Role Of Benzodiazepine Receptors Research Articles

Novel 2-substituted-5-(4-chloro-2-phenoxy)phenyl-1,3,4-oxadiazole derivatives, ligands of GABAA/benzodiazepine receptor complex: Design, synthesis, radioligand binding assay, and pharmacological evaluation.

Agonists of Benzodiazepine (BZD) receptor are exhaustively used in the control of muscle spasms, seizure, anxiety, and insomnia. BZDs have some unwanted effects; therefore, the development of new BZD receptor agonists with better efficacy and fewer unwanted effects is one of the subjects of interest. In this study, based on the pharmacophore/receptor model of the BZD binding site of GABAA receptors, a series of new 2-substituted-5-(4-chloro-2-phenoxy)phenyl-1,3,4-oxadiazole derivatives (6a-f) were designed. Energy minima conformers of the designed compounds and diazepam were well matched in conformational analysis and showed proper interaction with the BZD-binding site of the GABAA receptor model (α1β2ϒ2) in docking studies. The designed compounds were synthesized in acceptable yield and evaluated for their in vitro affinity to the benzodiazepine receptor of rat brains by radioligand receptor binding assay. The results demonstrated that the affinities of most of the novel compounds were even higher than diazepam. The novel compound 6a with the best affinity in radioligand receptor binding assay (Ki=0.44 nM and IC50= 0.73±0.17 nM) had considerable hypnotic activity and weak anticonvulsant and anxiolytic effects with no negative effect on memory in animal models. Flumazenil as a selective benzodiazepine receptor antagonist was able to prevent hypnotic and anticonvulsant effects of 6a indicating the role of BZD receptors in these effects.

Anti-Seizure Activity of 1-Adamantane Carboxylic Acid in Common Experimental Seizure Models: Role of Benzodiazepine-GABAA Receptors

Background:Despite introduction of modern antiepileptic drugs, 30% of epileptic patients are still drug resistant. Remarkable three-dimensional spatial structure of AdCA, yet the simplicity of the molecule, makes AdCA a promising lead compound. Methods:Sedative/motor impairment and 24-h mortality rate of AdCA were determined in mice. Impact of AdCA on (1) threshold and occurrence of clonic seizures induced by PTZ in mice, (2) incidence of tonic seizures induced by MES in mice, and (3) incidence of generalized seizures and duration of evoked afterdischarges in amygdala-kindled rats, were determined. The role of benzodiazepine receptors in the AdCA effect on clonic seizure threshold was also assessed. Results:AdCA showed sedative effect (TD50 = 224.5 [190.2-289.9] mg/kg). LD50 = 805.5 (715.2–988.1) mg/kg was obtained for AdCA. The compound increased PTZ seizure threshold from 180 mg/kg (p < 0.05) and also inhibited the incidence of clonic seizures (ED50 = 256.3 [107.4-417.3] mg/kg). AdCA also decreased afterdischarge duration (p < 0.01) and the incidence of generalized seizures (ED50 < 50 mg/kg) in the kindled rats. However, AdCA did not protect mice against tonic seizures induced by MES. The benzodiazepine receptor antagonist flumazenil prevented the increase of seizure threshold by AdCA. Conclusion:AdCA possesses anticonvulsant activity in kindling and PTZ models through the activation of benzodiazepine/GABAA receptors with acceptable therapeutic index.

Anti-Seizure Activity of 1-Adamantane Carboxylic Acid in Common Experimental Seizure Models: Role of Benzodiazepine-GABAA Receptors.

