The quinolines PK 8165 and PK 9084 possess benzodiazepine-like activity in vitro but not in vivo

Effect of psychotomimetics and some putative anxiolytics on stress-induced hyperthermia

Stress-induced hyperthermia (SIH), which is seen in the last mice removed from the cage, is a novel animal model sensitive to anxiolytic drugs. SIH is antagonized by CL 218872 (25 and 50 mg/kg, os), by tracazolate (5 and 7.5 mg/kg, ip) and by 2-AP-5 (50 and 100 mg/kg, ip). At higher dose, CL 218872 (100 mg/kg, os) and tracazolate (12.5 mg/kg, ip) lose their activity. PK 9084 (5-40 mg/kg, ip) and CGS 9896 (2-20 mg/kg, both ip and os) were also ineffective in preventing SIH. The anti-hyperthermic effect of CL 218872 (25 mg/kg) and tracazolate (7.5 mg/kg) was blocked by the benzodiazepine antagonist Ro 15-1788 (15 mg/kg), CGS 9896 (10 mg/kg, os) also reversed the effect of CL 218872 (25 mg/kg) on SIH. Differently from anxiolytics, MK-801 (0.5-1 mg/kg, os), PCP (2.5 mg/kg, ip) and d-amphetamine (10 mg/kg, ip) evoked hyperthermia in the first set of mice and prevented a further stress-induced rise of body temperature in the last set of mice.

Effects of non-sedative anxiolytic drugs on responses to GABA and on diazepam-induced enhancement of these responses on mouse neurones in cell culture

1. Intracellular microelectrode recording techniques were performed on mouse spinal cord and cerebral hemisphere neurones grown in primary dissociated cell culture. The effects of several anxiolytics applied by local pressure ejection on responses to gamma-aminobutyric acid (GABA) evoked by iontophoresis were investigated. Responses to GABA were depolarizing since intracellular chloride ion concentration was increased by injection from potassium chloride (3M)-filled recording micropipettes and neurones were held at large negative membrane potentials (-70 to -90 mV). The agents studied were six 'non-sedative anxiolytics', CL 218,872 (3-methyl-6-(3-trifluoromethyl-phenyl)1,2,4-triazolo(4,3-b) pyridazine), PK 8165 (2-phenyl-4-(2-(4-piperidinyl)ethyl)-quinoline), PK 9084 (2-phenyl-4-(2-(3-piperidinyl)ethyl)-quinoline), CGS 9896 (2-(4-chlorophenyl)-2,5-dihydropyrazolo(4,3-c)quinoline-3(3H)-one) , ZK 91296 (ethyl 5-benzyloxy-4-methoxymethyl-beta-carboline-3-beta-carboxylate), buspirone (8-4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl-8-azaspiro[4.5]decane- 7,9- dione), and two sedative anxiolytics, diazepam and zopiclone [( 6-(5-chloro-2-pyridyl)-6,7-dihydro-7-oxo-5H-pyrrolo[3,4-b]pyrazin- 5- yl]4-methyl-1-piperazinecarboxylate). 2. Direct effects on responses to GABA were studied for all drugs applied in varying concentrations. For the drugs which significantly altered responses to GABA, the effects of the benzodiazepine receptor antagonists Ro 15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo(1,5a)-(1,4)benzodi azepine - 3-carboxylate) and CGS 8216 (2-phenylpyrazolo(4,3-c)-quinolin-3(5H)-one) were evaluated. For the drugs devoid of significant direct effect on responses to GABA, the influence on diazepam-induced enhancement of responses to GABA was evaluated. 3. Diazepam, zopiclone and CL 218,872 concentration-dependently and reversibly enhanced responses to GABA. Maximal enhancement was 82% for diazepam (500 nM), 64% for zopiclone (10 microM) and 20% for CL 218,872 (10 microM). PK 8165 effects varied with concentration, enhancing responses to GABA (up to 18%) at nM concentrations and reducing responses to GABA (up to 90%) at microM concentrations. CGS 9896, ZK 9126, PK 9084 and buspirone, in concentrations ranging from 1 nM to 10 microM, lacked significant direct effects on responses to GABA. 4. The enhancing effects of diazepam, zopiclone, CL 218,872 and PK 8165 were antagonized by Ro 15-1788. However, the reducing effect on responses to GABA of PK 8165 at microM concentrations was not antagonized by CGS 8216. CGS 9896 and ZK 91296 concentration-dependently blocked the diazepam-induced enhancement of responses to GABA. However, PK 9084 and buspirone did not antagonize the diazepam-induced enhancement of responses to GABA. 5. These results indicate that diazepam and zopiclone may be full agonists, CL 218,872 and PK 8165 are partial agonists, and CGS 9896 and ZK 91296 are pure antagonists at benzodiazepine receptors. On the other hand, PK 9084 and buspirone do not interact with benzodiazepine receptors.

