Corticolimbic dysregulation and chronic methamphetamine abuse

Sex differences in behavior, cognitive, and physiological recovery following methamphetamine administration

Intact executive functions are required for proper performance of cognitive tasks and relies on balance of excitatory and inhibitory (E/I) transmission in the medial prefrontal cortex (mPFC). Hypofrontality is a state of decreased activity in the mPFC and is seen in several neuropsychiatric conditions, including substance use disorders. People who chronically use methamphetamine (meth) develop hypofrontality and concurrent changes in cognitive processing across several domains. Despite the fact that there are sex difference in substance use disorders, few studies have considered sex as a biological variable regarding meth-mediated hypoactivity in mPFC and concurrent cognitive deficits. Hypofrontality along with changes in cognition are emulated in rodent models following repeated meth administration. Here, we used a meth sensitization regimen to study sex differences in a Temporal Order Memory (TOM) task following short (7 days) or prolonged (28 days) periods of abstinence. GABAergic transmission, GABAA receptor (GABAAR) and GABA Transporter (GAT) mRNA expression in the mPFC were evaluated with patch-clamp recordings and RT-qPCR, respectively. Both sexes sensitized to the locomotor activating effects of meth, with the effect persisting in females. After short abstinence, males and females had impaired TOM and increased GABAergic transmission. Female rats recovered from these changes after prolonged abstinence, whereas male rats showed enduring changes. In general, meth appears to elicit an overall decrease in GABAAR expression after short abstinence; whereas GABA transporters are decreased in meth female rats after prolonged abstinence. These results show sex differences in the long-term effects of repeated meth exposure and suggest that females have neuroprotective mechanisms that alleviate some of the meth-mediated cognitive deficits.

The neuroprotective effects of caffeic acid phenethyl ester against methamphetamine-induced neurotoxicity

Methamphetamine (METH) is a highly abused substance on a global scale and has the capacity to elicit toxicity within the central nervous system. The neurotoxicity induced by METH encompasses neuronal degeneration and cellular demise within the substantia nigra-striatum and hippocampus. Caffeic acid phenethyl ester (CAPE), a constituent of propolis, is a diminutive compound that demonstrates antioxidative and anti-inflammatory characteristics. Numerous investigations have demonstrated the safeguarding effects of CAPE in various neurodegenerative ailments. Our hypothesis posits that CAPE may exert a neuroprotective influence on METH-induced neurotoxicity via specific mechanisms. In order to validate the hypothesis, a series of experimental techniques including behavioral tests, immunofluorescence labeling, RNA sequencing, and western blotting were employed to investigate the neurotoxic effects of METH and the potential protective effects of CAPE. The results of our study demonstrate that CAPE effectively ameliorates cognitive memory deficits and anxiety symptoms induced by METH in mice. Furthermore, CAPE has been observed to attenuate the upregulation of neurotoxicity-associated proteins that are induced by METH exposure and also reduced the loss of hippocampal neurons in mice. Moreover, transcriptomics analysis was conducted to determine alterations in gene expression within the hippocampus of mice. Subsequently, bioinformatics analysis was employed to investigate the divergent outcomes and identify potential key genes. Interferon-stimulated gene 15 (ISG15) was successfully identified and confirmed through RT-qPCR, western blotting, and immunofluorescence techniques. Our research findings unequivocally demonstrated the neuroprotective effect of CAPE against METH-induced neurotoxicity, with ISG15 may have an important role in the underlying protective mechanism. These results offer novel perspectives on the treatment of METH-induced neurotoxicity.

A Review on the Disruption of Novel Object Recognition Induced by Methamphetamine

Background

Methamphetamine (MA), is a widely abused synthetic psychostimulant that leads to irreversible brain damage manifested as cognitive impairments in humans and animals. The novel object recognition (NOR) task is a commonly used behavioral assay for the investigation of non-spatial memory in rodents. This test is based on the natural tendency of rodents to spend more time exploring a novel object than a familiar one. NOR test has been used in many studies investigating cognitive deficits caused by MA in rodents. The objective of the present study was to review neurobiological mechanisms that might be responsible for MA-induced NOR alterations.

Methods

A PubMed search showed 83 publications using novel object recognition and methamphetamine as keywords in the past 10 years.

Findings

The present study revealed different MA regimens cause recognition memory impairment in rodents. In addition, it was found that the main neurobiological mechanism involved in MA-induced recognition deficits is the dysfunction of monoaminergic systems.

Conclusion

NOR is a useful test to assess the cognitive functions following MA administration and evaluate the efficacy of new therapeutic agents in MA-addicted individuals.

Utilizing Soccer for Delivery of HIV and Substance Use Prevention for Young South African Men: 6-Month Outcomes of a Cluster Randomized Controlled Trial

Young men in South Africa face the intersecting epidemics of HIV, substance use and endemic poverty. We tested the effectiveness of a behavioral intervention using soccer training to reduce the cluster of risks associated with HIV and substance use. This cluster randomized controlled trial was conducted with men aged 18-29 years old in 27 neighborhoods in the townships of Cape Town, South Africa. Neighborhoods were randomized to receive for 6 months either: (1) Soccer League (SL; n = 18 neighborhoods, n = 778 men) who attended soccer three times weekly (72 sessions; 94% uptake, 45.5% weekly attendance rate), combined with an HIV/substance use, cognitive-behavioral intervention; or (2) a Control Condition (CC; n = 9; 415 men) who received educational materials and referrals at 3 month intervals. The primary outcome was the number of significant changes in a cluster of outcomes including HIV-related risks, substance abuse, employment/income, mental health, violence, and community engagement. There was only one significant difference on the rapid diagnostic tests for mandrax at 6 months, an insufficient number of changes to indicate a successful intervention. A group-based behavioral intervention was ineffective in addressing multiple risk behaviors among at-risk young men, similar to the findings of several recent soccer-related interventions. Early adulthood may be too late to alter well-established patterns of risk behaviors.Clinical Trial Registration This trial was prospectively registered on 24 November 2014 with ClinicalTrials.gov NCT02358226.

Cognitive effectiveness of high-intensity interval training for individuals with methamphetamine dependence: a study protocol for randomised controlled trial

INTRODUCTION

Cognitive deficit is a common syndrome of methamphetamine (MA) dependence. It is related to decision-making, control ability, and social functioning. High-intensity interval training (HIIT) is a training technique that requires people to work out at full intensity during a short period. Many studies have already shown the potential effects of HIIT on cognitive functions. The purpose of this trial is to evaluate the cognitive effects of HIIT on individuals with MA dependence.

METHODS AND ANALYSIS

A total of 240 individuals with MA dependence will be randomly assigned to the HIIT group, moderate-intensity continuous training (MICT) group and control (CON) group. HIIT will consist of a 24-min HIIT exercise on a treadmill. MICT will consist of a 1-h body-mind exercise. CON will be their traditional intervention. The experimental period will be 12 months with 3 interventions weekly for the first 6 months and follow-up for the next 6 months. All subjects will be given cognitive tests at baseline, after intervention and at follow-up. Cognitive performances will be compared by a mixed-model analysis for repeated measures.

DISCUSSION

HIIT training may reduce illicit drug cravings amongst individuals with MA dependence; hence, HIIT may have a good effect on the cognitive functions, such as memory and executive function, of individuals with MA dependence.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2000032492 . Registered on April 30, 2020 ( http://www.chictr.org.cn/edit.aspx?pid=52127&htm=4 ).

