Cognitive impairment in individuals currently using methamphetamine

Effects of sequential ethanol exposure and repeated high-dose methamphetamine on striatal and hippocampal dopamine, serotonin and glutamate tissue content in Wistar rats

Alcohol (ethanol) and methamphetamine (METH) co-abuse is a major public health issue. Ethanol or METH exposure has been associated with changes in neurotransmitter levels in several central brain regions. However, little is known about the effect of sequential exposure to ethanol and METH on glutamate, dopamine and serotonin tissue content in striatum and hippocampus. In this study, we investigated the effects of sequential exposure to ethanol and METH on tissue content of these neurotransmitters. Male Wistar rats were orally gavaged with either ethanol (6g/kg) or water for seven days. Rats were administered with high dose of METH (10mg/kg, i.p. every 2h×4) or saline on Day 8 and euthanized 48h of last METH or saline i.p. injection. In the striatum, sequential exposure to ethanol and METH increased glutamate tissue content while reducing dopamine and serotonin tissue content as compared to the group exposed to ethanol alone. In the hippocampus, sequential exposure to ethanol and METH decreased serotonin tissue content as compared to the group that was exposed to ethanol alone. However, this study showed that ethanol has no additive effect to METH on tissue content of dopamine and serotonin as compared to METH in the striatum and hippocampus. This study demonstrated that sequential exposure of ethanol and METH has an additive effect on tissue content of certain neurotransmitters in the brain.

Effect of three different regimens of repeated methamphetamine on rats' cognitive performance

Neurocognitive impairment in response to methamphetamine (MA) has been proven in a variety of experimental and clinical studies. Elucidation of the underlying mechanisms of MA-induced cognitive deficits and finding preventive/therapeutic approaches need best-suited animal models. In modeling repeated MA exposure, while some believes that escalating doses simulate drug abuse conditions, others believe this regimen confers a preconditioning protection. The present study aimed to compare the effects of three different regimens of repeated MA administration on memory and cognitive function of adult rats. Rats in two different experimental groups were treated with escalating paradigms consisted of twice-daily i.p. injections; 1-4 mg/kg over 7 days or 1-10 mg/kg over 10 days. The third group received twice-daily doses of 15 mg/kg every other day over 14 days. Spatial working memory, novel object recognition task and anxiety-like behavior were measured sequentially in all MA-treated rats and vehicle-treated controls started from day 8 after last injection. All MA regimens decreased rates of spontaneous alternation in Y-maze and increased anxiety-like response. Short-term recognition memory was unchanged across all MA-treated animals, while long-term memory was impaired in the second and third MA regimen. Though MA deleterious effect especially in recognition memory is somehow dose dependent, preconditioning effect of increasing doses may be ruled out at least in the case of parameters measured here.

Molecular, Behavioral, and Physiological Consequences of Methamphetamine Neurotoxicity: Implications for Treatment

Understanding the relationship between the molecular mechanisms underlying neurotoxicity of high-dose methamphetamine (METH) and related clinical manifestations is imperative for providing more effective treatments for human METH users. This article provides an overview of clinical manifestations of METH neurotoxicity to the central nervous system and neurobiology underlying the consequences of administration of neurotoxic METH doses, and discusses implications of METH neurotoxicity for treatment of human abusers of the drug.

Neuropsychological comparisons of cocaine versus methamphetamine users: A research synthesis and meta-analysis

BACKGROUND

Previous meta-analytical research examining cocaine and methamphetamine separately suggests potentially different neuropsychological profiles associated with each drug. In addition, neuroimaging studies point to distinct structural changes that might underlie differences in neuropsychological functioning.

OBJECTIVES

This meta-analysis compared the effect sizes identified in cocaine versus methamphetamine studies across 15 neuropsychological domains.

METHOD

Investigators searched and coded the literature examining the neuropsychological deficits associated with a history of either cocaine or methamphetamine use. A total of 54 cocaine and 41 methamphetamine studies were selected, yielding sample sizes of 1,718 and 1,297, respectively. Moderator analyses were conducted to compare the two drugs across each cognitive domain.

RESULTS

Data revealed significant differences between the two drugs. Specifically, studies of cocaine showed significantly larger effect-size estimates (i.e., poorer performance) in verbal working memory when compared to methamphetamine. Further, when compared to cocaine, methamphetamine studies demonstrated significantly larger effect sizes in delayed contextual verbal memory and delayed visual memory.

CONCLUSION

Overall, cocaine and methamphetamine users share similar neuropsychological profiles. However, cocaine appears to be more associated with working memory impairments, which are typically frontally mediated, while methamphetamine appears to be more associated with memory impairments that are linked with temporal and parietal lobe dysfunction.

Diversities of behavioral traits and neuropsychological function in different substance addiction

OBJECTIVE

There are various temperaments and personality characters that modulate the development of substance addiction. The pharmacological properties of substances would alter the homeostasis of brain function and influence the neuropsychological performance through different neurotransmissions which then facilitate diverse emotional and behavioral responses. Our goal is to assess the interaction between personality characteristics, neuropsychological performances and Stroop interference in alcoholics, heroin and amphetamine dependent persons.

METHODS

Subjects with alcohol (N=95), heroin (N=82) and amphetamine (N=57) dependence were recruited. Diagnostic interview and questionnaires evaluating the psychiatric symptoms were done, followed by neuropsychological assessments of Stroop and Wisconsin card sorting tests (WCST). Differences between the study groups were analyzed by one-way ANOVA with Scheffe's test.

RESULTS

The individuals with alcohol dependence had significantly higher scores of neurotic, dysphoric and impulsive traits (P<0.001) than heroin and amphetamine dependent groups. In Stroop tests, the alcohol dependent subjects also showed delayed response on incongruent naming interferences compared to both of heroin and amphetamine groups (P<0.001). Perseverative errors and responses of WCST were significantly higher in heroin than in alcoholic dependent persons (P<0.01).

CONCLUSIONS

Individuals with different substance dependence have distinct behavioral traits for developing addicted behaviors and had variant deficits of neuropsychological function.

Effects of Housing on Methamphetamine-Induced Neurotoxicity and Spatial Learning and Memory

Severe stress potentiates methamphetamine (MA) neurotoxicity. However, whether moderate stress increases or decreases the neurotoxic effects of MA is unknown. We assessed the effects of MA (4 × 10 mg/kg at 2 h intervals) in combination with prior barren-cage housing in adult male Sprague-Dawley rats on monoamines and glial fibrillary acid protein (GFAP) in one cohort and spatial learning and memory in the Morris water maze in another cohort. MA reduced dopamine (DA) and serotonin (5-HT) in the neostriatum and nucleus accumbens, 5-HT in the hippocampus, and increased GFAP in neostriatum and nucleus accumbens compared with saline controls. In neostriatum, barren-cage housing protected against MA-induced increases in GFAP, but it did not prevent DA and 5-HT reductions, although it did increase hippocampal norepinephrine. MA impaired spatial learning during acquisition, reversal, and shift phases and impaired reference memory on reversal and shift probe trials. Barren-cage housing enhanced performance during acquisition but not during reversal or shift or on probe trials. The data indicate that prior barren-cage housing moderates MA-induced neostriatal astrogliosis and initial spatial learning, but has no protective effect when the platform is smaller and relocated and therefore requires cognitive flexibility in relearning.

Pattern and related factors of cognitive impairment among chronic methamphetamine users

BACKGROUND AND OBJECTIVES

Methamphetamine (MA) use is increasingly prevalent in East and Southeast Asia and commonly associated with cognitive impairment. The present study estimated the characteristics of cognitive impairment and explored the associated potential factors among chronic MA users.

