CGS 8216: receptor binding characteristics of a potent benzodiazepine antagonist

The benzodiazepine antagonist CGS 8216 decreases both shocked and unshocked drinking in rats

Previous studies of the benzodiazepine antagonist CGS 8216 have reported that this compound may enhance the punishment-induced suppression of behaviour. In order to investigate this phenomenon further, water-deprived rats were trained to drink from a water spout during a multiple schedule with shocked and unshocked components. During the shocked components a very mild electric footshock was presented after every 20th lick. The shock slightly reduced the rate of licking during these components below that which occurred during periods without shock, although this effect decreased during the experiment. CGS 8216 (0.3-10 mg/kg) produced a dose-related reduction in licking during both schedule components. The overall volumes of water consumed were reduced by CGS 8216 as was the number of licks during the first, unshocked schedule component, before shock was applied, showing that the effect on unshocked licking was not due to a generalisation of suppression between periods with or without shock. In contrast to CGS 8216, a dose of 10 mg/kg pentylenetetrazol selectively reduced shocked licking. In a second group of rats which drank under identical conditions but without shock, CGS 8216 again reduced water intake. These results show that CGS 8216 can reduce water intake in rats regardless of whether drinking results in shock presentation.

Benzodiazepine ligands, nociception and 'defeat' analgesia in male mice

Recent studies have indicated that defeat experience induces acute non-opioid analgesia in intruder mice. To investigate the potential involvement of benzodiazepine receptors in this biologically-relevant form of environmentally-induced antinociception, we initially assessed the effects of some benzodiazepine ligands on basal nociception (tail-flick assay). Chlordiazepoxide (5-30 mg/kg), midazolam (0.625-5 mg/kg), diazepam (0.5-4 mg/kg), Ro15-1788 (5-80 mg/kg) and CGS8216 (5 mg/kg) were found to be ineffective in altering basal nociception. However, higher doses of CGS8216 (10-20 mg/kg) induced significant analgesia, an effect also observed with the beta-carboline derivatives FG7142 (5-20 mg/kg) and DMCM (1-2 mg/kg). Time-course analyses revealed that the onset of CGS8216 analgesia was slower than for FG7142 and DMCM, but that all three drugs produced long-lasting elevations in tail-flick latencies. The analgesic effects of FG7142 and DMCM were completely reversed by Ro15-1788 (20 mg/kg) and by chlordiazepoxide (20 mg/kg), suggesting mediation by benzodiazepine receptor mechanisms. Although CGS8216 analgesia was also reversed by Ro15-1788, it was unaffected by chlordiazepoxide; however, diazepam (5 mg/kg) did significantly attenuate the reaction. Further studies indicated that the antinociceptive consequences of defeat experience were dose-dependently blocked by Ro15-1788 (10-40 mg/kg) and by diazepam (0.5-2 mg/kg). Surprisingly, however, neither chlordiazepoxide (5-20 mg/kg) nor midazolam (1.25-2.5 mg/kg) blocked "defeat" analgesia under present test conditions. Although several issues remain unresolved, present findings would not be inconsistent with the proposal that stimuli associated with the acute stress of defeat experience release an endogenous ligand which acts in an "inverse agonist-like" manner at benzodiazepine sites.

A selective imidazobenzodiazepine antagonist of ethanol in the rat

Ethanol, at pharmacologically relevant concentrations of 20 to 100 mM, stimulates gamma-aminobutyric (GABA) receptor-mediated uptake of 36Cl-labeled chlorine into isolated brain vesicles. One drug that acts at GABA-benzodiazepine receptors, the imidazobenzodiazepine Ro15-4513, has been found to be a potent antagonist of ethanol-stimulated 36Cl- uptake into brain vesicles, but it fails to antagonize either pentobarbital- or muscimol-stimulated 36Cl- uptake. Pretreatment of rats with Ro15-4513 blocks the anticonflict activity of low doses of ethanol (but not pentobarbital) as well as the behavioral intoxication observed with higher doses of ethanol. The effects of Ro15-4513 in antagonizing ethanol-stimulated 36Cl- uptake and behavior are completely blocked by benzodiazepine receptor antagonists. However, other benzodiazepine receptor inverse agonists fail to antagonize the actions of ethanol in vitro or in vivo, suggesting a novel interaction of Ro15-4513 with the GABA receptor-coupled chloride ion channel complex. The identification of a selective benzodiazepine antagonist of ethanol-stimulated 36Cl- uptake in vitro that blocks the anxiolytic and intoxicating actions of ethanol suggests that many of the neuropharmacologic actions of ethanol may be mediated via central GABA receptors.

Effects of the benzodiazepine antagonists RO 15-1788, CGS-8216 and PK-11195 on amygdaloid kindled seizures and the anticonvulsant efficacy of diazepam

The anticonvulsant effectiveness of the benzodiazepine antagonists RO 15-1788, CGS-8216 and PK-11195 were evaluated against threshold and suprathreshold (400 microA) stimulation in fully amygdaloid-kindled rats. Pretreatment with either RO 15-1788 (3, 10 and 30 mg/kg), CGS-8216 (3, 10 and 30 mg/kg) or PK-11195 (10 and 60 mg/kg) failed in this study to modify consistently either the afterdischarge thresholds or elicited suprathreshold seizures or duration of afterdischarge. Using a double injection paradigm, the effectiveness of these three benzodiazepine antagonists to reverse the anti-convulsant and behavioral effects of diazepam were studied. When diazepam (3 mg/kg) was injected 15 min before or after a second injection of the vehicle control DMSO (0.25 ml/kg), a significant reduction in the duration of afterdischarge and seizure rank, elicited by a suprathreshold stimulation in amygdaloid-kindled rats, occurred. When either CGS 8216 (10 mg/kg) or RO 15-1788 (10 mg/kg) were given 15 min before diazepam (3 mg/kg) prior to stimulation, the anticonvulsant properties of diazepam were blocked. When RO 15-1788 (10 mg/kg) was given 15 min after diazepam, antagonism of the anticonvulsant effects on diazepam was shown. However, when either CGS-8216 (10 mg/kg) or PK-11195 (10 and 60 mg/kg) were given 15 min after diazepam (3 mg/kg), the anticonvulsant properties of diazepam were not blocked. The anticonvulsant effects of diazepam were reversed when CGS-8216 (10 mg/kg) was given 5 min after diazepam (3 mg/kg) or when a larger dose (30 mg/kg) was given at the same 15 min interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-carbolines characterized as benzodiazepine receptor agonists and inverse agonists produce bi-directional changes in palatable food consumption

