GABAA-benzodiazepine Receptor Complex Research Articles

Classics in Neuroimaging: Development of Positron Emission Tomography Tracers for Imaging the GABAergic Pathway.

Advances in drug discovery and diverse radiochemical methodologies have led to the discovery of novel positron emission tomography (PET) radiotracers used to image the GABAergic system, shaping our fundamental understanding of a variety of brain health illnesses, including epilepsy, stroke, cerebral palsy, schizophrenia, autism, Alzheimer's disease, and addictions. In this Viewpoint, we review the state-of-the art of PET imaging with radiotracers that target the GABAA-benzodiazepine receptor complex, challenges and opportunities for imaging GABAB receptors and GABA transporters, and highlight an ongoing need to develop more sensitive radiotracers for imaging GABA release in the central nervous system.

Kamishoyosan reduces conditioned fear-induced freezing behavior in socially isolated ovariectomized rats

In the present study, we investigated the effect of kamishoyosan (KSS) on conditioned fear-induced freezing in ovariectomized (OVX) rats. Socially isolated OVX rats showed the longest freezing time among the following four groups: group-housed sham-operated (Sham), isolated Sham, group-housed OVX, and isolated OVX rats. Repeated oral administration of KSS (30–300 mg/kg) reduced conditioned fear-induced freezing in socially isolated OVX rats. The reduction of freezing by KSS was reversed by flumazenil (3 mg/kg) and bicuculline (3 mg/kg). These findings suggest that the GABAA-benzodiazepine receptor complex is involved in the anxiolytic effect of KSS in socially isolated OVX rats.

Palladium–benzodiazepine derivatives as promising metallodrugs for the development of antiepileptic therapies

We synthesized two organometallic diazepam–palladium(II) derivatives by C–H activation of diazepam (DZP) with palladium salts, i.e., PdCl2 and Pd(OAc)2 (OAc=acetate). Both compounds obtained are air stable and were isolated in good yields. The anticonvulsant potential of the complexes, labeled [(DZP)PdCl]2 and [(DZP)PdOAc]2, was evaluated through two animal models: pentylenetetrazole (PTZ)- and picrotoxin (PTX)-induced convulsions. The organometallic DZP–palladium(II) acetate complex, [(DZP)PdOAc]2, significantly increased (p<0.01 or p<0.001) latencies and protected the animals against convulsions induced by PTZ and PTX, while the analogous chloro derivative, [(DZP)PdCl]2, was effective (p<0.01) only in the PTZ model. These effects appear to be mediated through the GABAergic system. The possible mechanism of action of the DZP–palladium(II) complexes was also confirmed with the use of flumazenil (FLU), a GABAA-benzodiazepine receptor complex site antagonist. Herein, we present the first report of the anticonvulsant properties of organometallic DZP–palladium(II) complexes as well as evidence that these compounds may play an important role in the study of new drugs to treat patients with epilepsy.

Anticonvulsant Activity of Glaucium vitellinum Boiss &amp; Buhse

The anticonvulsant activities of Glauciumvitellinum extract and alkaloid sub-fraction were assessed in pentylenetetrazole (PTZ)-induced convulsion and maximal electroshock test (MEST) in mice, with Diazepam as standard drug. While mechanistic studies were conducted using flumazenil, a GABAA-benzodiazepine receptorcomplex site antagonist.The extract and the alkaloid sub-fractionproduced protectionagainst convulsion at100, 200, 400 mg/kg and 50 mg/kg respectively compared with protection with benzodiazepine.The mean onset and percentage protection against convulsion in extract/sub-fraction-treated mice werereduced by flumazenil. We also showed that G. vitellinum extract (200 mg/kg) exhibited inhibition of the tonic convulsion induced by MES and decreased mortality rate.These results suggest that G. vitellinumpossesses biologically active constituent(s) mainly belong to isoquinoline alkaloid group that haveanticonvulsant activity which supports the ethnomedicinal claims of the use of the plant in the management of seizure.

Sleep Related Amnestic Behaviors due to Zolpidem

The imidazopyridine zolpidem, introduced to the market in 1988, is a non-benzodiazepine hypnotic acting as an agonist on the central GABA-A benzodiazepine receptor complex. Zolpidem is considered t...

