Effects of acute and repeated zolpidem treatment on pentylenetetrazole-induced seizure threshold and on locomotor activity: Comparison with diazepam

Zolpidem and diazepam are widely used drugs acting via benzodiazepine binding sites on GABA_A receptors. While diazepam is non-selective, zolpidem has a high affinity for α1-, and no affinity for α5-containing receptors. Several studies suggested that behavioral effects of zolpidem might be more similar to classical benzodiazepines than previously thought. To compare the sedative and anticonvulsant properties of these drugs and to evaluate the importance of GABA_A receptor subunits for development of tolerance during chronic treatment, we tested the effects of acute and repeated administration of zolpidem and diazepam on ambulatory locomotor activity (a measure of sedation) and on the threshold for myoclonic, clonic and tonic seizures in response to i.v. infusion of pentylenetetrazole (PTZ). Both drugs given acutely in doses 0.3, 1 and 3 mg/kg reduced locomotion, and in doses 1 and 3 mg/kg elevated the threshold for PTZ-induced seizures. The effects of zolpidem and diazepam on the tonic seizure threshold were greater than on myoclonus and clonic seizure threshold. Diazepam and zolpidem (3 mg/kg), given 18 or 42 h after repeated drug treatment (10 days, 5 mg/kg, twice daily), decreased the PTZ seizure threshold and increased the locomotor activity as compared to control mice, indicating development of tolerance to their anticonvulsant and sedative effects. After repeated treatment the PTZ seizure threshold was not different between the two drugs, while differences in sedation became larger than after the acute treatment. The results suggest that α5-containing GABA_A receptors are not crucial for the development of sedative and anticonvulsant tolerance.     

Pentobarbital tolerance and withdrawal: correlation with effects on the GABAA receptor

A model for the development of pentobarbital tolerance and dependence was characterized and correlated with changes in radioligand binding to the GABAA-benzodiazepine receptor chloride channel complex. While one day of pentobarbital exposure decreased the duration of loss of righting reflex, tolerance to the hypothermic effects of thiopental and barbital took 7 days to develop, indicating that pharmacokinetic and pharmacodynamic tolerance are separable. Increased sensitivity to pentylenetetrazol-induced seizures was first observed after 3 days of pentobarbital exposure, suggesting brain areas involved in seizure control develop tolerance to, and dependence on pentobarbital faster than those involved in temperature regulation. Acute exposure to pentobarbital in vivo did not affect cortical binding of [3H]muscimol in vitro, while tolerance caused a decrease in binding due to an increase in the low-affinity site KD. Pentobarbital tolerance also caused a decrease in the cortical binding of the benzodiazepine, [3H]flunitrazepam. These observations suggest that the acute effects of barbiturates on the GABAA receptor complex are reversible, while tolerance causes receptor modifications which may be related to the development of physical dependence.     

The benzodiazepine receptor and receptor tolerance produced by chronic treatment of diazepam

A characterization of the benzodiazepine receptor in vivo was carried out utilizing the up-and-down method for a quantitative determination of the maximal seizure threshold to diazepam. Wistar-Imamichi male rats of 21 days of age were used. The drug concentration in the brain at the steady-state was measured with radiolabeled diazepam. A kinetic analysis for the dose-response relation obtained gave 2.2 microM and 1.6 for the Kd and n, respectively, in the Langmuir adsorption isotherm. The results suggested the existence of a hitherto undiscovered endogenous ligand(s) suppressing the binding of benzodiazepine to the receptor, as compared with those in the in vitro binding-assay reported by other investigators. A chronic pretreatment with diazepam once a day for 13 days (0.2 and 2 mg/kg, s.c.) produced receptor tolerance, but did not affect the amount of the seizure threshold unless the drug was acutely administered 10 min before the electric shock. These results supported the argument that two distinct entities exist for both GABA and benzodiazepine recognition sites which are closely related to each other in their functioning.     

