[THE STUDY OF THE EFFECTS OF ANXYOLYTIC, ANTIOXIDANT, IMMUNOCORRECTOR AND HYPERBARIC OXYGENATION ON THE DYNAMICS OF MAIN BLOOD GAS AND ELECTROLYTE INDICES AND BEHAVIORAL RESPONSE IN EXPERIMENTAL STRESS MODEL]

Experiments on the model of immobilization stress in albino mice showed that a combination of mexidol, thymogen, and hyperbaric oxygenation reduced adverse effects of diazepam on behavioral response of animals in the black-and-white chamber and elevated cross maze tests and led to optimization of the blood gas composition as manifested by increased oxygen tension, normalization of the partial pressure of carbon dioxide, and restoration of the acid-base balance and blood bicarbonate level. The proposed combined treatment can be recommended for the treatment of patients with stress-induced pathology.

The anxiolytic-like effect of 5-HT1B receptor ligands in rats: a possible mechanism of action

We have examined the effect of lesions of 5-hydroxytryptamine (5-HT) neurons, produced by p-chloroamphetamine (p-CA; 2 times 10 mg kg−1), and the influence of flumazenil (Ro 15–1788, 10 mg kg−1), a benzodiazepine receptor antagonist, on the anxiolytic-like activity of CP 94253 (5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1-H-pyrrolo[3,2-b]pyridine), a 5-HT1B receptor agonist, SB 216641 (N-[3-[3-(dimethylamino)ethoxy]-4-methoxyphenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-[1,1′-biphenyl]-4-carboxamide), a 5-HT1B receptor antagonist, and GR 127935 (N-[4-methoxy-3-(4-methyl-l-piperazinyl)phenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-1, 1′-biphenyl-4-carboxamide), a 5-HT1B/1D receptor antagonist, in the Vogel conflict drinking test in rats. Diazepam was used as a reference compound. CP 94253 (2.5 mg kg−1), SB 216641 (2.5 mg kg−1), GR 127935 (10 mg kg−1) and diazepam (5 mg kg−1) significantly increased the number of shocks accepted during experimental sessions in the conflict drinking test in vehicle- and p-CA-pretreated rats. Flumazenil did not change the anxiolytic-like effect of CP 94253 (2.5 mg kg−1), but wholly blocked the anxiolytic-like effects of SB 216641 (2.5 mg kg−1), GR 127935 (10 mg kg−1) and diazepam (5 mg kg−1). p-CA and flumazenil alone were inactive in the conflict drinking test. The results suggested that the anxiolytic-like effect of the 5-HT1B receptor ligands CP 94253, SB 216641 and GR 127935 was possibly linked to the postsynaptic 5-HT1B receptors or/and 5-HT1B heteroreceptors. The results suggested also that benzodiazepine receptors were indirectly involved in the effects of SB 216641 and GR 127935 (but not of CP 94253), which might have been due to a possible interaction between the 5-HT and the GABA/benzodiazepine systems.

Role of nitric oxide in the development of tolerance to diazepam-induced motor impairment in mice

Chronic treatment with the benzodiazepines is well known to produce tolerance, which has been extensively documented to be attributed to modifications in the gamma-aminobutyric acid (GABA)ergic neurotransmission. However, literature data have also suggested the participation of different neurotransmitter systems, including glutamatergic, in benzodiazepine tolerance. The purpose of the present study was to determine the role of nitric oxide (NO) in the development of tolerance to the motor dysfunction induced by chronic administration of diazepam. The motor performance was assessed on the 1st and 10th day of experiment, using the rotarod and chimney tests in mice. Treatment of animals with both non-selective NO synthase (NOS) inhibitors: N(G)-nitro-L-arginine methyl ester (L-NAME), N(G)-nitro-L-arginine (L-NOARG) and selective NOS inhibitor: 7-nitroindazole was able to prevent the development of tolerance to the motor impairing effect of diazepam. Moreover, administration of L-arginine, a NO precursor, facilitated the development of diazepam-induced tolerance in rotarod test. These findings suggest that NO may be involved, at least in part, in the tolerance to the motor dysfunction, developed during the chronic administration of diazepam in mice.

Memory enhancing activity of Anwala churna (Emblica officinalis Gaertn.): An Ayurvedic preparation

Ayurveda means "the science of life". Ayur means "life" and Veda means "knowledge or science". It is the oldest medical system in the world. Its origins can be traced as far back as 4500 BC, to four ancient books of knowledge, (the "Vedas") and it is still officially recognized by the government of India. The present study was aimed at investigating the effects of Anwala churna (Emblica officinalis Gaertn.), an Ayurvedic preparation on memory, total serum cholesterol levels and brain cholinesterase activity in mice. Anwala churna was administered orally in three doses (50, 100 and 200 mg/kg) for fifteen days to different groups of young and aged mice. Elevated plus maze and passive avoidance apparatus served as the exteroceptive behavioral models for testing memory. Diazepam-, scopolamine- and ageing-induced amnesia served as the interoceptive behavioral models. Total serum cholesterol levels and brain cholinesterase activity also estimated. Anwala churna (50, 100 and 200 mg/kg, p.o.) produced a dose-dependent improvement in memory scores of young and aged mice. Furthermore, it reversed the amnesia induced by scopolamine (0.4 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.). Interestingly, brain cholinesterase activity and total cholesterol levels were reduced by Anwala churna administered orally for 15 days. Anwala churna may prove to be a useful remedy for the management of Alzheimer's disease on account of its multifarious beneficial effects such as, memory improving property, cholesterol lowering property and anticholinesterase activity.

First-line therapy for theophylline-associated seizures

Theophylline-associated seizures (TAS) are considered a neurologic emergency, as they can sometimes be intractable and difficult to stop with standard treatments such as intravenous administration of diazepam. As a consequence, a proportion of patients who experience status epilepticus while receiving theophylline will require endotracheal intubation. The optimal first-line therapy for TAS has not yet been fully investigated. We compared 54 cases of TAS with 779 cases of non-TAS, that had presented at a single institution between 1991 and 2002. Among the 54 cases of TAS, 36 experienced generalized tonic-clonic seizures, with the remainder experiencing partial seizures. TAS occurred mainly in children under 3 years of age, and serum theophylline levels were within the therapeutic range in 78% of the cases. The duration of TAS tended to be longer than for non-TAS, and intravenous administration of diazepam was less effective in controlling TAS (45%), compared with non-TAS (68%). Many cases required repeated injections of diazepam, and 15 cases (27%) eventually required endotracheal intubation. Reports concerning the therapy for TAS were also reviewed. Theophylline is known to antagonize the effects of benzodiazepines, and this may explain why drugs such as diazepam are relatively ineffective in treating TAS. In TAS, the prompt use of barbiturates is recommended when diazepam is not effective, to avoid potential brain injury secondary to status epilepticus.

Imidazenil: An antagonist of the sedative but not the anticonvulsant action of diazepam

Flumazenil (FLU), a specific benzodiazepine (BZ) receptor antagonist has been used in the treatment of acute BZ intoxication or the alleviation of BZ-induced withdrawal syndrome on the basis of its weak partial agonist action at GABA(A) receptors. However, given to patients, FLU can worsen diazepam-induced withdrawal syndrome by lowering seizure threshold. We therefore investigated whether imidazenil, a selective positive allosteric modulator of GABA action at GABA(A) receptors containing alpha5 subunit, can antagonize diazepam-induced sedative action and suppression of locomotor activity without affecting diazepam anti-bicuculline action. We report here that while FLU (16.5 micromol/kg) showed no effect on locomotor activity and bicuculline-induced convulsion, it completely antagonized diazepam (10.5 micromol/kg) anti-bicuculline action and the suppression of locomotor activity. However, imidazenil (0.76 micromol/kg) elicited anti-bicuculline action and was dose-dependently antagonized by FLU (16.5 and 33 micromol/kg). Furthermore, imidazenil showed no effect on path length traveled but slightly decreased (40%) horizontal activity when compared to diazepam (85%), and maintained the anti-bicuculline action of diazepam to a threshold level similar to that observed with diazepam. Whereas cross-tolerance between BZs has been reported in animals and humans, we previously reported the absence of cross-tolerance between imidazenil and diazepam. Thus, we suggest that imidazenil might be more effective than FLU at alleviating the withdrawal syndrome associated with long-term BZ administration.

