Andrew C. Meyer

Concurrent choice for social interaction and amphetamine using conditioned place preference in rats: Effects of age and housing condition

BACKGROUND Social interaction can serve as a natural reward that attenuates drug reward in rats; however, it is unknown if age or housing conditions alter the choice between social interaction and drug. METHODS Individually- and pair-housed adolescent and adult male rats were tested using conditioned place preference (CPP) in separate experiments in which: (1) social interaction was conditioned against no social interaction; (2) amphetamine (AMPH; 1mg/kg, s.c.) was conditioned against saline; or (3) social interaction was conditioned against AMPH. RESULTS Social interaction CPP was obtained only in individually-housed adolescents, whereas AMPH CPP was obtained in both individually-housed adolescents and adults; however, the effect of AMPH was not statistically significant in pair-housed adults. When allowed to choose concurrently between compartments paired with either social interaction or AMPH, individually-housed adolescents preferred the compartment paired with social interaction, whereas pair-housed adolescents preferred the compartment paired with AMPH. Regardless of housing condition, adults showed a similar preference for the compartments paired with either social interaction or AMPH. CONCLUSIONS Although some caution is needed in interpreting cross-experiment comparisons, the overall results suggest that individually-housed adolescents were most sensitive to the rewarding effect of social interaction, and this hypersensitivity to social reward effectively competed with AMPH reward.

GENETICS OF NOVELTY SEEKING, AMPHETAMINE SELF-ADMINISTRATION AND REINSTATEMENT USING INBRED RATS

Previous research using outbred rats indicates that individual differences in activity in a novel environment predict sensitivity to the reinforcing effect of psychostimulant drugs. The current study examined if the link between responses related to novelty and amphetamine self‐administration is heritable. Twelve inbred rat strains were assessed for locomotor activity in a novel environment, preference for a novel environment, and intravenous amphetamine self‐administration (acquisition, extinction and amphetamine‐induced reinstatement). Strain differences were observed in activity in a novel environment, novelty preference and amphetamine self‐administration, indicating a genetic influence for each of these behaviors. While there was no relation between activity in an inescapable novel environment and amphetamine self‐administration, strain‐dependent differences in novelty preference were positively correlated with the amount of amphetamine self‐administered. There was also a positive correlation between the dose‐dependent rate of amphetamine self‐administration and magnitude of reinstatement. These results show that the activity in an inescapable novel environment and the preference for a novel environment are different genetically, and thus likely to reflect different behavioral constructs. Moreover, these results implicate a genetic influence on the relation between novelty seeking and stimulant self‐administration, as well as on the relation between stimulant reward and reinstatement.

Tetrabenazine inhibition of monoamine uptake and methamphetamine behavioral effects: locomotor activity, drug discrimination and self-administration.

Tetrabenazine (TBZ), a benzoquinolizine derivative, binds with high affinity to the vesicular monoamine transporter-2 (VMAT2), inhibiting uptake of cytosolic monoamines. The current study aimed to provide preclinical evidence supporting the potential use of TBZ as a treatment for methamphetamine abuse. Effects of TBZ on function of the dopamine transporter (DAT) and serotonin transporter (SERT) in striatal and hippocampal synaptosomes, respectively, and on VMAT2 function in isolated striatal synaptic vesicles were determined. Effect of TBZ (acute, 0.1-3.0 mg/kg, s.c.; repeated, 1.0 mg/kg for 7 days) on locomotor activity in methamphetamine-sensitized rats was assessed. Ability of TBZ (0.1-3.0 mg/kg; s.c.) or vehicle to decrease the discriminative effect of methamphetamine also was determined. Ability of TBZ (acute, 0.1-1.0 mg/kg, s.c.; repeated, 0.1 or 1.0 mg/kg for 7 days) to specifically decrease methamphetamine self-administration was determined; for comparison, a separate group of rats was assessed for effects of TBZ on food-maintained responding. Results show that TBZ was 11-fold more potent inhibiting DAT than SERT, and 2.5-fold more potent inhibiting VMAT2 than DAT. Results from behavioral studies showed that the lowest dose of TBZ transiently increased methamphetamine self-administration, whereas higher TBZ doses decreased methamphetamine self-administration. Also, TBZ at high doses decreased methamphetamine locomotor sensitization and discriminative stimulus effects, as well as food-maintained responding. Thus, despite acting as a potent VMAT2 inhibitor, these preclinical results indicate that TBZ lacks behavioral specificity as an inhibitor of methamphetamine-induced reinforcement, diminishing its viability as a suitable treatment for methamphetamine abuse.