Effects of Tai Chi on the Executive Function and Physical Fitness of Female Methamphetamine Dependents: A Randomized Controlled Trial

Purpose: Exercise improves the health and mental status of drug dependents. The way by which Tai Chi (TC) as a special exercise treatment affects executive functions (EFs) of methamphetamine (MA) dependents is yet to be established. This study aimed to explore the effects of TC on the EFs and physical fitness of MA dependents. Methods: A total of 76 female MA dependents were randomly assigned to the exercise and control groups. The exercise group underwent three 60-min sessions of TC training per week for 12 weeks. The control group was trained with conventional exercises including the 9th Guang Bo Ti Cao and square dance. Physical fitness and EF assessments that evaluated inhibitory control (IC, go/no-go task), working memory (3-back task) and cognitive flexibility (switching task) were performed at baseline and at 12 weeks. A repeated-measures ANOVA was applied to analyze the differences of group and time. Results: The exercise group showed decreased response time (RT) with a significant main effect of time on the go/no-go task [F (1, 68) = 9.6, p < 0.05]. The interaction effect between time and group was significant on accuracy [F (1, 61) = 4.73, p < 0.05], and the main effect of time was significant on RT [F (1, 61) = 4.66, p < 0.05] in the 3-back task of the exercise group. Significant changes in BMI [F (1, 68) = 19.57, p < 0.05], vital capacity [F (1, 68) = 6.00, p < 0.05], and systolic blood pressure [F (1, 68) = 6.11, p < 0.05] were observed in the exercise group. Conclusion: These findings showed that 3 months of TC training can improve the IC and maintain the working memory and cognitive flexibility of MA dependents. Other data implied that TC may improve the physical fitness of MA dependents. Clinical Trial Registration: http://www.chictr.org.cn/, ChiCTR1900022091.

Female rats display higher methamphetamine-primed reinstatement and c-Fos immunoreactivity than male rats

Methamphetamine (meth) dependence is often characterized by persistent and chronic relapse (i.e., return to drug use). Previous work suggests females may be at greater risk to relapse. In this study, we extended this limited evidence and identified sex-dependent neural substrates related to meth-triggered reinstatement. Male and female Sprague-Dawley rats were implanted with indwelling jugular catheters. Half of the rats were then trained to self-administer meth (0.05 mg/kg/inf); the other half self-administered saline during 21 daily sessions (2 h). Rats were then given 12 extinction sessions. Twenty-four hours after the last extinction session, rats received reinstatement testing. Half of the rats received a meth-prime (0.3 mg/kg, IP) injection and the remaining rats received a saline injection. This design resulted in 4 separate groups for each sex, allowing for careful investigation of brain regions related to meth-triggered reinstatement. Brains were harvested following the reinstatement session and c-Fos immunoreactivity was measured in multiple brain regions. Meth triggered reinstatement in both sexes and this effect was more robust in females compared to males. Significant sex differences were detected. Females showed greater c-Fos immunoreactivity in the cingulate cortex area 1, lateral orbitofrontal cortex, prelimbic cortex, caudate-putamen, nucleus accumbens core and shell, and central nucleus of the amygdala following meth-primed reinstatement.

Protocol for the methamphetamine approach-avoidance training (MAAT) trial, a randomised controlled trial of personalised approach bias modification for methamphetamine use disorder

Background

Globally, methamphetamine use has increased in prevalence in recent years. In Australia, there has been a dramatic increase in numbers of people seeking treatment, including residential rehabilitation, for methamphetamine use disorder (MUD). While residential rehabilitation is more effective for MUD than withdrawal treatment (i.e. “detoxification”) alone, relapse rates remain high, with approximately half of rehabilitation clients using methamphetamine within 3 months of rehabilitation. “Approach bias modification” (ABM) is a computerised cognitive training approach that aims to dampen automatically triggered impulses to approach drugs and drug-related stimuli. ABM has been demonstrated to reduce alcohol relapse rates, but no randomised controlled trials of ABM for MUD have yet been conducted. We aim to test whether a novel “personalised” form of ABM, delivered during rehabilitation, reduces post-treatment methamphetamine use, relative to a sham-training control condition. Secondary outcomes will include dependence symptoms, cravings, and approach bias.

Methods

We aim to recruit 100 participants attending residential rehabilitation for MUD at 3 sites in the Melbourne metropolitan area. Participants will complete baseline measures of methamphetamine use, craving, dependence severity, and approach bias before being randomised to receiving 6 sessions of ABM or “sham” training. In the active condition, ABM will be personalised for each participant, using those methamphetamine images that they rate as most relevant to their recent methods of methamphetamine use as “avoidance” images and using positive images representing their goals or healthy sources of pleasure as “approach” images. Approach bias and craving will be re-assessed following completion of training, and methamphetamine use, dependence, and craving will be assessed 4 weeks and 3 months following discharge from residential treatment.

Discussion

This study is the first randomised controlled trial of ABM for MUD and also the first ABM study to test using a personalised set of both approach and avoid images for ABM training. If effective, the low cost and easy implementation of ABM means it could be widely implemented as a standard part of MUD treatment.

Trial registration

Australian New Zealand Clinical Trials Registry ACTRN12620000072910. Registered on 30 January 2020 (prospectively registered): https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=378804&isReview=true

SCH23390 Reduces Methamphetamine Self-Administration and Prevents Methamphetamine-Induced Striatal LTD

Extended-access methamphetamine self-administration results in unregulated intake of the drug; however, the role of dorsal striatal dopamine D1-like receptors (D1Rs) in the reinforcing properties of methamphetamine under extended-access conditions is unclear. Acute (ex vivo) and chronic (in vivo) methamphetamine exposure induces neuroplastic changes in the dorsal striatum, a critical region implicated in instrumental learning. For example, methamphetamine exposure alters high-frequency stimulation (HFS)-induced long-term depression in the dorsal striatum; however, the effect of methamphetamine on HFS-induced long-term potentiation (LTP) in the dorsal striatum is unknown. In the current study, dorsal striatal infusion of SCH23390, a D1R antagonist, prior to extended-access methamphetamine self-administration reduced methamphetamine addiction-like behavior. Reduced behavior was associated with reduced expression of PSD-95 in the dorsal striatum. Electrophysiological findings demonstrate that superfusion of methamphetamine reduced basal synaptic transmission and HFS-induced LTP in dorsal striatal slices, and SCH23390 prevented this effect. These results suggest that alterations in synaptic transmission and synaptic plasticity induced by acute methamphetamine via D1Rs could assist with methamphetamine-induced modification of corticostriatal circuits underlying the learning of goal-directed instrumental actions and formation of habits, mediating escalation of methamphetamine self-administration and methamphetamine addiction-like behavior.

Neurobiology, Clinical Presentation, and Treatment of Methamphetamine Use Disorder: A Review

IMPORTANCE

The prevalence of and mortality associated with methamphetamine use has doubled during the past 10 years. There is evidence suggesting that methamphetamine use disorder could be the next substance use crisis in the United States and possibly worldwide.

OBSERVATION

The neurobiology of methamphetamine use disorder extends beyond the acute effect of the drug as a monoaminergic modulator and includes intracellular pathways focused on oxidative stress, neurotoxic and excitotoxic effects, and neuroinflammation. Similarly, the clinical picture extends beyond the acute psychostimulatory symptoms to include complex cardiovascular and cerebrovascular signs and symptoms that need to be identified by the clinician. Although there are no pharmacologic treatments for methamphetamine use disorder, cognitive behavioral therapy, behavioral activation, and contingency management show modest effectiveness.

CONCLUSIONS AND RELEVANCE

There is a need to better understand the complex neurobiology of methamphetamine use disorder and to develop interventions aimed at novel biological targets. Parsing the disorder into different processes (eg, craving or mood-associated alterations) and targeting the neural systems and biological pathways underlying these processes may lead to greater success in identifying disease-modifying interventions. Finally, mental health professionals need to be trained in recognizing early cardiovascular and cerebrovascular warning signs to mitigate the mortality associated with methamphetamine use disorder.

Higher Risk Taking and Impaired Probability Judgment in Behavioral Addiction

BACKGROUND

Accumulating evidence suggests that deficits in decision-making and judgment may be involved in several psychiatric disorders, including addiction. Behavioral addiction is a conceptually new psychiatric condition, raising a debate of what criteria define behavioral addiction, and several impulse control disorders are equivalently considered as types of behavioral addiction. In this preliminary study with a relatively small sample size, we investigated how decision-making and judgment were compromised in behavioral addiction to further characterize this psychiatric condition.

