Two forms of the GABAA receptor distinguished by anion-exchange chromatography

The GABAA receptor complex was solubilized from rat brain membranes in Triton X-100, enriched by 1012-S affinity chromatography, and subjected to DEAE anion-exchange chromatography. Two forms were distinguished by their differential elution during this HPLC with a KCl gradient. They displayed similar [3H]muscimol- and [3H]flunitrazepam-binding characteristics, as well as [3H]flunitrazepam-binding inhibition by CL 218872. Rechromatography of these distinct ionic forms indicated that they were not in dynamic equilibrium during chromatography. Resolution of these two pharmacologically similar populations of GABAA receptor by anion-exchange HPLC suggests that they differ in charge densities, a condition which may reflect differing glycosylation or phosphorylation states of the complex.

Central- and peripheral-type benzodiazepine receptors: similar regulation by stress and GABA receptor agonists

Central- and peripheral-type benzodiazepine (BD) receptors were labelled either by 3H-flunitrazepam or 3H-Ro 5-4864 in vitro after stress and in vivo administration of GABAA and GABAB agonists. A significant increase in the density of cerebral cortex and kidney BD binding sites was observed in rats after forced swimming stress. Similar changes in both type of BD receptors were also followed when naive (stressed) and handling-habituated (unstressed) rats were used. Stress in both models was unable to change the affinity of BD receptors in cerebral cortex, but significantly lowered it in kidneys. Acute treatment of rats with muscimol (1.5 mg/kg) or (-)baclofen (5 mg/kg) resulted in marked increase in the affinity of BD binding not only in cerebral cortex but also in kidneys. After (-)baclofen treatment the number of BD binding sites was lowered in the structures studied. In a separate study mice selected according to their behavioral response to (-)baclofen (1 mg/kg) were studied. Two weeks after the selection it appeared that baclofen responders were behaviorally more "anxious" than baclofen nonresponders. The number of BD binding sites was reduced in cerebral cortex, cerebellum, heart and kidneys in baclofen responders as compared to baclofen nonresponders. In several cases the changes in peripheral BD binding sites were even more pronounced than those in central ones. The data presented here evidence that peripheral- and central-type BD receptors are regulated similarly by GABA and some models of stress. The physiological mechanisms involved in similar regulation of central- and peripheral-type BD receptors are yet unknown.

Type I and type II gamma-aminobutyric acid/benzodiazepine receptors: purification and analysis of novel receptor complex from neonatal cortex

The gamma-aminobutyric acid (GABA) type A receptor was purified several thousandfold by affinity chromatography from rat cerebellum, adult cortex, and neonatal cortex. Competition for the benzodiazepine binding site by CL 218872 indicated that cerebellar receptors were predominantly type I, adult cortical receptors were a mixture of subtypes, and neonatal cortex was enriched in type II receptor. The receptor purified from neonatal cortex contained predominantly a 54-kilodalton (kDa), beta-subunit-like protein, whereas receptors from cerebellum and adult cortex contained nearly equal amounts of a 50-kDa, alpha-subunit-like protein and a 54-kDa polypeptide. Peptide maps of trypsin-digested 54-kDa subunits from cerebellum, adult cortex, and neonatal cortex exhibited very similar profiles, a result indicating considerable homology between these proteins in the receptor subtypes. A 59-kDa subunit protein was detected in the receptor complex purified from neonatal cortex. Like the 50-kDa, alpha-subunit of the type I receptor, this protein was photolabeled with [3H]flunitrazepam. The photolabeled peptide fragments, produced by trypsin digestion of these alpha 50- and alpha 59-subunits, exhibited the same retention times on reverse-phase HPLC. A less highly purified GABAA receptor preparation from adult rat spinal cord possessed characteristics that were very similar to those of the receptors purified from neonatal cortex.

Differential effects of flunitrazepam on human sleep in combination with flumazenil

The experiments reported here were designed to characterize in detail the spectrum of activity of flunitrazepam in human sleep. The direct and residual effects of flunitrazepam, as well as the antagonism by flumazenil, an antagonist of benzodiazepine receptors, were studied in 28 normal subjects recorded in the sleep laboratory. The five categories of variables--sleep-wake balance, sleep organization, orthodox sleep, phasic events in sleep, and sleep waveforms--were all modified by flunitrazepam. Some of these modifications were observed only on the drug night and were antagonized by flumazenil, whereas others persisted in the placebo postdrug night and were not antagonized by flumazenil. A few variables showed changes intermediate between these two types of reactivity. The results do not fit well with the multiple benzodiazepine receptors theory, but instead support the concept of spare receptors. Along these lines, the study of the reactivity of sleep components to ligands of benzodiazepine receptors can contribute to the better understanding of the neuronal systems involved in their control.