METHODS

The data were from the baseline visit of a longitudinal study among synthetic drug users. The baseline survey was conducted in detoxification and rehabilitation centers in Guangdong province, China, from September to December in 2013. A total of 528 participants were included in our analysis. Cognitive impairment was measured by the Montreal Cognitive Assessment (MoCA). Logistic regression was performed to explore the risk factors associated with cognitive impairment.

RESULTS

Approximately 69.89% of the study participants exhibited cognitive impairment according to MoCA scores. Multiple logistic regression analyses indicated that older age (≥30 years old), a longer duration of MA use (>24 months), and a higher frequency of MA use (everyday) were associated with cognitive impairment, with adjusted odds ratios (ORs) of 1.58 (95% confidence interval [CI]: 1.07-2.34), 1.53 (95%CI: 1.01-2.31), and 1.55 (95%CI: 1.05-2.30), respectively. Methamphetamine users that had a higher level of education had a lower risk of cognitive impairment(OR = .59; 95%CI: .38-.93).

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Cognitive impairment occurred frequently among chronic MA users. The causal relationship between cognitive impairment and MA use needs to be ascertained in longitudinal studies in future work. Our study provides evidence for the development of intervention strategies for the prevention of MA use and associated cognitive impairment. (Am J Addict 2017;26:145-151).

Effects of drugs of abuse on hippocampal plasticity and hippocampus-dependent learning and memory: contributions to development and maintenance of addiction

It has long been hypothesized that conditioning mechanisms play major roles in addiction. Specifically, the associations between rewarding properties of drugs of abuse and the drug context can contribute to future use and facilitate the transition from initial drug use into drug dependency. On the other hand, the self-medication hypothesis of drug abuse suggests that negative consequences of drug withdrawal result in relapse to drug use as an attempt to alleviate the negative symptoms. In this review, we explored these hypotheses and the involvement of the hippocampus in the development and maintenance of addiction to widely abused drugs such as cocaine, amphetamine, nicotine, alcohol, opiates, and cannabis. Studies suggest that initial exposure to stimulants (i.e., cocaine, nicotine, and amphetamine) and alcohol may enhance hippocampal function and, therefore, the formation of augmented drug-context associations that contribute to the development of addiction. In line with the self-medication hypothesis, withdrawal from stimulants, ethanol, and cannabis results in hippocampus-dependent learning and memory deficits, which suggest that an attempt to alleviate these deficits may contribute to relapse to drug use and maintenance of addiction. Interestingly, opiate withdrawal leads to enhancement of hippocampus-dependent learning and memory. Given that a conditioned aversion to drug context develops during opiate withdrawal, the cognitive enhancement in this case may result in the formation of an augmented association between withdrawal-induced aversion and withdrawal context. Therefore, individuals with opiate addiction may return to opiate use to avoid aversive symptoms triggered by the withdrawal context. Overall, the systematic examination of the role of the hippocampus in drug addiction may help to formulate a better understanding of addiction and underlying neural substrates.

Chronic methamphetamine self-administration disrupts cortical control of cognition

Methamphetamine (meth) is one of the most abused substances worldwide. Chronic use has been associated with repeated relapse episodes that may be exacerbated by cognitive impairments during drug abstinence. Growing evidence demonstrates that meth compromises prefrontal cortex activity, resulting in persisting attentional and memory impairments. After summarizing recent studies of meth-induced cognitive dysfunction using a translationally relevant model of self-administered meth, this review emphasizes the cortical brain changes contributing to cognitive dysregulation during abstinence. Finally, we propose the use of cognitive enhancers during abstinence that may promote a drug-free state by reversing cortical dysfunction linked with prolonged meth abuse.

Long-Term Treatment with Low Doses of Methamphetamine Promotes Neuronal Differentiation and Strengthens Long-Term Potentiation of Glutamatergic Synapses onto Dentate Granule Neurons

Methamphetamine (METH) is a psychostimulant, affecting hippocampal function with disparate cognitive effects, which depends on the dose and time of administration, ranging from improvement to impairment of memory. Importantly, in the United States, METH is approved for the treatment of attention deficit hyperactivity disorder. Modifications of long-term plasticity of synapses originating from the entorhinal cortex onto dentate granule cells (DGCs) have been proposed to underlie cognitive alterations similar to those seen in METH users. However, the effects of METH on synaptic plasticity of the dentate gyrus are unknown. Here, we investigated the impact of long-term administration of METH (2 mg/kg/d) on neurogenesis and synaptic plasticity of immature and mature DGCs of juvenile mice. We used a mouse model of neurogenesis (the G42 line of GAD67-GFP), in which GFP is expressed by differentiating young DGCs. METH treatment enhanced the differentiation of GFP(+) cells, as it increased the fraction of GFP(+) cells expressing the neuronal marker NeuN, and decreased the amount of immature DGCs coexpressing doublecortin. Interestingly, METH did not change the magnitude of long-term potentiation (LTP) in more immature neurons, but facilitated LTP induction in more differentiated GFP(+) and strengthened plasticity in mature GFP(-) DGCs. The METH-induced facilitation of LTP in GFP(+) neurons was accompanied with spine enlargement. Our results reveal a specific action of long-term use of METH in the long-term plasticity of excitatory synapses onto differentiating DGCs and might have important implications toward the understanding of the synaptic basis of METH-induced cognitive alterations.

Reduced Prefrontal Cortex Hemodynamic Response in Adults with Methamphetamine Induced Psychosis: Relevance for Impulsivity

Patients with methamphetamine abuse/dependence often exhibit high levels of impulsivity, which may be associated with the structural abnormalities and functional hypoactivities observed in the frontal cortex of these subjects. Although near-infrared spectroscopy (NIRS) is a simple and non-invasive method for characterizing the clinical features of various psychiatric illnesses, few studies have used NIRS to directly investigate the association between prefrontal cortical activity and inhibitory control in patients with methamphetamine-induced psychosis (MAP). Using a 24-channel NIRS system, we compared hemodynamic responses during the Stroop color-word task in 14 patients with MAP and 21 healthy controls matched for age, sex and premorbid IQ. In addition, we used the Barrett Impulsivity Scale-11 (BIS-11) to assess impulsivity between subject groups. The MAP group exhibited significantly less activation in the anterior and frontopolar prefrontal cortex accompanied by lower Stroop color-word task performance, compared with controls. Moreover, BIS-11 scores were significantly higher in the MAP group, and were negatively correlated with the hemodynamic responses in prefrontal cortex. Our data suggest that reduced hemodynamic responses in the prefrontal cortex might reflect higher levels of impulsivity in patients with MAP, providing new insights into disrupted inhibitory control observed in MAP.

An Update of the Review of Neuropsychological Consequences of HIV and Substance Abuse: A Literature Review and Implications for Treatment and Future Research

Neuropyschological dysfunction, ranging from mild cerebral indicators to dementia has been a consistent part of the medical picture of HIV/AIDS. However, advances in medical supervision, particularly as a result of antiretroviral (ARV) treatment, have resulted in some mitigation of the neuropsychological effects of HIV and necessitate re-evaluation of the pattern and nature of HIV-related cognitive or mental deficits. The associated enhancements in morbidity and mortality that have occurred as a result of ARV medication have led to a need for interventions and programs that maintain behaviors that are healthy and stop the resurgence of the risk of HIV transmission. Risk factors such as mental illness and substance use that may have contributed to the initial infection with HIV still need consideration. These risk factors may also increase neuropsychological dysfunction and impact observance of prevention for treatment and recommendations. Explicitly, a better comprehension of the role of substance use on the progression of HIV-related mental decline can enlighten management and evaluation of persons living with HIV with concurrent disorders of substance use. This review provides a summary of the neurophyschology of substance use and HIV and the existing research that has looked at the effects of both substance use and HIV disease on neurophyscological function and suggestions for future research and treatment.