METHOD

Healthy control subjects (n = 31) and patients with kleptomania and paraphilia as behavioral addictions (n = 16) were recruited. A battery of questionnaires for assessments of cognitive biases and economic decision-making were conducted, as was a psychological test for the assessment of the jumping-to-conclusions bias, using functional near-infrared spectroscopy recordings of prefrontal cortical (PFC) activity.

RESULTS

Although behavioral addicts exhibited stronger cognitive biases than controls in the questionnaire, the difference was primarily due to lower intelligence in the patients. Behavioral addicts also exhibited higher risk taking and worse performance in economic decision-making, indicating compromised probability judgment, along with diminished PFC activity in the right hemisphere.

CONCLUSION

Our study suggests that behavioral addiction may involve impairments of probability judgment associated with attenuated PFC activity, which consequently leads to higher risk taking in decision-making.

β-Arrestin-Biased Allosteric Modulator of NTSR1 Selectively Attenuates Addictive Behaviors

Small molecule neurotensin receptor 1 (NTSR1) agonists have been pursued for more than 40 years as potential therapeutics for psychiatric disorders, including drug addiction. Clinical development of NTSR1 agonists has, however, been precluded by their severe side effects. NTSR1, a G protein-coupled receptor (GPCR), signals through the canonical activation of G proteins and engages β-arrestins to mediate distinct cellular signaling events. Here, we characterize the allosteric NTSR1 modulator SBI-553. This small molecule not only acts as a β-arrestin-biased agonist but also extends profound β-arrestin bias to the endogenous ligand by selectively antagonizing G protein signaling. SBI-553 shows efficacy in animal models of psychostimulant abuse, including cocaine self-administration, without the side effects characteristic of balanced NTSR1 agonism. These findings indicate that NTSR1 G protein and β-arrestin activation produce discrete and separable physiological effects, thus providing a strategy to develop safer GPCR-targeting therapeutics with more directed pharmacological action.

Gender differences in the behavioral and subjective effects of methamphetamine in healthy humans

RATIONALE

Methamphetamine (MA) use is steadily increasing and thus constitutes a major public health concern. Women seem to be particularly vulnerable to developing MA use disorder, as they initiate use at a younger age and transition more quickly to problematic use. Initial drug responses may predict subsequent use, but little information exists on potential gender differences in the acute effects of MA prior to dependence.

OBJECTIVE

We examined gender differences in the acute effects of MA on subjective mood and reward-related behavior in healthy, non-dependent humans.

METHODS

Men (n = 44) and women (n = 29) completed 4 sessions in which they received placebo or MA under double-blind conditions twice each. During peak drug effect, participants completed the monetary incentive delay task to assess reaction times to cues signaling potential monetary losses or gains, in an effort to determine if MA would potentiate reward-motivated behavior. Cardiovascular and subjective drug effects were assessed throughout sessions.

RESULTS

Overall, participants responded more quickly to cues predicting incentivized trials, particularly large-magnitude incentives, than to cues predicting no incentive. MA produced faster reaction times in women, but not in men. MA produced typical stimulant-like subjective and cardiovascular effects in all participants, but subjective ratings of vigor and (reduced) sedation were greater in women than in men.

CONCLUSIONS

Women appear to be more sensitive to the psychomotor-related behavioral and subjective effects of MA. These findings provide initial insight into gender differences in acute effects of MA that may contribute to gender differences in problematic MA use.

Intracerebroventricular microinjection of the 5-HT1F receptor agonist LY 344864 inhibits methamphetamine conditioned place preference reinstatement in rats

Relapse following a prolonged period of drug cessation is a key barrier in the treatment of methamphetamine (METH) addiction, for which pharmacological treatment exhibits little efficacy. Previous studies have suggested that this process involves alterations in levels of serotonin (5-HT) in the brain. Although the 5-HT1F receptor has been implicated in the reward pathway, its physiological functions remain unknown. In the present study, we examined the effect of the 5-HT1F agonist LY 344864 on the reinstatement of METH-seeking behavior in rats using a conditioned place preference (CPP) paradigm. The CPP paradigm was first used to determine the effective doses of LY and METH. Four groups were then conditioned with METH (5 mg/kg; i.p.), while the sham group received saline. METH-induced CPP was subsequently extinguished. On the 13th day of extinction, the rats received either METH (0, 1, or 2.5 mg/kg; i.p.) plus vehicle or priming METH plus LY (2 μg/5 μL; i.c.v.). On reinstatement day, preference scores were calculated as the difference in time spent in the drug-paired and vehicle-paired compartments. Rats conditioned with the lowest effective dose of METH (5 mg/kg) exhibited significant differences in pre- and post-testing preference scores. Preference scores were significantly higher in the saline + METH group than in the control group. Furthermore, preference scores were significantly higher in rats that had received priming METH treatment, and pre-treatment with LY significantly attenuated the reinstatement of METH-seeking behavior. These findings suggest that future studies should evaluate the therapeutic potential of 5-HT1F agonists for preventing relapse in individuals with METH addiction.

The neurobiological mechanisms of physical exercise in methamphetamine addiction

Methamphetamine (METH) is the primary drug within amphetamine-type stimulants which are the second most abused group of drugs worldwide. There is no pharmacological treatment addressed specifically to METH addiction, and behavioral therapy is shadowed by poor long-term recovery and relapse. Therefore, novel approaches to manage METH addiction are an urgent need. This review aims to describe the current state of physical exercise use on methamphetamine addiction management. The following searching terms in PubMed were used: ("physical exercise" OR "exercise") AND "methamphetamine." Relevant references from key publications and gray literature were also reviewed to identify additional citations for inclusion. Original investigation regarding physical exercise and methamphetamine addiction (clinical data) or neurobiological mechanisms of physical exercise in animal models of methamphetamine administration (preclinical data) was included. Overall, METH users demonstrated improvements, including better fitness and emotional measures, lower relapse rates, and sustained abstinence when compared to nonexercised individuals. The neurobiological mechanisms of physical exercise in METH users seem to reflect an interplay of several agents, including neurochemicals, oxidative stress, neurogenesis, gliogenesis, and blood-brain barrier as disclosed by preclinical data. Exercise-based interventions alone or as a conjoint therapy may be a useful tool for managing METH addiction.

AMPA Receptor Plasticity in Accumbens Core Contributes to Incubation of Methamphetamine Craving

BACKGROUND

The incubation of cue-induced drug craving in rodents provides a model of persistent vulnerability to craving and relapse in human addicts. After prolonged withdrawal, incubated cocaine craving depends on strengthening of nucleus accumbens (NAc) core synapses through incorporation of Ca²⁺-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (CP-AMPARs). Through metabotropic glutamate receptor 1 (mGluR1)-mediated synaptic depression, mGluR1 positive allosteric modulators remove CP-AMPARs from these synapses and thereby reduce cocaine craving. This study aimed to determine if similar plasticity accompanies incubation of methamphetamine craving.

METHODS

Rats self-administered saline or methamphetamine under extended-access conditions. Cue-induced seeking tests demonstrated incubation of methamphetamine craving. After withdrawal periods ranging from 1 to >40 days, rats underwent one of the following procedures: 1) whole-cell patch clamp recordings to characterize AMPAR transmission, 2) intra-NAc core injection of the CP-AMPAR antagonist 1-naphthyl acetyl spermine followed by a seeking test, or 3) systemic administration of a mGluR1 positive allosteric modulator followed by a seeking test.

RESULTS

Incubation of methamphetamine craving was associated with CP-AMPAR accumulation in NAc core, and both effects were maximal after ~1 week of withdrawal. Expression of incubated craving was decreased by intra-NAc core 1-naphthyl acetyl spermine injection or systemic mGluR1 positive allosteric modulator administration.