Strain differences in diazepam metabolism at its three metabolic sites in sprague-dawley, brown norway, dark agouti, and wistar strain rats

Knowledge of strain differences in drug metabolism is important for the selection of animals for pharmacokinetic, pharmacodynamic, and toxicological studies. Hepatic microsomes from Sprague-Dawley (SD) and Brown Norway (BN) rats had 300-fold higher diazepam p-hydroxylation activity than Dark Agouti (DA) and Wistar (W) rats at a low diazepam concentration (3 microM). Kinetic studies indicated that diazepam p-hydroxylation in SD and BN rats proceeded with lower K(m) and higher V(max) values than it did in DA and W rats. However, the expression levels of cytochrome P450 CYP2D1, the reported enzyme for diazepam p-hydroxylation, did not cosegregate with the activity. These results suggest the presence of a new high-affinity diazepam p-hydroxylation enzyme other than CYP2D1 in SD and BN rats. DA rats showed 3- and 2-fold higher diazepam 3-hydroxylation and N-desmethylation activities, respectively, than the other rat strains. In agreement with this, DA rat liver microsomes had a higher expression of CYP3A2, which is responsible for diazepam 3-hydroxylation and partly responsible for N-desmethylation. Values of CL(int) (V(max)/K(m)) indicated that p-hydroxy-diazepam is the major metabolite in SD and BN rats, whereas 3-hydroxy-diazepam is the major metabolite in DA and W rats. The sum of the CL(int) in each strain was in the order of DA > SD = BN >> W. Strain differences in the pharmacodynamics of diazepam between SD and DA rats may be due to these differences in diazepam metabolism. We found that both the rate of elimination of diazepam and the major metabolic pathways in diazepam metabolism differed among the different rat strains due to polymorphic expression of the two enzymes involved in diazepam metabolism.

Inhibition of the metabolism of etizolam by itraconazole in humans: evidence for the involvement of CYP3A4 in etizolam metabolism

OBJECTIVE

To clarify the involvement of cytochrome P450 (CYP) 3A4 in the metabolism of etizolam.

METHODS

The effects of itraconazole, a potent and specific inhibitor of CYP3A4, on the single oral dose pharmacokinetics and pharmacodynamics of etizolam were examined. Twelve healthy male volunteers received itraconazole (200 mg/day) or placebo for 7 days in a double-blind randomized crossover manner, and on the 6th day they received a single oral 1-mg dose of etizolam. Blood samplings and evaluation of psychomotor function using the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 24 h after etizolam dosing. Plasma concentration of etizolam was measured by means of high-performance liquid chromatography.

RESULTS

Itraconazole treatment significantly increased the total area under the plasma concentration-time curve (AUC; 213+/-106 ng rectangle h/ml versus 326+/-166 ng rectangle h/ml, P<0.001) and the elimination half-life (12.0+/-5.4 h versus 17.3+/-7.4 h, P<0.01) of etizolam. The 90% confidence interval of the itraconazole/placebo ratio of the total AUC was 1.38-1.68, indicating a significant effect of itraconazole. No significant change was induced by itraconazole in the two pharmacodynamic parameters.

CONCLUSION

The present study suggests that itraconazole inhibits the metabolism of etizolam, providing evidence that CYP3A4 is at least partly involved in etizolam metabolism.

Chronic pregnenolone effects in normal humans: attenuation of benzodiazepine-induced sedation

Pregnenolone is the major steroid precursor in humans. It is also a "neurosteroid" and possesses intrinsic behavioral and brain effects in animals, affecting the GABA(A) and other receptors. In two preliminary studies, we sought to characterize its tolerability and psychotropic effects in humans. In Study 1, 17 normal volunteers received pregnenolone and placebo for 4 weeks each (15 mg PO per day x2 weeks followed by 30 mg PO per day x2 weeks, vs. placebo x4 weeks) in a within-subject, double-blind, cross-over design, with a 4 week drug-free washout period separating the two arms. Subjects' behavioral responses were assessed at the beginning and end of the 4-week pregnenolone arm and the 4-week placebo arm. Pregnenolone was generally well-tolerated but, by itself, had no significant effects on mood, memory, self-rated sleep quality or subjective well-being. In Study 2, 11 subjects from Study 1 received a single dose of diazepam (0.2 mg/kg PO) immediately following completion of Study 1 in order to assess, in a between groups design, the impact of 4-weeks' pre-treatment with pregnenolone (N=5) vs. placebo (N=6) on the acute sedative, amnestic and anxiolytic effects of this benzodiazepine. Pregnenolone-pretreated subjects showed significantly less sedation following diazepam (p<0.03); this effect was clinically apparent. Diazepam's amnestic effects were non-significantly attenuated, and ratings of anxiety were unaffected. These pilot data, based on small samples, raise the possibility that chronically administered pregnenolone antagonizes certain acute effects of benzodiazepines and may enhance arousal via antagonist or inverse agonist actions at the benzodiazepine/GABA(A) receptor complex. Further larger-scale studies, utilizing a broader range of doses and experimental conditions, are warranted.

QUANTITATIVE PREDICTION OF THE IN VIVO INHIBITION OF DIAZEPAM METABOLISM BY OMEPRAZOLE USING RAT LIVER MICROSOMES AND HEPATOCYTES

The diazepam (DZ)-omeprazole (OMP) interaction has been selected as a prototype for an important drug-drug interaction involving cytochrome P450 inhibition. The availability of an in vivo K(i) value (unbound K(i), 21 microM) obtained from a series of steady-state inhibitor infusion studies allowed assessment of several in vitro-derived predictions of this inhibition interaction. Studies monitoring substrate depletion with time were used to obtain in vitro K(i) values that were evaluated against the more traditional metabolite formation approach using microsomes and hepatocytes. OMP inhibited the metabolism of DZ to its primary metabolites 4'-hydroxydiazepam, 3-hydroxydiazepam, and nordiazepam to different extents over a range of concentrations (0.3-150 microM), and a competitive inhibition model best fitted the data. The K(i) values observed using the substrate depletion approach (16 +/- 3 microM and 7 +/- 2 microM in microsomes and hepatocytes, respectively) were in good agreement with the overall weighted K(i) values obtained using the standard metabolite formation approach (12 +/- 2 microM and 16 +/- 5 microM in microsomes and hepatocytes, respectively). In vitro binding and cell uptake studies as well as human serum albumin studies in hepatocytes confirmed the importance of both intracellular and extracellular unbound concentrations of inhibitor when considering inhibition predictions. Both kinetic approaches and both in vitro systems predicted the in vivo interaction well and provide a good example of the ability of in vitro inhibition studies to quantitatively predict an in vivo drug-drug interaction successfully.

[How do diazepam and flumazenil influence respiratory control by the activities of both hypoglossal and phrenic nerves in rabbits?]

BACKGROUND

Upper airway obstruction and inadequate ventilation often arise during sedation and anesthesia by benzodiazepines. To estimate the influence of benzodiazepines on the respiratory control, we studied the effect of diazepam and flumazenil on the neural activity and the respiratory response caused by a brief (60 sec) respiratory arrest (RA) observed in the hypoglossal nerve (HG) and phrenic nerve (PH) in rabbits.

METHODS

Experiments were preformed on adult rabbits vagotomized, paralyzed and ventilated artificially with 50% N2O, 50% oxygen and 0.3-0.5% sevoflurane. We evaluated and compared the effects of diazepam and flumazenil on the peak amplitude (AMP-HG&PH) and the root mean square (RMS-HG&PH) of HG and PH, and respiratory cycle (Tc).

RESULTS

Diazepam depressed HG activity more than PH activity with no influence on Tc. But it did not cause dose-related depression. Flumazenil 0.2 mg.kg-1 completely reversed the respiratory depressions caused by diazepam with the increased Tc. In addition to augmentation of the hypoglossal activity in inspiration, flumazenil caused a rise in its activity in pan-expiratory period in some cases. Additional administration of diazepam 6 mg.kg-1 following flumazenil depressed PH activity again, but did not affect HG activity any more. There was no significant depression in cardiovascular parameters with tested dosages of diazepam and flumazenil. RA response was characterized by raised AMPs and augmented RMSs (delta AMPs, delta RMSs) with marked prolongation in Tc (delta Tc). Diazepam depressed RA response dose dependently, but flumazenil did not seem to antagonize this depression.

CONCLUSIONS

These results suggest that 1) flumazenil is not only a specific antagonist of benzodiazepines but also a potential excitatory agent of hypoglossal nerve activity, and that 2) there is some functional diversity in disposition of benzodiazepine-receptor binding GABAA-receptor responsible for neural respiratory control system.