Pride, Shame, and the Trouble with Trying to Be Normal

I performed 14 person-centered ethnographies with methamphetamine-using HIV-positive men who have sex with men in San Diego, California, who were all subjects of the "anti-meth apparatus," a collection of government and nongovernment organizations focused on meth use and its sequelae. The apparatus attempts to coerce addicts to develop and perform certain identities and emotions, though addicts are capable of both passive acceptance and active disruption. In my research, those who failed to become the apparatus's ideal subject felt shame, while those who succeeded expressed pride. Those hovering in the middle experienced a perpetual struggle to become normal and rarely, if ever, succeeded. [addiction, HIV/AIDS, subjectivity].

Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse

Adaptation of the nervous system to different chemical and physiologic conditions is important for the homeostasis of brain processes and for learning and remembering appropriate responses to challenges. Although processes such as tolerance and dependence to various drugs of abuse have been known for a long time, it was recently discovered that even a single pharmacologically relevant dose of various drugs of abuse induces neuroplasticity in selected neuronal populations, such as the dopamine neurons of the ventral tegmental area, which persist long after the drug has been excreted. Prolonged (self-) administration of drugs induces gene expression, neurochemical, neurophysiological, and structural changes in many brain cell populations. These region-specific changes correlate with addiction, drug intake, and conditioned drugs effects, such as cue- or stress-induced reinstatement of drug seeking. In rodents, adolescent drug exposure often causes significantly more behavioral changes later in adulthood than a corresponding exposure in adults. Clinically the most impairing and devastating effects on the brain are produced by alcohol during fetal development. In adult recreational drug users or in medicated patients, it has been difficult to find persistent functional or behavioral changes, suggesting that heavy exposure to drugs of abuse is needed for neurotoxicity and for persistent emotional and cognitive alterations. This review describes recent advances in this important area of research, which harbors the aim of translating this knowledge to better treatments for addictions and related neuropsychiatric illnesses.

Neuropsychological functioning among chronic khat users in Jazan region, Saudi Arabia

BACKGROUND

Khat chewing effects in the central nervous system are attributed to cathinone and cathine, which are structurally related to amphetamine. However, studies on neuropsychological problems arising from khat use in humans are not extensive and have only included observational and single-case studies. The aims of this study were to (1) to examine neuropsychological functions among khat chewers, and (2) to determine factors affecting neuropsychological outcomes among khat chewers.

METHODS

A sample of 70 adult male khat chewers and a control group of 72 nonchewers were recruited from the Jazan region in southwest Saudi Arabia. A questionnaire examining socioeconomic background, medical and occupational history, education, and khat chewing behaviors was administered. Neuropsychological performance was assessed using computerized tests from the Behavioral Assessment and Research System (BARS) that assessed learning, episodic and working memory, motor speed/coordination, attention/information processing speed, sustained attention, set-shifting/response inhibition, and perceptual functions; noncomputerized tests, Trail Making A and B, Block Design, and Benton Visual Retention tests were also administered.

RESULTS

Khat chewers performed significantly worse on 3 out of 14 neuropsychological subtests compared with the control group, representing learning, motor speed/coordination, and set-shifting/response inhibition functions. Age and educational level were identified as predictors of neuropsychological outcomes of khat chewers.

CONCLUSIONS

The chronic chewing of khat leaves is associated with deficits in some neuropsychological functions, which may affect the mental and neurological health of communities in which khat chewing is a common habit.

The implications of sleep disruption for cognitive and affective processing in methamphetamine abuse

Sleep is disrupted during active use of methamphetamine (MA), during withdrawal from the drug, and during abstinence from its use. However, relatively little is known about possible mediatory functions of disrupted sleep in the emergence, manifestation, and maintenance of cognitive and affective symptoms of MA abuse. We hypothesise that sleep functions as a mediator for stimulant drug effects. Specifically, we propose that objectively-measured sleep parameters can be used to explain some of the variability in the experience and presentation of memory deficits and emotion dysregulation in MA abusers. After describing how important healthy sleep is to unimpaired cognitive and affective functioning, we review literature describing how sleep is disrupted in MA abuse. Then, we provide a conceptual framework for our hypothesis by explaining the relationship between MA abuse, sleep disruption, memory deficits, emotion dysregulation, and changes in reward-related brain networks. We conclude by discussing implications of the hypothesis for research and treatment.

Characterization of binge-dosed methamphetamine-induced neurotoxicity and neuroinflammation

Methamphetamine (MA) is a potent, highly addictive psychostimulant abused by millions of people worldwide. MA induces neurotoxicity, damaging striatal dopaminergic terminals, and neuroinflammation, with striatal glial activation leading to pro-inflammatory cytokine and reactive oxygen species production. It is unclear whether MA-induced neuroinflammation contributes to MA-induced neurotoxicity. In the current study, we examined the linkage between the time course and dose response of MA-induced neurotoxicity and neuroinflammation. Adult male mice underwent a binge dosing regimen of four injections given every 2h with doses of 2, 4, 6, or 8 mg/kg MA per injection, and were sacrificed after 1, 3, 7, or 14 days. Binge MA treatment dose-dependently caused hyperthermia and induced hypoactivity after one day, though activity returned to control levels within one week. Striatal dopamine (DA) was diminished one day after treatment with at least 4 mg/kg MA, while DA turnover rates peaked after seven days. Although striatal tyrosine hydroxylase and DA transporter levels were also decreased one day after treatment with at least 4 mg/kg MA, they trended toward recovery by day 14. All doses of MA activated striatal glia within one day. While astrocyte activation persisted, microglial activation was attenuated over the two weeks of the study. These findings help clarify the relationship between MA-induced neuroinflammation and neurotoxicity, particularly regarding their temporal and dose-specific dynamics.

Nicotine Administration Attenuates Methamphetamine-Induced Novel Object Recognition Deficits

BACKGROUND

Previous studies have demonstrated that methamphetamine abuse leads to memory deficits and these are associated with relapse. Furthermore, extensive evidence indicates that nicotine prevents and/or improves memory deficits in different models of cognitive dysfunction and these nicotinic effects might be mediated by hippocampal or cortical nicotinic acetylcholine receptors. The present study investigated whether nicotine attenuates methamphetamine-induced novel object recognition deficits in rats and explored potential underlying mechanisms.

METHODS

Adolescent or adult male Sprague-Dawley rats received either nicotine water (10-75 μg/mL) or tap water for several weeks. Methamphetamine (4 × 7.5mg/kg/injection) or saline was administered either before or after chronic nicotine exposure. Novel object recognition was evaluated 6 days after methamphetamine or saline. Serotonin transporter function and density and α4β2 nicotinic acetylcholine receptor density were assessed on the following day.

RESULTS

Chronic nicotine intake via drinking water beginning during either adolescence or adulthood attenuated the novel object recognition deficits caused by a high-dose methamphetamine administration. Similarly, nicotine attenuated methamphetamine-induced deficits in novel object recognition when administered after methamphetamine treatment. However, nicotine did not attenuate the serotonergic deficits caused by methamphetamine in adults. Conversely, nicotine attenuated methamphetamine-induced deficits in α4β2 nicotinic acetylcholine receptor density in the hippocampal CA1 region. Furthermore, nicotine increased α4β2 nicotinic acetylcholine receptor density in the hippocampal CA3, dentate gyrus and perirhinal cortex in both saline- and methamphetamine-treated rats.

