Selective effects of zolpidem on human memory functions

Orexin 2 receptor antagonism sex-dependently improves sleep/wakefulness and cognitive performance in tau transgenic mice

BACKGROUND AND PURPOSE

Tau pathology contributes to a bidirectional relationship between sleep disruption and neurodegenerative disease. Tau transgenic rTg4510 mice model tauopathy symptoms, including sleep/wake disturbances, which manifest as marked hyperarousal. This phenotype can be prevented by early transgene suppression; however, whether hyperarousal can be rescued after onset is unknown.

EXPERIMENTAL APPROACH

Three 8-week experiments were conducted with wild-type and rTg4510 mice after age of onset of hyperarousal (4.5 months): (1) Tau transgene suppression with doxycycline (200 ppm); (2) inactive phase rapid eye movement (REM) sleep enhancement with the dual orexin receptor antagonist suvorexant (50 mg·kg-1 ·day-1 ); or (3) Active phase non-NREM (NREM) and REM sleep enhancement using the selective orexin 2 (OX2 ) receptor antagonist MK-1064 (40 mg·kg-1 ·day-1 ). Sleep was assessed using polysomnography, cognition using the Barnes maze, and tau pathology using immunoblotting and/or immunohistochemistry.

KEY RESULTS

Tau transgene suppression improved tauopathy and hippocampal-dependent spatial memory, but did not modify hyperarousal. Pharmacological rescue of REM sleep deficits did not improve spatial memory or tau pathology. In contrast, normalising hyperarousal by increasing both NREM and REM sleep via OX2 receptor antagonism restored spatial memory, independently of tauopathy, but only in male rTg4510 mice. OX2 receptor antagonism induced only short-lived hypnotic responses in female rTg4510 mice and did not improve spatial memory, indicating a tau- and sex-dependent disruption of OX2 receptor signalling.

CONCLUSIONS AND IMPLICATIONS

Pharmacologically reducing hyperarousal corrects tau-induced sleep/wake and cognitive deficits. Tauopathy causes sex-dependent disruptions of OX2 receptor signalling/function, which may have implications for choice of hypnotic therapeutics in tauopathies.

Optical probing of orexin/hypocretin receptor antagonists

Study Objectives

The present study investigated the function of Hypocretin (Hcrt or Orexin/OX) receptor antagonists in sleep modulation and memory function with optical methods in transgenic mice.

Methods

We used Hcrt-IRES-Cre knock-in mice and AAV vectors expressing channelrhodopsin-2 (ChR2) to render Hcrt neurons sensitive to blue light stimulation. We optogenetically stimulated Hcrt neurons and measured latencies to wakefulness in the presence or absence of OX1/2R antagonists and Zolpidem. We also examined endogenous Hcrt neuronal activity with fiber photometry. Changes in memory after optogenetic sleep disruption were evaluated by the novel object recognition test (NOR) and compared for groups treated with vehicle, OX1/2R antagonists, or Zolpidem. We also analyzed electroencephalogram (EEG) power spectra of wakefulness, rapid eye movement (REM) sleep, and non-REM (NREM) sleep following the injections of vehicle, OX1/2R antagonists, and Zolpidem in young adult mice.

Results

Acute optogenetic stimulation of Hcrt neurons at different frequencies resulted in wakefulness. Treatment with dual OX1/2R antagonists (DORAs) DORA12 and MK6096, as well as selective OX2R antagonist MK1064 and Zolpidem, but not selective OX1R antagonist 1SORA1, significantly reduced the bout length of optogenetic stimulation-evoked wakefulness episode. Fiber photometry recordings of GCaMP6f signals showed that Hcrt neurons are active during wakefulness, even in the presence of OXR antagonists. Treatment with dual OX1/2R antagonists improved memory function despite optogenetic sleep fragmentation caused impaired memory function in a NOR test.

Conclusions

Our results show DORAs and selective OX2R antagonists stabilize sleep and improve sleep-dependent cognitive processes even when challenged by optogenetic stimulation mimicking highly arousing stimuli.

The Dual Hypocretin Receptor Antagonist Almorexant is Permissive for Activation of Wake-Promoting Systems

