Effects of a methamphetamine vaccine, IXT-v100, on methamphetamine-related behaviors.

RATIONALE: Vaccines have been developed as a potential treatment for methamphetamine (meth) use disorder (MUD). Immunization with the meth vaccine IXT-v100 has previously been shown to elicit antibodies with high affinity for meth and thus may be an effective treatment for MUD. OBJECTIVES: These studies were designed to determine the efficacy of IXT-v100 on meth-taking and meth-seeking behaviors in rats. METHODS: In the acquisition and maintenance study, male and female rats were trained to self-administer meth (0.06 mg/kg/infusion) over an 8-week period following vaccination. In the last 4 weeks, the dose of meth was increased or decreased each week. To assess meth-seeking behavior, the meth-primed reactivity model was used. Rats were trained to self-administer meth for 5 weeks, followed by a 5-week or 11-week forced abstinence period during which the animals were vaccinated. Rats were then placed back into the self-administration chamber immediately after being injected with meth (1 mg/kg, i.p.) but did not receive meth during the session. Responses were recorded and used as a measure of meth seeking. RESULTS: Results from the acquisition and maintenance study in Wistar rats show that vaccination with IXT-v100 adjuvanted with glucopyranosyl lipid A stable emulsion decreases the percentage of animals that will self-administer a moderate level of meth. In the meth-primed reactivity studies, results from males showed that vaccination significantly attenuates meth-seeking behavior. CONCLUSION: Together, these results suggest vaccination with IXT-v100 may be effective at decreasing meth-taking and meth-seeking behaviors in humans suffering with MUD.

Intermittent bilateral deep brain stimulation of the nucleus accumbens shell reduces intravenous methamphetamine intake and seeking in Wistar rats.

OBJECTIVE There is increasing interest in neuromodulation for addiction. Methamphetamine abuse is a global health epidemic with no proven treatment. The objective of this study was to examine the effects of intermittent nucleus accumbens shell (AcbSh) deep brain stimulation (DBS) on operant methamphetamine intake and on methamphetamine seeking when stimulation is delivered in an environment different from that of drug use. METHODS Eighteen rats were implanted with intravenous (IV) catheters and bilateral AcbSh electrodes and subsequently underwent daily sessions in 2-lever (active/methamphetamine and inactive/no reward) operant chambers to establish IV methamphetamine self-administration. After stable responding was achieved, 3 hours of DBS or sham treatment was administered (sham: 0 µA, n = 8; active: 200 µA, n = 10) in a separate nondrug environment prior to the daily operant sessions for 5 consecutive days. Immediately following each DBS/sham treatment, rats were placed in the operant chambers to examine the effects of remote stimulation on methamphetamine intake. After the 5 days of therapy were finished, rats reestablished a posttreatment baseline, followed by extinction training, abstinence, and 1 day of relapse testing to assess methamphetamine-seeking behavior. RESULTS There was a decrease in total methamphetamine intake in rats receiving active DBS versus sham on Days 1 (42%) and 2 (44%). Methamphetamine administration returned to baseline levels following the cessation of DBS therapy. Compared with baseline drug responding, methamphetamine seeking was reduced (57%) in the DBS group but not in the sham group. CONCLUSIONS It is feasible to deliver noncontinuous DBS outside of the drug use environment with a resultant decrease in IV methamphetamine intake and seeking. The AcbSh is a neuroanatomical substrate for psychostimulant reinforcement and may be a target for intermittent neuromodulatory therapies that could be administered during brief periods of sobriety.

The differential effects of alprazolam and oxazepam on methamphetamine self-administration in rats.

BACKGROUND: Methamphetamine is the second most commonly used illicit drug in the world, and despite recent attempts by the Drug Enforcement Administration to combat this epidemic, methamphetamine use is still on the rise. As methamphetamine use increases so does polydrug use, particularly that involving methamphetamine and benzodiazepines. The present study was designed to examine the effects of two benzodiazepines on methamphetamine self-administration. METHODS: Five doses of methamphetamine (0.0075, 0.015, 0.03, 0.09, and 0.12mg/kg/infusion) were tested, producing an inverted U-shaped dose-response curve. Rats were then pretreated with oxazepam, alprazolam, or vehicle prior to methamphetamine self-administration. To determine if the effects of these drugs were due to the GABAA receptor and/or translocator protein (TSPO), we also pretreated rats with an antagonist for the benzodiazepine-binding site on the GABAA receptor (i.e., flumazenil) and a TSPO antagonist (i.e., PK11195) prior to alprazolam or oxazepam administration. RESULTS: Oxazepam significantly reduced methamphetamine self-administration as demonstrated by a downward shift of the dose-response curve. In contrast, alprazolam significantly enhanced methamphetamine self-administration as evidenced by a leftward shift of the dose-response curve. Flumazenil completely blocked the effects of alprazolam on methamphetamine self-administration. When administered individually, both flumazenil and PK11195 partially reversed the effects of oxazepam on methamphetamine self-administration. However, when these two antagonists were combined, the effects of oxazepam were completely reversed. CONCLUSIONS: The GABAA receptor is responsible for the alprazolam-induced enhancement of methamphetamine self-administration, while the activation of both the GABAA receptor and TSPO are responsible for the oxazepam-induced reduction of methamphetamine self-administration.

