Flunitrazepam and its metabolites induced brain toxicity: Insights from molecular dynamics simulation and transcriptomic analysis

Psychoactive drugs frequently contaminate aquatic environments after human consumption, raising concerns about their residues and ecological harm. This study investigates the effects of flunitrazepam (FLZ) and its metabolite 7-aminoflunitrazepam (7-FLZ), benzodiazepine-class psychoactive drugs, on brain accumulation, blood-brain barrier (BBB), and neuroinflammation of the model organism zebrafish. Molecular dynamics simulation and transcriptome sequencing were used to uncover their toxic mechanisms. Results demonstrate that both FLZ and 7-FLZ can accumulate in the brain, increasing Evans blue levels by 3.4 and 0.8 times, respectively. This increase results from abnormal expression of tight junction proteins, particularly ZO-1 and Occludin, leading to elevated BBB permeability. Furthermore, FLZ and 7-FLZ can also induce neuroinflammation, upregulating TNFα by 91% and 39%, respectively, leading to pathological changes and disrupted intracellular ion balance. Molecular dynamics simulation reveals conformational changes in ZO-1 and Occludin proteins, with FLZ exhibiting stronger binding forces and greater toxicity. Weighted gene co-expression network analysis identifies four modules correlated with BBB permeability and neuroinflammation. KEGG enrichment analysis of genes within these modules reveals pathways like protein processing in the endoplasmic reticulum, NOD-like receptor signaling pathway, and arginine and proline metabolism. This study enhances understanding of FLZ and 7-FLZ neurotoxicity and assesses environmental risks of psychoactive substances. ENVIRONMENTAL IMPLICATION: With the increasing prevalence of mental disorders and the discharge of psychoactive drugs into water, even low drug concentrations (ng/L-μg/L) can pose neurological risks. This study, utilizing molecular dynamic (MD) simulations and transcriptome sequencing, investigate the neurotoxicity and mechanisms of flunitrazepam and 7-aminoflunitrazepam. It reveals that they disrupt the blood-brain barrier in zebrafish and induce neuroinflammation primarily by inducing conformational changes in tight junction proteins. MD simulations are valuable for understanding pollutant-protein interactions. This research offers invaluable insights for the environmental risk assessment of psychoactive drugs and informs the development of strategies aimed at prevention and mitigation.

Flunitrazepam and its metabolites compromise zebrafish nervous system functionality: An integrated microbiome, metabolome, and genomic analysis

The psychotropic drug flunitrazepam (FLZ) is frequently detected in aquatic environments, yet its neurotoxicity to aquatic organisms has not received sufficient attention. In this study, microbiome, metabolome, and genome analyses were conducted to study the effects of FLZ and its metabolite 7-aminoflunitrazepam (7-FLZ) on the zebrafish nervous system and understand their toxic mechanisms. The results demonstrated that drug exposure induced gut dysbiosis, decreased short-chain fatty acids and promoted the production of lipopolysaccharides (LPS). LPS entered the brain and interacted with Toll-like receptors to cause neuroinflammation by upregulating the expression of proinflammatory cytokines TNFα and NF-κB. The increased ratio of S-adenosylmethionine to S-adenosylhomocysteine in brain tissues indicated abnormal expression of Dnmt1 gene. Whole-genome bisulfite sequencing displayed an increase in differentially methylated regions (DMRs) associated-genes and pertinent biological pathways encompassed the MAPK signaling pathway, calcium signaling pathway, and Wnt signaling pathway. Correlation analysis confirmed connections between gut microbiota, their metabolites, inflammatory factors, and DNA methylation-related markers in brain tissue. These findings indicate that while the toxicity is somewhat reduced in metabolized products, both FLZ and 7-FLZ can induce DNA methylation in brain tissue and ultimately affect the biological function of the nervous system by disrupting gut microbiota and their metabolites.

High Fat Diet Increases [3H] Flunitrazepam Binding in the Mouse Brain that is Dependent on the Expression of the Dopamine D2 Gene

Dopamine is an important neuromodulator in the brain that binds to dopamine D1-like receptors (D1, D5) as well as dopamine D2-like receptors (D2, D3, D4). The D2 receptor is known to play an integral role in a variety of physiological processes including addictive behaviors, locomotion, motivation, feeding behavior, and more. It was recently reported that dopamine is a direct-acting modulator of mammalian GABA(A) receptors. To this end, we wanted to examine how the expression of the dopamine D2 gene impacts the expression of GABA(A) receptors in the brain under different dietary conditions. Adult female Drd2 wild-type (WT), heterozygous (HT), and knockout (KO) mice were given either normal or high-fat diet for a period of 30 weeks. Following this, their brains were collected for [³H] Flunitrazepam binding in order to assess GABA(A) receptor expression. A high fat diet significantly increased [³H] Flunitrazepam binding in the regions of the somatosensory cortex, striatum, and various other cortical areas within WT mice. In contrast, no effect of diet was observed in HT or KO mice. As such, HT and KO mice displayed reduced [³H] Flunitrazepam binding in these areas relative to WT mice under high-fat dietary conditions. The effect of a high-fat diet on [³H] Flunitrazepam binding is consistent with recent evidence showing increases in GABA neurotransmitter levels following a high-fat diet. We demonstrate for the first time that the expression of the D2 gene plays a prominent role in the ability of a high-fat diet to impact GABA(A) receptors in the mouse brain.

Binding activity of Valeriana fauriei root extract on GABAA receptor flunitrazepam sites and distribution of its active ingredients in the brain of mice - A comparison with that of V. officinalis root

ETHNOPHARMACOLOGICAL RELEVANCE

Valeriana fauriei root (VF) is a crude drug registered in the Japanese Pharmacopeia 17th Edition and a known substitute for V. officinalis (VO). Although VO has been pharmacologically evaluated for its sedative effects and mechanism of action, data regarding VF remain scarce.

AIM OF THE STUDY

We compared the binding affinity of VF and VO extracts, as well as examined the active ingredients in the VF extract, on flunitrazepam sites of γ-aminobutyric acid receptor type A (GABA_A receptor). Furthermore, we confirmed whether these active ingredients were distributed in the brain of mice orally administered the VF extract.

MATERIALS AND METHODS

We prepared the assay system to evaluate the binding activity of flunitrazepam sites of GABA_A receptor using a 96-well plate and assessed the activities of VF and VO extracts. We then analyzed their constituents using HPLC with principal component analysis (PCA) and evaluated active ingredients correlated with their activities. The distribution of active ingredients in the plasma and brain of mice orally administered the VF extract prepared with different emulsifiers were analyzed by LC-MS/MS.

RESULTS

The ethanol extract of VF exhibited significantly higher activity on flunitrazepam sites of GABA_A receptor than VO. For the VF extract, kessyl glycol diacetate (KGD) was markedly associated with the binding activities; however, active ingredients included KGD, kessyl glycol 8-acetate (KG8), α-kessyl acetate (α-KA), and coniferyl isovalerate (CI). For VO, valerenic acid and five other compounds were associated with the binding affinity on flunitrazepam sites of GABA_A receptor. On emulsifying the VF extract with a fat-soluble glycerin fatty acid ester, the plasma and brain distributions of KGD tended to be higher, those of KG8 were significantly more than 10-times higher, and those of α-KA was lower than those of the VF extract emulsified with water-soluble gum arabic, after oral administration in mice.

CONCLUSIONS

Based on the binding activity on flunitrazepam sites of GABA_A receptor and brain distribution, KGD, KG8, and α-KA can be considered active ingredients of VF. The addition of a fat-soluble emulsifier promoted the absorption of KGD, the main active ingredient, and KGD was metabolized to KG8 in the body. The present results suggest a possible mechanism underlying the sedative effect for VF, and these three compounds can be used as marker compounds to evaluate the quality of VF products.

Characterization and tentative identification of new flunitrazepam metabolites in authentic human urine specimens using liquid chromatography-Q exactive-HF hybrid quadrupole-Orbitrap-mass spectrometry (LC-QE-HF-MS)

Flunitrazepam (FNZ) is a potent hypnotic, sedative, and amnestic drug used to treat severe insomnia. In our recent study, FNZ metabolic profiles were investigated carefully. Six authentic human urine samples were purified using solid phase extraction (SPE) without enzymatic hydrolysis, and urine extracts were then analyzed by liquid chromatography-Q exactive-HF hybrid quadrupole-Orbitrap-mass spectrometry (LC-QE-HF-MS), using the full scan positive ion mode and targeted MS/MS (ddms2) technique to make accurate mass measurements. There were 25 metabolites, including 13 phase I and 12 phase II metabolites, which were detected and tentatively identified by LC-QE-HF-MS. In addition, nine previously unreported phase II glucuronide conjugates and four phase I metabolites are reported here for the first time. Eight metabolic pathways, including N-reduction and O-reduction, N-glucuronidation, O-glucuronidation, mono-hydroxylation and di-hydroxylation, demethylation, acetylation, and combinations, were implicated in this work, and 2-O-reduction together with dihydroxylation were two novel metabolic pathways for FNZ that were identified tentatively. Although 7-amino FNZ is widely considered to be the primary metabolite, a previously unreported metabolites (M12) can also serve as a potential biomarker for FNZ misuse.

