Human methamphetamine pharmacokinetics simulated in the rat: single daily intravenous administration reveals elements of sensitization and tolerance

Development of a Semimechanistic Pharmacokinetic-Pharmacodynamic Model Describing Dextroamphetamine Exposure and Striatal Dopamine Response in Rats and Nonhuman Primates following a Single Dose of Dextroamphetamine

Acute central nervous system exposure to dextroamphetamine (d-amphetamine) elicits a multitude of effects, including dual action on the dopamine transporter (DAT) to increase extracellular dopamine, and induction of a negative feedback response to limit the dopamine increase. A semimechanistic pharmacokinetic and pharmacodynamic (PK/PD) model with consideration of these multiple effects as a basis was developed. Integrated pharmacokinetics of d-amphetamine in plasma, brain extracellular fluid (ECF) via microdialysis, and cerebrospinal fluid were characterized using a population approach. This PK model was then linked to an indirect-response pharmacodynamic model using as a basis the measurement of extracellular striatal dopamine, also via microdialysis. In both rats and nonhuman primates (NHPs), d-amphetamine stimulation of dopamine outflow (reverse transport) through DAT was primarily responsible for the dose-linear increase in dopamine. As well, in both species a moderator function was needed to account for loss of the dopamine response in the presence of a relatively sustained d-amphetamine ECF exposure, presumptive of an acute tolerance response. PK/PD model structure was consistent between species; however, there was a 10-fold faster return to baseline dopamine in NHPs in response to an acute d-amphetamine challenge. These results suggest preservation from rodents to NHPs regarding the mechanism by which amphetamine increases extracellular dopamine, but a faster system response in NHPs to tolerate this increase. This microdialysis-based PK/PD model suggests greater value in directing preclinical discovery of novel approaches that modify reverse transport stimulation to treat amphetamine abuse. General value regarding insertion of an NHP model in paradigm rodent-to-human translational research is also suggested.

Methamphetamine self-administration in a runway model of drug-seeking behavior in male rats

Cocaine administration has been shown to produce immediate positive (rewarding) and subsequent negative (anxiogenic) effects in humans and animals. These dual and opposing affective responses have been more difficult to demonstrate with administration of methamphetamine (meth). While animal studies have reliably demonstrated the positive reinforcing effects of the drug, reports of negative aftereffects following acute exposure have been few in number and contradictory in nature. The current research was devised to assess the effects of acute meth using a runway model of self-administration that is uniquely sensitive to both the positive and negative effects of a drug reinforcer in the same animal on the same trial. Male rats were allowed to traverse a straight alley once a day for 16 consecutive days/trials where entry into the goal box resulted in a single IV injection of meth (0.25, 0.5 or 1.0 mg/kg/inj.). The chosen doses were confirmed to be psychoactive as they produced dose-dependent increases in motoric/locomotor activation in these same subjects. The results demonstrated a U-shaped dose-response curve for the reinforcing effects of meth in that the intermediate dose group (0.5 mg/kg) produced the strongest approach behavior in the runway. Unlike other psychomotor stimulants, like cocaine, animals running for IV meth exhibited no evidence of any significant approach-avoidance behaviors reflective of the drug's negative anxiogenic effects. These results suggest that the abuse potential for meth is likely higher than for other shorter-acting psychomotor stimulants and reaffirms the utility of the runway procedure as a screen for a substance's abuse potential.

Methamphetamine Augments Concurrent Astrocyte Mitochondrial Stress, Oxidative Burden, and Antioxidant Capacity: Tipping the Balance in HIV-Associated Neurodegeneration

Methamphetamine (METH) use, with and without human immunodeficiency virus (HIV)-1 comorbidity, exacerbates neurocognitive decline. Oxidative stress is a probable neurotoxic mechanism during HIV-1 central nervous system infection and METH abuse, as viral proteins, antiretroviral therapy and METH have each been shown to induce mitochondrial dysfunction. However, the mechanisms regulating mitochondrial homeostasis and overall oxidative burden in astrocytes are not well understood in the context of HIV-1 infection and METH abuse. Here, we report METH-mediated dysregulation of astrocyte mitochondrial morphology and function during prolonged exposure to low levels of METH. Mitochondria became larger and more rod shaped with METH when assessed by machine learning, segmentation analyses. These changes may be mediated by elevated mitofusin expression coupled with inhibitory phosphorylation of dynamin-related protein-1, which regulate mitochondrial fusion and fission, respectively. While METH decreased oxygen consumption and ATP levels during acute exposure, chronic treatment of 1 to 2 weeks significantly enhanced both when tested in the absence of METH. Together, these changes significantly increased not only expression of antioxidant proteins, augmenting the astrocyte's oxidative capacity, but also oxidative damage. We propose that targeting astrocytes to reduce their overall oxidative burden and expand their antioxidant capacity could ultimately tip the balance from neurotoxicity towards neuroprotection.

Dopamine transporter (DAT) genetic hypofunction in mice produces alterations consistent with ADHD but not schizophrenia or bipolar disorder

ADHD, schizophrenia and bipolar disorder are psychiatric diseases with a strong genetic component which share dopaminergic alterations. Dopamine transporter (DAT) genetics might be potentially implicated in all these disorders. However, in contrast to DAT absence, the effects of DAT hypofunction especially in developmental trajectories have been scarcely addressed. Thus, we comprehensively studied DAT hypofunctional mice (DAT+/-) from adolescence to adulthood to disentangle DAT-dependent alterations in the development of psychiatric-relevant phenotypes. From pre-adolescence onward, DAT+/- displayed a hyperactive phenotype, while responses to external stimuli and sensorimotor gating abilities were unaltered. General cognitive impairments in adolescent DAT+/- were partially ameliorated during adulthood in males but not in females. Despite this, attentional and impulsivity deficits were evident in DAT+/- adult males. At the molecular level, DAT+/- mice showed a reduced expression of Homer1a in the prefrontal cortex, while other brain regions as well as Arc and Homer1b expression were mostly unaffected. Amphetamine treatments reverted DAT+/- hyperactivity and rescued cognitive deficits. Moreover, amphetamine shifted DAT-dependent Homer1a altered expression from prefrontal cortex to striatal regions. These behavioral and molecular phenotypes indicate that a genetic-driven DAT hypofunction alters neurodevelopmental trajectories consistent with ADHD, but not with schizophrenia and bipolar disorders.