Kososan, a standardized traditional Japanese herbal medicine, reverses sleep disturbance in socially isolated mice via GABAA-benzodiazepine receptor complex activation

PurposeKososan (KSS), a traditional Japanese medicine with a distinct aroma, is clinically used to treat affective disorders but its antidepressant-like effect has not been thoroughly investigated. In this study, we investigated the effects of inhaled and orally administered KSS on sleep disturbances in socially isolated mice. MethodsFour-weeks-old male ddy mice were housed either in social isolation or in groups for 4–6 weeks before the experiment. KSS was orally administered (0.5 or 1.0g/kg) or inhaled (0.5, 1.0, or 2.5g/0.125m3) 60min before pentobarbital administration. Stress levels in mice were evaluated by the duration of pentobarbital-induced sleeping time. ResultsSleeping time was shorter in socially-isolated mice than in group-housed mice. Oral and inhaled KSS prolonged sleeping time in stressed mice, but had no effect on sleeping time of group-housed mice. Prolonged sleeping time after oral KSS was significantly inhibited (p<0.05) by bicuculline (3mg/kg, i.p.), a GABAA antagonist, but not by flumazenil (3mg/kg, i.p.), a selective benzodiazepine antagonist. Prolonged sleeping time after KSS inhalation was significantly inhibited (p<0.05) by flumazenil but not by bicuculline. ConclusionsOur findings suggest that KSS activates GABAA-benzodiazepine receptor complex and reverses shortened pentobarbital-induced sleep caused by social isolation.

Anticonvulsant Effects of Fuzi Total Alkaloid on Pentylenetetrazole-Induced Seizure in Mice

We investigated the anticonvulsant effect of acute Fuzi total alkaloid (FTA) in seizure induced by the GABAA-receptor antagonist pentylenetetrazole (PTZ). FTA significantly increased the seizure latency and decreased the mortality in PTZ-treated mice. Administration of PTZ increased c-Fos expression in the hippocampus, medial prefrontal cortex, and piriform cortex; and this PTZ-induced effect was inhibited by FTA in a dose-dependent manner. Furthermore, the effects of FTA on PTZ-induced seizure and c-Fos expression were reversed by the GABAA/benzodiazepine receptor–selective antagonist flumazenil. These findings suggest that the anticonvulsant effects of FTA may be related to modulation of GABAA–benzodiazepine receptor complex.

Riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines

In this study, we investigated the anxiolytic-like effect of riluzole using three different innate anxiety models in rats. In the elevated plus-maze test, riluzole significantly increased the time spent in, and entries into, the open arm after 60 min administration. This finding was supported by results obtained from light/dark and open-field tests. The magnitude of the anxiolytic-like effects of riluzole in each of the behavioral models was similar to those produced by a benzodiazepine, diazepam, suggesting that riluzole has a robust anxiolytic-like activity in rats. To clarify the involvement of sodium channels in this anxiolytic activity, we examined the effect of a co-administered sodium channel activator, veratrine. The anxiolytic-like action of riluzole was diminished by veratrine in the elevated plus-maze, light/dark and open-field tests. Based on these results, it is suggested that the anxiolytic mechanism of riluzole is clearly distinct from that of diazepam. In addition, to examine whether riluzole directly and non-selectively affected the GABAA-benzodiazepine receptor complex, we performed three behavioral tests (footprint analysis, Y-maze test and the ethanol-induced sleeping time test) that are closely related to the GABAA-benzodiazepine pathways. In contrast to diazepam, riluzole produced no significant effects in these tests. Here, we provide the first report demonstrating that riluzole produces distinct anxiolytic-like effects in rats without the adverse effects associated with benzodiazepines.

