A Mouse Model for Binge-Level Methamphetamine Use

Neuropharmacological Evidence Implicating Drug-Induced Glutamate Receptor Dysfunction in Affective and Cognitive Sequelae of Subchronic Methamphetamine Self-Administration in Mice

Methamphetamine (MA) is a highly addictive drug, and MA use disorder is often comorbid with anxiety and cognitive impairment. These comorbid conditions are theorized to reflect glutamate-related neurotoxicity within the frontal cortical regions. However, our prior studies of MA-sensitized mice indicate that subchronic, behaviorally non-contingent MA treatment is sufficient to dysregulate glutamate transmission in mouse brain. Here, we extend this prior work to a mouse model of high-dose oral MA self-administration (0.8, 1.6, or 3.2 g/L; 1 h sessions × 7 days) and show that while female C57BL/6J mice consumed more MA than males, MA-experienced mice of both sexes exhibited some signs of anxiety-like behavior in a behavioral test battery, although not all effects were concentration-dependent. No MA effects were detected for our measures of visually cued spatial navigation, spatial learning, or memory in the Morris water maze; however, females with a history of 3.2 g/L MA exhibited reversal-learning deficits in this task, and mice with a history of 1.6 g/L MA committed more working-memory incorrect errors and relied upon a non-spatial navigation strategy during the radial-arm maze testing. Relative to naïve controls, MA-experienced mice exhibited several changes in the expression of certain glutamate receptor-related proteins and their downstream effectors within the ventral and dorsal areas of the prefrontal cortex, the hippocampus, and the amygdala, many of which were sex-selective. Systemic pretreatment with the mGlu1-negative allosteric modulator JNJ 162596858 reversed the anxiety-like behavior expressed by MA-experienced mice in the marble-burying test, while systemic pretreatment with NMDA or the NMDA antagonist MK-801 bi-directionally affected the MA-induced reversal-learning deficit. Taken together, these data indicate that a relatively brief history of oral MA is sufficient to induce some signs of anxiety-like behavior and cognitive dysfunction during early withdrawal that reflect, at least in part, MA-induced changes in the corticolimbic expression of certain glutamate receptor subtypes of potential relevance to treating symptoms of MA use disorder.

Maternal use of methamphetamine alters cardiovascular function in the adult offspring

Methamphetamine is one of the most commonly used illicit drugs during pregnancy. Most studies investigating the impact of maternal use of methamphetamine on children have focused on neurological outcomes. In contrast, cardiovascular outcomes in these children have not been characterized. Recent studies in rodents provide evidence that prenatal exposure to methamphetamine induces changes in cardiac gene expression, changes in the heart's susceptibility to ischemic injury, and changes in vascular function that may increase the risk of developing cardiovascular disorders later in life. Importantly, these changes are sex-dependent. This review summarizes our current understanding of how methamphetamine use during pregnancy impacts the cardiovascular function of adult offspring and highlights gaps in our knowledge of the potential cardiovascular risks associated with prenatal exposure to methamphetamine.

Methamphetamine causes cardiovascular dysfunction via cystathionine gamma lyase and hydrogen sulfide depletion

Methamphetamine (METH) is an addictive illicit drug used worldwide that causes significant damage to blood vessels resulting in cardiovascular dysfunction. Recent studies highlight increased prevalence of cardiovascular disease (CVD) and associated complications including hypertension, vasospasm, left ventricular hypertrophy, and coronary artery disease in younger populations due to METH use. Here we report that METH administration in a mouse model of 'binge and crash' decreases cardiovascular function via cystathionine gamma lyase (CSE), hydrogen sulfide (H2S), nitric oxide (NO) (CSE/H2S/NO) dependent pathway. METH significantly reduced H2S and NO bioavailability in plasma and skeletal muscle tissues co-incident with a significant reduction in flow-mediated vasodilation (FMD) and blood flow velocity revealing endothelial dysfunction. METH administration also reduced cardiac ejection fraction (EF) and fractional shortening (FS) associated with increased tissue and perivascular fibrosis. Importantly, METH treatment selectively decreased CSE expression and sulfide bioavailability along with reduced eNOS phosphorylation and NO levels. Exogenous sulfide therapy or endothelial CSE transgenic overexpression corrected cardiovascular and associated pathological responses due to METH implicating a central molecular regulatory pathway for tissue pathology. These findings reveal that therapeutic intervention targeting CSE/H2S bioavailability may be useful in attenuating METH mediated cardiovascular disease.

