CCK-8 modulates GABA-stimulated [3H]-flunitrazepam binding in vitro

In membranes from rat cerebral cortex, cholecystokinin-8 (CCK-8) did not modulate basal [(3)H]-flunitrazepam binding at either 4 degrees C or 37 degrees C. At a concentration of 10(-6) M, CCK(-8) significantly decreased gamma-amino-butyric acid (GABA)-stimulated (10(-6) M) [(3)H]-flunitrazepam binding at 37 degrees C. Scatchard analyses suggest that the decreased GABA-stimulated binding might be due to a decrease in the affinity of benzodiazepine receptors rather than to a decrease of number of binding sites. The observed modulation of benzodiazepine receptors by CCK-8 in vitro might explain some of the functional interactions between CCK and benzodiazepine systems.

[State of GABA-benzodiazepine receptor complex in diabetic neuropathy: effect of nicotinamide and nicotinoyl-GABA]

An increase in GABA uptake by isolated rat brain synaptic endings as well as a decrease of pharmacologically active GABA analogue muscimol specific binding have indicated a physiologically drastic failure in realization of GABA-mediated inhibitory effects in CNS induced by diabetic encephalopathy. In spite of the impairment of inhibitory function of GABAergic transmission in diabetes a crucial activation of benzodiazepine receptors was determined, as it is tested by the increase in specific binding of flunitrazepam by synaptic membranes. This increase may play an important role in endogenous control of neural activity associated with the factors undefined so far. Using the approach that GABA, and several synthetic GABA agonists, appear to increase the affinity of the benzodiazepine recognition sites for such ligands, presumably by some allosteric mechanism, the findings concerning the in vitro binding assay technique confirm at least some of the functional characteristics observed between GABA and benzodiazepine receptors in vivo under pathological conditions. Indeed, the absence of activating effect on the affinity of flunitrazepam specific binding in the presence of micromolar concentrations of exogenous GABA implicate diabetes-induced alterations in coupling GABA- and benzodiazepine receptors that might be linked to changes in conformantial state of this membrane-bound complex and could partially explain diabetes-induced impairments of GABAergic transmission evaluated in the present study. Our study suggests that nicotinamide and especially GABA play an important role in improving the functioning of brain GABA-benzodiazepine complex impaired in diabetes through specific ligand-mediated mechanism and can be useful in the management of diabetes-associated brain failures.

Benzodiazepine and kainate receptor binding sites in the RCS rat retina

BACKGROUND

The effect of age and photoreceptor degeneration on the kainate subtype of glutamate receptors and on the benzodiazepine-sensitive gamma-aminobutyric acid-A receptors (GABA(A)) in normal and RCS (Royal College of Surgeons) rats were investigated.

METHODS

[(3)H]Kainate and [(3)H]flunitrazepam were used as radioligands for kainate and GABA(A)/benzodiazepine()receptors, respectively, using the quantitative receptor autoradiography technique.

RESULTS

In both normal and RCS rat retina we observed that [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were several times higher in inner plexiform layer (IPL) than in outer plexiform layer (OPL) at all four ages studied (P17, P35, P60 and P180). Age-related changes in receptor binding were observed in normal rat retina: [(3)Eta]flunitrazepam binding showed a significant decrease of 25% between P17 and P60 in IPL,and [(3)Eta]kainate binding showed significant decreases between P17 and P35 in both synaptic layers (71% in IPL and 63% in OPL). Degeneration-related changes in benzodiazepine and kainate receptor binding were observed in RCS rat retina. In IPL, [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were higher than in normal retina at P35 (by 24% and 86%, respectively). In OPL, [(3)Eta]flunitrazepam binding was higher in RCS than in normal retina on P35 (74%) and also on P60 (62%).

CONCLUSIONS

The results indicate that postnatal changes occur in kainate and benzodiazepine receptor binding sites in OPL and IPL of the rat retina up to 6 months of age. The data also suggest that the receptor binding changes observed in the RCS retina could be a consequence of the primary photoreceptor degeneration.

