The α1 Antagonist Doxazosin Alters the Behavioral Effects of Cocaine in Rats

Evaluation of multitarget drugs on the expression of cocaine-induced locomotor sensitization in male rats: A comparative study

Purpose

- Cocaine use disorder (CUD) is a complex disease. Several studies have shown the efficacy of multitarget drugs used to treat CUD. Here we compare the efficacy of mirtazapine (MIR), pindolol (PIN), fluoxetine (FLX), risperidone (RIS), trazodone (TRZ), ziprasidone (ZPR), ondansetron (OND), yohimbine (YOH), or prazosin (PRZ), to reduce long-term cocaine-induced locomotor activity and the expression of cocaine-induced locomotor sensitization in rats.

Methods

- The study consists of four experiments, which were divided into four experimental phases. Induction (10 days), cocaine withdrawal (30 days), expression (10 days), and post-expression phase (10 days). Male Wistar rats were daily dosed with cocaine (10 mg/kg; i.p.) during the induction and post-expression phases. During drug withdrawal, the MIR, PIN, FLX, RIS, TRZ, ZPR, OND, YOH, or PRZ were administered 30 min before saline. In the expression, the multitarget drugs were administered 30 min before cocaine. After each administration, locomotor activity for each animal was recorded for 30 min.During the agonism phase, in experiment four, 8-OH-DPAT, DOI, CP-809-101, SR-57227A, or clonidine (CLO) was administered 30 min before MIR and 60 min before cocaine. After each administration, locomotor activity for each animal was recorded for 30 min.

Results

-MIR, FLX, RIS, ZPR, OND, or PRZ attenuated the cocaine-induced locomotor activity and cocaine locomotor sensitization. PIN, TRZ, and YOH failed to decrease cocaine locomotor sensitization. At the optimal doses used, PIN, FLX, RIS, TRZ, ZPR, OND, YOH, or PRZ failed to attenuate long-term cocaine locomotor activation. MIR generated a decrease in cocaine-induced locomotor activity of greater magnitude and duration than the other multitarget drugs evaluated.

Conclusion

- At the optimal doses of multitarget drugs evaluated, MIR was the multitarget drug that showed the greatest long-term cocaine-induced behavior effects compared to other multitarget drugs.

Assessing attention and impulsivity in the variable stimulus duration and variable intertrial interval rodent continuous performance test schedules using noradrenaline receptor antagonists in female C57BL/6JRj mice

RATIONALE

Noradrenergic dysfunction is associated with disorders of impulsivity and inattention. The rodent continuous performance test (rCPT) quantifies changes in attention and impulsivity.

OBJECTIVE

To use NA receptor antagonists to examine the roles of NA on attention and impulsivity behaviours measured in the rCPT variable stimulus duration (vSD) and the variable intertrial interval (vITI) schedules.

METHODS

Two cohorts of 36 female C57BL/6JRj mice were examined separately in the rCPT vSD and vITI schedules. Both cohorts received antagonists of the following adrenoceptors: α1 (doxazosin, DOX: 1.0, 3.0, 10.0 mg/kg), α2 (yohimbine, YOH: 0.1, 0.3, 1.0 mg/kg), and β1/2 (propranolol, PRO: 1.0, 3.0, 10.0 mg/kg) in consecutive balanced Latin square designs with flanking reference measurements. The antagonists were subsequently examined for effects on locomotor activity.

RESULTS

DOX showed similar effects in both schedules, improving discriminability and accuracy, and reducing responding and impulsivity, and DOX also reduced locomotor activity. YOH showed prominent effects in the vSD schedule to increase responding and impulsivity, while impairing discriminability and accuracy. YOH did not affect locomotor activity. PRO increased responding and impulsivity, decreased accuracy, but did not affect discriminability or locomotor activity.

CONCLUSION

Antagonism of α2 or β1/2 adrenoceptors caused similar increases in responding and impulsivity and worsened attentional performance, while α1 adrenoceptor antagonism showed the opposite effects. Our results suggest that endogenous NA exerts bidirectional control of most behaviours in the rCPT. The parallel vSD and vITI studies showed a substantial overlap in effects, but also some differences that indicate differing sensitivity towards noradrenergic manipulations.

