Self-administration of bretazenil under progressive-ratio schedules: behavioral economic analysis of the role intrinsic efficacy plays in the reinforcing effects of benzodiazepines

Anhedonia modulates benzodiazepine and opioid demand among persons in treatment for opioid use disorder

Background

Benzodiazepine (BZD) misuse is a significant public health problem, particularly in conjunction with opioid use, due to increased risks of overdose and death. One putative mechanism underlying BZD misuse is affective dysregulation, via exaggerated negative affect (e.g., anxiety, depression, stress-reactivity) and/or impaired positive affect (anhedonia). Similar to other misused substances, BZD consumption is sensitive to price and individual differences. Although purchase tasks and demand curve analysis can shed light on determinants of substance use, few studies have examined BZD demand, nor factors related to demand.

Methods

This ongoing study is examining simulated economic demand for alprazolam (among BZD lifetime misusers based on self-report and DSM-5 diagnosis; n = 23 total; 14 male, 9 female) and each participant's preferred-opioid/route using hypothetical purchase tasks among patients with opioid use disorder (n = 59 total; 38 male, 21 female) who are not clinically stable, i.e., defined as being early in treatment or in treatment longer but with recent substance use. Aims are to determine whether: (1) BZD misusers differ from never-misusers on preferred-opioid economic demand, affective dysregulation (using questionnaire and performance measures), insomnia/behavioral alertness, psychiatric diagnoses or medications, or urinalysis results; and (2) alprazolam demand among BZD misusers is related to affective dysregulation or other measures.

Results

Lifetime BZD misuse is significantly (p < 0.05) related to current major depressive disorder diagnosis, opioid-negative and methadone-negative urinalysis, higher trait anxiety, greater self-reported affective dysregulation, and younger age, but not preferred-opioid demand or insomnia/behavioral alertness. Alprazolam and opioid demand are each significantly positively related to higher anhedonia and, to a lesser extent, depression symptoms but no other measures of negative-affective dysregulation, psychiatric conditions or medications (including opioid agonist therapy or inpatient/outpatient treatment modality), or sleep-related problems.

Conclusion

Anhedonia (positive-affective deficit) robustly predicted increased BZD and opioid demand; these factors could modulate treatment response. Routine assessment and effective treatment of anhedonia in populations with concurrent opioid and sedative use disorder may improve treatment outcomes.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT03696017, identifier NCT03696017.

Abuse-related effects of subtype-selective GABAA receptor positive allosteric modulators in an assay of intracranial self-stimulation in rats

RATIONALE

GABA_A positive allosteric modulators (GABA_A PAMs), such as diazepam and zolpidem, are used clinically for anxiety and insomnia, but abuse liability is a concern. Novel GABA_A PAMS may have lower abuse liability while retaining clinical utility.

OBJECTIVE

The present study compared abuse-related effects of the non-selective GABA_A PAM diazepam, the α1-selective GABA_A PAM zolpidem, and three novel GABA_A PAMs (JY-XHe-053, XHe-II-053, and HZ-166) using intracranial self-stimulation (ICSS) in rats. These novel compounds have relatively low efficacy at α1-, α2-, and α3-containing GABA_A receptors, putative in vivo selectivity at α2/α3-containing GABA_A receptors, and produce anxiolytic-like effects with limited sedation in non-human primates.

METHODS

Adult, male Sprague-Dawley rats (n = 17) were each implanted with a bipolar electrode in the medial forebrain bundle and trained to respond under a fixed-ratio 1 schedule of reinforcement for electrical brain stimulation. The potency and time course of effects were compared for diazepam (0.1-10 mg/kg), zolpidem (0.032-3.2 mg/kg), and the three novel compounds (JY-XHe-053, XHe-II-053, and HZ-166; all 3.2-32 mg/kg).

RESULTS

Zolpidem and diazepam produced transient facilitation of ICSS at small doses and more sustained rate-decreasing effects at larger doses. JY-XHe-053 and HZ-166 produced weak and inconsistent ICSS facilitation, whereas XHe-II-053 had no effect on ICSS.

CONCLUSIONS

These results support a key role for α1-containing GABA_A receptors in mediating GABA_A PAM-induced ICSS facilitation. These results are concordant with drug self-administration studies in monkeys in suggesting that GABA_A PAMs with low α1 efficacy and putative α2/α3 selectivity have lower abuse liability than high-efficacy non-selective or α1-selective GABA_A PAMs.

Intracranial self-stimulation to evaluate abuse potential of drugs

Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.

The behavioral pharmacology of zolpidem: evidence for the functional significance of α1-containing GABA(A) receptors

RATIONALE

Zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) with preferential binding affinity and efficacy for α1-subunit containing GABA(A) receptors (α1-GABA(A)Rs). Over the last three decades, a variety of animal models and experimental procedures have been used in an attempt to relate the behavioral profile of zolpidem and classic benzodiazepines (BZs) to their interaction with α1-GABA(A)Rs.