Drugs which bind to specific benzodiazepine recognition sites fall into three categories: agonists, antagonists, and inverse agonists. A set of biochemical parameters is available which distinguishes between the three. In addition, actions of the drugs result in physiological and behavioural effects which are distinguishable. beta-Carboline derivatives provide a group of compounds which show high affinity for the benzodiazepine sites, and which contains examples belonging to each of the three categories. Evidence is reviewed which shows that beta-carboline benzodiazepine receptor agonists (ZK 93423, ZK 91296) produce increases in the consumption of a palatable diet by non-deprived rats, that beta-carboline inverse agonists (FG 7142, DMCM) produce an anorectic effect, and that the beta-carboline ZK 93426 acts as a benzodiazepine receptor antagonist. The results support the proposal of bi-directional control of feeding responses through the action of drugs at a common benzodiazepine receptor. Furthermore, benzodiazepine receptor inverse agonists provide a novel class of anorectic agents. Evidence is also reviewed which is suggestive of the modulation of food-related reward by drug actions at benzodiazepine receptors.

Aversive and appetitive properties of anxiogenic and anxiolytic agents

The place-conditioning paradigm was used to assess the appetitive or aversive nature of anxiolytic and anxiogenic drugs. Rats were given a pre-conditioning preference test in which the time that they spent on each side of a two-compartment chamber was measured; each side was visually distinct. On two days they were confined to one side immediately after drug injection, and on alternate days they were confined to the other side after vehicle injection. The rats were then given a postconditioning preference test. The change in preference was used as the measure of the reinforcing properties of the drugs. The anxiolytic drugs diazepam, lorazepam, alprazolam, adinazolam, U-43, 465 and tracazolate produced a clear preference for the drug-associated side, indicating the appetitive qualities of these drugs. Preference was less clear for the anxiolytics chlordiazepoxide and buspirone. This suggests that it is possible to dissociate the rewarding and anxiolytic properties of drugs. All the anxiogenic drugs tested (CGS 8216, picrotoxin and yohimbine) produced conditioned aversion.

Investigation of the actions of the benzodiazepine antagonists Ro 15-1788 and CGS 8216 using the schedule-controlled behavior of rats

Ro 15-1788 and CGS 8216 antagonise many of the pharmacological effects of benzodiazepines but both of these compounds have also been shown to exert behavioral effects when administered alone. In the present study the effects of Ro 15-1788 and CGS 8216, alone and in combination with diazepam and with the benzodiazepine receptor ligand zolpidem, were investigated. Diazepam and zolpidem produced dose-related decreases in rates of food-reinforced lever-pressing maintained by a fixed-ratio (FR 10) schedule. CGS 8216 also reduced response rates although Ro 15-1788, at several doses, produced small, but statistically significant, increases in responding. When the diazepam and zolpidem dose-response curves were re-established in the presence of a dose of Ro 15-1788 or CGS 8216 the depressant effects of the higher doses were antagonised. However, neither diazepam nor zolpidem blocked the rate reducing effect of CGS 8216 which may not therefore be due to an action at benzodiazepine receptors.

Muscle relaxant action of phenobarbitone in genetically spastic rats: an electromyographic study

The muscle relaxant effect of phenobarbitone was studied in genetically spastic rats which exhibit spontaneous tonic activity in the electromyogram (EMG) of the gastrocnemius muscle. Phenobarbitone, 10-30 mg/kg i.p., reduced the tonic activity in the EMG of the gastrocnemius muscle of such rats in a dose- and time-dependent manner. The GABA antagonists bicuculline, 2 mg/kg i.p., and picrotoxin, 2 and 3 mg/kg i.p., reduced the muscle relaxant effect of phenobarbitone, 20 and 30 mg/kg. The benzodiazepine receptor antagonists, Ro 15-1788, 5 mg/kg, and CGS 8216, 5 mg/kg (doses which do not affect tonic activity in the EMG), failed to alter the depressant effect of phenobarbitone 30 mg/kg, in the EMG. Beta-Carboline-3-carboxylic acid methylester (beta-CCM), 2 mg/kg i.p., while not affecting the tonic activity in the EMG, reversed the depressant effect of phenobarbitone, 30 mg/kg. Both Ro 15-1788, 5 mg/kg, and CGS 8216, 5 mg/kg, prevented the reversal of the depressant action of phenobarbitone, 30 mg/kg, produced by beta-CCM, 2 mg/kg. The results indicate that the muscle relaxant action of phenobarbitone in genetically spastic rats is mediated via GABA-related mechanisms and add further support to the hypothesis that both Ro 15-1788 and CGS 8216 are specific antagonists at benzodiazepine receptors, devoid of intrinsic activity at moderate doses. The results also suggest that reversal of the muscle relaxant action of phenobarbitone by beta-CCM is mediated via a GABA/benzodiazepine receptor/chloride ionophore complex.

CGS 8216, a novel anorectic agent, selectively reduces saccharin solution consumption in the rat

The pyrazoloquinoline CGS 8216, a high-affinity ligand for benzodiazepine recognition sites, significantly reduced the consumption of a preferred 0.05% sodium saccharin solution in a 30 min two-bottle test. A highly significant effect was detected at 5.0 mg/kg, IP and at higher doses. The consumption of water and 0.6% saline, in two-bottle tests, or of quinine solution and water, in a forced-choice test, was not reliably affected by CGS 8216. The results point to a sensitive and selective intrinsic effect of CGS 8216 on ingestional responses in the rat.

Benzodiazepine antagonist, CGS-8216, in diazepam- or pentobarbital-dependent and non-dependent rats

CGS-8216, a benzodiazepine antagonist, was administered to rats acutely dosed with diazepam, and to rats chronically dosed with diazepam or pentobarbital. The effects of an acute dose of diazepam were antagonized by CGS-8216 but signs of precipitated abstinence were not observed. An apparent arousing effect was seen in non-dependent rats when CGS-8216 was administered after placebo, but no arousal was observed when Ro15-1788 was administered after placebo in non-dependent rats. A precipitated abstinence syndrome was elicited with CGS-8216 in rats chronically dosed with diazepam and was very similar to the abstinence syndrome precipitated by Ro15-1788 in diazepam-dependent rats. Like Ro15-1788, CGS-8216 elevated Precipitated Abstinence Scale (PAS) scores in a dose-related manner until a plateau was reached with 5 mg/kg. No signs of precipitated abstinence were observed when CGS-8216 was administered to rats dependent on phenobarbital.

