Emergence of anti-conflict effects of zolpidem in rhesus monkeys following extended post-injection intervals.

RATIONALE: Zolpidem is a hypnotic drug that binds to γ-aminobutyric acid type A receptors but lacks consistently demonstrable anxiolytic efficacy. METHODS: Rhesus monkeys (N = 4) were trained under a multiple schedule in which food-maintained responding was programmed (18-response fixed ratio) for a 5-min period, followed by a 5-min period in which the food-maintained responding was suppressed by response-contingent electric shock (20-response fixed ratio). Doses of zolpidem (range = 0.03 to 1.0 mg/kg, i.v.) were administered 5 min before the session, and responding was re-assessed at three additional 20-min intervals. A similar experiment also was carried out with the non-selective benzodiazepine, triazolam, over a dose range of 0.001 to 0.1 mg/kg, i.v. RESULTS: Zolpidem did not engender a significant increase in average rates of suppressed responding at earlier time points; however, rates of non-suppressed responding were robustly decreased. At 45- and 65-min post-injection, zolpidem treatment resulted in a dose-dependent increase in rates of suppressed responding. In contrast, the non-selective benzodiazepine triazolam increased rates of suppressed responding in a dose-dependent manner at all four time points, although decreases in non-suppressed responding were less at the later time points. CONCLUSIONS: These findings suggest that zolpidem has anxiolytic-like effects, but only >25 min after i.v. injection in this rhesus monkey conflict model. It was hypothesized that time-dependent effects on the response rate-suppressing properties of zolpidem become tolerant (i.e., acute tolerance). Because anxiolytic-like effects remain stable throughout the session, the absence of rate-decreasing effects may "unmask" anti-conflict effects.

Retrograde effects of triazolam and zolpidem on sleep-dependent motor learning in humans.

Drugs that act as allosteric activators at the benzodiazepine site of the gamma-aminobutyric acid (GABA(A)) receptor complex are used commonly to treat insomnia but relatively little is known of how such use affects learning and memory. Although anterograde effects on memory acquisition have been shown, possible retrograde effects on consolidation are more relevant when such agents are administered at bedtime. We tested the effects of two GABA(A) allosteric activators on sleep-dependent motor skill memory consolidation in 12 healthy male subjects. Subjects slept in a sleep laboratory for four consecutive nights (one accommodation night followed by three experimental nights). Placebo, triazolam 0.375 mg, and zolpidem 10 mg were given to each subject in counterbalanced order on the experimental nights. Polysomnographic (PSG) sleep measurement and sleep-dependent motor learning were assessed at each condition. Triazolam was associated with longer total sleep time and increased Stage 2 sleep. Both zolpidem and triazolam were associated with increased latency to rapid eye movement (REM) sleep. Overnight motor learning correlated with total sleep time in the placebo condition but not in the triazolam or zolpidem conditions. A statistically significant impairment in motor performance occurred overnight in the triazolam condition only. Triazolam, given in sufficient doses to prolong sleep in healthy people, affected overnight motor learning adversely. Zolpidem, in a dose sufficient to prolong REM onset latency but without other effects on PSG-measured sleep, degraded the relationship between total sleep time and overnight motor learning. These data indicate that non-selective or alpha1-preferring benzodiazepine site allosteric activators can interfere with sleep-dependent memory consolidation.