4-dihydroxyphenylalanine (L-DOPA). In contrast, we here found that MPH increased the DA release while it did not affect the L-DOPA release from the dorsolateral striatum. Nevertheless, MPH-induced hyperlocomotion was reduced in Gpr143 (L-DOPA receptor) gene-deficient (Gpr143^-/y) mice. The rewarding effect and increased c-fos expression induced by MPH were also attenuated in Gpr143^-/y mice. Together, these findings suggest that GPR143 is involved in the acute and chronic actions of MPH.

Movement disorders associated with substance use in adults living in precarious housing or homelessness

OBJECTIVE

Many individuals living in precarious housing or homelessness have multimorbid illnesses, including substance use, psychiatric, and neurological disorders. Movement disorders (MDs) associated substance use are amongst the poorly studied subtopics of drug-induced MDs. The aim of the present study was, therefore, to determine the proportion affected and severity of different signs of MDs, as well as their associations with substance use in a community-based sample of precariously housed and homeless individuals.

METHODS

Participants were recruited from an impoverished urban neighborhood and were assessed for substance dependence and self-reported substance use (alcohol, cannabis, cocaine, methamphetamine, nicotine, and opioids), as well as for the severity of signs of MDs (akathisia, dyskinesia, dystonia, and parkinsonism). Adjusted regression models were used to estimate the associations of the severity of signs with the frequency of substance use over the past 4 weeks and with the baseline diagnosis of substance dependence.

RESULTS

The proportion of the sample with clinically relevant signs of MDs in any of the four categories was 18.6% (n = 401), and these participants demonstrated lower levels of functioning than those without signs. Of the different types of substance use, only methamphetamine (its frequency of use and dependence) was significantly associated with greater severity of overall signs of MDs. Frequency of methamphetamine use significantly interacted with age and sex, whereby older female participants exhibited the greatest overall severity with increased methamphetamine use. Of the different signs of MDs, methamphetamine use frequency was positively associated with the severity of trunk/limb dyskinesia and hypokinetic parkinsonism. Relative to no use, concurrent use of antipsychotics demonstrated lower severity of trunk/limb dyskinesia and greater severity of hypokinetic parkinsonism with methamphetamine use, and greater severity of dystonia with cocaine use.

CONCLUSIONS

Our study found a high proportion of MDs in a relatively young sample, and their severity was consistently associated with methamphetamine use, moderated by participant demographics and antipsychotic use. These disabling sequelae represent an important and understudied neurological condition that may affect quality of life and will require further study.

Sexual satiety modifies methamphetamine-induced locomotor and rewarding effects and dopamine-related protein levels in the striatum of male rats

RATIONALE

Drug and natural rewarding stimuli activate the mesolimbic dopaminergic system. Both methamphetamine (Meth) and copulation to satiety importantly increase dopamine (DA) release in the nucleus accumbens (NAc), but with differences in magnitude. This paper analyzes the interaction between Meth administration and the intense sexual activity associated with sexual satiety.

OBJECTIVES

To evaluate possible changes in Meth-induced behavioral effects and striatal DA-related protein expression due to sexual satiety.

METHODS

Meth-induced locomotor activity and conditioned place preference (CPP) were tested in sexually experienced male rats that copulated to satiety (S-S) or ejaculated once (1E) the day before or displayed no sexual activity (control group; C). DA receptors and DA transporter expression were determined by western blot in the striatum of animals of all sexual conditions treated with specific Meth doses.

RESULTS

Meth's locomotor and rewarding effects were exacerbated in S-S animals, while in 1E rats, only locomotor effects were enhanced. Sexual activity, by itself, modified DA-related protein expression in the NAc core and in the caudate-putamen (CPu), while Meth treatment alone changed their expression only in the NAc shell. Meth-induced changes in the NAc shell turned in the opposite direction when animals had sexual activity, and additional changes appeared in the NAc core and CPu of S-S rats.

CONCLUSION

Sexual satiety sensitizes rats to Meth's behavioral effects and the Meth-induced striatal DA-related protein adaptations are modified by sexual activity, evidencing cross-sensitization between both stimuli.