Despite introduction of modern antiepileptic drugs, 30% of epileptic patients are still drug resistant. Remarkable three-dimensional spatial structure of 1-Adamantane carboxylic acid (AdCA), yet the simplicity of the molecule, makes AdCA a promising lead compound. Sedative/motor impairment and 24-h mortality rate of AdCA were determined in mice. Impact of AdCA on (1) threshold and occurrence of clonic seizures induced by pentylenetetrazole (PTZ) in mice, (2) incidence of tonic seizures induced by maximal electroshock (MES) in mice, and (3) incidence of generalized seizures and duration of evoked afterdischarges in amygdala-kindled rats, were determined. The role of benzodiazepine receptors in the AdCA effect on clonic seizure threshold was also assessed. AdCA showed sedative effect (median toxic dose [TD50] = 224.5 [190.2-289.9] mg/kg). Median lethal dose (LD50) = 805.5 (715.2–988.1) mg/kg was obtained for AdCA. The compound increased PTZ seizure threshold from 180 mg/kg (p < 0.05) and also inhibited the incidence of clonic seizures (ED50 = 256.3 [107.4-417.3] mg/kg). AdCA also decreased afterdischarge duration (p < 0.01) and the incidence of generalized seizures (ED50 < 50 mg/kg) in the kindled rats. However, AdCA did not protect mice against tonic seizures induced by MES. The benzodiazepine receptor antagonist flumazenil prevented the increase of seizure threshold by AdCA. AdCA possesses anticonvulsant activity in kindling and PTZ models through the activation of benzodiazepine/GABAA receptors with acceptable therapeutic index.

Role of benzodiazepine receptor in amnesic effect of different intravenons anesthetics in mice

Objective To investigate the role of the benzodiazepine receptor in the amnesic effect of propofol, etomidate and ketamine in mice. Methods Two hundred and eighty-eight Kunming mice of both sexes weighing 18-23 g were randomly divided into 9 groups（ n = 32 each） ： group normal saline ＋ normal saline （group NN） ; group normal saline ＋ fat emulsion （group NF） ; group flumazenil ＋ normal saline （group FN） ; group nor- mal saline ＋ propofol （group NP） ; group flumazenil ＋ propofol （group FP） ;group normal saline ＋ etomidate （group NE）; group flumazenil ＋ etcimidate （group FE ）; group normal saline ＋ ketamine （group NK ） and group flumazenil ＋ ketamine （group NK）. Normal saline 10 ml/kg was given IP at 10 min before the tests, and normal saline 10 ml/kg, fat emulsion 10 ml/kg, propofol 25 mg/kg, etomidate 3 mg/kg and ketamine 20 mg/kg at 5 min before the tests in groups NN, NF, NP, NE and NK respectively. Flumazenil 1 mg/kg was given IP at 10 rain before the tests, and normal saline 10 ml/kg, fat emulsion 10 ml/kg, propofol 25 mg/kg, etomidate 3 mg/kg and ketamine 20 mg/kg at 5 min before the tests in groups NN, NF, NP, NE and NK respectively. Darkness-avoiding test, platform-mounting test and Morris water maze test were performed to assess the cognition function. The latency of response and number of error were recorded in each test. Results Propofol, etomidate and ketamine signifi-canfly shortened the duration of latency of response in platform-mounting test as compared with group NN. Etomidate also significantly increased the number of error in platform-mounting test as compared with group NN, while ketamine prolonged the duration of latency of response in Morris water maze test as compared with group NN. Flumazcnil significantly counteracted the above action of the 3 intravenous anesthetics. Conclusion Benzodiazepine receptor may play an important role in the amnesic effect induced by propofol, etomidate and ketamine. Key words: Receptors, GABA-A ; Amnesia; Propofol ; Etomidate ; Ketamine

Enhancement of lactate metabolism in the basolateral amygdala by physical and psychological stress: Role of benzodiazepine receptors

Lactate is considered to play a significant role in energy metabolism and reflect neural activity in the brain. Using in vivo microdialysis technique, we measured extracellular lactate concentrations in the basolateral amygdaloid nucleus (BLA) of rats under electric footshock or psychological stress. We also attempted to determine whether the stress-induced changes of extracellular lactate concentrations in the BLA are attenuated by diazepam, an agonist at benzodiazepine receptors, and whether FG7142, an inverse agonist at benzodiazepine receptors, have a facilitative effect on energy metabolism in the BLA. Both footshock and psychological stress led to an increase in extracellular lactate concentrations in the BLA. Similar increment of extracellular lactate levels was observed by administration of FG7142. Pretreatment with diazepam attenuated the ability of FG7142, as well as physical or psychological burden, to increase lactate levels in the BLA. These results indicate that a variety of stressors enhances energy metabolism in the BLA, and suggest that some stress-induced changes in energy metabolism are regulated by benzodiazepine receptors.

