Comparison of the behavioral effects of bretazenil and flumazenil in triazolam-dependent and non-dependent baboons

Tolerance and dependence following chronic alprazolam treatment in rhesus monkeys: Role of GABAA receptor subtypes

BACKGROUND

To assess GABA_A receptor subtypes involved in benzodiazepine tolerance and dependence, we evaluated the ability of subtype-selective and non-selective ligands to substitute for (i.e., produce "cross-tolerance") or precipitate withdrawal during chronic alprazolam treatment.

METHODS

Four female rhesus monkeys (Macaca mulatta) were implanted with chronic intravenous catheters and administered alprazolam (1.0 mg/kg every 4 h). Following 14+ days of chronic alprazolam, acute administration of selected doses of non-selective and subtype-selective ligands were substituted for, or administered with, alprazolam, followed by quantitative behavioral observations. The ligands included alprazolam and midazolam (positive modulators, non-selective), zolpidem (positive modulator, preferential affinity for α1-containing GABA_A receptors), HZ-166 (positive modulator, preferential efficacy at α2- and α3-containing GABA_A receptors), and βCCT (antagonist, preferential affinity for α1-containing GABA_A receptors).

RESULTS

Acutely, alprazolam and midazolam both induced observable ataxia along with a mild form of sedation referred to as "rest/sleep posture" at a lower dose (0.1 mg/kg, i.v.), whereas at a higher dose (1.0 mg/kg, i.v.), induced deep sedation and observable ataxia. With chronic alprazolam treatment, observable ataxia and deep sedation were reduced significantly, whereas rest/sleep posture was unchanged or emerged. Zolpidem showed a similar pattern of effects, whereas no behaviors engendered by HZ-166 were changed by chronic alprazolam. Administration of βCCT, but not HZ-166, resulted in significant withdrawal signs.

CONCLUSIONS

These results are consistent with a role for α1-containing GABA_A receptor subtypes in tolerance and dependence observed with chronic alprazolam, although other receptors may be involved in the withdrawal syndrome.

Tolerance and dependence following chronic alprazolam treatment: quantitative observation studies in female rhesus monkeys

RATIONALE

In order to understand mechanisms underlying tolerance and dependence following chronic benzodiazepine treatments, quantitative and reproducible behavioral models of these phenomena are required.

OBJECTIVES

This research evaluated the ability of chronic treatment with a commonly prescribed benzodiazepine, alprazolam, to induce tolerance to sedative effects and physical dependence using a novel set of behavioral measurements in rhesus monkeys.

METHODS

Four female rhesus monkeys (Macaca mulatta) were implanted with chronic intravenous catheters and administered i.v. alprazolam (1.0 mg/kg every 4 h, 38 days total). Quantitative observation measures were obtained during the 38 days of treatment. Acute administration of the benzodiazepine receptor antagonist flumazenil (0.1, 0.3 mg/kg, i.v.) was given to assess precipitated withdrawal. On day 39, saline was substituted for alprazolam and withdrawal signs were assessed for 7 days.

RESULTS

Maximal sedation ("deep sedation") was evident on day 1 but was not significantly different from baseline levels by day 4 and was absent for the remainder of the 38 days of treatment. A milder form of sedation, "rest/sleep posture," emerged by day 3 and did not decline over 38 days. Cessation of alprazolam treatment resulted in significant withdrawal signs (nose rub, vomit, procumbent posture, tremor/jerk, rigid posture) that dissipated by day 3. These signs also were observed with flumazenil (0.3 mg/kg).

CONCLUSIONS

Chronic alprazolam treatment resulted in rapid tolerance to some behaviors (e.g., deep sedation) but no tolerance to others (e.g., rest/sleep posture). Physical dependence was observed via both spontaneous and precipitated withdrawal. Based on previous research, these phenomena may reflect differential plasticity at GABA_A receptor subtypes.

Evaluation of mifepristone effects on alcohol-seeking and self-administration in baboons

Mifepristone, a type II glucocorticoid receptor antagonist, is under investigation as a potential pharmacotherapy for alcohol use disorder. This study examined effects of chronic administration of mifepristone on alcohol-seeking and self-administration in large nonhuman primates. Adult baboons (n = 5) self-administered alcohol 7 days/week under a chained schedule of reinforcement (CSR). The CSR comprised 3 components in which distinct cues were paired with different schedule requirements, with alcohol available for self-administration only in the final component, to model different phases of alcohol anticipation, seeking, and consumption. Under baseline conditions, baboons self-administered an average of 1g/kg/day of alcohol in the self-administration period. Mifepristone (10, 20, and 30 mg/kg) or vehicle was administered orally 30 min before each CSR session for 7 consecutive days. In a separate group of baboons (n = 5) acute doses of mifepristone (10, 20, and 30 mg/kg) were administered, and blood samples were collected over 72 hr to examine mifepristone pharmacokinetics. Some samples also were collected from the baboons that self-administered alcohol under the CSR after the chronic mifepristone condition. Mifepristone did not alter alcohol-seeking or self-administration under the CSR when compared with the vehicle condition. Mifepristone pharmacokinetics were nonlinear, and appear to be capacity limited. In sum, mifepristone did not reduce alcohol-maintained behaviors when administered to baboons drinking 1g/kg daily. (PsycINFO Database Record (c) 2019 APA, all rights reserved).