Effects of Moderate-Intensity Interval Training on Gene Expression and Antioxidant Status in the Hippocampus of Methamphetamine-Dependent Rats

Methamphetamine (METH) can cause neurotoxicity and increase the risk of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. This study aimed to investigate the effect of moderate-intensity interval training (MIIT) on gene expression and antioxidant status of the hippocampus of METH-dependent rats. Thirty-two male Wistar rats were randomly divided into four equal groups (n = 8): saline, METH, MIIT, and METH + MIIT. METH was injected intraperitoneally at 5 mg/kg for 21 days. The MIIT(interval running) was performed on the treadmill 5 days a week for 8 weeks. Morris water maze test was performed to measure learning and memory. Then, the hippocampal tissue was extracted to evaluate changes in gene expression and biochemical enzymes. The data were analyzed using one-way and two-way ANOVA methods at p < 0.05. The results showed that METH injection significantly reduced spatial memory and antioxidant enzymes and increased the expression of α-synuclein (α-syn), cyclin-dependent kinase 5 (CDK5), tau, and phosphorylated tau (p-tau) genes compared to the saline group. MIIT significantly increased spatial memory and antioxidant enzymes. However, it reduced α-syn, CDK5, tau, and p-tau expression. Thus, this study depicted that methamphetamine-dependent rats with memory deficits have lower antioxidant enzyme levels and higher expression of α-syn, CDK5, tau, and p-tau genes, and that an 8-week MIIT may have beneficial effects on the memory impairments as well as antioxidant status and gene expression in male rats.

The Many Faces of G Protein-Coupled Receptor 143, an Atypical Intracellular Receptor

GPCRs transform extracellular stimuli into a physiological response by activating an intracellular signaling cascade initiated via binding to G proteins. Orphan G protein-coupled receptors (GPCRs) hold the potential to pave the way for development of new, innovative therapeutic strategies. In this review we will introduce G protein-coupled receptor 143 (GPR143), an enigmatic receptor in terms of classification within the GPCR superfamily and localization. GPR143 has not been assigned to any of the GPCR families due to the lack of common structural motifs. Hence we will describe the most important motifs of classes A and B and compare them to the protein sequence of GPR143. While a precise function for the receptor has yet to be determined, the protein is expressed abundantly in pigment producing cells. Many GPR143 mutations cause X-linked Ocular Albinism Type 1 (OA1, Nettleship-Falls OA), which results in hypopigmentation of the eyes and loss of visual acuity due to disrupted visual system development and function. In pigment cells of the skin, loss of functional GPR143 results in abnormally large melanosomes (organelles in which pigment is produced). Studies have shown that the receptor is localized internally, including at the melanosomal membrane, where it may function to regulate melanosome size and/or facilitate protein trafficking to the melanosome through the endolysosomal system. Numerous additional roles have been proposed for GPR143 in determining cancer predisposition, regulation of blood pressure, development of macular degeneration and signaling in the brain, which we will briefly describe as well as potential ligands that have been identified. Furthermore, GPR143 is a promiscuous receptor that has been shown to interact with multiple other melanosomal proteins and GPCRs, which strongly suggests that this orphan receptor is likely involved in many different physiological actions.

Khat and neurobehavioral functions: A systematic review

Background

Khat is a plant that is used for its amphetamine-like stimulant properties. However, although khat is very popular in Eastern Africa, Arabian Peninsula, and the Middle East, there is still a lack of studies researching the possible neurobehavioral impairment derived from khat use.

Methods

A systematic review was conducted to identify studies that assessed the effects of khat use on neurobehavioral functions. MedLine, Scopus, Cochrane, Web of Science and Open Grey literature were searched for relevant publications from inception to December 2020. Search terms included (a) khat and (b) several cognitive domains. References from relevant publications and grey literature were also reviewed to identify additional citations for inclusion.

Results

A total of 142 articles were reviewed, 14 of which met the inclusion criteria (nine human and five rodent studies). Available human studies suggest that long term khat use is associated with significant deficits in several cognitive domains, including learning, motor speed/coordination, set-shifting/response inhibition functions, cognitive flexibility, short term/working memory, and conflict resolution. In addition, rodent studies indicated daily administration of khat extract resulted in dose-related impairments in behavior such as motor hyperactivity and decreased cognition, mainly learning and memory.

Conclusions

The findings presented in this review indicates that long-term khat use may be contributing to an impairment of neurobehavioral functions. However, gaps in literature were detected that future studies could potentially address to better understand the health consequences of khat use.

