A review of the clinical pharmacology of methamphetamine

MDMA and methamphetamine: some paradoxical negative and positive mood changes in an acute dose laboratory study

RATIONALE

This study investigated the acute mood effects of oral MDMA, methamphetamine, and placebo in a double-blind laboratory study.

METHODS

Fifty-two healthy participants comprised abstinent recreational users of stimulant drugs, 27 female and 25 male, mean age 24.8 years. Three test sessions involved acute 100 mg oral 3.4-methylendioxymethamphetamine (MDMA), 0.42 mg/kg oral methamphetamine, and matching placebo. Drug administration was counterbalanced, testing was double-blind, and medical supervision was present throughout. Car-driving performance on a laboratory simulator was assessed after 3 and 24 h, with the findings being presented elsewhere. Positive and negative moods (PANAS self-ratings) were completed before drug administration, 3, 4.5, and 24 h later. Blood samples were taken to monitor drug plasma levels.

RESULTS

Following MDMA, there were no significant increases in positive moods, whereas negative moods were significantly higher than under placebo. Methamphetamine led to significant increases in both positive and negative moods. The MDMA findings contrast with the elated moods, typically noted by dance clubbers on Ecstasy. However, they are consistent with some previous laboratory findings, since a wide array of positive and negative mood changes have been demonstrated. One possible explanatory factor was the neutral environmental situation, particularly if a primary action of MDMA is to intensify ongoing psychological states. Other explanatory factors, such as dosage, gender, post-drug timing, neurohormonal aspects, and social factors, are also discussed.

CONCLUSIONS

In the laboratory, acute methamphetamine led to significantly higher positive moods. However, against expectations, MDMA did not generate a significant increase in positive moods.

Sensitivity to rewarding or aversive effects of methamphetamine determines methamphetamine intake

Amphetamines have rewarding and aversive effects. Relative sensitivity to these effects may be a better predictor of vulnerability to addiction than sensitivity to one of these effects alone. We tested this hypothesis in a dose-response study in a second replicate set of mouse lines selectively bred for high vs. low methamphetamine (MA) drinking (MADR). Replicate 2 high (MAHDR-2) and low (MALDR-2) MA drinking mice were bred based on MA consumption in a two-bottle choice procedure and examined for novel tastant drinking. Sensitivities to the rewarding and aversive effects of several doses of MA (0.5, 2 and 4 mg/kg) were measured using a place conditioning procedure. After conditioning, mice were tested in a drug-free and then drug-present state for time spent in the saline- and MA-paired contexts. Similar to the first set of MADR lines, by the end of selection, MAHDR-2 mice consumed about 6 mg MA/kg/18 h, compared to nearly no MA in MALDR-2 mice, but had similar taste preference ratios. MAHDR-2 mice exhibited place preference in both the drug-free and drug-present tests, and no significant place aversion. In contrast, MALDR-2 mice exhibited no place preference or aversion during the drug-free test, but robust place aversion in the drug-present test. These data extend our preliminary findings from the first set of MADR lines and support the hypothesis that the combination of greater sensitivity to the rewarding effects of MA and insensitivity to the aversive effects of MA is genetically associated with heightened risk for MA consumption.

The ugly side of amphetamines: short- and long-term toxicity of 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy'), methamphetamine and D-amphetamine

Amphetamine ('Speed'), methamphetamine ('Ice') and its congener 3,4-methylenedioxymethamphetamine (MDMA; 'Ecstasy') are illicit drugs abused worldwide for their euphoric and stimulant effects. Despite compelling evidence for chronic MDMA neurotoxicity in animal models, the physiological consequences of such toxicity in humans remain unclear. In addition, distinct differences in the metabolism and pharmacokinetics of MDMA between species and different strains of animals prevent the rationalisation of realistic human dose paradigms in animal studies. Here, we attempt to review amphetamine toxicity and in particular MDMA toxicity in the pathogenesis of exemplary human pathologies, independently of confounding environmental factors such as poly-drug use and drug purity.

Histamine-dependent behavioral response to methamphetamine in 12-month-old male mice

Methamphetamine (MA) use is a large problem across the United States. Effects of MA include hyperactivity and increased anxiety. Using a mouse model system, we examined behavioral performance in the open field and elevated zero maze and shock-startle response of 12-month-old wild-type mice injected with MA once (1 mg/kg) 30 min prior to behavioral testing. MA treatment resulted in behavioral sensitization in the open field, consistent with studies in younger mice. There was an increased activity in the elevated zero maze and an increased shock-startle response 30 and 60 min post-injection. Since histamine mediates some effects of MA in the brain, we assessed whether 12-month-old mice lacking histidine decarboxylase (Hdc⁻/⁻), the enzyme required to synthesize histamine, respond differently to MA than wild-type (Hdc+/+) mice. Compared to saline treatment, acute and repeated MA administration increased activity in the open field and measures of anxiety, though more so in Hdc⁻/⁻ than Hdc+/+ mice. In the elevated zero maze, opposite effects of MA on activity and measures of anxiety were seen in Hdc+/+ mice. In contrast, MA similarly increased the shock-startle response in Hdc⁻/⁻ and Hdc+/+ mice, compared to saline-treated genotype-matched mice. These results are similar to those in younger mice, suggesting that the effects are not age-dependent. Overall, single or repeated MA treatment causes histamine-dependent changes in 12-month-old mice in the open field and elevated zero maze, but not in the shock-startle response.