Midazolam, methamphetamine, morphine and nicotine intake in high‐drinking‐in‐the‐dark mice

The high-drinking-in-the-dark (HDID) lines of mice were selectively bred for achieving high blood alcohol levels in the drinking-in-the-dark (DID) task and have served as a unique genetic risk model for binge-like alcohol intake. However, little is known about their willingness to consume other addictive drugs. Here, we examined (a) whether the HDID-1 and HDID-2 lines of mice would voluntarily consume midazolam, methamphetamine, morphine and nicotine in a DID test and (b) whether the HDID lines differ from their founders, heterogeneous stock/Northport (HS/NPT), in consumption levels of these drugs at the concentrations tested. Separate groups of HDID-1, HDID-2 and HS/NPT mice were given 4 days of access to each drug, using the single-bottle, limited-access DID paradigm. Male and female mice of both HDID lines consumed all four offered drugs. We observed no genotype differences in 40 μg/ml methamphetamine intake, but significant differences in nicotine, midazolam and morphine intake. Both HDID lines drank significantly more (150 μg/ml) midazolam than their founders, providing strong support for a shared genetic contribution to binge ethanol and midazolam intake. HDID-2 mice, but not HDID-1 mice, consumed more morphine (700 μg/ml) and more nicotine across a range of concentrations than HS/NPT mice. These results demonstrate that the HDID mice can be utilized for tests of voluntary drug consumption other than ethanol and highlight potentially important differences between HDID lines in risk for elevated drug intake.

Effects and associated transcriptomic landscape changes of methamphetamine on immune cells

Background

Methamphetamine (METH) abuse causes serious health problems, including injury to the immune system, leading to increased incidence of infections and even making withdrawal more difficult. Of course, immune cells, an important part of the immune system, are also injured in methamphetamine abuse. However, due to different research models and the lack of bioinformatics, the mechanism of METH injury to immune cells has not been clarified.

Methods

We examined the response of three common immune cell lines, namely Jurkat, NK-92 and THP-1 cell lines, to methamphetamine by cell viability and apoptosis assay in vitro, and examined their response patterns at the mRNA level by RNA-sequencing. Differential expression analysis of two conditions (control and METH treatment) in three types of immune cells was performed using the DESeq2 R package (1.20.0). And some of the differentially expressed genes were verified by qPCR. We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of differentially expressed genes by the clusterProfiler R package (3.14.3). And gene enrichment analysis was also performed using MetaScape (www.metascape.org).

Results

The viability of the three immune cells was differentially affected by methamphetamine, and the rate of NK-cell apoptosis was significantly increased. At the mRNA level, we found disorders of cholesterol metabolism in Jurkat cells, activation of ERK1 and ERK2 cascade in NK-92 cells, and disruption of calcium transport channels in THP-1 cells. In addition, all three cells showed changes in the phospholipid metabolic process.

Conclusions

The results suggest that both innate and adaptive immune cells are affected by METH abuse, and there may be commonalities between different immune cells at the transcriptome level. These results provide new insights into the potential effects by which METH injures the immune cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01295-9.

Combined prior chronic methamphetamine treatment and gp120 expression reduce PPI in aged male but not female mice

Methamphetamine (METH) use disorder is highly prevalent among people with HIV and is a significant public health problem. Furthermore, people with HIV are living longer and using drugs such as METH even into old age, making it important to understand the effects of METH use and aging in this population. HIV, METH, and aging negatively impact a variety of brain functions, including sensorimotor gating (i.e. - automatic, pre-conscious information processing). Sensorimotor gating is often measured using prepulse inhibition (PPI), a paradigm that can be conducted in animals, thereby allowing for preclinical studies. Little is known about how HIV, METH, and aging interact to affect PPI. The goal of this study was therefore to examine how METH affects PPI in aged gp120 mice, a mouse model of HIV. PPI was measured at 8, 14, and 22 months in male and female wild type (WT) and gp120 mice. PPI was also measured during and after METH treatment at 23-24 months. Aging was associated with decreased PPI in both sexes and genotypes. Combined prior METH treatment and gp120 expression caused the greatest reduction in PPI in aged male mice. Prior METH treatment decreased PPI in aged WT female mice, but not aged gp120 female mice. Overall, these results suggest the effects of HIV and METH on information processing seem to be influenced by age and sex. Combined HIV and METH may impair information processing in older men, but not older women.