Chronic methamphetamine exposure significantly decreases microglia activation in the arcuate nucleus

Methamphetamine is a powerful psychostimulant drug and its use and abuse necessitates a better understanding of its neurobiobehavioral effects. The acute effects of binge dosing of methamphetamine on the neurons in the CNS are well studied. However, the long-term effects of chronic, low-dose methamphetamine are less well characterized, especially in other cell types and areas outside of the major dopamine pathways. Mice were administered 5mg/kg/day methamphetamine for ten days and brain tissue was analyzed using histochemistry and image analysis. Increased microglia activity in the striatum confirmed toxic effects of methamphetamine in this brain region using this dosing paradigm. A significant decrease in microglia activity in the arcuate nucleus of the hypothalamus was observed with no effect noted on dopamine neurons in the arcuate nucleus. Given the importance of this area in homeostatic and neuroendocrine regulation, the current study highlights the need to more fully understand the systemic effects of chronic, low-dose methamphetamine use. The novel finding of microglia downregulation after chronic methamphetamine could lead to advances in understanding neuroinflammatory responses towards addiction treatment and protection from psychostimulant-induced neurotoxicity.

Effects of chronic methamphetamine on psychomotor and cognitive functions and dopamine signaling in the brain

Methamphetamine (MA) studies in animals usually involve acute, binge, or short-term exposure to the drug. However, addicts take substantial amounts of MA for extended periods of time. Here we wished to study the effects of MA exposure on brain and behavior, using an animal model analogous to this pattern of MA intake. MA doses, 4 and 8mg/kg/day, were based on previously reported average daily freely available MA self-administration levels. We examined the effects of 16 week MA treatment on psychomotor and cognitive function in the rat using open field and novel object recognition tests and we studied the adaptations of the dopaminergic system, using in vitro and in vivo receptor imaging. We show that chronic MA treatment, at doses that correspond to the average daily freely available self-administration levels in the rat, disorganizes open field activity, impairs alert exploratory behavior and anxiety-like state, and downregulates dopamine transporter in the striatum. Under these treatment conditions, dopamine terminal functional integrity in the nucleus accumbens is also affected. In addition, lower dopamine D1 receptor binding density, and, to a smaller degree, lower dopamine D2 receptor binding density were observed. Potential mechanisms related to these alterations are discussed.

Drug effects on responses to emotional facial expressions: recent findings

Many psychoactive drugs increase social behavior and enhance social interactions, which may, in turn, increase their attractiveness to users. Although the psychological mechanisms by which drugs affect social behavior are not fully understood, there is some evidence that drugs alter the perception of emotions in others. Drugs can affect the ability to detect, attend to, and respond to emotional facial expressions, which in turn may influence their use in social settings. Either increased reactivity to positive expressions or decreased response to negative expressions may facilitate social interaction. This article reviews evidence that psychoactive drugs alter the processing of emotional facial expressions using subjective, behavioral, and physiological measures. The findings lay the groundwork for better understanding how drugs alter social processing and social behavior more generally.

Potential Molecular Mechanisms on the Role of the Sigma-1 Receptor in the Action of Cocaine and Methamphetamine

The sigma-1 receptor (Sig-1R) is an endoplasmic reticulum membrane protein that involves a wide range of physiological functions. The Sig-1R has been shown to bind psychostimulants including cocaine and methamphetamine (METH) and thus has been implicated in the actions of those psychostimulants. For example, it has been demonstrated that the Sig-1R antagonists mitigate certain behavioral and cellular effects of psychostimulants including hyperactivity and neurotoxicity. Thus, the Sig-1R has become a potential therapeutic target of medication development against drug abuse that differs from traditional monoamine-related strategies. In this review, we will focus on the molecular mechanisms of the Sig-1R and discuss in such a manner with a hope to further understand or unveil unexplored relations between the Sig-1R and the actions of cocaine and METH, particularly in the context of cellular biological relevance.

An Acute Methamphetamine Injection Downregulates the Expression of Several Histone Deacetylases (HDACs) in the Mouse Nucleus Accumbens: Potential Regulatory Role of HDAC2 Expression

Methamphetamine (METH) administration alters gene expression in the nucleus accumbens (NAc). We recently demonstrated that an acute METH injection produced prolonged increases in the expression of immediate early genes in the NAc of HDAC2-deficient mice, suggesting that HDAC2 might be an important regulator of gene expression in the rodent brain. Here, we tested the possibility that HDAC2 deletion might also impact METH-induced changes in the expression of various HDAC classes in the NAc. Wild-type (WT) and HDAC2 knockout (KO) mice were given a METH (20 mg/kg) injection, and NAc tissue was collected at 1, 2, and 8 h post treatment. We found that METH decreased HDAC3, HDAC4, HDAC7, HDAC8, and HDAC11 mRNA expression but increased HDAC6 mRNA levels in the NAc of WT mice. In contrast, the METH injection increased HDAC3, HDAC4, HDAC7, HDAC8, and HDAC11 mRNA levels in HDAC2KO mice. These observations suggest that METH may induce large-scale transcriptional changes in the NAc by regulating the expression of several HDACs, in part, via HDAC2-dependent mechanisms since some of the HDACs showed differential responses between the two genotypes. Our findings further implicate HDACs as potential novel therapeutic targets for neurotoxic complications associated with the abuse of certain psychostimulants.