Effects of picrotoxin treatment on GABAA receptor supramolecular complexes in rat brain

The effects of acute and chronic administration of a subconvulsive dose of picrotoxin on t-[35S]butylbicyclophosphorothionate ([3S]TBPS), [3H]muscimol, and [3H]flunitrazepam binding characteristics in various regions and on the convulsant potency of picrotoxin in Sprague-Dawley rats were examined. Acute administration of a subconvulsive dose of picrotoxin (3 mg/kg, i.p.) significantly increased [35S]TBPS and [3H]muscimol binding in cerebellum (CB) with no change in frontal cortex (FC). In rats treated chronically with picrotoxin (3 mg/kg, i.p., daily for 10 days), the Bmax of [35S]TBPS binding site was significantly decreased in the FC, striatum (ST), and CB with no change in KD values. Neither [3H]muscimol binding in the FC and CB nor [3H]flunitrazepam binding in the FC was affected in these rats. In addition, the potency of pentobarbital to inhibit [35S]TBPS binding in vitro was not altered following acute or chronic treatment of picrotoxin. Chronic administration of picrotoxin did not affect convulsive ED50 or LD50 of picrotoxin; however, it delayed the onset of convulsions and increased the time to death. These results suggest that treatment with picrotoxin at a subconvulsive dose for 10 days causes down-regulation of [35S]TBPS binding sites and that this down-regulation might be related, at least in part, to the decreased extent of convulsant potency of picrotoxin. In addition, the results indicate possible interaction between convulsant binding sites and GABAA receptor sites in the CB following picrotoxin treatment.

Distribution and pharmacological properties of the GABAA/benzodiazepine/chloride ionophore receptor complex in the brain of the fish Anguilla anguilla

In the present study, we characterized the distribution and the pharmacological properties of the different components of the GABAA receptor complex in the brain of the eel (Anguilla anguilla). Benzodiazepine recognition sites labeled "in vitro" with [3H]flunitrazepam ([3H]FNT) were present in highest concentration in the optic lobe and in lowest concentration in the medulla oblongata and spinal cord. A similar distribution was observed in the density of gamma-[3H]aminobutyric acid ([3H]GABA) binding sites. GABA increased the binding of [3H]FNT in a concentration-dependent manner, with a maximal enhancement of 45% above the control value, and, vice versa, diazepam stimulated the binding of [3H]GABA to eel brain membrane preparations. The density of benzodiazepine and GABA recognition sites and their reciprocal regulation were similar to those observed in the rat brain. In contrast, the binding of the specific ligand for the Cl- ionophore, t-[35S]butylbicyclophosphorothionate ([35S]TBPS), to eel brain membranes was lower than that found in the rat brain. In addition, [35S]TBPS binding in eel brain was less sensitive to the inhibitory effects of GABA and muscimol and much more sensitive to the stimulatory effect of bicuculline, when compared with [35S]TBPS binding in the rat brain. Moreover, the uptake of 36Cl- into eel brain membrane vesicles was only marginally stimulated by concentrations of GABA or muscimol that significantly enhanced the 36Cl- uptake into rat brain membrane vesicles. Finally, intravenous administration of the beta-carboline inverse agonist 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylic acid methyl ester (20 mg/kg) and of the chloride channel blocker pentylenetetrazole (80 mg/kg) produced convulsions in eels that were antagonized by diazepam at doses five to 20 times higher than those required to produce similar effects in rats. The results may indicate a different functional activity of the GABA-coupled chloride ionophore in the fish brain as compared with the mammalian brain.

