A 7-phenyl substituted triazolopyridazine has inverse agonist activity at the benzodiazepine receptor site

Combination of buspirone and other drugs with beta-CCE in monkeys: effects on respiration and behavior

The respiratory and behavioral effects of the benzodiazepine receptor (BZR) inverse agonist ethyl-beta-carboline-3-carboxylate (beta-CCE) were determined alone and in combination with buspirone, lorazepam, flumazenil, and SR 95195 in rhesus monkeys. For the respiratory studies, one group of monkeys inhaled either air or 5% CO2 mixed in air according to a fixed alternating schedule; respiratory frequency and minute volume were monitored. For the behavioral studies, another group of monkeys responded under a fixed-ratio (FR 30) schedule of food presentation. The respiratory stimulant effects of beta-CCE in both air and 5% CO2 were enhanced by prior treatment with the 5-hydroxytryptamine1A (5-HT1A) partial agonist buspirone (0.03 and 0.3 mg/kg) and a weak BZR inverse agonist, SR 95195 (10.0 mg/kg). Coadministration of buspirone (0.1 and 0.3 mg/kg) also potentiated the rate-decreasing effects of beta-CCE under the FR schedule. The BZR agonist lorazepam (3.0 mg/kg) and BZR antagonist flumazenil (1.0 mg/kg) attenuated the effects of beta-CCE on respiratory frequency and minute volume particularly under the 5% CO2 condition, and lorazepam (0.1 and 0.3 mg/kg) and flumazenil (0.1 and 0.3 mg/kg) attenuated the effects of beta-CCE on FR responding. These latter results show that the respiratory and behavioral effects of beta-CCE in rhesus monkeys are at least in part due to effects at BZRs. Moreover, the findings suggest either that coactivation of benzodiazepine and 5-HT1A sites lead to a greater than additive effect or that beta-CCE and buspirone share a common mechanism of action that is unrelated to the receptor at which BZR inverse agonists act.

Cerebral-activating (EEG) properties of two inverse agonists and of an antagonist at the benzodiazepine receptor in the rat

In order to assess the effects of inverse benzodiazepine agonists and antagonists on brain function, computerized EEG (CEEG) analysis was performed in rats following the i.p. administration of SR 95195 (7-phenyl-3-methyl-1,2,4 triazolo-[4,3-b]pyridazine) and CGS 8216 (2-phenylpyrazolo-[4,3c]-quinoline-3-[5H]-one) two benzodiazepine receptor inverse agonists (BRIAGs) and of flumazepil (Ro 15-1788), a benzodiazepine receptor antagonist (BRANT). The EEG effects of SR 95195 (3, 10, 30 and 60 mg/kg), CGS 8216 (10 and 30 mg/kg) and flumazepil (3, 10, 30 and 60 mg/kg) were compared to those of the psychostimulant drugs DL-amphetamine (0.1, 0.3 and 1 mg/kg), and caffeine (10 and 30 mg/kg) and those of aniracetam (100 and 300 mg/kg), a nootropic pyrrolidone derivative. The CEEG profiles of SR 95195, CGS 8216 and flumazepil were mainly characterized by a power increase in the 20-32 Hz frequency range and by a power reduction in the 8-16 Hz range. These effects were quite similar to those of the psychostimulants DL-amphetamine and caffeine as well as to those of the nootropic aniracetam. Other psychotropic drugs with CNS-depressant properties, namely diazepam (10 mg/kg p.o.), pentobarbital (30 mg/kg p.o.), chlorpromazine (10 mg/kg i.p.) and imipramine (10 mg/kg i.p.) induced quite different EEG power modifications. These results show that BRIAGs and BRANTs possess a marked intrinsic activity at the central level and suggest that this activity is CNS-activating in nature.

The active analog approach applied to the pharmacophore identification of benzodiazepine receptor ligands

Applied to seven potent benzodiazepine-receptor ligands belonging to chemically different classes, the active analog approach allowed the stepwise identification of the pharmacophoric pattern associated with the recognition by the benzodiazepine receptor. A unique pharmacophore model was derived which involves six critical zones: (a) a pi-electron rich aromatic (PAR) zone; (b) two electron-rich zones delta 1 and delta 2 placed at 5.0 and 4.5 A respectively from the reference centroid in the PAR zone; (c) a freely rotating aromatic ring (FRA) region; (d) an out-of-plane region (OPR), strongly associated with agonist properties; and (e) an additional hydrophobic region (AHR). The model accommodates all presently known ligands of the benzodiazepine receptor, identifies sensitivity to steric hindrance close to the delta 1 zone, accounts for R and S differential affinities and distinguishes requirements for agonist versus non-agonist activity profiles.