Distribution of mRNA for GPR143, a receptor of 3,4-L-dihydroxyphenylalanine, and of immunoreactivities for nicotinic acetylcholine receptors in the nigrostriatal and mesolimbic regions

Nicotine exerts its reinforcing actions by activating nicotinic acetylcholine receptors (nAChRs), but the detailed mechanisms remain unclear. Nicotine releases 3, 4-dihydroxyphenylalanine (DOPA), a neurotransmitter candidate in the central nervous system. Here, we investigated the distribution of GPR143, a receptor of DOPA, and nAChR subunits in the nigrostriatal and mesolimbic regions. We found GPR143 mRNA-positive cells in the striatum and nucleus accumbens. Some of them were surrounded by tyrosine hydroxylase (TH)-immunoreactive fibers. There were some GPR143 mRNA-positive cells coexpressing TH, and nAChR subunit α4 or α7 in the substantia nigra and ventral tegmental area. These findings suggest that DOPA-GPR143 signaling may be involved in the nicotine action in the nigrostriatal and mesolimbic dopaminergic systems.

Genetic associations of single nucleotide polymorphisms in the l-DOPA receptor (GPR143) gene with severity of nicotine dependence in Japanese individuals, and attenuation of nicotine reinforcement in Gpr143 gene-deficient mice

l-3,4-dihydroxyphenylalanine (l-DOPA) is a candidate neurotransmitter. l-DOPA is released by nicotine through nicotinic receptors. Recently, G-protein coupled receptor GPR143, was identified as a receptor for l-DOPA. In this study, genetic association studies between GPR143 genetic polymorphisms and smoking behaviors revealed that the single-nucleotide polymorphism rs6640499, in the GPR143 gene, was associated with traits of smoking behaviors in Japanese individuals. In Gpr143 gene-deficient mice, nicotine-induced hypolocomotion and rewarding effect were attenuated compared to those in wild-type mice. Our findings suggest the involvement of GPR143 in the smoking behaviors.

The consequences of regular methamphetamine use in Tehran: qualitative content analysis

BACKGROUND

In recent years, methamphetamine use has increased noticeably in Iran, and this can make harmful consequences for the health of individuals and society. Therefore, the study aimed to investigate the consequences of regular methamphetamine use in Tehran.

METHODS

This study was conducted based on a conventional content analysis approach. Data were collected through observation and in-depth interviews with 20 regular adult users of methamphetamine in Tehran (including 15 males and 5 females). Participants were selected using snowball sampling and purposeful sampling, which continued until data saturation. Guba and Lincoln's criteria were used to assess the strength of the study.

RESULTS

The extraction of the codes resulted in three main categories: (1)the short-term consequences, consisting of the sub-categories of individual and social consequences, (2) the long-term consequences, consisting of the sub-categories of psychological and physical consequences, high-risk behaviors, severely decayed memory and changes in the eating pattern, and (3) hallucinations and delusions including the sub-categories of visual and auditory hallucinations, persecutory delusions and delusion of having supernatural power.

CONCLUSION

Regular methamphetamine use may have serious adverse effects on the overall health of individuals. It is therefore highly recommended that educational programs must implement with the use of methamphetamine in the high- risk groups in order to raise awareness and change attitudes about the short and long term consequences. is highly recommended.

An Adenosine A2A Receptor Antagonist Improves Multiple Symptoms of Repeated Quinpirole-Induced Psychosis

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder characterized by the repeated rise of concerns (obsessions) and repetitive unwanted behavior (compulsions). Although selective serotonin reuptake inhibitors (SSRIs) is the first-choice drug, response rates to SSRI treatment vary between symptom dimensions. In this study, to find a therapeutic target for SSRI-resilient OCD symptoms, we evaluated treatment responses of quinpirole (QNP) sensitization-induced OCD-related behaviors in mice. SSRI administration rescued the cognitive inflexibility, as well as hyperactivity in the lateral orbitofrontal cortex (lOFC), while no improvement was observed for the repetitive behavior. D₂ receptor signaling in the central striatum (CS) was involved in SSRI-resistant repetitive behavior. An adenosine A_2A antagonist, istradefylline, which rescued abnormal excitatory synaptic function in the CS indirect pathway medium spiny neurons (MSNs) of sensitized mice, alleviated both of the QNP-induced abnormal behaviors with only short-term administration. These results provide a new insight into therapeutic strategies for SSRI-resistant OCD symptoms and indicate the potential of A_2A antagonists as a rapid-acting anti-OCD drug.