Discriminative stimulus effects of positive GABAA modulators and other anxiolytics, sedatives, and anticonvulsants in untreated and diazepam-treated monkeys

Positive GABAA modulators and other sedatives, anxiolytics, and anticonvulsants were used to evaluate mechanisms underlying the discriminative stimulus effects of midazolam in untreated monkeys and of flumazenil in monkeys treated with diazepam (5.6 mg/kg/day). Positive GABAA modulators at benzodiazepine (e.g., flunitrazepam and abecarnil) and neuroactive steroid sites (e.g., androsterone) substituted for midazolam in all monkeys; the neuroactive steroids dihydroandrosterone and epipregnanolone substituted for midazolam in two of three monkeys. All positive GABAA modulators attenuated flumazenil in diazepam-treated monkeys; doses of flunitrazepam and abecarnil larger than doses substituting for midazolam were required to attenuate flumazenil, whereas doses of neuroactive steroids smaller than doses substituting for midazolam attenuated flumazenil. Drugs with mechanisms that do not predominantly involve allosteric modulation of GABA (e.g., buspirone, ketamine, valproic acid, and diphenhydramine) did not substitute for midazolam or flumazenil. However, valproic acid enhanced the midazolam discriminative stimulus and attenuated the flumazenil discriminative stimulus; diphenhydramine attenuated the midazolam discriminative stimulus. These results suggest that drugs not sharing a mechanism of action with benzodiazepines can modulate the behavioral effects of benzodiazepines. In addition, this study demonstrates that endogenous ligands, presumably by acting at neuroactive steroid sites on the GABAA receptor complex, share discriminative stimulus effects with benzodiazepines. This study also suggests that positive GABAA-modulating neuroactive steroids are especially potent in attenuating behavioral effects that are related to diazepam withdrawal.

Stereoselective discriminative stimulus effects of zopiclone in rhesus monkeys

RATIONALE

The behavioral effects of racemic zopiclone are similar to those of benzodiazepines that positively modulate GABA at the GABA(A) receptor complex; however, it is not clear how enantiomers or metabolites of zopiclone contribute to the benzodiazepine-like behavioral effects of racemic zopiclone.

OBJECTIVES

Racemic zopiclone, its ( R)- and ( S)- enantiomers, and the ( S)-N-desmethyl metabolite, were evaluated for discriminative stimulus effects in untreated and diazepam treated rhesus monkeys.

METHODS

One group of monkeys discriminated the benzodiazepine midazolam and another group, treated daily with the benzodiazepine diazepam (5.6 mg/kg, PO), discriminated the benzodiazepine antagonist flumazenil.

RESULTS

( RS)-Zopiclone (0.32-17.8 mg/kg) and ( S)-zopiclone (0.1-10 mg/kg) substituted with similar potencies for midazolam (>/=80% midazolam-appropriate responding). The midazolam-like discriminative stimulus effects of ( RS)-zopiclone were antagonized by flumazenil (p K(B)=7.52). ( R)-Zopiclone occasioned a maximum 45% midazolam-appropriate responding at a dose of 100 mg/kg; ( S)-desmethylzopiclone produced saline-appropriate responding up to a dose of 100 mg/kg. All four test compounds occasioned predominantly vehicle-appropriate responding in diazepam treated monkeys discriminating flumazenil. ( RS)-Zopiclone (10 mg/kg) attenuated the discriminative stimulus effects of flumazenil in diazepam treated monkeys.

CONCLUSIONS

These results clearly demonstrate that in rhesus monkeys the discriminative stimulus effects of zopiclone are stereoselective and qualitatively similar to those of midazolam. These results fail to show any benzodiazepine-like or benzodiazepine antagonist-like discriminative stimulus effects for ( S)- N-desmethylzopiclone, suggesting that any behavioral (e.g. anxiolytic) effects of this compound are not the result of actions at benzodiazepine receptors.

Reversal of benzodiazepine-induced renal vasculature relaxation with flumazenil

The effects of the central-type benzodiazepine receptor antagonist flumazenil on renal vascular tone and its ability to reverse the benzodiazepine-induced vasodilation were investigated. The isolated and perfused rat kidney model was used. Flumazenil was unable to modify renal vascular resistance under basal conditions and in noradrenaline-pretreated kidneys. Relaxation induced by diazepam or clonazepam of noradrenaline-preconstricted renal vasculature was blunted by 10 microM flumazenil. These results suggest that central-type benzodiazepine receptors could be involved in benzodiazepine-induced renal vasodilation.

Cardiorespiratory effects of medetomidine-butorphanol, medetomidine-butorphanol-diazepam, and medetomidine-butorphanol-ketamine in captive red wolves (Canis rufus)

Safe, effective, and reversible immobilization protocols are essential for the management of free-ranging red wolves (Canis rufus). Combinations using an alpha2-adrenoceptor agonist and ketamine have been shown to be effective for immobilization but are not reversible and can produce severe hypertension and prolonged or rough recoveries. To minimize hypertension and provide reversibility, 24 red wolves were immobilized using three medetomidine-butorphanol (MB) combinations without the use of ketamine in the initial injection. All wolves were administered medetomidine (0.04 mg/kg i.m.) and butorphanol (0.4 mg/kg i.m.). Seven wolves received no other immobilization agents (MB wolves), nine received diazepam (0.2 mg/kg i.v.) at the time they were instrumented (MBD wolves), and eight received ketamine (1 mg/kg i.v.) 30 min after instrumentation (MBK30 wolves). Physiologic parameters were monitored during immobilization. The heart rate was similar among the three groups for the first 30 min, and marked bradycardia was noted in one wolf from each group. Hypertension was observed initially in all three groups but was resolved within 10-30 min. The MBK30 wolves had significant elevations in heart rate and transient hypertension after intravenous ketamine administration. Most wolves had mild to moderate metabolic acidemia. Immobilizing drugs were antagonized in all wolves with atipamezole (0.2 mg/kg i.m.) and naloxone (0.02 mg/kg i.m.). The medetomidine-butorphanol-diazepam wolves were also given flumazenil (0.04 mg/kg i.v.). All wolves were standing within 12 min and were fully recovered within 17 min. Medetomamine-butorphanol and MBD combinations provided effective and reversible immobilization of red wolves without the sustained hypertension associated with the use of alpha2-adrenoceptor agonist-ketamine combinations. Delaying the administration of ketamine reduced its hypertensive effects.

Effects of acute and subchronic administration of dexefaroxan, an alpha(2)-adrenoceptor antagonist, on memory performance in young adult and aged rodents

The present study examined the influence of dexefaroxan, a potent and selective alpha(2)-adrenoceptor antagonist, on cognitive performance in rodents. In young adult rats, dexefaroxan reversed the deficits induced by UK 14304 [5-bromo-N-(4,5-dihydro-1-H-imidazol-2-yl)-6-quinoxalinamine], scopolamine, and diazepam in a passive avoidance task. In this test, dexefaroxan also attenuated the spontaneous forgetting induced by a 15-week training-testing interval. Moreover, dexefaroxan, given immediately after training, increased the memory performance of rats trained with a weak electric footshock in the passive avoidance test, facilitated spatial memory processes in the Morris water maze task in rats, and increased the performance of mice in an object recognition test. Thus, dexefaroxan appears to have a promnesic effect in these tests by facilitating the processes of memory retention, rather than acquisition or other noncognitive influences. The facilitatory effects of dexefaroxan in young adult rats persisted even after a 21- to 25-day constant subcutaneous infusion by using osmotic minipumps, indicating that tolerance to the promnesic effect of the drug did not occur during this prolonged treatment interval. Furthermore, in the passive avoidance and Morris water maze tests, dexefaroxan ameliorated the age-related memory deficits of 24-month-old rats to a level that was comparable to that of young adult animals, and reversed the memory deficits induced by excitotoxin lesions of the nucleus basalis magnocellularis region. Together, these findings support a potential utility of dexefaroxan in the treatment of cognitive deficits occurring in Alzheimer's disease.