A General Method for Evaluating Deep Brain Stimulation Effects on Intravenous Methamphetamine Self-Administration.

Substance use disorders, particularly to methamphetamine, are devastating, relapsing diseases that disproportionally affect young people. There is a need for novel, effective and practical treatment strategies that are validated in animal models. Neuromodulation, including deep brain stimulation (DBS) therapy, refers to the use of electricity to influence pathological neuronal activity and has shown promise for psychiatric disorders, including drug dependence. DBS in clinical practice involves the continuous delivery of stimulation into brain structures using an implantable pacemaker-like system that is programmed externally by a physician to alleviate symptoms. This treatment will be limited in methamphetamine users due to challenging psychosocial situations. Electrical treatments that can be delivered intermittently, non-invasively and remotely from the drug-use setting will be more realistic. This article describes the delivery of intracranial electrical stimulation that is temporally and spatially separate from the drug-use environment for the treatment of IV methamphetamine dependence. Methamphetamine dependence is rapidly developed in rodents using an operant paradigm of intravenous (IV) self-administration that incorporates a period of extended access to drug and demonstrates both escalation of use and high motivation to obtain drug.

A therapeutic combination of metyrapone and oxazepam increases brain levels of GABA-active neurosteroids and decreases cocaine self-administration in male rats.

In rodents, the behavioral and neurochemical effects resulting from the pharmacological blockade of the hypothalamo-pituitary-adrenal (HPA) axis are unclear. Metyrapone, a corticosterone synthesis inhibitor, has been demonstrated to reduce cocaine-related behaviors, especially in a low-dose combination with oxazepam, a benzodiazepine. Although this combination therapy (MET/OX) also reduces drug-taking and drug-seeking behaviors in both rodents and cocaine-dependent humans, these effects are not correlated with plasma glucocorticoid levels. In this brief report, we present data demonstrating that this MET/OX combination enhances brain levels of the GABA-active steroid metabolites, tetrahydrodeoxycorticosterone (THDOC) and allopregnanolone. Male rats, trained to self-administer cocaine or that received yoked-saline infusions, were pretreated with MET/OX, at doses that reduced cocaine-motivated responding, or vehicle. Allopregnanolone and THDOC were measured using liquid chromatography-mass spectroscopy (LC-MS/MS) in the prefrontal cortex and amygdala in the brains from these rats. THDOC levels were enhanced following MET/OX pretreatment in both brain regions, regardless of cocaine self-administration experience. However, allopregnanolone was selectively enhanced in the rats that self-administered cocaine, but not in rats in the yoked-saline group. Thus, the MET/OX combination increased neurosteroid content in brain regions important for drug addiction. These neurosteroids have been shown to reduce cocaine-related behaviors and may contribute to the behavioral effects of MET/OX combination therapy.

Role of GABA-active neurosteroids in the efficacy of metyrapone against cocaine addiction.

Previous research has demonstrated a complicated role for stress and HPA axis activation in potentiating various cocaine-related behaviors in preclinical models of drug dependence. However, the investigation of several antiglucocorticoid therapies has yielded equivocal results in reducing cocaine-related behaviors, possibly because of varying mechanisms of actions. Specifically, research suggests that metyrapone (a corticosterone synthesis inhibitor) may reduce cocaine self-administration in rats via a nongenomic, extra-adrenal mechanism without altering plasma corticosterone. In the current experiments, male rats were trained to self-administer cocaine infusions and food pellets in a multiple, alternating schedule of reinforcement. Metyrapone pretreatment dose-dependently decreased cocaine self-administration as demonstrated previously. Pharmacological inhibition of neurosteroid production by finasteride had significant effects on cocaine self-administration, regardless of metyrapone pretreatment. However, metyrapone's effects on cocaine self-administration were significantly attenuated with bicuculline pretreatment, suggesting a role for GABA-active neurosteroids in cocaine-reinforced behaviors. In vitro binding data also confirmed that metyrapone does not selectively bind to GABA-related proteins. The results of these experiments support the hypothesis that metyrapone may increase neurosteroidogenesis to produce effects on cocaine-related behaviors.