CONCLUSIONS

Overall, these findings suggest that nicotine-induced increases in α4β2 nicotinic acetylcholine receptors in the hippocampus and perirhinal cortex might be one mechanism by which novel object recognition deficits are attenuated by nicotine in methamphetamine-treated rats.

Gray matter abnormalities in cocaine versus methamphetamine-dependent patients: a neuroimaging meta-analysis

BACKGROUND

Voxel-based morphometry has been used to explore gray matter alterations in cocaine and methamphetamine dependence. However, the results of this research are inconsistent.

OBJECTIVES

The current study meta-analytically examined neuroimaging findings of all studies published before 2014 using the Anisotropic Effect-Size Signed Differential Mapping (ES-SDM).

METHODS

Independent investigators searched four major databases for relevant neuroimaging studies involving cocaine and methamphetamine dependence. Nine cocaine and four methamphetamine studies met inclusion criteria.

RESULTS

Results indicated that cocaine- and methamphetamine-dependent patients share overlapping regional gray matter abnormalities compared to healthy controls. However, subgroup analysis showed some regional differences; with methamphetamine showing more prominent reductions in the left superior temporal gyrus and the right inferior parietal lobe. Reductions in the right insula and the left superior frontal gyrus were more prominent in cocaine dependence. Moderator analyses indicated that with longer use, cocaine is associated with reductions in the right hippocampus, right middle temporal gyrus, and right inferior frontal gyrus, while methamphetamine is associated with reductions in the left precentral gyrus and the right supramarginal gyrus.

CONCLUSION

These findings indicate that cocaine and methamphetamine dependence are significantly and differentially associated with gray matter abnormalities. Results also point to possible gray matter recovery after abstinence from methamphetamine. Although the sample size was adequate, these findings should be considered preliminary and analyses should be revisited with additional primary research focusing on long or short-term duration of use, as well as the length of abstinence.

Memory impairment and alterations in prefrontal cortex gamma band activity following methamphetamine sensitization

RATIONALE

Repeated methamphetamine (MA) use leads to increases in the incentive motivational properties of the drug as well as cognitive impairments. These behavioral alterations persist for some time following abstinence, and neuroadaptations in the structure and function of the prefrontal cortex (PFC) are particularly important for their expression. However, there is a weak understanding of the changes in neural firing and oscillatory activity in the PFC evoked by repeated drug use, thus complicating the development of novel treatment strategies for addiction.

OBJECTIVES

The purpose of the current study was to assess changes in cognitive and brain function following MA sensitization.

METHODS

Sensitization was induced in rats, then temporal and recognition memory were assessed after 1 or 30 days of abstinence. Electrophysiological recordings from the medial PFC were also acquired from rats whereupon simultaneous measures of oscillatory and spiking activity were examined.

RESULTS

Impaired temporal memory was observed after 1 and 30 days of abstinence. However, recognition memory was only impaired after 1 day of abstinence. An injection of MA profoundly decreased neuronal firing rate and the anesthesia-induced slow oscillation (SO) in both sensitized (SENS) and control (CTRL) rats. Strong correlations were observed between the SO and gamma band power, which was altered in SENS animals. A decrease in the number of neurons phase-locked to the gamma oscillation was also observed in SENS animals.

CONCLUSIONS

The changes observed in PFC function may play an integral role in the expression of the altered behavioral phenotype evoked by MA sensitization.

Neuropsychological Consequences of Chronic Drug Use: Relevance to Treatment Approaches

Heavy use of drugs impacts of the daily activities of individuals in these activities. Several groups of investigators have indeed documented changes in cognitive performance by individuals who have a long history of chronic drug use. In the case of marijuana, a wealth of information suggests that heavy long-term use of the drug may have neurobehavioral consequences in some individuals. In humans, heavy cocaine use is accompanied by neuropathological changes that might serve as substrates for cognitive dysfunctions. Similarly, methamphetamine users suffer from cognitive abnormalities that may be consequent to alterations in structures and functions. Here, we detail the evidence for these neuropsychological consequences. The review suggests that improving the care of our patients will necessarily depend on the better characterization of drug-induced cognitive phenotypes because they might inform the development of better pharmacological and behavioral interventions, with the goal of improving cognitive functions in these subsets of drug users.

Neurobehavioral Effects from Developmental Methamphetamine Exposure

Intrauterine methamphetamine exposure adversely affects the neurofunctional profile of exposed children, leading to a variety of higher order cognitive deficits, such as decreased attention, reduced working-memory capability, behavioral dysregulation, and spatial memory impairments (Kiblawi et al. in J Dev Behav Pediatr 34:31-37, 2013; Piper et al. in Pharmacol Biochem Behav 98:432-439 2011; Roussotte et al. in Neuroimage 54:3067-3075, 2011; Twomey et al. in Am J Orthopsychiatry 83:64-72, 2013). In animal models of developmental methamphetamine, both neuroanatomical and behavioral outcomes critically depend on the timing of methamphetamine administration. Methamphetamine exposure during the third trimester human equivalent period of brain development results in well-defined and persistent wayfinding and spatial navigation deficits in rodents (Vorhees et al. in Neurotoxicol Teratol 27:117-134, 2005, Vorhees et al. in Int J Dev Neurosci 26:599-610, 2008; Vorhees et al. in Int J Dev Neurosci 27:289-298, 2009; Williams et al. in Psychopharmacology (Berl) 168:329-338, 2003b), whereas drug delivery during the first and second trimester equivalents produces no such effect (Acuff-Smith et al. in Neurotoxicol Teratol 18:199-215, 1996; Schutova et al. in Physiol Res 58:741-750, 2009a; Slamberova et al. in Naunyn Schmiedebergs Arch Pharmacol 380:109-114, 2009, Slamberova et al. in Physiol Res 63:S547-S558, 2014b). In this review, we examine the impact of developmental methamphetamine on emerging neural circuitry, neurotransmission, receptor changes, and behavioral outcomes in animal models. The review is organized by type of effects and timing of drug exposure (prenatal only, pre- and neonatal, and neonatal only). The findings elucidate functional patterns of interconnected brain structures (e.g., frontal cortex and striatum) and neurotransmitters (e.g., dopamine and serotonin) involved in methamphetamine-induced developmental neurotoxicity.

Exercise training improves heart rate variability after methamphetamine dependency

PURPOSE

Heart rate variability (HRV) reflects a healthy autonomic nervous system and is increased with physical training. Methamphetamine dependence (MD) causes autonomic dysfunction and diminished HRV. We compared recently abstinent methamphetamine-dependent participants with age-matched, drug-free controls (DF) and also investigated whether HRV can be improved with exercise training in the methamphetamine-dependent participants.

METHODS

In 50 participants (MD = 28; DF = 22), resting heart rate (HR; R-R intervals) was recorded over 5 min while seated using a monitor affixed to a chest strap. Previously reported time domain (SDNN, RMSSD, pNN50) and frequency domain (LFnu, HFnu, LF/HF) parameters of HRV were calculated with customized software. MD were randomized to thrice-weekly exercise training (ME = 14) or equal attention without training (MC = 14) over 8 wk. Groups were compared using paired and unpaired t-tests. Statistical significance was set at P ≤ 0.05.