Effects of cholecystokinin tetrapeptide (CCK(4)) and anxiolytic drugs on the electrically evoked [(3)H]5-hydroxytryptamine outflow from rat cortical slices

The outflow of [(3)H]5-hydroxytryptamine ([(3)H]5-HT) from electrically stimulated rat cortical slices was measured to ascertain the modulatory role of endogenous cholecystokinin (CCK) on the amine outflow and to test the hypothesis that different anxiolytic compounds inhibit 5-HT secretion. The [(3)H]5-HT outflow evoked at 10 Hz was increased up to +30% by CCK(4) 300-1000 nM, the effect being prevented by the CCK(B) receptor antagonist GV 150013, 3 nM. The limited sensitivity to CCK(4) seemed to depend on 5-HT auto-receptor feedback because pre-treatment with 100 nM methiothepin enhanced the [(3)H]5-HT outflow and lowered the CCK(4) threshold concentration from 300 to 30 nM. In addition, pre-treatment with 1 microM bacitracin to inhibit CCK metabolism increased [(3)H]5-HT efflux. This effect was concentration-dependently counteracted by GV150013 suggesting the presence of an endogenous CCK positive modulation. GV150013 30 nM, the 5-HT(1A) partial agonist buspirone 300 nM and the GABA(A) receptor modulator diazepam 10 nM, known to have anxiolytic properties, all significantly reduced the [(3)H] amine outflow from cortical slices by about 20%. This inhibition depended on their interaction with their respective receptors, which seemed to restrain the activity of functionally interconnected glutamatergic interneurones. In fact, APV (50 microM) and NBQX (10 microM) prevented the effect of the anxiolytic compounds. Thus, anxiolytic drugs with different receptor targets can reduce 5-HT outflow by dampening the glutamatergic signal, and in turn, the secretory process of the serotonergic nerve ending.

Chemical anesthesia of northern sea otters (Enhydra lutris): results of past field studies

Between 1987 and 1997, we chemically immobilized 597 wild sea otters (Enhydra lutris) in Alaska for the collection of biological samples or for surgical instrumentation. One drug-related sea otter fatality occurred during this time. Fentanyl in combination with diazepam produced consistent, smooth inductions with minimal need for supplemental anesthetics during procedures lasting 30-40 min. Antagonism with naltrexone or naloxone was rapid and complete, although we observed narcotic recycling in sea otters treated with naloxone. For surgical procedures, we recommend a fentanyl target dose of 0.33 mg/kg of body mass and diazepam at 0.11 mg/kg. For nonsurgical biological sample collection procedures, we recommend fentanyl at 0.22 mg/kg and diazepam at 0.07 mg/kg. We advise the use of the opioid antagonist naltrexone at a ratio of 2:1 to the total fentanyl administered during processing.

[3H]Ro 15-1788 binding sites to brain membrane of the saltwater Mugil cephalus

The equilibrium binding parameters of the benzodiazepine antagonist [3H]Ro 15-1788 (8-fluoro-3-carboethoxy-5,6-dihydro-5-methyl-6-oxo-4H-imidazol-[1,5-a]-1,4 benzodiazepine) were evaluated in brain membranes of the saltwater teleost fish, Mugil cephalus. To test receptor subtype specificity, displacement studies were carried out by competitive binding of [3H]Ro 15-1788 against six benzodiazepine receptor ligands, flunitrazepam [5-(2-fluoro-phenyl)-1,3-dihydro-1-methyl-7-nitro-2H-1,4-benzodiazepin-2-one], alpidem [N,N-dipropyl-6-chloro-2-(4-chlorophenyl)imidazo[1,2-a]pyridine-3-acetamide], zolpidem [N,N-6 trimethyl-2-(4-methyl-phenyl)imidazo[1,2-a]pyridine-3-acetamide hemitartrate], and beta-CCM (methyl beta-carboline-3-carboxylate). Saturation studies showed that [3H]Ro 15-1788 bound saturatably, reversibly and with a high affinity to a single class of binding sites (Kd value of 1.18-1.5 nM and Bmax values of 124-1671 fmol/mg of protein, depending on brain regions). The highest concentration of benzodiazepine recognition sites labeled with [3H]Ro 15-1788 was present in the optic lobe and the olfactory bulb and the lowest concentration was found in the medulla oblongata, cerebellum and spinal cord. The rank order of displacement efficacy of unlabelled ligands observed suggested that central-type benzodiazepine receptors are present in one class of binding sites (Type I-like) in brain membranes of Mugil cephalus. Moreover, the uptake of 36Cl- into M. cephalus brain membrane vesicles was only marginally stimulated by concentrations of GABA that significantly enhanced the 36Cl- uptake into mammalian brain membrane vesicles. The results may indicate a different functional activity of the GABA-coupled chloride ionophore in the fish brain as compared with the mammalian brain.

Anxiolytic effects of valproate and diazepam in mice are differentially sensitive to picrotoxin antagonism

Although it is widely believed that the anxiolytic effects of benzodiazepines are mediated through facilitation of GABA(A) receptor function, behavioural studies have to date provided rather weak support for this hypothesis. In particular, considerable inconsistency has been noted both for the effects of GABAergic manipulations in animal models of anxiety and the ability of GABA(A) receptor antagonists to block the anxiolytic effects of diazepam (DZ) and chlordiazepoxide. In view of the sensitivity of the murine plus-maze to the anxiety-modulating effects of GABAergic agents as well as classical benzodiazepines, the current study examined the extent to which the anxiolytic actions of valproic acid (VPA) and DZ in this test involve picrotoxin (PX)-sensitive receptor mechanisms. Subjects were male DBA/2 mice, test duration was 5 min, and ethological scoring methods were employed. Our results show that, while devoid of intrinsic behavioural effects under present test conditions, PX (0.25-0.5 mg/kg) selectively antagonised the anxiolytic-like (but not other) effects of VPA (400 mg/kg). In contrast, the same doses of PX failed to block any of the behavioural changes induced by DZ (1.5 mg/kg), including disinhibition of open arm exploration. These data suggest that the plus-maze anxiolytic effects of DZ in DBA/2 mice are not mediated through PX-sensitive GABA(A) receptors. Further studies will be required to assess the generality of present findings to other mouse strains, species and behavioural paradigms.

Diazepam-binding inhibitor-like activity in rat cerebrospinal fluid after stimulation by an aversive quinine taste

Cerebrospinal fluid (CSF) taken from rats after stimulation by an aversive quinine taste (hereafter called quinine CSF) administered into the fourth ventricle of mice suppressed their intake of 5% sucrose solution. We examined the effects of CSF on glutathione-induced tentacle ball formation (TBF) of hydra to determine the change in CSF components associated with aversive taste stimuli. The suppressive activity of quinine CSF on TBF in the presence of 3 microM S:-methyl-glutathione (GSM) was markedly lower than that of CSF obtained from control rats (control CSF). Pronase-treated quinine CSF had suppressive activity similar to that of control CSF. The active principle passed through an ultrafiltration membrane, with a molecular weight cut-off of 30 kDa, but not through one with a cut-off of 3 kDa. A peptide fragment of diazepam-binding inhibitor (DBI) nullified the suppression of TBF at 3 microM GSM by control CSF. The nullifying activity of quinine CSF was not observed after treatment with a benzodiazepine receptor preparation that was able to bind DBI. When flumazenil, a benzodiazepine receptor antagonist, was given to mice, the suppression of the intake of 5% sucrose solution by quinine CSF was partially reversed. It is suggested that quinine CSF contains a DBI-like substance.

Flumazenil prevents diazepam-elicited anticonvulsant action and concomitant attenuation of glutamate overflow

Systemic administration of diazepam (5 mg/kg, i.p.) produced a prompt anticonvulsant effect in pilocarpine-induced seizures in freely moving rats. The anticonvulsant effect was associated with significant attenuation of pilocarpine-evoked increases in extracellular hippocampal glutamate levels to below the baseline levels. The purpose of the present microdialysis study, therefore, was to investigate if the effect of diazepam on glutamate release was mediated at the level of the benzodiazepine gamma-aminobutyric acid(A) (GABA(A)) receptor complex to preclude any non-GABAergic mechanisms. Systemic administration of the specific benzodiazepine-receptor antagonist flumazenil (10 mg/kg, i.p. )-elicited complete reversal of diazepam-evoked anticonvulsant action and concomitant attenuation of extracellular glutamate efflux below the baseline levels. This provides evidence that under the given experimental conditions, diazepam-evoked alterations in glutamate overflow associated with the anticonvulsant action were indeed mediated at the level of benzodiazepine-GABA(A) receptor complex, possibly involving the modulation of both pre- and post-synaptic sites of the receptor complex.