CGS 8216, a benzodiazepine antagonist, reduces food intake in food-deprived rats

CGS 8216, a benzodiazepine receptor antagonist with weak inverse agonist properties, reduced food intake in food-deprived rats when administered orally or intraperitoneally at doses that antagonize diazepam. This effect was sustained when CGS 8216 was administered daily for five days, indicating no rapid tolerance to the anorectic effect. Ro 15-1788 did not reduce feeding when administered orally, and was active only at high intraperitoneal doses (54 and 100 mg/kg). CGS 9896, a close analog of CGS 8216 but a benzodiazepine partial agonist with anxiolytic properties, did not reduce food intake at doses as high as 100 mg/kg IP or PO. These results support prior suggestions that benzodiazepine receptors may modulate feeding behavior, and suggest that CGS 8216 may have appetite suppressant properties.

Differential interactions between chlordiazepoxide, pentobarbital and benzodiazepine antagonists Ro 15-1788 and CGS 8216 in a drug discrimination procedure

Rats were trained to discriminate either chlordiazepoxide (CDP, 4 mg/kg, IP, N = 8) or pentobarbital (PB, 10 mg/kg, IP, N = 8) from saline in a two-lever food-reinforced procedure. CDP and PB dose-dependently substituted for each other (greater than or equal to 90% drug lever responses); indicating that their discriminative stimulus properties were closely similar. However, discriminative stimulus control induced by CDP and PB differentially was affected by the proposed benzodiazepine (BDZ) antagonists Ro 15-1788 (0.08-20 mg/kg, IP) and CGS 8216 (2.5-20 mg/kg, IP) in each experimental group; suggesting that the discriminative stimulus properties of CDP and PB are mediated by different mechanisms of action. When administered alone, Ro 15-1788 (5 and 20 mg/kg), but not CGS 8216, induced CDP like discriminative effects, suggesting that Ro 15-1788 may have partial (BDZ like) agonist properties, not shown by CGS 8216. Additional evidence for a behavioral difference between Ro 15-1788 and CGS 8216 is suggested by differential effects of both compounds on response rate. The results may reflect differential interactions of the compounds with the BDZ receptor-GABA receptor-Cl- ionophore complex.

Behavioral effects of CGS 8216 alone, and in combination with diazepam and pentobarbital in dogs

Beagle dogs (N = 3) responded under a multiple fixed-interval (FI) 300 sec, fixed-ratio (FR) 30 schedule of food presentation. The pyrazoloquinoline derivative CGS 8216, given either intravenously (0.01-3.0 mg/kg) or orally (0.1-30.0 mg/kg) had little effect on either the rate or temporal pattern of responding during either component. Both diazepam (0.3 to 17.5 mg/kg, PO) and pentobarbital (0.1-17.5 mg/kg, PO) produced qualitatively similar effects on behavior. Rates of responding during the FI components first increased, then decreased with increasing doses; both drugs produced only dose-related decreases in the rate of responding during the FR components. CGS 8216 antagonized some of the behavioral effects of diazepam; FI and FR response rates returned to baseline, however the effects of diazepam on quarter-life values were not appreciably altered by CGS 8216. The effects of pentobarbital on schedule-controlled responding were not antagonized by CGS 8216. These results indicate CGS 8216 is a selective benzodiazepine antagonist that does not produce benzodiazepine-like behavioral effects.

Interactions of Ro 15-1788, CGS 8216 and diazepam on head-turning in rats

Ro 15-1788 (10 mg/kg, ip) and CGS 8216 (10 mg/kg, ip) significantly reversed the inhibitory effect of diazepam (5 mg/kg, ip) on electrically induced head-turning in rats. Neither antagonist alone, at the dose level which blocked diazepam, had any intrinsic activity in this model. The specificity of the interaction between CGS 8216 and diazepam was further confirmed by the lack of antagonism by CGS 8216 of muscimol's inhibitory effect on head-turning. These results provide additional evidence that the inhibition of head-turning induced by diazepam is mediated via the benzodiazepine binding site. Furthermore, this model provides a functional expression of the interaction between the benzodiazepine recognition site, the chloride ionophore, and the GABA receptor complex.

Evaluation of the binding of the A-1 selective adenosine radioligand, cyclopentyladenosine (CPA), to rat brain tissue

The binding of [3H]-Cyclopentyladenosine (CPA), an N6-substituted analog of adenosine, was examined in vitro. CPA bound with high affinity (Kd = 0.48 nmol/l) to rat brain membranes. Specific binding, which represented 90-97% of the total counts bound at a ligand concentration of 1 nmol/l, was saturable, reversible and sensitive to protein denaturation. The pharmacology of binding was consistent with the labeling of an A-1 receptor, the R- and S-diasteromers of N6-phenylisopropyladenosine (PIA) showing a sixteenfold difference in their ability to displace CPA. The prototypic A-1 selective adenosine agonist, N6-cyclohexyladenosine (CHA) was twofold less active than CPA in displacing radiolabeled CPA. Comparison of the ability of cold CHA and CPA to displace [3H]-CPA gave rate dissociation constants of 1.88 and 1.80 X 10(4) s-1, respectively suggesting that both CHA and CPA bound to the same recognition site. In contrast however, comparison of the binding of [3H]-CPA with that of [3H]-CHA showed distinct differences. The Kd for CHA was approximately twice that of CPA while the apparent Bmax was 60% greater. In comparing the pharmacology of CPA binding with that of CHA, it was found that CHA, S-PIA and the antagonist, PACPX were more active in displacing CHA than CPA. In general however, CPA has a binding profile very similar to that observed with CHA.