RESULTS

Participant characteristics were matched between groups (mean ± SD): age = 33 ± 6 yr; body mass = 82.7 ± 12 kg, body mass index = 26.8 ± 4.1 kg·min. Compared with DF, the MD group had significantly higher resting HR (P < 0.05), LFnu, and LF/HF (P < 0.001) as well as lower SDNN, RMSSD, pNN50, and HFnu (all P < 0.001). At randomization, HRV indices were similar between ME and MC groups. However, after training, the ME group significantly (all P < 0.001) increased SDNN (+14.7 ± 2.0 ms, +34%), RMSSD (+19.6 ± 4.2 ms, +63%), pNN50 (+22.6% ± 2.7%, +173%), HFnu (+14.2 ± 1.9, +60%), and decreased HR (-5.2 ± 1.1 bpm, -7%), LFnu (-9.6 ± 1.5, -16%), and LF/HF (-0.7 ± 0.3, -19%). These measures did not change from baseline in the MC group.

CONCLUSIONS

HRV, based on several conventional indices, was diminished in recently abstinent, methamphetamine-dependent individuals. Moreover, physical training yielded a marked increase in HRV, representing increased vagal modulation or improved autonomic balance.

Methamphetamine-induced neurotoxicity disrupts pharmacologically evoked dopamine transients in the dorsomedial and dorsolateral striatum

Phasic dopamine (DA) signaling, during which burst firing by DA neurons generates short-lived elevations in extracellular DA in terminal fields called DA transients, is implicated in reinforcement learning. Disrupted phasic DA signaling is proposed to link DA depletions and cognitive-behavioral impairment in methamphetamine (METH)-induced neurotoxicity. Here, we further investigated this disruption by assessing effects of METH pretreatment on DA transients elicited by a drug cocktail of raclopride, a D2 DA receptor antagonist, and nomifensine, an inhibitor of the dopamine transporter (DAT). One advantage of this approach is that pharmacological activation provides a large, high-quality data set of transients elicited by endogenous burst firing of DA neurons for analysis of regional differences and neurotoxicity. These pharmacologically evoked DA transients were measured in the dorsomedial (DM) and dorsolateral (DL) striatum of urethane-anesthetized rats by fast-scan cyclic voltammetry. Electrically evoked DA levels were also recorded to quantify DA release and uptake, and DAT binding was determined by means of autoradiography to index DA denervation. Pharmacologically evoked DA transients in intact animals exhibited a greater amplitude and frequency and shorter duration in the DM compared to the DL striatum, despite similar pre- and post-drug assessments of DA release and uptake in both sub-regions as determined from the electrically evoked DA signals. METH pretreatment reduced transient activity. The most prominent effect of METH pretreatment on transients across striatal sub-region was decreased amplitude, which mirrored decreased DAT binding and was accompanied by decreased DA release. Overall, these results identify marked intrastriatal differences in the activity of DA transients that appear independent of presynaptic mechanisms for DA release and uptake and further support disrupted phasic DA signaling mediated by decreased DA release in rats with METH-induced neurotoxicity.

Perceived risk of methamphetamine among Chinese methamphetamine users

BACKGROUND

Methamphetamine use has grown considerably in China in recent years. Information about perceptions of risk on methamphetamine is important to facilitate health promotion efforts.

METHODS

Using both survey data and qualitative interview data, the authors evaluate the perceived risk of methamphetamine use among Chinese users using a mixed-methods approach. Through Respondent Driven Sampling, the authors recruited a sample of 303 methamphetamine users in Changsha, China.

RESULTS

A majority (59.1%) perceive that infrequent methamphetamine use poses no risk to the user, while 11.2% perceive at least moderate risk for light use. A majority (56.7%) perceived at least moderate risk associated with regular methamphetamine use. Most (82.2%) also perceive methamphetamine to be easily obtainable. A path model indicates that perceived risk shapes intentions to use and expectations of future use, as does perceived availability. Qualitatively, while addiction was the most common risk discussed by users, they differed on whether they perceived the drug addictive. Other concerns raised by interviewees included impaired cognition, mental health problems, physical harm, and social dysfunction.

CONCLUSION

While some users identify significant risks with methamphetamine, others do not perceive its use to be problematic. Collectively, these findings indicate that intervening upon perceptions of risk among Chinese methamphetamine users may be a means to influence intentions to use.

Prior stimulation of the endocannabinoid system prevents methamphetamine-induced dopaminergic neurotoxicity in the striatum through activation of CB2 receptors

Methamphetamine toxicity is associated with cell death and loss of dopamine neuron terminals in the striatum similar to what is found in some neurodegenerative diseases. Conversely, the endocannabinoid system (ECS) has been suggested to be neuroprotective in the brain, and new pharmacological tools have been developed to increase their endogenous tone. In this study, we evaluated whether ECS stimulation could reduce the neurotoxicity of high doses of methamphetamine on the dopamine system. We found that methamphetamine alters the levels of the major endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in the striatum, suggesting that the ECS participates in the brain responses to methamphetamine. Δ(9)-tetrahydrocannabinol (THC), a cannabis-derived agonist of both CB1 and CB2 cannabinoid receptors, or inhibitors of the main enzymes responsible for the degradation of AEA and 2-AG (URB597 and JZL184, respectively), blunted the decrease in striatal protein levels of tyrosine hydroxylase induced by methamphetamine. In addition, antagonists of CB2, but not of CB1, blocked the preventive effects of URB597 and JZL184, suggesting that only the former receptor subtype is engaged in neuroprotection exerted by ECS stimulation. Finally, we found that methamphetamine increases striatal levels of the cytokine tumor necrosis factor alpha, an effect that was blocked by ECS stimulation. Altogether, our results indicate that stimulation of ECS prior to the administration of an overdose of methamphetamine considerably reduces the neurotoxicity of the drug through CB2 receptor activation and highlight a protective function for the ECS against the toxicity induced by drugs and other external insults to the brain. This article is part of the Special Issue entitled 'CNS Stimulants'.

The effects of methylphenidate on cognitive control in active methamphetamine dependence using functional magnetic resonance imaging

Methamphetamine (MA) dependence is associated with cognitive deficits. Methylphenidate (MPH) has been shown to improve inhibitory control in healthy and cocaine-dependent subjects. This study aimed to understand the neurophysiological effects before and after acute MPH administration in active MA-dependent and control subjects. Fifteen MA-dependent and 18 control subjects aged 18-46 years were scanned using functional magnetic resonance imaging before and after either a single oral dose of MPH (18 mg) or placebo while performing a color-word Stroop task. Baseline accuracy was lower (p = 0.026) and response time (RT) was longer (p < 0.0001) for the incongruent compared to congruent condition, demonstrating the task probed cognitive control. Increased activation of the dorsolateral prefrontal cortex (DLPFC) and parietal cortex during the incongruent and Stroop effect conditions, respectively was observed in MA-dependent compared to control subjects (p < 0.05), suggesting the need to recruit neural resources within these regions for conflict resolution. Post- compared to pre-MPH treatment, increased RT and DLPFC activation for the Stroop effect were observed in MA-dependent subjects (p < 0.05). In comparison to MPH-treated controls and placebo-treated MA-dependent subjects, MPH-treated MA-dependent subjects showed decreased activation of parietal and occipital regions during the incongruent and Stroop effect conditions (p < 0.05). These findings suggest that in MA-dependent subjects, MPH facilitated increased recruitment of the DLPFC for Stroop conflict resolution, and a decreased need for recruitment of neural resources in parietal and occipital regions compared to the other groups, while maintaining a comparable level of task performance to that achieved pre-drug administration. Due to the small sample size, the results from this study are preliminary; however, they inform us about the effects of MPH on the neural correlates of cognitive control in active MA-dependent subjects.