The GABA(A) receptor complex in the chicken brain: immunocytochemical distribution of alpha 1- and gamma 2-subunits and autoradiographic distribution of BZ1 and BZ2 binding sites

Two antibodies, raised against the rat GABA(A) receptor alpha1- and gamma2-subunits, were used for an immunocytochemical study of the distribution of these proteins in the chicken brain. The immunoreactive bands obtained by Western blotting and the similar labelling distribution found in the rat and chicken brain support the suitability of these antibodies for the labelling of GABA(A) receptors in birds. We found abundant alpha1 and gamma2 immunoreactivity throughout the chicken brain, mainly in the paleostriata and lobus paraolfactorius, dorsal thalamus and some nuclei of the brainstem. The alpha1-subunit was more abundant in the telencephalon, thalamus and cerebellum, while the presence of the gamma2-subunit was stronger in the optic tectum and brainstem. We also report the autoradiographic distribution of the BZ1 and BZ2 benzodiazepine receptor subtypes in the chicken brain using [3H]flunitrazepam. Benzodiazepine binding was unevenly distributed throughout the chicken brain, and the anatomical distribution of the BZ1 and BZ2 subtypes was similar to that described in mammals. The highest binding values were found in the olfactory bulb, paleostriatum primitivum, optic tectum, nucleus mesencephalicus lateralis pars dorsalis and nucleus isthmi pars parvocellularis, the BZ2 subtype being predominant in the paleostriatum primitivum and optic tectum. A general agreement in the distribution of BZ1 and alpha1 immunoreactivity was observed in structures such as the olfactory bulb, paleostriata, lobus parolfactorius and dorsal thalamus, although some discrepancies were observed in areas such as the optic tectum or nucleus isthmi pars parvocellularis, with high BZ1 binding and low or no alpha1 immunolabelling.

Mild thyroid hormones deficiency modifies benzodiazepine and mu-opioid receptor binding in rats

The effects of a mild hypothyroidism condition on benzodiazepine (BDZ) and mu opioid receptor levels was investigated. Female Wistar rats were randomly divided into two groups: 1) hypothyroid rats (n=7), which received methimazole (60 mg/kg per day) in drinking water for four weeks, and 2) euthyroid rats (n=8), which drank only tap water. Animals were sacrificed and their brains were used for autoradiography experiments. When compared to the euthyroid group, the hypothyroid group presented reduced benzodiazepine receptor binding in medial amygdala (24%) and high mu-receptor levels in frontal (25%), sensorimotor (65%) and temporal (29%) cortices, basolateral amygdala (50%) and ventroposterior thalamic nucleus (49%). The present data suggest that alterations in BDZ and mu-receptor binding could be associated with the higher excitability observed in animals with triiodothyronine (T(3)) deficiency.

Acrylamide disturbs the subcellular distribution of GABAA receptor in brain neurons

Mechanisms underlying the action of acrylamide on neurons were studied by monitoring the expression of GABA(A) receptor (R) in cultured brain neurons derived from chicken embryos. In situ trypsinization of the neurons and 3H-flunitrazepam binding assay were employed to examine the subcellular distribution of GABA(A)R. A 3-h exposure of the cultured neurons to 10 mM of acrylamide raised reversibly the proportion of intracellular (trypsin-resistant) 3H-flunitrazepam binding sites by about 48% and decreased cell surface binding 24% from respective control values, without altering total cellular binding and the affinity of the ligand. Moreover, the acrylamide treatment induced more intense perikaryal immunostaining of GABA(A)R alpha subunit proteins than that in control neurons but did not change the total level of cellular alpha immunostain, in accordance with the binding data. In the cell bodies of acrylamide-treated neurons, the level of neurofilament-200 kDa proteins was similar to control, whereas the tubulin protein content was significantly lowered approximately 51% from control, as revealed by quantifying the immunostained cytoskeletal elements. In addition, electron microscopic observations found reductions in the numbers of microtubules and neurofilaments in the perikarya of acrylamide-treated neurons. As exhibited by the 3H-leucine and 3H-monosaccharide incorporation experiments, the exposure to acrylamide inhibited the rate of general protein synthesis in the culture by 21%, while the rate of glycosylation remained unaltered. Furthermore, in situ hybridization analysis showed that acrylamide did not modify the expression of GABA(A)R alpha subunit mRNAs. Taken together, these data suggest that acrylamide may downregulate the microtubular system and disintegrate neurofilaments, and thereby block the intracellular transport of GABA(A)R, resulting in the accumulation of intracellular receptors.

GABA(A) receptor alpha-1 subunit deletion alters receptor subtype assembly, pharmacological and behavioral responses to benzodiazepines and zolpidem