Prenatal methamphetamine exposure causes dysfunction in glucose metabolism and low birthweight

Methamphetamine (METH) is a psychostimulant drug that induces addiction. Previous epidemiological studies have demonstrated that maternal METH abuse during pregnancy causes low birthweight (LBW) in the offspring. As a source of essential nutrients, in particular glucose, the placenta plays a key role in fetal development. LBW leads to health problems such as obesity, diabetes, and neurodevelopmental disorders (NDDs). However, the detailed mechanism underlying offspring's LBW and health hazards caused by METH are not fully understood. Therefore, we investigated the effects of prenatal METH exposure on LBW and fetal-placental relationship by focusing on metabolism. We found dysfunction of insulin production in the pancreas of fetuses exposed to METH. We also found a reduction of the glycogen cells (GCs) storing glycogens in the junctional zone of placenta, all of which suggest abnormal glucose metabolism affects the fetal development. These results suggest that dysfunction in fetal glucose metabolism may cause LBW and future health hazards. Our findings provide novel insights into the cause of LBW via the fetal-placental crosstalk.

A Zebrafish Model of Neurotoxicity by Binge-Like Methamphetamine Exposure

Hyperthermia is a common confounding factor for assessing the neurotoxic effects of methamphetamine (METH) in mammalian models. The development of new models of methamphetamine neurotoxicity using vertebrate poikilothermic animals should allow to overcome this problem. The aim of the present study was to develop a zebrafish model of neurotoxicity by binge-like methamphetamine exposure. After an initial testing at 20 and 40 mg/L for 48 h, the later METH concentration was selected for developing the model and the effects on the brain monoaminergic profile, locomotor, anxiety-like and social behaviors as well as on the expression of key genes of the catecholaminergic system were determined. A concentration- and time-dependent decrease in the brain levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) was found in METH-exposed fish. A significant hyperactivity was found during the first hour of exposure, followed 3 h after by a positive geotaxis and negative scototaxis in the novel tank and in the light/dark paradigm, respectively. Moreover, the behavioral phenotype in the treated fish was consistent with social isolation. At transcriptional level, th1 and slc18a2 (vmat2) exhibited a significant increase after 3 h of exposure, whereas the expression of gfap, a marker of astroglial response to neuronal injury, was strongly increased after 48 h exposure. However, no evidences of oxidative stress were found in the brain of the treated fish. Altogether, this study demonstrates the suitability of the adult zebrafish as a model of METH-induced neurotoxicity and provides more information about the biochemical and behavioral consequences of METH abuse.

Voluntary oral methamphetamine increases memory deficits and contextual sensitization during abstinence associated with decreased PKMζ and increased κOR in the hippocampus of female mice

BACKGROUND

Female populations exhibit vulnerabilities to psychostimulant addiction, as well as cognitive dysfunction following bouts of abuse.

AIMS

The goal for this study was to advance our understanding of the mechanisms that produce sex disparities in drug addiction.

METHODS

We used an animal model for voluntary oral methamphetamine administration (VOMA) and focused on male and female mice that consumed 7.6-8.2 mg/kg of methamphetamine (MA) per day during the last 18 days of the paradigm.

RESULTS

The VOMA-exposed female mice displayed increased locomotor activity in the drug-administration context compared to male mice, demonstrating sex-specific changes in contextual sensitization. During 2 weeks of forced abstinence, mice underwent further behavioral testing. We show that abstinence increased open-arm entries on the elevated plus maze in both sexes. There were no differences in immobility on the tail suspension test. In a hippocampal-dependent radial arm maze task, VOMA-treated female mice, but not male mice, showed working memory deficits. Hippocampal tissue was collected and analyzed using Western blotting. VOMA-exposed female mice exhibited increased kappa opioid receptor (κOR) expression in the hippocampus compared to male mice, suggesting a vulnerability toward abstinence-induced dysphoria. Female VOMA mice also exhibited a decrease in the memory protein marker, protein kinase M zeta (PKMζ), in the hippocampus.

CONCLUSIONS

Our study reveals sex-specific effects following abstinence from chronic MA consumption on hippocampal κOR and PKMζ expression, suggesting that these neural changes in female mice may underlie spatial memory deficits and identify an increased susceptibility to dysregulated neural mechanisms. These data validate VOMA as a model sensitive to sex differences in behavior and hippocampal neurochemistry following chronic MA exposure.