Synaptosomal membrane-based Langmuir-Blodgett films: a platform for studies on γ-aminobutyric acid type A receptor binding properties

In this work we used Langmuir-Blodgett films (LB) as model membranes to study the effect of molecular packing on the flunitrazepam (FNZ) accessibility to the binding sites at the GABAA receptor (GABAA-R). Ligand binding data were correlated with film topography analysis by atomic force microscopy images (AFM) and SDS-PAGE. Langmuir films (LF) were prepared by the spreading of synaptosomal membranes (SM) from bovine brain cortex at the air-water interface. LBs were obtained by the transference, at 15 or 35 mN/m constant surface pressure (π), of one (LB15/1c and LB35/1c) or two (LB35/2c) LFs to a film-free hydrophobic alkylated substrate (CONglass). Transference was performed in a serial manner, which allowed the accumulation of a great number of samples. SDS-PAGE clearly showed a 55 kDa band characteristic of GABAA-R subunits. Detrended fluctuation analysis of topographic data from AFM images exhibited a single slope value (self-similarity parameter α) in CONglass and a discontinuous slope change in the α value at an autocorrelation length of ∼100 nm in all LB samples, supporting the LF transference to the substrate. AFM images of CONglass and LB15/1c exhibited roughness and average heights that were similar between measurements and significantly lower than those of LB35/1c and LB35/2c, suggesting that the substrate coverage in the latter was more stable than in LB15/1c. While [(3)H]FNZ binding in LB15/1c did not reach saturation, in LB35/1c the binding kinetics became sigmoid with a binding affinity lower than in the SM suspension. Our results highlight the π dependence of both binding and topological data and call to mind the receptor mechanosensitivity. Thus, LB films provide a tool for bionanosensing GABAA-R ligand binding as well as GABAA-R activity modulation induced by the environmental supramolecular organization.

[Brain benzodiazepine receptors in humans and rats with alcohol addiction]

OBJECTIVE

Benzodiazepine receptors (BDR) in synaptosomal and mitochondrial membranes from different brain areas of alcohol abused patients (postmortem) and the brain cortex of male rats (Vistar line) with different preference to alcohol were studied.

METHODS

Synaptosomal and mitochondrial receptors of membranes from different brain areas of patients with alcohol addiction and controls were explored using radioreceptor analysis with selective ligands [3H]flunitrazepam and [3H]PK-11195. BDR in the rat brain were studied using [3H]flunitrazepam and [3H]Ro5-4864.

RESULTS

An analysis of kinetic parameters (Kd and Bmax) of [3H]flunitrazepam and [3H]PK-11195 binding with synaptosomal and mitochondrial membranes in the human brain showed that BDR was decreased and capacity increased in different human brain areas under the influence of alcohol abuse. The most distinct changes were found in the prefrontal cortex, nucleus caudatus and cerebella cortex. Alcohol abuse induced greater changes in mitochondrial membranes compared to synaptosomal membranes that was consistent with physiological and defensive functions of mitochondrial membranes and CNS under the influence of toxic substances. The affinity of [3H]flunitrazepam and [3H]Ro5-4864 binding with membranes was decreased, but the capacity of receptors was increased in the brain cortex of alcohol-preferring male rats compared to alcohol non-preferring rats. Administration of anticonvulsant meta-chloro-benzhydryl-urea to rats prefer ethanol increased the affinity of BDR.

Anxiolytic-like effect of lavender essential oil inhalation in mice: participation of serotonergic but not GABAA/benzodiazepine neurotransmission

ETHNOPHARMACOLOGICAL RELEVANCE

Lavandula angustifolia (lavender) inhalation has been used in folk medicine for the treatment of anxiety, and clinical and animal studies have corroborated its anxiolytic effect, although its mechanism of action is still not fully understood.

AIMS OF THE STUDY

The objective of the present study was to determine whether the GABAA/benzodiazepine complex or serotonin neurotransmission mediates the anxiolytic-like effect of lavender essential oil.

MATERIALS AND METHODS

Male Swiss mice were subjected to the marble-burying test after being exposed to the aroma of lavender essential oil (1-5%), amyl acetate (5%; used as a behaviorally neutral odor), or distilled water for 15 min via inhalation. Additionally, the effect of 5% lavender essential oil was also evaluated in mice subjected to the elevated plus maze. GABAA/benzodiazepine mediation was evaluated by pretreating the mice with the GABAA receptor antagonist picrotoxin before the marble burying test and [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Serotonergic mediation was studied by pretreating the mice with O-methyl-[3H]-N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY100635), a serotonin 5-HT1A receptor antagonist before the marble burying test. We also evaluated changes in the pharmacologically induced serotonin syndrome and the effects of combined administration of subeffective doses of lavender essential oil and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT).

RESULTS

Lavender essential oil (1-5%) decreased the number of marbles buried compared with the control and amyl acetate groups. In the elevated plus maze, 5% lavender essential oil inhalation increased the percentage of time spent on and number of entries into the open arms compared with controls. No effect was seen in the number of closed arm entries or number of beam interruptions in the automated activity chamber. Pretreatment with the GABAA receptor antagonist picrotoxin (0.5mg/kg) did not modify the behavioral effect of 5% lavender essential oil in the marble-burying test. Lavender essential oil also did not alter [(3)H]flunitrazepam binding to the benzodiazepine site on the GABAA receptor. Pretreatment with the serotonin 5-HT1A receptor antagonist WAY100635 (3mg/kg) blocked the anxiolytic-like effect of lavender essential oil and the 5-HT1A receptor agonist 8-OH-DPAT (3mg/kg). A combination of ineffective doses of 8-OH-DPAT (0.5mg/kg) and lavender essential oil (0.1%) reduced the number of marbles buried. Finally, 5% lavender essential oil attenuated the serotonin syndrome induced by 40 mg/kg fluoxetine plus 80 mg/kg 5-hydroxytryptophan.

CONCLUSIONS

These results indicate an important role for the serotonergic system in the anxiolytic-like effect of lavender essential oil.

Central nervous system activities of two diterpenes isolated from Aloysia virgata

Using the guide of a competitive assay for the benzodiazepine binding site in the γ-aminobutyric acid type A receptor (GABA(A)), two active diterpenes were isolated from the aerial parts of Aloysia virgata (Ruíz & Pavón) A.L. Jussieu var. platyphylla (Briquet) Moldenke. These compounds, identified as (16R)-16,17,18-trihydroxyphyllocladan-3-one (1) and (16R)-16,17-dihydroxyphyllocladan-3-one (2) on the basis of spectral data, competitively inhibited the binding of [(3)H]-FNZ to the benzodiazepine binding site with K(i)±S.E.M. values of 56±19 μM and 111±13 μM, respectively. The behavioral actions of these diterpenes, intraperitoneally (i.p.) administered in mice, were examined in the plus-maze, holeboard, locomotor activity and light/dark tests. Compound 1 exhibited anxiolytic-like effects in mice evidenced by a significant increase of the parameters measured in the holeboard test (the number of head dips at 0.3 mg/kg and 3 mg/kg, the rears at 1 mg/kg and the time spent head-dipping at 3 mg/kg), in the plus-maze assay (the percentage of open arm entries at 1 mg/kg) and in the light/dark test (the time in light and the number of transitions at 1 mg/kg). Compound 2 augmented the number of rearings in the holeboard apparatus (at 0.3 mg/kg and 1 mg/kg) and the locomotor activity (at 1 mg/kg). These results reveal the presence of neuroactive compounds in Aloysia virgata.

[Analysis of the binding capacity of the benzodiazepine site of gabaa receptor in mice C57BL/6 and BALB/C pretreated with anxiolytics]

The level of specific 3H-flunitrazepam binding in synaptosomal membranes of C57BL/6 and BALB/c mice brain underwent to the stress of different types has been studied. Mild stress (Elevated Plus Maze) was shown to induce the decrease of benzodiazepine binding in BALB/c mice only, while the strong one (Exposure to a predator) was revealed to cause this decrease in both strains. Behavioral effects of different non-benzodiazepine drugs possessing anxiolytic properties (Afobazol, Ladasten and Noopept) was accompanied with the normalization of the level of benzodiazepine reception, reduced by the stress of both modalities.

Antidepressant activity of standardised extract of Marsilea minuta Linn

AIM OF THE STUDY

Marsilea minuta Linn. (Marsileaceae) has been referred in Indian traditional medicine system (Ayurveda) for the treatment of insomnia and other mental disorders. Marsiline isolated from Marsilea minuta was reported to have sedative and anticonvulsant property. The ethanol extract of Marsilea minuta was standardised for marsiline (1.15%, w/w) and studied for its antidepressant activity.

MATERIALS AND METHODS

Antidepressant activity was studied using forced swimming test (FST), tail suspension test (TST), learned helplessness test (LHT) and 5-hydroxytryptophan (5-HTP) induced head twitches response in rodents. Standardised extract of Marsilea minuta in doses of 100, 200 and 400 mg/kg/day were administered orally for three consecutive days and evaluated on day 3, 1h after the last dose treatment. Imipramine (15 mg/kg/day, i.p.) was used as the standard drug. Neurochemical mechanism of antidepressant activity was elucidated by using radioligand receptor binding assays for 5-HT2A and benzodiazepine receptors in rat frontal cortex.

RESULTS

Immobility time in FST and TST was significantly (P<0.05) reduced by ethanol extract of Marsilea minuta treated animals. A decrease in number of escape failures in LHT was also observed in Marsilea minuta treated rats. Head twitch response induced by 5-HTP was significantly attenuated by Marsilea minuta (400 mg/kg, p.o.) and imipramine showing the involvement of serotonergic system. This effect was corroborated with radioligand receptor binding study where Marsilea minuta (400 mg/kg, p.o.) significantly (P<0.05) down regulated 5-HT2A receptor in frontal cortex, whereas, no marked effect was observed for benzodiazepine receptor.