The dual hypocretin receptor (HcrtR) antagonist almorexant (ALM) may promote sleep through selective disfacilitation of wake-promoting systems, whereas benzodiazepine receptor agonists (BzRAs) such as zolpidem (ZOL) induce sleep through general inhibition of neural activity. Previous studies have indicated that HcrtR antagonists cause less-functional impairment than BzRAs. To gain insight into the mechanisms underlying these differential profiles, we compared the effects of ALM and ZOL on functional activation of wake-promoting systems at doses equipotent for sleep induction. Sprague-Dawley rats, implanted for EEG/EMG recording, were orally administered vehicle (VEH), 100 mg/kg ALM, or 100 mg/kg ZOL during their active phase and either left undisturbed or kept awake for 90 min after which their brains were collected. ZOL-treated rats required more stimulation to maintain wakefulness than VEH- or ALM-treated rats. We measured Fos co-expression with markers for wake-promoting cell groups in the lateral hypothalamus (Hcrt), tuberomammillary nuclei (histamine; HA), basal forebrain (acetylcholine; ACh), dorsal raphe (serotonin; 5HT), and singly labeled Fos(+) cells in the locus coeruleus (LC). Following SD, Fos co-expression in Hcrt, HA, and ACh neurons (but not in 5HT neurons) was consistently elevated in VEH- and ALM-treated rats, whereas Fos expression in these neuronal groups was unaffected by SD in ZOL-treated rats. Surprisingly, Fos expression in the LC was elevated in ZOL- but not in VEH- or ALM-treated SD animals. These results indicate that Hcrt signaling is unnecessary for the activation of Hcrt, HA, or ACh wake-active neurons, which may underlie the milder cognitive impairment produced by HcrtR antagonists compared to ZOL.

The hypocretin/orexin antagonist almorexant promotes sleep without impairment of performance in rats

The hypocretin receptor (HcrtR) antagonist almorexant (ALM) has potent hypnotic actions but little is known about neurocognitive performance in the presence of ALM. HcrtR antagonists are hypothesized to induce sleep by disfacilitation of wake-promoting systems whereas GABA_A receptor modulators such as zolpidem (ZOL) induce sleep through general inhibition of neural activity. To test the hypothesis that less functional impairment results from HcrtR antagonist-induced sleep, we evaluated the performance of rats in the Morris Water Maze in the presence of ALM vs. ZOL. Performance in spatial reference memory (SRM) and spatial working memory (SWM) tasks were assessed during the dark period after equipotent sleep-promoting doses (100 mg/kg, po) following undisturbed and sleep deprivation (SD) conditions. ALM-treated rats were indistinguishable from vehicle (VEH)-treated rats for all SRM performance measures (distance traveled, latency to enter, time within, and number of entries into, the target quadrant) after both the undisturbed and 6 h SD conditions. In contrast, rats administered ZOL showed impairments in all parameters measured compared to VEH or ALM in the undisturbed conditions. Following SD, ZOL-treated rats also showed impairments in all measures. ALM-treated rats were similar to VEH-treated rats for all SWM measures (velocity, time to locate the platform and success rate at finding the platform within 60 s) after both the undisturbed and SD conditions. In contrast, ZOL-treated rats showed impairments in velocity and in the time to locate the platform. Importantly, ZOL rats only completed the task 23–50% of the time while ALM and VEH rats completed the task 79–100% of the time. Thus, following equipotent sleep-promoting doses, ZOL impaired rats in both memory tasks while ALM rats performed at levels comparable to VEH rats. These results are consistent with the hypothesis that less impairment results from HcrtR antagonism than from GABA_A-induced inhibition.

Allosteric modulation of GABA(A) receptor subtypes:effects on visual recognition and visuospatial working memory in rhesus monkeys [corrected]

Non-selective positive allosteric modulators (PAMs) of GABAA receptors (GABAARs) are known to impair anterograde memory. The role of the various GABAAR subtypes in the memory-impairing effects of non-selective GABAAR PAMs has not been fully elucidated. The current study assessed, in rhesus monkeys, effects of modulation of α1, α2/3, and α5GABAARs on visual recognition and spatial working memory using delayed matching-to-sample (DMTS) and self-ordered spatial search (SOSS) procedures, respectively. The DMTS procedure (n=8) involved selecting a previously presented 'sample' image from a set of multiple images presented after a delay. The SOSS procedure (n=6) involved touching a number of boxes without repeats. The non-selective GABAAR PAM triazolam and the α1GABAA preferential PAMS zolpidem and zaleplon reduced accuracy in both procedures, whereas the α5GABAA preferential PAMs SH-053-2'F-R-CH3 and SH-053-2'F-S-CH3, and the α2/3GABAA preferential PAM TPA023B were without effects on accuracy or trial completion. The low-efficacy α5GABAAR negative allosteric modulator (NAM) PWZ-029 slightly increased only DMTS accuracy, whereas the high-efficacy α5GABAAR NAMs RY-23 and RY-24 did not affect accuracy under either procedure. Finally, the slopes of the accuracy dose-effect curves for triazolam, zolpidem, and zaleplon increased with box number in the SOSS procedure, but were equivalent across DMTS delays. The present results suggest that (1) α1GABAARs, compared with α2/3 and α5GABAARs, are primarily involved in the impairment, by non-selective GABAAR PAMs, of visual recognition and visuospatial working memory in nonhuman primates; and (2) relative cognitive impairment produced by positive modulation of GABAARs increases with number of locations to be remembered, but not with the delay for remembering.