Neuroreceptor changes in the putamen of alcohol abusers

The purpose of this study was to determine if alcohol abuse affects muscarinic cholinergic and benzodiazepine receptors in histologically normal brains obtained at autopsy in a general hospital population. Patients were excluded from this study if they had clinical brain (including Wernicke's) disease, died in coma, had liver disease, significant brain atrophy, or dementia severe enough to require institutionalization. We found that muscarinic cholinergic synaptic receptor density determined with [3H]quinuclidinyl benzilate was decreased by 40% in homogenates of the putamen of 27 alcohol abusers compared with 37 matched nonalcoholic controls. In contrast, receptor densities and affinities of benzodiazepine receptors determined with [3H]flunitrazepam were not significantly different in the two groups. Age and death-autopsy time interval had no significant effects on either wet tissue protein concentrations, yields of protein after centrifugation, or receptor binding. The contributions of age and time interval were each less than 3% of the total variance of protein concentrations and receptor binding. When patients who had received cholinergic, anticholinergic, or benzodiazepine medications before death were excluded or included we observed no significant effects on the final results. Pneumonia, known to be associated with acute hypoxia, and chronic obstructive pulmonary disease, known to be associated with chronic hypoxia, were approximately equally distributed between the two groups and had no significant effects on the results reported here. It is significant that the loss of muscarinic and the sparing of benzodiazepine receptors in the putamen occurs in histologically normal brains in the absence of significant atrophy and gross dementia. It implies that these changes are early in the development of alcoholic encephalopathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional reconstitution of the bovine brain GABAA receptor from solubilized components

The GABAA/benzodiazepine receptor has been solubilized from membrane preparations of bovine cerebral cortex and has been reconstituted, in a functionally active form, into phospholipid vesicles. In preliminary experiments, the receptor was labeled with the photoactive benzodiazepine [3H]flunitrazepam prior to solubilization. A peptide of apparent molecular weight 53,500 was specifically labeled by this method, and this was used as a marker for the receptor during the reconstitution procedures. The labeled protein was solubilized with approximately 40% efficiency by 1% beta-octyl glucoside. Reconstitution was achieved by mixing the solubilized proteins with a 4:1 mixture of soybean asolectin and bovine brain phospholipids, followed by chromatography on Sephadex G-50-80 to remove detergent. The incorporation of the GABAA receptor into membrane vesicles has been verified by sucrose gradient centrifugation in which the [3H]-flunitrazepam-labeled peptide comigrated with [14C]phosphatidylcholine used as a lipid marker. Vesicles prepared without labeled markers retained the ability to bind both [3H]flunitrazepam and the GABA analogue [3H]muscimol. Furthermore, the binding parameters were very similar to those measured using native membrane preparations. A novel fluorescence technique has been used to measure chloride transport mediated by the GABAA receptor in reconstituted vesicles. Chloride influx was rapidly stimulated in the presence of micromolar concentrations of muscimol and was blocked by preincubation of the membranes with muscimol (desensitization). Flux was also blocked by pretreatment with the competitive GABAA receptor blocker bicuculline or with the noncompetitive GABAA receptor antagonist picrotoxin.

[Solubilization of the central benzodiazepine receptor and study of its interaction with nicotinamide]

It was shown that nicotinamide and NAD inhibit the specific binding of [3H]flunitrazepam to benzdiazepine receptors without causing a direct influence of gamma-aminobutyric acid (GABA) receptors. The GABA-benzdiazepine complex was separated by solubilization with 0.5% lubrol PX. The solubilized preparations contain the binding sites for [3H]flunitrazepam alone (Kd = 5.9 nm). The Kd value for the membrane-bound benzdiazepine receptor is 2.9 nM. NAD inhibited the specific binding of [3H]flunitrazepam to the solubilized membrane preparation when used at concentrations by several orders of magnitude lower than that of nicotinamide. Using gel filtration on Sepharose 6B-CL, the molecular mass of the soluble benzdiazepine receptor protein was determined.

n-[3H]butyl-beta-carboline-3-carboxylate, a putative endogenous ligand, binds preferentially to subtype 1 of central benzodiazepine receptors