Hyperphagic and anorectic effects of beta-carbolines in a palatable food consumption test: comparisons with triazolam and quazepam

The triazolobenzodiazepine triazolam (0.1-1.0 mg/kg i.p.) and quazepam (0.3-30.0 mg/kg i.p.) were administered to non-food-deprived rats which had been partially-satiated on a palatable diet. In a subsequent 30 min feeding test, both compounds produced a significant increase in the level of food consumption. While triazolam had a dose-related effect and produced a 151.5% increase in the level of food intake, quazepam exerted only a partial effect, achieving a 73.9% increase in food intake at 3.0 mg/kg but no additional increase in food intake at higher doses. The two beta-carbolines, ZK 93423 (0.1-3.0 mg/kg i.p.) and ZK 91296 (1.0-30.0 mg/kg i.p.), a full agonist and a partial agonist at benzodiazepine receptors respectively, also produced significant increases in food consumption under the same experimental conditions. ZK 93423 had effects which were similar to those of triazolam, ZK 91296 had effects similar to quazepam. The beta-carboline benzodiazepine inverse agonist FG 7142 (10.0 mg/kg i.p.) had an anorectic effect in non-food-deprived rats given 30 min access to the highly palatable diet. This effect was reversed by the beta-carboline benzodiazepine receptor antagonist ZK 93426 in a dose-dependent manner. These results emphasize that within the series of beta-carboline ligands for benzodiazepine receptors, their characterization in terms of agonists, antagonists and inverse agonists has validity with respect to the behavioural response of palatable food consumption in non-food-deprived rats.

Benzodiazepine receptor-mediated effect of CGS 8216 on milk consumption in the non-deprived rat

The pyrazoloquinoline CGS 8216, which binds with high affinity to central benzodiazepine recognition sites, produced a highly significant reduction in the consumption of familiar, sweetened milk by non-deprived male rats, when administered in a dose of 20 mg/kg, IP. The anorectic effect was present during the first 5 min period of a 20-min drinking test, and remained in evidence throughout the remainder of the test. The benzodiazepine receptor antagonist Ro15-1788, administered 15 min before the consumption test, produced a dose-related (10-40 mg/kg, IP) reversal of the anorectic effect of CGS 8216, during the first 10 min of the test. Injection of Ro15-1788 alone had no significant effect on milk ingestion. This experiment shows that the reduction in the consumption of a palatable liquid food by CGS 8216 can be attributed to an action at benzodiazepine receptors. The result is consistent with the characterization of CGS 8216 as a weak benzodiazepine receptor inverse agonist.

The Ro 15-1788 cue: evidence for benzodiazepine agonist and inverse agonist properties

Rats discriminating Ro 15-1788 (10 mg/kg, i.p.) from vehicle completely generalized this cue to typical benzodiazepines, and partially generalized it to barbiturates, pentylenetetrazol, CGS 8216, beta-CCM and PK 8165. CL 218872, Ro 5-4864, phenytoine, progabide, propranolol, yohimbine and various CNS stimulants predominantly induced vehicle-appropriate responding. Chlordiazepoxide, pentobarbital, CL 218 872, PK 8165, pentylenetetrazol, CGS 8216 and beta-CCM failed to block the Ro 15-1788 cue. Generalization to both anxiolytics/anticonvulsants and anxiogenics/(pro) convulsants suggests that Ro 15-1788 has benzodiazepine agonist and inverse agonist properties.

[3H]-Flunitrazepam binding in the presence of beta-phenylethylamine and its metabolites

It has recently been reported that the concentration of beta-phenylethylamine (PEA) was elevated in the plasma of an individual experiencing convulsions because of an overdose of tranylcypromine. Also, high concentrations of PEA, injected into mice, were reported to induce convulsions. This convulsive effect was prevented by pretreatment with the benzodiazepines diazepam and chlordiazepoxide. In this study, PEA in concentrations from 0.5 to 100 microM failed to alter the binding of [3H]-flunitrazepam ([3H]-FLU) in membrane preparations from mouse rostral forebrain. The metabolites of PEA: phenylacetic acid, phenylethanolamine, octopamine and tyramine, also failed to affect [3H]-FLU binding. This suggests that although there are substances that act as convulsants by interacting with the benzodiazepine receptor sites, the convulsant effect of PEA and its metabolites is mediated elsewhere.

Benzodiazepine binding characteristics of embryonic rat brain neurons grown in culture

The binding of [3H]diazepam to cell homogenates of embryonic rat brain neurons grown in culture was examined. Under the conditions used to prepare and maintain these neurons, only a single, saturable, high-affinity binding site was observed. The binding of [3H]diazepam was potently inhibited by the CNS-specific benzodiazepine clonazepam (Ki = 0.56 +/- 0.08 nM) but was not affected by the peripheral-type receptor ligand Ro5-4864. The KD for [3H]diazepam bound specifically to cell homogenates was 2.64 +/- 0.24 nM, and the Bmax was 952 +/- 43 fmol/mg of protein. [3H]Diazepam binding to cell membranes washed three times was stimulated dose-dependently by gamma-aminobutyric acid (GABA), reaching 112 +/- 7.5% above control values at 10(-4) M. The rank order for potency of drug binding to the benzodiazepine receptor site in cultured neurons was clonazepam greater than diazepam greater than beta-carboline-3-carboxylate ethyl ester greater than Ro15-1788 greater than CL218,872 much greater than Ro5-4864. The binding characteristics of this site are very similar to those of the Type II benzodiazepine receptors present in rat brain. These data demonstrate that part, if not all, of the benzodiazepine-GABA-chloride ionophore receptor complex is being expressed by cultured embryonic rat brain neurons in the absence of accompanying glial cells and suggest that these cultures may serve as a model system for the study of Type II benzodiazepine receptor function.

Aminophylline and CGS 8216 reverse the protective action of diazepam against electroconvulsions in mice

Aminophylline (50 and 100 mg/kg) and CGS 8216 (20 and 40 mg/kg) decreased the anticonvulsant potency of diazepam (5 and 10 mg/kg) against electroshock-induced seizures. It should be emphasized that aminophylline moderately affected the protective action of the benzodiazepine at a dose of 5 mg/kg, whereas it was equipotent with CGS 8216 with regard to diazepam at a dose of 10 mg/kg. Consequently, participation of a purinergic component in the anticonvulsant action of diazepam is suggested. On the other hand, the use of aminophylline in epileptic patients suffering from asthma seems unjustified.