The Structures of Imidazenil and Iodoimidazenil

The iodinated analogue of imidazobenzodiazepine, imidazenil (1), has been prepared with the aim of radiolabelling it with iodine-123 and including it in a study to determine the role of benzodiazepine receptors in neurodegenerative diseases using single photon emission computer tomography (SPECT) imaging. A comparison of the bromo- and iodo-derivatives, as well as the conformational changes resulting from bromine–iodine substitution are described, and it is concluded that the substitution has no clear effect on the geometry. Crystal structures of (1) and iodoimidazenil (2) have been determined by X-ray diffraction methods and refined to R values of 0.059 (3817 F) and 0.048 (1318 F), respectively. The crystals of imidazenil are triclinic, space group P1–,a 12.537(4), b 18.211(6), c 7.852(2) Å, α 91.07(2), β 106.26(2), γ 77.86(2)�, Z 4, and those of iodoimidazenil are monoclinic, space group P21/a, a 12.185(2), b 7.558(2), c 18.287(2) Å, β 95.23(1)�, Z 4.

Evidence that long-lasting potentiation in limbic circuits mediating defensive behaviour in the right hemisphere underlies pharmacological stressor (FG-7142) induced lasting increases in anxiety-like behaviour: role of benzodiazepine receptors.

The hypothesis that benzodiazepine receptors mediate initiation of lasting behavioural changes induced by FG-7142 was supported in this study. Behavioural changes normally induced by FG-7142 were blocked by prior administration of the competitive benzodiazepine receptor blocker, Flumazenil. When cats were subsequently given FG-7142 alone, the drug produced lasting behavioural changes in species characteristic defensive responses to rodent and cat vocal threat. FG-7142 also induced long-lasting potentiation (LLP) of evoked potentials in a number of efferent pathways from the amygdala in both hemispheres. Flumazenil given prior to FG-7142 blocked LLP in all but one of the amygdala efferent pathways, suggesting benzodiazepine receptor dependence of initiation of LLP. Three physiological changes were most closely correlated with behavioural changes. LLP in the right amygdalo-ventromedial hypothalamic (VMH) and amygdalo-periacqueductal gray (PAG) pathways coincided closely with behavioural changes, as did a reduced threshold for the right amygdalo-VMH evoked potential. Administration of Flumazenil after FG-7142 returned defensive behaviour to pre FG-7142 baseline levels in a drug-dependent manner. At the same time LLP only in the right amygdalo-PAG pathway was reduced by Flumazenil. LLP in other pathways and amygdalo-VMH threshold were unaltered by Flumazenil. Moreover, covariance analyses indicated that increased defensiveness depended solely on LLP in the right amygdalo-PAG. These findings support the view that maintenance of lasting increases in defensive behaviour depend upon LLP of excitatory neural transmission between amygdala and lateral column of the PAG in the right hemisphere. Moreover, FG-7142 may be a useful model of the effects of traumatic stressors on limbic system function in anxiety, especially in view of the recent data in humans implicating right hemispheric function in persisting negative affective states in post-traumatic stress disorder.

The Role of Benzodiazepine Receptors in the Acquisition and Expression of Behavioral Sensitization to Methamphetamine

The GABA–benzodiazepine neurotransmission has been reported to be implicated in various forms of plasticity such as kindling and learning. In a previous study, we have shown that clonazepam (CZP), a GABA–benzodiazepine agonist, prevents the acquisition of behavioral sensitization to methamphetamine (MA). The present study was conducted to extend this finding by examining the effect of flumazenil (Flu), a GABA–benzodiazepine antagonist on the prevention by CZP. Rats (male Wistar–King rats) treated with MA (1 mg/kg, SC) for 10 days showed significantly enhanced motor activity compared to those treated with saline when tested with MA (1 mg/kg) after a 7–8-day withdrawal, indicating the acquisition of behavioral sensitization. Representing the previous finding, pretreatment with CZP (0.5 mg/kg) prior to MA administration prevented the acquisition of the phenomenon. Pretreatment with Flu (10 mg/kg) prior to MA administration has no influence on the acquisition of sensitization. However, pretreatment with Flu prior to CZP administration reversed the inhibitory effect of CZP. CZP showed no effect on the expression of sensitization in the sensitized rats when given prior to the MA readminisiration. These results strengthen the suggestion that stimulation of GABA–benzodiazepine receptors plays a role in the acquisition but not in the expression of behavioral sensitization to MA.