Effects of zolpidem on sedation, anxiety, and memory in the plus-maze discriminative avoidance task

RATIONALE

Zolpidem (Zolp), a hypnotic drug prescribed to treat insomnia, may have negative effects on memory, but reports are inconsistent.

OBJECTIVES

We examined the effects of acute doses of Zolp (2, 5, or 10 mg/kg, i.p.) on memory formation (learning, consolidation, and retrieval) using the plus-maze discriminative avoidance task.

METHODS

Mice were acutely treated with Zolp 30 min before training or testing. In addition, the effects of Zolp and midazolam (Mid; a classic benzodiazepine) on consolidation at different time points were examined. The possible role of state dependency was investigated using combined pre-training and pre-test treatments.

RESULTS

Zolp produced a dose-dependent sedative effect, without modifying anxiety-like behavior. The pre-training administration of 5 or 10 mg/kg resulted in retention deficits. When administered immediately after training or before testing, memory was preserved. Zolp post-training administration (2 or 3 h) impaired subsequent memory. There was no participation of state dependency phenomenon in the amnestic effects of Zolp. Similar to Zolp, Mid impaired memory consolidation when administered 1 h after training.

CONCLUSIONS

Amnestic effects occurred when Zolp was administered either before or 2-3 h after training. These memory deficits are not related to state dependency. Moreover, Zolp did not impair memory retrieval. Notably, the memory-impairing effects of Zolp are similar to those of Mid, with the exception of the time point at which the drug can modify consolidation. Finally, the memory effects were unrelated to sedation or anxiolysis.

Drugs for insomnia

INTRODUCTION

Sleep is a vital neurochemical process involving sleep-promoting and arousal centers in the brain. Insomnia is a pervasive disorder characterized by difficulties in initiating or maintaining or non-refreshing (poor quality) sleep and clinically significant daytime distress. Insomnia is more prevalent in women and old age and puts sufferers at significant physical and mental health risks. This review summarizes published data on the current and emerging insomnia drug classes, rationale for development and associated risks/benefits. (Summary of Product Characteristics and Medline search on "hypnotic" or specific drug names and "Insomnia").

AREAS COVERED

GABA(A) receptor modulators facilitate sleep onset and some improve maintenance but increase risk of dependence, memory, cognitive and psychomotor impairments, falls, accidents and mortality. Melatonin receptor agonists improve quality of sleep and/or sleep onset but response may develop over several days. They have more benign safety profiles and are indicated for milder insomnia, longer usage and (prolonged release melatonin) older patients. Histamine H-1 receptor antagonists improve sleep maintenance but their effects on cognition, memory and falls remain to be demonstrated. Late-stage pipeline orexin OX1/OX2 and serotonin 5HT2A receptor antagonists may hold the potential to address several unmet needs in insomnia pharmacotherapy but safety issues cast some doubts over their future.

EXPERT OPINION

Current and new insomnia drugs in the pipeline target different sleep regulating mechanisms and symptoms and have different tolerability profiles. Drug selection would ideally be based on improvement in the quality of patients' sleep, overall quality of life and functional status weighed against risk to the individual and public health.

Acute effects of zolpidem extended-release on cognitive performance and sleep in healthy males after repeated nightly use

The extended-release formulation of zolpidem (Ambien CR) is approved for the treatment of insomnia without a treatment duration limit. Acutely zolpidem impairs performance, and no research to date has examined whether tolerance develops to these performance impairments during nighttime awakening. The present double-blind, placebo-controlled study examined whether tolerance develops to zolpidem-induced acute performance impairment after repeated (22-30 days) nightly use. Effects of bedtime administration of zolpidem extended-release (ZOL; 12.5 mg) were tested on a battery of performance measures assessed during a forced nighttime awakening in 15 healthy male volunteers who completed overnight polysomnographic recording sessions in our laboratory at baseline and after approximately a month of at-home ZOL. As expected, bedtime ZOL administration was associated with changes in sleep architecture and impairments across all performance domains during nighttime testing (psychomotor function, attention, working memory, episodic memory, metacognition) with no residual next morning impairment. Tolerance did not develop to the observed ZOL-related impairments on any outcome. Possible evidence of acute abstinence effects after discontinuation of ZOL was observed on some performance and sleep outcomes. Overall, these findings suggest that performance is significantly impaired during nighttime awakening even after a month of nightly ZOL administration, and these impairments could significantly impact safety should nighttime awakening require unimpaired functioning (e.g., driving; combat-related activities in the military).