The anorectic effect of FG 7142, a partial inverse agonist at benzodiazepine recognition sites, is reversed by CGS 8216 and clonazepam but not food deprivation

The benzodiazepine partial inverse agonist N'-methyl-beta-carboline-3-carboxamide (FG 7142; 5.0 and 10.0 mg/kg, i.p.) produced a dose-dependent reduction in the consumption of a familiar, highly palatable diet by non-food-deprived male rats. At dose levels which exhibited no significant intrinsic effects, the benzodiazepine receptor antagonist 2-phenylpyrazolo-[4,3-c]-quinoline-3(5H)-one (CGS 8216; 1.25-5.0 mg/kg, i.p.) reversed the anorectic effect of FG 7142. When clonazepam and FG 7142 were given in combination, mutual cancelling of their opposite effects occurred. These results are consistent with an action of FG 7142 at benzodiazepine recognition sites to reduce the level of palatable food consumption, and imply that a bidirectional control of food intake via benzodiazepine recognition sites can be achieved. The anorectic effect of FG 7142 was not reversed by 24-h food deprivation, indicating a possible separation from the effects of hunger mechanisms.

CGS 8216 and CGS 9896, novel pyrazoloquinoline benzodiazepine ligands with benzodiazepine agonist and antagonist properties

CGS 8216 and CGS 9896 are two recently described compounds which interact with benzodiazepine binding sites but have pharmacological, biochemical and behavioral characteristics which distinguish them from classical benzodiazepines. CGS 8216 shows properties of a weak inverse agonist, while CGS 9896 shows properties of a mixed agonist/antagonist. Experiments using quantitative autoradiography to determine benzodiazepine binding site interactions of these compounds in discrete anatomical areas are described. Results indicate that [3H]-CGS 8216 does not show any regional differentiation in binding characteristics in 7 brain areas studied. CGS 9896 preferentially inhibited [3H]-flunitrazepam from cerebellar sites compared to hippocampal dentate gyrus sites, but the magnitude of this effect was small. These data support the conclusion that CGS 9896 is acting preferentially at putative benzodiazepine type 1 sites and is consistent with the mixed agonist/antagonist profile of the compound.

Electroencephalographic investigations in rabbits of drugs acting at GABA-benzodiazepine-barbiturate/picrotoxin receptors complex

This paper describes the EEG profiles, observed in rabbits, of drugs which affect GABA synaptic activity at GBB complex. Drugs which enhance GABA synaptic activity induce sedation associated with EEG synchronization. However, muscimol, THIP, GHB and baclofen induce signs of CNS stimulation (light tremors of the forelimbs, chewing, light nystagmus and hyperpnea) associated with EEG spikes. Signs of light stimulation (chewing and jerks of the head) also occur after BDZs and barbiturates, and are associated with the presence of 12-24 and 20-25 Hz waves, respectively. Drugs which reduce GABA synaptic activity (bicuculline, inverse BDZ agonists, PTZ, picrotoxin and Ro 5-3663) induce three dose-dependent stages of EEG changes: trains of slow waves, trains of spike-and-wave complexes and paroxysmal activity in the rostral encephalic structures without apparent changes of the electrical activity in the spinal cord. The first two stages are associated with a behavioral state of alert and the third stage with tonico-clonic convulsions. Among the inverse BDZ agonists, DMCM and beta-CCM elicit all three stages, whereas FG 7142 and beta-CCE induce only the first two and CGS 8216 only the first. The BDZ antagonists Ro 15-1788 and Ro 15-3505 (0.2-30 mg/kg IV) do not significantly affect the EEG pattern. However, they selectively inhibit the effects of diazepam and of the inverse BDZ agonists. In both cases, the inhibition is observed with doses as low as 0.2 mg/kg IV and leads to an EEG desynchronization. The possible involvement of the modifications of GABA synaptic activity in the etiology of both petit mal and grand mal epilepsies is discussed.

Bidirectional control of palatable food consumption through a common benzodiazepine receptor: theory and evidence

A classical approach to the control of food consumption has been to assume separate mechanisms for the arousal to eat, on the one hand, and the satiation of feeding responses, on the other. The present paper is concerned with a single, and a comparatively simple, neuronal mechanism which is endowed with properties to allow the complete determination of the level of feeding, from hyperphagia to anorexia. The model for the control of feeding, which is presented here, draws attention to the benzodiazepine receptor found distributed through the brain, and present in certain hypothalamic nuclei. Recent evidence which characterizes the receptor is reviewed, and the various categories of benzodiazepine receptor ligands are described. Pharmacological data, collected in a palatable food consumption model using non-food-deprived rats, demonstrate that benzodiazepine receptor agonists produce hyperphagia, benzodiazepine receptor inverse agonists produce anorexia, and benzodiazepine receptor antagonists block both effects. Hence, bidirectional control of food intake can be achieved through differential ligand action at a common set of receptors. Speculatively, these data can be extended, if it is assumed that two endogenous ligands exist in the brain which act like benzodiazepine agonist and inverse agonist, respectively. Evidence for the presence in hypothalamic nuclei of endogenous ligands of the latter kind is discussed. Benzodiazepine withdrawal-induced anorexia is also described, and is taken as evidence for the part played by feeding mechanisms in the development of benzodiazepine physical dependence.

Pyrazoloquinoline benzodiazepine receptor ligands: effects on schedule-controlled behavior in dogs

The effects of diazepam and the pyrazoloquinoline benzodiazepine receptor ligands CGS8216, CGS9896, and CGS9895 on schedule-controlled responding were studied in dogs. Responding was maintained under a multiple fixed-interval (FI) 5-min fixed-ratio (FR) 30 response schedule of food presentation. Diazepam (PO) produced dose-related decreases in response rates under FR component. Under the FI, rates first increased and then decreased with increasing doses of diazepam. Diazepam also produced a dose-related disruption of the temporal pattern of responding under the FI as measured by decreases in quarter-life values. CGS8216 IV produced dose-related decreases in response rates under both components. The highest oral dose of CGS8216 also decreased rates in both components. CGS8216 was approximately 100 times more potent by the IV route as compared to the oral route. CGS9896 IV had no significant effect on responding under either component of the multiple schedule. However, with increasing doses of CGS9896 PO, response rates under both components first decreased and then returned to control values. CGS9895 PO was without significant effect on responding. When CGS8216 was administered concomitantly with graded doses of diazepam, the former drug blocked the rate-decreasing effects of diazepam under the FR component, but not the rate-increasing effects of diazepam under the FI. The present results demonstrate that although these three pyrazoloquinolines are benzodiazepine receptor ligands, they do not exhibit diazepam-like effects on schedule-controlled behavior.