Synthetic n-butyl beta-carboline-3-carboxylate, an endogenous central benzodiazepine receptor inhibitor found in brain, was tritium-labeled from the butenyl ester. Binding of this [3H]beta-carboline was concentrated particularly in the synaptosomal membrane fraction of the cerebral cortex; this fraction showed a single type of high-affinity site (KD = 2.7 +/- 0.1 nM) with a Bmax of 1.16 +/- 0.08 pmol/mg of protein. The number of sites labeled was about half of that obtained with [3H]flunitrazepam binding (Bmax = 2.36 +/- 0.06 pmol/mg of protein). On the other hand, in the cerebellum, both ligands bound to practically the same number of sites. When [3H]flunitrazepam binding was done in the presence of 10(-11)-10(-5) M butyl beta-carboline, the differences between the two brain regions were more apparent. In cerebellar membranes the data fitted a straight line in the Eadie-Hofstee plot; this finding and a Hill number near unity suggest a single type of binding site. In the cortical membranes the data of binding fitted a concave curve, and the Hill number was 0.6. These are characteristics of two types of binding sites with different affinities (KD1 = 0.6-1.5 nM and KD2 = 12-18 nM). The differentiation of a high- and low-affinity site in the cerebral cortex was corroborated by experiments in which [3H]butyl beta-carboline binding was displaced by the triazolopyridazine CL 218,872. These results demonstrate that in the cerebral cortex there are two subtypes of sites (1 and 2) of central benzodiazepine receptors and that CL 218,872 binds preferentially to subtype 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Tricyclic heteroaromatic systems: synthesis, [3H]flunitrazepam brain membrane binding inhibition, and structure-activity relationships of 2,3-dihydro-2-aryl-4-R-[1]benzopyrano[4,3-c]pyrazole-3-ones

We report the synthesis and binding activity to the central benzodiazepine receptors of some 2,3-dihydro-2-aryl-4-R-[1]benzopyrano[4,3-c]pyrazole-3-ones, which are isosteres of the CGS series. Although the compounds of the CGS series are potent ligands of the benzodiazepine receptors, none of the isosteres tested showed any significant inhibiting potency. This may be due to the change in electronic properties brought about by the replacement of the NH of the CGS series with an oxygen atom.

Photolabeled tryptic degradation products of benzodiazepine-binding proteins are glycopeptides. Implications for localization of cleavage sites

Crude synaptic membranes of avian and mammalian brain tissue were photolabeled with the benzodiazepine-receptor ligand [3H]flunitrazepam and subsequently treated extensively with trypsin followed by incubation with endoglycosidase F. SDS-polyacrylamide gel electrophoresis and fluorography revealed that the final tryptic degradation product of 25 kDa in both pigeon and calf brain is deglycosylated in two steps. These results were confirmed by immunoblots of similarly pretreated membranes of pig brain using the alpha-subunit-specific monoclonal antibody bd-24. Benzodiazepine-receptor binding and its enhancement by GABA are largely retained after trypsinization. Based on the proposed transmembrane topology for the alpha-subunits of the GABA/benzodiazepine receptor, we suggest that the large N-terminal domain of benzodiazepine-binding proteins is protected against tryptic cleavage.

Benzodiazepines and the mammalian retina. I. Autoradiographic localisation of receptor sites and the lack of effect on the electroretinogram

The majority of specific benzodiazepine binding sites were found to be restricted to the innerplexiform layer of the rat retina, although there were minor amounts of binding in the inner nuclear and ganglion cell layers. Relatively high levels of non-specific benzodiazepine binding sites were, on the other hand, found in the pigment epithelium and ciliary body, as well as in the corneal epithelium. The specific binding was enhanced by the GABA-A agonist, muscimol. In both rats and cats, neither acute nor chronic administration of benzodiazepines or their antagonists altered the retinal functions, as determined by the electroretinogram. These results suggest that retinal benzodiazepine receptors do not influence visually induced preganglionic retinal activity.

A novel class of "GABAergic" agents: 1-aryl-3-(aminoalkylidene)oxindoles

Antagonism of mercaptopropionic acid (MPA) induced convulsions, reflecting a GABAergic mechanism, was observed in a series of 1-aryl-3-(aminoalkylidene)oxindoles. Optimal MPA antagonism was associated with 3-halo, 3-alkyl, and/or 4-alkoxy substituents in the pendant aryl ring and with (dimethylamino)methylene, 1-(dimethylamino)-ethylidene and N-methyl-2-pyrrolidinylidene side chains. The precise mechanism of action of these agents is unclear at this time; however, they are not GABA mimics and they do not affect GABA levels. Like other GABAergic agents, these compounds are potent enhancers of benzodiazepine binding and they antagonize cyclic GMP elevations induced by isoniazid. Compounds from this series may therefore have potential therapeutic utility as anticonvulsants or anxiolytics.