Efficacy and safety of 6-month nightly ramelteon administration in adults with chronic primary insomnia

STUDY OBJECTIVES

Long-duration (> or = 6 months) polysomnographic studies of insomnia medications are lacking. This study evaluated the long-term efficacy of ramelteon, a selective MT1/MT2 melatonin-receptor agonist used for insomnia treatment.

DESIGN

Six-month, randomized, double-blind, placebo-controlled study.

SETTING

Forty-six investigative sites in the United States, Europe, Russia, and Australia.

PARTICIPANTS

Four hundred fifty-one adults (age > or = 18 years) with chronic primary insomnia.

INTERVENTIONS

Ramelteon, 8 mg, or placebo 30 minutes before bedtime nightly for 6 months.

MEASUREMENTS

Sleep was evaluated by polysomnography and morning questionnaires on the first 2 nights of Week 1; the last 2 nights of Months 1, 3, 5, and 6; and Nights 1 and 2 of the placebo run-out. Next-morning residual effects as well as adverse effects and vital signs were recorded at each visit. Rebound insomnia and withdrawal effects were evaluated during placebo run-out.

RESULTS

Over the 6 months of treatment, ramelteon consistently reduced latency to persistent sleep compared with baseline and with placebo; significant decreases were observed at Week 1 and Months 1, 3, 5, and 6 (P < 0.05). Ramelteon significantly reduced subjective sleep latency relative to placebo at Week 1, Month 1, and Month 5 (P < 0.05), with reductions nearing statistical significance at Months 3 and 6 (P < or = 0.08). No significant next-morning residual effects were detected during ramelteon treatment. No withdrawal symptoms or rebound insomnia were detected after ramelteon discontinuation. Most adverse events were mild or moderate in severity.

CONCLUSIONS

In adults with chronic insomnia, long-term ramelteon treatment consistently reduced sleep onset, with no next-morning residual effects or rebound insomnia or withdrawal symptoms upon discontinuation.

Spared unconscious influences of spatial memory in diencephalic amnesia

Spatial memory is crucial to our daily lives and in part strongly depends on automatic, implicit memory processes. This study investigates the neurocognitive basis of conscious and unconscious influences of object–location memory in amnesic patients with Korsakoff’s syndrome (N = 23) and healthy controls (N = 18) using a process-dissociation procedure in a computerized spatial memory task. As expected, the patients performed substantially worse on the conscious memory measures but showed even slightly stronger effects of unconscious influences than the controls. Moreover, a delayed test administered after 1 week revealed a strong decline in conscious influences in the patients, while unconscious influences were not affected. The presented results suggest that conscious and unconscious influences of spatial memory can be clearly dissociated in Korsakoff’s syndrome.

Segregating two inhibitory circuits in human motor cortex at the level of GABAA receptor subtypes: a TMS study

OBJECTIVE

To investigate if different interneuronal circuits in human motor cortex mediate inhibition through different subtypes of the gamma-aminobutyric acid A receptor (GABAAR).

METHODS

Two distinct forms of motor cortical inhibition were measured in 10 healthy subjects by established transcranial magnetic stimulation (TMS) protocols: short interval intracortical inhibition (SICI) and short latency afferent inhibition (SAI). Their modification by a single oral dose of three different positive GABAAR modulators (20 mg of diazepam, 2.5 mg of lorazepam and 10 mg of zolpidem) with different affinity profiles at the various alpha-subunit bearing subtypes of the GABAAR (diazepam: non-selective, lorazepam: unknown, zolpidem: 10-fold higher affinity to alpha1- than alpha2- or alpha3-subunit bearing GABAARs, no affinity to alpha5-subunits) was tested in a randomized crossover design. In addition, the sedative drug effects were recorded by a visual analogue scale.

RESULTS

Diazepam and lorazepam increased SICI, whereas zolpidem did not change SICI. In contrast, diazepam had no effect on SAI, whereas lorazepam and zolpidem decreased SAI. The sedative effects were not different between drugs.

CONCLUSIONS

The dissociating patterns of drug modification of SICI versus SAI strongly suggest that different GABAAR subtypes are involved in SICI and SAI.

SIGNIFICANCE

We provide evidence, for the first time, for a dissociation of effects of diazepam and zolpidem on SAI and confirm the previously reported differential effect of zolpidem and of diazepam and lorazepam on SICI. The differential effects of the three benzodiazepines on SAI and SICI suggest that neuronal circuits in human motor cortex that mediate inhibition through different GABAAR subtypes can be segregated by TMS.