Chlordiazepoxide enhances the anxiogenic action of CGS 8216 in the social interaction test: evidence for benzodiazepine withdrawal?

The benzodiazepine receptor 'inverse agonist' CGS 8216 has a specific anxiogenic action in the social interaction test that cannot be reversed by other compounds acting at the benzodiazepine site: Ro 15-1788, FG 7142 or beta-CCE. We tried to reverse the anxiogenic effect with chlordiazepoxide, which is able to antagonise the anxiogenic effects of several other compounds acting at benzodiazepine or related sites. Chlordiazepoxide given acutely (10-20 mg/kg) was unable to antagonise the anxiogenic action of CGS 8216 (5-10 mg/kg); instead there was a tendency to enhance its effects. The effects of chlordiazepoxide after 5 days pretreatment were then assessed, since chronic treatment is necessary to reverse the anxiogenic actions of Ro 15-1788 and Ro 5-4864. At 5 mg/kg chronically, chlordiazepoxide was unable to antagonise the anxiogenic effect of CGS 8216, and at 20 mg/kg there was a significant enhancement of the effects of CGS 8216 on social interaction without an effect on locomotor activity. These results are discussed in terms of withdrawal from benzodiazepine treatment.

Chlordiazepoxide-induced hyperphagia in non-food-deprived rats: effects of Ro15-1788, CGS 8216 and ZK 93 426

Chlordiazepoxide (1.25-20.0 mg/kg i.p.) was administered to non-food-deprived male rats given 30 min access to a highly palatable, familiar diet, and produced a potent stimulation of food consumption. At the maximum dose effect, the rats consumed about 24 g food in the 30 min test. The benzodiazepine receptor antagonist, Ro15-1788 (2.5-40.0 mg/kg i.p.) had no effect on food intake when given alone, but did dose-dependently attenuate chlordiazepoxide's hyperphagic effect. The antagonist CGS 8216 (5.0-20.0 mg/kg i.p.) completely abolished the hyperphagic effect, and in doses of 10.0 and 20.0 mg/kg produced significant suppression of feeding when administered by itself. ZK 93 426, in doses (0.625-10.0 mg/kg i.p.) which have previously been shown to antagonize the discriminative cue of chlordiazepoxide produced no significant change in chlordiazepoxide's hyperphagic effect. These data point to an interesting and important distinction between ZK 93426 and the other two benzodiazepine receptor antagonists when given in combination with chlordiazepoxide in the palatable food consumption test.

Clonazepam-induced hyperphagia in nondeprived rats: tests of pharmacological specificity with Ro5-4864, Ro5-3663, Ro15-1788 and CGS 9896

Nondeprived male rats were familiarised with daily 60 min access to a highly palatable diet, consisting of powdered rat diet, sweetened condensed milk and water. Clonazepam (0.625-5.0 mg/kg, IP) produced a substantial increase in food consumption within the first 30 min of access. The increase was similar across all dose conditions, suggesting that a maximal effect may have been achieved with a dose as small as 0.625 mg/kg. The hyperphagia induced by clonazepam was reversed by the benzodiazepine receptor antagonist, Ro15-1788 (5.0-20.0 mg/kg), indicating that the effect was benzodiazepine receptor-mediated. Treatments with the peripheral-type benzodiazepine agonist, Ro5-4864, did not induce a hyperphagic response. Instead, food consumption was significantly depressed following the administration of Ro5-4864 at 20 and 40 mg/kg, IP. A comparison of the clonazepam and Ro5-4864 data suggests that benzodiazepine-induced hyperphagia is mediated by central-type benzodiazepine binding sites. The pyrazoloquinoline, CGS 9896, binds with high affinity to benzodiazepine sites and has recently been described as a nonsedating anxiolytic. CGS 9896 (2.5-20.0 mg/kg, administered either IP or PO) did not affect consumption of the highly palatable diet. In consequence, anxiolytic and hyperphagic effects of drug actions at benzodiazepine receptors may be dissociated in the case of this compound. The atypical 1,4-benzodiazepine, Ro5-3663, a GABA antagonist which may act at the picrotoxinin site, produced a dose-related reduction in food consumption. Comparison with the results for Ro5-4864 rules out an interpretation for the anorexia in terms of anxiogenic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepines and the developing rat: a critical review

This paper reviews: the development of benzodiazepine binding-sites and the GABA system; the evidence that prenatal exposure to benzodiazepines can cause malformations; other persisting effects of developmental exposure to benzodiazepines; and the behavioral effects of benzodiazepines (and other relevant drugs) in immature animals. The review concentrates on the rat, since fundamental work in other species is scarce. The data on neurochemical development are found to be generally consistent; however, reports that the enhancement of benzodiazepine binding by GABA varies with age are controversial. The physical development of the rat is disturbed only by extremely high doses of benzodiazepines. The evidence for persisting effects after early exposure to benzodiazepines is impressive at first sight, but in most studies, confounding variables have not been eliminated. Startle and some learning tasks are affected by prenatal diazepam; submissiveness is affected by neonatal lorazepam; social behaviour and convulsions are affected by neonatal CGS 8216. Benzodiazepines inhibit chemically-induced seizures in neonatal rats, but the developmental profile of sensitivity to the convulsants is disputed. Benzodiazepines stimulate motor behavior in the neonatal rat.

Behavioural pharmacology of food, water and salt intake in relation to drug actions at benzodiazepine receptors

Drugs which are agonists at benzodiazepine receptors produce many interesting behavioural effects, and amongst these are the stimulation of food, water and salt intake. This review examines the evidence for benzodiazepine effects on these forms of ingestion, and makes tentative proposals about their modes of action. The recent advent of putative benzodiazepine antagonists and inverse agonists provides important new pharmacological tools for the analysis of factors which control ingestion. Preliminary data on examples of such drugs are considered. Anorectic effects of inverse agonists are described. It is clear, though, that the categorization of a drug in one test situation may not apply to another. For example, the compound Ro15-1788 appears as a specific antagonist in one test, a partial agonist in another, and apparently lacks effect in a third. We are not yet sufficiently forward in our understanding of drug actions at benzodiazepine receptors, and their interactions with particular test circumstances, to predict and account for divergent effects of this kind.

