CGS 8216: receptor binding characteristics of a potent benzodiazepine antagonist

RO5-4864, a ligand for benzodiazepine micromolar and peripheral binding sites: antagonism and enhancement of behavioural effects

RO5-4864, a ligand for both the peripheral and for the central nervous system micromolar benzodiazepine binding sites, was investigated in the holeboard, alone and in combination with several other drugs. RO5-4864 alone caused a marked reduction in rears and motor activity and reduced head-dipping when objects were placed under the holes. All these reductions were enhanced by picrotoxin (2 and 4 mg/kg) and by CGS 8216 (3 mg/kg). RO15-1788 (10 mg/kg) reversed the reduction in rears and PK11195 (30 mg/kg), a putative antagonist for the peripheral binding site, reversed the reduction in head-dipping. The results are discussed in terms of the various benzodiazepine binding sites and possible non-specific drug effects.

Evidence for distinct benzodiazepine receptors for anticonvulsant and sedative actions: implications for the treatment of temporal lobe epilepsy

An imidazobenzodiazepine, Ro15-1788, has anticonvulsant effects in the kindling model for epilepsy. Ro15-1788 reverses the sedative actions of diazepam (3 mg/kg i.p.) but does not reverse the anticonvulsant effects. The anticonvulsant effects of Ro15-1788 are prevented by the pyrazoloquinolinone CGS-8216 which interacts with benzodiazepine receptors but has no anticonvulsant actions itself. It is suggested that Ro15-1788 is a partial agonist at the BZ2 (anticonvulsant) receptor but is an antagonist at the BZ1 (sedative, anxiolytic) receptor. CGS-8216 is an antagonist at both receptors. Ro15-1788 or related compounds may be effective anticonvulsants without the sedative side-effects usually found with the benzodiazepines.

Blockade of 3-carbomethoxy-beta-carboline induced seizures by diazepam and the benzodiazepine antagonists, Ro 15-1788 and CGS 8216

The benzodiazepine antagonists Ro 15-1788 and CGS 8216 blocked the clonic and tonic convulsions elicited by 3-carbomethoxy-beta-carboline (beta-CCM). The PD50 values for Ro 15-1788, CGS 8216, and diazepam were: 2.0, 0.6, and 2.0 mg/kg, respectively. Neither Ro 15-1788 nor CGS 8216 potentiated the effect of a threshold convulsant dose of beta-CCM. Moreover, these benzodiazepine antagonists neither attenuated nor potentiated the tremorigenic actions of another beta-carboline, harmaline. Diazepam, however, considerably reduced the tremorigenic actions of this drug.

The effect of GABA on in vitro binding of two novel non-benzodiazepines, PK 8165 and CGS 8216, to benzodiazepine receptors in the rat brain

The effect of gamma-aminobutyric acid (GABA) on the binding of PK 8165, a quinoline derivative, and CGS 8216, a pyrazoloquinoline, was assessed in two different regions of the rat brain. PK 8165, a compound with reported anxiolytic properties, inhibited [3H]-propyl beta-carboline-3-carboxylate labeled receptors in the cerebellum with an IC50 of 844 nM and 370 nM in the absence and presence of micro M GABA, respectively. GABA (100 micro M) was less effective in the cerebral cortex, decreasing the IC50 value from 280 to 197 nM. In saturation isotherm studies with [3H]-CGS 8216, a benzodiazepine receptor antagonist, GABA (100 micro M) induced a small but significant reduction in the apparent affinity of [3H]-CGS 8216 for benzodiazepine receptors in the cerebral cortex but the Bmax was unchanged.

A novel pyrazoloquinoline that interacts with brain benzodiazepine receptors: characterization of some in vitro and in vivo properties of CGS 9896

The novel pyrazoloquinoline, CGS, 9896, was a potent inhibitor of specific [3H]-flunitrazepam binding in several brain regions with subnanomolar KI values. The inhibition of [3H] propyl beta-carboline-3-carboxylate ([3H]-PCC-) binding by CGS 9896 was enhanced by gamma-aminobutyric acid (GABA) but not by chloride ion. GABA enhancement of CGS 9896 inhibition of [3H]-PCC binding predicts this compound has benzodiazepine (BZD) agonist-type activity. Behavioral studies support this prediction. CGS 9896 was found to protect mice against bicuculline and metrazol induced seizure at doses that did not induce ataxia or sedation. CGS 9896 may represent a class of compounds with potential therapeutic value. The high affinity of this non-BZD compound suggests that CGS 9896 may also be of value as a high affinity ligand for the continued study of BZD receptors.