Characterizing methamphetamine withdrawal in recently abstinent methamphetamine users: a pilot field study

BACKGROUND

Methamphetamine dependence has become a significant problem, but methamphetamine withdrawal symptoms have not been well studied.

METHODS

This prospective observational pilot study was designed to examine withdrawal symptoms, mood, anxiety, cognitive function, and subjective measures of sleep over a 4-week period in six patients entering residential treatment for methamphetamine dependence.

RESULTS

Methamphetamine withdrawal symptoms, mood, and anxiety symptoms all resolve fairly quickly within 2 weeks of cessation of methamphetamine. Sleep was disrupted over the course of the 4-week study. No clinically significant alterations in blood pressure or heart rate were identified. This study did not demonstrate any alterations in cognitive function over the 4 weeks of the residential stay.

CONCLUSIONS

This pilot study points toward the need for a double-blind, placebo-controlled amphetamine withdrawal paradigm in humans where changes in sleep, cognitive function, and withdrawal measures can be explored more fully.

SCIENTIFIC SIGNIFICANCE

This study extends the literature by pointing toward a methamphetamine withdrawal syndrome that includes alterations in measures of sleep quality and refreshed sleep, early improvement in depression and anxiety symptoms, most striking during the first week, but persisting into the second week.

Role of dopamine D1- and D2-like receptor mechanisms in drug-seeking following methamphetamine self-administration in rats

It has been suggested that dopaminergic mechanisms mediate relapse to drug-seeking behavior and both D1- and D2-like receptor mechanisms have been implicated. In contrast to self-administration of other drugs, there is a relative paucity of studies that has examined the pharmacological basis of methamphetamine (MA) seeking. Accordingly, the present study used an animal model of drug-seeking to determine the role of D1- and D2-like receptor mechanisms in relapse to MA abuse. Rats were trained to self-administer MA, and then responding was extinguished by replacing the MA solution with vehicle. Experimenter-administered injections of MA or the dopamine uptake inhibitor, GBR 12909, reinstated extinguished responding in a dose-dependent manner. The D1-like antagonist, SCH 23390 attenuated drug-seeking but the D2-like antagonist, eticlopride, was ineffective. The results suggest that MA-seeking is predominantly mediated by DA D1-like receptor mechanisms. These findings are in contrast to the literature on drug-seeking following self-administration of other drugs, and suggest that relapse to different drugs of abuse may rely upon different DA receptor mechanisms.

A randomized, placebo-controlled trial of sustained-release dextroamphetamine for treatment of methamphetamine addiction

Sixty treatment-seeking individuals with methamphetamine (MA) dependence entered a randomized, placebo-controlled, double-blind clinical trial of oral dextroamphetamine (d-AMP) as a replacement therapy for MA dependence. The subjects took 60 mg sustained-release d-AMP for 8 weeks, during which time they received eight 50-min sessions of individual psychotherapy. Adverse events and urine toxicology for MA were assessed two times a week. There were no serious adverse events. Urine samples containing <1,000 ng/ml of MA were classified as negative for MA. The MA-negative scores in the d-AMP group (3.1 ± SD 4.6) were no higher than those in the placebo group (3.3 ± SD 5.3; P > 0.05). However, withdrawal and craving scores were significantly lower in the d-AMP group (P < 0.05 for both). Although subjects taking d-AMP did not reduce their use of MA, the significant reductions observed in withdrawal and craving scores in this group support the need for further exploration of d-AMP as a pharmacologic intervention for MA dependence, possibly at higher doses.