Effects of VMAT2 inhibitors lobeline and GZ‐793A on methamphetamine‐induced changes in dopamine release, metabolism and synthesis in vivo

Vesicular monoamine transporter‐2 (VMAT2) inhibitors reduce methamphetamine (METH) reward in rats. The current study determined the effects of VMAT2 inhibitors lobeline (LOB; 1 or 3 mg/kg) and N‐(1,2R‐dihydroxylpropyl)‐2,6‐cis‐di(4‐methoxyphenethyl)piperidine hydrochloride (GZ‐793A; 15 or 30 mg/kg) on METH‐induced (0.5 mg/kg, SC) changes in extracellular dopamine (DA) and its metabolite dihydroxyphenylacetic acid (DOPAC) in the reward‐relevant nucleus accumbens (NAc) shell using in vivo microdialysis. The effect of GZ‐793A (15 mg/kg) on DA synthesis in tissue also was investigated in NAc, striatum, medial prefrontal cortex and orbitofrontal cortex. In NAc shell, METH produced a time‐dependent increase in extracellular DA and decrease in DOPAC. Neither LOB nor GZ‐793A alone altered extracellular DA; however, both drugs increased extracellular DOPAC. In combination with METH, LOB did not alter the effects of METH on DA; however, GZ‐793A, which has greater selectivity than LOB for inhibiting VMAT2, reduced the duration of the METH‐induced increase in extracellular DA. Both LOB and GZ‐793A enhanced the duration of the METH‐induced decrease in extracellular DOPAC. METH also increased tissue DA synthesis in NAc and striatum, whereas GZ‐793A decreased synthesis; no effect of METH or GZ‐793A on DA synthesis was found in medial prefrontal cortex or orbitofrontal cortex. These results suggest that selective inhibition of VMAT2 produces a time‐dependent decrease in DA release in NAc shell as a result of alterations in tyrosine hydroxylase activity, which may play a role in the ability of GZ‐793A to decrease METH reward.

Interim Buprenorphine vs. Waiting List for Opioid Dependence

In 50 opioid users on a waiting list for maintenance treatment, those assigned to interim treatment with buprenorphine submitted a higher percentage of urine specimens that were negative for illicit opioids than those in the control group at 4 weeks (88% vs. 0%), 8 weeks (84% vs. 0%), and 12 weeks (68% vs. 0%).

Role of Medial Prefrontal and Orbitofrontal Monoamine Transporters and Receptors in Performance in an Adjusting Delay Discounting Procedure

Performance in an adjusting delay discounting procedure is predictive of drug abuse vulnerability; however, the shared underlying specific prefrontal neural systems linking delay discounting and increased addiction-like behaviors are unclear. Rats received direct infusions of methylphenidate (MPH; 6.25, 25.0, or 100μg), amphetamine (AMPH; 0.25, 1.0, or 4.0μg), or atomoxetine (ATO; 1.0, 4.0, or 16.0μg) into either medial prefrontal cortex (mPFC) or orbitofrontal cortex (OFC) immediately prior to performance in an adjusting delay task. These drugs were examined because they are efficacious in treating impulse control disorders. Because dopamine (DA) and serotonin (5-HT) receptors are implicated in impulsive behavior, separate groups of rats received microinfusions of the DA receptor-selective drugs SKF 81297 (0.1 or 0.4µg), SCH 23390 (0.25 or 1.0µg), quinpirole (1.25 or 5.0µg), and eticlopride (0.25 or 1.0µg), or received microinfusions of the 5-HT receptor-selective drugs 8-OH-DPAT (0.025 or 0.1μg), WAY 100635 (0.01 or 0.04μg), DOI (2.5 or 10.0μg), and ketanserin (0.1 or 0.4μg). Impulsive choice was not altered significantly by MPH, AMPH, or ATO into either mPFC or OFC, indicating that neither of these prefrontal regions alone may mediate the systemic effect of ADHD medications on impulsive choice. However, quinpriole (1.25μg) and eticlopride infused into mPFC increased impulsive choice, whereas 8-OH-DPAT infused into OFC decreased impulsive choice. These latter results demonstrate that blockade of DA D2 receptors in mPFC or activation of 5-HT1A receptors in OFC increases impulsive choice in the adjusting delay procedure.