Potentiation of GABA(A) receptor activation through allosteric benzodiazepine (BZ) sites produces the anxiolytic, anticonvulsant and sedative/hypnotic effects of BZs. Using a mouse line lacking alpha1 subunit expression, we investigated the contribution of the alpha1 subunit to GABA(A) receptor pharmacology, function and related behaviors in response to BZ site agonists. Competitive [(3)H]flunitrazepam binding experiments using the Type I BZ site agonist, zolpidem, and the Type I and II BZ site non-specific agonist, diazepam, demonstrated the complete loss of Type I BZ binding sites in alpha1(-/-) mice and a compensatory increase in Type II BZ binding sites (41+/-6%, P<0.002). Chloride uptake analysis in alpha1(-/-) mice revealed an increase (108+/-10%, P<0.001) in the efficacy (E(max)) of flunitrazepam while the EC(50) of zolpidem was increased 495+/-26% (alpha1(+/+): 184+/-56 nM; alpha1(-/-): 1096+/-279 nM, P<0.01). An anxiolytic effect of diazepam was detected in both alpha1(+/+) and alpha1(-/-) mice as measured on the elevated plus maze; however, alpha1(-/-) mice exhibited a greater percentage of open arm entries and percentage of open arm time following 0.6 mg/kg diazepam. Furthermore, alpha1(-/-) mice were more sensitive to the motor impairing/sedative effects of diazepam (1-10 mg/kg) as measured by locomotor activity in the open field. Knockout mice were insensitive to the anticonvulsant effect of diazepam (1-15 mg/kg, P<0.001). The hypnotic effect of zolpidem (60 mg/kg) was reduced by 66% (P<0.001) in alpha1(-/-) mice as measured by loss of righting reflex while the effect of diazepam (33 mg/kg) was increased 57% in alpha1(-/-) mice (P<0.05). These studies demonstrate that compensatory adaptations in GABA(A) receptor subunit expression result in subunit substitution and assembly of functional receptors. Such adaptations reveal important relationships between subunit expression, receptor function and behavioral responses.

The bindings of [3H]muscimol and [3H]flunitrazapam are elevated in discrete brain regions of butorphanol-withdrawal rats

We have investigated the effects of continuous infusion of butorphanol on the modulation of GABA(A) receptor binding. Butorphanol was infused continuously into intracerebroventricle (ICV) at a constant rate of 26 nmol/microl/h for 3 days, and the withdrawal from opioid was rendered 7 h after the cessation of infusion. The GABA(A) receptor bindings in rat brain slices were analyzed by quantitative autoradiography using [3H]muscimol and [3H]flunitrazepam. In the rats withdrawn from butorphanol, the levels of [3H]muscimol binding were significantly elevated in cortex, thalamus, and part of the hippocampus. The levels of [3H]flunitrazepam binding were elevated in almost all of brain regions including cortex, caudate putamen, thalamus, hippocampus, brainstem, and cerebellum in the rats withdrawn from butorphanol. The levels of binding of either [3H]muscimol or [3H]flunitrazepam were not changed in the rats tolerant to butorphanol. However, the activity of GABAergic neuron was not found to have been modulated by butorphanol withdrawal, because the level of glutamic acid decarboxylase was not changed markedly either in rats that were tolerant to or withdrawn from butorphanol by Western blot and immunohistochemical data. These results suggest that the withdrawal from butorphanol infusion markedly elevates the binding of [3H]muscimol and [3H]flunitrazepam throughout the brain in a region-specific manner, and that the regulatory mechanisms in butorphanol tolerance and withdrawal may be different.

Effect of zaleplon on learning and memory in rats

Although structurally not a benzodiazepine, 3'-(3-cyanopyrazolo [1,5-a] pyrimidin-7-yl)- N-ethylacetamide (zaleplon) it acts via the benzodiazepine site of the GABA(A) receptor. In the present study, we investigated the effects of zaleplon on learning and memory in rats in comparison with triazolam and nitrazepam. Oral administration of zaleplon and the reference drugs dose-dependently lessened the step-through latency in the test session of a passive avoidance task and increased the latency for reaching the hidden platform in the Morris water maze task, indicating the amnesic effect of the test drugs. The amnesic liability ratio for zaleplon in the passive avoidance task to sleep inducing activity was 19.6, for triazolam and nitrazepam 4.2 and 5.9, respectively. The liability ratios derived from the Morris water maze task for zaleplon, triazolam and nitrazepam were 10.2, 0.9 and 0.6, respectively. The results may indicate that zaleplon has a preferential sedative effect and that the sedative dose does not interfere with learning and memory. In a binding study, zaleplon displaced bound [(3)H]flunitrazepam from membrane preparations from the rat hippocampus with an IC(50) of 4,454.5 nM. In contrast, triazolam and nitrazepam displaced the binding of [(3)H]flunitrazepam to the membrane with IC(50) values of 15.5 nM and 83.6 nM, respectively. The efficacy of zaleplon for the competitive inhibition of [(3)H]flunitrazepam binding to the membrane preparation from hippocampus was thus less than that of triazolam and nitrazepam. These results suggest that zaleplon is characterized by a reduced amnesic liability, which may be due to its low affinity for the benzodiazepine site of the GABA(A) receptor in the hippocampus.