Confirmation of a Causal Taar1 Allelic Variant in Addiction-Relevant Methamphetamine Behaviors

Sensitivity to rewarding and reinforcing drug effects has a critical role in initial use, but the role of initial aversive drug effects has received less attention. Methamphetamine effects on dopamine re-uptake and efflux are associated with its addiction potential. However, methamphetamine also serves as a substrate for the trace amine-associated receptor 1 (TAAR1). Growing evidence in animal models indicates that increasing TAAR1 function reduces drug self-administration and intake. We previously determined that a non-synonymous single nucleotide polymorphism (SNP) in Taar1 predicts a conformational change in the receptor that has functional consequences. A Taar1 ^m1J mutant allele existing in DBA/2J mice expresses a non-functional receptor. In comparison to mice that possess one or more copies of the reference Taar1 allele (Taar1 ^+/+ or Taar1 ^+/m1J ), mice with the Taar1 ^m1J/m1J genotype readily consume methamphetamine, express low sensitivity to aversive effects of methamphetamine, and lack sensitivity to acute methamphetamine-induced hypothermia. We used three sets of knock-in and control mice in which one Taar1 allele was exchanged with the alternative allele to determine if other methamphetamine-related traits and an opioid trait are impacted by the same Taar1 SNP proven to affect MA consumption and hypothermia. First, we measured sensitivity to conditioned rewarding and aversive effects of methamphetamine to determine if an impact of the Taar1 SNP on these traits could be proven. Next, we used multiple genetic backgrounds to study the consistency of Taar1 allelic effects on methamphetamine intake and hypothermia. Finally, we studied morphine-induced hypothermia to confirm prior data suggesting that a gene in linkage disequilibrium with Taar1, rather than Taar1, accounts for prior observed differences in sensitivity. We found that a single SNP exchange reduced sensitivity to methamphetamine conditioned reward and increased sensitivity to conditioned aversion. Profound differences in methamphetamine intake and hypothermia consistently corresponded with genotype at the SNP location, with only slight variation in magnitude across genetic backgrounds. Morphine-induced hypothermia was not dependent on Taar1 genotype. Thus, Taar1 genotype and TAAR1 function impact multiple methamphetamine-related effects that likely predict the potential for methamphetamine use. These data support further investigation of their potential roles in risk for methamphetamine addiction and therapeutic development.

Effects of naltrexone on alcohol, sucrose, and saccharin binge-like drinking in C57BL/6J mice: a study with a multiple bottle choice procedure

Chronic alcohol (ethyl alcohol, EtOH) binging has been associated with long-term neural adaptations that lead to the development of addiction. Many of the neurobiological features of EtOH abuse are shared with other forms of binging, like pathological feeding. The drinking-in-the-dark (DID) paradigm has been used extensively to study the neurobiology of EtOH binge-like drinking due to its ability to promote high intakes relevant to human behavior. DID can also generate high consumption of other tastants, but this procedure has not been fully adapted to study forms of binging behavior that are not alcohol-driven. In the present study, we used a modified version of DID that uses multiple bottle availability to promote even higher levels of EtOH drinking in male C57BL/6J mice and allows a thorough investigation of tastant preferences. We assessed whether administration of systemic naltrexone could reduce binging on EtOH, sucrose, and saccharin separately as well as in combination. Our multiple bottle DID procedure resulted in heightened levels of consumption compared with previously reported data using this task. We found that administration of the opioid receptor antagonist naltrexone reduced intakes of preferred, highly concentrated EtOH, sucrose, and saccharin. We also report that naltrexone was able to reduce overall intakes when animals were allowed to self-administer EtOH, sucrose, or saccharin in combination. Our modified DID procedure provides a novel approach to study binging behavior that extends beyond EtOH to other tastants (i.e. sucrose and artificial sweeteners), and has implications for the study of the neuropharmacology of binge drinking.

Non-genetic factors that influence methamphetamine intake in a genetic model of differential methamphetamine consumption

RATIONALE

Genetic and non-genetic factors influence substance use disorders. Our previous work in genetic mouse models focused on genetic factors that influence methamphetamine (MA) intake. The current research examined several non-genetic factors for their potential influence on this trait.

OBJECTIVES

We examined the impact on MA intake of several non-genetic factors, including MA access schedule, prior forced MA exposure, concomitant ethanol (EtOH) access, and gamma-aminobutyric acid type B (GABAB) receptor activation. Selectively bred MA high drinking (MAHDR) and low drinking (MALDR) mice participated in this research.