Evaluation of the effect of doxasozin and zonisamide on voluntary ethanol intake in mice that experienced chronic intermittent ethanol exposure and stress

The comorbidity between alcohol use disorder and post-traumatic stress disorder represents a serious health care burden with few effective treatment options. The current study was designed to evaluate the effect of an alpha 1 receptor antagonist (doxazosin) and a novel anticonvulsant (zonisamide) in a model of alcohol (ethanol) dependence and stress exposure. The main dependent variable was voluntary ethanol intake in mice that experienced chronic intermittent ethanol (CIE) exposure and forced swim stress (FSS) alone, and in combination. Adult male and female C57BL/6J mice had access to a single bottle of 15% (v/v) ethanol for 1-hr in the home cage, 3-hr into the dark phase of the light/dark cycle. Once stable ethanol intake was established (~4 weeks), mice were separated into four groups (CTL, CIE, FSS, CIE + FSS). Mice in the FSS condition received 10-min FSS exposure 4-hr prior to drinking sessions (remaining mice were not disturbed). During baseline and the first two test cycles, all mice received vehicle (saline) injections (IP) 30-min before ethanol access. As previously observed, FSS increased ethanol drinking in dependent (CIE-exposed) mice but not in nondependent control (CTL) mice. In the following test cycles mice were evaluated for ethanol intake after administration of doxazosin, zonisamide or their combination. Results indicated that the three doses of doxazosin evaluated significantly reduced voluntary ethanol intake in all mice. Zonisamide had a more modest effect and may require a more prolonged treatment regime. The combined administration of both compounds was not more effective than each drug alone. This study suggests that doxazosin is reliable at reducing voluntary ethanol intake in mice independently of their history of ethanol dependence and stress exposure.

Pharmacogenetics of Dopamine β-Hydroxylase in cocaine dependence therapy with doxazosin

The α₁ -adrenergic antagonist, doxazosin, has improved cocaine use disorder (CUD) presumably by blocking norepinephrine (NE) stimulation and reward from cocaine-induced NE increases. If the NE levels for release were lower, then doxazosin might more readily block this NE stimulation and be more effective. The NE available for release can be lower through a genetic polymorphism in dopamine β-hydroxylase (DBH) (C-1021T, rs1611115), which reduces DβH's conversion of dopamine to NE. We hypothesize that doxazosin would be more effective in CUD patients who have these genetically lower DβH levels. This 12-week, double-blind, randomized, placebo-controlled trial included 76 CUD patients: 49 with higher DβH levels from the DBH CC genotype and 27 with lower DβH levels from T-allele carriers (CT or TT). Patients were randomized to doxazosin (8 mg/day, N = 47) or placebo (N = 29) and followed with thrice weekly urine toxicology and once weekly cognitive behavioral psychotherapy. Cocaine use was reduced at a higher rate among patients in the doxazosin than in the placebo arm. We found significantly lower cocaine use rates among patients carrying the T-allele (CT/TT) than the CC genotype. The percentage of cocaine positive urines was reduced by 41 percent from baseline in the CT/TT group with low DβH and NE levels, as compared with no net reduction in the CC genotype group with normal DβH and NE levels. The DBH polymorphism appears play an important role in CUD patients' response to doxazosin treatment, supporting a pharmacogenetic association and potential application for personalized medicine.

Monoaminergic Involvement in Decreased Locomotor Activity of Mice Treated with α and β-amyrin from Protium heptaphyllum

A triterpenic mixture of α and β-amyrin (AMY) extracted from Protium heptaphyllum has demonstrated several pharmacological effects, including activity in the central nervous system. The aim of this study was to evaluate the effect of AMY administration on locomotor activity of mice by the open field test using some monoaminergic agonists and antagonists and the cerebral cortex levels of monoamines and their major metabolites by high-performance liquid chromatography. Mice were treated acutely with AMY at doses of 1, 2.5 and 5 mg/kg given intraperitoneally and with the pharmacological agents and placed in open field test, then the animals were sacrificed and the cerebral cortex extracted, and monoamines were assayed in tissue homogenates. AMY at 1, 2.5 and 5 mg/kg decreased locomotor activity of animals by 25, 31 and 39%, respectively in the open field test. Ondasentron, doxazosin, oxymetazoline and clonidine did not reverse the inhibitory effect of 5 mg/kg AMY. Venlafaxine and yohimbine reversed the inhibitory effect of 5 mg AMY. In the cortex, the 5-HT and 5-HIAA were significantly reduced by the administration of AMY. NE and HVA were also reduced with 2.5 and 5 mg/kg AMY, while Dopamine and DOPAC were not increased with AMY. In conclusion, AMY decreased locomotor activity of animals accompanied by a decrease in 5-HT and NE levels in the cerebral cortex, this locomotor effect is reversed by drug that blocker the α-2-adrenoreceptor.