Microemulsion electrokinetic chromatography versus capillary electrochromatography-UV-mass spectrometry for the analysis of flunitrazepam and its major metabolites

Benzodiazepines, namely flunitrazepam and its three major metabolites, were successfully separated by microemulsion electrokinetic chromatography. Separation was achieved using an untreated fused-silica capillary (48 cm (effective length 40 cm) x 50 num) at 25 kV; detection was performed by UV at 220 nm. The microemulsion system consisted of 70 mM octane, 800 mM 1-butanol, 80 mM sodium dodecyl sulfate (SDS) and 10 mM borate buffer, pH 9. Very high efficiencies (up to 400 000 plates) and resolution better than 3 were achieved. Since this technique is not compatible with mass spectrometry (MS) detection, a capillary electrochromatographic (CEC) method was developed to separate flunitrazepam and its metabolites. The effects of mobile phase composition and pH as well as voltage and temperature were systematically investigated. The optimized CEC method allowed the baseline separation of the investigated compounds. For the on-line coupling of CEC with electrospray ionization-mass spectrometry, the column was connected to a void fused-silica capillary using a Teflon connection. This configuration was found efficient and suitable for hyphenation of commercial CEC and MS instrumentation using commercially available CEC columns.

Stress-induced decrement in the plasticity of the physical properties of chick brain membranes

The molecular basis underlying the stress-induced increment in the density of central benzodiazepine receptor from chick forebrain, observed previously at 4 degrees C, was studied from a biophysical perspective. The thermal dependence of [3H]flunitrazepam binding to the central benzodiazepine receptor and the supramolecular organization were studied in forebrain membranes from chicks submitted to partial water immersion. The equilibrium dissociation constants increased with temperature in membrane from both control and stressed chicks. The heat capacity values in control samples (deltaC(p, CON)) were significantly less negative than deltaC(p STR). Changes in deltaH and deltaS between 4-37 degrees C were greater in stressed chicks compared to control; however, the binding was exothermic and driven by enthalpy in both conditions. At 4 degrees C, the receptor density (B(max)) was higher in stressed chicks compared to control. Such a difference was lost irreversibly upon temperature elevation, possibly due to the hysteresis between the heating and cooling behaviour of B(max, CON) and the constancy in B(max, STR). The fluorescence anisotropy of diphenylhexatriene was higher in control samples with respect to stressed chicks below 10 degrees C. A temperature-induced increment in protein intrinsic-fluorescence was observed only in control, and was quenched by acrylamide more easily at 4 degrees C than at 25 degrees C. A higher microviscosity at 4 degrees C in control favoured more external localizations of integral proteins; at higher temperatures, tryptophan residues moved to hydrophobic membrane-regions. Changes in the membrane-organization towards more fluid states favoured the accessibility of benzodiazepine to the central benzodiazepine receptor, expressed by the higher values of B(max) found in stressed samples at low temperatures with respect to control samples.

Simultaneous analysis of flunitrazepam and its major metabolites in human plasma by high performance liquid chromatography tandem mass spectrometry

A sensitive and specific high performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS-MS) method has been developed for the simultaneous determination of flunitrazepam and its major metabolites, 7-aminoflunitrazepam and N-desmethylflunitrazepam, in human plasma. After the addition of a deuterium labelled internal standard of flunitrazepam, plasma samples were extracted using Oasis(R) MCX solid phase extraction cartridges. The compounds were separated on a 5 microm Symmetry C18 (Waters) column (3.0 x 150 mm, i.d.) with a step gradient of acetonitrile-0.1% formic acid at a flow rate of 0.6 ml/min. The overall extraction efficiency was more than 89% for all three compounds. The limits of detection were 0.25 g/l for flunitrazepam, 0.5 microg/l for 7-aminoflunitrazepam, and 2.0 microg/l for N-desmethylflunitrazepam. Within-run accuracies for quality-control samples were between 92.5 and 101.3% of the target concentration, with coefficients of variation <8%. The proposed method enables the unambiguous identification and quantitation of flunitrazepam and its major metabolites in both clinical and forensic specimens.