Effects of agents which interact with central benzodiazepine binding sites on stress-induced ultrasounds in rat pups

Compounds of different chemical classes, with affinity for central benzodiazepine receptors, were investigated for effects on handling-induced ultrasonic cries in rat pups. Diazepam and clobazam inhibited ultrasounds and impaired motor performance at higher doses. Suriclone showed a similar profile to diazepam but premazepam clearly separated ultrasound inhibition from motor impairment. ZK 91296, CGS 9896, RU 39419 and RU 43028 inhibited ultrasounds with a lower maximal response but induced little or no motor incoordination. CL 218872 inconsistently inhibited sounds with no motor impairment and PK 8165 and PK 9084 had no consistent effects. Benzodiazepine antagonists weakly inhibited (RU 40410) or did not affect (Ro 15-1788 or CGS 8216) ultrasounds alone but fully (Ro 15-1788 or CGS 8216) or partially (RU 40410) antagonised the effects of benzodiazepines. Inverse agonists FG 7142, methyl-beta-carboline-3-carboxylate (BCM) and DMCM tended to increase ultrasounds alone, particularly when less stressful handling stimuli were used, and antagonised benzodiazepines. This procedure detects the differing behavioural effects of benzodiazepines receptor ligands and is proposed as a simple model of anxiety.

Anxiolytic and anxiogenic drug effects on exploratory activity in an elevated plus-maze: a novel test of anxiety in the rat

The current studies further investigated the effects, in animal models of anxiety, of novel putative anxiolytic and anxiogenic compounds believed to induce their effects by actions at the GABA-benzodiazepine receptor complex. It was expected that the results would also provide further validation for a novel test of anxiety based on the ratio of open to closed arm entries in an elevated plus maze in the rat. The novel putative anxiolytics CL 218,872 (10-20 mg/kg) and tracazolate (5 mg/kg) significantly elevated the percentage of time spent on the open arms of an elevated plus-maze, consistent with their anxiolytic activity in several other animal tests. Also consistent with results from other animal tests, no anxiolytic activity was observed for the phenylquinoline PK 8165 (10-25 mg/kg), the 3,4-benzodiazepine tofisopam (25-50 mg/kg), or buspirone (0.5-20 mg/kg). The benzodiazepine receptor inverse agonists FG 7142 (1-5 mg/kg) and CGS 8216 (3-10 mg/kg) had anxiogenic activity in this test, as did the atypical benzodiazepine Ro 5-4864 (1-5 mg/kg). Interestingly, however, the benzodiazepine receptor antagonists Ro 15-1788 (10-20 mg/kg) and ZK 93426 (5-10 mg/kg) had no anxiogenic activity in this test.

Antagonism of flurazepam and other effects of Ro15-1788, PK8165 and Ro5-4864 on the GABA-A receptor complex in rat cuneate nucleus

In slices of rat cuneate nucleus, responses to the GABA-A receptor agonist muscimol were potentiated by flurazepam. The maximal potentiation by 1 microM flurazepam was antagonized by the neuronal benzodiazepine receptor ligand Ro15-1788 3 microM, by the quinoline derivative PK8165 0.1 microM and by the peripheral-type benzodiazepine receptor ligand Ro5-4864 0.1 microM. Another ligand for the peripheral-type benzodiazepine receptor, PK11195 10 microM, enhanced the potentiating effect of a submaximal concentration of flurazepam 0.1 microM and prevented the antagonism of flurazepam by Ro5-4864. At much higher concentrations of these drugs, additional effects were seen. Ro15-1788 30 microM and PK11195 30 microM each caused small potentiations of muscimol while Ro5-4864 30 microM caused a small antagonism. Ro15-1788 30 microM, PK8165 100 microM and Ro5-4864 30 microM all antagonized the potentiation of muscimol by pentobarbitone 10 microM; also, PK8165 and Ro5-4864 enhanced the potency of picrotoxin as an antagonist of muscimol. It is concluded that both Ro5-4864 and PK8165 have several distinct effects on the GABA-A receptor complex, all of which could result in reduced responses to muscimol.