Benzodiazepines and their antagonists: a pharmacoethological analysis with particular reference to effects on "aggression"

A review of the literature on chlordiazepoxide indicates that the traditional view of benzodiazepines as antiaggressive drugs represents an inaccurate generalization. In fact, highly variable findings have been reported with the most significant factor in the variability being the type of aggression studied. Furthermore, considerable controversy surrounds the nature of chlordiazepoxide's influence on social conflict in rodents, with opinion divided regarding the selectivity of its inhibitory effect on offensive responding. It is argued that inappropriate behavioural methodology may have substantially contributed to this controversy. A pharmacoethological approach to the analysis of drug effects on social behaviour is described and exemplified by new data on chlordiazepoxide and midazolam. Both agents inhibit offense at doses which do not result in general response inhibition, yet their overall behavioural profiles are somewhat different. Evidence is also presented indicating low dose behavioural activity of the benzodiazepine antagonist Ro15-1788 in two test situations and suggesting possible differences in the effects of Ro15-1788 and CGS8216 on novelty-related responding. Several avenues of research are discussed which may yield insights into the manner whereby benzodiazepines influence social patterns and the significance of benzodiazepine-GABA interactions in such processes.

What can be learned from the effects of benzodiazepines on exploratory behavior?

The purpose of this review is to assess the value of using tests of exploratory behavior to study the actions of benzodiazepines. The methods of measuring exploration and the factors influencing it are briefly described. The effects of benzodiazepines on exploratory behavior of rats and mice are reviewed; and the dangers of interpreting the results of such tests in terms of any of the clinical effects of the benzodiazepines is stressed. Finally, the interactions between benzodiazepines and other drugs acting at the GABA-benzodiazepine receptor complex are described. The results of these experiments caution against global classification of compounds as benzodiazepine "antagonists."

Evidence that 2-phenylpyrazolo[4,3-c]-quinolin-3(5H)-one antagonises pharmacological, electrophysiological and biochemical effects of diazepam in rats

The effects of the acute administration of 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one on diazepam-induced behaviour and electrophysiological activity were studied in rat. The compound, in doses of 5-10 mg/kg (i.p.), which per se did not induce alterations in spontaneous locomotor activity, antagonised the sedative effect induced by 5-10 mg/kg (i.p.) of diazepam. The injection of diazepam in rats, induced a profound reduction in the first negative wave of the recording of the visual evoked potential used as a sensitive electrophysiological test, in vivo. 2-Phenylpyrazolo[4,3-c]quinolin-3(5H)-one (10 mg/kg, i.p.) caused a recovery of the amplitude of the first negative wave within a few minutes. This result was confirmed by the finding that 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one, injected acutely in rats, pretreated with diazepam exhibited the capacity to antagonise the binding of [3H]diazepam determined in vitro on synaptic membrane preparations from cortex. The comparison of the pattern of the visual-evoked potential, recorded after the injection of 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one (50 mg/kg) with the patterns recorded after the injection of ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazolo(1,5a) (1,4)benzodiazepine-3-carboxylate (50 mg/kg) and ethyl-beta-carboline-3-carboxylate and 1-methyl-beta-carboline demonstrated that 2-phenylpyrazolo[4,3-c]quinolin-3(5H)-one is devoid of intrinsic activity.

Lorazepam and pentobarbital discrimination: interactions with CGS 8216 and caffeine

Baboons and rats were trained under a two-lever, food-reinforced drug discrimination procedure. The training drug was either lorazepam (1.0 mg/kg) or pentobarbital (5.6 mg/kg in baboons, 10.0 mg/kg in rats). Under test conditions, a range of training drug doses occasioned 100% drug lever responding. CGS 8216 (3.2-10.0 mg/kg) combined with lorazepam produced a complete shift to the no-drug lever in both species; this shift was surmountable with higher doses of lorazepam. CGS 8216 (32.0 mg/kg) combined with pentobarbital produced a statistically significant decrease in drug-lever responding in rats, and in baboons CGS 8216 initially, but not subsequently, produced a complete shift to the no-drug lever. Caffeine (0.32-10.0 mg/kg) combined with lorazepam inconsistently decreased drug-lever responding across multiple determinations in baboons and significantly decreased drug lever responding in rats. Caffeine combined with pentobarbital also yielded an inconsistent decrease in drug lever responding in baboons but there was no effect in rats. Thus the most reliable and complete antagonism across species was obtained with the CGS 8216/lorazepam combinations.

Benzodiazepine receptor ligands and the consumption of a highly palatable diet in non-deprived male rats

Non-deprived rats were familiarized with a highly palatable diet until baseline consumption in a 60-min daily access period had stabilised. The benzodiazepine receptor agonist midazolam (1.25-10.0 mg/kg, IP) produced a large, dose-related increase in food consumption during the first 30 min of access. It also produced significant, short-term hyperphagia in animals which had been partially pre-satiated on the diet before drug administration, an effect which was reversible by the benzodiazepine receptor antagonist Ro15-1788. Administered alone, Ro15-1788 (1.25-10.0 mg/kg, IP) had no intrinsic activity in the food consumption test. In contrast, CGS 8216 (2.5-40.0 mg/kg, IP) produced a marked dose-related suppression of food intake. This anorectic effect was shared by two benzodiazepine receptor inverse agonists, FG 7142 and DMCM, which also produced dose-dependent reductions in consumption. The effects on feeding produced by FG 7142 (20 mg/kg, IP) and DMCM (1.25 mg/kg, IP) were reversed by either Ro15-1788 (2.5 and 5.0 mg/kg) or midazolam (5.0 and 10.0 mg/kg). A matched anorectic effect produced by CGS 8216 (40 mg/kg) was not, however, reversed by either Ro15-1788 or midazolam. This suggests that at a high dose CGS 8216 may act by a mechanism different from that of the two inverse agonists. The feeding test described in the report proved sensitive to both hyperphagic and anorectic effects of drugs active at benzodiazepine receptors, pointing to a possible bi-directional control of palatable food consumption.