CONCLUSIONS

These results are the first to demonstrate a role for the NAc in the incubation of methamphetamine craving and describe adaptations in synaptic transmission associated with this model. They establish that incubation of craving and associated CP-AMPAR plasticity occur much more rapidly during withdrawal from methamphetamine compared with cocaine. However, a common mGluR1-based therapeutic strategy may be helpful for recovering cocaine and methamphetamine addicts.

Projection neurons in the cortex and hippocampus: differential effects of chronic khat and ethanol exposure in adult male rats

BACKGROUND

Recent evidence suggests that many individuals who chew khat recreationally also drink ethanol to offset the stimulating effect of khat. The objective of this study was to describe the separate and interactive effects of chronic ethanol and khat exposure on key projection neurons in the cortex and hippocampus of young adult male rats.

METHODS

Young adult male Sprague Dawley rats were divided into six treatment groups: 2 g/kg khat, 4 g/kg khat, 4 g/kg ethanol, combined khat and ethanol (4 g/kg each), a normal saline control, and an untreated group. Treatments were administered orally for 28 continuous days; brains were then harvested, sectioned, and routine hematoxylin-eosin staining was done. Following photomicrography, ImageJ® software captured data regarding neuron number and size.

RESULTS

No differences occurred in counts of both granular and pyramidal projection neurons in the motor cortex and all four subfields of the hippocampal formation. Khat dose-dependently increased pyramidal neuron size in the motor cortex and the CA3 region, but had different effects on granular neuron size in the dentate gyrus and the motor cortex. Mean pyramidal neuron size for the ethanol-only treatment was larger than that for the 2 g/kg khat group, and the saline control group, in CA3 and in the motor cortex. Concomitant khat and ethanol increased granular neuron size in the motor cortex, compared to the 2 g/kg khat group, the 4 g/kg khat group, and the 4 g/kg ethanol group. In the CA3 region, the 4 g/kg ethanol group showed a larger mean pyramidal neuron size than the combined khat and ethanol group.

CONCLUSION

These results suggest that concomitant khat and ethanol exposure changes granular and pyramidal projection neuron sizes differentially in the motor cortex and hippocampus, compared to the effects of chronic exposure to these two drugs separately.

Reduced Neural Recruitment for Bayesian Adjustment of Inhibitory Control in Methamphetamine Dependence

Delineating the processes that contribute to the progression and maintenance of substance dependence is critical to understanding and preventing addiction. Several previous studies have shown inhibitory control deficits in individuals with stimulant use disorder. We used a Bayesian computational approach to examine potential neural deficiencies in the dynamic predictive processing underlying inhibitory function among recently abstinent methamphetamine-dependent individuals (MDIs), a population at high risk of relapse. Sixty-two MDIs were recruited from a 28-day inpatient treatment program at the San Diego Veterans Affairs Medical Center and compared with 34 healthy control subjects. They completed a stop-signal task during functional magnetic resonance imaging. A Bayesian ideal observer model was used to predict individuals' trial-to-trial probabilistic expectations of inhibitory response, P(stop), to identify group differences specific to Bayesian expectation and prediction error computation. Relative to control subjects, MDIs were more likely to make stop errors on difficult trials and had attenuated slowing following stop errors. MDIs further exhibited reduced sensitivity as measured by the neural tracking of a Bayesian measure of surprise (unsigned prediction error), which was evident across all trials in the left posterior caudate and orbitofrontal cortex (Brodmann area 11), and selectively on stop error trials in the right thalamus and inferior parietal lobule. MDIs are less sensitive to surprising task events, both across trials and upon making commission errors, which may help explain why these individuals may not engage in switching strategy when the environment changes, leading to adverse consequences.

Psychological intervention with working memory training increases basal ganglia volume: A VBM study of inpatient treatment for methamphetamine use

BACKGROUND

Protracted methamphetamine (MA) use is associated with decreased control over drug craving and altered brain volume in the frontostriatal network. However, the nature of volumetric changes following a course of psychological intervention for MA use is not yet known.

METHODS

66 males (41 MA patients, 25 healthy controls, HC) between the ages of 18-50 were recruited, the MA patients from new admissions to an in-patient drug rehabilitation centre and the HC via public advertisement, both in Cape Town, South Africa. 17 MA patients received 4 weeks of treatment as usual (TAU), and 24 MA patients completed TAU plus daily 30-minute cognitive training (CT) using an N-back working memory task. Magnetic resonance imaging (MRI) at baseline and 4-week follow-up was acquired and voxel-based morphometry (VBM) was used for analysis.

RESULTS

TAU was associated with larger bilateral striatum (caudate/putamen) volume, whereas CT was associated with more widespread increases of the bilateral basal ganglia (incorporating the amygdala and hippocampus) and reduced bilateral cerebellum volume coinciding with improvements in impulsivity scores.

CONCLUSIONS

While psychological intervention is associated with larger volume in mesolimbic reward regions, the utilisation of additional working memory training as an adjunct to treatment may further normalize frontostriatal structure and function.

Prefrontal glutamate correlates of methamphetamine sensitization and preference

Methamphetamine (MA) is a widely misused, highly addictive psychostimulant that elicits pronounced deficits in neurocognitive function related to hypo-functioning of the prefrontal cortex (PFC). Our understanding of how repeated MA impacts excitatory glutamatergic transmission within the PFC is limited, as is information about the relationship between PFC glutamate and addiction vulnerability/resiliency. In vivo microdialysis and immunoblotting studies characterized the effects of MA (ten injections of 2 mg/kg, i.p.) upon extracellular glutamate in C57BL/6J mice and upon glutamate receptor and transporter expression, within the medial PFC. Glutamatergic correlates of both genetic and idiopathic variance in MA preference/intake were determined through studies of high vs. low MA-drinking selectively bred mouse lines (MAHDR vs. MALDR, respectively) and inbred C57BL/6J mice exhibiting spontaneously divergent place-conditioning phenotypes. Repeated MA sensitized drug-induced glutamate release and lowered indices of N-methyl-d-aspartate receptor expression in C57BL/6J mice, but did not alter basal extracellular glutamate content or total protein expression of Homer proteins, or metabotropic or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors. Elevated basal glutamate, blunted MA-induced glutamate release and ERK activation, as well as reduced protein expression of mGlu2/3 and Homer2a/b were all correlated biochemical traits of selection for high vs. low MA drinking, and Homer2a/b levels were inversely correlated with the motivational valence of MA in C57BL/6J mice. These data provide novel evidence that repeated, low-dose MA is sufficient to perturb pre- and post-synaptic aspects of glutamate transmission within the medial PFC and that glutamate anomalies within this region may contribute to both genetic and idiopathic variance in MA addiction vulnerability/resiliency.

Effects of self-administered methamphetamine on discrimination learning and reversal in nonhuman primates

RATIONALE

Frequent exposure to methamphetamine has been reported to adversely influence cognitive behavior and, in particular, inhibitory control processes.

OBJECTIVE

The present studies were conducted in squirrel monkeys to assess the effects of daily intravenous methamphetamine self-administration on touch screen-based repeated acquisition and discrimination reversal tasks thought to reflect behavioral dimensions of, respectively, learning and response inhibition.

METHODS

First, stable methamphetamine-maintained behavior was established in each subject (0.35-1.6 mg/kg/session), and subsequently, a second daily session of discrimination learning was conducted (20 h later). Subjects first learned to discriminate between two simultaneously presented stimuli (acquisition) and, subsequently, to re-learn the discrimination with the contingencies switched (reversal). The role of the interval between self-administration and touch screen sessions was evaluated, as well as the effects of abrupt methamphetamine discontinuation.