Relationship between discriminative stimulus effects and plasma methamphetamine and amphetamine levels of intramuscular methamphetamine in male rhesus monkeys

Methamphetamine is a globally abused drug that is metabolized to amphetamine, which also produces abuse-related behavioral effects. However, the contributing role of methamphetamine metabolism to amphetamine in methamphetamine's abuse-related subjective effects is unknown. This preclinical study was designed to determine 1) the relationship between plasma methamphetamine levels and methamphetamine discriminative stimulus effects and 2) the contribution of the methamphetamine metabolite amphetamine in the discriminative stimulus effects of methamphetamine in rhesus monkeys. Adult male rhesus monkeys (n=3) were trained to discriminate 0.18mg/kg intramuscular (+)-methamphetamine from saline in a two-key food-reinforced discrimination procedure. Time course of saline, (+)-methamphetamine (0.032-0.32mg/kg), and (+)-amphetamine (0.032-0.32mg/kg) discriminative stimulus effects were determined. Parallel pharmacokinetic studies were conducted in the same monkeys to determine plasma methamphetamine and amphetamine levels after methamphetamine administration and amphetamine levels after amphetamine administration for correlation with behavior in the discrimination procedure. Both methamphetamine and amphetamine produced full, ≥90%, methamphetamine-like discriminative stimulus effects. Amphetamine displayed a slightly, but significantly, longer duration of action than methamphetamine in the discrimination procedure. Both methamphetamine and amphetamine behavioral effects were related to methamphetamine and amphetamine plasma levels by a clockwise hysteresis loop indicating acute tolerance had developed to the discriminative stimulus effects. Furthermore, amphetamine levels after methamphetamine administration were absent when methamphetamine stimulus effects were greatest and peaked when methamphetamine discriminative stimulus effects returned to saline-like levels. Overall, these results demonstrate the methamphetamine metabolite amphetamine does not contribute to methamphetamine's abuse-related subjective effects.

CAMKII-conditional deletion of histone deacetylase 2 potentiates acute methamphetamine-induced expression of immediate early genes in the mouse nucleus accumbens

Methamphetamine (METH) produces increases in the expression of immediate early genes (IEGs) and of histone deacetylase 2 (HDAC2) in the rat nucleus accumbens (NAc). Here, we tested whether HDAC2 deletion influenced the effects of METH on IEG expression in the NAc. Microarray analyses showed no baseline differences in IEG expression between wild-type (WT) and HDAC2 knockout (KO) mice. Quantitative-PCR analysis shows that an acute METH injection produced time-dependent increases in mRNA levels of several IEGs in both genotypes. Interestingly, HDAC2KO mice displayed greater METH-induced increases in Egr1 and Egr2 mRNA levels measured at one hour post-injection. The levels of Fosb, Fra2, Egr1, and Egr3 mRNAs stayed elevated in the HDAC2KO mice 2 hours after the METH injection whereas these mRNAs had normalized in the WT mice. In WT mice, METH caused increased HDAC2 recruitment to the promoters some IEGs at 2 hours post injection. METH-induced prolonged increases in Fosb, Fra2, Egr1, and Egr3 mRNA levels in HDAC2KO mice were associated with increased enrichment of phosphorylated CREB (pCREB) on the promoters of these genes. Based on our observations, we hypothesize that HDAC2 may regulate the expression of these genes, in part, by prolonging the actions of pCREB in the mouse NAc.

The Effect of Prenatal Methamphetamine Exposure on Recognition Memory in Adult Rats

The use of methamphetamine (MA) among pregnant women is an increasing world-wide health problem. Prenatal MA exposure may cause changes in foetus but the exact effects have remained unclear. The aim of this study is to present the effect of prenatal MA exposure on recognition memory in adult rats. Adult female Wistar rats were injected daily with D-methamphetamine HCl (MA; 5 mg/kg, s.c.) during the entire gestation period. Control females were treated with saline in the same regime. Adult male offspring was administrated acutely by MA (1 mg/kg i.p.) or saline 30 minutes before beginning of an experiment. For testing recognition memory two tasks were chosen: Novel Object Recognition Test (NORT) and Object Location Test (OLT). Our results demonstrate that prenatally MA-exposed animals were worse in NORT independently on an acute administration of MA in adulthood. Prenatally MA-exposed rats did not deteriorate in OLT, but after acute administration of MA in adulthood, there was significant worsening compared to appropriate control. Prenatally saline-exposed offspring did not deteriorate in any test even after acute administration of MA. Our data suggest that prenatal MA exposure in rats cause impairment in recognition memory in adult offspring, but not in spatial memory. In addition, acute administration of MA to controls did not deteriorate either recognition or spatial memory.

Chronic wheel running-induced reduction of extinction and reinstatement of methamphetamine seeking in methamphetamine dependent rats is associated with reduced number of periaqueductal gray dopamine neurons

Exercise (physical activity) has been proposed as a treatment for drug addiction. In rodents, voluntary wheel running reduces cocaine and nicotine seeking during extinction, and reinstatement of cocaine seeking triggered by drug-cues. The purpose of this study was to examine the effects of chronic wheel running during withdrawal and protracted abstinence on extinction and reinstatement of methamphetamine seeking in methamphetamine dependent rats, and to determine a potential neurobiological correlate underlying the effects. Rats were given extended access to methamphetamine (0.05 mg/kg, 6 h/day) for 22 sessions. Rats were withdrawn and were given access to running wheels (wheel runners) or no wheels (sedentary) for 3 weeks after which they experienced extinction and reinstatement of methamphetamine seeking. Extended access to methamphetamine self-administration produced escalation in methamphetamine intake. Methamphetamine experience reduced running output, and conversely, access to wheel running during withdrawal reduced responding during extinction and, context- and cue-induced reinstatement of methamphetamine seeking. Immunohistochemical analysis of brain tissue demonstrated that wheel running during withdrawal did not regulate markers of methamphetamine neurotoxicity (neurogenesis, neuronal nitric oxide synthase, vesicular monoamine transporter-2) and cellular activation (c-Fos) in brain regions involved in relapse to drug seeking. However, reduced methamphetamine seeking was associated with running-induced reduction (and normalization) of the number of tyrosine hydroxylase immunoreactive neurons in the periaqueductal gray (PAG). The present study provides evidence that dopamine neurons of the PAG region show adaptive biochemical changes during methamphetamine seeking in methamphetamine dependent rats and wheel running abolishes these effects. Given that the PAG dopamine neurons project onto the structures of the extended amygdala, the present findings also suggest that wheel running may be preventing certain allostatic changes in the brain reward and stress systems contributing to the negative reinforcement and perpetuation of the addiction cycle.