Diazepam attenuation of somatostatin binding and effect of somatostatin on accumulation of inositol 1,4,5-trisphosphate in the rat frontoparietal cortex

Numerous reports in both humans and animals have confirmed that benzodiazepines produce amnesia; however, mechanisms mediating this effect are not clear. In view of the important role of brain somatostatin (SRIF) in the cognitive function of rats, this study sought to determine if the benzodiazepine, diazepam, alters somatostatinergic system in the rat frontoparietal cortex. Intraperitoneal (i.p.) administration of diazepam (5 mg/kg/day) to male Wistar rats (200-250 g) for 3 or 7 days decreased the number of SRIF receptors (26 and 37%, respectively) in synaptosomes from the frontoparietal cortex, without influencing their apparent affinity. This decrease in the tracer binding was not attributable to a direct effect of diazepam on SRIF receptors, because no decrease of SRIF binding was induced by a large concentration of diazepam (10(-4) M) when the drug was added to a preparation of synaptosomes from frontoparietal cortex of untreated rats. To determine if the effect of diazepam on SRIF binding is related to the binding of diazepam to its recognition site on the GABA(A) receptor, a benzodiazepine antagonist, 2-phenylpyrazolo[3,4-c]quinolin-3(5H)-one (CGS 8216) was administered before the diazepam injection. Pretreatment with CGS 8216 (20 mg/kg/day, i.p.) blocked completely the diazepam-induced decrease in the number of SRIF receptors. CGS 8216 alone had no observable effect. The decrease in the number of 125I-Tyr11-SRIF receptor induced by diazepam was accompanied by a decrease in the effect of SRIF, after 15 seconds of stimulation, on inositol 1,4, 5-trisphosphate (IP3) mass accumulation in the rat frontoparietal cortex at 3 (64%) or 7 days (59%) after its administration. Diazepam alone had no observable effect on mass accumulation of IP3. After 14 days of daily diazepam injections, the levels of binding of 125I-Tyr11-SRIF in the frontoparietal cortex returned to control values, coinciding with the tolerance that develops to this benzodiazepine agonists when administered chronically. The decrease in IP3 levels was still observed after 14 days (57%) diazepam administration. Diazepam and CGS 8216 did not affect SRIF-like immunoreactivity levels in the frontoparietal cortex at the three time intervals studied (3, 7 or 14 days). The alteration of frontoparietal cortex SRIF receptor-effector system after 3 or 7 days of diazepam treatment suggests that somatostatinergic neurotransmission plays a role in the mechanism of diazepam action on memory.

The role of the benzodiazepine-GABA system in the memory processes of the day-old chick

This series of experiments investigated the effect of the benzodiazepine diazepam on memory formation in day-old chicks trained on a single-trial, passive-avoidance task. The findings indicate that diazepam has a dose-specific and time-dependent effect on memory processes. A 0.125-mg/kg dose of diazepam administered immediately after training led to amnesia in these subjects only after 30 min following learning. Pretreatment with bicuculline and flumazenil were effective in ameliorating the memory deficits caused by diazepam, and consolidated memory function in saline-treated controls following strong and weak aversant training. These findings suggest that benzodiazepine effects on memory are mediated by their effects on arousal, possibly by the release of noradrenaline, which is critical to the establishment of long-term memory.

3-Aryl-[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-ones: tricyclic heteroaromatic derivatives as a new class of benzodiazepine receptor ligands

A series of 3-substituted [1,2,4]triazino[4,3-c]benzimidazoles V were prepared and tested at the central benzodiazepine receptor (BzR). These compounds were designed as rigid analogues of the previously described N-benzylindolylglyoxylylamide derivatives IV. The title compounds V showed an affinity which depended directly on the presence of the N(10)-H group and an aromatic ring at position 3. Some of them elicited a 2- or 3-fold higher affinity with respect to that of the indolylglyoxylylamide derivatives IV (R = H). The GABA ratio and [(35)S]-tert-butylcyclophosphorothionate binding data revealed an efficacy profile of partial inverse agonists/antagonists for compounds 1c,e,f,j,k, and of a partial agonist for 2c. This last compound proved to be effective in antagonizing pentylenetetrazole-induced seizures in mice. Attempts were made to interpret the structure-affinity relationships of compounds V in the light of possible tautomeric equilibria involving the ligands.

NMDA- but not kainate-mediated events reduce efficacy of some antiepileptic drugs against generalized tonic-clonic seizures in mice

PURPOSE

The aim of this study was to evaluate the efficacy of conventional antiepileptic drugs (AEDs) against the generalized tonic-clonic seizures in mice subjected to the subconvulsive doses of N-methyl-D-aspartate (NMDA) or kainate.

METHODS

Mice were given NMDA and kainate in the doses of 50.0 and 9.0 mg/kg i.p., respectively [i.e., equal to 75% of their CD16 values (convulsive dose in 16% of the animals studied)]. Subsequently the anticonvulsive potential of conventional AEDs against the maximal electroshock-induced seizures was estimated. Where necessary, the plasma levels of AEDs were assessed.

RESULTS

NMDA or kainate application did not affect the electroconvulsive threshold. NMDA, but not kainate, diminished the antiepileptic activity of diazepam (DZP) and carbamazepine (CBZ), increasing their 50% effective doses (ED50s) from 14.1 and 8.6 to 19.0 and 12.1 mg/kg i.p., respectively. Neither NMDA nor kainate affected the ED50 for valproate (VPA), phenobarbital (PB), or diphenylhydantoin (DPH) against electroconvulsions. NMDA-evoked effects were reversed with the use of the NMDA antagonist, D-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 40116) and were not accompanied by the alterations in the free plasma levels of AEDs.

CONCLUSIONS

The NMDA-mediated events, but not kainate-related ones, seem to be involved in the protective action of DZP and CBZ against maximal electroshock-induced seizures. Moreover, it might be concluded that when subthreshold activation of NMDA receptors adds to other epileptogenic factors, DZP and CBZ are less efficacious. Presented data indicate that in such situations, adding the NMDA receptor antagonist (at very low doses) to the AED may yield beneficial therapeutic effects.

Diazepam-induced hyperphagia in mice is sensitive to quinpirole

The present trial examined the possibility that diazepam (DZP, 1 mg/kg) induces hyperphagia by acting on the dopaminergic system. Quinpirole (QP), dopamine D-2 receptor agonist, was used for this purpose. Mice fasted for 24 hr were treated with QP 1 (QP-1) or 2 (QP-2) mg/kg 30 min prior to termination of the starvation. DZP was given to untreated mice and half of the QP-1 and QP-2 treated mice 10 min before the termination of the starvation. Food consumed during six 30 min intervals (30 min-feeding), food consumed for 3 hr (total feeding), time required to enter the room containing food by passing through a maze with four multiple routes (time to banquet), latent period to commencement of eating food after entering the banquet room (latent period), and feeding frequency for the 30 min intervals as well as for 3 hr were measured. DZP stimulated feeding, shortened the latent period without affecting the time to banquet and increased the feeding frequency. The hyperphagic effect was restricted to the first 30 min interval only. Both QP-1 and QP-2 first reduced, then progressively stimulated, and finally reduced feeding without modifying total feeding, thus making a bell-shaped profile. They also prolonged both the time to banquet and the latent period, and reduced the feeding frequency of the first 30 min interval but not that for 3 hr. Both QP-1 and QP-2 canceled all the effects of DZP. These results imply that dopamine D2 receptor is involved in the induction of hyperphagia by DZP.

Flumazenil in children after esophagogastroduodenoscopy

OBJECTIVE

Our aim was to evaluate if the routine use of the benzodiazepine antagonist flumazenil would shorten postprocedure recovery times after esophagogastroduodenoscopy in pediatric patients receiving standard intravenous conscious sedation with the benzodiazepine diazepam in combination with meperidine.

METHODS

Upper endoscopy was performed using intravenous conscious sedation with standardized doses of diazepam and meperidine on 29 children, age range 6-18 yr. Patients were randomized in a double-blind fashion to receive either intravenous normal saline (placebo) or 0.01 mg/kg (maximum, 1.0 mg) flumazenil within 5 min of procedure completion. Evaluation of the degree of sedation using a modified Observer' s Assessment of Alertness/Sedation Scale was performed presedation, immediately before reversal solution administration, and serially over 60 min after reversal solution injection.

RESULTS

Fifteen patients received flumazenil and 14 received placebo; patient group composition did not vary significantly in age and weight. Fifty-four percent of flumazenil patients and 30% of control patients achieved full alertness within 10 min of reversal solution injection. However, this difference between groups was not significant (p > 0.45). Resedation or side effects directly attributable to flumazenil were not observed.