CONCLUSION

The antidepressant effect exhibited by Marsilea minuta extract may be due to its effect on 5-HT2A density in rat frontal cortex.

Acute stress or systemic insulin injection increases flunitrazepam sensitive-GABAA receptor density in synaptosomes of chick forebrain: Modulation by systemic epinephrine

Interactions between acute stress and systemic insulin and epinephrine on GABAA receptor density in the forebrain were studied. Here, 10 day-old chicks were intraperitoneally injected with insulin, epinephrine or vehicle and then immediately stressed by partial water immersion for 15 min and killed by decapitation. Non-stressed controls were similarly injected, then returned to their rearing boxes for 15 min and then killed. Forebrains were dissected and GABAA receptor density was measured ex vivo in synaptosomes by 3[H]-flunitrazepam binding assay. In non-stressed chicks, insulin at 1.25, 2.50 and 5.00 IU/kg of body weight (non-hypoglycemic doses) increased Bmax by 33, 53 and 44% compared to saline, respectively. A similar increase of 41% was observed in receptor density after stress. However, the insulin effect was not additive to the stress-induced increase suggesting that both effects occur through similar mechanisms. In contrast, epinephrine, at 0.25 and 0.5 mg/kg did not induce any changes in Bmax in non-stressed chicks. Nevertheless, after stress these doses increased the receptor density by about 13 and 27%, respectively. Similarly, the same epinephrine doses co-administered with insulin (2.50 IU/kg), increased the receptor density by about 20% compared to insulin alone. These results suggest that systemic epinephrine, perhaps by evoking central norepinephrine release, modulates the increase in forebrain GABAA receptor binding induced by both insulin and stress.

Contribution of specific binding to the central benzodiazepine site to the brain concentrations of two novel benzodiazepine site ligands

The in vivo occupancy of brain benzodiazepine binding sites by compounds A and B was measured using a [(3)H]Ro 15-1788 binding assay and related to plasma and brain drug concentrations. The plasma concentration associated with 50% occupancy was higher for compound A than compound B (73 and 3.7 nM, respectively), however, there was little difference in the brain concentrations required (73 and 63 nM). Both compounds showed a non-linear relationship between plasma and brain concentrations such that above brain concentrations of approximately 100 nM increasing plasma concentrations did not result in a concomitant increase in brain concentrations. This is consistent with brain concentrations being dependent on a saturable compartment which was postulated to be the benzodiazepine binding site-containing GABA(A) receptors. This hypothesis was tested in alpha1H101R mice, in which the alpha1 subunit of the GABA(A) receptor is rendered insensitive to benzodiazepine binding resulting in an approximate 50% reduction in the total benzodiazepine-containing GABA(A) receptor population. It was shown that the Occ(50) brain concentrations in the alpha1H101R animals was lower (17 nM) than in wild type mice (63 nM), as was the plateau concentration in the brain (105 and 195 nM, respectively). These data suggest measured concentrations of compounds A and B in brain tissue are dependent on receptor expression with a minimal contribution from unbound and non-specifically bound compound.

Anxiolytic-like effects of obovatol isolated from Magnolia obovata: involvement of GABA/benzodiazepine receptors complex

This experiment was performed to investigate whether obovatol isolated from the leaves of Magnolia obovata has anxiolytic-like effects through GABA-benzodiazepine-receptors Cl(-) channel activation. The anxiolytic-like effects of obovatol in mice were examined using the elevated plus-maze and the automatic hole-board apparatus. Oral administration of obovatol (0.2, 0.5 and 1.0 mg/kg) significantly increased the number of open arm entries and the spent time on open arm in the elevated plus-maze test, compared with those of saline. Obovatol (0.2, 0.5 and 1.0 mg/kg) also produced anxiolytic-like effects, as reflected by an increase in head-dipping behaviors. These effects were comparable to those of diazepam (1.0 mg/kg), a well known anxiolytic drug. On the other hand, the anxiolytic-like effects of obovatol and diazepam were reversed by flumazenil, a benzodiazepine receptor antagonist, suggesting that the anxiolytic-like effects of obovatol were involved in GABA-benzodiazepine receptors complex. Obovatol was muscle relaxant by rota-rod test, but its effect was weaker than diazepam. Spontaneous locomotor activity also was inhibited by obovatol. Obovatol selectively increased the GABA(A) receptors alpha(1) subunit expression in amygdala of mouse brain. Obovatol also showed to bind to benzodiazepine receptors competitively in experiments using [(3)H]flunitrazepam in the cerebral cortex of mouse brain. Moreover, obovatol (10, 20 and 50 microM) increased Cl(-) influx and the increased Cl(-) influx was inhibited by flumazenil, in primary cultured neuronal cells and IMR-32 human neuroblastoma cells. These results suggest that obovatol has anxiolytic-like effects, and these pharmacological effects may be mediated by GABA-benzodiazepine receptors-activated Cl(-) channel opening.

Postnatal development and kinetics of [3H]gaboxadol binding in rat brain: in vitro homogenate binding and quantitative autoradiography

The postnatal development of the binding of the GABA(A) receptor agonist [(3)H]gaboxadol in rat brain was investigated. Using brain tissue from rats obtained at postnatal days 1, 10, 25, and >25 (adult), the binding of [(3)H]gaboxadol and the benzodiazepine [(3)H]flunitrazepam to GABA(A) receptors was compared in homogenate binding assays and quantitative receptor autoradiography. Kinetic and equilibrium data obtained in homogenate binding studies revealed two different [(3)H]gaboxadol affinities. A kinetically derived K(D) of 3.7 nM in adult cerebellum, calculated from the association and dissociation rate constants k(on) (1.45 x 10(8) M(-1) min(-1)) and k(off) (0.54 min(-1)) was contrasted by an equilibrium K(D) of 38.6 nM, obtained by homologous competition experiments. Quantitative analysis of autoradiographic data revealed an increase in specific [(3)H]gaboxadol binding sites during brain development, which resembles the anatomical and temporal pattern of the postnatal expression of the extrasynaptic delta subunit of GABA(A) receptors. In conclusion, by the radioligand binding data obtained on native tissue, binding of gaboxadol to GABA(A) receptors located outside the synaptic junctions could be postulated.

Autoradiographic analysis of GABAA receptors in mu-opioid receptor knockout mice

Anatomical evidence indicates that gamma-aminobutyric acid (GABA)-ergic and opioidergic systems are closely linked and act on the same neurons. However, the regulatory mechanisms between GABAergic and opioidergic system have not been well characterized. In the present study, we investigated whether there are changes in GABA(A) receptors in mice lacking mu-opioid receptor gene. The GABA(A) receptor binding was carried out by autoradiography using [(3)H]-muscimol (GABA(A)), [(3)H]-flunitrazepam (FNZ, native type 1 benzodiazepine) and [(35)S]-t-butylbicyclophosphorothionate (TBPS, binding to GABA(A)-gated chloride channels) in brain slices of wild type and mu-opioid receptor knockout mice. The binding of [(3)H]-FNZ in mu-opioid receptor knockout mice was significantly higher than that of the wild type controls in most of the cortex and hippocampal CA1 and CA2 formations. mu-Opioid receptor knockout mice show significantly lower binding of [(35)S]-TBPS than that of the wild type mice in few of the cortical areas including ectorhinal cortex layers I, III, and V, but not in the hippocampus. There was no significant difference in binding of [(3)H]-muscimol between mu-opioid receptor knockout and wild type mice in the cortex and hippocampus. These data indicate that there are specific regional changes in GABA(A) receptor binding sites in mu-opioid receptor knockout mice. These data also suggest that there are compensatory up-regulation of benzodiazepine binding site of GABA(A) receptors in the cortex and hippocampus and down-regulation of GABA-gated chloride channel binding site of GABA(A) receptors in the cortex of the mu-opioid receptor knockout mice.

Exploring ligand recognition and ion flow in comparative models of the human GABA type A receptor

We present two comparative models of the GABA(A) receptor. Model 1 is based on the 4-A resolution structure of the nicotinic acetylcholine receptor from Torpedo marmorata and represents the unliganded receptor. Two agonists, GABA and muscimol, two benzodiazepines, flunitrazepam and alprazolam, together with the general anaesthetic halothane, have been docked to this model. The ion flow is also explored in model 1 by evaluating the interaction energy of a chloride ion as it traverses the extracellular, transmembrane and intracellular domains of the protein. Model 2 differs from model 1 only in the extracellular domain and represents the liganded receptor. Comparison between the two models not only allows us to explore commonalities and differences with comparative models of the nicotinic acetylcholine receptor, but also suggests possible protein sub-domain interactions with the GABA(A) receptor not previously addressed.