Abolition of zolpidem sensitivity in mice with a point mutation in the GABAA receptor gamma2 subunit

Agonists of the allosteric benzodiazepine site of GABAA receptors bind at the interface of the alpha and gamma subunits. Here, we tested the in vivo contribution of the gamma2 subunit to the actions of zolpidem, an alpha1 subunit selective benzodiazepine agonist, by generating mice with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the gamma2 subunit. The gamma2F77I mutation has no major effect on the expression of GABAA receptor subunits in the cerebellum. The potency of zolpidem, but not that of flurazepam, for the inhibition of [3H]flunitrazepam binding to cerebellar membranes is greatly reduced in gamma2I77/I77 mice. Zolpidem (1 microM) increased both the amplitude and decay of miniature inhibitory postsynaptic currents (mIPSCs) in Purkinje cells of control C57BL/6 (34% and 92%, respectively) and gamma2F77/F77 (20% and 84%) mice, but not in those of gamma2F77I mice. Zolpidem tartrate had no effect on exploratory activity (staircase test) or motor performance (rotarod test) in gamma2I77/I77 mice at doses up to 30 mg/kg (i.p.) that strongly sedated or impaired the control mice. Flurazepam was equally effective in enhancing mIPSCs and disrupting performance in the rotarod test in control and gamma2I77/I77 mice. These results show that the effect of zolpidem, but not flurazepam, is selectively eliminated in the brain by the gamma2F77I point mutation.     

The acute effects of zolpidem compared to diazepam and lorazepam using radiotelemetry

The present study used a radiotelemetric method to compare the muscle relaxant, hypothermic and locomotor depressant actions of the imidazopyridine zolpidem, with those of the benzodiazepines lorazepam and diazepam. Rats, n=7 per group, were divided into 3 dose-dependent treatment groups (highest, middle, and lowest). Each rat within a treatment group received a single dose of diazepam, lorazepam, zolpidem and vehicle. All three drugs induced dose-dependent decreases in body temperature, locomotor activity and electromyographic (EMG) activity. Administration of zolpidem (5 and 10 mg/kg) resulted in maximal decrements in locomotor activity that were comparable to those elicited by both diazepam (10 and 20 mg/kg) and lorazepam (12.5 and 25 mg/kg). Zolpidem (10 mg/kg) decreased EMG activity levels to approximately 45% of vehicle treated controls; a value similar to that induced by diazepam (2.5 mg/kg). These data suggest that the imidazopyridine zolpidem has a similar profile of acute effects in comparison to the benzodiazepines diazepam and lorazepam. However, the relative magnitude of the effects differed, with zolpidem producing less hypothermia and muscle relaxation than the two benzodiazepines.     

Sensitisation to repeated withdrawal, in mice treated chronically with diazepam, is blocked by an NMDA receptor antagonist

 Mice were treated either with diazepam (15 mg/kg SC in oil), for 21 days, or for 3×7-day periods interspersed with two 72-h drug-free periods. Convulsant thresholds to pentylentetrazole infused into the tail vein 72 h following the final chronic treatment were lower in multiple-withdrawal mice than in mice which had experienced the same drug load, but only a single withdrawal, consistent with sensitisation of withdrawal events following previous withdrawal experience. The increase in seizure sensitivity of repeatedly withdrawn mice was prevented by treatment with the NMDA receptor antagonist CGP 39551 (20 mg/kg, IP) given once daily during the 3-day breaks in diazepam treatment, suggesting a role of glutamatergic transmission in the sensitisation process. Received: 5 December 1997 / Final version: 22 December 1997     