Methamphetamine causes sustained depression in cerebral blood flow

The use prevalence of the highly addictive psychostimulant methamphetamine (MA) has been steadily increasing over the past decade. MA abuse has been associated with both transient and permanent alterations in cerebral blood flow (CBF), hemorrhage, cerebrovascular accidents and death. To understand MA-induced changes in CBF, we exposed C56BL/6 mice to an acute bolus of MA (5mg/kg MA, delivered IP). This elicited a biphasic CBF response, characterized by an initial transient increase (~ 5 minutes) followed by a prolonged decrease (~ 30 minutes) of approximately 25% relative to baseline CBF--as measured by laser Doppler flowmetry over the somatosensory cortex. To assess if this was due to catecholamine derived vasoconstriction, phentolamine, an α-adrenergic antagonist was administered prior to MA treatment. This reduced the initial increase in CBF but failed to prevent the subsequent, sustained decrease in CBF. Consistent with prior reports, MA caused a transient increase in mean arterial blood pressure, body temperature and respiratory rate. Elevated respiratory rate resulted in hypocapnia. When respiratory rate was controlled by artificially ventilating mice, blood PaCO(2) levels after MA exposure remained unchanged from physiologic levels, and the MA-induced decrease in CBF was abolished. In vivo two-photon imaging of cerebral blood vessels revealed sustained MA-induced vasoconstriction of pial arterioles, consistent with laser Doppler flowmetry data. These findings show that even a single, acute exposure to MA can result in profound changes in CBF, with potentially deleterious consequences for brain function.

Anxiety disorders among methamphetamine dependent adults: association with post-treatment functioning

Although anxiety is one of the most prominent psychiatric complaints of methamphetamine (MA) users, little is known about the association between anxiety disorders and treatment outcomes in this population. Using data from 526 adults in the largest psychosocial clinical trial of MA users conducted to date, this study examined psychiatric, substance use, and functional outcomes of MA users with concomitant anxiety disorders 3 years after treatment. Anxiety disorders were associated with poorer alcohol and drug use outcomes, increased health service utilization, and higher levels of psychiatric symptomatology, including suicidality. Addressing anxiety symptoms and syndromes in MA users may be helpful as a means of optimizing treatment outcomes.

Systemically administered oxytocin decreases methamphetamine activation of the subthalamic nucleus and accumbens core and stimulates oxytocinergic neurons in the hypothalamus

Recent preclinical evidence indicates that the neuropeptide oxytocin may have potential in the treatment of drug dependence and drug withdrawal. Oxytocin reduces methamphetamine self-administration, conditioned place preference and hyperactivity in rodents. However, it is unclear how oxytocin acts in the brain to produce such effects. The present study examined how patterns of neural activation produced by methamphetamine were modified by co-administered oxytocin. Male Sprague-Dawley rats were pretreated with either 2 mg/kg oxytocin (IP) or saline and then injected with either 2 mg/kg methamphetamine (IP) or saline. After injection, locomotor activity was measured for 80 minutes prior to perfusion. As in previous studies, co-administered oxytocin significantly reduced methamphetamine-induced behaviors. Strikingly, oxytocin significantly reduced methamphetamine-induced Fos expression in two regions of the basal ganglia: the subthalamic nucleus and the nucleus accumbens core. The subthalamic nucleus is of particular interest given emerging evidence for this structure in compulsive, addiction-relevant behaviors. When administered alone, oxytocin increased Fos expression in several regions, most notably in the oxytocin-synthesizing neurons of the supraoptic nucleus and paraventricular nucleus of the hypothalamus. This provides new evidence for central actions of peripheral oxytocin and suggests a self-stimulation effect of exogenous oxytocin on its own hypothalamic circuitry. Overall, these results give further insight into the way in which oxytocin might moderate compulsive behaviors and demonstrate the capacity of peripherally administered oxytocin to induce widespread central effects.

Withdrawal symptoms in abstinent methamphetamine-dependent subjects

AIMS

Withdrawal symptoms have been linked to a propensity for relapse to drug abuse. Inasmuch as this association applies to methamphetamine (MA) abuse, an understanding of the course of MA withdrawal symptoms may help to direct treatment for MA dependence. Previous studies of symptoms manifested during abstinence from MA have been limited in size and scope. We asked (i) whether debilitating psychological and/or physical symptoms appear during the first several weeks of MA abstinence, (ii) how craving for MA evolves and (iii) whether psychiatric symptoms (e.g. depression, psychosis) persist beyond a month of abstinence.

DESIGN

A study of MA-dependent participants, who initiated and maintained abstinence from the drug for up to 5 weeks, compared to a matched healthy comparison group.

SETTING

In-patient research hospital ward (MA-dependent subjects) and out-patient (comparison subjects).

PARTICIPANTS

Fifty-six MA-dependent and eighty-nine comparison subjects.

MEASUREMENTS

Rater-assessed MA withdrawal questionnaire and self-report assessment of craving (MA-dependent subjects) and self-report assessment of psychiatric symptoms (both groups).

FINDINGS

At study entry, MA-dependent subjects exhibited a wide range in severity of depressive symptoms, with the average score at a mild-moderate level of severity. Symptoms of psychosis were also prevalent. While depressive and psychotic symptoms largely resolved within a week of abstinence, craving did not decrease significantly from the time of initiating abstinence until the second week, and then continued at a reduced level to the fifth week.

CONCLUSIONS

Depressive and psychotic symptoms accompany acute withdrawal from methamphetamine but resolve within 1 week. Craving is also present and lasts at least 5 weeks.