A Comparison of Methamphetamine-Induced Psychosis and Schizophrenia: A Review of Positive, Negative, and Cognitive Symptomatology

Methamphetamine is a potent psychostimulant that can induce psychosis among recreational and chronic users, with some users developing a persistent psychotic syndrome that shows similarities to schizophrenia. This review provides a comprehensive critique of research that has directly compared schizophrenia with acute and chronic METH psychosis, with particular focus on psychiatric and neurocognitive symptomatology. We conclude that while there is considerable overlap in the behavioral and cognitive symptoms between METH psychosis and schizophrenia, there appears to be some evidence that suggests there are divergent aspects to each condition, particularly with acute METH psychosis. Schizophrenia appears to be associated with pronounced thought disorder, negative symptoms more generally and cognitive deficits mediated by the parietal cortex, such as difficulties with selective visual attention, while visual and tactile hallucinations appear to be more prevalent in acute METH-induced psychosis. As such, acute METH psychosis may represent a distinct psychotic disorder to schizophrenia and could be clinically distinguished from a primary psychotic disorder based on the aforementioned behavioral and cognitive sequelae. Preliminary evidence, on the other hand, suggests that chronic METH psychosis may be clinically similar to that of primary psychotic disorders, particularly with respect to positive and cognitive symptomatology, although negative symptoms appear to be more pronounced in schizophrenia. Limitations of the literature and avenues for future research are also discussed.

A comparison of psychotic symptoms in subjects with methamphetamine versus cocaine dependence

RATIONALE

The psychostimulant drugs cocaine and methamphetamine are potent indirect dopamine receptor agonists which act through similar but not identical mechanisms. Studies in humans have observed that a large proportion of those who chronically use these drugs experience psychotic symptoms. However, direct comparisons of psychotic symptom severity between cocaine and methamphetamine users are lacking.

OBJECTIVES

The goal of the present study was to directly compare severity of psychotic symptoms between cocaine- and methamphetamine-dependent individuals. Additionally, we sought to determine how concurrent cocaine + methamphetamine dependence would influence psychotic symptoms.

METHODS

We recruited 153 polysubstance-using subjects meeting DSM-IV-TR criteria for cocaine dependence, 38 with methamphetamine dependence, and 32 with cocaine + methamphetamine dependence. Psychotic symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS) and analyzed using a five-factor model. All participants were also assessed for physical and mental illnesses as well as recent substance use. Most subjects completed a comprehensive neurocognitive battery.

RESULTS

While all three groups exhibited high total PANSS scores, the positive symptom subscale was significantly higher in the methamphetamine-dependent (17.03 ± 6.3) than the cocaine-dependent group (13.51 ± 4.12) and non-significantly higher (p = 0.08) than the cocaine + methamphetamine group (14.44 ± 5.50). Groups also differed on demographic variables, viral infection, and other indices of substance use, which were unlikely to account for the difference in positive symptoms. There were only modest differences between groups in neurocognitive function.

CONCLUSIONS

Methamphetamine dependence was associated with more severe positive symptoms of psychosis than cocaine dependence. Concurrent cocaine + methamphetamine dependence did not increase psychosis severity.

Subchronic oral administration of crude khat extract (Catha edulis forsk) induces schizophernic-like symptoms in mice

Background

Chewing fresh leaves of the khat plant (Catha edulis forsk) is a deep rooted and widespread habit in East Africa and the Middle East. Although a body of knowledge exists about the adverse effects of khat on health, data are sparse with regard to the consequences of long-term khat chewing in resulting schizophrenic like symptoms.

Methods

A crude extract of khat at different doses (100 mg/kg (K (khat)100), 200 mg/kg (K200) and 400 mg/kg (K400)) were administered for experimental group of mice whereas standard (ketamine (KT) 10 mg/kg- positive controls (KT10)) and vehicle (2 % v/v Tween-80 in distilled water – negative control groups (CON)) were administered for control groups of mice daily for two months to evaluate subchronic oral administration of crude khat extract to induce schizophrenic-like symptoms in mice. Mice were subjected to a battery of behavioural tests and parameters like locomotor activity, total time spent in social interaction and level of cognition among different groups of mice were measured and analyzed.