The α-1 adrenoceptor (ADRA1A) genotype moderates the magnitude of acute cocaine-induced subjective effects in cocaine-dependent individuals

OBJECTIVES

We examined whether a functional variant of the ADRA1A gene moderated cocaine-induced subjective effects in a group of cocaine-dependent individuals.

METHODS

This study was a within-participant, double-blind, placebo-controlled inpatient human laboratory evaluation of 65 nontreatment-seeking, cocaine-dependent [Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV)] individuals aged 18-55 years. Participants received both placebo (saline, IV) and cocaine (40 mg, IV), and subjective responses were assessed 15 min before receiving an infusion and at 5 min intervals for the subsequent 20 min. The rs1048101 variant of the α1A-adrenoceptor (ADRA1A) gene was genotyped and it was evaluated whether the Cys to Arg substitution at codon 347 in exon 2 (Cys347Arg) moderated the magnitude of the subjective effects produced by cocaine.

RESULTS

Thirty (46%) participants were found to have the major allele CC genotype and 35 (44%) carried at least one minor T-allele of rs1048101 (TT or TC genotype). Individuals with the CC genotype showed greater responses for 'desire' (P<0.0001), 'high' (P<0.0001), 'any drug effect' (P<0.0001), 'like cocaine' (P<0.0001), and 'likely to use cocaine if given access' (P<0.05) with experiment-wise significance.

CONCLUSION

This study indicates that the ADRA1A genotype could be used to identify individuals for whom acute cocaine exposure may be more rewarding and by inference may result in greater difficulty in establishing and/or maintaining abstinence from cocaine.

Subjective and Cardiovascular Effects of Intravenous Methamphetamine during Perindopril Maintenance: A Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study

BACKGROUND

Our pilot study suggested that the angiotensin-converting enzyme inhibitor perindopril might reduce some subjective effects produced by i.v. methamphetamine. We characterized the impact of a wider range of perindopril doses on methamphetamine-induced effects in a larger group of non-treatment-seeking, methamphetamine-using volunteers.

METHODS

Before treatment, participants received 30mg methamphetamine. After 5 to 7 days of perindopril treatment (0, 4, 8, or 16mg/d), participants received 15 and 30mg of methamphetamine on alternate days. Before and after treatment, participants rated subjective effects and cardiovascular measures were collected.

RESULTS

Prior to treatment with perindopril, there were no significant differences between treatment groups on maximum or peak subjective ratings or on peak cardiovascular effects. Following perindopril treatment, there were significant main effects of treatment on peak subjective ratings of "anxious" and "stimulated"; compared to placebo treatment, treatment with 8mg perindopril significantly reduced peak ratings of both anxious (P=.0009) and stimulated (P=.0070). There were no significant posttreatment differences between groups on peak cardiovascular effects.

CONCLUSIONS

Moderate doses of perindopril (8mg) significantly reduced peak subjective ratings of anxious and stimulated as well as attenuated many other subjective effects produced by methamphetamine, likely by inhibiting angiotensin II synthesis. Angiotensin II is known to facilitate the effects of norepinephrine, which contributes to methamphetamine's subjective effects. The lack of a classic dose-response function likely results from either nonspecific effects of perindopril or from between-group differences that were not accounted for in the current study (i.e., genetic variations and/or caffeine use). The current findings suggest that while angiotensin-converting enzyme inhibitors can reduce some effects produced by methamphetamine, more consistent treatment effects might be achieved by targeting components of the renin-angiotensin system that are downstream of angiotensin-converting enzyme.