Amphetamine-induced release of dopamine in primate prefrontal cortex and striatum: striking differences in magnitude and timecourse

The psychostimulant amphetamine (AMPH) is frequently used to increase catecholamine levels in attention disorders and positron emission tomography imaging studies. Despite the fact that most radiotracers for positron emission tomography studies are characterized in non-human primates (NHPs), data on regional differences of the effect of AMPH in NHPs are very limited. This study examined the impact of AMPH on extracellular dopamine (DA) levels in the medial prefrontal cortex and the caudate of NHPs using microdialysis. In addition to differences in magnitude, we observed striking differences in the temporal profile of extracellular DA levels between these regions that can likely be attributed to differences in the regulation of dopamine uptake and biosynthesis. The present data suggest that cortical DA levels may remain elevated longer than in the caudate which may contribute to the clinical profile of the actions of AMPH. Using microdialysis probes implanted in the cortex and caudate region of non-human primate brains, we observed in vivo differences in the magnitude and temporal profile of extracellular dopamine levels in response to intravenous amphetamine administration.

Mesocorticolimbic monoamine correlates of methamphetamine sensitization and motivation

Methamphetamine (MA) is a highly addictive psychomotor stimulant, with life-time prevalence rates of abuse ranging from 5–10% world-wide. Yet, a paucity of research exists regarding MA addiction vulnerability/resiliency and neurobiological mediators of the transition to addiction that might occur upon repeated low-dose MA exposure, more characteristic of early drug use. As stimulant-elicited neuroplasticity within dopamine neurons innervating the nucleus accumbens (NAC) and prefrontal cortex (PFC) is theorized as central for addiction-related behavioral anomalies, we used a multi-disciplinary research approach in mice to examine the interactions between sub-toxic MA dosing, motivation for MA and mesocorticolimbic monoamines. Biochemical studies of C57BL/6J (B6) mice revealed short- (1 day), as well as longer-term (21 days), changes in extracellular dopamine, DAT and/or D2 receptors during withdrawal from 10, once daily, 2 mg/kg MA injections. Follow-up biochemical studies conducted in mice selectively bred for high vs. low MA drinking (respectively, MAHDR vs. MALDR mice), provided novel support for anomalies in mesocorticolimbic dopamine as a correlate of genetic vulnerability to high MA intake. Finally, neuropharmacological targeting of NAC dopamine in MA-treated B6 mice demonstrated a bi-directional regulation of MA-induced place-conditioning. These results extend extant literature for MA neurotoxicity by demonstrating that even subchronic exposure to relatively low MA doses are sufficient to elicit relatively long-lasting changes in mesocorticolimbic dopamine and that drug-induced or idiopathic anomalies in mesocorticolimbic dopamine may underpin vulnerability/resiliency to MA addiction.

96-hour methamphetamine self-administration in male and female rats: a novel model of human methamphetamine addiction

Methamphetamine (MA) is a highly addictive psychostimulant drug of abuse for which no FDA-approved treatment exists. While high on MA, both male and female MA users report engaging in risky behaviors and are more likely to be involved in violent criminal activities and to engage in domestic and sexual violence. A unique aspect of MA is that it is typically used in binges. However, there is no animal model of MA self-administration that appears to represent a human MA self-administration binge. We recently developed a 96-hour MA self-administration paradigm in rats that more closely resembles how human MA users take the drug. Male and female rats were trained to self-administer MA for 96 consecutive hours for 5 weeks. Responding by female and male rats tended to escalate to binge-like behavior, as the animals responded continuously during their normal periods of activity as well as during their inactive periods for up to 72 h, followed by a crash of 6 or more hours. Thus, this 96-hour model of MA self-administration is a novel way to study MA addition in rats that may contribute to the development of improved treatments for recovering human MA users.

Methamphetamine use: a comprehensive review of molecular, preclinical and clinical findings

Methamphetamine (MA) is a highly addictive psychostimulant drug that principally affects the monoamine neurotransmitter systems of the brain and results in feelings of alertness, increased energy and euphoria. The drug is particularly popular with young adults, due to its wide availability, relatively low cost, and long duration of psychoactive effects. Extended use of MA is associated with many health problems that are not limited to the central nervous system, and contribute to increased morbidity and mortality in drug users. Numerous studies, using complementary techniques, have provided evidence that chronic MA use is associated with substantial neurotoxicity and cognitive impairment. These pathological effects of the drug, combined with the addictive properties of MA, contribute to a spectrum of psychosocial issues that include medical and legal problems, at-risk behaviors and high societal costs, such as public health consequences, loss of family support and housing instability. Treatment options include pharmacological, psychological or combination therapies. The present review summarizes the key findings in the literature spanning from molecular through to clinical effects.