Brain neurotransmitter receptor binding and nootropic studies on Indian Hypericum perforatum Linn

The high affinity binding sites for serotonin and benzodiazepine in the frontal cortex, for dopamine in the striatum and muscarinic cholinergic receptors in the hippocampus were investigated in the brains of Charles Foster rats treated for 3 days. Transfer latency on elevated plus maze (TL), passive and active avoidance behaviour (PA and AA) and electroconvulsive shock (ECS) induced amnesia were also studied. Pilot studies indicated that single dose administration of Indian Hypericum perforatum (IHp) had little or no acute behavioural effects and hence the extract of IHp was administered orally at two dose levels (100 and 200 mg/kg, p.o.) once daily for 3 consecutive days, while piracetam (500 mg/kg, i.p.), a clinically used nootropic agent, was administered acutely to rats as the standard nootropic agent. Control rats were treated with an equal volume of vehicle (0.3% carboxymethyl cellulose). The results indicate that IHp treatment caused a significant decrease in the binding of [3H] spiroperone (DA-D2 receptor) to the striatum and an increase in the binding of [3H] ketanserin (5-HT2A receptor) and [3H] flunitrazepam (BDZ receptor) to the frontal cortex in rats. Preliminary pharmacological studies with IHp extract indicate the presence of two major behavioural actions, namely, antidepressant and anxiolytic. The present findings tend to elucidate the mechanism of earlier observations, the downregulation of the dopamine D2 receptor being consonant with anxiolytic and the upregulation of 5-HT2A and BDZ receptors being consonant with antidepressant activity. Piracetam when given alone, shortened the TL on days 1, 2 and 9 day and also antagonized the amnesic effects of ECS on the TL significantly, whereas IHp antagonized the amnesia produced by ECS. IHp had no significant effect per se on the retention of the PA in rats but produced a significant reversal of ECS induced PA retention deficit. Piracetam showed a significant facilitatory effect per se on PA retention and also reversed the ECS induced impaired PA retention. In the AA test, piracetam facilitated the acquisition and retention of AA in rats but IHp had no effect per se. Both the doses of IHp and piracetam significantly attenuated the ECS induced impaired retention of AA. These results indicate a possible nootropic action of IHp in amnesic animals, which was comparable qualitatively to piracetam.

[Determination of 7-aminoflunitrazepam, the major metabolite of flunitrazepam in urine by high performance thin-layer chromatography]

A rapid and highly sensitive method, based on high performance thin-layer chromatography, is described for the qualitative and semiquantitative determination of 7-aminoflunitrazepam, the main metabolite of flunitrazepam in human urine. 7-Aminoflunitrazepam in specimen was extracted by solid phase extraction using GDX-403 porous polymer bead as sorbent and ethyl ether as eluant. Fluorescamine was used as a reagent to produce fluorescent product on the plate. The limit of detection was 5 micrograms/L and the limit of quantitation was 15 micrograms/L for 7-aminoflunitrazepam in urine. The method can be successfully used for measuring 7-aminoflunitrazepam in urine samples of the subjects excreted over a 48 h period after receiving 1 mg flunitrazepam orally. The method is applicable to drug examination for the cases of drug-facilitated robbery and rape.

Binding and neuropharmacological profile of zaleplon, a novel nonbenzodiazepine sedative/hypnotic

The binding properties of CL284,846 (zaleplon), a novel nonbenzodiazepine sedative/hypnotic, at benzodiazepine receptor subtypes were evaluated. Zaleplon was 14.3 times more potent at inhibiting [3H]flunitrazepam binding to membrane preparations of the cerebellum than to membrane preparations of the spinal cord. The gamma-aminobutyric acid (GABA) ratio of zaleplon was 2.07. Zaleplon produced significant increases in muscimol binding similar to those of diazepam, and it was antagonized by flumazenil. Furthermore, zaleplon showed little affinity for other receptors. Spectral analysis of the electroencephalogram (EEG) of rabbits showed that zaleplon and 3-methyl-6-[3-(trifluoromethyl) phenyl]-1,2,4,-triazolo [4,3-beta] pyridazine (CL218,872), an omega(1) receptor-selective compound (1 mg/kg, i.v., respectively), produced large increases in energy of the delta frequency band without affecting the energy of the alpha and beta frequency bands. In contrast, intravenous administration of triazolam and zopiclone increased the energy of the beta frequency band at doses of 0.1 and 2 mg/kg, respectively. In addition, the zaleplon-induced increase in the energy of the delta frequency band was antagonized by pretreatment with flumazenil (1 mg/kg, i.v.), which did not affect the spontaneous EEG alone. The present results clearly demonstrate that zaleplon is a selective full agonist of the omega(1) receptor subtype, and thus, zaleplon may induce responses closely resembling the physiological pattern of slow wave sleep.

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.