Psychostimulants affect dopamine transmission through both dopamine transporter-dependent and independent mechanisms

The precise mechanisms by which cocaine and amphetamine-like psychostimulants exert their reinforcing effects are not yet fully defined. It is widely believed, however, that these drugs produce their effects by enhancing dopamine neurotransmission in the brain, especially in limbic areas such as the nucleus accumbens, by inducing dopamine transporter-mediated reverse transport and/or blocking dopamine reuptake though the dopamine transporter. Here, we present the evidence that aside from dopamine transporter, non-dopamine transporter-mediated mechanisms also participate in psychostimulant-induced dopamine release and contribute to the behavioral effects of these drugs, such as locomotor activation and reward. Accordingly, psychostimulants could increase norepinephrine release in the prefrontal cortex, the latter then alters the firing pattern of dopamine neurons resulting in changes in action potential-dependent dopamine release. These alterations would further affect the temporal pattern of dopamine release in the nucleus accumbens, thereby modifying information processing in that area. Hence, a synaptic input to a nucleus accumbens neuron may be enhanced or inhibited by dopamine depending on its temporal relationship to dopamine release. Specific temporal patterns of dopamine release may also be required for certain forms of synaptic plasticity in the nucleus accumbens. Together, these effects induced by psychostimulants, mediated through a non-dopamine transporter-mediated mechanism involving norepinephrine and the prefrontal cortex, may also contribute importantly to the reinforcing properties of these drugs.

Accumbal α-adrenoceptors, but not β-adrenoceptors, regulate behaviour that is mediated by reserpine-sensitive storage vesicles

It has previously been demonstrated that mesolimbic α-adrenoceptors, but not β-adrenoceptors, control the release of dopamine that is derived from reserpine-sensitive storage vesicles. The aim of the present study was to investigate whether these storage vesicles also regulate α-adrenoceptor-mediated or β-adrenoceptor-mediated changes in behaviour. Accordingly, rats were pretreated with reserpine before the α-adrenoceptor antagonist phentolamine or the β-adrenoceptor agonist isoproterenol was locally applied to the nucleus accumbens. Both phentolamine and isoproterenol increased the duration of walking, rearing and grooming and decreased the duration of sitting. Reserpine counteracted the behavioural response elicited by phentolamine but not by isoproterenol. The results of the present study demonstrate that mesolimbic α-adrenoceptors, but not β-adrenoceptors, regulate behaviour that is mediated by reserpine-sensitive storage pools. It is hypothesized that the observed α-adrenoceptor-mediated increase in locomotor activity is due to the α-adrenoceptor-mediated increase in the release of accumbal intravesicular dopamine. Our finding that α-adrenoceptors inhibit, whereas β-adrenoceptors stimulate, locomotor activity may help explain why noradrenaline or environmental stressors have previously been found to have opposing effects on the regulation of behaviour.

Pharmacotherapy for stimulant-related disorders

Stimulant-related disorders (SRD) continue to be an important public health problem for which there are presently no approved pharmacotherapies. Although behavioral interventions provide some benefit response varies. The development of novel and effective pharmacotherapies continues to be a research priority. Understanding neural mechanisms critical to the action of stimulants has helped reveal several potential pharmacotherapies that have already shown promise in controlled clinical trials. Common to some of these medications is the ability to reverse neural deficits in individuals with SRD. Results from thoroughly conducted clinical trials continue to broaden our knowledge increasing the possibility of soon developing effective pharmacotherapies for SRD.

Pharmacotherapeutics for substance-use disorders: a focus on dopaminergic medications

INTRODUCTION

Illicit substance-use is a substantial public health concern, contributing over $150 billion in costs annually to Americans. A complex disease, a substance-use disorder affects neural circuits involved in reinforcement, motivation, learning and memory, and inhibitory control.

AREAS COVERED

The modulatory influence of dopamine in mesocorticolimbic circuits contributes to encoding the primary reinforcing effects of substances and numerous studies suggest that aberrant signaling within these circuits contributes to the development of a substance-use disorder in some individuals. Decades of research focused on the clinical development of medications that directly target dopamine receptors has led to recent studies of agonist-like dopaminergic treatments for stimulant-use disorders and, more recently, cannabis-use disorder. Human studies evaluating the efficacy of dopaminergic agonist-like medications to reduce reinforcing effects and substance-use provide some insight into the design of future pharmacotherapy trials. A search of PubMed using specific brain regions, medications, and/or the terms 'dopamine', 'cognition', 'reinforcement', 'cocaine', 'methamphetamine', 'amphetamine', 'cannabis', 'treatment/pharmacotherapy', 'addiction/abuse/dependence' identified articles relevant to this review.

EXPERT OPINION

Conceptualization of substance-use disorders and their treatment continues to evolve. Current efforts increasingly focus on a strategy fostering combination pharmacotherapies that target multiple neurotransmitter systems.