RESULTS

Results indicate that daily methamphetamine self-administration markedly disrupted the development of discrimination learning, initially requiring nearly twice the number of trials to master discriminations. The magnitude of adverse effects in individual subjects correlated to the level of daily methamphetamine intake. Importantly, however, behavioral disruption of discrimination learning was surmounted following remedial training. Once criterion levels of discrimination performance were achieved, subsequent development of reversal performance was largely unaffected except when the interval between self-administration and touch screen session was short and, thus, likely a result of methamphetamine’s direct effects. Discontinuation of methamphetamine produced no disruption in acquisition or reversal.

CONCLUSION

These results indicate that self-administered methamphetamine can markedly disrupt learning processes and highlight key differences in its effects on different aspects of discrimination learning.

Comparative Study of the Activity of Brain Behavioral Systems in Methamphetamine and Opiate Dependents

BACKGROUND

Substance dependency is a major problem for the general health of a society. Different approaches have investigated the substance dependency in order to explain it. Gray's reinforcement sensitivity theory (RST) is an advanced and important neuropsychological theory in this area.

OBJECTIVES

The aim of this study was to compare three systems of the revised reinforcement sensitivity theory the behavioral activation system (r-BAS), the revised behavioral inhibition system (r-BIS), and the revised fight/flight/freezing system (r-FFFS) between patients dependent on methamphetamine and opiates, and a group of controls.

PATIENTS AND METHODS

This research was a causal-comparative study that was conducted in the first six months of 2012. The population of the study was males of Mashhad city, who were dependent on methamphetamine or opiates, and ruling out psychotic disorders and prominent Axis II. Twenty-five people were selected by the convenient sampling method. Also, 25 non-dependent people from the patients' relatives were selected and matched for the variables of age, gender, and education to participate in this study. Participants were evaluated using a structured clinical interview (SCID) for DSM-IV, demographic questionnaire information, and a Jackson-5 questionnaire (2009). Data were analyzed by Chi-square, K-S, and independent t-test.

RESULTS

The methamphetamine dependent group had a higher sensitivity in the r-BAS, r-BIS, and the r-Fight and r-Freezing systems compared to the control group (P < 0.05). However, there was no significant difference in r-Flight between the two groups (P > 0.05). "The scores of r-BIS were also significantly higher in the methamphetamine-dependent group than the opioid-dependent and control groups. For the r-Fight variable, the methamphetamine-dependent group was higher than the opioid-dependent group".

CONCLUSIONS

The personality patterns of patients dependent on methamphetamines were different from the controls. These people have a high sensitivity to punishment cues, such as being compared in social conditions and a tendency for reinforcement and reward, because of their higher sensitivity in the behavioral inhibition and activation systems.

Predisposition to and effects of methamphetamine use on the adolescent brain

Adolescence is a period of heightened vulnerability both to addictive behaviors and drug-induced brain damage. Yet, only limited information exists on the brain mechanisms underlying these adolescent-specific characteristics. Moreover, distinctions in brain correlates between predisposition to drug use and effects of drugs in adolescents are unclear. Using cortical thickness and diffusion tensor image analyses, we found greater and more widespread gray and white matter alterations, particularly affecting the frontostriatal system, in adolescent methamphetamine (MA) users compared with adult users. Among adolescent-specific gray matter alterations related to MA use, smaller cortical thickness in the orbitofrontal cortex was associated with family history of drug use. Our findings highlight that the adolescent brain, which undergoes active myelination and maturation, is more vulnerable to MA-related alterations than the adult brain. Furthermore, MA-use-related executive dysfunction was greater in adolescent MA users than in adult users. These findings may provide explanation for the severe behavioral complications and relapses that are common in adolescent-onset drug addiction. Additionally, these results may provide insights into distinguishing the neural mechanisms that underlie the predisposition to drug addiction from effects of drugs in adolescents.

Glutamatergic neurometabolites during early abstinence from chronic methamphetamine abuse

BACKGROUND

The acute phase of abstinence from methamphetamine abuse is critical for rehabilitation success. Proton magnetic resonance spectroscopy has detected below-normal levels of glutamate+glutamine in anterior middle cingulate of chronic methamphetamine abusers during early abstinence, attributed to abstinence-induced downregulation of the glutamatergic systems in the brain. This study further explored this phenomenon.

METHODS

We measured glutamate+glutamine in additional cortical regions (midline posterior cingulate, midline precuneus, and bilateral inferior frontal cortex) putatively affected by methamphetamine. We examined the relationship between glutamate+glutamine in each region with duration of methamphetamine abuse as well as the depressive symptoms of early abstinence. Magnetic resonance spectroscopic imaging was acquired at 1.5 T from a methamphetamine group of 44 adults who had chronically abused methamphetamine and a control group of 23 age-, sex-, and tobacco smoking-matched healthy volunteers. Participants in the methamphetamine group were studied as inpatients during the first week of abstinence from the drug and were not receiving treatment.

RESULTS

In the methamphetamine group, small but significant (5-15%, P<.05) decrements (vs control) in glutamate+glutamine were observed in posterior cingulate, precuneus, and right inferior frontal cortex; glutamate+glutamine in posterior cingulate was negatively correlated (P<.05) with years of methamphetamine abuse. The Beck Depression Inventory score was negatively correlated (P<.005) with glutamate+glutamine in right inferior frontal cortex.

CONCLUSIONS

Our findings support the idea that glutamatergic metabolism is downregulated in early abstinence in multiple cortical regions. The extent of downregulation may vary with length of abuse and may be associated with severity of depressive symptoms emergent in early recovery.

Methamphetamine: an update on epidemiology, pharmacology, clinical phenomenology, and treatment literature

BACKGROUND

Despite initial reports of a decline in use in the early 2000s, methamphetamine remains a significant public health concern with known neurotoxic and neurocognitive effects to the user. The goal of this review is to update the literature on methamphetamine use and addiction since its assent to peak popularity in 1990s.

METHODS

We first review recent epidemiological reports with a focus on methamphetamine accessibility, changes in use and disorder prevalence rates over time, and accurate estimates of the associated burden of care to the individual and society. Second, we review methamphetamine pharmacology literature with emphasis on the structural and functional neurotoxic effects associated with repeated use of the drug. Third, we briefly outline the findings on methamphetamine-related neurocognitive deficits as assessed via behavioral and neuroimaging paradigms. Lastly, we review the clinical presentation of methamphetamine addiction and the evidence supporting the available psychosocial and pharmacological treatments within the context of an addiction biology framework.

CONCLUSION

Taken together, this review provides a broad-based update of the available literature covering methamphetamine research over the past two decades and concludes with recommendations for future research.

New perspectives on using brain imaging to study CNS stimulants

While the recent application of brain imaging to study CNS stimulants has offered new insights into the fundamental factors that contribute to their use and abuse, many gaps remain. Brain circuits that mediate pleasure, dependence, craving and relapse are anatomically, neurophysiologically and neurochemically distinct from one another, which has guided the search for correlates of stimulant-seeking and taking behavior. However, unlike other drugs of abuse, metrics for tolerance and physical dependence on stimulants are not obvious. The dopamine theory of stimulant abuse does not sufficiently explain this disorder as serotonergic, GABAergic and glutamagergic circuits are clearly involved in stimulant pharmacology and so tracking the source of the "addictive" processes must adopt a more multimodal, multidisciplinary approach. To this end, both anatomical and functional magnetic resonance imaging (MRI), MR spectroscopy (MRS) and positron emission tomography (PET) are complementary and have equally contributed to our understanding of how stimulants affect the brain and behavior. New vistas in this area include nanotechnology approaches to deliver small molecules to receptors and use MRI to resolve receptor dynamics. Anatomical and blood flow imaging has yielded data showing that cognitive enhancers might be useful adjuncts in treating CNS stimulant dependence, while MRS has opened opportunities to examine the brain's readiness to accept treatment as GABA tone normalizes after detoxification. A desired outcome of the above approaches is being able to offer evidence-based rationales for treatment approaches that can be implemented in a more broad geographic area, where access to brain imaging facilities may be limited. This article is part of the Special Issue entitled 'CNS Stimulants'.