Anxiolytic effect of aridanin isolated from Tetrapleura tetraptera in mice

The study was carried out to investigate the anxiolytic properties of aridanin isolated from Tetrapleura tetraptera in mice. Elevated plus-maze was used to investigate the effect. The possible involvement of the GABAA - benzodiazepine receptor complex was also investigated using flumazenil. Aridanin at doses of 5 and 10 mg/kg, i.p. administered 30 min prior induced anxiolytic effect expressed by increase number of entries in and time spent in the open arms and percentage of open arm entries and decrease number of entries and time spent in the closed arms. The treatment of mice with flumazenil (2.0 mg/kg, i.p.) 15 min before the administration of aridanin (10 mg/kg, i.p.) blocked the aridanin induced anxiolytic effect. It was found out that aridanin induced an anxiolytic effect in mice which may be mediated through interaction with GABAAbenzodiazepine receptor complex

Reduced parahippocampal and lateral temporal GABAA-[11C]flumazenil binding in major depression: preliminary results

Major depressive disorder (MDD) has been related to both a dysfunctional gamma-amino butyric acid (GABA) system and to hyperactivity of the hypothalamic-pituitary-adrenal axis (HPA). Although GABA has been suggested to inhibit HPA axis activity, their relationship has never been studied at the level of the central GABA(A)-benzodiazepine receptor in depressed patients or in relation to antidepressant treatment. Eleven depressed outpatients were compared, before and after treatment with citalopram, with nine age-matched healthy controls. The subjects were scanned using the positron emission tomography (PET) tracer [(11)C]flumazenil ([(11)C]FMZ). Parametric voxel-by-voxel Logan plots were compared with methods based on regions of interest (ROI), to provide volume of distribution (V(T)) and binding potential (BP(ND)) values. Plasma GABA levels were determined and a dexamethasone-corticotropin releasing hormone (DEX-CRH) test was performed. In MDD, parametric voxel-by-voxel Logan plots showed bilateral reduced [(11)C]FMZ binding in the parahippocampal gyrus and right lateral superior temporal gyrus (p uncorrected < or =0.001). In the temporal area, [(11)C]FMZ binding showed a strong inverse correlation with HPA axis activity. Plasma GABA did not discriminate MDD from controls, but correlated inversely with [(11)C]FMZ binding in the right insula. Following treatment with citalopram, voxel-based analysis revealed reduced binding in the right lateral temporal gyrus and dorsolateral prefrontal cortex. The bilateral reduction in limbic parahippocampal and right temporal [(11)C]FMZ binding found in MDD indicates decreased GABA(A)-benzodiazepine receptor complex affinity and/or number. The inverse relationship between GABA(A) binding in the temporal lobe and HPA axis activity, suggests that HPA axis hyperactivity is partly due to reduced GABA-ergic inhibition.

Similar anxiolytic-like effects following intra-amygdala infusions of benzodiazepine receptor agonist and antagonist: Evidence for the release of an endogenous benzodiazepine inverse agonist in mice exposed to elevated plus-maze test

Previous studies have demonstrated that microinjections of midazolam, a benzodiazepine receptor agonist, into the amygdala produce anxiolytic-like effects in elevated plus-maze (EPM)-naïve rodents. However, systemic or intracerebral administration of benzodiazepines (BDZ) fails to alter anxiety in maze-experienced animals, a phenomenon defined as “one trial tolerance” (OTT). This study focused on the effects of intra-amygdala infusion of midazolam in maze-experienced mice. In addition, the effects of flumazenil in the amygdala of maze-naïve and experienced mice were also investigated. To investigate intrinsic effects of intra-amygdala flumazenil on anxiety, animals were systemically treated with the BDZ receptor inverse agonist, DMCM (4-ethyl-6,7-dimethoxy-9H-pyrido[3,4-b]indole-3-carboxylic acid methyl ester hydrochloride). Conventional measures of anxiety (% open arm entries and % open arm time), locomotor activity (frequency of closed arm entries) and a range of ethological measures related to risk assessment were recorded. Intra-amygdala midazolam (3.0 and 30 nmol) attenuated anxiety in maze-experienced mice. A similar behavioral profile was produced by intra-amygdala flumazenil in maze-naïve (4.0 and 16 nmol) and maze-experienced (16 nmol) mice. Intra-amygdala flumazenil (at 2.0 nmol, a dose devoid of any intrinsic effect on anxiety measures in the EPM) selectively and completely blocked the anxiogenic-like effects of systemic administration of DMCM (1.0 mg/kg, i.p.) in maze-naïve mice. Together, these results demonstrate that the GABA A-benzodiazepine receptor complex located within the amygdala does not play a role in the OTT phenomenon. Present results also suggest that the release of an endogenous BDZ receptor inverse agonist within the amygdala seems to be an important correlate of the emotional state induced by the plus-maze test.