四氢孕酮和地西泮对暴露于架高十字迷宫小鼠的作用

目的比较孕酮的还原性代谢产物四氢孕酮和地西泮抗焦虑作用。方法C57小鼠腹腔注射四氢孕酮、地西泮或赋形剂 ,20min后观察在架高十字迷宫试验中的表现 ,测定其自发活动。结果腹腔注射四氢孕酮0.1mg·kg-1,明显缩短小鼠进入十字迷宫开臂的潜伏期[从(31.30±8.39)s减少到(8.80±6.00)s ,P<0.001] ,并显著增加进入十字迷宫开臂的次数(从1.20±0.42增到4.80±1.75,P<0.001)及在开臂的滞留时间占总时间的百分比 (从7.13 %增加到32.50 %,P<0.001)。而腹腔注射地西泮0.25mg·kg-1的抗焦虑作用弱于四氢孕酮。自发活动实验显示 ,0.5mg·kg-1地西泮明显减少小鼠自发活动 (P<0.01) ,而0.1mg·kg-1地西泮和0.25mg·kg-1 的四氢孕酮均不影响小鼠自发活动。结论试验结果提示神经甾体和地西泮对小鼠行为有不同的作用。四氢孕酮具选择性抗焦虑作用而不影响自发活动 ,可望成为地西泮抗焦虑的代用品     

Comparison of the effects of secobarbital and diazepam on the repeated acquisition of response sequences in humans

The present study was conducted to compare the acute effects of secobarbital (0–300 mg) and diazepam (0–30 mg) on learning in normal volunteers. The repeated acquisition of behavioral chains procedure was used to assess learning. Subjects were exposed to varying doses of secobarbital, diazepam, and placebo under double-blind conditions. Both compounds increased overall percent errors and decreased overall response rates as an orderly function of dose. No statistically significant differences were observed between these two compounds in onset, magnitude, or duration of effects. As expected, potency differences were observed with diazepam being approximately 10 times more potent than secobarbital. Overall these results indicate that secobarbital and diazepam produce a comparable profile of effects in humans responding under a repeated acquisition of behavioral chains procedure. Thus, with regard to learning impairment, the liability associated with using or abusing secobarbital vs. diazepam appears to be the same.     

Short-term steroid treatment increases delta GABAA receptor subunit expression in rat CA1 hippocampus: pharmacological and behavioral effects

In this study, 48 h administration of 3alpha-OH-5beta-pregnan-20-one (3alpha,5beta-THP) or 17beta-estradiol (E2)+progesterone (P) to female rats increased expression of the delta subunit of the GABA(A) receptor (GABAR) in CA1 hippocampus. Coexpression of alpha4 and delta subunits was suggested by an increased response of isolated pyramidal cells to the GABA agonist 4,5,6,7- tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), following 48 h steroid treatment, and nearly complete blockade by 300 microM lanthanum (La3+). Because alpha4betadelta GABAR are extrasynaptic, we also recorded pharmacologically isolated GABAergic holding current from CA1 hippocampal pyramidal cells in the slice. The La3+-sensitive THIP current, representative of current gated by alpha4betadelta GABAR, was measurable only following 48 h steroid treatment. In contrast, the bicuculline-sensitive current was not altered by steroid treatment, assessed with or without 200 nM gabazine to block synaptic current. However, 48 h steroid treatment resulted in a tonic current insensitive to the benzodiazepine agonists lorazepam (10 microM) and zolpidem (100 nM). These results suggest that 48 h steroid treatment increases expression of alpha4betadelta GABAR which replace the ambient receptor population. Increased anxiolytic effects of THIP were also observed following 48 h steroid treatment. The findings from the present study may be relevant for alterations in mood and benzodiazepine sensitivity reported across the menstrual cycle.     

Morphine tolerance and dependence in mice with history of repeated exposures to NMDA receptor channel blockers.

Mice were subjected to two successive treatment protocols: first with NMDA receptor channel blockers (14 days, once a day) and second with morphine (5 mg/kg, 8 days, once a day). Treatment with the higher doses of dizocilpine (1 mg/kg), memantine (30 mg/kg), and MRZ 2/576 (30 mg/kg) upon discontinuation revealed only minor behavioral abnormalities attributable to the state of withdrawal. Following repeated administration of low-dose morphine, tolerance to morphine analgesia developed in mice preexposed to dizocilpine (1 mg/kg but not 0.3 mg/kg) but not memantine (10 and 30 mg/kg), MRZ 2/579 (10 and 30 mg/kg), or saline. There were no signs of morphine dependence in any treatment group. Overall, the present study found only minor effects of the subchronic administration of high doses of NMDA receptor channel blockers, suggesting that clinical use of NMDA receptor channel blockers such as memantine will not be accompanied by increased propensity to induction of morphine tolerance and dependence.     