Results

Khat at all doses significantly increased (p < 0.001) the mean locomotor activity score of mice compared to CON. However, the mean locomotor activity score of mice treated with khat was significantly lower (p < 0.001) compared to the mean locomotor activity score of KT10 mice (p < 0.001).

The mean total time score (in seconds) spent in social interaction, mean total time score (in seconds) spent in sniffing and following the partner was significantly higher (p < 0.001) in CON groups of mice compared to khat and ketamine treated groups. Moreover, in spatial memory task, the mean latency score (in seconds) to find the platform of khat and ketamine treated mice was significantly higher (p < 0.05) when compared to CON.

Conclusions

Subchronic oral administration of khat showed an enhanced locomotor activity, reduced social interaction and impaired cognitive function, which demonstrated that long-term use of khat is associated with schizophernic-like symptoms.

Alcohol enhances the psychostimulant and conditioning effects of mephedrone in adolescent mice; postulation of unique roles of D3 receptors and BDNF in place preference acquisition

BACKGROUND AND PURPOSE

The psychostimulant mephedrone is often consumed in combination with alcohol (EtOH). This kind of drug consumption during adolescence is a matter of concern.

EXPERIMENTAL APPROACH

We studied, in adolescent CD-1 mice, whether EtOH could enhance the psychostimulant (locomotor acivity) and rewarding [conditioned place preference (CPP)] effects of mephedrone. We also determined the transcriptional changes associated with a conditioning treatment with these drugs.

KEY RESULTS

Mephedrone (10 mg·kg(-1)) increased locomotor activity, which was further enhanced by 40% when combined with EtOH (1 g·kg(-1)). This enhancement was blocked by haloperidol. Furthermore, mephedrone (25 mg·kg(-1)) induced CPP, which increased by 70% when administered with a dose of EtOH that was not conditioning by itself (0.75 g·kg(-1)). There was enhanced expression of the D3 dopamine receptor mRNA (Drd3) and Arpc5 in all drug-treated groups. The D3 receptor antagonist SB-277011A and the BDNF receptor antagonist ANA-12 completely prevented CPP as well as the increases in Drd3 in all groups. Accordingly, increased expression of BDNF mRNA in medial prefrontal cortex was detected at 2 and 4 h after mephedrone administration.

CONCLUSIONS AND IMPLICATIONS

If translated to humans, the enhancement of mephedrone effects by ethanol could result in increased abuse liability. D3 receptors and BDNF play a key role in the establishment of CPP by mephedrone, although an accompanying increase in other synaptic plasticity-related genes may also be necessary.

Comparative neuropharmacology of three psychostimulant cathinone derivatives: butylone, mephedrone and methylone

BACKGROUND AND PURPOSE

Here, we have compared the neurochemical profile of three new cathinones, butylone, mephedrone and methylone, in terms of their potential to inhibit plasmalemmal and vesicular monoamine transporters. Their interaction with 5-HT and dopamine receptors and their psychostimulant effect was also studied.

EXPERIMENTAL APPROACH

Locomotor activity was recorded in mice following different doses of cathinones. Monoamine uptake assays were performed in purified rat synaptosomes. Radioligand-binding assays were carried out to assess the affinity of these compounds for monoamine transporters or receptors.

KEY RESULTS

Butylone, mephedrone and methylone (5-25 mg·kg(-1) ) caused hyperlocomotion, which was prevented with ketanserin or haloperidol. Methylone was the most potent compound inhibiting both [(3) H]5-HT and [(3) H]dopamine uptake with IC(50) values that correlate with its affinity for dopamine and 5-HT transporter. Mephedrone was found to be the cathinone derivative with highest affinity for vesicular monoamine transporter-2 causing the inhibition of dopamine uptake. The affinity of cathinones for 5-HT(2A) receptors was similar to that of MDMA.

CONCLUSIONS AND IMPLICATIONS

Butylone and methylone induced hyperlocomotion through activating 5-HT(2A) receptors and increasing extra-cellular dopamine. They inhibited 5-HT and dopamine uptake by competing with substrate. Methylone was the most potent 5-HT and dopamine uptake inhibitor and its effect partly persisted after withdrawal. Mephedrone-induced hyperlocomotion was dependent on endogenous 5-HT. Vesicular content played a key role in the effect of mephedrone, especially for 5-HT uptake inhibition. The potency of mephedrone in inhibiting noradrenaline uptake suggests a sympathetic effect of this cathinone.