Chronic co-administration of nicotine and methamphetamine causes differential expression of immediate early genes in the dorsal striatum and nucleus accumbens of rats

Nicotine and methamphetamine (METH) cause addiction by triggering neuroplastic changes in brain reward pathways though they each engage distinct molecular targets (nicotine receptors and dopamine transporters respectively). Addiction to both drugs is very prevalent, with the vast majority of METH users also being smokers of cigarettes. This co-morbid occurrence thus raised questions about potential synergistic rewarding effects of the drugs. However, few studies have investigated the chronic neurobiological changes associated with co-morbid nicotine and METH addiction. Here we investigated the effects of these two drugs alone and in combination on the expression of several immediate early genes (IEGs) that are sensitive to drug exposures. Chronic exposure to either nicotine or METH caused significant decreases in the expression of fosb, fra1, and fra2 in the nucleus accumbens (NAc) but not in the dorsal striatum whereas the drug combination increased fra2 expression in both structures. Except for junB mRNA levels that were decreased by the three drug treatments in the NAc, there were no significant changes in the Jun family members. Of the Egr family members, NAc egr2 expression was decreased after nicotine and the drug combination whereas NAc egr3 was decreased after METH and the drug combination. The drug combination also increased striatal egr3 expression. The Nr4a family member, nr4a2/nurr1, showed increased striatal expression after all three drug treatments, while striatal nr4a3/nor-1 expression was increased by the drug combination whereas NAc nr4a1/nurr77 was decreased by nicotine and the drug combination. These observations suggest that, when given in combination, the two drugs exert distinct effects on the expression of IEGs in dopaminergic projection areas from those elicited by each drug alone. The significance of these changes in IEG expression and in other molecular markers in fostering co-morbid METH and nicotine abuse needs to be further evaluated.

Alterations in the striatal dopamine system during intravenous methamphetamine exposure: effects of contingent and noncontingent administration

The continuing spread of methamphetamine (METH) abuse has stimulated research aimed at understanding consequences of its prolonged exposure. Alterations in nigrostriatal dopamine (DA) system parameters have been characterized in experimental studies after discontinuation of long-term METH but fewer studies have included similar assessments during METH exposure. Here, we report METH plasma pharmacokinetics and striatal DA system alterations in rat after noncontingent and contingent METH administration for 7.5 weeks. Escalating METH exposure was delivered by dynamic infusion (DI) that incorporated a "humanized" plasma METH half life or by intravenous self-administration (IVSA) that included binge intakes. Kinetic modeling of DI and IVSA for 24 h periods during the final week of METH exposure showed that plasma METH levels remained between 0.7 and 1.5 µM. Animals were sacrificed during their last METH administration for autoradiography assessment using [³H]ligands and D2 agonist-induced [³⁵S]GTPγS binding. DA transporter binding was decreased (DI, 34%; IVSA, 15%) while vesicular monoamine transporter binding and substantia nigra DA cell numbers were unchanged. Decreases were measured for D2 receptor (DI and IVSA, 15-20%) and [³⁵S]GTPγS binding (DI, 35%; IVSA, 18%). These similar patterns of DI and IVSA associated decreases in striatal DA markers reflect consequences of cumulative METH exposure and not the drug delivery method. For METH IVSA, individual differences were observed, yet each animal's total intake was similar within and across three 24-h binges. IVSA rodent models may be useful for identifying molecular mechanisms that are associated with METH binges in humans.

Development of stereotyped behaviors during prolonged escalation of methamphetamine self-administration in rats

RATIONALE

Experimental animal studies have shown that repeated administration of psychostimulants, such as methamphetamine (METH), results in an altered behavioral response profile, which includes the sensitization of both locomotor and stereotyped behaviors. Although sensitization of these behaviors has been characterized in detail during bolus, investigator-administered drug administration, little is known about the development or expression of stereotypies during psychostimulant self-administration.

OBJECTIVE/METHODS

The present study investigated in rats the expression of focused stereotyped behaviors during an extended access, escalation procedure of METH self-administration. Over several weeks during stepwise-extended daily access to METH (3, 6, and 12 h) followed by exposure to 24-h "binges," rats gradually increased daily drug intake.

RESULTS

During the escalation procedure, the rats' behavioral response evolved from locomotor activation to progressively more focused stereotypies, culminating in continuous oral behaviors (licking, gnawing, and chewing), interrupted only by episodic lever presses. Sensitization of stereotyped behaviors was evident, particularly with regard to oral behaviors that exhibited a more rapid onset and intensification in the apparent absence of greater drug intake.

CONCLUSIONS

Our data demonstrate that stepwise-extended daily access to METH (3, 6, 12, and 24 h) self-administration in rats closely approximates motivational, pharmacokinetic, as well as behavioral patterns of human METH abuse. The accompanied appearance of sensitization of intense focused stereotyped behaviors, which is probably a consequence of escalation of drug intake, resembles stereotypies associated with investigator-initiated METH administration and may parallel the development of stimulant-induced psychosis seen in human abusers.

Chronic pre-exposure to methamphetamine following 31 days of withdrawal impairs sexual performance but not sexual conditioning in male Japanese quail

In the current study, male quail were administered methamphetamine (3.0 or 5.6 mg/kg IP) or saline once daily for 10 days and locomotor activity was assessed. Following a 31-day withdrawal period, sexual conditioning trials were conducted such that a conditioned stimulus (CS) was presented prior to a copulatory opportunity with a female quail. Male quail treated with methamphetamine (5.6 mg/kg) showed a decrease in locomotor activity from Trial 1 to Trial 10 suggesting a potential tolerance effect. Following the 31-day withdrawal period, all male quail that received the CS paired with a copulatory opportunity showed enhanced approach to the CS, regardless of treatment history. Thus, chronic pre-exposure to methamphetamine did not alter sexual conditioning. In contrast, chronic pre-exposure to methamphetamine (3.0 mg/kg) decreased the frequency of successful copulations suggesting that it impaired sexual performance. The findings suggest that methamphetamine may differentially affect the neural circuitry involved in motivational systems compared with those involved in consummatory aspects of sexual behavior. These effects may last long after drug cessation.

Methods in drug abuse models: comparison of different models of methamphetamine paradigms

Methamphetamine (METH) is a widely abused psychomotor stimulant. Investigating the effects of METH use on the brain has been applied in different animal models, including rats, mice, and nonhuman primates. Human abuse of METH occurs in different paradigms ranging from episodes of binge abuse to chronic abuse over years; different animal models have been established to replicate these various patterns of human behavior. In this chapter, we discuss the different models of METH abuse, including the acute model which assesses the immediate effects of METH on the brain and chronic exposure model which simulates the more common long-term use observed in humans; additionally, two other relevant models, escalating dose paradigm and METH self-administration, are examined. In comparing the models, this chapter briefly considers the METH-induced neurotoxic effects associated with each METH administration paradigm and the behavioral changes observed.