RESULTS

MAHDR, but not MALDR, mice increased MA intake when given intermittent access, compared with continuous access, with a water choice under both schedules. MA intake was not altered by previous exposure to forced MA consumption. Male MAHDR mice given simultaneous access to MA, EtOH, and an EtOH+MA mixture exhibited a strong preference for MA over EtOH and EtOH+MA; MA intake was not affected by EtOH in female MAHDR mice. When independent MAHDR groups were given access to MA, EtOH, or EtOH+MA vs. water in each case, MA intake was reduced in the water vs. EtOH+MA group, compared with the water vs. MA group. The GABAB receptor agonist R(+)-baclofen (BAC) not only reduced MA intake but also reduced water intake and locomotor activity in MAHDR mice. There was a residual effect of BAC, such that MA intake was increased after termination of BAC treatment.

CONCLUSIONS

These findings demonstrate that voluntary MA intake in MAHDR mice is influenced by non-genetic factors related to MA access schedule and co-morbid EtOH exposure.

Neurochemical and behavioral comparisons of contingent and non-contingent methamphetamine exposure following binge or yoked long-access self-administration paradigms

RATIONALE

Abuse of the psychostimulant methamphetamine (METH) can cause long-lasting damage to brain monoaminergic systems and is associated with profound mental health problems for users, including lasting cognitive impairments. Animal models of METH exposure have been useful in dissecting the molecular effects of the drug on cognition, but many studies use acute, non-contingent "binge" administrations of METH which do not adequately approximate human METH use. Long-term METH exposure via long-access (LgA) self-administration paradigms has been proposed to more closely reflect human use and induce cognitive impairments.

OBJECTIVE

To better understand the role of contingency and patterns of exposure in METH-induced cognitive impairments, we analyzed behavioral and neurochemical outcomes in adult male rats, comparing non-contingent "binge" METH administration with contingent (LgA) METH self-administration and non-contingent yoked partners.

RESULTS

Binge METH (40 mg/kg, i.p., over 1 day) dramatically altered striatal and hippocampal dopamine, DOPAC, 5-HT, 5-HIAA, BDNF, and TrkB 75 days after drug exposure. In contrast, 6-h LgA METH self-administration (cumulative 24.8-48.9 mg METH, i.v., over 16 days) altered hippocampal BDNF in both contingent and yoked animals but reduced striatal 5-HIAA in only contingent animals. Neurochemical alterations following binge METH administration were not accompanied by cognitive deficits in Morris water maze, novel object recognition, or Y-maze tests. However, contingent LgA METH self-administration resulted in impaired spatial memory in the water maze.

CONCLUSIONS

Overall, substantial differences in neurochemical markers between METH exposure and self-administration paradigms did not consistently translate to deficits in cognitive tasks, highlighting the complexity of correlating METH-induced neurochemical changes with cognitive outcomes.

A breeding strategy to identify modifiers of high genetic risk for methamphetamine intake

Trace amine-associated receptor 1 (Taar1) impacts methamphetamine (MA) intake. A mutant allele (Taar1^m1J ) derived from the DBA/2J mouse strain codes for a non-functional receptor, and Taar1^m1J/m1J mice consume more MA than mice possessing the reference Taar1⁺ allele. To study the impact of this mutation in a genetically diverse population, heterogeneous stock-collaborative cross (HS-CC) mice, the product of an eight-way cross of standard and wild-derived strains, were tested for MA intake. HS-CC had low MA intake, so an HS-CC by DBA/2J strain F2 intercross was created to transfer the mutant allele onto the diverse background, and used for selective breeding. To study residual variation in MA intake existing in Taar1^m1J/m1J mice, selective breeding for higher (MAH) vs lower (MAL) MA intake was initiated from Taar1^m1J/m1J F2 individuals; a control line of Taar1^+/+ individuals (MAC) was retained. The lines were also examined for MA-induced locomotor and thermal responses, and fluid and tastant consumption. Taar1^m1J/m1J F2 mice consumed significantly more MA than Taar1^+/+ F2 mice. Response to selection was significant by generation 2 and there were corresponding differences in fluid consumed. Fluid consumption was not different in non-MA drinking studies. Taar1^m1J/m1J genotype (MAL or MAH vs MAC mice) was associated with heighted MA locomotor and reduced hypothermic responses. MAL mice exhibited greater sensitization than MAH mice, but the selected lines did not consistently differ for thermal or tastant phenotypes. Residual variation among high-risk Taar1^m1J/m1J mice appears to involve mechanisms associated with neuroadaptation to MA, but not sensitivity to hypothermic effects of MA.