The extra-adrenal effects of metyrapone and oxazepam on ongoing cocaine self-administration.

Investigation of the role of stress in cocaine addiction has yielded an efficacious combination of metyrapone and oxazepam, hypothesized to decrease relapse to cocaine use by reducing stress-induced craving. However, recent data suggest an extra-adrenal role for metyrapone in mediating stress- and addiction-related behaviors. The interactions between the physiological stress response and cocaine self-administration were characterized in rodents utilizing surgical adrenalectomy and pharmacological treatment. Male Wistar rats were trained to self-administer cocaine (0.25mg/kg/infusion) and food pellets under a concurrent alternating fixed-ratio schedule of reinforcement. Surgical removal of the adrenal glands resulted in a significant decrease in plasma corticosterone and a consequent increase in ACTH, as expected. However, adrenalectomy did not significantly affect ongoing cocaine self-administration. Pretreatment with metyrapone, oxazepam and their combinations in intact rats resulted in a significant decrease in cocaine-reinforced responses. These same pharmacological treatments were still effective in reducing cocaine- and food-reinforced responding in adrenalectomized rats. The results of these experiments demonstrate that adrenally-derived steroids are not necessary to maintain cocaine-reinforced responding in cocaine-experienced rats. These results also demonstrate that metyrapone may produce effects outside of the adrenal gland, presumably in the central nervous system, to affect cocaine-related behaviors.

The combination of metyrapone and oxazepam for the treatment of cocaine and other drug addictions.

Although scientists have been investigating the neurobiology of psychomotor stimulant reward for many decades, there is still no FDA-approved treatment for cocaine or methamphetamine abuse. Research in our laboratory has focused on the relationship between stress, the subsequent activation of the hypothalamic-pituitary-adrenal (HPA) axis, and psychomotor stimulant reinforcement for almost 30 years. This research has led to the development of a combination of low doses of the cortisol synthesis inhibitor, metyrapone, and the benzodiazepine, oxazepam, as a potential pharmacological treatment for cocaine and other substance use disorders. In fact, we have conducted a pilot clinical trial that demonstrated that this combination can reduce cocaine craving and cocaine use. Our initial hypothesis underlying this effect was that the combination of metyrapone and oxazepam reduced cocaine seeking and taking by decreasing activity within the HPA axis. Even so, doses of the metyrapone and oxazepam combination that consistently reduced cocaine taking and seeking did not reliably alter plasma corticosterone (or cortisol in the pilot clinical trial). Furthermore, subsequent research has demonstrated that this drug combination is effective in adrenalectomized rats, suggesting that these effects must be mediated above the level of the adrenal gland. Our evolving hypothesis is that the combination of metyrapone and oxazepam produces its effects by increasing the levels of neuroactive steroids, most notably tetrahydrodeoxycorticosterone, in the medial prefrontal cortex and amygdala. Additional research will be necessary to confirm this hypothesis and may lead to the development of improved and specific pharmacotherapies for the treatment of psychomotor stimulant use.

Combinations of oxazepam and metyrapone attenuate cocaine and methamphetamine cue reactivity.

BACKGROUND: We have previously reported that combining low doses of oxazepam and metyrapone (OX/MET) reduces intravenous cocaine self-administration without affecting stress-hormone levels. We hypothesized that the combination of OX/MET would also inhibit the reinstatement of cocaine or methamphetamine seeking induced by the presentation of a conditioned reinforcer and that stress hormone levels would not be influenced by this treatment. METHODS: Male rats were implanted with jugular catheters and trained to self-administer cocaine or methamphetamine during daily 2-h sessions. During training, cocaine or methamphetamine delivery was paired with the presentation of a tone and the illumination of a house light. Following stable self-administration, rats were placed into forced abstinence. During cue-reactivity testing, rats were placed back into the operant chambers and responding only resulted in the presentation of the conditioned reinforcer; no cocaine or methamphetamine was delivered. Blood was collected on the last day of self-administration and on the day of cue-reactivity testing (either 15-min or 2-h session) to assess plasma corticosterone. RESULTS: The response-contingent presentation of the conditioned reinforcer reliably maintained cocaine or methamphetamine seeking following vehicle pretreatment. Pretreatment with OX/MET resulted in a dose-related attenuation of both cocaine and methamphetamine seeking. Corticosterone levels were significantly different at the end of the 15-min session, but not following the 2-h session. CONCLUSION: These data suggest that OX/MET may be useful in blocking the ability of environmental cues to stimulate both cocaine and methamphetamine seeking and that this effect is not entirely dependent on stress hormone levels.