The anxiogenic action of RO 5-4864 in the social interaction test: effect of chlordiazepoxide, RO 15-1788 and CGS 8216

RO 5-4864 (20 mg/kg), a benzodiazepine with high affinity for peripheral-type benzodiazepine binding sites in rat kidney and brain, but not for the "classical" CNS sites, reduced the time spent by pairs of rats in active social interaction, without reducing locomotor activity, possibly reflecting an anxiogenic action. This anxiogenic effect was not reversed by chlordiazepoxide (5 or 10 mg/kg) given acutely, but was reversed by chlordiazepoxide (5 mg/kg) given for 5 days prior to testing. RO 15-1788 (10 mg/kg), a drug that antagonises several effects of benzodiazepines but has little affinity for peripheral-type sites, had no action on the reduction in social interaction induced by RO 5-4864. However, CGS 8216 (10 mg/kg) which also antagonises the effects of benzodiazepines and has little affinity for RO 5-4864 recognition sites, significantly enhanced the reduction in social interaction caused by RO 5-4864, and the combination produced a significant decrease in locomotor activity. These results are discussed in terms of possible sites of action of RO 5-4864 on the GABA-benzodiazepine receptor complex.

Midazolam-induced increase in NaCl solution ingestion: differential effect of the benzodiazepine antagonists Ro 15-1788 and CGS 8216

After adaptation to a 23-hr water deprivation regimen, under which rats were allowed a daily 1-hr water rehydration session, they were injected (SC) with 1 or 2 drugs presession and given 1.5% NaCl solution to drink in place of water. Midazolam (0.5-1.0 mg/kg) increased the intake of 1.5% NaCl solution as did Ro 15-1788 (2.5-10.0 mg/kg). This confirmed a previously noted agonist effect of midazolam and partial agonist action of Ro 15-1788. When injected in combination with midazolam, Ro 15-1788 (2.5-10.0 mg/kg) antagonized the effect of midazolam. CGS 8216 (2.5-20.0 mg/kg) revealed no partial agonist action on the NaCl solution ingestion procedure nor did it block the effect of midazolam.

Modification of seizures elicited by the benzodiazepine Ro 5-3663--a comparison with picrotoxin

Ro 5-3663 is a convulsant 1,4-benzodiazepine that does not act at the benzodiazepine, but at the picrotoxin, site. To characterize the behavioural actions of Ro 5-3663, a comparison was made between its effects and those of picrotoxin, when combined with several compounds that act at the GABA-benzodiazepine receptor complex. The quinolines, PK 8165, PK 9084 and CGS 8216 caused myoclonic jerks when combined with subconvulsant doses of Ro 5-3663 or picrotoxin; in combination with picrotoxin they also caused full tonic-clonic convulsions. Ro 15-1788 (1, 10 mg kg-1) caused myoclonic jerks when it was given 10 min before, or at the same time as, subconvulsant doses of either compound. Diazepam (2, 4 mg kg-1) was anticonvulsant against both compounds. However, Ro 15-1788 (10, 20 mg kg-1, 20 min before), PK 8165 (80 mg kg-1) and PK 9084 (60 mg kg-1) were effective only against the convulsions induced by Ro 5-3663. It is not possible to determine whether these differences between Ro 5-3663 and picrotoxin are quantitative or qualitative.

Benzodiazepine agonist-type activity of raubasine, a rauwolfia serpentina alkaloid

Raubasine produced a dose-related inhibition of specific [3H]flunitrazepam binding to rat brain membranes. Scatchard analyses revealed a significant increase in the affinity constant but no change in the number of binding sites, suggesting that raubasine acts as a competitive inhibitor. Raubasine also inhibited the in vivo binding of [3H]flunitrazepam to mouse brain sites. Behavioral studies showed raubasine to possess anticonvulsant properties against pentylenetetrazol- and bicuculline-induced convulsions in mice. These effects were inhibited by the benzodiazepine antagonist, Ro 15-1788. The results suggest that raubasine interacts directly at benzodiazepine sites with a benzodiazepine agonist-type activity.

CGS 8216 fails to modify novelty-related behaviour in mice: further evidence for differential actions of benzodiazepine antagonists

Recent evidence has indicated that, in rats, benzodiazepine antagonists exhibit low-dose intrinsic behavioural properties. In this study, the influence of CGS 8216 (1-20 mg/kg, i.p.) on the responsiveness of male mice to environmental novelty was examined. Unlike Ro 15-1788, which has previously been reported to enhance rearing under the present test conditions, analysis revealed that CGS 8216 was without effect on novelty-related responding. Results are discussed in relation to possible differences in the mode of action of various benzodiazepine antagonists.

CGS 8216, Ro 15-1788 and methyl-beta-carboline-3-carboxylate, but not EMD 41717 antagonize the muscle relaxant effect of diazepam in genetically spastic rats

Diazepam (0.4-4 mg/kg i.p.) reduced the spontaneous tonic activity in the electromyogram (EMG) recorded from the gastrocnemius-soleus muscle of spastic mutant Han-Wistar rats in a dose-dependent manner. The muscle relaxant effect of diazepam was antagonized by the benzodiazepine antagonists Ro 15-1788 (5 mg/kg i.p.), beta-CCM (2 mg/kg i.p.) and CGS 8216 (5 mg/kg i.p.), but not by EMD 41717 (50 mg/kg i.p.). These results add further support to the hypothesis that Ro 15-1788, CGS 8216 and beta-CCM do antagonize all pharmacological effects of benzodiazepines while EMD 41717 displays more selectivity in antagonizing the different actions of benzodiazepines.

Behavioural effects of PK 8165 that are not mediated by benzodiazepine binding sites

The phenylquinoline, PK 8165 (5-25 mg/kg), produced dose-related reductions in locomotor activity, rearing and exploratory head-dipping in a holeboard. Neither Ro 15-1788 (1, 10 or 20 mg/kg) nor CGS 8216 (1 or 10 mg/kg) was able to reverse the reductions in locomotor activity or rearing. This suggests that at least some of the behavioural effects of PK 8165 are not mediated by a site on the GABA-benzodiazepine receptor complex. This conclusion is supported by the recent report [9] that, whereas PK 8165 potently displaces benzodiazepines from their binding site in vitro, it is without effect in vivo.