Anticonvulsant activity of Carissa edulis (Vahl) (Apocynaceae) root bark extract

Aim of the study To investigate the anticonvulsant activity of root bark extract of Carissa edulis. Materials and methods The median lethal dose (LD 50) of Carissa edulis extract was determined using Lork’s method (1983). The anticonvulsant activity of the extract was assessed in pentylenetetrazole (PTZ)-induced convulsion in mice and maximal electroshock test (MEST) in chicks, with benzodiazepine and phenytoin as standard drugs, respectively. While mechanistic studies were conducted using both flumazenil, a GABA A-benzodiazepine receptor complex site antagonist and naloxone a non-specific opioid receptor antagonist. Results The median lethal dose (LD 50) of Carissa edulis was 282.8 mg/kg and over 5000 mg/kg following intraperitoneal and oral administration, respectively. Carissa edulis produced 40% and 20% protection against convulsion at 5 and 20 mg/kg, respectively, compared with 100% protection with benzodiazepine. The mean onset and percentage protection against convulsion in Carissa edulis extract-treated mice were reduced by flumazenil and naloxone. Carissa edulis exhibited dose-dependent inhibition of the convulsion induced by MEST with 20 mg/kg providing 90% protection while phenytoin (20 mg/kg) produced 100% protection. Conclusion These results suggest that Carissa edulis possesses biologically active constituent(s) that have anticonvulsant activity which supports the ethnomedicinal claims of the use of the plant in the management of epilepsy.

Seizure following sudden zolpidem withdrawal

Zolpidem is a short acting hypnotic drug belonging to imidazopyridine family. It produces its hypnotic effects via the GABA-A benzodiazepine receptor complex, and binds preferentially to those receptors containing the alpha-1 subunit. In comparison with benzodiazepines this mechanism is thought to reduce liability to induce dependence. Several case reports of zolpidem abuse and dependence have been published along with a small number of cases demonstrating seizures after sudden zolpidem withdrawal. We describe a case of a 29-year-old Caucasian woman who developed a generalized seizure following sudden zolpidem withdrawal subsequent to drug dependence to 160 mg of zolpidem. The clinical effects of zolpidem seem to be comparable to those of benzodiazepines and abuse, dependence and withdrawal seizures belong to the spectrum of its adverse drug reactions.

Activity of traditional South African sedative and potentially CNS-acting plants in the GABA-benzodiazepine receptor assay

Several plants are traditionally used to treat mental diseases in South Africa. Forty-six ethanol extracts from 35 species, both indigenous and exotic that are traditionally used predominantly as sedatives or to treat various CNS-related ailments were tested in the GABA A-benzodiazepine receptor-binding assay. In this assay, the binding of 3H-Ro 15-1788 (flumazenil) to the benzodiazepine site is measured. The GABA A-benzodiazepine receptor complex is involved in sedation, epilepsy and convulsions. Out of the 46 extracts tested, seven showed good activity and 10 showed moderate activity. The most active extracts were the ethanolic leaf extracts of Arctopus echinatus, Artemisa afra, four Helichrysum species and Mentha aquatica which all showed good dose-dependent activity.

Development of Radioligands for In Vivo Imaging of GABAA-Benzodiazepine Receptors

Changes in the biochemical integrity and function of the GABA(A)-benzodiazepine receptor (BZR) complex have been implicated in various neurological and psychiatric disorders. The development of specific radioligands for the GABA(A)-BZR have not only contributed to the elucidation of the receptor's biochemical functions, but also provided a means by which these changes are correlated to disease states when studied with the functional imaging modalities of positron emission tomography (PET) and single photon emission computed tomography (SPECT).