Biphasic dopamine regulation in mesoaccumbens pathway in response to non-contingent binge and escalating methamphetamine regimens in the Wistar rat.

RATIONALE: Methamphetamine (MA) increases extracellular dopamine (DA) and at chronic high doses induces toxicity as indicated by decreased expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT). Notably, rats will self-administer MA in escalating quantities producing such toxicity. However, the impact of MA at sub-toxic doses on DA regulation is not well established. OBJECTIVE: The temporal dynamics of DA regulation following cessation of sub-toxic escalating and binge doses of non-contingent MA were investigated as changes therein may be associated with escalation of MA intake. MATERIALS AND METHODS: MA was administered 3×/day using an established 14-day escalating-dose regimen (0.1-4.0 mg/kg) or a single-day binge-style administration (3 × 4 mg/kg). DA tissue content, DA turnover, TH protein, TH phosphorylation, DAT, and vesicular monoamine transporter 2 were measured in nigrostriatal and mesoaccumbens pathways 48 h and 2 weeks after MA cessation. RESULTS: Changes in striatal DA regulation were limited to increased DA turnover. However, in the mesoaccumbens pathway, escalating MA had biphasic effects. DA was increased in ventral tegmental area (VTA) and decreased in nucleus accumbens at 48 h post-MA while the reverse was seen at 2 weeks. These changes were matched by similar changes in TH protein and, in the VTA, by changes in DAT. CONCLUSION: Escalation of MA intake produces both transient and long-lasting effects upon DA, TH, and DAT in the mesoaccumbens pathway. The eventual decrease of DA in the VTA is speculated to contribute to craving for MA and, thus, may be associated with MA escalation and resulting dopaminergic toxicity.

Alprazolam and oxazepam block the cue-induced reinstatement of extinguished cocaine seeking in rats.

RATIONALE: We have previously reported that pretreatment with benzodiazepines reduces intravenous cocaine self-administration in rats. OBJECTIVE: This experiment was designed to investigate whether or not benzodiazepines would also inhibit the reinstatement of cocaine seeking induced by the presentation of a conditioned reinforcer. MATERIALS AND METHODS: Adult male rats were implanted with jugular catheters and trained to self-administer cocaine (0.25 mg/kg/infusion) during daily 2-h sessions. During training, cocaine delivery was paired with the presentation of a tone and the illumination of a houselight. Once a stable baseline of cocaine self-administration was observed, lever pressing was extinguished to less than 20% of baseline rates. During reinstatement testing, responding resulted in the presentation of the conditioned reinforcer (i.e., the houselight and tone previously paired with self-administered cocaine). RESULTS: The response-contingent presentation of the conditioned reinforcer reliably reinstated cocaine seeking. Pretreatment with alprazolam (2 or 4 mg/kg, ip) or oxazepam (20 or 40 mg/kg, ip) reversed the conditioned reinforcer-induced reinstatement of extinguished cocaine-seeking behavior at doses that did not reliably affect the conditioned reinforcer-induced reinstatement of extinguished food seeking, suggesting that benzodiazepines may not have reduced reinstatement responding due to non-specific reductions in behavior. CONCLUSIONS: These data suggest that benzodiazepines may be useful in blocking the ability of environmental cues to stimulate cocaine seeking.

Effects of the combination of metyrapone and oxazepam on cocaine and food self-administration in rats.

For several years, our laboratory has investigated the role for the HPA axis in cocaine reinforcement. Two classes of drugs that we have studied include corticosterone synthesis inhibitors (e.g., metyrapone) and benzodiazepine receptor agonists (e.g., oxazepam). In the experiments described in this manuscript, we tested the effects of various doses of metyrapone and oxazepam against several doses of self-administered cocaine. Behavioral, endocrine and pharmacokinetic measures of the effects of the combination of metyrapone and oxazepam on cocaine reward are presented. Combinations of metyrapone and oxazepam at doses that produced no observable effects when administered separately significantly reduced cocaine self-administration without affecting food-maintained responding during the same sessions. Changes in pharmacokinetics or endocrine function do not appear to mediate these effects, suggesting a central mechanism of action. Therefore, although these drugs produce their effects through distinct mechanisms, an additive effect on cocaine self-administration is obtained when these drugs are administered together, suggesting that combinations of low doses of metyrapone and oxazepam may be useful in reducing cocaine seeking with a reduced incidence of unwanted side effects and a decreased potential for abuse.