CONCLUSIONS

A single postsedation dose of flumazenil is well-tolerated in children >6 yr old. However, its routine use after esophagogastroduodenoscopy is of questionable benefit in shortening recovery time in this age group.

A role for AMPA/kainate receptors in conditioned place preference induced by diazepam in the rat

There is increasing evidence for a role of glutamate receptors in the reinforcing properties of dependence producing drugs such as the psychostimulants and opiates. Activation of AMPA/kainate receptors are implicated in the acquisition of amphetamine-induced reinforcement but a role for this receptor in benzodiazepine-induced reinforcement has not been examined. In the present study the ability of the orally active AMPA/kainate antagonist GYKI 52466 was assessed for its ability to block the reinforcing properties of diazepam in a conditioned place preference paradigm. Diazepam (2.5 and 5.0 mg/kg, i.p.) produced a robust place preference and GYKI 52466 inhibited the acquisition of place preference conditioning-induced by diazepam. These results suggest that glutamatergic pathways are an important component of the circuitry involved in the acquisition of a benzodiazepine induced place preference.

Behavioral effects of diazepam in the murine plus-maze: flumazenil antagonism of enhanced head dipping but not the disinhibition of open-arm avoidance

Although it is widely believed that benzodiazepines reduce anxiety through positive allosteric modulation of the GABA(A)-chloride channel complex, this is not the only mechanism through which agents of this class can modify CNS function. Furthermore, a significant number of reports of apparent flumazenil blockade of diazepam anxiolysis in animal models have paid limited attention to possible intrinsic behavioral actions of the antagonist per se. In the present study, ethological methods were employed to assess in detail the effects of diazepam, flumazenil, and their combination on the behavior of male DBA/2 mice in the elevated plus-maze paradigm. In two experiments, diazepam (1.5 mg/kg) alone reduced open-arm avoidance and increased head dipping, whereas flumazenil (10-40 mg/kg) alone was without significant behavioral effect. However, with the sole exception of head dipping, prior administration of flumazenil (10 and 40 mg/kg) failed to block the behavioral effects of diazepam under present test conditions. These findings imply that the anxiolytic effects of diazepam in the mouse plus-maze are not mediated through flumazenil-sensitive benzodiazepine receptors and that alternate mechanisms must be considered.

[The intracerebral route of kynurenine administration is one of the reasons for the resistance of kynurenine-induced seizures to diazepam]

It has been shown many times that in experiments on mice systemic administration of anticonvulsive doses of diazepam caused a 15-20-fold higher effect against the endogenous convulsant kynurenine (injection into the brain ventricles) than against corasol (systemic injection). In the present work diazepam (0.5-2.0 mg/kg, intraperitoneal injection) prevented convulsions induced in nonbred and C57B1/6 mice by equally effective doses of corasol injected subcutaneously (80 mg/kg) better than in injection into the brain ventricles (500 micrograms). In injection of the three drugs into the ventricles diazepam (0.5-10 micrograms) relieved to a similar degree convulsions induced by equally effective doses of corasol (500 micrograms) and kynurenine (50 micrograms). It follows from this that the unique resistance the kynurenine convulsions to diazepam is due to the fact that only kynurenine is injected into the brain ventricles whereas all the other convulsants compared with it are administered systemically. It is suggested that besides the route of administration, the more significant dependence of kynurenine convulsions on GAMA(B) receptors and the activity of the brain dopaminergic system is responsible for the difference in the diazepam sensitivity of kynurenine and corasol convulsions.

The effect of chronic benzodiazepines exposure on body weight in rats

Changes in body weight (BW) in female rats treated for 5 weeks (wk) with weekly subcutaneous implantation of silastic capsules containing different benzodiazepines (BZs): diazepam (DZ) 90, 180, 360 and 540 mg wk-1; nordiazepam (ND) 600 mg wk-1; oxazepam (OX) 600 mg wk-1 and flunitrazepam (FN) 540 mg wk-1 and in male rats exposed to DZ (540 mg wk-1) were evaluated herein. Rats (female and male) implanted with empty capsules served as controls. The BW gain was significantly higher in male than in female rats (both DZ-treated and controls). The BW gain increased with increasing doses of DZ but slowed with time of exposure. In comparison to control rats, the BW gain was significantly higher in DZ-(540 mg wk-1) and OX- but not in ND- and FN-treated female rats. However, the differences between BZs were not of statistical significance. In rats exposed to empty capsules (male, female); DZ (male); ND and OX (female) the BW gain increased with time (1-4 wk) while in rats exposed to DZ and FN (female) the BW stabilised within 2 wk. Acute injection of the central BZ receptor antagonist, flumazenil (40 mg kg-1, i.v., 5th wk of chronic exposure), tended to inhibit the time-related BW gain in rats exposed to empty capsules (male, female), DZ (male), ND and OX (female) but did not affect the BW in DZ- (540 mg wk-1) and FN-exposed rats (female) where BW stabilised prior to FLU injection. Repeated administration of flumazenil (30 mg kg-1 wk-1, i.p.) did not affect the BW gain in DZ- and ND-treated female rats. The present data indicate that different BZs have different effects on BW gain in the rat suggesting that different subtypes of BZ receptors are involved.

Posttraining administration of substance P and its N-terminal fragment block the amnestic effects of diazepam

This study examined the effects of posttraining administration of substance P (SP) and of certain N- or C-terminal SP-fragments on retention performance of rats treated with diazepam (DZP). Twenty minutes before the training on an inhibitory avoidance task rats were given intraperitoneal injections of either DZP (2 mg/kg) or vehicle. Immediately after they were injected with SP (50 micrograms/kg), SPN 1-7 (167 micrograms/kg), SPC 6-11 (134 micrograms/kg), or vehicle. The posttrial administration of SP and SPN, but not SPC, facilitated avoidance behavior. Animals that received DZP before training and vehicle after the conditioning trial showed impaired retention. In contrast, in animals injected with SP and SPN after the training trial, DZP did not affect retention. These findings suggest that the amnestic effects of DZP can be blocked by the administration of SP and that the amino acid sequence responsible for this effect may be encoded by its N-terminal part.

Hippocampal GABA(A) channel conductance increased by diazepam

Benzodiazepines, which are widely used clinically for relief of anxiety and for sedation, are thought to enhance synaptic inhibition in the central nervous system by increasing the open probability of chloride channels activated by the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Here we show that the benzodiazepine diazepam can also increase the conductance of GABAA channels activated by low concentrations of GABA (0.5 or 5 microM) in rat cultured hippocampal neurons. Before exposure to diazepam, chloride channels activated by GABA had conductances of 8 to 53pS. Diazepam caused a concentration-dependent and reversible increase in the conductance of these channels towards a maximum conductance of 70-80 pS and the effect was as great as 7-fold in channels of lowest initial conductance. Increasing the conductance of GABAA channels tonically activated by low ambient concentrations of GABA in the extracellular environment may be an important way in which these drugs depress excitation in the central nervous system. That any drug has such a large effect on single channel conductance has not been reported previously and has implications for models of channel structure and conductance.

Naloxone blocks anxiolytic-like effects of benzodiazepines in Swiss but not in Balb/c mice

The ability of naloxone to block the effects of the benzodiazepines chlordiazepoxide and diazepam was evaluated in Swiss and Balb/c mice subjected to the light/dark choice test of anxiety or to a choice paradigm for measuring spontaneous exploratory behaviour. In Swiss mice, naloxone (5 or 10 mg/kg) completely or partially suppressed the anxiolytic-like effects of chlordiazepoxide (5 mg/kg) and diazepam (1 mg/kg) in the light/dark test. Naloxone alone was ineffective. None of these compounds affected locomotion in the free exploratory test. In Balb/c mice, naloxone did not reduce the anxiolytic-like action of benzodiazepines in the light/dark test. Moreover, naloxone did not antagonize the decrease in neophobia observed after anxiolytic treatment in Balb/c mice in the free exploratory paradigm. In this strain, benzodiazepines produced an increase of locomotor activity, whereas naloxone decreased it. The stimulant effects of benzodiazepines on locomotor activity were abolished by naloxone. As naloxone (2 mg/kg) reversed the morphine-induced hyperthermia both in Swiss and in Balb/c mice, differences in possible pharmacokinetic factors between the two strains can be ruled out as an explanation for the failure of naloxone to antagonize anxiolytic-like effects in Balb/c mice. Therefore, the ability of naloxone to reverse anxiolytic effects does not hold for all strains of mice.