Trace amine-associated receptor gene polymorphism increases drug craving in individuals with methamphetamine dependence

BACKGROUND

Methamphetamine (MA) is a potent agonist at the trace amine-associated receptor 1 (TAAR1). This study evaluated a common variant (CV) in the human TAAR1 gene, synonymous single nucleotide polymorphism (SNP) V288V, to determine the involvement of TAAR1 in MA dependence.

METHODS

Participants (n = 106) with active MA dependence (MA-ACT), in remission from MA dependence (MA-REM), with active polysubstance dependence, in remission from polysubstance dependence, and with no history of substance dependence completed neuropsychiatric symptom questionnaires and provided blood samples. In vitro expression and function of CV and wild type TAAR1 receptors were also measured.

RESULTS

The V288V polymorphism demonstrated a 40% increase in TAAR1 protein expression in cell culture, but message sequence and protein function were unchanged, suggesting an increase in translation efficiency. Principal components analysis resolved neuropsychiatric symptoms into four components, PC1 (depression, anxiety, memory, and fatigue), PC2 (pain), PC3 (drug and alcohol craving), and PC4 (sleep disturbances). Analyses of study group and TAAR1 genotype revealed a significant interaction for PC3 (craving response) (p = 0.003). The control group showed no difference in PC3 associated with TAAR1, while adjusted mean craving for the MA-ACT and MA-REM groups, among those with at least one copy of V288V, was estimated to be, respectively, 1.55 (p = 0.036) and 1.77 (p = 0.071) times the adjusted mean craving for those without the TAAR1 SNP.

CONCLUSIONS

Neuroadaptation to chronic MA use may be altered by TAAR1 genotype and result in increased dopamine signaling and craving in individuals with the V288V genotype.

Taar1 gene variants have a causal role in methamphetamine intake and response and interact with Oprm1

We identified a locus on mouse chromosome 10 that accounts for 60% of the genetic variance in methamphetamine intake in mice selectively bred for high versus low methamphetamine consumption. We nominated the trace amine-associated receptor 1 gene, Taar1, as the strongest candidate and identified regulation of the mu-opioid receptor 1 gene, Oprm1, as another contributor. This study exploited CRISPR-Cas9 to test the causal role of Taar1 in methamphetamine intake and a genetically-associated thermal response to methamphetamine. The methamphetamine-related traits were rescued, converting them to levels found in methamphetamine-avoiding animals. We used a family of recombinant inbred mouse strains for interval mapping and to examine independent and epistatic effects of Taar1 and Oprm1. Both methamphetamine intake and the thermal response mapped to Taar1 and the independent effect of Taar1 was dependent on genotype at Oprm1. Our findings encourage investigation of the contribution of Taar1 and Oprm1 variants to human methamphetamine addiction.

Methamphetamine binge administration dose-dependently enhanced negative affect and voluntary drug consumption in rats following prolonged withdrawal: role of hippocampal FADD

While prior studies have established various interacting mechanisms and neural consequences (i.e. monoaminergic nerve terminal damage) that might contribute to the adverse effects caused by methamphetamine administration, the precise mechanisms that mediate relapse during withdrawal remain unknown. This study evaluated the long-term consequences of binge methamphetamine administration (three pulses/day, every 3 hours, 4 days, i.p.; dose-response: 2.5, 5 and 7.5 mg/kg) in adult Sprague-Dawley rats at two behavioral levels following 25 days of withdrawal: (1) negative affect (behavioral despair-forced-swim test, and anhedonia-1% sucrose consumption, two-bottle choice test) and (2) voluntary methamphetamine consumption (20 mg/l, two-bottle choice test). Striatal and hippocampal brain samples were dissected to quantify monoamines content by high-performance liquid chromatography and to evaluate neurotoxicity (dopaminergic and serotonergic markers) and neuroplasticity markers [i.e. cell fate regulator (Fas-associated protein with death domain) FADD] by Western blot. The results showed that methamphetamine administration induced dose-dependent negative effects during prolonged withdrawal in adult rats. In particular, rats treated repeatedly with methamphetamine (7.5 mg/kg) showed (1) enhanced negative affect-increased anhedonia associated with behavioral despair, (2) increased voluntary methamphetamine consumption, (3) enhanced neurotoxicity-decreased dopamine and metabolites in striatum and decreased serotonin in hippocampus, (4) altered neuroplasticity markers-decreased FADD protein and increased p-FADD/FADD balance selectively in hippocampus and (5) higher consumption rates of methamphetamine that were associated with lower FADD content in hippocampus. These results confirm that methamphetamine withdrawal dose-dependently induced negative affect and decreased monoamines content, while also increased voluntary methamphetamine consumption and suggested a role for hippocampal FADD neuroplasticity in these drug-withdrawal adaptations.