Behavioral changes and brain energy metabolism dysfunction in rats treated with methamphetamine or dextroamphetamine

Studies have demonstrated that AMPHs produce long-term damage to the brain dopaminergic, serotoninergic and glutamatergic regions. Prefrontal cortex, amygdala, hippocampus and striatum appear to be involved in the toxicity and behavioral changes induced by AMPHs. A single dose of AMPH causes mitochondrial dysfunction and oxidative stress in rat brain. The goal of the present study was thus to investigate the potency of two amphetamines, dextroamphetamine (d-AMPH) and methamphetamine (m-AMPH), on the behavior and energetic dysfunction in the brain of rats. d-AMPH and m-AMPH increased the crossing and rearing behaviors. The numbers of visits to the center were increased by d-AMPH and m-AMPH only at 2mg/kg. Likewise, at a high dose (2 mg/kg), the injection of m-AMPH increased the amount of sniffing. The AMPHs significantly decreased the activities of Krebs cycle enzymes (citrate synthase and succinate dehydrogenase) and mitochondrial respiratory chain complexes (I-IV); nevertheless, this effect varied depending on the brain region evaluated. In summary, this study demonstrated that at high doses, m-AMPH, increased stereotyped (sniffing) behavior in rats, but d-AMPH did not. However, this study shows that d-AMPH and m-AMPH seem to have similar effects on the brains energetic metabolism.

Powerful behavioral interactions between methamphetamine and morphine

Use of drugs of abuse in combination is common among recreational users and addicts. The combination of a psychomotor stimulant with an opiate, known as a 'speedball,' reportedly produces greater effects than either drug alone and has been responsible for numerous deaths. Historically, the most popular speedball combination is that of cocaine and heroin. However, with the growing popularity of methamphetamine in recent years, there has been increased use of this drug in combination with other drugs of abuse, including opiates. Despite this, relatively little research has examined interactions between methamphetamine and opiates. In the current research, behavioral interactions between methamphetamine and the prototypical opiate, morphine, were examined across a variety of dose combinations in Sprague-Dawley rats. The combination of methamphetamine and morphine produced stimulation of behavior that was dramatically higher than either drug alone; however, the magnitude of the interaction was dependent on the dose of the drugs and the specific behaviors examined. The results demonstrate complex behavioral interactions between these drugs, but are consistent with the idea that this combination is used because it produces a greater effect than either drug alone.

Inhibitory role of oxytocin in psychostimulant-induced psychological dependence and its effects on dopaminergic and glutaminergic transmission

Psychostimulants are frequently abused as a result of their stimulatory effects on several neurotransmitter systems within the central nervous system. Both dopaminergic and glutaminergic neurotransmissions have been closely associated with psychostimulant dependence. In addition to its classical endocrine function in the periphery, oxytocin, an important neurohypophyseal neuropeptide in the central nervous system, has a wide range of behavioral effects, including regulating drug abuse. The present paper reviews the progress of research into the role of oxytocin in reducing psychostimulant-induced psychological dependence and the mechanisms by which oxytocin mediates its effects.

Prenatal methamphetamine exposure affects the mesolimbic dopaminergic system and behavior in adult offspring

Methamphetamine is a commonly abused psychostimulant that causes addiction and is often abused by pregnant women. Acute or chronic administration of methamphetamine elevates the levels of the extracellular monoamine neurotransmitters, such as dopamine. The aim of the present study was to show whether prenatal exposure to methamphetamine (5mg/kg, entire gestation) or saline in Wistar rats induces changes in dopamine levels and its metabolites in the nucleus accumbens, and in behavior (locomotor activity, rearing, and immobility) after the administration of a challenge dose of methamphetamine (1mg/kg) or saline in male offspring. We found that adult offspring prenatally exposed to methamphetamine had higher basal levels of dopamine (about 288%), dihydroxyphenylacetic acid (about 67%) and homovanillic acid (about 74%) in nucleus accumbens. An increased basal level of dopamine corresponds to lower basal immobility in offspring prenatally exposed to methamphetamine. The acute injection of methamphetamine in adulthood increased the level of dopamine in the nucleus accumbens, which is related to an increase of locomotion and rearing (exploration). In addition, prenatally methamphetamine-exposed rats showed higher response to the challenge dose of methamphetamine, when compared to prenatally saline-exposed rats. In conclusion, rats exposed to methamphetamine in utero have shown changes in the mesolimbic dopaminergic system and were more sensitive to the administration of the acute dose of methamphetamine in adulthood.