The effects of acute and repeated doses of zolpidem on subjective sleep,psychomotor performance and cognitive function in elderly volunteers

Summary We gave 24 healthy elderly volunteers with a perceived sleep onset of at least 30 minutes zolpidem 5 mg, zolpidem 10 mg, or placebo for 7 days in a double-blind, three-way, crossover study.The morning after nocturnal dosing, psychomotor performance and cognitive ability were measured using tests which are sensitive to the residual effects of hypnotics and to the effects of drugs on various indicators of sleep quality. The tests were: Choice Reaction Time; Tracking; Critical Flicker Fusion Threshold; Memory Scanning; Word Recognition; the Leeds Sleep Evaluation Questionnaire and Line Analogue Rating Scales.Zolpidem produced a subjective improvement in sleep but did not impair performance the following day. Furthermore, during repeated administration, there was no tolerance to the effects of sleep latency and quality of sleep, nor adverse effects on task performance.     

卡马西平对青霉素点燃惊厥大鼠脑内GABA_A受体mRNA表达的作用

目的研究两种剂量卡马西平对青霉素慢性点燃大鼠的抗惊厥作用及对脑内GABAA受体mRNA表达的影响,从基因水平探讨卡马西平抗惊厥的作用机制。方法采用腹腔注射(ip)青霉素(3×106U.kg-1.d-1)慢性点燃大鼠惊厥模型,两种剂量卡马西平(50,100mg.kg-1×13d)ig给药,以痫性发作潜伏期和Racine惊厥行为分级标准为判定药效指标,观察卡马西平的抗惊厥作用。运用RT-PCR技术测定大鼠脑内GABAA受体mRNA表达量,分析卡马西平抗惊厥作用的新机制。结果两种剂量卡马西平ig给药后,均可使青霉素慢性点燃大鼠痫性发作的潜伏期延长,与模型对照组相比差异有统计学意义(P<0.01),同时使惊厥大鼠的发作程度均较模型对照组减轻。青霉素慢性点燃大鼠脑内GABAA受体mRNA表达减少,与正常对照组比较,差异有统计学意义(P<0.01);两种剂量卡马西平预防性干预组的GABAA受体mRNA表达量分别与模型对照组相比,差异均无显著性。结论两种剂量卡马西平对青霉素慢性点燃的惊厥发作均有明显的对抗作用,但抗惊厥机制与GABAA受体的基因表达无关。     

The effects of chronic oxotremorine treatment on spatial learning and tolerance development in mice

C57BL mice were treated with 0.5 mg/kg/hr oxotremorine through an implanted subcutaneous cannula for 6 days. Tolerance to oxotremorine was evaluated after treatment by constructing cumulative dose-response curves and measuring body temperature and rotarod performance. At 2 hr after removal, mice exhibited a 15-fold tolerance as measured by body temperature and a 4-fold tolerance as measured by rotarod performance. This tolerance as measured by body temperature was lost by two days after removal from treatment. Immediately after treatment, 3H-QNB binding was reduced in cortex, hippocampus, midbrain, hindbrain, and hypothalamus. Receptors returned to normal within 4 to 8 days after cessation of treatment depending on the brain region. Spatial learning was examined using the Morris water task. Mice that began their training in this task 1 day after they were removed from oxotremorine treatment were impaired in their spatial ability as evidenced by a lack of preference for the trained site during a probe trial. Mice that began their training 2 days after cessation of oxotremorine treatment showed no evidence of impairment in spatial learning. These results suggest that a loss of muscarinic receptors after oxotremorine treatment can be dissociated from tolerance loss and spatial learning deficits.     