Methamphetamine-induced locomotor changes are dependent on age, dose and genotype

Adolescence is a critical age for addiction formation as a large percentage of pathological drug-seeking behaviors manifest during this time. The extent to which the neurotoxic effects of drugs of abuse influence subsequent drug seeking behaviors and impulsivity is an understudied area of research. Methamphetamine (METH) is a widely abused drug that produces locomotor responses ranging from behavioral sensitization to tolerance, both of which are behaviors that may relate to risk of abuse. Here we investigated the effects of age, genotype, METH dose, including a neurotoxic dose, and METH metabolism on open-field activity (OFA) to gain insight into the complex disease of drug abuse. C57Bl/6 (B6), DBA/2 (D2), and 129S6SvEv/Tac (129) mouse strains were administered saline or either a high dose (4×5 mg/kg in 2 h intervals for 2 days) or low dose (2×1 mg/kg in 24 h intervals) METH pretreatment during adolescence (post natal day (PND) 40) or early adulthood (PND 80) followed by behavioral testing with a METH (1 mg/kg) or saline challenge 40 days later. Striatal concentrations of METH and AMPH were also determined. Significant findings include: 1) METH pretreated adolescent B6 mice displayed significant sensitization for horizontal locomotion due to high dose METH pretreatment; 2) METH pretreated B6 adults showed significant tolerance for the vertical activity measure caused by low dose METH pretreatment; 3) METH pretreated adult D2 mice exhibited significant sensitization for vertical activity induced by low dose METH pretreatment, and 4) 129 mice metabolized METH significantly faster than the B6 and D2 mice, but METH pretreatment did not alter metabolism. No significant behavioral responses to either METH pretreatment dose were observed for the D2 adolescent studies or either 129 age group. Our results highlight the importance of the interactions of age, strain and METH dose on locomotor behavioral outcomes.

Challenge dose of methamphetamine affects kainic acid-induced seizures differently depending on prenatal methamphetamine exposure, sex, and estrous cycle

Even though it is obvious that glutamate plays an important role in the effect of psychostimulants on seizures, the role of non-NMDA receptors remains uncertain. The aim of the present study was to determine whether acute methamphetamine (MA) administration changes sensitivity to seizures induced with kainic acid in prenatally MA-exposed adult rats. Adult male and female rats (prenatally MA exposed, prenatally saline exposed, and controls) were divided into groups that received a challenge dose (1mg/kg) of MA and groups that did not receive the MA challenge (saline injected). Systemic administration of 15 mg/kg kainic acid was used as a seizure model. Our results demonstrated that a single injection of MA (1mg/kg) affects kainic acid-induced seizures differently depending on prenatal exposure, sex, and female estrous cycle. Even though daily injections of MA (5mg/kg) in maternal rats did not have a long-term effect on susceptibility to seizures induced with kainic acid in adult progeny, sensitivity to the challenge dose of MA differed between the prenatal exposure groups.

Methamphetamine increases brain viral load and activates natural killer cells in simian immunodeficiency virus-infected monkeys

Methamphetamine (Meth) abuse increases risky behaviors that contribute to the spread of HIV infection. In addition, because HIV and Meth independently affect physiological systems including the central nervous system, HIV-induced disease may be more severe in drug users. We investigated changes in blood and brain viral load as well as differences in immune cells in chronically simian immunodeficiency virus-infected rhesus macaques that were either administered Meth or used as controls. Although Meth administration did not alter levels of virus in the plasma, viral load in the brain was significantly increased in Meth-treated animals compared with control animals. Meth treatment also resulted in an activation of natural killer cells. Given the prevalence of Meth use in HIV-infected and HIV at-risk populations, these findings reveal the likely untoward effects of Meth abuse in such individuals.

Effect of an electronic control device exposure on a methamphetamine-intoxicated animal model

OBJECTIVES

Because of the prevalence of methamphetamine abuse worldwide, it is not uncommon for subjects in law enforcement encounters to be methamphetamine-intoxicated. Methamphetamine has been present in arrest-related death cases in which an electronic control device (ECD) was used. The primary purpose of this study was to determine the cardiac effects of an ECD in a methamphetamine intoxication model.

METHODS

Sixteen anesthetized Dorset sheep (26-78 kg) received 0.0 mg/kg (control animals, n = 4), 0.5 mg/kg (n = 4), 1.0 mg/kg (n = 4), or 1.5 mg/kg (n = 4) of methamphetamine hydrochloride as a slow intravenous (IV) bolus during continuous cardiac monitoring. The animals received the following exposures in sequence from a TASER X26 ECD beginning at 30 minutes after the administration of the drug: 1) 5-second continuous exposure, 2) 15-second intermittent exposure, 3) 30-second intermittent exposure, and 4) 40-second intermittent exposure. Darts were inserted at the sternal notch and the cardiac apex, to a depth of 9 mm. Cardiac motion was determined by thoracotomy (smaller animals, < or = 32 kg) or echocardiography (larger animals, > 68 kg). Data were analyzed using descriptive statistics and chi-square tests.

RESULTS

Animals given methamphetamine demonstrated signs of methamphetamine toxicity with tachycardia, hypertension, and atrial and ventricular ectopy in the 30-minute period immediately after administration of the drug. Smaller animals (n = 8, < or = 32 kg, mean = 29.4 kg) had supraventricular dysrhythmias immediately after the ECD exposures. Larger animals (n = 8, > 68 kg, mean = 72.4) had only sinus tachycardia after the exposures. One of the smaller animals had frequent episodes of ventricular ectopy after two exposures, including runs of delayed onset, nonsustained six- to eight-beat unifocal and multifocal ventricular tachycardia that spontaneously resolved. This animal had significant ectopy prior to the exposures as well. Thoracotomy performed on three smaller animals demonstrated cardiac capture during ECD exposure consistent with previous animal studies. In the larger animals, none of the methamphetamine-intoxicated animals demonstrated cardiac capture. Two control sheep showed evidence of capture similar to the smaller animals. No ventricular fibrillation occurred after the exposure in any animal.