Mercury interaction with the GABA(A) receptor modulates the benzodiazepine binding site in primary cultures of mouse cerebellar granule cells

Mercury compounds are neurotoxic compounds with a great specificity for cerebellar granule cells. The interaction of mercury compounds with proteins in the central nervous system may underlie some of their effects on neurotransmission. In this work we study the interaction of mercuric chloride (HgCl2) and methylmercury (MeHg) with the GABA(A) receptor in primary cultures of cerebellar granule cells. Both compounds increased, dose dependently, the binding of [3H]flunitrazepam to the benzodiazepine recognition site. EC50 values for this effect were 3.56 and 15.24 microM for HgCl2 and MeHg, respectively, after 30 min exposure of intact cultured cerebellar granule cells. The increase of [3H]flunitrazepam binding by mercury compounds was completely inhibited by the GABA(A) receptor antagonists bicuculline and picrotoxinin, and by the organochlorine pesticide alpha-endosulfan. It was also partially inhibited by the anion transporter blocker DIDS, however this effect could be due to a possible chelation of mercury by DIDS. Intracellular events, like intracellular calcium, kinase activation/inactivation or antioxidant conditions did not affect [3H]flunitrazepam binding or its increase induced by mercury compounds. The sulfhydryl alkylating agent N-ethylmaleimide mimicked the effect of mercury compounds on [3H]flunitrazepam binding suggesting a common mechanism. We conclude that mercury compounds interact with the GABA(A) receptor by the way of alkylation of SH groups of cysteinyl residues found in GABA(A) receptor subunit sequences.

Characterization of [3H]flunitrazepam binding to melanin

In both clinical and forensic toxicology, the analysis of hair for drugs is an important tool to determine drug use in the past or to verify abstinence from illegal drugs during extended periods. Melanin is proposed as one of the factors that influences drug incorporation to hair and we have characterized the binding of the drug flunitrazepam to melanin in vitro. The drug was 3H labeled and melanin granules from cuttlefish, Sepia officinalis, were used according to the suggested standard for melanin studies. We observed a rapid Langmuir-like binding followed by a slower diffusion-limited binding that may be interpreted as an initial surface binding followed by deeper bulk binding. From three concentrations of melanin, with a 60-min incubation time, a mean saturation value of 180 +/- 20 pmol/mg was calculated. The binding of a group of benzodiazepines and tranquilizers was compared to the binding of [3H]flunitrazepam by means of displacement experiments. These drugs showed binding characteristics similar to [3H]flunitrazepam except phenobarbital, which had a lower affinity to melanin. The method presented in this study allowed measurements with low melanin and drug concentrations and it has the strength of directly measuring the amount of drug bound to melanin, in contrast to previous indirect methods.

Serum and urine concentrations of flunitrazepam and metabolites, after a single oral dose, by immunoassay and GC-MS

A clinical study was conducted to assess the ability of commercially available immunoassays to detect flunitrazepam (FNP) in plasma and urine samples and to compare the results with those obtained by gas chromatography-mass spectrometry (GC-MS). The clinical study consisted of four individuals (two male and two female) who had taken a single 2-mg dose of FNP. Serum was collected over a 48-h period and urine was collected over a 72-h period. The serum and urine samples were analyzed by the COBAS INTEGRA Serum Benzodiazepines assay (SBENZ), the TDx serum and urine Benzodiazepines assay, and GC-MS. The GC-MS procedure was developed for analysis of FNP and metabolites in plasma and urine using an acid hydrolysis step resulting in the formation of specific benzophenones corresponding to FNP and its metabolites. The relative sensitivities of the assays for the detection of FNP and metabolites in serum and urine were GC-MS > SBENZ > TDx. The immunoassay results for serum samples showed peak concentrations of FNP metabolites at 8 h after FNP ingestion for three individuals and at about 1 h for the fourth individual. The GC-MS, SBENZ, and TDx urine immunoassays detected drug above the stated limit of detection (LOD) in 44, 41, and 35 serial FNP urine samples, respectively. FNP metabolites were detected in urine samples with all three assays for up to 72 h after a 2-mg dose. The improved detection rate with the SBENZ assay as compared to the TDx assay is likely explained by its higher cross-reactivity with the major metabolite, 7-amino-flunitrazepam (7-amino-FNP), and its lower LOD.

Pressure-sensitive and -insensitive coupling in gamma-aminobutyric acid(A) receptors

RATIONALE

Previous behavioral and biochemical studies suggest that allosteric coupling processes initiated by benzodiazepines, barbiturates and neuroactive steroids can be sub-categorized on the basis of their sensitivities to antagonism by increased atmospheric pressure. However, biochemical evidence supporting this hypothesis was limited to single concentration studies in long sleep (LS) mice.

OBJECTIVE

The present paper addresses these issues by extending biochemical investigation of pressure effects on allosteric modulators across a range of concentrations that allosterically enhance gamma-aminobutyric acid (GABA)A receptor function and alter behavior using two mouse genotypes. In addition, the effects of pressure on ligand binding were explored to further investigate the mechanism of pressure antagonism of allosteric modulation.