Bridging waitlist delays with interim buprenorphine treatment: Initial feasibility

Despite the effectiveness of agonist maintenance for opioid dependence, individuals can remain on waitlists for months, during which they are at significant risk for morbidity and mortality. Interim dosing, consisting of daily medication without counseling, can reduce these risks. In this pilot study, we examined the initial feasibility of a novel technology-assisted interim buprenorphine treatment for waitlisted opioid-dependent adults. Following buprenorphine induction during Week 1, participants (n=10) visited the clinic at Weeks 2, 4, 6, 8, 10 and 12 to ingest their medication under staff observation, provide a urine specimen and receive their remaining doses via a computerized Med-O-Wheel Secure device. They also received daily monitoring via an Interactive Voice Response (IVR) platform, as well as random call-backs for urinalysis and medication adherence checks. The primary outcome was percent of participants negative for illicit opioids at each 2-week visit, with secondary outcomes of past-month drug use, adherence and acceptability. Participants achieved high levels of illicit opioid abstinence, with 90% abstinent at the Week 2 and 4 visits and 60% at Week 12. Significant reductions were observed in self-reported past-month illicit opioid use (p<.001), opioid withdrawal (p<.001), opioid craving (p<.001) and ASI Drug composite score (p=.008). Finally, adherence with buprenorphine administration (99%), daily IVR calls (97%) and random call-backs (82%) was high. Interim buprenorphine treatment shows promise for reducing patient and societal risks during delays to conventional treatment. A larger-scale, randomized clinical trial is underway to more rigorously examine the efficacy of this treatment approach.

Lifetime history of heroin use is associated with greater drug severity among prescription opioid abusers

BACKGROUND While research suggests primary prescription opioid (PO) abusers may exhibit less severe demographic and drug use characteristics than primary heroin abusers, less is known about whether a lifetime history of heroin use confers greater severity among PO abusers. OBJECTIVE In this secondary analysis, we examined demographic and drug use characteristics as a function of lifetime heroin use among 89 PO-dependent adults screened for a trial evaluating the relative efficacy of buprenorphine taper durations. Exploratory analyses also examined contribution of lifetime heroin use to treatment response among a subset of participants who received a uniform set of study procedures. METHODS Baseline characteristics were compared between participants reporting lifetime heroin use ≥5 (H(+); n=41) vs. <5 (H(-); n=48) times. Treatment response (i.e., illicit opioid abstinence and treatment retention at end of study) was examined in the subset of H(+) and H(-) participants randomized to receive the 4-week taper condition (N=22). RESULTS H(+) participants were significantly older and more likely to be male. They reported longer durations of illicit opioid use, greater alcohol-related problems, more past-month cocaine use, greater lifetime IV drug use, and greater lifetime use of cigarettes, amphetamines and hallucinogens. H(+) participants also had lower scores on the Positive Symptom Distress and Depression subscales of the Brief Symptom Inventory. Finally, there was a trend toward poorer treatment outcomes among H(+) participants. CONCLUSION A lifetime history of heroin use may be associated with elevated drug severity and unique treatment needs among treatment-seeking PO abusers.

Brief Opioid Overdose Knowledge (BOOK): A Questionnaire to Assess Overdose Knowledge in Individuals Who Use Illicit or Prescribed Opioids.

Background:Opioid overdose is a public health crisis. This study describes efforts to develop and validate the Brief Opioid Overdose Knowledge (BOOK) questionnaire to assess patient knowledge gaps related to opioid overdose risks. Methods:Two samples of illicit opioid users and a third sample of patients receiving an opioid for the treatment of chronic pain (total N = 848) completed self-report items pertaining to opioid overdose risks. Results:A 3-factor scale was established, representing Opioid Knowledge (4 items), Opioid Overdose Knowledge (4 items), and Opioid Overdose Response Knowledge (4 items). The scale had strong internal and face validity. Patients with chronic pain performed worse than illicit drug users in almost all items assessed, highlighting the need to increase knowledge of opioid overdose risk to this population. Conclusions:This study sought to develop a brief, internally valid method for quickly assessing deficits in opioid overdose risk areas within users of illicit and prescribed opioids, to provide an efficient metric for assessing and comparing educational interventions, facilitate conversations between physicians and patients about overdose risks, and help formally identify knowledge deficits in other patient populations.

Promoting smoking abstinence among patients with chronic obstructive pulmonary disease: Initial feasibility

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death in the U.S., with the majority of COPD deaths attributable to cigarette smoking. Despite this, individuals with COPD have a higher prevalence of smoking, poorer quit rates, and higher relapse rates compared to smokers without a COPD diagnosis. We examined the feasibility of an incentives-based intervention for producing an initial period of biochemically-verified smoking abstinence among daily smokers with COPD. Participants were randomly assigned to a Contingent (n = 13) or Noncontingent (n = 16) incentives condition and visited the clinic for 14 consecutive days. Contingent participants earned vouchers with monetary value contingent on breath carbon monoxide (CO) levels during Study Days 1–5 and urinary cotinine during Days 6–14. Voucher earnings began at