Postnatal evolution of the gamma-aminobutyric acid/benzodiazepine receptor complex in a model of inherited epilepsy: the quaking mouse

Binding assays of [3H]muscimol and [3H]-flunitrazepam have been performed on brain homogenates of brainstem, cerebellum, and forebrain of genetically epileptic quaking (qk) mutant mice 20, 40, 70, and 90 days old and their corresponding controls of the same strain (C57BL/6J). The endogenous gamma-aminobutyric acid (GABA) content has been determined in various brain regions of 70-day-old qk and control mice. Finally, the behavioral effects of diazepam, of the mixed GABAA/GABAB receptor agonist progabide, and of the selective GABAB receptor agonist baclofen have been assessed in adult qk mutants. Our results strongly suggest a lack of involvement of GABAergic neurotransmission in the inherited epilepsy of the qk mutant mouse.

Polychlorinated convulsant insecticides potentiate the protective effect of NaCl against heat inactivation of [3H]flunitrazepam binding sites

Six polychlorinated convulsant insecticides that potently inhibit t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to rat brain membranes also potentiate the protective effect of NaCl (200 mM) against heat inactivation of [3H]flunitrazepam binding sites on the same membranes. Similar effects were obtained with all "cage" convulsants tested. The rank order of potencies as heat protection potentiators was similar to the rank order of potencies as inhibitors of [35S]TBPS binding (alpha-endosulfan greater than endrin greater than dieldrin greater than toxaphene greater than lindane). alpha-Endosulfan and endrin are more potent in both respects than any previously reported picrotoxin-like (cage) convulsant, but are much less toxic to mammals. The greatly reduced toxicities of alpha-endosulfan and endrin in mammals may reflect partial gamma-aminobutyric acid (GABA)-neutral properties of these compounds. Time courses of heat inactivation of [3H]flunitrazepam binding sites in the presence of 200 mM NaCl plus saturating concentrations of endrin or picrotoxin revealed monophasic components constituting about 88% of the binding sites, suggesting that virtually all [3H]flunitrazepam binding sites are coupled to picrotoxin binding sites in the GABA/benzodiazepine/picrotoxin receptor complex. Protection against heat inactivation constitutes a useful tool for characterizing the various allosterically linked binding sites in neurotransmitter receptor complexes.

In vivo and in vitro modulation of central type benzodiazepine receptors by phosphatidylserine

The in vivo and in vitro modulation of central benzodiazepine binding sites (BDZ-R) by phosphatidylserine purified from bovine cerebral cortex (BC-PS) was studied. Five days i.p. administration of 15 mg/kg/day of BC-PS liposomes increased the maximal number of binding sites (Bmax) for [3H]flunitrazepam in cerebral cortical membranes. In contrast, the density of hippocampal benzodiazepine recognition binding sites decreased. In cerebellar membranes, BC-PS treatment did not alter the characteristics of [3H]flunitrazepam binding. Similar experiments using phosphatidylcholine extracted from bovine brain (BC-PC) resulted in no changes in the [3H]flunitrazepam binding in the 3 neural structures studied. Confirming previous results, rats submitted to an acute swimming stress showed a decrease in the density of cerebral cortex BDZ-R. Animals treated with BC-PS liposomes before stress showed cortical [3H]flunitrazepam binding significantly below treated, unstressed animals but not below controls. The effects of BC-PS liposomes appeared to be selective for the central type of BDZ-R since no changes were observed in [3H]RO 5-4864 binding, a radioligand specific for the peripheral type BDZ-R. Preincubation of cerebral cortical and cerebellar synaptosomal membranes with BC-PS liposomes (1-300 micrograms per assay) significantly increased in a concentration-dependent manner (up to 100 micrograms) the [3H]flunitrazepam binding. Scatchard analysis revealed changes in the apparent affinity without alterations in the Bmax. Very similar results were obtained using a purified PS from spinal cord. BC-PC, phosphatidylinositol, phosphatidic acid and the lyso derivatives of PS and PC (lysoPS and lysoPC) were found to be ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Transmembrane topology of the gamma-aminobutyric acidA/benzodiazepine receptor: subcellular distribution and allosteric coupling determined in situ