Repeated Acquisition in the Morris Swim Task: Effects of MDMA, Methamphetamine and Methylphenidate

Acute effects of methylenedioxymethamphetamine (MDMA), methamphetamine (MA) and methylphenidate (MPD) were studied using a within-subject, repeated acquisition/performance procedure adapted to the Morris Swim Task. To investigate place learning, the acquisition component consisted of a hidden platform that varied in location across experimental sessions. As a control for drug effects not specific to acquisition, a performance component was included in which the hidden platform was in the same pool location in every experimental session. All three drugs increased escape latencies and swim distances in dose-dependent fashion. However, impairment in the acquisition component was generally observed only at doses that also produced impairment in the performance component, suggesting that effects were not selective to place learning. None of the drugs produced enhancement of learning or performance at any dose. Taken together, the results suggest that acute exposure to these psychomotor stimulants produce global impairment of performance in the Morris task, rather than specific deficits in place learning.

Dysregulation of dopamine and glutamate release in the prefrontal cortex and nucleus accumbens following methamphetamine self-administration and during reinstatement in rats

Methamphetamine (meth) addicts often exhibit enduring cognitive and neural deficits that likely contribute to persistent drug seeking and the high rates of relapse. These deficits may be related to changes in the prefrontal cortex (PFC) and its glutamatergic projections to the nucleus accumbens (NAc). Here, we performed in vivo microdialysis in the PFC and NAc in rats following either meth self-administration or yoked-saline control histories to assess baseline glutamate (GLU) levels, or reinstatement-evoked GLU and dopamine (DA) efflux in both regions simultaneously under cue-induced, meth-primed, or combined cues+meth reinstatement conditions. Our results show that meth self-administration (1) reduced basal GLU levels in both the dmPFC and NAc, (2) concurrently increased dmPFC and NAc GLU efflux during reinstatement, and (3) increased DA efflux in the dmPFC, but not in the NAc, under all reinstatement conditions when compared with yoked-saline controls. These data demonstrate for the first time that a history of psychostimulant self-administration alters GLU homeostasis not only in the NAc, but also in the dmPFC, its primary GLU projection source. Furthermore, combined cues+meth-primed reinstatement conditions produced the most pronounced increases in mPFC and NAc extracellular GLU, suggesting that the cue and meth prime conditions are additive in promoting reinstatement. Finally, increased efflux of DA in the dmPFC, but not in the NAc, across reinstatement conditions suggests that DA release in the dmPFC may be an important mediator of drug seeking initiated by multiple relapse triggers.

Childhood maltreatment and amygdala connectivity in methamphetamine dependence: a pilot study

INTRODUCTION

Childhood maltreatment, a well-known risk factor for the development of substance abuse disorders, is associated with functional and structural abnormalities in the adult brain, particularly in the limbic system. However, almost no research has examined the relationship between childhood maltreatment and brain function in individuals with drug abuse disorders.

METHODS

We conducted a pilot study of the relationship between childhood maltreatment (evaluated with the Childhood Trauma Questionnaire; Bernstein and Fink 1998) and resting-state functional connectivity of the amygdala (bilateral region of interest) with functional magnetic resonance imaging in 15 abstinent, methamphetamine-dependent research participants. Within regions that showed connectivity with the amygdala as a function of maltreatment, we also evaluated whether amygdala connectivity was associated positively with negative affect and negatively with healthy emotional processing.

RESULTS

The results indicated that childhood maltreatment was positively associated with resting-state connectivity between the amygdala and right hippocampus, right parahippocampal gyrus, right inferior temporal gyrus, right orbitofrontal cortex, cerebellum, and brainstem. Furthermore, connectivity between the amygdala and hippocampus was positively related to measures of depression, trait anxiety, and emotion dysregulation, and negatively related to self-compassion and dispositional mindfulness.

CONCLUSIONS

These findings suggest that childhood maltreatment may contribute to increased limbic connectivity and maladaptive emotional processing in methamphetamine-dependent adults, and that healthy emotion regulation strategies may serve as a therapeutic target to ameliorate the associated behavioral phenotype. Childhood maltreatment warrants further investigation as a potentially important etiological factor in the neurobiology and treatment of substance use disorders.

Low frequency repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex transiently increases cue-induced craving for methamphetamine: a preliminary study

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) can temporarily interrupt or facilitate activity in a focal brain region. Several lines of evidence suggest that rTMS of the dorsolateral prefrontal cortex (DLPFC) can affect processes involved in drug addiction. We hypothesized that a single session of low-frequency rTMS of the left DLPFC would modulate cue-induced craving for methamphetamine (MA) when compared to a sham rTMS session.

METHODS

In this single-blind, sham-controlled crossover study, 10 non-treatment seeking MA-dependent users and 8 healthy controls were randomized to receive 15 min of sham and real (1 Hz) DLPFC rTMS in two experimental sessions separated by 1h. During each rTMS session, participants were exposed to blocks of neutral cues and MA-associated cues. Participants rated their craving after each cue block.

RESULTS

In MA users, real rTMS over the left DLPFC increased self-reported craving as compared to sham stimulation (17.86 ± 1.46 vs. 24.85 ± 1.57, p=0.001). rTMS had no effect on craving in healthy controls. One Hertz rTMS of the left DLPFC was safe and tolerable for all participants.

CONCLUSIONS

Low frequency rTMS of the left DLPFC transiently increased cue-induced craving in MA participants. These preliminary results suggest that 1 Hz rTMS of the left DLPFC may increase craving by inhibiting the prefrontal cortex or indirectly activating subcortical regions involved in craving.

Methamphetamine and other substance use trends among street-recruited men who have sex with men, from 2008 to 2011

BACKGROUND

It is particularly important to survey substance use trends in populations most impacted by the consequences of substance use. Men who have sex with men (MSM) exhibit rates of methamphetamine and other substance use that exceeds those observed among other populations in the United States. Such substance use has been associated with numerous negative health sequelae.

METHODS

An outreach program performed street encounters with 5599 unique substance-using MSM from January 1, 2008 through December 31, 2011 to collect data on self-reported sociodemographics and recent substance use. Data were aggregated into six-month cohorts for comparisons of recent substance use patterns across time

RESULTS

Participants averaged 33 years of age (SD=8), most were Caucasian/white (47%) or Hispanic/Latino (32%), and the self-reported HIV seroprevalence rate was 13.4%. Across cohorts, reported use of alcohol (range=91-93%), marijuana (range=36-46%), and/or methamphetamine (range=23-27%) was common; prevalence of amyl nitrite (max=14%), ecstasy (max=12%), powder cocaine (max=8%) and/or crack cocaine (max=4%) use, although less common, were still elevated relative to the United States general population.

CONCLUSIONS

Methamphetamine and other substance use remained common among substance-using MSM, demonstrating the need for continued substance use interventions geared toward this high-risk population.

Methamphetamine-induced increases in putamen gray matter associate with inhibitory control

RATIONALE

Problematic drug use is associated with difficulty in exerting self-control over behaviors, and this difficulty may be a consequence of atypical morphometric characteristics that are exhibited by drug-experienced individuals. The extent to which these structural abnormalities result from drug use or reflect neurobiological risk factors that predate drug use, however, is unknown.

OBJECTIVES

The purpose of this study is to determine how methamphetamine affects corticostriatal structure and how drug-induced changes relate to alterations in inhibitory control.

METHODS

Structural magnetic resonance images and positron emission tomography (PET) scans, assessing dopamine D₂-like receptor and transporter availability, were acquired in monkeys trained to acquire, retain, and reverse three-choice visual discrimination problems before and after exposure to an escalating dose regimen of methamphetamine (or saline, as a control). Voxel-based morphometry was used to compare changes in corticostriatal gray matter between methamphetamine- and saline-exposed monkeys. The change in gray matter before and after the dosing regimen was compared to the change in the behavioral performance and in dopaminergic markers measured with PET.