Allosteric uncoupling and up-regulation of benzodiazepine and GABA recognition sites following chronic diazepam treatment of HEK 293 cells stably transfected with alpha1beta2gamma2S subunits of GABA (A) receptors

Benzodiazepines are drugs known to produce tolerance and dependence and also to be abused and co-abused. The aim of this study was to further explore the mechanisms that underlie adaptive changes in GABA(A) receptors following prolonged exposure to these drugs. Human embryonic kidney (HEK 293) cells stably expressing recombinant alpha1beta2gamma2s GABA(A) receptors were exposed for 72 h to a high concentration of diazepam (50 microM) in the absence or presence of other drugs. Radioligand binding studies were used to determine the parameters of [(3)H]flunitrazepam and [(3)H]muscimol binding sites and allosteric interactions between these sites. Prolonged treatment with diazepam increased the maximum number (B (max)) of [(3)H]flunitrazepam and [(3)H]muscimol binding sites in the membranes, and of [(3)H]muscimol binding sites on the surface of HEK 293 cells. There was no change in the affinity (K (d)) of binding sites. The diazepam-induced increase in the B (max) value of [(3)H]flunitrazepam binding sites was reduced by two GABA(A) receptor antagonists, gabazine (1 and 10 microM) and picrotoxin (100 microM). In addition, it was reduced by cycloheximide (5 microg/ml), a protein synthesis inhibitor, and actinomycin D (7.5 microg/ml), an RNA synthesis inhibitor. Flumazenil (5 microM), the antagonist of benzodiazepine binding sites, also up-regulated [(3)H]flunitrazepam recognition sites. Simultaneous treatment with diazepam and flumazenil failed to produce an additive up-regulation. GABA (1 nM - 1 mM)-induced potentiation of [(3)H]flunitrazepam binding to membranes obtained from diazepam (50 microM)-pretreated cells was markedly reduced, suggesting functional uncoupling between GABA and benzodiazepine binding sites. The results suggest that diazepam up-regulated benzodiazepine binding sites on stably expressed GABA(A) receptors by stimulating their synthesis at both the transcriptional and translational levels. A comparable increase of [(3)H]muscimol binding sites expressed on the surface of intact HEK 293 cells suggests that internalisation of surface receptors presumably can not explain the uncoupling.

Characterization of two classes of benzodiazepine binding sites in Schistosoma mansoni

As we have recently shown that GABA should be considered a putative neurotransmitter inSchistosoma mansoni, the present work aimed to search for GABAAreceptors in adult worms using [3H]-flunitrazepam to label the allosteric benzodiazepine binding site which is classically present on GABAAreceptor complexes. We detected a large population (Bmax=8·25±1·1 pmol . mg protein−1) of high affinity (Kd=33·6±1·5 nm) binding sites for flunitrazepam. These sites harboured a singular pharmacological modulation that does not fit well with a mammalian central benzodiazepine receptor, mainly due to a very high affinity for Ro5-4864 and a very low affinity for clonazepam. We also detected a second population of benzodiazepine binding sites labelled with high affinity (IC50=85 nm) by [3H]-PK11195, a selective ligand of the mammalian peripheral benzodiazepine receptor. In conclusion, this work describes the pharmacological properties of a large population of central-like benzodiazepine receptors supporting their study as putative new targets for the development of anti-parasitic agents. We also describe, for the first time, the presence of peripheral benzodiazepine receptors in this parasite.

Indorenate modifies a1-adrenergic and benzodiazepine receptor binding in the rat brain: an autoradiography study

Indorenate (5-methoxytryptamine-beta-methylcarboxylate) is a 5-HT1A receptor agonist that produces antihypertensive, anxiolytic, antidepressant and anticonvulsant effects. However, there is evidence suggesting that these effects could involve the activation of benzodiazepine (BZD) receptors but not the activation of a1-adrenergic receptors. The goal of this study was to analyse the effect of indorenate on a1-adrenergic and BZD receptor binding in specific rat brain areas by using in-vitro autoradiography. Coronal brain sections from male Wistar rats were used for labelling 5-HT1A (3H-8-OH-DPAT, 2 nM), a1-adrenergic (3H-prazosin, 2 nM) and BZD (3H-flunitrazepam, 2 nM) receptor binding in the presence or absence of indorenate (1 microM). Indorenate totally displaced 3H-8-OH-DPAT binding in all the brain areas evaluated. It decreased 3H-prazosin binding just in the frontal (30%) and sensorimotor (32%) cortices and in the thalamus (21%). Additionally, indorenate diminished 3H-flunitrazepam binding only in the cingulate (16%) and piriform (18%) cortices as well as in the dorsal raphe nucleus (18%). These results confirm that indorenate is a 5-HT1A ligand and suggest the possible participation of a1-adrenergic and BZD receptors in its pharmacological properties.

Hyperthermia-Induced Seizures Modify the GABAA and Benzodiazepine Receptor Binding in Immature Rat Brain

Effects of hyperthermia-induced seizures (HS) on GABA(A) and benzodiazepine (BDZ) receptor binding in immature rat brain were evaluated using in vitro autoradiography. HS were induced in 10-days-old rats by a regulated stream of moderately heated air directed 50 cm above the animals. Rats were killed 30 min, 24 h or 20 days after HS and their brains were used for in vitro autoradiography experiments to determine GABA(A) and BDZ receptor binding. GABA(A) binding was significantly enhanced in all brain areas evaluated 30 min after HS, an effect that endures 24 h and 20 days after seizures. Concerning BDZ receptor binding, a significant increase was detected in entorhinal and perirhinal cortices and decreased in basolateral amygdala 30 min following HS. One day after HS, animals demonstrated enhanced BDZ binding in the cingulate, frontal, posterior parietal, entorhinal, temporal and perirhinal cortices; striatum, accumbens, substantia nigra pars compacta and amygdala nuclei. Twenty days after HS enhanced BDZ binding was restricted in the cingulated, frontal, anterior and posterior parietal cortices, as well as in substantia nigra pars reticulata, whereas decreased values were found in accumbens nucleus and substantia nigra pars compacta. Our data indicate differential effects of HS in GABA(A) and BDZ binding in immature brain. HS-induced GABA(A) and BDZ changes are different from those previously described in experimental models of temporal lobe epilepsy in adult animals.

The anxiolytic-like effects of Aloysia polystachya (Griseb.) Moldenke (Verbenaceae) in mice

The aim of the present work is to demonstrate the putative sedative and anxiolytic-like effects of a hydro-ethanolic extract obtained from the aerial parts of Aloysia polystachya (Verbenaceae) in male mice using several behavioural assays. Groups of male mice orally treated with doses of 1.0, 10.0 and 100.0 mg/kg of the extract did not show any significant alteration of their locomotor activity, body temperature or motor coordination. The same treatment increased the duration of the sleeping time induced by 30.0 mg/kg i.p. of sodium pentobarbital. However, the sleeping time induced by ethyl ether was not modified by the oral administration of the extract, not confirming the putative sedative effect of the plant. The ethanolic extract also significantly increased the percentage of both entries (1.0 and 100.0 mg/kg) and the time spent (10.0 and 100.0 mg/kg) into the open arms of the elevated plus maze (EPM). Nevertheless, the binding of (3)H-flunitrazepam ((3)H-FNZ) to the benzodiazepine binding site (BDZ-bs), in washed crude synaptosomal membranes from rat cerebral cortex, was not affected by the semi-purified components from Aloysia polystachya. These results indicate an anxiolytic-like profile of action for the extract of Aloysia polystachya without sedative side effect, being this activity probably mediated by other mechanism than BDZ-bs modulation at the GABA(A) receptors.

Increased levels of pregnenolone and its neuroactive metabolite allopregnanolone in autopsied brain tissue from cirrhotic patients who died in hepatic coma

It has been suggested that neurosteroids with agonist properties at the central GABA-A receptor are implicated in the pathogenesis of hepatic encephalopathy (HE) in chronic liver disease. In order to address this issue, gas chromatography/mass spectrometry was used to measure the neurosteroids pregnenolone, allopregnanolone, and tetrahydrodeoxycorticosterone (THDOC) in postmortem brain tissue from controls, cirrhotic patients who died without HE, a patient who died in uremic coma, and cirrhotic patients who died in hepatic coma. Exposure of rat cerebral cortical membranes to brain extracts from hepatic coma patients resulted in a 53% (p < 0.001) increase in binding of [3H]muscimol, a GABA-A receptor ligand. Subsequent GC/MS analysis showed that concentrations of the GABA-A receptor agonist neurosteroid allopregnanolone were significantly increased in brain tissue from hepatic coma patients compared to patients without HE or controls (p < 0.001). Brain allopregnanolone concentrations were significantly correlated with the magnitude of induction of [3H]muscimol binding (r2 = 0.82, p < 0.0001). Concentrations of allopregnanolone comparable to those observed in hepatic coma brains are pathophysiologically relevant. Concentrations of the neurosteroid precursor pregnenolone were also increased in brain tissue from hepatic coma patients, while those of a second neurosteroid THDOC were below the levels of detection in all groups. Brain concentrations of benzodiazepine receptor ligands estimated by radioreceptor assay were not significantly increased in cirrhotic patients with or without hepatic coma. These findings suggest that increased levels of allopregnanolone rather than "endogenous benzodiazepines" offer a cogent explanation for the phenomenon of "increased GABAergic tone" previously proposed in HE.

Do subtype-selective gamma-aminobutyric acid A receptor modulators have a reduced propensity to induce physical dependence in mice?