Blockade of alcohol's amnestic activity in humans by an alpha5 subtype benzodiazepine receptor inverse agonist

Alcohol produces many subjective and objective effects in man including pleasure, sedation, anxiolysis, plus impaired eye movements and memory. In human volunteers we have used a newly available GABA-A/benzodiazepine receptor inverse agonist that is selective for the alpha5 subtype (a5IA) to evaluate the role of this subtype in mediating these effects of alcohol on the brain. After pre-treatment with a5IA, we found almost complete blockade of the marked impairment caused by alcohol (mean breath concentration 150mg/100ml) of word list learning and partial but non-significant reversal of subjective sedation without effects on other measures such as intoxication, liking, and slowing of eye movements. This action was not due to alterations in alcohol kinetics and so provides the first proof of concept that selectively decreasing GABA-A receptor function at a specific receptor subtype can offset some actions of alcohol in humans. It also supports growing evidence for a key role of the alpha5 subtype in memory. Inverse agonists at other GABA-A receptor subtypes may prove able to reverse other actions of alcohol, and so offer a new approach to understanding the actions of alcohol in the human brain and in the treatment of alcohol related disorders in humans.

Functional evaluation of cerebral cortex in dementia with Lewy bodies

Neurochemical investigations have demonstrated central cholinergic dysfunction in patients with dementia with Lewy bodies (DLB). Central cholinergic circuits of the human brain can be tested non-invasively by coupling peripheral nerve stimulation with transcranial magnetic stimulation of the contralateral motor cortex. This test, named short latency afferent inhibition has been shown in healthy subjects to be sensitive to the blockage of muscarinic acetylcholine receptors and it is impaired in patients with Alzheimer disease (AD), a cholinergic form of dementia, while it is normal in non-cholinergic forms of dementia such as fronto-temporal dementia. We evaluated short latency afferent inhibition in a group of patients with DLB and compared the data with that from a group of AD patients and a control group of age-matched healthy individuals. Short latency afferent inhibition was significantly reduced in DLB and AD patients. The findings suggest that this method can be used as a non-invasive test for the assessment of cholinergic pathways in patients with dementia and may represent a useful additional tool for discriminating between cholinergic and non-cholinergic forms of dementia.

New drugs for insomnia: comparative tolerability of zopiclone, zolpidem and zaleplon

Insomnia affects 30-35% of people living in developed countries. The impact of insomnia on daytime functioning and its relationship with medical and psychiatric illnesses necessitate early treatment to prevent insomnia becoming persistent and to avoid the development of complications. However, pharmacological strategies must achieve a balance between sedative and adverse effects. In the last 30 years, benzodiazepines have been the preferred drugs for the treatment of insomnia. Benzodiazepines act nonselectively at two central receptor sites, named omega(1) and omega(2), which are located in different areas of the CNS. The sedative action of benzodiazepines is related to omega(1) receptors, whereas omega(2) receptors are responsible for their effects on memory and cognitive functioning. According to their pharmacokinetic profile, benzodiazepines can be classified into three groups: short half-life (<3 hours), medium half-life (8-24 hours) and long half-life (>24 hours). The newer non-benzodiazepine agents zopiclone, zolpidem and zaleplon have a hypnosedative action comparable with that of benzodiazepines, but they display specific pharmacokinetic and pharmacodynamic properties. These three 'Z' agents all share a short plasma half-life and limited duration of action. In addition, these agents are selective compounds that interact preferentially with omega(1) receptors (sedative effect), whereas benzodiazepines also interact with omega(2) receptors (adverse effects on cognitive performance and memory). Zaleplon is characterised by an ultrashort half-life (approximately 1 hour). Zolpidem and zopiclone have longer half-lives (approximately 2.4 and 5 hours, respectively). These properties, together with the low risk of residual effect, may explain the limited negative influences of these agents on daytime performance. Psychomotor tasks and memory capacities appear to be better preserved by non-benzodiazepine agents than by benzodiazepines. When present, cognitive deficits almost exclusively coincide with the peak plasma concentration. In particular, impairment can emerge in the first hours after drug administration, whereas psychomotor and memory tests carried out 7-8 hours later (i.e. in the morning) generally show no relevant alterations. As with benzodiazepines, the three 'Z' non-benzodiazepine agents should be used for a limited period, even in chronic relapsing conditions. Further evaluation is needed of the safety of hypnosedative medications in the long-term management of insomnia.

Effects on postural oscillation and memory functions of a single dose of zolpidem 5 mg, zopiclone 3.75 mg and lormetazepam 1 mg in elderly healthy subjects. A randomized, cross-over, double-blind study versus placebo

OBJECTIVE

In elderly patients, both falls and impaired memory are considerable medical problems. Hypnotics, which are frequently administered to this patient group for the treatment of insomnia, should ideally not impair equilibrium or memory functions. This double-blind, randomised, four-way, cross-over study investigated the effects of frequently prescribed hypnotics from different classes on postural oscillation and memory under real life conditions. Zolpidem 5 mg, zopiclone 3.75 mg, lormetazepam 1 mg (i.e. usual starting doses in elderly) or placebo were administered at night to 48 healthy elderly volunteers aged 65 years or more. The study included four treatment periods separated by wash-out periods of at least 1 week.