Predictors of methamphetamine psychosis: history of ADHD-relevant childhood behaviors and drug exposure

The goal of this study was to extend our previous research that reported a significant association between Attention Deficit Hyperactivity Disorder (ADHD)-relevant childhood behaviors and the frequency of methamphetamine (MA)-induced psychotic symptoms in an expanded sample. 190 participants who met DSM-IV criteria for MA dependence were administered the Methamphetamine Experience Questionnaire that assessed MA-induced psychosis. Data related to MA exposure, comorbid drug use, education, familial psychiatric history and assessments of ADHD-relevant childhood behaviors as measured by the Wender Utah Rating Scale (WURS) were collected. Although WURS scores did not differ between 145 MAP+ and 45 MAP- subjects, MAP+ subjects with higher WURS scores were significantly more likely to report more frequent psychosis. Although mean daily MA dosage did not differ between the MAP+ and MAP- subjects, MAP+ subjects who consumed larger doses of MA were significantly more likely to experience frequent psychosis. These data suggest that ADHD-relevant childhood behaviors may interact with MA exposure to reflect a neurobiological vulnerability related to the emergence of frequent MA-induced psychotic symptoms. These results may elucidate factors that contribute to the psychiatric sequelae of MA abuse.

Concurrent use of khat and tobacco is associated with verbal learning and delayed recall deficits

AIMS

The present study assessed whether cigarette smokers who are also regular khat users would demonstrate greater impairments in verbal learning and recall compared to both non-smokers who are khat users and control subjects.

DESIGN

An independent-measures, between-subjects design with two covariates.

SETTING

An out-patient, university research center in Taiz, Yemen.

PARTICIPANTS

Subjects were 175 Yemeni college students (90 men, 85 women) ranging in age from 18 to 38 years. Seventy-five subjects were self-reported chronic cigarette smokers and khat users, 48 non-smoking subjects were self-reported to be chronic khat users and 52 non-smoking subjects reported no current use or history of khat use.

MEASUREMENTS

Verbal learning and verbal memory recall was assessed by subject performance on the Arabic version of the Rey Auditory Verbal Learning Test (RAVLT).

FINDINGS

Statistically significant differences (P < 0.05) were observed in RAVLT acquisition learning trials 2-5 and on delayed recall measures between concurrent khat and cigarette users compared to both the khat-only group and the control group of non-users of khat and cigarettes. On each of these trials, concurrent users recalled fewer words, demonstrating a slowed rate of verbal learning. This same pattern of performance was also seen on delayed recall measures. Khat use alone did not affect immediate or delayed recall of previously learned words.

CONCLUSIONS

Khat users who smoke cigarettes have a lower rate of verbal learning and delayed recall of previously learned verbal material than khat users who do not smoke cigarettes. This may be due to pre-existing differences between these groups of subjects.

Poor working memory and reduced blood pressure levels in concurrent users of khat and tobacco

INTRODUCTION

The purpose of this study was to examine the extent in which concurrent use of khat and tobacco was associated with decrements in working memory. We also tested whether cardiovascular activity during a cognitive task was related to performance outcomes, as research has shown linkages between maladaptive physiological adjustments and cognitive functions.

METHODS

Seventy-four concurrent users of khat and tobacco, 49 khat-only users, and 52 nonusers (M age ± SD: 23.8±4.8) completed a laboratory session including 10 min of a mental arithmetic challenge task. Systolic blood pressure (SBP) and diastolic blood pressure and heart rate were collected throughout the task. Analyses of variance and correlational analyses were conducted.

RESULTS

We found that concurrent users evidenced the lowest number of correct responses on the math task among these 3 groups (ps < .05). Concurrent users also showed fewer number of attempts than khat-only users (ps < .01) and lower accuracy rate than nonusers (ps < .05). The performance of khat-only users and nonusers were comparable on these 3 measures (p > .76). Overall blood pressure levels were lower in concurrent users than in nonusers (p < .05). Correlational analysis found that lower SBP during the math task was associated with fewer number of correct responses and attempts and lower accuracy rate on the task (ps < .05). Multiple regression analysis controlling for gender found that concurrent use predicted math performance (ps < .05). Reported duration and frequency of khat and tobacco use and nicotine dependence predicted performance measures (ps < .05).

CONCLUSIONS

These findings suggest potential linkages between concurrent use of khat and tobacco and impaired working memory.

Extended-access, but not limited-access, methamphetamine self-administration induces behavioral and nucleus accumbens dopamine response changes in rats

To better understand the neurobiology of methamphetamine (METH) dependence and the cognitive impairments induced by METH use, we compared the effects of extended (12 h) and limited (1 h) access to METH self-administration on locomotor activity and object place recognition, and on extracellular dopamine levels in the nucleus accumbens and caudate-putamen. Rats were trained to self-administer intravenous METH (0.05 mg/kg). One group had progressively extended access up to 12-h sessions. The other group had limited-access 1-h sessions. Microdialysis experiments were conducted during a 12-h and 1-h session, in which the effects of a single METH injection (self-administered, 0.05 mg/kg, i.v.) on extracellular dopamine levels were assessed in the nucleus accumbens and caudate-putamen compared with a drug-naive group. The day after the last 12-h session and the following day experimental groups were assessed for their locomotor activities and in a place recognition procedure, respectively. The microdialysis results revealed tolerance to the METH-induced increases in extracellular dopamine only in the nucleus accumbens, but not in the caudate-putamen in the extended-access group compared with the control and limited-access groups. These effects may be associated with the increased lever-pressing and drug-seeking observed during the first hour of drug exposure in the extended-access group. This increase in drug-seeking leads to higher METH intake and may result in more severe consequences in other structures responsible for the behavioral deficits (memory and locomotor activity) observed in the extended-access group, but not in the limited-access group.

Substance use and mental health characteristics associated with cognitive functioning among adults who use methamphetamine

This study describes cognitive functioning and its relation to psychiatric and substance use severity among adults with long duration methamphetamine use. Study participants (N = 405) completed a battery of tests from the Automated Neuropsychological Assessment Metrics that examined cognitive accuracy, processing speed, and efficiency. Multivariate analyses indicate that lower accuracy but faster speed on learning, spatial memory and delayed memory were correlated with more days of past-month methamphetamine use. Lifetime months of methamphetamine use was not related to cognitive functioning. Poorer cognitive efficiency was related to other problems, including crack/cocaine use, symptoms of depression, and poorer emotional state.

Eight weeks of exercise training improves fitness measures in methamphetamine-dependent individuals in residential treatment

OBJECTIVES

Physical exercise has been shown to benefit diverse medical and behavioral conditions. This study assesses the feasibility and efficacy of an 8-week endurance and resistance training program on fitness measures in individuals undergoing residential treatment for methamphetamine (MA) dependence.

METHODS

A total of 39 MA-dependent individuals were randomized to 3 days/week of exercise training (ET, n = 15) or health education without training (equal attention [EA], n = 14) over 8 weeks. Aerobic performance ((Equation is included in full-text article.)VO2max) was measured by indirect calorimetry, body composition by skinfolds, muscle strength by 1-repetition maximum (1-RM), and endurance at 85% of 1-RM for both leg press (LP) and chest press (CP).

RESULTS

A total of 29 individuals completed the study for a 74% adherence rate. Baseline characteristics (mean ± SD) were balanced between groups: age 31 ± 7 years; height = 1.74 ± 0.07 m; weight 82.0 ± 15.0 kg. The ET group significantly improved (Equation is included in full-text article.)O2max by 0.63 ± 0.22 L/min (+21%), LP strength by 24.4 ± 5.6 kg (+40%), and CP strength by 20.6 ± 5.7 kg (+49%). The ET group increased LP and CP endurance by 120% and 96%, respectively and showed significant reductions in body weight of 1.7 ± 2.4 kg (-2%), % body fat of 2.8 ± 1.3% (-15%), and fat weight 2.8 ± 1.8 kg (-18%). All changes were significant (P < 0.001) for ET, and no changes were seen for the EA group.