Anxiolytic-like effects of PNU-101017, a partial agonist at the benzodiazepine receptor

PNU-101017 is a chemically novel ligand at the benzodiazepine recognition site of cloned GABAA receptors. It was reported to potentiate GABA-mediated chloride current in cultured cells with a moderate intrinsic activity and a biphasic dose-response relationship. In this study, we confirmed that PNU-101017 has a partial agonist-like effect in the antagonism of metrazole-induced seizures in mice. It produced no sedation or ataxia, but did antagonize diazepam-induced motor deficit of mice in the rotarod test. PNU-101017 was weakly active in anti-conflict anxiolytic tests, but attenuated the plasma corticosteroid response to mild stress in rats. It also antagonized stress-induced elevation of cerebellar cGMP levels in mice. Like chlordiazepoxide, it increased drinking of saline solution in thirsty rats. PNU-101017 did not potentiate the CNS-depressant effects of ethanol, and produced no evidence of physical dependence when administered repeatedly. Agonists with low intrinsic activity at the benzodiazepine receptor, such as PNU-101017, should be further explored for therapeutic uses.

Use of inhalational and intravenous sedation in dentistry

Having gained knowledge of the advantages of inhalational and intravenous sedation many dental practitioners use these techniques to supplement local anaesthesia for dental procedures. Inhalational sedation is commonly carried out with nitrous oxide and oxygen while isoflurane in oxygen has also been tried out. Intravenous sedation is commonly carried out with midazolam or diazepam given as a single titrated dose to an end point which does not result in anaesthesia. When sedation with benzodiazepines is carried out, the specific antagonist, flumazenil should always be available for use in emergencies such as accidental oversedation, iatrogenic overdose or paradoxical reactions. Patient controlled sedation with midazolam, the modern technique of intravenous sedation, is comparable to anaesthetist controlled sedation and patients may be administered increments of one milligram at one minute intervals. Computer controlled sedation has been carried out with propofol. Mortality following sedation is low in the United Kingdom, partly due to the strict guidelines of the General Dental Council in the United Kingdom.

A placebo controlled study of flumazenil in bronchoscopic procedures

METHODS

A double-blind, randomized, placebo controlled trial of the efficacy of flumazenil was conducted in 22 consecutive patients admitted for bronchoscopy. Sedation was induced by individually titrated amounts of intravenous diazepam (mean +/- s.d., 15.75 +/- 4.4 mg). Post bronchoscopy, patients received up to 1 mg of the benzodiazepine antagonist flumazenil (Anexate) or placebo intravenously. Clinical scores for the degree of sedation, orientation in time and space, co-operation and anterograde amnesia were used. These, together with three psychometric tests were performed twice prior to bronchoscopy and on eight occasions in the following 24 h. The psychometric tests were: Tapping Test (TT), Simple Reaction Time (SRT) and Critical Flicker Fusion (CFF) and these were carried out using the automated Multipsy test system.

RESULTS

The level of co-operation, orientation in time and space and anterograde amnesia were similar in both groups pre-and-post procedure. However compared with the pre-bronchoscopy assessment, the maximum degree of apparent sedation was significantly less in the flumazenil group in the first 4 h. In support of this, the patients in the flumazenil group also showed a significantly greater proficiency with the TT and CFF test post bronchoscopy (P < 0.05). There was no difference in the incidence of side effects and flumazenil was well tolerated.

CONCLUSIONS

In this highly controlled setting, the use of flumazenil (Anexate) was shown to be safe and effective in aiding recovery from benzodiazepine facilitated bronchoscopy and as such provides an additional level of safety for this procedure.

Characterisation of the furanocoumarin phellopterin as a rat brain benzodiazepine receptor partial agonist in vitro

Phellopterin, a naturally occurring furanocoumarin found in the roots of Angelica dahurica, inhibits [3H]diazepam and ethyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4] benzodiazepine-3-carboxylate ([3H]Ro 15-1788) binding to the benzodiazepine site of the rat brain gamma-aminobutyric acidA (GABAA) receptor in vitro with IC50 values of 400 and 680 nM, respectively. Two other naturally occurring furanocoumarins, byakangelicol and imperatorin were significantly less potent, with IC50 values for inhibition of [3H]diazepam binding of 8.0 and 12.3 microM, respectively. Scatchard plot analysis showed that the inhibitory activity of phellopterin was due to competitive inhibition of the benzodiazepine ligand binding. The results of GABA- and t-butylbicyclophosphorothionate (TBPS)-shift assays suggest that phellopterin is a partial agonist of the central benzodiazepine receptors in vitro.

Effect of inhalation of chamomile oil vapour on plasma ACTH level in ovariectomized-rat under restriction stress

We found that inhaling chamomile oil vapour decreased restriction stress-induced increases of plasma ACTH level in ovariectomized rat. The plasma ACTH level decreased further when diazepam was administered along with inhaling chamomile oil vapour. Flumazenile blocked the decrease in plasma ACTH level induced by inhaled chamomile oil vapour.

The possible involvement of GABAA systems in the antinarcotic effect of majonoside-R2, a major constituent of Vietnamese ginseng, in mice

The effect of majonoside-R2 on morphine- and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine- and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated CI- channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

Involvement of the opioid system in the anxiolytic effect of diazepam in mice

In the present study, the anticonflict effect of diazepam was significantly abolished by pretreatment with naloxone, beta-funaltrexamine or nor-binaltorphimine but not naltrindole, using a Vogel-type conflict paradigm in mice. However, naloxone alone had a significant proconflict effect, and beta-funaltrexamine alone tended to produce a proconflict effect. Spontaneous drinking behavior was not affected by treatment with diazepam and nor-binaltorphimine. In addition, nor-binaltorphimine had no effect on diazepam-induced motor incoordination, hypothermia or anticonvulsant action, respectively. Moreover, the stable dynorphin analog E2078 ([N-methyl-Tyr1, N-alpha-methyl-Arg7-D-Leu8]dynorphin A-(1-8) ethylamide) and the highly selective kappa-opioid receptor agonist U50,488H (trans-3,4-dichloro-N-(2-(1-pyrrolidinyl)cyclohexyl)benzenacetamide++ + methanesulfonate hydrochloride) produced a significant anticonflict effect, which was completely antagonized by pretreatment with nor-binaltorphimine. These findings suggested that the kappa-opioid system may play an important role in the anxiolytic effect of benzodiazepine and the regulation of anxiety.

Selective cyclodextrin inhibition of alfaxolone-induced ataxia

The effect of the use of a number of popular solubility treatments was examined on alfaxolone- and diazepam-induced ataxia. The effects of diazepam were not significantly altered by solution in cyclodextrin, Alkamuls EL-620 or a mixture of propylene glycol and ethanol. The effects of alfaxolone were not altered by solution in Alkamuls EL-620, but were significantly lessened by solution in cyclodextrin. In a dose-response experiment, the ED50 of alfaxolone increased from 15.3 mg kg-1 (in Alkamuls EL-620) to 25.6 mg kg-1 (in hydroxypropyl-beta-cyclodextrin). The results suggest that although cyclodextrins are popular and effective solubilizers, their use must be considered carefully in the context of the experiments in which they are to be used.

PK 11195 antagonizes the positive inotropic response of the isolated rat heart to diazepam but not the negative inotropic response

The influence of the ligand PK 11195 (1-(2-chlorophenyl)-N-methyl-N-(1- methylpropyl)-3-isoquinolinecarboxamide), antagonist of the peripheral-type benzodiazepine receptor, on the inotropic response of the perfused rat heart to diazepam (7-chloro-5-phenyl-methyl- 1,3-dihydro-2H-1,4-benzodiazepin-2-one) was studied. Diazepam induced a positive inotropic response which was preceded by a transient negative inotropic response. Concentrations of 10(-7) M PK 11195 were ineffective, whereas concentrations of 10(-6) and 10(-5) M PK 11195 reduced the positive inotropic response significantly. At 5 x 10(-5) M PK 11195 the response was completely abolished. The negative inotropic response was not changed by either concentration of PK 11195 used. It is concluded that the positive inotropic response of the isolated rat heart to diazepam may well be mediated through peripheral-type benzodiazepine receptors; the negative inotropic response must be related to other (more complex) mechanisms.