The effects of D-histiding on the expression of morphine tolerance and physical dependence in mice

D-Histidine, administered in the 'wthdrawal' phase of morphine addiction, failed to modify the expression of tolerance and physical dependence in mice. L-Histidine, on the contrary, can enhance tolerance and inhibit physical dependence. Whole brain histamine is markedly increased by L-histidine administration, but only minimally by D-histidine. This confirms that the actions of L-histidine on morphine addiction are stereospecific, and so can be more confidently correlated with the increase in brain histamine levels produced by the natural amino acid precursor.     

Chronic curcumin treatment normalizes depression-like behaviors in mice with mononeuropathy: involvement of supraspinal serotonergic system and GABAA receptor

Rationale

Comorbid depression is commonly observed in individuals who suffer from neuropathic pain, which necessitates improved treatment. Curcumin, a phenolic compound derived from Curcuma longa, possesses both antinociceptive and antidepressant-like activities in animal studies, suggesting its possible usefulness in treating this comorbidity.

Objective

We investigated the effect of curcumin on depressive-like behaviors in mice with mononeuropathy, and explored the mechanism(s).

Methods

Chronic constriction injury (CCI) was produced by loosely ligating the sciatic nerves in mice. The nociceptive behaviors were examined using Hargreaves test, and the depressive-like behaviors were determined by forced swim test (FST) and tail suspension test (TST).

Results

After CCI injury, the neuropathic mice developed nociceptive and depressive-like behaviors, as shown by thermal hyperalgesia in Hargreaves test and protracted immobility time in FST and TST. Chronic treatment of neuropathic mice with curcumin (45 mg/kg, p.o., twice per day for 3 weeks) corrected their exacerbated nociceptive and depressive-like behaviors, which was abolished by chemical depletion of brain serotonin rather than noradrenaline. The paralleled antinociceptive and antidepressant-like actions of curcumin seem to be pharmacologically segregated, since intrathecal and intracerebroventricular injection of methysergide, a nonselective 5-HT receptor antagonist, separately counteracted the two actions of curcumin. Further, this antidepression was abrogated by repeated co-treatment with 5-HT_1A receptor antagonist WAY-100635 and greatly attenuated by acute co-treatment with GABA_A receptor antagonist bicuculline.

Conclusion

Curcumin can normalize the depressive-like behaviors of neuropathic mice, which may be independent of the concurrent analgesic action and possibly mediated via the supraspinal serotonergic system and downstream GABA_A receptor.     

Comparison of the effects of zaleplon,zolpidem, and triazolam at various GABA(A) receptor subtypes

The pyrazolopyrimidine zaleplon is a hypnotic agent that acts at the benzodiazepine recognition site of GABA(A) receptors. Zaleplon, like the hypnotic agent zolpidem but unlike classical benzodiazepines, exhibits preferential affinity for type I benzodiazepine (BZ(1)/omega(1)) receptors in binding assays. The modulatory action of zaleplon at GABA(A) receptors has now been compared with those of zolpidem and the triazolobenzodiazepine triazolam. Zaleplon potentiated GABA-evoked Cl(-) currents in Xenopus oocytes expressing human GABA(A) receptor subunits with a potency that was higher at alpha1beta2gamma2 receptors than at alpha2- or alpha3-containing receptors. Zolpidem, but not triazolam, also exhibited selectivity for alpha1-containing receptors. However, the potency of zaleplon at these various receptors was one-third to one-half that of zolpidem. Zaleplon and zolpidem also differed in their actions at receptors containing the alpha5 or gamma3 subunit. Zaleplon, zolpidem, and triazolam exhibited similar patterns of efficacy among the different receptor subtypes. The affinities of zaleplon for [(3)H]flunitrazepam or t-[(35)S]butylbicyclophosphorothionate ([(35)S]TBPS) binding sites in rat brain membranes were lower than those of zolpidem or triazolam. Furthermore, zaleplon, unlike zolpidem, exhibited virtually no affinity for the peripheral type of benzodiazepine receptor.     