Depression-like symptoms of withdrawal in a genetic mouse model of binge methamphetamine intake

Binge methamphetamine (MA) users have higher MA consumption, relapse rates and depression-like symptoms during early periods of withdrawal, compared with non-binge users. The impact of varying durations of MA abstinence on depression-like symptoms and on subsequent MA intake was examined in mice genetically prone to binge-level MA consumption. Binge-level MA intake was induced using a multiple-bottle choice procedure in which mice were offered one water drinking tube and three tubes containing increasing concentrations of MA in water, or four water tubes (control group). In two studies, depression-like symptoms were measured using a tail-suspension test and a subsequent forced-swim test, after forced abstinence of 6 and 30 hours from a 28-day course of chronic MA intake. An additional study measured the same depression-like symptoms, as well as MA intake, after prolonged abstinence of 1 and 2 weeks. MA high drinking mice and one of their progenitor strains DBA/2J escalated their MA intake with increasing MA concentration; however, MA high drinking mice consumed almost twice as much MA as DBA/2J mice. Depression-like symptoms were significantly higher early after MA access was withdrawn, compared to levels in drug-naïve controls, with more robust effects of MA withdrawal observed in MA high drinking than DBA/2J mice. When depression-like symptoms were examined after 1 or 2 weeks of forced abstinence in MA high drinking mice, depression-like symptoms dissipated, and subsequent MA intake was high. The MA high drinking genetic mouse model has strong face validity for human binge MA use and behavioral sequelae associated with abstinence.

A Spontaneous Mutation in Taar1 Impacts Methamphetamine-Related Traits Exclusively in DBA/2 Mice from a Single Vendor

Major gene effects on traits associated with substance use disorders are rare. Previous findings in methamphetamine drinking (MADR) lines of mice, bred for high or low voluntary MA intake, and in null mutants demonstrate a major impact of the trace amine-associated receptor 1 (Taar1) gene on a triad of MA-related traits: MA consumption, MA-induced conditioned taste aversion and MA-induced hypothermia. While inbred strains are fundamentally genetically stable, rare spontaneous mutations can become fixed and result in new or aberrant phenotypes. A single nucleotide polymorphism in Taar1 that encodes a missense proline to threonine mutation in the second transmembrane domain (Taar1^m1J) has been identified in the DBA/2J strain. MA is an agonist at this receptor, but the receptor produced by Taar1^m1J does not respond to MA or endogenous ligands. In the present study, we used progeny of the C57BL/6J × DBA/2J F2 cross, the MADR lines, C57BL/6J × DBA/2J recombinant inbred strains, and DBA/2 mice sourced from four vendors to further examine Taar1-MA phenotype relations and to define the chronology of the fixation of the Taar1^m1J mutation. Mice homozygous for Taar1^m1J were found at high frequency early in selection for high MA intake in multiple replicates of the high MADR line, whereas Taar1^m1J homozygotes were absent in the low MADR line. The homozygous Taar1^m1J genotype is causally linked to increased MA intake, reduced MA-induced conditioned taste aversion, and reduced MA-induced hypothermia across models. Genotype-phenotype correlations range from 0.68 to 0.96. This Taar1 polymorphism exists in DBA/2J mice sourced directly from The Jackson Laboratory, but not DBA/2 mice sourced from Charles River (DBA/2NCrl), Envigo (formerly Harlan Sprague Dawley; DBA/2NHsd) or Taconic (DBA/2NTac). By genotyping archived samples from The Jackson Laboratory, we have determined that this mutation arose in 2001–2003. Our data strengthen the conclusion that the mutant Taar1^m1J allele, which codes for a non-functional receptor protein, increases risk for multiple MA-related traits, including MA intake, in homozygous Taar1^m1J individuals.