Recent evidence suggests that GABA(A) receptors containing an alpha1 subunit mediate the sedative effect of diazepam, whereas receptors with an alpha2 subunit mediate this benzodiazepine's anxiolytic effect. Thus, compounds selective for GABA(A)-alpha2 receptors may offer advantages, i.e., lack of sedation, over current benzodiazepines. Whether such compounds would offer additional advantages over benzodiazepines is unclear. Here, we address the issue of physical dependence by comparing the GABA(A)-alpha1 affinity-selective drug zolpidem, the novel compounds 7-(1,1-dimethylethyl)-6-(2-methyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2,5-difluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (L-838,417) and 6-fluoro-9-methyl-2-phenyl-4-(pyrrolidin-1-yl-carbonyl)-2,9-dihydro-1H-pyridol[3,4-b]indol-1-one (SL651498) with functional selectivity for certain non-alpha(1) GABA(A) receptors, nonselective partial agonists [bretazenil, 1-[1-[3-(3-pyridyl)phenyl]benzimidazol-5-yl]ethanone O-ethyloxime (NS2710), and 5-furan-3-yl-1-(3-imidazol-1-phenyl)-1H-benzoimidazole (NS2664)], and nonselective full efficacy benzodiazepines, in a rapid precipitated withdrawal assay using the inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142). For all compounds, we determined in vitro IC50 values to displace [3H]flunitrazepam from rat cortex and in vivo ED50 values for displacement of [3H]flunitrazepam from mouse forebrain (including length of in vivo occupancy). In the precipitated withdrawal model, compounds were administered at a dose giving approximately 80% receptor occupancy, obviating major differences in central nervous system bioavailability. Mice were administered compounds twice daily for 4 days and on day 5, 20 h after the final dose, given a dose of FG-7142 (40 mg/kg i.p.) that did not induce seizures in control animals. In mice treated with the three subtype-selective compounds, FG-7142 did not induce seizures. Moreover, there was a low propensity for FG-7142 to induce seizures in animals treated with the partial agonists, whereas seizures were clearly seen in animals treated with most benzodiazepines. Nonetheless, differences among the benzodiazepines themselves, similarities between the partial agonists and subtype-selective compounds, the in vitro/in vivo potency, and in vivo receptor exposure time data suggest a complex interaction among selectivity, efficacy, potency, and receptor exposure in determining physical dependence liability of benzodiazepine site modulators in mice.

Differential effects of mild repeated restraint stress on behaviors and GABA(A) receptors in male and female rats

We previously reported that the very mild stress of individual housing influenced seizure risk and gamma-amino butyric acid (GABA(A)) receptor activity differentially between male and female rats. The aim of the present set of studies was to assess sex differences in behavioral responses to a more pronounced type of stressor, repeated restraint stress. We also wanted to determine the role of GABA(A) receptors in effects of this stressor. Our data suggest that repeated restraint stress afforded short-term protection against seizure induction in both male and female rats. Moreover, this protection was more persistent in female than male rats. This stress paradigm also elicited a reduction in general activity in male rats, whereas female rats displayed prolonged increased activity following the repeated restraint stress exposure. However, there were limited effects on anxiety-like behaviors, as determined by time spent in the open arms on the elevated plus maze. Sex differences in stress-induced increases in plasma corticosterone levels were observed, which generally correlated with sex differences in behavioral measures. There were no significant effects of the repeated restraint stress exposure on benzodiazepine/GABA(A) receptor density or affinity nor on receptor function. Taken together, these findings provide additional evidence to support the important influences of sex in responding to stress and highlight the need to consider this context when addressing the role of stress in health issues for women and men.

Radioligand binding studies of caloporoside and novel congeners with contrasting effects upon [35S] TBPS binding to the mammalian GABAA receptor

Caloporoside is a natural active fungal metabolite, which was isolated from Caloporous dichrous and was described to exhibit antibacterial, antifungal and phospholipase C inhibitory activity. We have previously reported evidence that related beta-linked compounds, lactose and octyl-beta-d-mannoside, bind and functionally modulate rodent GABA(A) receptors, respectively. We have characterized the binding pharmacology of synthetic caloporoside and two further congeners, 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid and octyl-beta-d-glucoside on GABA(A) receptors using a [35S]-t-butylbicyclophosphoorothionate (TBPS) radioligand binding assay. Caloporoside and 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid produced concentration-dependent complete inhibition of specific [35S] TBPS binding with overall apparent IC50 values of 14.7+/-0.1 and 14.2+/-0.1 microM, respectively. In contrast, octyl-beta-d-glucoside elicited a concentration-dependent stimulation of specific [35S] TBPS binding (E(max)=144+/-4%; EC50=39.2+/-22.7 nM). The level of stimulation was similar to that elicited by diazepam (E(max)=147+/-6%; EC50=0.8+/-0.1 nM), and was occluded by GABA (0.3 microM). However, the three test compounds failed to elicit any significant effect (positive or negative) upon [3H] flunitrazepam or [3H] muscimol binding, indicating that they did not bind directly, or allosterically couple, to the benzodiazepine or agonist binding site of the GABA(A) receptor, respectively. The constituent monosaccharide, glucose, and both the closely related congeners octyl-beta-d-glucoside or hexyl-beta-d-glucoside have no significant effect upon [35S] TBPS binding. These data, together, provide strong evidence that a beta-glycosidic linkage and chain length are crucial for the positive modulation of [35S] TBPS binding to the GABA(A) receptor by this novel chemical class.

Characterization of benzodiazepine binding site on human α1-acid glycoprotein using flunitrazepam as a photolabeling agent

The binding of flunitrazepam (FNZP) by human alpha1-acid glycoprotein (hAGP) and the relationships between the extent of drug binding and desialylation and the genetic variants of hAGP were examined. The photolabeling specificity of [3H]FNZP was confirmed by findings in which other hAGP-binding ligands inhibited the formation of covalent bonds between [3H]FNZP and hAGP. The photolabeling of asialo-hAGP suggested that sialic acid does not involve in the binding of [3H]FNZP. No difference in the labeling could be found between the F1*S variants and A variant. Similarly, FNZP did not show a difference in binding affinity to the two genetic variants of hAGP. Sequence analysis of the photolabeled peptide indicated a sequence corresponding to Tyr91-Arg105 of hAGP.

Allosteric positive interaction of thymol with the GABAA receptor in primary cultures of mouse cortical neurons

Thymol is a naturally occurring phenolic monoterpene known for its anti-microbial and anti-oxidant properties. It is used in dental practice and in anaesthetic halothane preparations. Recent studies have reported enhanced GABA(A) receptor-operated chloride channel activity and increased binding affinity of [(3)H]flunitrazepam in the presence of thymol. In the present work, we more closely examined the pharmacological action of thymol on the native GABA(A) receptor by using primary cultures of cortical neurons. Thymol enhanced GABA-induced (5 microM) chloride influx at concentrations lower than those exhibiting direct activity in the absence of GABA (EC(50) = 12 microM and 135 microM, respectively). This direct effect was inhibited by competitive and non-competitive GABA(A) receptor antagonists. Thymol increased [(3)H]flunitrazepam binding (EC(50) = 131 microM) and showed a tendency to increase [(3)H]muscimol binding. These results confirm that thymol is a positive allosteric modulator of the GABA(A) receptor. The thymol structural analogues menthol and cymene, which lack an aromatic ring or a hydroxyl group, did not affect [(3)H]flunitrazepam binding. Using a pharmacophoric model that includes a hydrogen bond donor group as well as an aromatic ring with two aliphatic substituents, we propose to demonstrate the molecular essential features of these compounds to interact with GABA(A) receptors. Thymol (0-1 mM) did not affect cellular viability.

Differential effects of ammonia on the benzodiazepine modulatory site on the GABA-A receptor complex of human brain

Ammonia is a key factor in the pathogenesis of encephalopathies associated with liver failure. A direct effect of ammonia on GABAergic neurotransmission was proposed as a mechanism that may explain its neurotoxic effect on the basis of electrophysiological and biochemical studies performed in animal models of liver failure. In the present study, we investigated using a radiometric assay the effect of ammonia on the binding of GABA-A receptor ligands to membranes from normal human brains. Ammonium tartrate significantly decreased the maximal binding of [3H]flunitrazepam to well-washed frontal cortical membranes (366+/-63 fmol/mg protein in absence of ammonia versus 294.1+/-51 fmol/mg protein in presence of 2 mM ammonia; p<0.05). The efficacy of the effects of ammonia was within the millimolar range (IC50=4.8 mM). This effect was not seen in cerebellum or hippocampus. Ammonia exposure decreased the maximal binding of [3H]flumazenil (284.9+/-24.2 fmol/mg protein in absence of ammonia versus 146.4+/-15.6 fmol/mg protein in presence of 2 mM ammonia; p<0.01). This effect was seen with a greater potency (Imax=32.4%) and a lower IC50 (0.1 mM). Inhibition of [3H]flumazenil binding was significant in all brain regions. The apparent ammonia-induced decrease of [3H]flunitrazepam and [3H]flumazenil binding was due to a decrease in the binding affinities of these ligands for the benzodiazepine site. In contrast, ammonium tartrate exposure did not cause significant changes to the binding of [3H]muscimol in any brain region. These findings demonstrate that ammonia interacts negatively with components of the benzodiazepine-associated site at the GABA-A receptor complex in human brain in contrast to previous reports in the rat, and thus, does not support the notion that ammonia directly activates the GABA-A receptor complex resulting in increased GABAergic neurotransmission in human hepatic encephalopathy. These findings also suggest that positron emission tomography studies in cirrhotic patients using [11C]flumazenil may be underestimating GABA-A receptor sites depending upon the degree of hyperammonemia of the patient.