CONCLUSIONS

Individuals recovering from MA dependence showed substantial improvements in aerobic exercise performance, muscle strength and endurance, and body composition with ET. These findings demonstrate the feasibility of an ET intervention in these participants and also show excellent responsiveness to the exercise stimulus resulting in physiological changes that might enhance recovery from drug dependency.

Polysubstance and alcohol dependence: unique abnormalities of magnetic resonance-derived brain metabolite levels

BACKGROUND

Although comorbid substance misuse is common in alcohol dependence, and polysubstance abusers (PSU) represent the largest group of individuals seeking treatment for drug abuse today, we know little about potential brain abnormalities in this population. Brain magnetic resonance spectroscopy studies of mono-substance use disorders (e.g., alcohol or cocaine) reveal abnormal levels of cortical metabolites (reflecting neuronal integrity, cell membrane turnover/synthesis, cellular bioenergetics, gliosis) and altered concentrations of glutamate and γ-aminobutyric acid (GABA). The concurrent misuse of several substances may have unique and different effects on brain biology and function compared to any mono-substance misuse.

METHODS

High field brain magnetic resonance spectroscopy at 4 T and neurocognitive testing were performed at one month of abstinence in 40 alcohol dependent individuals (ALC), 28 alcohol dependent PSU and 16 drug-free controls. Absolute metabolite concentrations were calculated in anterior cingulate (ACC), parieto-occipital (POC) and dorso-lateral prefrontal cortices (DLPFC).

RESULTS

Compared to ALC, PSU demonstrated significant metabolic abnormalities in the DLPFC and strong trends to lower GABA in the ACC. Metabolite levels in ALC and light drinking controls were statistically equivalent. Within PSU, lower DLPFC GABA levels are related to greater cocaine consumption. Several cortical metabolite concentrations were associated with cognitive performance.

CONCLUSIONS

While metabolite concentrations in ALC at one month of abstinence were largely normal, PSU showed persistent and functionally significant metabolic abnormalities, primarily in the DLPFC. Our results point to specific metabolic deficits as biomarkers in polysubstance misuse and as targets for pharmacological and behavioral PSU-specific treatment.

More alike than different: health needs, services utilization, and outcomes of Asian American and Pacific Islander (AAPI) populations treated for substance use disorders

Asian Americans and Pacific Islanders (AAPIs) are often portrayed as a healthy group with minor substance use problems. Using data from two studies of patients treated in 44 community-based substance use treatment sites located in three states, 298 AAPIs and a matched comparison group of 298 non-AAPI patients were compared on demographic characteristics, treatment experiences, and 1-year outcomes. At treatment entry, more AAPIs reported recent drug use and fewer injected drugs, AAPIs had less severe medical and alcohol problems, and AAPIs reported worse general health but less desire for medical and alcohol services. After controlling for baseline problem severity, there were no differences in treatment retention, completion, or outcomes. Contrary to the model minority stereotype, AAPIs have mostly similar treatment needs, experiences, and outcomes as other racial/ethnic groups in drug treatment.

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

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

Methamphetamine-induced neurotoxicity disrupts naturally occurring phasic dopamine signaling

Methamphetamine (METH) is a highly addictive drug that is also neurotoxic to central dopamine (DA) systems. Although striatal DA depletions induced by METH are associated with behavioral and cognitive impairments, the link between these phenomena remains poorly understood. Previous work in both METH-pretreated animals and the 6-hydroxydopamine model of Parkinson's disease suggests that a disruption of phasic DA signaling, which is important for learning and goal-directed behavior, may be such a link. However, previous studies used electrical stimulation to elicit phasic-like DA responses and were also performed under anesthesia, which alters DA neuron activity and presynaptic function. Here we investigated the consequences of METH-induced DA terminal loss on both electrically evoked phasic-like DA signals and so-called 'spontaneous' phasic DA transients measured by voltammetry in awake rats. Not ostensibly attributable to discrete stimuli, these subsecond DA changes may play a role in enhancing reward-cue associations. METH pretreatment reduced tissue DA content in the dorsomedial striatum and nucleus accumbens by ~55%. Analysis of phasic-like DA responses elicited by reinforcing stimulation revealed that METH pretreatment decreased their amplitude and underlying mechanisms for release and uptake to a similar degree as DA content in both striatal subregions. Most importantly, characteristics of DA transients were altered by METH-induced DA terminal loss, with amplitude and frequency decreased and duration increased. These results demonstrate for the first time that denervation of DA neurons alters naturally occurring DA transients and are consistent with diminished phasic DA signaling as a plausible mechanism linking METH-induced striatal DA depletions and cognitive deficits.

Perseverative behavior in rats with methamphetamine-induced neurotoxicity

Methamphetamine induces monoamine depletions thought to contribute to cognitive and behavioral dysfunctions. Previously, we reported that methamphetamine-induced neurotoxicity is associated with impaired formation of stimulus-response associations. Additionally, subjective observations suggested that behavioral flexibility might be affected. Thus, the present study examined whether methamphetamine neurotoxicity induces perseverative behavior. Rats were pretreated with (±)-methamphetamine (4 × 10 mg/kg, 2-hr intervals) or saline. Three weeks later, rats were trained to press a lever on one side of an operant chamber and then retrieve the reinforcer from a magazine on the opposite side until they reached criterion (>50 reinforcers/30-min). After four consecutive sessions performing the task at criterion, rats were sacrificed and brains removed for monoamine determinations. Methamphetamine-pretreated rats had ∼50% loss of striatal dopamine and prefrontal serotonin. Methamphetamine- and saline-pretreated rats were not different in the number of sessions required to reach criterion or in the total numbers of lever presses and/or head entries made across the four consecutive sessions at criterion-level performance. However, methamphetamine-pretreated rats earned fewer reinforcers, because they made extra lever-presses and head entries when they should have been retrieving the reinforcer or returning to the lever. Latencies for methamphetamine-pretreated rats to switch between the two behaviors also were significantly slower than latencies for controls. Interestingly, the degree of additional lever-presses negatively correlated with serotonin-transporter binding in the prefrontal cortex, even in saline-pretreated controls. These data suggest that methamphetamine-induced partial monoamine toxicity is associated with perseveration and that the degree of perseveration may depend on serotonin innervation of the frontal cortex.

Relationship between sex hormones and cognitive performance in men with substance use

BACKGROUND

Hypogonadism is common with opiate-like drug use and may contribute to cognitive abnormalities. With the increasing epidemic of HIV and substance use (SU) worldwide, it is important to understand the impact of these conditions on cognition, which may affect quality of life and possibly decrease adherence to treatment. We hypothesized that men with SU, by virtue of hypogonadism secondary to HIV and/or SU, may demonstrate impaired cognition.

METHODS

We recruited men aged 18-50 from a population of low income, inner-city individuals. Details of HIV and SU status, serum blood levels of total testosterone (TT), free testosterone (FT) and estradiol (E2) were assessed. All subjects were administered ten neuropsychological tests.

RESULTS

Our sample consisted of 68 men (mean age: 43.2 years (SD 5.8), African Americans: 86.6%). The recruited population was primarily from low socioeconomic status and unemployed. The mean level of TT was 553.9 ng/dL (SD 262.0), the mean level of FT was 69.5 pg/mL (SD 34.8), mean E2 was 3.2 pg/mL (SD 4.4). We found that 30.9% were hypogonadal and it was associated with higher SU. We observed some relationships between sex hormones and cognitive domains, however, after adjustment for age, drug use category, education, depression, HIV, there was no statistically significant correlation between cognitive performance and sex hormone levels.

