Characteristics of the Association of Brotizolam, a Thieno-Triazolo Diazepine Derivative, with the Benzodiazepine Receptor: A Selective and High Affinity Ligand of the Central Type I Benzodiazepine Receptor.

Abstract

ABSTRACT-Characteristics of the association of brotizolam, a thieno-triazolo diazepine derivative, to central benzodiazepine receptors were examined. Brotizolam significantly displaced the [3H]flunitraz epam and [3H]/3-carboline carboxylate ethylester bindings to crude synaptic membrane from the rat brain. This agent had the highest affinity for benzodiazepine receptors in the cerebellum, and it was found to be 2.1 times that in the spinal cord. Furthermore, a low concentration of brotizolam poten tiated the GABA-stimulated 36C1 influx into membrane vesicles. In contrast, the bindings of [3H]8 hydroxy-2-(di-n-propylamino) tetralin to 5-hydroxytryptaminelA receptors and [3H]ketanserin to 5 hydroxytryptamine2 receptors were not affected by brotizolam. The present results suggest that brotizo lam may be a selective and high affinity ligand for the type I central benzodiazepine receptor. The anx iolytic and hypnotic actions of brotizolam seem to be not due to the association with 5-hydroxytrypta mine receptor, but due to the activation of the GABAA receptor complex. Furthermore, the present results suggest that the lower affinity of brotizolam to benzodiazepine receptors in the spinal cord than those in the cerebellum may be related to the low muscle relaxation action of this drug. Brotizolam (8-bromo-6-(o-chlorophenyl)-1-methyl-4H triazolo [3,4-c]thieno[2,3-e]-1,4-diazepine), one of the thieno-triazolo diazepine derivatives, has been clinically used as a hypnotic drug (5). The pharmacological sig nificances of this drug are reported to be no alteration in the duration and frequency of REM sleep in addition to a low potency in muscle relaxation.On the other hand, it has been well-established that the activation of central BZP receptor induces various central actions by affecting GABAergic neurons, since central BZP receptor couples with the GABAA recep tor/Cl channel complex (6). Furthermore, recent phar macological and molecular biological studies have indi cated that both type I BZP receptor, a binding site hav ing high affinity for CL218,872, and type II BZP recep tor, which has lower affinity for CL218,872, are present in the mammalian central nervous system (7,8).In this study, we have examined the characteristics of the actions of brotizolam on the central GABAA receptor/BZP receptor/Cl channel complex using crude synaptic membrane and membrane vesicle prepa rations from the brain and spinal cord.

Distinct effects of orexin receptor antagonist and GABA A agonist on sleep and physical/cognitive functions after forced awakening

“…This lack of residual effects of hypnotic agents 9.75 h after dosing suggested that the dose of the hypnotic agents was within a reasonable range. Consistently, it has been reported that, after single and repeated doses of suvorexant, its residual effects on driving performance in the morning were negligible (35,36). As this was an initial study with forced awakening under the maximal influence of suvorexant, a new class of hypnotics, we enrolled relatively young, healthy individuals in consideration of their safety.…”

“…The differential effects of suvorexant and brotizolam are likely related to the fundamental differences in their mechanisms of action. Balance is coordinated by the cerebellum (35), in which benzodiazepine receptors are abundantly expressed (36). In contrast, the cerebellum is free from the direct effects of orexin; orexin-producing neurons essentially send no projections to the cerebellum (37), where very little expression of orexin receptors has been documented (38).…”

Pharmacological Characterization of the Novel Anxiolytic β-Carboline Abecarnil in Rodents and Primates

“…In our study, it was ascertained that zolpidem (data not shown) and ~-CCE, BZ,-selective ligands (6,10), had about five times higher affinities for the BZ receptors in the cerebellum than those in the spinal cord. The physiological roles of the BZ, and BZ2 receptors in brain function are not yet clarified, but the sedative and ataxic effects by BZs have been proposed to be due to the over activation of the BZ, and BZ2 receptors, respectively (16)(17)(18). Findings that abecarnil had no ataxic effects may be partly due to its lower affinity for spinal cord BZ2 receptors, but it does not explain the antagonism of diazepam-induced ataxia.…”

Changes in Mouse Hippocampal EEG Characteristics after Oral Administration of Ro 41-3696, Nitrazepam, or Zopiclone Alone and in Combination with Ethanol

“…It is reported that there are two dis tinct central types of BDZ-binding site (BDZ| and BDZ?) and one peripheral type (BDZ3) [17,18].BDZ| is related to hypnotic, anticon vulsant, and anxiolytic effects, while BDZ2 is related to the muscle-relaxant effect [17][18][19], Furthermore, BDZr binding sites predomi nate in the cerebellum, while BDZ2 is en riched in the spinal cord; the limbic area con tains both central types [17][18][19]. In prelimina ry observations, Ro 41-3696, like zopiclone [18,20], exhibited higher affinity binding in the rat cerebellum than in the limbic area.…”