METHODS

Psychomotor tests up to 9 h or 10 h after drug intake included, for attention and body sway, clinical stabilometric platform (CSP) tests, simple reaction time (SRT), and the critical tracking test (CTT); for memory, the learning memory tasks (LMT) and the Sternberg memory scanning test (mean reaction time [MRT] and percentage of correct answers) were used. For subjective sleep evaluation the Leeds sleep evaluation questionnaire (LSEQ) and for sedation a visual analogue scale (VAS) were used. For safety evaluations, adverse events (AEs) were recorded.

RESULTS

The results demonstrate that compared with placebo, the active drugs increased body sway (area eyes open and closed in the CSP); however, this effect disappeared after 5 h with zolpidem, while it disappeared only after 8 h with lormetazepam and zopiclone. All three drugs did not affect attention assessed by the SRT and CTT. Concerning memory, Sternberg MRT at 9 h was not significantly different up to 5 digits for all groups in comparison with placebo, while for 6 digits it was significantly increased with lormetazepam and zopiclone. In the LMT, an impairment of performance was observed with lormetazepam relative to both zolpidem and placebo.

CONCLUSION

The safest compared drug with regard to body sway was zolpidem, because of its short-lasting effect. In addition, zolpidem did not show any significant effect on memory functions, in the present dose comparison.

Zolpidem dependence case series: possible neurobiological mechanisms and clinical management

Zolpidem is a short-acting imidazopyridine hypnotic that is an agonist at the gamma-aminobutyric acid A type (GABAA) receptor. It has been suggested that it acts selectively on alpha1 subunit-containing GABAA benzodiazepine (BZ1) receptors presenting (contrary to classic benzodiazepines) low or no affinity for other subtypes. Therefore, it has been proposed that it lacks the benzodiazepines-like side-effects, having minimal abuse and dependence potential. Nevertheless, there is a considerable number of zolpidem dependence case reports in the literature. We present eight cases of zolpidem abuse and dependence without criminal record, without history of substance abuse (except for one alcohol abuser), with minor psychiatric disorders, who took zolpidem after physicians prescription in order to deal with their insomnia. However, they became zolpidem abusers not craving its sedative, but its anxiolytic and stimulating action, which helped them to cope with everyday activities. It is possible that, in the high doses that our patients used, zolpidem abandons its selectivity for BZ1 receptors and demonstrates all the actions of classic benzodiazepines. Molecular biology, via possible mutations on GABA receptors, may provide some answers as to why our eight patients (who did not differ much from the thousands of insomniacs who use zolpidem) and other zolpidem abusers, raised the dose progressively, and sought something from the drug other than hypnotic action.

Residual effects of middle-of-the-night administration of zaleplon and zolpidem on driving ability, memory functions, and psychomotor performance

Thirty healthy volunteers participated in this two-part study. Part 1 was a single-blind, two-period crossover design to determine the effects of a single dose of ethanol (0.03% < BAC < 0.05%) or ethanol-placebo on driving ability, memory, and psychomotor performance. Part 2 was a double-blind, five-period crossover design to measure the effects of a middle-of-the-night administration of zaleplon 10 or 20 mg, zolpidem 10 or 20 mg, or placebo on driving ability 4 hours after administration and memory and psychomotor performance 6 hours after administration. The on-the-road driving test consisted of operating an instrumented automobile over a 100-km highway circuit at a constant speed (95 km/h) while maintaining a steady lateral position between the right lane boundaries. The standard deviation of lateral position (SDLP) was the primary performance parameter of the driving test. The psychomotor and memory test battery consisted of the Word Learning Test, the Critical Tracking Test, the Divided Attention Test, and the Digit Symbol Substitution Test. Data for each part were analyzed separately using ANOVA for crossover designs. Zaleplon 10 and 20 mg did not significantly impair driving ability 4 hours after middle-of-the-night administration. Relative to placebo, after zolpidem 10 mg, SDLP was significantly elevated, but the magnitude of the difference was small and not likely to be of clinical importance. Memory and psychomotor test performance was unaffected after both doses of zaleplon and zolpidem 10 mg. In contrast, zolpidem 20 mg significantly increased SDLP and speed variability. Further, zolpidem 20 mg significantly impaired performance on all psychomotor and memory tests. Finally, driving performance, Digit Symbol Substitution Test, Divided Attention Test, and immediate and delayed free recall of the Word Learning Test were significantly impaired after ethanol. The results show that zaleplon (10 and 20 mg) is a safe hypnotic devoid of next-morning residual impairment when used in the middle of the night.