METHODS

The effects of 12 times normal atmospheric pressure (ATA) of helium-oxygen gas (heliox) on allosteric modulation of GABA(A) receptor function and [3H]flunitrazepam binding was tested in LS and C57BL mouse brain membranes (microsacs) using chloride flux and high-affinity binding assays.

RESULTS

In both genotypes, exposure to 12 ATA heliox antagonized the allosteric enhancement of GABA(A) receptor function by flunitrazepam (0.1-10 microM) and pentobarbital (0.1-50 microM) but did not affect allosteric modulation by 3alpha-hydroxy-5beta-pregnan-20-one (0.1-1 microM). Pressure did not affect benzodiazepine receptor affinity (Kd) or the number of benzodiazepine receptors (Bmax).

THE RESULTS

(1) confirm that there are differences in sensitivity to pressure antagonism of allosteric coupling among GABA(A) allosteric modulators; (2) demonstrate that these differences are not concentration or genotype dependent; (3) add evidence that pressure antagonizes allosteric modulation by uncoupling the receptor and (4) support the hypothesis that allosteric modulation of receptor function can be sub-categorized on the basis of sensitivity to pressure antagonism.

Distinct signal transduction pathways for GABA-induced GABA(A) receptor down-regulation and uncoupling in neuronal culture: a role for voltage-gated calcium channels

Changes in GABA receptor (GABA(A)R) gene expression are detected in animal models of epilepsy, anxiety and in post-mortem schizophrenic brain, suggesting a role for GABA(A)R regulation in neurological disorders. Persistent (48 h) exposure of brain neurons in culture to GABA results in down-regulation of GABA(A)R number and uncoupling of GABA and benzodiazepine (BZD) binding sites. Given the central role of GABA(A)Rs in fast inhibitory synaptic transmission, GABA(A)R down-regulation and uncoupling are potentially important mechanisms of regulating neuronal excitability, yet the molecular mechanisms remain unknown. In this report we show that treatment of brain neurons in culture with tetrodotoxin, glutamate receptor antagonists, or depolarization with 25 mM K(+) fails to alter GABA(A)R number or coupling. Changes in neuronal activity or membrane potential are therefore not sufficient to induce either GABA(A)R down-regulation or uncoupling. Nifedipine, a voltage-gated Ca(2+) channel (VGCC) blocker, inhibits both GABA-induced increases in [Ca(2+)](i) and GABA(A)R down-regulation, suggesting that VGCC activation is required for GABA(A)R down-regulation. Depolarization with 25 mM K(+) produces a sustained increase in intracellular [Ca(2+)] without causing GABA(A)R down-regulation, suggesting that activation of VGCCs is not sufficient to produce GABA(A)R down-regulation. In contrast to GABA(A)R down-regulation, nifedipine and 25 mM K(+) fail to inhibit GABA-induced uncoupling, demonstrating that GABA-induced GABA(A)R down-regulation and uncoupling are mediated by independent molecular events. Therefore, GABA(A)R activation initiates at least two distinct signal transduction pathways, one of which involves elevation of intracellular [Ca(2+)] through VGCCs.

Honokiol and magnolol selectively interact with GABAA receptor subtypes in vitro

Honokiol and magnolol have been identified as modulators of the GABAA receptors in vitro. Our previous study suggested a possible selectivity of honokiol and magnolol on GABAA receptor subtypes. This possibility was examined in the current study by 3H-muscimol and 3H-flunitrazepam binding assays on various rat brain membrane preparations and human recombinant GABA(A) receptor subunit combinations expressed by the Sf-9/baculovirus system. Generally, honokiol and magnolol have a similar enhancing effect on (3)H-muscimol binding to various membrane preparations in nonsaturation binding assays. Honokiol and magnolol preferentially increased (3)H-muscimol binding to hippocampus compared to cortex and cerebellum (with a maximum enhancement of 400% of control). As for subunit combinations, honokiol and magnolol have a more potent enhancing effect on alpha2 subunit containing combinations (with a maximum enhancement of 400-450% of control). This action was independent of the gamma subunit. In saturation binding assays, magnolol affected either the number of binding sites (ca. 4-fold on alpha2 containing combinations) or the binding affinity (on alpha1 containing combinations) of (3)H-muscimol binding to various GABAA receptor subunit combinations. In contrast, honokiol increased only binding sites on alpha2beta3gamma2s and alpha2beta3 combinations, but both the number of binding sites and the binding affinity on alpha1beta2gamma2S and alpha(1)beta2 combinations. These results indicate that honokiol and magnolol have some selectivity on different GABAA receptor subtypes. The property of interacting with GABAA receptors and their selectivity could be responsible for the reported in vivo effects of these two compounds.