RESULTS

Methamphetamine exposure, compared to saline, increased gray matter within the right putamen. These changes were positively correlated with changes in performance of methamphetamine-exposed monkeys in the reversal phase, and were negatively correlated with alterations in D₂-like receptor and DAT availability.

CONCLUSIONS

The results provide the first evidence that exposure to a methamphetamine dosing regimen that resembles human use alters the structural integrity of the striatum and that gray-matter abnormalities detected in human methamphetamine users are due, at least in part, to the pharmacological effects of drug experience.

Altered visual perception in long-term ecstasy (MDMA) users

RATIONALE

The present study investigated the long-term consequences of ecstasy use on visual processes thought to reflect serotonergic functions in the occipital lobe. Evidence indicates that the main psychoactive ingredient in ecstasy (methylendioxymethamphetamine) causes long-term changes to the serotonin system in human users. Previous research has found that amphetamine-abstinent ecstasy users have disrupted visual processing in the occipital lobe which relies on serotonin, with researchers concluding that ecstasy broadens orientation tuning bandwidths. However, other processes may have accounted for these results.

OBJECTIVES

The aim of the present research was to determine if amphetamine-abstinent ecstasy users have changes in occipital lobe functioning, as revealed by two studies: a masking study that directly measured the width of orientation tuning bandwidths and a contour integration task that measured the strength of long-range connections in the visual cortex of drug users compared to controls.

METHOD

Participants were compared on the width of orientation tuning bandwidths (26 controls, 12 ecstasy users, 10 ecstasy + amphetamine users) and the strength of long-range connections (38 controls, 15 ecstasy user, 12 ecstasy + amphetamine users) in the occipital lobe.

RESULTS

Amphetamine-abstinent ecstasy users had significantly broader orientation tuning bandwidths than controls and significantly lower contour detection thresholds (CDTs), indicating worse performance on the task, than both controls and ecstasy + amphetamine users.

CONCLUSION

These results extend on previous research, which is consistent with the proposal that ecstasy may damage the serotonin system, resulting in behavioral changes on tests of visual perception processes which are thought to reflect serotonergic functions in the occipital lobe.

Working memory and speed of information processing in chronic khat users: preliminary findings

To date there are very few laboratory data available regarding the long-term effect of the psychostimulant khat on human neurocognitive functioning. The purpose of the present study was to assess whether chronic khat users would demonstrate impairments in working memory and speed of information processing compared to control subjects. Working memory was assessed using the forward and backward digit span test. Speed of information processing was assessed using the Digit Symbol Substitution Test. Results of the present study indicate that chronic khat use may have a long-term deleterious effect on working memory, particularly on digit backwards measures of short-term/working memory. The finding is consistent with results seen by several investigators in samples of methamphetamine users.

Addiction

Drug and alcohol addiction is a debilitating disorder characterized by persistent drug-seeking behaviors despite negative physiological, medical, or social consequences. Neurobiological models of addiction propose that the reinforcing effects of addictive drugs are associated with altered neurotransmission within the reward 'mesocorticolimbic' circuitry in the brain. Immense efforts are therefore designed to target the mesocorticolimbic circuitry in attenuating drug dependence and addiction-related behaviors. Yet, to date, most addiction treatments have demonstrated only limited success in reducing addiction-related behaviors. Accumulating and compelling evidence suggests that novel nonsurgical brain stimulation techniques, such as transcranial magnetic stimulation and transcranial direct current stimulation, could serve as promising tools for indexing altered neurotransmission associated with repetitive drug use, and moreover, may hold therapeutic potential for the treatment of drug dependence and addiction-related behaviors. This chapter reviews and discusses the current and potential applications of such techniques in the study and treatment of addiction; we focus on a number of common drugs of abuse, including nicotine, alcohol, cocaine, cannabis, and ecstasy.

Negative moods correlate with craving in female methamphetamine users enrolled in compulsory detoxification

Background

Methamphetamine (METH) use, especially in females, has become a growing public health concern in China. In this study, we aimed to characterize the factors that contributed to drug craving in female METH users under isolated compulsory detoxification. We characterized factors contributing to craving such as duration of detoxification, history of drug use and self-reported mood state.

Methods

Subjects (N=113) undergoing a 1- to 3-year METH detoxification program were recruited from the Zhejiang Compulsory Detoxification Center for Women. The Questionnaire of METH-use Urge (QMU) was used to evaluate the level of craving for METH. The Abbreviate Profile of Mood States (A-POMS) was applied as an assessment for the negative mood disturbances.

Results

The participants were at a mean age of 25.2, primarily lowly educated and unemployed, and single. Smoking was the only route of METH administration at an average dose of 0.5 g/day, and 4 times/week. The reported craving level was positively correlated with the negative mood disturbances and the weekly dose of METH, but independent of the duration of detoxification. Furthermore, all five aspects of negative mood disturbances, including fatigue, bewilderment, anxiety, depression and hostility, were shown to positively correlate to the self-reported craving level after controlling for weekly dose of METH.

Conclusions

The data demonstrate a robust correlation between mood distress and craving for METH. Our results call for close evaluation of mood distress in treatment of METH users in China.

Restricted psychological horizon in active methamphetamine users: future, past, probability, and social discounting

Methamphetamine users (MAU) exhibit an exaggerated bias for immediate rewards that reflects a restricted time horizon, where outcomes in the future are excessively discounted. An accumulating literature indicates that time in the future shares features with other dimensions of psychological distances including time in the past, probability, and social distance, suggesting that bias for immediacy may be reducible to a more general restriction of psychological horizon. The purpose of the present study was to explore generalized restricted psychological horizon in active MAU by assessing future, past, probability, and social discounting. Compared with nonusing controls, MAU preferred psychologically proximal outcomes, resulting in higher rates for all types of discounting, which supports the conceptualization that MAU insufficiently integrate outcomes of psychological distance (i.e. in the future, the past, probabilistic, for others) into the valuation of current behavioral alternatives. The present results are suggestive of a more fundamental process of problematic decision-making associated with methamphetamine use, indicating the necessity of more comprehensive approaches to address the generalized limitations of restricted psychological horizon.

Comparison of intranasal methamphetamine and d-amphetamine self-administration by humans

AIMS

There are no studies directly comparing self-administration of methamphetamine and d-amphetamine by humans. This study compared intranasal methamphetamine- and d-amphetamine self-administration and characterized the mood, performance and physiological effects produced by the drugs.

DESIGN

A randomized, double-blind, placebo-controlled, cross-over study.

SETTING

An out-patient research unit at the New York State Psychiatric Institute.

PARTICIPANTS

Male recreational methamphetamine users (n = 13).

MEASUREMENTS

Five 2-day blocks of sessions were conducted. On the first day of each block, participants 'sampled' a single methamphetamine or d-amphetamine dose (0, 12, 50 mg/70 kg) and a monetary reinforcer ($5 or $20). Amphetamine plasma levels, cardiovascular, mood, and psychomotor performance effects were assessed before drug administration and repeatedly thereafter. On the second day of each block, participants chose between the sampled reinforcers (drug or money).

FINDINGS

There were no significant differences between the drugs on the majority of measures. Under the $5 condition, both amphetamines increased self-administration dose-dependently, with 41% drug choices overall. Under the $20 condition, only 17% drug options were selected. Both drugs increased cardiovascular activity and 'positive' mood, although methamphetamine produced more prominent effects on some measures (e.g. heart rate and ratings of 'high').

CONCLUSIONS

Methamphetamine and d-amphetamines appear to produce a similar dose-related profile of effects in humans, which supports their equivalence for abuse potential.