Potentiation of muscimol-induced long-term depression by benzodiazepines but not zolpidem

Zolpidem is a rapid-onset, short-duration, quickly eliminated imidazopyridine hypnotic. It has been suggested that zolpidem may produce less memory and cognitive impairment than benzodiazepines (BZs) due to its low binding affinity for BZ receptor subtypes found in areas of the brain that are involved in learning and memory, in particular the hippocampus. A novel protocol for inducing long-term synaptic depression through activation of gamma-aminobutyric acid (GABA(A)) receptors in the hippocampal slices has been recently reported. The authors used the CA1 region of rat hippocampal slices to compare the effects of classic BZs, which bind equipotently to BZ1 and BZ2 sites, and of nonbenzodiazepine zolpidem, which binds preferentially to the BZ1 sites of GABA(A) receptors, on the GABA(A)-induced long-term depression (LTD), a possible cellular mechanism for their different cognition-impairment profile. Extracellular recordings were made in the CA1 pyramidal cell layer of rat hippocampal slices following orthodromic stimulation of Schaffer collateral fibres in stratum radiatum (0.01 Hz). It was observed that diazepam and cholordiazepoxide at concentrations of 10 and 20 microM, which did not have any effect themselves on the population spike, potentiate the ability of muscimol to induce LTD, whereas zolpidem at concentrations of 10 and 20 microM failed to potentiate muscimol-induced LTD. The results suggest that the potentiation of muscimol-induced LTD by diazepam or chlordiazepoxide and the lack of this effect by zolpidem may explain their different cognition impairment profiles.

Mechanism-based pharmacodynamic modeling of the interaction of midazolam, bretazenil, and zolpidem with ethanol

The pharmacokinetic and pharmacodynamic interactions of ethanol with the full benzodiazepine agonist midazolam, the partial agonist bretazenil and the benzodiazepine BZ1 receptor subtype selective agonist zolpidem have been determined in the rat in vivo, using an integrated pharmacokinetic-pharmacodynamic approach. Ethanol was administered as a constant rate infusion resulting in constant plasma concentrations of 0.5 g/l. The pharmacokinetics and pharmacodynamics of midazolam, bretazenil, and zolpidem were determined following an intravenous infusion of 5.0, 2.5, and 18 mg/kg respectively. The amplitude in the 11.5-30 Hz frequency band of the EEG was used as measure of the pharmacological effect. For each of the benzodiazepines the concentration-EEG effect relationship could be described by the sigmoid Emax pharmacodynamic model. Significant differences in both EC50 and Emax were observed. The values of the EC50 were 76 +/- 11, 12 +/- 3, and 512 +/- 116 ng/ml for midazolam, bretazenil, and zolpidem respectively. The values of the Emax were 113 +/- 9, 44 +/- 3, and 175 +/- 10 microV/s. In the presence of ethanol the values of the EC50 of midazolam and zolpidem were reduced to approximately 50% of the original value. The values for Emax and Hill-factor were unchanged Due to a large interindividual variability no significant change in EC50 was observed for bretazenil. Analysis of the data on basis of a mechanism-based model showed only a decrease in the apparent affinity constant KPD for all three drugs, indicating that changes in EC50 can be explained entirely by a change in the apparent affinity constant KPD without concomitant changes in the efficacy parameter ePD and the stimulus-effect relationship. The findings of this study show that the pharmacodynamic interactions with a low dose of ethanol in vivo are qualitatively and quantitatively similar for benzodiazepine receptor full agonists, partial agonists, and benzodiazepine BZ1 receptor subtype selective agonists. This interaction can be explained entirely by a change in the affinity of the biological system for each benzodiazepine.

Passionflower in the treatment of generalized anxiety: a pilot double-blind randomized controlled trial with oxazepam

OBJECTIVE

Passionflower (Passiflora incarnata) is a folk remedy for anxiety. A double-blind randomized trial compared the efficacy of Passiflora incarnata extract with oxazepam in the treatment of generalized anxiety disorder.

METHODS

The study was performed on 36 out-patients diagnosed with GAD using DSM IV criteria. Patients were allocated in a random fashion: 18 to the Passiflora extract 45 drops/day plus placebo tablet group, and 18 to oxazepam 30 mg/day plus placebo drops for a 4-week trial.

RESULTS

Passiflora extract and oxazepam were effective in the treatment of generalized anxiety disorder. No significant difference was observed between the two protocols at the end of trial. Oxazepam showed a rapid onset of action. On the other hand, significantly more problems relating to impairment of job performance were encountered with subjects on oxazepam.

CONCLUSION

The results suggest that Passiflora extract is an effective drug for the management of generalized anxiety disorder, and the low incidence of impairment of job performance with Passiflora extract compared to oxazepam is an advantage. A large-scale trial is justified.