Hyperthermia-Induced Seizures Modify the GABAA and Benzodiazepine Receptor Binding in Immature Rat Brain

Effects of hyperthermia-induced seizures (HS) on GABAA and benzodiazepine (BDZ) receptor binding in immature rat brain were evaluated using in vitro autoradiography. HS were induced in 10-day-old rats by a regulated stream of moderately heated air directed 50 cm above the animals. Rats were killed 30 min, 24 h, or 20 days after HS and their brains were used for in vitro autoradiography experiments to determine GABAA and BDZ receptor binding. GABAA binding was significantly enhanced in all brain areas evaluated 30 min after HS, an effect that endures 24 h and 20 days after seizures. Concerning BDZ receptor binding, a significant increase was detected in entorhinal and perirhinal cortices and decreased in basolateral amygdala 30 min following HS. One day after HS, animals demonstrated enhanced BDZ binding in the cingulate, frontal, posterior parietal, entorhinal, temporal, and perirhinal cortices; striatum, accumbens, substantia nigra pars compacta, and amygdala nuclei. Twenty days after HS enhanced BDZ binding was restricted in the cingulated, frontal, anterior and posterior parietal cortices, as well as in substantia nigra pars reticulata, whereas decreased values were found in accumbens nucleus and substantia nigra pars compacta. Our data indicate differential effects of HS in GABAA and BDZ binding in immature brain. HS-induced GABAA and BDZ changes are different from those previously described in experimental models of temporal lobe epilepsy in adult animals.

Ethyl 2-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-4-imidazolecarboxylate is a novel positive modulator of GABAA receptors

Ethyl 2-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-4-imidazolecarboxylate (TG41) enhanced the binding both of gamma-aminobutyric acid (GABA) and of flunitrazepam to rat cerebral cortical membranes. Electrophysiological recordings from Xenopus oocytes expressing various recombinant GABA(A) receptor subtypes revealed that TG41 enhanced the function of all receptor subunit combinations tested. The potency of TG41 at receptors containing alpha1, beta2, and gamma2L subunits was greater than that of alphaxalone, etomidate, propofol, or pentobarbital. The potency of TG41 was also greater at receptors containing alpha1 or alpha2 subunits than at those containing alpha4 and it was markedly higher at receptors containing beta2 or beta3 subunits than at those containing beta1. This drug induced a reversible loss of the righting reflex in Xenopus tadpoles and it elicited hypnosis (5 mg/kg) after intravenous administration in rats. These results indicate that the pharmacological profile of TG41 is similar to that of general anesthetics which potentiate the activity of GABA(A) receptors containing the beta2 or beta3 subunit.

Regulation of gephyrin and GABAA receptor binding within the amygdala after fear acquisition and extinction

Both the acquisition and extinction of conditioned fear appear to require the basolateral amygdala (BLA). Because these two forms of learning have opposing effects on the expression of conditioned fear, we hypothesized that they may modulate GABAergic tone differentially within the BLA. Previously, we reported that gene expression for the GABA(A) receptor clustering protein gephyrin was significantly downregulated in the BLA after fear acquisition (Ressler et al., 2002). Here we demonstrate an analogous decrease in BLA gephyrin protein levels, together with a decrease in the surface expression of GABA(A) receptors in the BLA after fear acquisition, as evidenced by decreased binding of H3-flunitrazepam. In marked contrast, gephyrin mRNA and protein levels in the BLA significantly increased after extinction training, as did H3-flunitrazepam binding. These results implicate the protein gephyrin in both fear acquisition and extinction and suggest that the modulation of gephyrin and GABA(A) receptor expression in the BLA may play a role in the experience-dependent plasticity underlying both of these types of learning. Furthermore, these results demonstrate that physiologically relevant, dynamic alterations of GABAergic synapses occur during the consolidation phase of BLA-dependent learning and may interact with previously described alterations in glutamatergic transmission to initiate and stabilize memory formation in vivo.

Synergistic interaction between hesperidin, a natural flavonoid, and diazepam

It has been recently reported the presence in Valeriana of the flavone 6-methylapigenin and the flavanone glycoside hesperidin. The apigenin derivative is a ligand for the benzodiazepine binding site in the gamma-aminobutyric acid receptor type A (GABA(A)) and has anxiolytic properties. Hesperidin has sedative and sleep-enhancing properties but is not a ligand for the benzodiazepine binding site. 6-Methylapigenin is able to potentiate the sleep-enhancing effect of hesperidin. In this work we demonstrate that this property is shared with various GABA(A) receptor ligands, among them the agonist diazepam, which was used to study the potentiation as measured in the hole board test. Isobolar analysis of the results showed the interaction being synergistic. We discarded pharmacokinetic effects or a direct action of hesperidin on the benzodiazepine binding site. A possible use of hesperidin properties to decrease the effective therapeutic doses of benzodiazepines is suggested.

Novel Plant Substances Acting as β Subunit Isoform-Selective Positive Allosteric Modulators of GABAAReceptors

GABAA receptors are modulated by a large variety of compounds. A common chemical characteristic of most of these modulators is that they contain a cyclic entity. Three linear molecules of a polyacetylene structure were isolated from the East African medicinal plant Cussonia zimmermannii Harms and shown to allosterically stimulate GABAA receptors. Stimulation was not abolished by the absence of the gamma2 subunit, the benzodiazepine antagonist Ro15-1788 (8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid ethyl ester), or the point mutation beta2N265S that abolishes effects by loreclezole. At a concentration of 30 microM, the substances by themselves elicited only tiny currents. Maximal stimulation at alpha1beta2gamma2 amounted to 110 to 450% for the three substances, and half-maximal stimulation was observed at concentrations of 1 to 2 muM. Stimulation was subunit composition-dependent and was for the substance MS-1, alpha1beta2gamma2 approximately alpha1beta2 approximately alpha3beta2gamma2 > alpha2beta2gamma2 > alpha5beta2gamma2 approximately alpha1beta3gamma2 approximately alpha6beta2gamma2 > alpha1beta1gamma2, for MS-2 alpha1beta2gamma2 approximately alpha3beta2gamma2 approximately alpha1beta2 > alpha2beta2gamma2 approximately alpha6beta2gamma2 approximately alpha5beta2gamma2 > alpha1beta1gamma2, and for MS-4, alpha1beta2gamma2 approximately alpha1beta2 approximately alpha5beta2gamma2 approximately alpha3beta2gamma2 approximately alpha2beta2gamma2 > alpha6beta2gamma2 >> alpha1beta1gamma2. Maximal stimulation by MS-1 was 450% at alpha1beta2gamma2, 80% at alpha1beta1gamma2, and 150% at alpha1beta3gamma2. MS-1 was thus specific for receptors containing the beta2 subunit. The reversal potential was unaffected by 10 microM MS-1, whereas apparent picrotoxin affinity for current inhibition was increased approximately 3-fold. In summary, these positive allosteric modulators of GABAA receptors of plant origin have a novel unusual chemical structure and act at a site independent of that of benzodiazepines and loreclezole.

Selective anxiolysis produced by ocinaplon, a GABA(A) receptor modulator

Benzodiazepines remain widely used for the treatment of anxiety disorders despite prominent, often limiting side effects including sedation, muscle relaxation, and ataxia. A compound producing a robust anxiolytic action comparable to benzodiazepines, but lacking these limiting side effects at therapeutic doses (an anxioselective agent), would represent an important advance in the treatment of generalized anxiety disorder, and perhaps other anxiety disorders. Here we report that the pyrazolo[1,5-a]-pyrimidine, ocinaplon, exhibits an anxioselective profile in both preclinical procedures and in patients with generalized anxiety disorder, the most common of the anxiety disorders. In rats, ocinaplon produces significant muscle relaxation, ataxia, and sedation only at doses >25-fold higher than the minimum effective dose (3.1 mg/kg) in the Vogel "conflict" test. This anticonflict effect is blocked by flumazenil (Ro 15-1788), indicating that like benzodiazepines, ocinaplon produces an anxiolytic action through allosteric modulation of GABA(A) receptors. Nonetheless, in eight recombinant GABA(A) receptor isoforms expressed in Xenopus oocytes, the potency and efficacy of ocinaplon to potentiate GABA responses varied with subunit composition not only in an absolute sense, but also relative to the prototypical benzodiazepine, diazepam. In a double blind, placebo controlled clinical trial, a 2-week regimen of ocinaplon (total daily dose of 180-240 mg) produced statistically significant reductions in the Hamilton rating scale for anxiety scores. In this study, the incidence of benzodiazepine-like side effects (e.g., sedation, dizziness) in ocinaplon-treated patients did not differ from placebo. These findings indicate that ocinaplon represents a unique approach both for the treatment and understanding of anxiety disorders.

Novel anellated pyrazoloquinolin-3-ones: synthesis and in vitro BZR activity

A series of pyrazolo[4,3-c]pyrrolo[3,2-f]quinolin-3-one derivatives 6, 7a-c, 8a,b, 9a,b and 10-12 were synthesized as modified pyrazoloquinolinone analogs (PQs) and evaluated for their ability to inhibit radioligand to central and peripheral benzodiazepine receptors (BZRs) and their effect on GABA(A) alpha1beta2gamma2L receptors expressed in Xenopus laevis oocytes. Multistep synthesis starting from 5-nitroindole, via the Gould-Jacobs reaction to the quinoline nucleus, yielded key intermediates 9-chloro-3H-pyrrolo[3,2-f]quinoline-8-carboxylates. The reaction of the latter with methyl-hydrazine and various phenyl-hydrazines furnished the final compounds. In order to confirm the expected tetracyclic 2-substituted-2H-pyrazolopyrroloquinolin-3-one structure, IR spectrophotometric, mono-1H and 13C and bi-dimensional spectrometric and HRMS analyses were carried out: all compounds were found to be 2-substituted 3-keto tautomers; compound 6 only differed because it turned out to be 1-methyl-2H-pyrazolo[4,3-c]pyrrolo[3,2-f]quinolin-3-olo. The results of this work are consistent with those previously reported for PQs: 7-9 show high potency in displacing specific [3H]flunitrazepam from its receptor site; no compound was active in inhibiting the binding of [3H]PK 11195. They all act as antagonists at central BZR.