CONCLUSIONS

In this cross-sectional study of men with a high prevalence of SU and hypogonadism, endogenous levels of TT, FT or E2 were not related to cognitive performance. Other factors need to be identified which may contribute to poor cognitive function in the setting of SU.

Impulsivity is associated with treatment non-completion in cocaine- and methamphetamine-dependent patients but differs in nature as a function of stimulant-dependence diagnosis

Greater impulsivity, assessed by the Barratt Impulsiveness Scale-11 (BIS-11) and Stroop interference scores, has been associated with treatment completion in cocaine-dependent patients. This study evaluated the relationships among impulsivity, stimulant-dependence diagnosis, and treatment completion. Six sites evaluating 12-step facilitation for stimulant abusers obtained the BIS-11 and Stroop from 182 methamphetamine- and/or cocaine-dependent participants. Methamphetamine-dependent, relative to cocaine-dependent, participants evidenced significantly greater BIS-11 non-planning and total scores. There was a trend for poorer response inhibition, measured by the Stroop, in cocaine-dependent, relative to methamphetamine-dependent, participants. Accounting for other factors related to treatment completion, BIS-11 motor score, assessing the tendency to act without thinking, predicted treatment completion for both cocaine-dependent and methamphetamine-dependent patients. These results suggest that methamphetamine-dependent and cocaine-dependent patients may have different impulsivity profiles but that the BIS-11 may be useful in identifying both methamphetamine-dependent and cocaine-dependent patients who are at risk for treatment non-completion.

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.

An evaluation of the evidence that methamphetamine abuse causes cognitive decline in humans

Methamphetamine (MA) is one of the most commonly abused illicit substances worldwide. Among other problems, abuse of the drug has been associated with reduced cognitive function across several domains. However, much of the literature has not attempted to differentiate cognitive difficulties caused by MA abuse from preexisting cognitive difficulties that are likely caused by other factors. Here, we address this question, evaluating evidence for a priori hypotheses pertaining to six lines of research: (a) animal studies; (b) cross-sectional human studies; (c) a twin study; (d) studies of changes in cognition with abstinence from MA; (e) studies of changes in brain structure and function with abstinence from MA; and (f) studies of the relationship between the severity of MA abuse and the extent of cognitive deficits observed. Overall the findings were mixed, with some support for a causal relationship between MA abuse and cognitive decline, and other findings suggesting that there is no relationship. The preponderance of the data, however, does support the possibility that MA abuse causes cognitive decline, of unknown duration, in at least some users of the drug. When averaged across individuals, this decline is likely to be mild in early-to-middle adulthood. However, moderator variables are likely to contribute to the presence and/or severity of cognitive decline exhibited by a given individual.

Gender differences in abusers of amphetamine-type stimulants and ketamine in southwestern China

The objective of this study was to investigate abuse conditions of new-type drugs for users who are seeking treatment, gender differences, and differences between the amphetamine-type stimulants (ATS) users and mixed amphetamine-type stimulants and ketamine (ATS+K) poly-drug users. A retrospective analysis was conducted of patients with a final diagnosis of the substance use disorder according to the Diagnoses and Statistical Manual of Mental Disorders Fourth Edition (DSM-IV) who underwent treatment for exposure to new-type drugs at the mental health center of the West China Hospital from March 2009 to May 2011. A questionnaire was used to collect information about socio-demographics, drug abuse conditions and psychiatric co-morbidities. Male subjects were older (p=0.026), had low level education (p=0.003), were less previously married (p<0.001), were more likely to be employed and to hold higher status jobs (p=0.007); 77.1% of subjects had a psychotic disorder, 28.0% of subjects had a mood disorder, 39.7% had an anxiety disorder, and 45.0% had a cognitive impairment disorder. More men used methamphetamine MA (p<0.001), tobacco (p=0.014) and more than one drug substance (p=0.004) compared to women; women were more vulnerable to mood disorders (p=0.034) than men. For the males, the ATS+K patients were more likely to use 3, 4-methylenedioxymethamphetamine MDMA (p<0.001) and develop more psychotic disorders (p=0.04) than the ATS patients; for females, the ATS+K patients were more likely to use MDMA (p=0.002), alcohol (p=0.014) and develop more cognitive impairment disorder (p=0.034). The present study found that the new-type drug patients have a high degree of psychiatric morbidities; more men were using MA, tobacco and multi-substance and more women patients experience mood disorder in the gender differences. For the males, the ATS+K patients were more likely to use MDMA (3, 4-methylenedioxymethamphetamine) and develop more psychotic disorders than the ATS patients; for females, the ATS+K patients were more likely to use MDMA, alcohol and develop more cognitive impairment disorder. These results suggested that the psychiatrists should focus on the mood disorder among females, psychotic disorders among males who abuse ATS and ketamine, and cognitive impairment disorder for the females who abuse ATS and ketamine.

Profiles of executive functioning: associations with substance dependence and risky sexual behavior

The present investigations applied a theoretical perspective regarding the impact of executive functioning (EF) on sexual risk among substance users, using a methodological approach designed to examine whether EF subtypes differentially predict behavior patterns. Participants included 104 substance-using HIV-negative gay and bisexual men. Participants completed 5 neuropsychological assessment tasks selected to tap discrete EF components, and these data were linked to data on substance dependence and behavioral reports of substance use and sexual risk in the past 30 days. Cluster analysis identified 3 EF subtypes: (a) high performing (good performance across all measures); (b) low performing (poor performance across all measures); and (c) poor IGT performance (impairment on the Iowa Gambling Task [IGT] and its variant, but good performance on all other tasks). The 3 subtypes did not differ in amount of substance use, but the low-performing subtype was associated with greater rates of substance dependence. The low-performing subtype reported the highest rates of sexual behavior and risk, while the poor-IGT-performance subtype reported the lowest rates of sexual risk taking. Global associations between substance use and sexual risk were strongest among the low-performing subtype, but event-level associations appeared strongest among individuals in the high-performing subtype. These data suggest complex associations between EF and sexual risk among substance users, and suggest that the relationship between substance use and sexual risk may vary by EF subtypes.

Distinct roles of methamphetamine in modulating spatial memory consolidation, retrieval, reconsolidation and the accompanying changes of ERK and CREB activation in hippocampus and prefrontal cortex

Drugs of abuse modulated learning and memory in humans yet the underlying mechanism remained unclear. The extracellular signal-regulated kinase (ERK) and the transcription factor cAMP response element-binding protein (CREB) were involved in neuroplastic changes associated with learning and memory. In the current study, we used a Morris water maze to examine the effect of methamphetamine (METH) on different processes of spatial memory in mice. We then investigated the status of ERK and CREB in the hippocampus and prefrontal cortex (PFC). We found that 1.0 mg/kg dose of METH facilitated spatial memory consolidation when it was injected immediately after the last learning trial. In contrast, the same dose of METH had no effect on spatial memory retrieval when it was injected 30 min before the test. Furthermore, 1.0 mg/kg dose of METH injected immediately after retrieval had no effect on spatial memory reconsolidation. Activation of both ERK and CREB in the hippocampus was found following memory consolidation but not after retrieval or reconsolidation in METH-treated mouse groups. In contrast, activation of both ERK and CREB in the PFC was found following memory retrieval but not other processes in METH-treated mouse groups. These results suggested that METH facilitated spatial memory consolidation but not retrieval or reconsolidation. Moreover, activation of the ERK and CREB signaling pathway in the hippocampus might be involved in METH-induced spatial memory changes.