Methamphetamine reduces LTP and increases baseline synaptic transmission in the CA1 region of mouse hippocampus

Methamphetamine (METH) is an addictive psychostimulant whose societal impact is on the rise. Emerging evidence suggests that psychostimulants alter synaptic plasticity in the brain--which may partly account for their adverse effects. While it is known that METH increases the extracellular concentration of monoamines dopamine, serotonin, and norepinephrine, it is not clear how METH alters glutamatergic transmission. Within this context, the aim of the present study was to investigate the effects of acute and systemic METH on basal synaptic transmission and long-term potentiation (LTP; an activity-induced increase in synaptic efficacy) in CA1 sub-field in the hippocampus. Both the acute ex vivo application of METH to hippocampal slices and systemic administration of METH decreased LTP. Interestingly, the acute ex vivo application of METH at a concentration of 30 or 60 microM increased baseline synaptic transmission as well as decreased LTP. Pretreatment with eticlopride (D2-like receptor antagonist) did not alter the effects of METH on synaptic transmission or LTP. In contrast, pretreatment with D1/D5 dopamine receptor antagonist SCH23390 or 5-HT1A receptor antagonist NAN-190 abrogated the effect of METH on synaptic transmission. Furthermore, METH did not increase baseline synaptic transmission in D1 dopamine receptor haploinsufficient mice. Our findings suggest that METH affects excitatory synaptic transmission via activation of dopamine and serotonin receptor systems in the hippocampus. This modulation may contribute to synaptic maladaption induced by METH addiction and/or METH-mediated cognitive dysfunction.

Randomized, double-blind, placebo-controlled trial of modafinil for the treatment of methamphetamine dependence

OBJECTIVE

To compare modafinil to placebo for reducing methamphetamine (MA) use, improving retention, and reducing depressive symptoms and MA cravings. Rates of adverse events and cigarette smoking with modafinil versus placebo were also compared.

METHODS

Following a 2-week, non-medication lead-in period, 71 treatment-seeking MA-dependent participants were randomly assigned to modafinil (400mg once daily; N=34) or placebo (once daily; N=37) for 12 weeks under double-blind conditions. Participants attended clinic thrice-weekly to provide urine samples analyzed for MA-metabolite, to complete research assessments, and to receive contingency management and weekly cognitive behavioral therapy (CBT) sessions.

RESULTS

There were no statistically significant effects for modafinil on MA use, retention, depressive symptoms, or MA cravings in pre-planned analyses. Outcomes for retention and MA use favored modafinil in a post hoc analysis among participants with low CBT attendance and among participants with baseline high-frequency of MA use (MA use on >18 of past 30 days), but did not reach statistical significance in these small subgroups. Modafinil was safe and well tolerated and did not increase cigarette smoking.

CONCLUSIONS

Modafinil was no more effective than placebo at 400mg daily in a general sample of MA users. A post hoc analysis showing a trend favoring modafinil among subgroups with baseline high-frequency MA use and low CBT attendance suggests that further evaluation of modafinil in MA users is warranted.

Extinction of drug cue reactivity in methamphetamine-dependent individuals

Conditioned responses to drug-related environmental cues (such as craving) play a critical role in relapse to drug use. Animal models demonstrate that repeated exposure to drug-associated cues in the absence of drug administration leads to the extinction of conditioned responses, but the few existing clinical trials focused on extinction of conditioned responses to drug-related cues in drug-dependent individuals show equivocal results. The current study examined drug-related cue reactivity and response extinction in a laboratory setting in methamphetamine-dependent individuals. Methamphetamine cue-elicited craving was extinguished during two sessions of repeated (3) within-session exposures to multi-modal (picture, video, and in-vivo) cues, with no evidence of spontaneous recovery between sessions. A trend was noted for a greater attenuation of response in participants with longer (4-7 day) inter-session intervals. These results indicate that extinction of drug cue conditioned responding occurs in methamphetamine-dependent individuals, offering promise for the development of extinction- based treatment strategies.

Modeling withdrawal syndrome in zebrafish

The zebrafish (Danio rerio) is rapidly becoming a popular model species in behavioral neuroscience research. Zebrafish behavior is robustly affected by environmental and pharmacological manipulations, and can be examined using exploration-based paradigms, paralleled by analysis of endocrine (cortisol) stress responses. Discontinuation of various psychotropic drugs evokes withdrawal in both humans and rodents, characterized by increased anxiety. Sensitivity of zebrafish to drugs of abuse has been recently reported in the literature. Here we examine the effects of ethanol, diazepam, morphine and caffeine withdrawal on zebrafish behavior. Overall, discontinuation of ethanol, diazepam and morphine produced anxiogenic-like behavioral or endocrine responses, demonstrating the utility of zebrafish in translational research of withdrawal syndrome.