CONCLUSIONS

In smaller animals (32 kg or less), ECD exposure exacerbated atrial and ventricular irritability induced by methamphetamine intoxication, but this effect was not seen in larger, adult-sized animals. There were no episodes of ventricular fibrillation after exposure associated with ECD exposure in methamphetamine-intoxicated sheep.

Human methamphetamine pharmacokinetics simulated in the rat: behavioral and neurochemical effects of a 72-h binge

Bingeing is one pattern of high-dose methamphetamine (METH) abuse, which involves continuous drug taking over several days and can result in psychotic behaviors for which the brain pathology remains poorly defined. A corresponding animal model of this type of METH exposure may provide novel insights into the neurochemical and behavioral sequelae associated with this condition. Accordingly, to simulate the pharmacokinetic profile of a human METH binge exposure in rats, we used a computer-controlled, intravenous METH procedure (dynamic infusion, DI) to overcome species differences in METH pharmacokinetics and to replicate the human 12-h plasma METH half-life. Animals were treated over 13 weeks with escalating METH doses, using DI, and then exposed to a binge in which drug was administered every 3 h for 72 h. Throughout the binge, behavioral effects included unabated intense oral stereotypies in the absence of locomotion and in the absence of sleep. Decrements in regional brain dopamine, norepinephrine, and serotonin levels, measured at 1 and 10 h after the last injection of the binge, had, with the exception of caudate-putamen dopamine and frontal cortex serotonin, recovered by 48 h. At 10 h after the last injection of the binge, [(3)H]ligand binding to dopamine and vesicular monoamine transporters in caudate-putamen were reduced by 35 and 13%, respectively. In a separate METH binge-treated cohort, post-binge behavioral alterations were apparent in an attenuated locomotor response to a METH challenge infusion at 24 h after the last injection of the binge. Collectively, the changes we characterized during and after a METH binge suggest that for human beings under similar exposure conditions, multiple time-dependent neurochemical deficits contribute to their behavioral profiles.

Agmatine: identification and inhibition of methamphetamine, kappa opioid, and cannabinoid withdrawal in planarians

Agmatine blocks morphine physical dependence in mammals, but its effects on withdrawal signs caused by other abused drugs have been less studied. One of the reasons is that withdrawal to some of these drugs is difficult to quantify in mammals. An alternative to mammals is planarians, a type of flatworm. Planarians possess mammalian-like neurotransmitters and display withdrawal from amphetamines, benzodiazepines, cannabinoids, cocaine, and opioids. The withdrawal is manifested as a reduction in locomotor behavior following discontinuation of drug exposure. In the present study, our goal was to identify agmatine in planarians and to determine if planarians exposed to agmatine display withdrawal to methamphetamine, a cannabinoid receptor agonist (WIN 55,212-2), or a kappa-opioid receptor agonist (U-50,488H). Neurochemical experiments revealed that the concentration of agmatine in planarians was 185 +/- 33.7 pmol per mg of planarian weight (dry weight). In behavioral experiments, withdrawal (i.e., reduced locomotor activity) was observed when planarians exposed to each drug (10 microM) for 60 min were placed into water. The withdrawal was attenuated when methamphetamine- or U-50,488H-exposed planarians were tested in agmatine (100 microM). Withdrawal was inhibited similarly when planarians coexposed to agmatine (100 microM) plus methamphetamine (10 microM), WIN 55,212-2 (10 microM), or U-50,488H (10 microM) were tested in water. Arginine, the metabolic precursor to agmatine, was ineffective. Our results identify endogenous agmatine in planarians and demonstrate that agmatine exposure blocks withdrawal to three different drugs in planarians. This suggests that a change in agmatine signaling is a common mechanism in the withdrawal caused by these drugs, at least in planarians.

Prenatal lead exposure enhances methamphetamine sensitization in rats

Adult female rats were exposed to lead-free sodium acetate via gavage [0 mg (vehicle control)] or to 16 mg lead as lead acetate for 30 days prior to breeding. Following confirmation of breeding, the female animals continued to be exposed to their respective doses throughout gestation and lactation. When weaned, 16 control and 16 lead-exposed offspring were placed on regular water and food (lead-exposure was discontinued) until postnatal day (PND) 70. At this time, one-half of the control animals and one-half of the lead-treatment animals received intraperitoneal (i.p.) injections of the vehicle (saline) for 10 successive days and the remaining animals in each exposure conditions received daily injections of 1.0 mg/kg (+)-methamphetamine (METH) for 10 days (N=8/group). Locomotion in automated chambers was monitored daily for 45 min post-injection. Subsequently, during dose-effect testing, all animals received consecutive daily i.p. injections of 0, 1.0, 2.0, and then 4.0 mg/kg METH. The results of the experiment showed that both control and lead-exposed animals exhibited heightened locomotor activity (i.e. behavioral sensitization) to the repeated administration of 1.0 mg/kg METH. More importantly, animals developmentally (perinatally) exposed to lead showed more rapid sensitization than did their control counterparts. These data indicate that early lead exposure increases sensitivity to the locomotor-stimulating effects of METH. In contrast, identically exposed lead animals exhibit diminished METH dose-effect responding when tested in an intravenous (i.v.) self-administration paradigm [Rocha A., Valles R., Bratton G.R., Nation J.R. Developmental lead exposure alters methamphetamine self-administration in the male rat: acquisition and reinstatement. Drug Alcohol Depend 2008a;95:23-29, Rocha A., Valles R., Hart N., Bratton G.R., Nation J.R. Developmental lead exposure attenuates methamphetamine dose-effect self-administration performance and progressive ratio responding in the male rat. Pharmacol Biochem Behav 2008b;89:508-514].