OBJECTIVES

This paper reviews the results of rodent and non-human primate studies that have evaluated the effects of zolpidem on motor behaviors, anxiety, memory, food and fluid intake, and electroencephalogram (EEG) sleep patterns. Also included are studies that examined zolpidem's discriminative, reinforcing, and anticonvulsant effects as well as behavioral signs of tolerance and withdrawal.

RESULTS

The literature reviewed indicates that α1-GABA(A)Rs play a principle role in mediating the hypothermic, ataxic-like, locomotor- and memory-impairing effects of zolpidem and BZs. Evidence also suggests that α1-GABA(A)Rs play partial roles in the hypnotic, EEG sleep, anticonvulsant effects, and anxiolytic-like of zolpidem and diazepam. These studies also indicate that α1-GABA(A)Rs play a more prominent role in mediating the discriminative stimulus, reinforcing, hyperphagic, and withdrawal effects of zolpidem and BZs in primates than in rodents.

CONCLUSIONS

The psychopharmacological data from both rodents and non-human primates suggest that zolpidem has a unique pharmacological profile when compared with classic BZs. The literature reviewed here provides an important framework for studying the role of different GABA(A)R subtypes in the behavioral effects of BZ-type drugs and helps guide the development of new pharmaceutical agents for disorders currently treated with BZ-type drugs.

Reinforcing effects of compounds lacking intrinsic efficacy at α1 subunit-containing GABAA receptor subtypes in midazolam- but not cocaine-experienced rhesus monkeys

Benzodiazepines are prescribed widely but their utility is limited by unwanted side effects, including abuse potential. The mechanisms underlying the abuse-related effects of benzodiazepines are not well understood, although α1 subunit-containing GABAA receptors have been proposed to have a critical role. Here, we examine the reinforcing effects of several compounds that vary with respect to intrinsic efficacy at α2, α3, and α5 subunit-containing GABAA receptors but lack efficacy at α1 subunit-containing GABAA receptors ('α1-sparing compounds'): MRK-623 (functional selectivity for α2/α3 subunit-containing receptors), TPA023B (functional selectivity for α2/α3/α5 subunit-containing receptors), and TP003 (functional selectivity for α3 subunit-containing receptors). The reinforcing effects of the α1-sparing compounds were compared with those of the non-selective benzodiazepine receptor partial agonist MRK-696, and non-selective benzodiazepine receptor full agonists, midazolam and lorazepam, in rhesus monkeys trained to self-administer midazolam or cocaine, under a progressive-ratio schedule of intravenous (i.v.) drug injection. The α1-sparing compounds were self-administered significantly above vehicle levels in monkeys maintained under a midazolam baseline, but not under a cocaine baseline over the dose ranges tested. Importantly, TP003 had significant reinforcing effects, albeit at lower levels of self-administration than non-selective benzodiazepine receptor agonists. Together, these results suggest that α1 subunit-containing GABAA receptors may have a role in the reinforcing effects of benzodiazepine-type compounds in monkeys with a history of stimulant self-administration, whereas α3 subunit-containing GABAA receptors may be important mediators of the reinforcing effects of benzodiazepine-type compounds in animals with a history of sedative-anxiolytic/benzodiazepine self-administration.

Anticonflict and reinforcing effects of triazolam + pregnanolone combinations in rhesus monkeys

Combinations of positive modulators of benzodiazepine and neuroactive steroid sites on GABA(A) receptors have been shown to act in an additive or supra-additive manner depending on the endpoint under study, but they have not been assessed on experimentally induced conflict or drug self-administration. The present study examined the interactive effects of the benzodiazepine triazolam and the neuroactive steroid pregnanolone in a rhesus monkey conflict procedure (a model of anxiolysis) and on a progressive-ratio schedule of drug self-administration (a model of abuse potential). Both triazolam and pregnanolone decreased rates of nonsuppressed responding, whereas only triazolam consistently increased rates of suppressed responding (i.e., had an anticonflict effect). Fixed-ratio mixtures of triazolam and pregnanolone also decreased rates of nonsuppressed responding and did so in an additive manner. In contrast, mixtures of triazolam and pregnanolone produced either additive or supra-additive rate-increasing effects on suppressed responding, depending on the proportion of drugs in the mixture. Both triazolam and pregnanolone were self-administered significantly, and triazolam and pregnanolone mixtures had either proportion-dependent additive or infra-additive reinforcing effects. These results suggest that combinations of triazolam and pregnanolone may have enhanced anxiolytic effects with reduced behavioral disruption and abuse potential compared with either drug alone.