Characterization in Rats of the Anxiolytic Potential of ELB139 [1-(4-Chlorophenyl)-4-piperidin-1-yl-1,5-dihydro-imidazol-2-on], a New Agonist at the Benzodiazepine Binding Site of the GABAA Receptor

Benzodiazepines are among the most effective drugs for the treatment of anxiety disorders. However, their use is limited by undesired side effects, including sedation, development of tolerance, and drug abuse. The aim of this study was to evaluate the pharmacological profile of ELB139 [1-(4-chlorophenyl)-4-piperidin-1-yl-1,5-dihydro-imidazol-2-on] in different models of anxiety and to correlate these effects with its activity in vitro. ELB139 binds with an IC(50) of 1390 nM to the flunitrazepam binding site in rat forebrain cortical membranes. In rat hippocampal neurons, ELB139 potentiated GABA-induced currents without reaching the maximum effect of diazepam, indicating a partial benzodiazepine agonism. The potentiation was antagonized by the benzodiazepine antagonist flumazenil. ELB139 (10 and 30 mg/kg p.o.) was active in three different animal models of anxiety, i.e., in the elevated plus-maze, the light and dark box, and the Vogel conflict test. The anxiolytic activity in the elevated plus-maze was almost completely reversed by flumazenil (5 mg/kg i.p.), indicating that interaction with the benzodiazepine binding site is central to the pharmacological activity. No hint of sedation was observed at the doses tested in the three anxiety models and the open field. Also, no development of tolerance was observed within 6 weeks b.i.d. treatment with ELB139 in the elevated plus-maze test. In summary, ELB139 elicits strong effects on anxiety-related behavior in rats mediated by its benzodiazepine-like activity without showing sedation or the development of tolerance, a major side effect of benzodiazepines. These characteristics make the compound a prime candidate for clinical development.

Characterization of a new synthetic isoflavonoid with inverse agonist activity at the central benzodiazepine receptor

Research aimed at developing selective drugs acting on gamma-aminobutyric acid (GABA)A receptors introduced compounds from diverse chemical classes unrelated to the 1,4-benzodiazepines, including flavonoids. These studies also revealed the potential use of inverse agonists as cognition-enhancing agents. Here we report pharmacological properties of the novel synthetic isoflavonoid 2-methoxy-3,8,9-trihydroxy coumestan (PCALC36). PCALC36 displaced [3H]flunitrazepam binding to rat brain synaptosomes with an IC50 of 13.8 microM. Scatchard analysis of the effect of PCALC36 showed a concentration-dependent reduction of the Bmax of [3H]flunitrazepam, without a marked change in Kd. This effect could be reversed by diluting and washing the preparation. Addition of 20-microM GABA shifted to the right the inhibition curve of PCALC36 on [3H]flunitrazepam binding (IC50 ratio of 0.68), which is characteristic for inverse agonists. PCALC36 produced little change in the GABAergic tonic currents recorded by whole-cell patch clamp in cultured rat hippocampal neurones, but it caused a 20% reduction in miniature inhibitory postsynaptic current amplitude and completely antagonised the full (direct) agonist midazolam in a quickly reversible manner. The data suggest that the coumestan backbone can be useful for developing novel ligands at the GABAA receptor.

Effects of single and repeated phencyclidine administration on [3H]flunitrazepam binding in rat brain

Repeated administration of phencyclidine (PCP) induces behavioral sensitization to dopaminergic neural transmission. This phenomenon has been implicated in the pathophysiology of schizophrenia. Recently, GABAergic agonists have been shown to reduce behavioral activity induced by enhanced dopaminergic neural transmission, which is mediated by the GABA(A)/benzodiazepine (BZD) receptor complex. Thus, to investigate the role of BZD receptors during induction and expression of behavioral sensitization in PCP-sensitized animals, the effects of both single and repeated PCP administration on BZD receptors in rat brain were examined using in vitro quantitative autoradiography. Repeated PCP administration failed to significantly alter levels of [3H]flunitrazepam (FNZ) binding in any of the regions examined. However, significant increases in levels of [3H]FNZ binding were found in the nucleus accumbens and ventral pallidum 1 h after single administration of PCP. These results suggest that BZD binding sites may not play important roles in the development of PCP-induced sensitization at several sites of GABA(A)/BZD receptor complex, while changes in GABA function in the nucleus accumbens differ from other areas following single administration of N-methyl-D-aspartate (NMDA) antagonist.

Effect of chronic administration of ethanol on GABAA receptor assemblies derived from α2-, α3-, β2- and γ2-subunits in the rat cerebral cortex

Chronic administration of ethanol decreased the immunoprecipitation of the [(3)H]flunitrazepam binding activity for GABA(A) receptor assemblies derived from alpha(2)-, alpha(3)- and gamma(2)-subunits in the rat cerebral cortex. However, the [(3)H]muscimol binding sites derived from these subunits were not affected. Thus, chronic ethanol causes the down-regulation of the benzodiazepine sites derived from the alpha(2)-, alpha(3)- and gamma(2)-subunits without affecting the GABA binding sites.

Chronic exposure of cells expressing recombinant GABAA receptors to benzodiazepine antagonist flumazenil enhances the maximum number of benzodiazepine binding sites

The aim of this study was to better understand the mechanisms that underlie adaptive changes in GABAA receptors following their prolonged exposure to drugs. Exposure (48 h) of human embryonic kidney (HEK) 293 cells stably expressing recombinant alpha1beta2gamma2S GABAA receptors to flumazenil (1 or 5 microM) in the presence of GABA (1 microM) enhanced the maximum number (Bmax) of [3H]flunitrazepam binding sites without affecting their affinity (Kd). The flumazenil-induced enhancement in Bmax was not counteracted by diazepam (1 microM). GABA (1 nM-1 mM) enhanced [3H]flunitrazepam binding to membranes obtained from control and flumazenil-pretreated cells in a concentration-dependent manner. No significant differences were observed in either the potency (EC50) or efficacy (Emax) of GABA to potentiate [3H]flunitrazepam binding. However, in flumazenil pretreated cells the basal [3H]flunitrazepam and [3H]TBOB binding were markedly enhanced. GABA produced almost complete inhibition of [3H]TBOB binding to membranes obtained from control and flumazenil treated cells. The potencies of GABA to inhibit this binding, as shown by a lack of significant changes in the IC50 values, were not different between vehicle and drug treated cells. The results suggest that chronic exposure of HEK 293 cells stably expressing recombinant alpha1beta2gamma2S GABAA receptors to flumazenil (in the presence of GABA) up-regulates benzodiazepine and convulsant binding sites, but it does not affect the allosteric interactions between these sites and the GABA binding site. Further studies are needed to elucidate these phenomena.

Changes of [3H]Muscimol, [3H]Flunitrazepam and [3H]MK-801 Binding in Rat Brain by Prolonged Ventricular Infusion of 7-Nitroindazole

In the present study, we have investigated the effects of prolonged inhibition of nitric oxide synthase (NOS) by infusion of neuronal NOS (nNOS) inhibitor, 7-nitroindazole (7-NI), to examine modulation of NMDA and GABAA receptor binding in rat brain. The duration of sleeping time was significantly increased by the pre-treatment with 7-NI (100 mg/kg) 30 min before pentobarbital (40 mg/kg) treatment in rats. However, the duration of pentobarbital-induced sleep was shortened by the prolonged infusion of 7-NI into cerebroventricle for 7 days. We have investigated the effect of NOS inhibitor on NMDA and GABAA receptor binding characteristics in discrete areas of brain regions by using autoradiographic techniques. The GABAA receptors were analyzed by quantitative autoradiography using [3H]muscimol and [3H]flunitrazepam binding, and NMDA receptor binding was analyzed by using [3H]MK-801 binding in rat brain slices. Rats were infused with 7-NI (500 pmol/10 microl/h, i.c.v.) for 7 days, through pre-implanted cannula by osmotic minipumps. The levels of [3H]muscimol were markedly elevated in cortex, caudate putamen, and thalamus while the levels of [3H]flunitrazepam binding were only elevated in cerebellum by NOS inhibitor. However, there was no change in the level of [3H]MK-801 binding except decreasing in the thalamus. These results show that the prolonged inhibition of NOS by 7-NI-infusion highly elevates [3H]muscimol binding in a region-specific manner and decreases the pentobarbital-induced sleep.

EVIDENCE OF SIGNIFICANT CONTRIBUTION FROM CYP3A5 TO HEPATIC DRUG METABOLISM

CYP3A4 and CYP3A5 exhibit significant overlap in substrate specificity but can differ in product regioselectivity and formation activity. To further explore this issue, we compared the kinetics of product formation for eight different substrates, using heterologously expressed CYP3A4 and CYP3A5 and phenotyped human liver microsomes. Both enzymes displayed allosteric behavior toward six of the substrates. When it occurred, the "maximal" intrinsic clearance was used for quantitative comparisons. Based on this parameter, CYP3A5 was more active than CYP3A4 in catalyzing total midazolam hydroxylation (3-fold) and lidocaine demethylation (1.4-fold). CYP3A5 exhibited comparable metabolic activity as CYP3A4 (90-110%) toward dextromethorphan N-demethylation and carbamazepine epoxidation. CYP3A5-catalyzed erythromycin N-demethylation, total flunitrazepam hydroxylation, testosterone 6beta-hydroxylation, and terfenadine alcohol formation occurred with an intrinsic clearance that was less than 65% that of CYP3A4. Using two sets of human liver microsomes with equivalent CYP3A4-specific content but markedly different CYP3A5 content (group 1, predominantly CYP3A4; group 2, CYP3A4 + CYP3A5), we assessed the contribution of CYP3A5 to product formation rates determined at low substrate concentrations (< or = Km). Mean product formation rates for group 2 microsomes were 1.4- to 2.2-fold higher than those of group 1 (p < 0.05 for 5 of 8 substrates). After adjusting for CYP3A4 activity (itraconazole hydroxylation), mean product formation rates for group 2 microsomes were still significantly higher than those of group 1 (p < 0.05 for 3 substrates). We suggest that, under conditions when CYP3A5 content represents a significant fraction of the total hepatic CYP3A pool, the contribution of CYP3A5 to the clearance of some drugs may be an important source of interindividual variability.