Comparison of systemic and local methamphetamine treatment on acetylcholine and dopamine levels in the ventral tegmental area in the mouse

Acetylcholine (ACh) is an important mediator of dopamine (DA) release and the behavioral reinforcing characteristics of drugs of abuse in the mesocorticolimbic pathway. Within the ventral tegmental area (VTA), the interaction of DA with ACh appears to be integral in mediating motivated behaviors. However, the effects of methamphetamine on VTA ACh and DA release remain poorly characterized. The current investigation performed microdialysis to evaluate the effects of methamphetamine on extracellular levels of ACh and DA. Male C57BL/6J mice received an i.p. injection (saline, 2 mg/kg, or 5 mg/kg) and an intra-VTA infusion (vehicle, 100 microM or 1 mM) of methamphetamine. Locally perfused methamphetamine resulted in no change in extracellular ACh compared with vehicle, but caused a strong, immediate and dose-dependent increase in extrasynaptic DA levels (1240% and 2473% of baseline, respectively) during the 20-min pulse perfusion. An i.p. injection of methamphetamine increased extrasynaptic DA to 275% and 941% of baseline (2 mg/kg and 5 mg/kg, respectively). Systemic methamphetamine significantly increased ACh levels up to 275% of baseline for 40-60 min (2 mg/kg) and 397% of baseline for 40-160 min (5 mg/kg) after injection. ACh remained elevated above baseline for 2-3 h post injection, depending on the methamphetamine dose. Methamphetamine-induced locomotor activity was dose-dependently correlated with extrasynaptic VTA ACh, but not DA levels. These data suggest that methamphetamine acts in the VTA to induce a robust and short-lived increase in extracellular DA release but acts in an area upstream from the VTA to produce a prolonged increase in ACh release in the VTA. We conclude that methamphetamine may activate a recurrent loop in the mesocorticolimbic DA system to stimulate pontine cholinergic nuclei and produce a prolonged ACh release in the VTA.

DOPA cyclohexyl ester, a DOPA antagonist, blocks the depressor responses elicited by microinjections of nicotine into the nucleus tractus solitarii of rats

Nicotinic cholinergic receptors play a role in cardiovascular regulation in the lower brain stem. Herein, we present evidence that l-3,4-dihydroxyphenylalanine (DOPA), a putative neurotransmitter in the central nervous system, is involved in the depressor response to microinjection of nicotine into the nucleus tractus solitarii (NTS). Microinjection of nicotine into the medial area of the NTS led to decreases in arterial blood pressure and heart rate in anesthetized rats. Mecamylamine, a nicotinic receptor antagonist, microinjected into NTS, blocked the depressor and bradycardic responses to nicotine. Nicotine-induced depressor and bradycardic responses were blocked by DOPA cyclohexyl ester (DOPA CHE), an antagonist for DOPA. DOPA CHE did not modify the action of carbachol on excitatory postsynaptic potential in rat cortical slices. These results suggest that endogenous DOPA is involved in nicotine-induced depressor responses in the NTS of anesthetized rats.

Effects of nicotine, methamphetamine and cocaine on extracellular levels of acetylcholine in the interpeduncular nucleus of rats

There is increasing evidence that the cholinergic habenulo-interpeduncular pathway and the dopaminergic mesolimbic pathway may jointly mediate the reinforcing properties of addictive drugs. However, the effects of addictive drug on the functioning of the habenulo-interpeduncular pathway have not been well-characterized. Thus, several drugs of abuse (i.e., nicotine, cocaine, amphetamine) have been shown to alter the morphology of the habenulo-interpeduncular pathway, causing selective degeneration of the cholinergic neurons in this area. On the other hand, morphine was shown to alter the neurochemistry of the habenulo-interpeduncular pathway, inducing biphasic changes in acetylcholine release in the interpeduncular nucleus. In order to determine the effects of cocaine, amphetamine and nicotine on cholinergic neurotransmission in the habenulo-interpeduncular pathway, levels of acetylcholine were assessed during microdialysis in freely moving rats. Nicotine (0.1 and 0.4 mg/kg s.c.) produced a dose-dependent decrease in extracellular levels of acetylcholine, while methamphetamine (1 and 4 mg/kg i.p.) produced an increase in acetylcholine release in the interpeduncular nucleus. Cocaine (5 and 20 mg/kg i.p.) produced a biphasic effect on extracellular acetylcholine release, i.e., a low dose enhanced the release of acetylcholine and a high dose decreased its release. These results suggest that the habenulo-intepeduncular pathway may be a common target for drugs of abuse and, by modulating the mesolimbic pathway, may mediate unique aspects of the rewarding effects of different drugs.