Discriminative stimulus properties of alprazolam

The triazolobenzodiazepine alprazolam has a unique clinical profile compared to most other benzodiazepines (e.g. diazepam, chlordiazepoxide), in that it is used to treat panic disorder and is effective in depression, two disorders that are usually treated with anti-depressants. Previous drug discrimination studies suggested that alprazolam has stimulus properties in common with antidepressants. In the present study, the discriminative stimulus properties of alprazolam were investigated to test more conclusively the role of benzodiazepine receptors and whether alprazolam has stimulus properties in common with antidepressants. Male Wistar rats (n=12) were trained to discriminate between alprazolam (2.0 mg/kg, PO) and vehicle in an operant two-lever drug discrimination procedure under a tandem VI40"-FR10 schedule of reinforcement. Generalization and antagonism tests were carried out under 2 min extinction. In generalization tests, a number of benzodiazepines (alprazolam, chlordiazepoxide, midazolam, lorazepam) and the barbiturate pentobarbital substituted completely, while zolpidem and abecarnil substituted partially for alprazolam. In contrast, no significant degree of generalization to the antidepressants imipramine and fluvoxamine and the putative antidepressants buspirone and flesinoxan was found. In antagonism studies alprazolam could be antagonized (almost) completely by flumazenil, partially by pentylenetetrazole, but not by methyl 6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), N-methyl-beta-carboline-3-carboxamide (FG-7142) and picrotoxin. These results show that the discriminative stimulus properties of alprazolam are mediated by benzodiazepine receptors and that the finding that antidepressants share discriminative stimulus effects with alprazolam may have limited generality.

Visual evoked potentials and nitrous oxide-induced neuronal depression: role for benzodiazepine receptors

We have examined the role of benzodiazepine receptors in nitrous oxide-induced neuronal depression in rats. The changes in neuronal excitability induced by nitrous oxide and the benzodiazepine inverse agonist, Ro15-4513, were monitored by measurement of visual evoked potentials (VEP). Administration of Ro15-4513 10 mg kg-1 i.p., in rats breathing air, did not affect the amplitude or latency of VEP. However, the same concentrations of Ro15-4513 antagonized nitrous oxide-induced depression of VEP amplitudes. We conclude that antagonism of nitrous oxide-induced depression by Ro15-4513 indicates that at least part of the decreased neuronal excitability caused by nitrous oxide could be ascribed to interactions with the GABAA receptor complex.

The role of benzodiazepine receptors in the induction of differentiation of HL‐60 leukemia cells by benzodiazepines and purines

A series of benzodiazepines was evaluated for their capacity to induce the differentiation of HL-60 acute promyelocytic leukemia cells. Benzodiazepines were effective initiators of maturation in the concentration range of 50 to 150 microM. The possible involvement of benzodiazepine receptors in mediating the differentiation induced by these agents was investigated. The presence of high affinity, peripheral type benzodiazepine binding sites (KD = 7.3 nM, TB = 14.5 pmol/mg protein with Ro5-4864) was demonstrated in HL-60 membranes. The occupancy of peripheral type high affinity benzodiazepine receptors by various benzodiazepines showed some correlation (r = 0.76) with their differentiation-inducing capabilities, but binding potencies were 1,000-fold higher than the concentrations required to produce differentiation. A class of benzodiazepine receptors with lower binding affinity was also detected in HL-60 membranes (KD = 28.6 microM; TB = 199 pmol/mg protein with diazepam). A higher level of correlation (r = 0.88) was demonstrated between benzodiazepine occupancy of these lower affinity receptors and the capacity to induce maturation. Significantly, benzodiazepine concentrations needed for low affinity binding and induction of differentiation were the same (25-200 microM), suggesting that low affinity benzodiazepine receptors may be involved in the induction process. We have shown that the molecular form responsible for the induction of the differentiation of HL-60 cells to mature forms by 6-thioguanine (TGua) is the free base, TGua, itself [Ishiguro, Schwartz, and Sartorelli (1984) J. Cell. Physiol., 121:383-390]. Since hypoxanthine (Hyp) and inosine (Ino) have been identified as putative endogenous ligands for high affinity benzodiazepine receptors in brain tissue, the potential involvement of benzodiazepine receptors in the differentiation of HL-60 cells by the purines was investigated. Physiological purines such as Hyp and Ino were inactive in displacing the benzodiazepines from their high and low affinity binding sites in HL-60 membranes. In contrast, TGua caused inhibition of benzodiazepine binding to high and low affinity sites. The inhibition of Ro5-4864 binding to high affinity binding sites by TGua appeared to be due to the binding of TGua to membranes through the formation of a mixed disulfide between the 6-thiopurine and protein thiols, since the inhibition was reversed by the presence of 2-mercaptoethanol. The findings suggest a possible relationship between the occupancy of benzodiazepine receptors by TGua and the induction of leukemic cell differentiation.