High affinity central benzodiazepine receptor ligands. Part 3: insights into the pharmacophore and pattern recognition study of intrinsic activities of pyrazolo[4,3-c]quinolin-3-ones

Novel 2-phenyl-2,5-dihydropyrazolo[4,3-c]quinolin-3-(3H)-ones (PQs) endowed with high affinity for central benzodiazepine receptor (BzR) were synthesized. In particular, 9-fluoro-2-(2-fluorophenyl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinolin-3-one (2(2)) showed binding affinity in the subnanomolar concentration range and proved to be in vitro a potent antagonist. This finding allowed the nature of the hydrogen bonding receptor site H(2) to be established, as located between the N-1 nitrogen of the PQ nucleus and the ortho position of the N-2-aryl group. [35S]tert-Butylbicyclophosphorothionate ([35S]TBPS) binding assays and electrophysiological measurements of the effects on GABA-evoked Cl(-) currents at recombinant human alpha(1)beta(2)gamma(2)(L) GABA(A) receptors, expressed in Xenopus laevis oocytes, were used to assess the intrinsic activities of a large series of PQs. With the aim of extracting discriminant information and distinguishing BzR ligands with different profiles of efficacy, 51 PQ derivatives, including full and partial agonists, antagonists, and inverse agonists, were analyzed in a multidimensional chemical descriptor space, defined by the lipophilicity parameter CLOG P and 3-D molecular WHIM descriptors, by means of principal component analysis, k-nearest neighbors (k-NN) method, and linear discriminant analysis (LDA). The classification methods were applied to subsets of pairs of efficacy classes, and lipophilicity and 3-D size descriptors were detected as the discriminant variables by a stepwise linear discriminant analysis. LDA proved to be superior to k-NN, especially in classifying PQ ligands (60-84% of success in prediction ability) into categories of efficacies which were contiguous and quite overlapped in the hyperspace of variables.

Inhibition by miltirone of up-regulation of GABAA receptor α4 subunit mRNA by ethanol withdrawal in hippocampal neurons

Miltirone, a tanshinone isolated from the root of Salvia miltiorrhiza, has been characterized as a low-affinity ligand for central benzodiazepine receptors. We have now shown that this compound bound with low affinity (micromolar range) to central benzodiazepine recognition sites but did not interact with peripheral benzodiazepine receptors. It failed to potentiate Cl(-) currents induced by gamma-aminobutyric acid (GABA) both in Xenopus oocytes expressing recombinant human GABA(A) receptors and in cultured rat hippocampal pyramidal cells, but it inhibited the ability of diazepam to potentiate the effect of GABA in these systems. Miltirone (1-10 microM) also partially inhibited the increase in the abundance of the mRNA for the alpha(4) subunit of the GABA(A) receptor induced by ethanol withdrawal in cultured hippocampal neurons. These results suggest that miltirone might ameliorate the symptoms associated with discontinuation of long-term administration of ethanol or of other positive modulators of the GABA(A) receptor.

NADPH-cytochrome P-450 reductase is involved in flunitrazepam reductive metabolism in Hep G2 and Hep 3B cells

Flunitrazepam (FNTZ), like other benzodiazepines, has a high affinity for the benzodiazepine receptor within the gama-aminobutyric acid (GABA) complex. These affinities correlate with the pharmacological and therapeutic potencies of the drug. FNTZ is a drug commonly abused by young adults. In humans, FNTZ is oxidized to the major metabolites N-demethylflunitrazepam (DM FNTZ) and 3-hydroxyflunitrazepam (3-OH FNTZ) and reduced to 7-aminoflunitrazepam (7A FNTZ). Human CYP2C19 and CYP3A4 are the principal P-450 cytochromes involved in DM FNTZ and 3-OH FNTZ formation. However, it is not clear which enzyme is responsible for the reduction of FNTZ to 7-aminoflunitrazepam (7A FNTZ). In this study, the involvement of NADPH-cytochrome P-450 reductase in the conversion of FNTZ to 7A FNTZ was investigated in two human hepatoma cell lines, human lymphoblast microsomes specifically expressing human NADPH-cytochrome P-450 reductase and purified recombinant human HADPH-cytochrome P-450 reductase. Significantly more FNTZ was converted to 7A FNTZ in Hep G2 than in Hep 3B cells, and this difference was associated with the catalytic activity and protein levels of NADPH-cytochrome P-450 reductase in these cells. In Hep G2 cells, conversion of FNTZ to 7A FNTZ was effectively inhibited by alpha-lipoic acid, an NADPH-cytochrome P-450 reductase inhibitor. In addition, formation of 7A FNTZ by the microsomal fraction of Hep G2 cells was specifically inhibited by antibody against NADPH-cytochrome P-450 reductase. Under hypoxia (N2 85%; CO2 5%; H2 10%), human lymphoblast microsomes specifically expressing human NADPH-cytochrome P-450 reductase and purified recombinant human NADPH-P-450 reductase catabolized FNTZ to 7A FNTZ in a concentration-dependent manner. These results suggest that NADPH-cytochrome P-450 reductase is involved in the reductive metabolism of FNTZ to 7A FNTZ under hypoxic conditions.

Potentiated modulation of pregnolone on GABAA receptors in behaviorally stressed borderline-hypertensive rats

The modulatory effects of behavioral stress on [(3)H]flunitrazepam, an agonist for the central-type benzodiazepine receptor binding to the GABA(A)-benzodiazepine receptor complex, in borderline hypertensive rats (BHR) were examined. In repeatedly immobilized (for 2 weeks, for 2 h/d) BHR, enhancement of [(3)H]flunitrazepam binding to the receptor was observed to be potentiated. The percent enhancement of [(3)H]flunitrazepam binding in BHR was higher than that in normotensive control Wistar-Kyoto rats. Pregnanolone, a neuroactive steroid that has been reported to be a putative endogenous modulator in the stress response, concentration dependently enhanced [(3)H]flunitrazepam binding to the receptor. Enhancement of [(3)H]flunitrazepam binding was observed to be potentiated by the same immobilized stress, and the EC(50) values of pregnanolone in BHR was significantly lower than those in controls and E(max) values were higher. From the above results, it can be concluded that neural modulation to behavioral stress, especially in GABAergic neurotransmission, is exaggerated in BHR. We propose strain-specific differences of stress reactivity as an important pathogenetic factor in psychosomatic disorders including stress-induced hypertension. This is supported by reports showing exaggerated cardiovascular and symathoadrenal responses to stress in BHR.

Modafinil prevents the MPTP-induced increase in GABAA receptor binding in the internal globus pallidus of MPTP-treated common marmosets

The psychostimulant drug modafinil induces a reversal of motor deficits in MPTP treated primates and prevents MPTP toxicity to substantia nigra but its mechanism of action is not clear. In common marmosets acutely treated with MPTP in the presence or absence of modafinil, we have studied changes in GABA(A) receptor binding in the basal ganglia. MPTP treatment had no effect on [(3)H]-flunitrazepam (FNZ) binding density in the striatum or external globus pallidus (GPe) but increased [(3)H]-FNZ binding density in the internal globus pallidus (GPi). Administration of modafinil (10-100 mg/kg) with MPTP did not alter [(3)H]-FNZ binding density in the striatum or GPe. Low doses of modafinil (10 and 30 mg/kg) had no effect on the increased [(3)H]-FNZ binding density in the GPi but high dose modafinil (100 mg/kg) significantly decreased [(3)H]-FNZ binding density in GPi. These findings suggest that modafinil can selectively alter GABA binding density in the GPi either by preventing MPTP-induced toxicity or through an action on striatal output pathway related to its antiparkinsonian activity and its ability to inhibit MPTP toxicity.

Automated solid-phase extraction and liquid chromatography-electrospray ionization-mass spectrometry for the determination of flunitrazepam and its metabolites in human urine and plasma samples

A sensitive and specific method using reversed-phase liquid chromatography coupled with electrospray ionization-mass spectrometry (LC-ESI-MS) has been developed for the quantitative determination of flunitrazepam (F) and its metabolites 7-aminoflunitrazepam (7-AF), N-desmethylflunitrazepam (N-DMF) and 3-hydroxyflunitrazepam (3-OHF) in biological fluids. After the addition of deuterium labelled standards of F,7-AF and N-DMF, the drugs were isolated from urine or plasma by automated solid-phase extraction, then chromatographed in an isocratic elution mode with a salt-free eluent. The quantification was performed using selected ion monitoring of protonated molecular ions (M+H(+)). Experiments were carried out to improve the extraction recovery (81-100%) and the sensitivity (limit of detection 0.025 ng/ml for F and 7-AF, 0.040 ng/ml for N-DMF and 0.200 ng/ml for 3-OHF). The method was applied to the determination of F and metabolites in drug addicts including withdrawal urine samples and in one date-rape plasma and urine sample.