Effects of benzodiazepines on potassium-induced increase in free cytosolic calcium concentration in astrocytes: interactions with nifedipine and the peripheral-type benzodiazepine antagonist PK 11195

The benzodiazepines diazepam and midazolam at submicromolar concentrations potentiated the increase in free cytosolic calcium concentration in astrocytes in primary cultures evoked by an elevation of the extracellular potassium concentration ([K+]0), but they had little stimulatory effect at normal [K+]0 and none at maximally elevated [K+]0. Nifedipine, an inhibitor of the L-channel, counteracted both the effect of the elevated [K+]0 as such and the benzodiazepine modulation. PK 11195, an antagonist of the peripheral-type benzodiazepine receptor, counteracted the effect of the benzodiazepines, but had no effect on the increase in free cytosolic calcium evoked by the elevated [K+]0.

Low level hyperbaric antagonism of diazepam's locomotor depressant and anticonvulsant properties in mice

Exposure to 12 atmospheres absolute (12 ATA) helium oxygen gas (heliox) (low level hyperbaric exposure) antagonizes the behavioral effects of ethanol and n-propanol, but not morphine. These and other results indicate that the mechanism of the antagonism is direct (pharmacodynamic) and selective. Our study further investigates the selectivity of low level hyperbaric antagonism by testing its effectiveness against diazepam, a high affinity binding drug that acts via allosteric modulation of GABAA receptors. C57BL/6J mice received injections i.p. of vehicle or diazepam, and were then exposed to 1 ATA air, 1 ATA heliox or 12 ATA heliox. Exposure to 12 ATA heliox antagonized the locomotor depressant effect of 4 and 6 mg/kg, but not 8 mg/kg diazepam. Hyperbaric exposure also antagonized the anticonvulsant effect of 8 and 24 mg/kg, but not 4 mg/kg, diazepam vs. 300 mg/kg isoniazid. Exposure to 12 ATA heliox did not significantly affect blood concentrations of diazepam or its metabolite n-desmethyl diazepam. The pharmacological characteristics of the antagonism (direct, surmountable, rightward shift in diazepam's dose-response curve) closely matched those seen in previous studies for hyperbaric antagonism of ethanol. The results add to the evidence that low level hyperbaric exposure is a direct, mechanistic antagonist that selectively antagonizes drugs that act via perturbation or allosteric modulation of receptor function. Moreover, the results suggest that allosteric coupling pathways, which transduce binding events on ligand-gated ion channels, may represent initial sites of action for ethanol.

Benzodiazepine-withdrawal-induced gastric emptying disturbances in rats: evidence for serotonin receptor involvement

This study was performed in rats to determine if serotonin and its receptors are involved in the increase of gastric emptying (GE) induced by benzodiazepine (BZ) withdrawal. GE was measured with a test meal (2 ml) containing 1 microCi/ml of 51Cr sodium chromate administered in rats, either previously receiving injections with diazepam (15 mg/kg/day i.p.) or with DMSO (0.9 ml/day i.p.) during 7 days. On the 8th day, animals received the different serotonin (5-HT) agonists or antagonists, and flumazenil (BZ antagonist; 15 mg/kg i.p.) 30 and 15 min, respectively, before the test meal. Methiotepin (5-HT1 antagonist) either i.p. (0.1-1 mg/kg) or intracerebroventricularly (10 micrograms/kg) had no effect on the increase of GE induced by precipitated-withdrawal. 8-OH-DPAT (5-HT1A agonist) administered i.c.v. (1-10 micrograms/kg) dose dependently reduced GE increase. Administered i.p. (0.1 mg/kg), it blocked GE increase in control and diazepam-withdrawn rats. Ritanserin (5-HT2 antagonist) antagonized GE increase only when administered i.p. (0.1 mg/kg). Granisetron (5-HT3 antagonist) was active both i.p. (0.01-0.1 mg/kg) and intracerebroventricularly (1-10 micrograms/kg). Administered intracerebroventricularly (1 microgram/kg) in diazepam-treated rats, 5-HTP mimicked the effect of flumazenil. It is concluded that diazepam-withdrawal increases GE by stimulating central release of 5-HT and/or central activation of 5-HT neurons. At least central 5-HT3 receptors, and in less extend, peripheral 5-HT2 receptors are involved in this mechanism.

Role of GABAergic systems in the development of morphine tolerance in formalin-treated mice

Since the development of tolerance to morphine antinociception in formalin-treated mice was delayed and diazepam normalized the delay, the involvement of GABAergic systems in the process was investigated. Gamma amino-n-butyric acid (GABA) at 10 mg/kg and the GABAA-receptor agonist muscimol at 0.05 mg/kg, i.p., 30 min before daily morphine injection at 10 mg/kg, s.c. completely reversed the delay in the development of morphine tolerance in the formalin-treated mice. The GABAA antagonist bicuculline at 1 mg/kg and the Cl(-)-channel blocker picrotoxin at 1 mg/kg extinguished the reverse effect of muscimol and GABA, respectively. In contrast, the GABAB antagonist CGP 35348 (3-aminopropane-diethoxymethyl-phosphinic acid) up to 100 mg/kg, i.p. failed to abolish the GABA effect; and baclofen, a GABAB-receptor agonist, at 0.5 and 2 mg/kg, i.p., 30 min before morphine was without effect on the delay. On the other hand, bicuculline was incapable of abolishing the reverse effects of diazepam on the delay of tolerance development; and likewise, the reverse effect of muscimol was not affected by flumazenil. No appreciable influence of these GABA-related compounds was seen on morphine antinociception itself nor the development of tolerance in normal mice. These results suggest that the benzodiazepine-GABAA-Cl- channel complex is involved in the mechanism underlying the delay of the development of morphine tolerance in formalin-treated mice; however, it is deduced that benzodiazepine-receptor and GABAergic systems are not always functionally coupled to each other in the mechanisms.

[The effect of flumazenil in reversing midazolam, flunitrazepam or diazepam]

In 31 adult patients who had undergone spinal or epidural anesthesia, we evaluated the effect of flumazenil in reversing midazolam, flunitrazepam or diazepam. The patients received midazolam 5 mg, flunitrazepam 1 mg or diazepam 5 mg 15 min after the spinal or epidural anesthesia. After the completion of operation, flumazenil (0.2 mg-1.0 mg) was administered until the patient became awake. Blood pressure, pulse rate and respiratory rate before and after administration of flumazenil showed no statistically significant changes in these groups. There were no significant differences in necessary amount of flumazenil among these groups. The time necessary for the patient to be awake in midazolam group was significantly shorter than that in flunitrazepam or diazepam group. Half of the patients in flunitrazepam and diazepam groups slept again after leaving the operating room, but they presented no clinical problems. In conclusion, we consider that flumazenil does not affect circulation and respiration, so it seems to be safe and effective for reversing benzodiazepins in clinical situation.

Antagonism of some cyclohexamine-based drug combinations used for chemical restraint of southern elephant seals (Mirounga leonina)

This study examined the use of 4 antagonists of chemical restraint in mature female southern elephant seals (Mirounga leonina) that were restrained with ketamine and diazepam, ketamine and xylazine, or tiletamine and zolazepam. The antagonists were: 4-aminopyridine, yohimbine, doxapram and sarmazenil. The effects of the antagonists on the animal's time to first movement forward and recovery, heart rate, respiratory rate and venous blood gas and pH values, and level of chemical restraint were recorded. Sarmazenil (1.0 mg/kg) and doxapram (5.0 mg/kg) partially antagonised 50:1 ketamine: diazepam (ketamine = 3.0 mg/kg, diazepam = 0.06 mg/kg) and tiletamine and zolazepam (tiletamine = 0.5 mg/kg, zolazepam = 0.5 mg/kg). However, the rapid recovery after low doses of anaesthetics means that antagonism is usually unnecessary, and it may increase the likelihood of shaking. Routine antagonism of ketamine and xylazine (ketamine = 3.0 mg/kg, xylazine = 0.5 mg/kg) is more useful given its usually delayed recovery time and potential for thermoregulatory problems. For this purpose yohimbine (0.06 mg/kg) offered advantages over doxapram in giving a smoother recovery with less aggression. 4-aminopyridine (0.2 mg/kg) prolonged chemical restraint by 100:1 ketamine:diazepam (ketamine = 3.0 mg/kg, diazepam = 0.03 mg/kg) and ketamine and xylazine, and should be contraindicated. Doxapram (5.0 mg/kg) was the most useful general antagonist for all groups of drugs but shaking was seen and a lower dose is recommended.