Inhibition of diazepam on morphine-induced hyperactivity, reverse tolerance and postsynaptic dopamine receptor supersensitivity

The effects of diazepam on the development of reverse tolerance and postsynaptic dopamine receptor supersensitivity induced by morphine were examined in mice. A single administration of morphine induced hyperactivity and the morphine-induced hyperactivity was inhibited dose-dependently by the administration of diazepam (1, 2 and 4 mg x kg(-1), i.p.), an agonist for benzodiazepine receptor linked to the GABA(A) receptor. Daily repeated administration of morphine developed reverse tolerance to the hyperactivity of morphine. The concomitant administration of diazepam inhibited the morphine-induced hyperactivity and the diazepam administration prior to and during the chronic administration of morphine in mice inhibited the development of reverse tolerance to the hyperactivity of morphine (10 mg x kg(-1), s.c.). Postsynaptic dopamine receptor supersensitivity was also developed in reverse tolerant mice that had received the same morphine. The development of postsynaptic dopamine receptor supersensitivity was evidenced by the enhanced ambulatory activity of apomorphine (2 mg x kg(-1), s.c.). Diazepam also inhibited the development of postsynaptic dopamine receptor supersensitivity induced by the chronic administration of morphine. These results suggest that the hyperactivity, reverse tolerance and postsynaptic dopamine receptor supersensitivity induced by morphine may be modulated via the activation of the GABA(A) receptor induced by diazepam.     

苯二氮类受体的结构功能与苯二氮类耐受性和依赖性机制的研究进展

ＧＡＢＡＡ受体是脑内重要的抑制性受体。该受体是由５种亚基组成的五聚体大分子,目前已知的亚基种类共有６类１９种。苯二氮艹卓类通过作用于ＧＡＢＡＡ受体发挥其药理作用,而其慢性使用引起的耐受性和依赖性也与ＧＡＢＡＡ受体的改变密切相关,包括ＧＡＢＡＡ受体功能和数量的改变以及亚基的转录水平和翻译后的变化。本文简要综述了ＧＡＢＡＡ受体的功能结构及苯二氮艹卓类耐受性和依赖性的分子机制。     

The effect of treatment regimen on the development of tolerance to the sedative and anxiolytic effects of diazepam

Rationale: Chronic treatment with benzodiazepines results in tolerance to their sedative and anxiolytic effects and there is considerable evidence that different mechanisms underlie the development of tolerance to different behavioural effects. Objective: The purpose of the present experiment was to compare the behavioural effects of chronic treatment with diazepam (15 mg/kg per day) given as daily subcutaneous injections or by osmotic minipump. Both regimens resulted in continual receptor occupancy, but the daily injections also provided a period of higher brain concentrations. Methods: Rats were tested in the holeboard, which provides measures of exploration and locomotor activity, and in the elevated plus-maze and social interaction tests of anxiety. For those in the subcutaneous injection group the tests were 2 h after injection, when brain concentrations were highest. Results: Despite a higher brain concentration in the injected group, both groups showed tolerance to diazepam’s sedative effects, after 7 days of treatment. In contrast, in the elevated plus-maze, there was tolerance to the anxiolytic effects in the pump group after 14 days, but a persisting anxiolytic effect in the injected group at 14 and 28 days. Whilst higher brain concentrations could explain this result in the plus-maze, they cannot account for the pattern observed in the social interaction test, where the injection group showed a significant anxiogenic effect at 28 days. Conclusions: Whereas the mechanism underlying tolerance to the sedative effects of diazepam was insensitive to the different treatment regimens, the results suggest that different adaptive mechanisms were triggered in the two tests of anxiety with a differential sensitivity to the treatment regimen. The adaptive mechanism predominating in the social interaction test was favoured by the injection regimen which produced intermittent peak concentrations. This mechanism seems to be an oppositional one, leading to an anxiogenic response, which was manifest despite high brain concentrations of diazepam at the time of testing. Received: 12 July 1998 / Final version: 9 March 1999