Pro- and anti-convulsant drug effects in combination with the convulsant benzodiazepine Ro 5-4864

The effects of several compounds believed to act at the GABA-benzodiazepine receptor complex and which have anticonvulsant or proconvulsant properties when administered in combination with picrotoxin and pentetrazol (leptazol, pentylenetetrazole) were investigated in combination with the convulsant benzodiazepine Ro 5-4864. Tracazolate (25-100 mg kg-1) failed to affect convulsions induced by Ro 5-4864; however, they were prevented by treatment with CL 218,872 (20 mg kg-1). Compounds having proconvulsant activity in combination with a subthreshold dose of Ro 5-4864 were: CL 218,872 (5 mg kg-1), and CGS 8216 (20 mg kg-1) and FG 7142 (40 mg kg-1), two compounds characterized as 'inverse agonists' at benzodiazepine receptors. The phenylquinolines PK 8165 and PK 9084, originally believed to have anxiolytic properties, had no significant effect in combination with Ro 5-4864 (25-100 mg kg-1). The convulsant profile of Ro 5-4864 is compared with that of picrotoxin and pentetrazol.

Effects of PK 8165, a partial benzodiazepine receptor agonist, on cholecystokinin-induced activation of hippocampal pyramidal neurons: a microiontophoretic study in the rat

Benzodiazepines (BZD) have been reported to suppress cholecystokinin-8S (CCK-8S)-induced activation. PK 8165, a ligand of BZD receptors, is an anxiolytic devoid of sedative and anticonvulsant effects. PK 8165, applied microiontophoretically or administered i.v. at low doses, suppressed CCK-8S-induced activation of hippocampal pyramidal neurons, whereas, at high doses it antagonized the effect of microiontophoretic applications of flurazepam. These results indicate that PK 8165 acts as a mixed agonist-antagonist at BZD receptors and suggest that the suppression of CCK-8S-induced activation by BZD might be related to their anxiolytic property rather than to their sedative or anticonvulsant activity.

Effects of acute and chronic treatment on the pro- and anti-convulsant actions of CL 218, 872, PK 8165 and PK 9084, putative ligands for the benzodiazepine receptor

CL 218,872 is a triazolopyridazine that acts at the benzodiazepine binding site. At low doses (0.5-7.5 mg kg-1) it is proconvulsant when combined with subconvulsant doses of picrotoxin but not when combined with pentetrazol (leptazol, pentylenetetrazol). At high doses (20-60 mg kg-1) CL 218,872 counteracted seizures caused by pentetrazol but not those caused by picrotoxin. There was tolerance to the proconvulsant effects after five days of treatment and to the anticonvulsant effects after 15-20 days. Two phenylquinolines, PK 8165 and PK 9084, that also act at the GABA-benzodiazepine receptor complex have proconvulsant actions in combination with picrotoxin. Significant tolerance to these effects had not developed even after 20 days of treatment. It is concluded that three different sites on the GABA-benzodiazepine complex mediate the pro- and anti-convulsant actions of CL 218,872 and the proconvulsant actions of PK 8165 and PK 9084.

Can drug effects on anxiety and convulsions be separated?

The effects of benzodiazepines, barbiturates, a series of novel putative anxiolytic compounds and anxiogenic compounds are reviewed in animal tests of anxiety and on experimentally-induced seizures. It is clear from the data that drug effects on anxiety and convulsions are not always in the same direction; certain compounds are apparently both anxiolytic and proconvulsant, others are anxiogenic and anticonvulsant, others have varied effects depending on the test situation. It is suggested that this work necessitates considerable revision of our traditional concepts of an "anticonvulsant." The extent to which drug-induced anxiety is correlated with weak epileptiform activity in the brain is discussed. Finally, the Discussion considers a number of possible mechanisms that could underlie the separation of drug effects on anxiety and convulsions that is observed.

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."

Anxiolytic drugs and the acquisition of conditioned fear in mice

Previous studies have shown that, in rodents, chlordiazepoxide and other benzodiazepines can interfere with learning in passive avoidance or conditioned suppression procedures. The most consistent effects are observed when the drugs are administered before the acquisition trial and subjects are re-tested in the non-drugged state. It is not clear, however, whether this effect on learning is associated with the behavioural depressant actions of these drugs. In the present study mice were injected with chloridiazepoxide, diazepam, zopiclone, or CGS 9896 and locomotor activity measured in a two-compartment box. The animals were then enclosed in one of the compartments and received a series of footshocks. On a second trial, 24 h after the first, the mice were returned to the box without injection and locomotion and time spent in each compartment were measured. During trial 1 chlordiazepoxide, diazepam, and zopiclone produced dose-related decreases in locomotor activity. The same doses disrupted fear conditioning. CGS 9896 also interfered with the conditioning of fear but did not reduce exploratory activity during the first trial at any of a wide range of doses, showing that learning can be affected without direct behavioural depressant activity. In a further experiment, chlordiazepoxide and CGS 9896 disrupted fear conditioning when injected before trial 1 but not when injected immediately after this trial. Mice drugged with chlordiazepoxide or CGS 9896 before both trials 1 and 2 also showed disrupted conditioning, demonstrating that the drug effects cannot be interpreted in terms of state dependent learning.

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.