Trace amine-associated receptor 1 regulation of methamphetamine-induced neurotoxicity

Trace amine-associated receptor 1 (TAAR1) is activated by methamphetamine (MA) and modulates dopaminergic (DA) function. Although DA dysregulation is the hallmark of MA-induced neurotoxicity leading to behavioral and cognitive deficits, the intermediary role of TAAR1 has yet to be characterized. To investigate TAAR1 regulation of MA-induced neurotoxicity, Taar1 transgenic knock-out (KO) and wildtype (WT) mice were administered saline or a neurotoxic regimen of 4 i.p. injections, 2h apart, of MA (2.5, 5, or 10mg/kg). Temperature data were recorded during the treatment day. Additionally, striatal tissue was collected 2 or 7days following MA administration for analysis of DA, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and tyrosine hydroxylase (TH) levels, as well as glial fibrillary acidic protein (GFAP) expression. MA elicited an acute hypothermic drop in body temperature in Taar1-WT mice, but not in Taar1-KO mice. Two days following treatment, DA and TH levels were lower in Taar1-KO mice compared to Taar1-WT mice, regardless of treatment, and were dose-dependently decreased by MA. GFAP expression was significantly increased by all doses of MA at both time points and greater in Taar1-KO compared to Taar1-WT mice receiving MA 2.5 or 5mg/kg. Seven days later, DA levels were decreased in a similar pattern: DA was significantly lower in Taar1-KO compared to Taar1-WT mice receiving MA 2.5 or 5mg/kg. TH levels were uniformly decreased by MA, regardless of genotype. These results indicate that activation of TAAR1 potentiates MA-induced hypothermia and TAAR1 confers sustained neuroprotection dependent on its thermoregulatory effects.

Verification of a genetic locus for methamphetamine intake and the impact of morphine

A quantitative trait locus (QTL) on proximal chromosome (Chr) 10 accounts for > 50% of the genetic variance in methamphetamine (MA) intake in mice selectively bred for high (MAHDR) and low (MALDR) voluntary MA drinking. The µ-opioid receptor (MOP-r) gene, Oprm1, resides at the proximal end of Chr 10, and buprenorphine reduces MA intake in MAHDR mice. However, this drug has only partial agonist effects at MOP-r. We investigated the impact of a full MOP-r agonist, morphine, on MA intake and saccharin intake, measured MOP-r density and affinity in several brain regions of the MA drinking lines and their C57BL/6J (B6) and DBA/2J (D2) progenitor strains, and measured MA intake in two congenic strains of mice to verify the QTL and reduce the QTL interval. Morphine reduced MA intake in the MAHDR line, but also reduced saccharin and total fluid intake. MOP-r density was lower in the medial prefrontal cortex of MAHDR, compared to MALDR, mice, but not in the nucleus accumbens or ventral midbrain; there were no MOP-r affinity differences. No significant differences in MOP-r density or affinity were found between the progenitor strains. Finally, Chr 10 congenic results were consistent with previous data suggesting that Oprm1 is not a quantitative trait gene, but is impacted by the gene network underlying MA intake. Stimulation of opioid pathways by a full agonist can reduce MA intake, but may also non-specifically affect consummatory behavior; thus, a partial agonist may be a better pharmacotherapeutic.

Parallel Effects of Methamphetamine on Anxiety and CCL3 in Humans and a Genetic Mouse Model of High Methamphetamine Intake

BACKGROUND

Methamphetamine (MA) abuse causes immune dysfunction and neuropsychiatric impairment. The mechanisms underlying these deficits remain unidentified.

METHODS

The effects of MA on anxiety-like behavior and immune function were investigated in mice selectively bred to voluntarily consume high amounts of MA [i.e., MA high drinking (MAHDR) mice]. MA (or saline) was administered to mice using a chronic (14-day), binge-like model. Performance in the elevated zero maze (EZM) was determined 5 days after the last MA dose to examine anxiety-like behavior. Cytokine and chemokine expressions were measured in the hippocampus using quantitative polymerase chain reaction (qPCR). Human studies were also conducted to evaluate symptoms of anxiety using the General Anxiety Disorder-7 Scale in adults with and without a history of MA dependence. Plasma samples collected from human research participants were used for confirmatory analysis of murine qPCR results using an enzyme-linked immunosorbent assay.

RESULTS

During early remission from MA, MAHDR mice exhibited increased anxiety-like behavior on the EZM and reduced expression of chemokine (C-C motif) ligand 3 (ccl3) in the hippocampus relative to saline-treated mice. Human adults actively dependent on MA and those in early remission had elevated symptoms of anxiety as well as reductions in plasma levels of CCL3, relative to adults with no history of MA abuse.

CONCLUSIONS

The results highlight the complex effects of MA on immune and behavioral function and suggest that alterations in CCL3 signaling may contribute to the mood impairments observed during remission from MA addiction.