A role for neuronal nicotinic acetylcholine receptors in ethanol-induced stimulation, but not cocaine- or methamphetamine-induced stimulation

RATIONALE

Cocaine (COC), ethanol (EtOH), and methamphetamine (MA) are widely abused substances and share the ability to induce behavioral stimulation in mice and humans. Understanding the biological basis of behavioral stimulation to COC, EtOH, and MA may provide a greater understanding of drug and alcohol abuse.

OBJECTIVES

In these studies we set out to determine if neuronal nicotinic acetylcholine receptors were involved in the acute locomotor responses to these drugs, our measure of behavioral stimulation.

METHODS

A panel of acetylcholine receptor antagonists was used to determine if nicotinic receptors were involved in EtOH- and psychostimulant-induced stimulation. We tested the effect of these drugs in genotypes of mice (FAST and DBA/2J) that are extremely sensitive to this drug effect. To determine which acetylcholine receptor subunits may be involved in this response, relative expression of the alpha3, alpha6, beta2, and beta4 subunit genes was examined in mice selectively bred for high and low response to EtOH.

RESULTS

Mecamylamine, but not hexamethonium, attenuated the acute locomotor response to EtOH. The acetylcholine receptor antagonist dihydro-beta-erythroidine and methyllycaconitine had no effect on this response. The alpha6 and beta4, but not alpha3 or beta2, subunits of the acetylcholine receptor were differentially expressed between mice bred for extreme differences in EtOH stimulation. Mecamylamine had no effect on psychostimulant-induced locomotor activity.

CONCLUSIONS

Neuronal nicotinic receptors are involved in EtOH, but not psychostimulant, stimulation. These studies suggest a lack of involvement of some nicotinic receptor subtypes, but more work is needed to determine the specific receptor subtypes involved in this behavior.

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.

Cocaine increases endoplasmic reticulum stress protein expression in striatal neurons

Cocaine administration upregulates the levels of extracellular glutamate and dopamine in the striatum. Activation of the receptors alters calcium homeostasis in striatal neurons leading to the expression of the endoplasmic reticulum (ER) stress proteins. It was therefore hypothesized that cocaine upregulates the expression of the ER stress proteins, immunoglobulin heavy chain binding protein (BiP), Ire1alpha and perk via glutamate and dopamine receptor activation. A novel glutamate microbiosensor and Western immunoblot analyses were mainly performed to test the hypothesis in the rat dorsal striatum. The results showed that i.p. injection of repeated cocaine (20 mg/kg) for nine consecutive days significantly increased extracellular glutamate levels while acute cocaine injection did not. However, the immunoreactivities (IR) of the ER stress proteins in the dorsal striatum were significantly increased by either acute or repeated cocaine injections as compared with saline controls. Intrastriatal injection (i.s.) of the selective group I metabotropic glutamate receptor (mGluR) antagonist N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC; 25 nmol) or the mGluR5 subtype antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP; 2 and 25 nmol) significantly decreased repeated cocaine-induced increases in the IR of the ER stress proteins in the injected dorsal striatum. Similarly, the selective D1 antagonist (R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH23390; 0.1 mg/kg, i.p.) or the N-methyl-d-aspartate antagonist dizocilpine/(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-ibenzo[a,d]cyclohepten-5,10-imine maleate (MK801; 2 nmol, i.s.) decreased acute or repeated cocaine-induced the IR of the ER stress proteins in the dorsal striatum. These data suggest that cocaine upregulates expression of the ER stress proteins in striatal neurons via a mechanism involving activation of glutamate and dopamine receptors.