In ovo chronic neurosteroid treatment affects the function and allosteric interactions of GABAA receptor modulatory sites

We investigated the effects of in ovo chronic administration of the endogenous neurosteroid epipregnanolone (5beta-pregnan-3beta-ol-20-one) on the GABA(A) receptor complex present in chick optic lobe synaptic membranes. Chronic epipregnanolone treatment failed to exert any effect on the chick optic lobe total protein content and wet weight at the different doses tested. [3H]Flunitrazepam control binding remained unaltered after neurosteroid exposure, however, the positive allosteric modulation of this ligand by 4 microM allopregnanolone was reduced in a dose-dependent manner by neurosteroid treatment. Embryo exposure to 30 microM epipregnanolone decreased allopregnanolone EC(50) and E(max) values. Analyses of saturation binding isotherms disclosed that such administration had no effect on K(d) and B(max) values for [3H]flunitrazepam and [3H]GABA binding. [3H]GABA binding modulation disclosed an increase in allopregnanolone EC(50) value with a decrease in its E(max) value. Diazepam EC(50) and E(max) values were enhanced, while low affinity sodium pentobarbital EC(50) value was reduced by epipregnanolone treatment. The investigation of the GABA(A) receptor function revealed that administration of this neurosteroid reduces the efficacy of GABA to induce 36Cl(-) influx into microsacs prepared from chick optic lobe. These results indicate that endogenous neurosteroid epipregnanolone chronically administered in ovo produces homologous uncoupling between steroid modulatory sites, and those corresponding to benzodiazepine and GABA receptors. Thus epipregnanolone is able to induce heterologous changes in the allosteric linkage between benzodiazepine and barbiturate modulatory sites, and the GABA receptor site. Taken jointly with results on epipregnanolone enhancing effects on [3H]flunitrazepam and [3H]GABA binding, in the context of its endogenous synthesis, our present findings support this neurosteroid as the endogenous modulator of GABA(A) receptor sites and function during chick optic lobe development.

[3H]Flunitrazepam binding to recombinant alpha1beta2gamma2S GABAA receptors stably expressed in HEK 293 cells

The interaction of selected compounds with the binding of the benzodiazepine [3H]flunitrazepam to membranes isolated from human embryonic kidney (HEK) 293 cells, stably transfected with the aI( 2 2S subtype of GABAA receptors, was studied. This subtype of GABAA receptors is the most common type of GABAA receptor found in the brain, and benzodiazepines are drugs known to enhance the effects of the inhibitory neurotransmitter gamma-amino butyric acid (GABA) by binding to the benzodiazepine binding sites which are part of the GABAA receptor complex. Scatchard analysis of binding data revealed the existence of a single type of binding site for [3H]flunitrazepam. GABA and thiopental enhanced, while the antagonist of central benzodiazepine binding sites--flumazenil, benzodiazepines such as clonazepam, flunitrazepam and diazepam, and the triazolopyridazine CI 218,872--displaced with nanomolar potency the binding of [3H]flunitrazepam. A partial displacement was obtained with the antagonist of the peripheral benzodiazepine binding sites--PK 11195--and with the neurosteroid dehydroepiandrosterone sulfate. The potency of drugs to enhance or inhibit [3H]flunitrazepam binding mainly corresponded to that observed for the modulation of the binding of [3H]flunitrazepam to the native type 1 benzodiazepine binding sites. This, as well as a high density of expressed binding sites, makes the cell line under study a very reliable and economical model for the testing of effects of different compounds at the GABAA receptor.

High-performance liquid chromatography determination of flunitrazepam and its metabolites in plasma by use of column-switching technique: comparison of two extraction columns

A study, using on-line column-switching high-performance liquid chromatography, evaluated two different extraction columns for the determination of flunitrazepam and its major metabolites: 7-aminoflunitrazepam, 7-acetamidoflunitrazepam and desmethylflunitrazepam. The procedure was based on the enrichment of benzodiazepines on the extraction column, followed by transfer of the compounds to the analytical column. The two extraction columns were compared: the first column was a BioTrap 500 MS (hydrophobic polymer), 20x4 mm I.D., and the second was a LiChrospher RP-18 ADS, 25x4 mm I.D. The analytical column used was a LiChrospher select B RP-8, 125x3 mm I.D. with 5 microm particle size. The extraction conditions for the two pre-concentration columns, such as extraction temperature, buffer concentration, buffer pH, acetonitrile percentage and flow-rate, were studied for the extraction from plasma of flunitrazepam and its metabolites mentioned above. The mobile phase of the analytical column was isocratic and composed of acetonitrile-20 mM phosphate buffer at pH 2.1 (35:65, v/v) and at a flow-rate of 0.3 ml/min.