The possible role of benzodiazepine receptors in morphine analgesia

Diazepam within its therapeutic dose range, was shown to have no effect on nociception, but was shown to antagonize the analgesic action of morphine. This antagonism was found to be statistically significant at 0.5 mg/kg diazepam. To elucidate the mechanism of this inhibitory action of diazepam against morphine analgesia, Ro 15-1788, the specific antagonist of benzodiazepine receptors was used. As a result, Ro 15-1788 was found to partially reverse the inhibitory action of diazepam against morphine analgesia. This overall interaction between the supramolecular GABA receptor complex and morphine is discussed.

The role of benzodiazepine receptors in the discriminative stimulus properties of delta-9-tetrahydrocannabinol

Twenty male Sprague-Dawley rats were trained to discriminate 3.0 mg/kg delta-9-tetrahydrocannabinol (THC) from its vehicle. Following acquisition of this discrimination animals were tested for generalization to 3.0 mg/kg diazepam. Thirteen animals showed a generalization from THC to diazepam, whereas the remaining seven animals did not. The generalization curve for diazepam was dose-dependent from 0.1 to 10.0 mg/kg in the first group; the latter group showed no generalization from THC at any dose of diazepam in this range. No differences were found between these groups in the generalization curve for THC. The benzodiazepine antagonist Ro 15-1788 (2.0 mg/kg) antagonized the generalization to diazepam in the group that discriminated diazepam as THC. In contrast, Ro 15-1788 increased THC lever responding of 10 mg/kg diazepam in the group which did not generalize from THC. Ro 15-1788 did not alter the discriminability of THC in either group. THC also showed partial generalization to pentobarbital (1 to 10 mg/kg). The generalization was again complete in one subgroup and absent in another, but there was only a 43 percent overlap between the subgroups found with testing for generalization to diazepam. The percent THC lever responding with 3.0 mg/kg pentobarbital was increased by Ro 15-1788 in the group which generalized to diazepam, but not the other group. These data suggest that the discriminative stimulus properties of THC may have some commonality with the effects of diazepam in a subpopulation of rats trained to discriminate THC. These THC- like effects of diazepam are probably mediated by benzodiazepine receptors since they are antagonized by a specific benzodiazepine receptor antagonist.

Role of benzodiazepine receptors in realization of the anxiolytic effect of compounds in alcohol-dependent and control rats

Role of benzodiazepine receptors in realization of the anxiolytic effect of compounds in alcohol-dependent and control rats

Effect of a ten-day course of fenibut and diazepam on gaba and benzodiazepine receptors in mouse brain

The clinical spectrum of action of fenibut (B-phenyl-GABA), which is used in clinical practice as a tranquilizer [2], differs in many respects from that of tranquilizers of the benzodiazepine series [3]. The writers showed previously that bicuculline-insensitive receptors take part in the mechanism of action of fenibut, whereas bicuculline-sensitive GABA receptors take part in the mechanism of action of diazepam [I]. Evidence has now been obtained to suggest that the tranquilizing effect of the benzodiazepines is closely linked with their effect on benzodiazepine receptors [7]. However, the role of benzodiazepine receptors in the mechanism of action of fenibut still remains unexplained.