Screening of plants used in southern Africa for epilepsy and convulsions in the GABA A-benzodiazepine receptor assay

A number of plants are traditionally used to treat mental diseases in South Africa. Aqueous and ethanol extracts of 43 plants that are traditionally used to treat against epilepsy and convulsions, were tested in the GABA A-benzodiazepine receptor binding assay, where the binding of 3 H -Ro 15-1788 (flumazenil) to the benzodiazepine site is measured. The GABA A-benzodiazepine receptor complex is involved in epilepsy and convulsions. Out of the 118 extracts tested, one aqueous and 18 ethanol extracts showed activity. The most active extracts were the ethanolic leaf extracts of Rhus tridentata, Rhus rehmanniana and Hoslundia opposita and the ethanolic corm extract of Hypoxis colchicifolia, which all showed good dose-dependent activity.

Melatonin microinjection into the medial preoptic area increases sleep in the rat

A wide variety of hypnotic compounds including triazolam, pentobarbital, ethanol and adenosine have been reported to enhance sleep when microinjected into the medial preoptic area (MPA) of the anterior hypothalamus of the rat. It is uncertain whether the pineal hormone melatonin, which may alter sleep/wake physiology in mammals, acts at this site. A previous report has indicated that a more widespread injection of melatonin into the hypothalamus of the cat induces sleep. In the present study we have examined the possibility that the MPA may mediate this effect. Nine adult rats were microinjected with melatonin 1 and 50 ug and vehicle into the MPA during the daytime in a repeated measures design study. It was found that melatonin increased total sleep time in a dose-dependent manner, primarily by increasing NREM sleep, and that wake time after sleep onset was significantly reduced. These data add melatonin to the growing list of compounds that increase total sleep after administration into the MPA, and suggest that the MPA may be a common site of action for such agents from a variety of pharmacologic classes. Based on previous studies, the possibility is raised that this sleep enhancement results from an alteration in function of the GABA A-benzodiazepine receptor complex.

Effects of striatal injections of GABA A receptor agonists and antagonists in a genetic animal model of paroxysmal dystonia

The underlying mechanisms of idiopathic dystonias are poorly understood. The dystonic phenotype in the dt sz mutant hamster, a model of paroxysmal dystonia, has been suggested to be based on a deficit of γ-aminobutyric acid (GABA)ergic interneurons and changes of the GABA A-benzodiazepine receptor complex in the striatum. In order to confirm and extend previous observations, the effects of compounds which bind to different sites of the GABA A receptor on the severity of dystonia were determined after striatal microinjections in comparison to systemic treatments in dt sz mutants. The GABA A receptor agonist (muscimol) and the benzodiazepine (flurazepam) reduced the severity of dystonia after striatal and systemic injections. The antidystonic effects of the barbiturate phenobarbital were less marked both after striatal and intraperitoneal administration of drugs. Intrastriatal injections of GABA delayed the onset of dystonic attacks. Striatal and systemic treatments with the GABA A receptor antagonist, bicuculline, and with pentylenetetrazole, which reduces GABAergic function, accelerated the onset of dystonia at subconvulsant doses. The benzodiazepine receptor antagonists flumazenil aggravated dystonia after systemic and intrastriatal injections. In all, the present data substantiate the relevance of striatal GABAergic disinhibition in the pathogenesis of paroxysmal dystonia in dt sz mutants.

Modulation of radioligand binding to the GABA(A)-benzodiazepine receptor complex by a new component from Cyperus rotundus.

Four sesquiterpenes, beta-selinene, isocurcumenol, nootkatone and aristolone and one triterpene, oleanolic acid were isolated from the ethylacetate fraction of the rhizomes of Cyperus rotundus and tested for their ability to modulate gamma-aminobutyric acid (GABA(A))-benzodiazepine receptor function by radioligand binding assays using rat cerebrocortical membranes. Among these compounds, only isocurcumenol, one of the newly identified constituents of this plant, was found to inhibit [3H]Ro15-1788 binding and enhance [3H]flunitrazepam binding in the presence of GABA. These results suggest that isocurcumenol may serve as a benzodiazepine receptor agonist and allosterically modulate GABAergic neurotransmission via enhancement of endogenous receptor ligand binding.

Benzodiazepine receptor quantification in Huntington's disease with [123I]iomazenil and SPECT

OBJECTIVESIncreasing evidence suggests that metabolic changes predate neuronal death in Huntington's disease and emission tomography methods (PET and SPECT) have shown changes in glucose consumption and receptor function in early...