Pharmacodynamic profile of Zaleplon, a new non-benzodiazepine hypnotic agent

The challenge in developing hypnotic agents for the treatment of insomnia is to balance the sedative effect needed at bedtime with the residual sedation on awakening. Zaleplon is a novel pyrazolopyrimidine hypnotic agent that acts as a selective agonist to the brain omega(1) receptor situated on the alpha(1) subunit of the GABA(A) receptor complex. Zaleplon was proven to be an effective hypnotic drug as it consistently and significantly reduced latency to persistent sleep in insomniac patients for doses of 10 mg and above in polysomnography studies. The pharmacodynamic profile of zaleplon on psychomotor performance, actual driving and cognitive function, including memory, was assessed in several randomized, double-blind, placebo-controlled studies in healthy young subjects as well as insomniac patients by using various positive controls (zolpidem, zopiclone, triazolam and flurazepam). The recommended hypnotic dose of zaleplon in young adults (10 mg) produced minimal or no impairment of psychomotor and memory performance even when administered during the night as little as 1 h before waking. No impairment of actual driving was observed when zaleplon 10 mg was administered either at bedtime or in the middle of the night as little as 4 h before waking. Zaleplon 20 mg, twice the recommended dose, generally produced significant impairment of performance and cognitive functions when these functions were measured at the time of peak plasma concentration, i.e. 1 h after dose administration, and no impairment of driving abilities was observed 4 h after a middle-of-the-night administration. In contrast, consistent detrimental residual effects on various aspects of psychomotor and cognitive functions were observed with the therapeutic doses of the various commonly prescribed hypnotic agents used as comparators, e.g. zolpidem 10 mg up to 5 h after dose administration, zopiclone 7.5 mg up to 10 h after, flurazepam 30 mg up to 14 h after and triazolam 0.25 mg up to 6 h after. Also, zolpidem 10 mg and zopiclone 7.5 mg were also shown to significantly impair driving ability the next morning when this was measured 4 h and up to 10 h after dose administration, respectively. The present review shows that zaleplon 10 mg has little or no residual effect when administered in the middle of the night, as late as 1 h before waking, and is devoid of impairment of driving abilities as assessed by actual driving 4 h after dose administration. The lack of clinically significant or minimally statistically significant residual effects of zaleplon even at its peak concentration may be explained by its unique pharmacokinetic (rapid elimination half-life) and pharmacodynamic (low affinity, and specific binding profile to various subunits of the GABA(A)receptor) profiles. These properties allow zaleplon to be used for treatment of symptoms only when they occur, either at bedtime or later in the night, without incurring significant risk of developing next-day impairment of psychomotor and cognitive functioning. Copyright 2001 John Wiley & Sons, Ltd.

The effect of midazolam on the modality-match effect in implicit memory

Prominent theories of implicit memory claim that perceptual processes play a central role in implicit memory. The modality-match effect, the finding that priming is greater when the modality of stimulus presentation matches at study and test, provides the central evidence for these approaches. In this paper we use the benzodiazepine, midazolam, to explore the nature of the modality-match effect in implicit memory. We compared the modality-match effect in a midazolam and a saline (i.e., a placebo) condition. Our experimental results demonstrate that the modality-match effect is diminished substantially in a midazolam condition even though components of priming are preserved. Given the empirically-validated assumption that midazolam minimizes explicit memory, these results suggest that there exist components of implicit memory that are not mediated by perceptual processes and raise questions about the generality of prominent theories of implicit memory.

Flunitrazepam and triazolam: a comparison of behavioral effects and abuse liability

The performance, observer-rated, and participant-rated effects of orally administered placebo, and two benzodiazepines, flunitrazepam (2, 4 and 8 mg/70 kg) and triazolam (0.25, 0.5 and 1 mg/70 kg), were compared in 14 sedative drug abusers using a double-blind crossover design. Both flunitrazepam and triazolam produced dose-related decrements in memory and psychomotor/cognitive performance, and increases in many participant- and observer-rated measures. Effects of flunitrazepam had an earlier onset and a longer duration than those of triazolam. Although there was evidence that the flunitrazepam doses selected for study were somewhat higher overall relative to the selected triazolam doses, analysis of the participant-rated measures collected 24 h after drug administration (next-day) suggests that flunitrazepam may have a greater abuse liability than triazolam when abuse liability is assessed 24 h after drug administration. The highest flunitrazepam dose produced effects that were significantly greater than those of the highest triazolam dose on next-day ratings of good effects, take again, and worth; all tested flunitrazepam doses produced effects greater than any triazolam dose on next-day ratings of liking and take again. The highest flunitrazepam dose, but no triazolam dose, significantly increased the maximum dollar value at which participants chose drug over money in a Drug versus Money Choice Procedure.