The beta-lactam antibiotic ceftriaxone inhibits physical dependence and abstinence-induced withdrawal from cocaine, amphetamine, methamphetamine, and clorazepate in planarians

Ceftriaxone (a beta-lactam antibiotic) has recently been identified as having the rare ability to increase the expression and functional activity of the glutamate transporter subtype 1 (GLT-1) in rat spinal cord cultures. GLT-1 has been implicated in diverse neurological disorders and in opioid dependence and withdrawal. It has been speculated that it might also be involved in the physical dependence and withdrawal of other abused drugs, but demonstration of this property can be difficult in mammalian models. Here, we demonstrate for the first time using a planarian model that ceftriaxone attenuates both the development of physical dependence and abstinence-induced withdrawal from cocaine, amphetamine, methamphetamine, and a benzodiazepine (clorazepate) in a concentration-related manner. These results suggest that physical dependence and withdrawal from several drugs involve a common - beta-lactam-sensitive - mechanism in planarians. If these findings can be shown to extend to mammals, beta-lactam antibiotics might represent a novel pharmacotherapy or adjunct approach for treating drug abuse or serve as a template for drug discovery efforts aimed at treating drug abuse, recovery from drug abuse, or ameliorating the withdrawal from chronic use of therapeutic medications.

Differential neurochemical consequences of an escalating dose-binge regimen followed by single-day multiple-dose methamphetamine challenges

Chronic intake of methamphetamine (METH) causes tolerance to its behavioral and subjective effects. To better mimic human patterns of drug abuse, the present study used a rodent model that took into account various facets of human drug administration and measured METH-induced effects on brain monoamine levels. Adult male Sprague-Dawley rats were injected with METH or saline according to an escalating dose schedule for 2 weeks. This was followed by a challenge regimen of either saline or one of two doses of METH (3 x 10 mg/kg every 2 h or 6 x 5 mg/kg given every hour, both given within a single day). Both challenge doses of METH caused significant degrees of depletion of dopamine in the striatum and norepinephrine and serotonin in the striatum, cortex, and hippocampus. Animals pre-treated with METH showed significant attenuation of METH-induced striatal dopamine depletion but not consistent attenuation of norepinephrine and serotonin depletion. Unexpectedly, METH pre-treated animals that received the 3 x 10 mg/kg challenge showed less increases in tympanic temperatures than saline pre-treated rats whereas METH pre-treated animals that received the 6 x 5 mg/kg METH challenge showed comparable increases in temperatures to saline pre-treated rats. Therefore, pre-treatment-induced partial protection against monoamine depletion is probably not because of attenuated METH-induced hyperthermia in those rats.

Methamphetamine induces ectopic expression of tyrosine hydroxylase and increases noradrenaline levels within the cerebellar cortex

Methamphetamine produces locomotor activation and typical stereotyped motor patterns, which are commonly related with increased catecholamine activity within the basal ganglia, including the dorsal and ventral striatum. Since the cerebellum is critical for movement control, and for learning of motor patterns, we hypothesized that cerebellar catecholamines might be a target of methamphetamine. To test this experimental hypothesis we injected methamphetamine into C57 Black mice at the doses of 5 mg/kg two or three times, 2 h apart. This dosing regimen is known to be toxic for striatal dopamine terminals. However, we found that in the cerebellum, methamphetamine increased the expression of the primary transcript of the tyrosine hydroxylase (TH) gene, followed by an increased expression of the TH protein. Increased TH was localized within Purkinje cells, where methamphetamine increased the number of TH-immunogold particles, and produced a change in the distribution of the enzyme by increasing the cytoplasmic percentage. Increased TH expression was accompanied by a slight increase in noradrenaline content. This effect was highly site-specific for the cortex of posterior vermal lobules, while only slight effects were detectable in the hemispheres. The present data indicate that the cerebellum does represent a target of methamphetamine, which produces specific and fine alterations of the catecholamine system involving synthesis, amount, and compartmentalization of TH as well as increased noradrenaline levels. This may be relevant for motor alterations induced by methamphetamine. In line with this, inherited cerebellar movement disorders in various animal species including humans are associated with increased TH immunoreactivity within intrinsic neurons of the same lobules of the cerebellar cortex.

Long-term effects of a single adult methamphetamine challenge: minor impact on dopamine fibre density in limbic brain areas of gerbils

BACKGROUND

The aim of the study was to test long-term effects of (+)-methamphetamine (MA) on the dopamine (DA) innervation in limbo-cortical regions of adult gerbils, in order to understand better the repair and neuroplasticity in disturbed limbic networks.

METHODS

Male gerbils received a single high dose of either MA (25 mg/kg i.p.) or saline on postnatal day 180. On postnatal day 340 the density of immunoreactive DA fibres and calbindin and parvalbumin cells was quantified in the right hemisphere.

RESULTS

No effects were found in the prefrontal cortex, olfactory tubercle and amygdala, whereas the pharmacological impact induced a slight but significant DA hyperinnervation in the nucleus accumbens. The cell densities of calbindin (CB) and parvalbumin (PV) positive neurons were additionally tested in the nucleus accumbens, but no significant effects were found. The present results contrast with the previously published long-term effects of early postnatal MA treatment that lead to a restraint of the maturation of DA fibres in the nucleus accumbens and prefrontal cortex and a concomitant overshoot innervation in the amygdala.

CONCLUSION

We conclude that the morphogenetic properties of MA change during maturation and aging of gerbils, which may be due to physiological alterations of maturing vs. mature DA neurons innervating subcortical and cortical limbic areas. Our findings, together with results from other long-term studies, suggest that immature limbic structures are more vulnerable to persistent effects of a single MA intoxication; this might be relevant for the assessment of drug experience in adults vs. adolescents, and drug prevention programs.