Pain, affective symptoms, and cognitive deficits in patients with cerebral dopamine dysfunction

Converging preclinical, and human epidemiological, neuroimaging, and genetic evidence suggests a central role for dopamine neurotransmission in modulating pain perception and analgesia. Dysregulation in dopamine signaling may modulate the experience of pain both directly, by enhancing or diminishing the propagation of nociceptive signals, and indirectly, by influencing affective and cognitive processes, which affect the expectation, experience, and interpretation of nociceptive signals. Hypersensitivity to pain and high rates of comorbid chronic pain are common in disorders linked with deficits in dopamine system function, including disorders of mood and affect, substance abuse, and Parkinson disease. Hyposensitivity to pain, however, is common in patients with schizophrenia, which has been linked with excessive dopamine neurotransmission. Although patients are typically affected most by the primary symptoms of their disorders, alterations in pain perception may further increase the burden of their illness, compromising their quality of life. The present review focuses on this relationship, and discusses clinical and potential therapeutic implications for both patients with dopamine-related disorders and those with chronic pain syndromes.

Residual effects of ecstasy (3,4-methylenedioxymethamphetamine) on low level visual processes

'Ecstasy' (3,4-methylenedioxymethamphetamine) induces impaired functioning in the serotonergic system, including the occipital lobe. This study employed the 'tilt aftereffect' paradigm to operationalise the function of orientation-selective neurons among ecstasy consumers and controls as a means of investigating the role of reduced serotonin on visual orientation processing. The magnitude of the tilt aftereffect reflects the extent of lateral inhibition between orientation-selective neurons and is elicited to both 'real' contours, processed in visual cortex area V1, and illusory contours, processed in V2. The magnitude of tilt aftereffect to both contour types was examined among 19 ecstasy users (6 ecstasy only; 13 ecstasy-plus-cannabis users) and 23 matched controls (9 cannabis-only users; 14 drug-naive). Ecstasy users had a significantly greater tilt magnitude than non-users for real contours (Hedge's g = 0.63) but not for illusory contours (g = 0.20). These findings provide support for literature suggesting that residual effects of ecstasy (and reduced serotonin) impairs lateral inhibition between orientation-selective neurons in V1, which however suggests that ecstasy may not substantially affect this process in V2. Multiple studies have now demonstrated ecstasy-related deficits on basic visual functions, including orientation and motion processing. Such low-level effects may contribute to the impact of ecstasy use on neuropsychological tests of visuospatial function.

Effects of methamphetamine abuse and serotonin transporter gene variants on aggression and emotion-processing neurocircuitry

Individuals who abuse methamphetamine (MA) exhibit heightened aggression, but the neurobiological underpinnings are poorly understood. As variability in the serotonin transporter (SERT) gene can influence aggression, this study assessed possible contributions of this gene to MA-related aggression. In all, 53 MA-dependent and 47 control participants provided self-reports of aggression, and underwent functional magnetic resonance imaging while viewing pictures of faces. Participants were genotyped at two functional polymorphic loci in the SERT gene: the SERT-linked polymorphic region (SERT-LPR) and the intron 2 variable number tandem repeat polymorphism (STin2 VNTR); participants were then classified as having high or low risk for aggression according to individual SERT risk allele combinations. Comparison of SERT risk allele loads between groups showed no difference between MA-dependent and control participants. Comparison of self-report scores showed greater aggression in MA-dependent than control participants, and in high genetic risk than low-risk participants. Signal change in the amygdala was lower in high genetic risk than low-risk participants, but showed no main effect of MA abuse; however, signal change correlated negatively with MA use measures. Whole-brain differences in activation were observed between MA-dependent and control groups in the occipital and prefrontal cortex, and between genetic high- and low-risk groups in the occipital, fusiform, supramarginal and prefrontal cortex, with effects overlapping in a small region in the right ventrolateral prefrontal cortex. The findings suggest that the investigated SERT risk allele loads are comparable between MA-dependent and healthy individuals, and that MA and genetic risk influence aggression independently, with minimal overlap in associated neural substrates.

Treatment outcomes for methamphetamine users: California Proposition 36 and comparison clients

Methamphetamine (meth) is a major drug of abuse in California and several other states, particularly among criminal offender populations. Over the past decade, substance abuse treatment systems have had to adapt to and accommodate the increasing needs of meth users and, in California, deal with the impact of Proposition 36, which has resulted in a greater number of criminal offenders entering the treatment system. This study examines selected treatment performance and outcome indicators for California Proposition 36 offenders entering substance abuse treatment for meth use and compares their performance and outcomes to other subgroups of California treatment clients differentiated by whether or not they were admitted to treatment through Proposition 36 and whether or not their primary substance was meth. Significant improvements in all outcome domains were seen across the populations, and treatment performance and outcomes were not substantively inferior for the offender or meth-using groups.

The mGluR5 Positive Allosteric Modulator CDPPB Does Not Alter Extinction or Contextual Reinstatement of Methamphetamine-Seeking Behavior in Rats

Extinction of drug-seeking behavior is a form of new and active learning. Facilitation of extinction learning is of clinical interest since cue exposure therapies for the treatment of addiction have largely been unsuccessful in preventing relapse, primarily due to the context specificity of extinction learning. Recently, several studies have shown that potentiation of glutamatergic transmission can facilitate extinction learning in rodent models of cocaine addiction. In this study we investigated the effects of the type 5 metabotropic glutamate receptor (mGluR5) positive allosteric modulator (PAM) 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) on the extinction and contextual reinstatement of methamphetamine-seeking behavior. Rats were trained and allowed to self-administer methamphetamine (0.1 mg/kg/infusion) in 2 hr daily sessions in Context A where self-administration chambers had distinct tactile, visual, auditory, and olfactory cues. Next, CDPPB (60 mg/kg) or vehicle was administered prior to subsequent extinction training sessions that were conducted in modified self-administration chambers (Context B) that were Context A. Following 16 days of extinction training in Context B, animals were placed back in Context A for assessment of contextual reinstatement of methamphetamine-seeking behavior. CDPPB failed to produce significant reductions in extinction responding or in the magnitude of contextual reinstatement of methamphetamine-seeking compared to vehicle treated controls. We postulate that numerous factors, including methamphetamine-induced changes in mGluR5 receptor expression or function, may have contributed to the observed lack of effects. Although these findings initially suggest that mGluR5 PAMs may be ineffective in facilitating extinction learning or preventing context-induced relapse in methamphetamine addiction, additional studies are warranted examining effects of other mGluR5 PAMs, particularly those with improved pharmacological properties and devoid of potential side effects at higher doses.

A direct comparison of the behavioral and physiological effects of methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) in humans

RATIONALE

Despite their chemical similarities, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) produce differing neurochemical and behavioral responses in animals. In humans, individual studies of methamphetamine and MDMA indicate that the drugs engender overlapping and divergent effects; there are only limited data comparing the two drugs in the same individuals.

OBJECTIVES

This study examined the effects of methamphetamine and MDMA using a within-subject design.

METHODS

Eleven adult volunteers completed this 13-day residential laboratory study, which consisted of four 3-day blocks of sessions. On the first day of each block, participants received oral methamphetamine (20, 40 mg), MDMA (100 mg), or placebo. Drug plasma concentrations, cardiovascular, subjective, and cognitive/psychomotor performance effects were assessed before drug administration and after. Food intake and sleep were also assessed. On subsequent days of each block, placebo was administered and residual effects were assessed.

RESULTS

Acutely, both drugs increased cardiovascular measures and "positive" subjective effects and decreased food intake. In addition, when asked to identify each drug, participants had difficulty distinguishing between the amphetamines. The drugs also produced divergent effects: methamphetamine improved performance and disrupted sleep, while MDMA increased "negative" subjective-effect ratings. Few residual drug effects were noted for either drug.

CONCLUSIONS

It is possible that the differences observed could explain the differential public perception and abuse potential associated with these amphetamines. Alternatively, the route of administration by which the drugs are used recreationally might account for the many of the effects attributed to these drugs (i.e., MDMA is primarily used orally, whereas methamphetamine is used by routes associated with higher abuse potential).