The subcellular distribution, allosteric coupling, and topology of the gamma-aminobutyric acidA (GABA)/benzodiazepine receptor were investigated in situ. We have shown previously that a transmembrane fragment (Mr = 24,000) of the benzodiazepine receptor remains in the plasma membrane after trypsin treatment of embryonic brain neurons maintained in primary monolayer cell culture. Here we report a study of the effects of exhaustive trypsinization on the binding of ligands to the GABA recognition site. Approximately 60% of the binding sites for [3H]muscimol in intact cells are inactivated by extracellular trypsin and, therefore, are associated with cell surface GABA receptors, whereas 40% of the sites are trypsin resistant. GABA potentiates [3H]flunitrazepam binding to intact cells and trypsin-treated intact cells. GABA-induced enhancement of [3H]flunitrazepam binding to intact cells is eliminated when cell-surface benzodiazepine receptors are blocked with Ro7-0213 (a charged benzodiazepine), but some enhancement remains after extracellular trypsinization. This provides indirect evidence for the existence of a population of trypsin-resistant GABA recognition sites associated with cell-surface receptors and indicates that trypsin-resistant cell-surface GABA recognition sites are allosterically linked to trypsin-resistant cell-surface benzodiazepine recognition sites, which we have shown previously to be associated with the trypsin-generated Mr 24,000 transmembrane fragment. The results are discussed in terms of a model of the transmembrane topology of the GABA/benzodiazepine receptor.

Photoaffinity labeling of [3H]flunitrazepam- and [3H]Ro15-4513-bound pellets in rat cerebral cortex and cerebellum

Irreversible incorporation of [3H]flunitrazepam and [3H]Ro15-4513 into GABA/benzodiazepine receptor subunits was studied by UV irradiation using ligand-bound membrane pellets from rat cerebral cortical and cerebellar synaptic membranes. Specific incorporation for [3H]flunitrazepam was greater in the pellet than in the suspension. The incorporation was identical for [3H]Ro15-4513 in both pellet and suspension. With the ligand-bound pellets, 50% of the available binding sites were photolabeled by both ligands in cortex and cerebellum. SDS polyacrylamide gel electrophoresis and fluorography of [3H]flunitrazepam photo-labeled receptor revealed the same number of major sites in both brain regions. In contrast, [3H]Ro15-4513 appears to label fewer sites in cortex and cerebellum. Photoaffinity labeling with [3H]flunitrazepam in ligand-bound membrane pellet provides a more selective and reliable method for studying the subunit structure of GABA/benzodiazepine receptor complex.

Amoxapine inhibition of GABA-stimulated chloride conductance: investigations of potential sites of activity

Amoxapine inhibits GABA-stimulated chloride conductance by acting on the GABAA-receptor chloride-ionophore complex which can be studied using membrane vesicles prepared from rat cerebral cortex. Amoxapine produces a right shift in the GABA concentration-response curve for the stimulation of 36Cl- uptake into these vesicles with no apparent change in the maximum response. Schild analysis of these data gave a pA2 value of 5.52 with a slope of 0.79. Amoxapine inhibits the binding of the GABAA receptor selective antagonist [3H]SR 95531 with an IC50 value of 3.45 microM and a pseudo Hill coefficient of 0.83. In contrast, 10 microM amoxapine inhibits [3H]flunitrazepam binding by less than 25% while the benzodiazepine antagonist Ro 15-1788 reduces the amoxapine inhibition of GABA-stimulated chloride conductance only at high concentrations. These data suggest that amoxapine does not inhibit chloride conductance by acting as a benzodiazepine inverse agonist and either acts directly on the GABAA receptor as an antagonist or blocks GABA activity at a site closely coupled to it. The ability of amoxapine to inhibit GABA-stimulated chloride conductance is a likely explanation for its proconvulsant activity observed at high doses.

Chiral 1,4-benzodiazepin-2-ones: relationship between stereochemistry and pharmacological activity

Pure enantiomers of 3-substituted-1,4-benzodiazepin-2-ones, obtained by HPLC resolution on chiral stationary phases, show significant differences in their pharmacological activity. The occurrence of biotransformation during the pharmacological test is monitored using a new chromatographic method. The reliability of the pharmacological activity data is discussed.

Biochemical characterization of [3H]tryptamine binding sites from rat brain

Rat brain membranes were treated with different protein modifying reagents, all of which were able to reduce [3H]tryptamine binding. However, inactivation by N-ethylmaleimide and iodoacetamide only was counteracted by coincubation with tryptamine. Thus, the [3H]tryptamine binding molecule is a membrane protein with an essential sulfhydryl group at the binding site. After incubation of digitonin-solubilized membranes with seven different lectins, no precipitation of [3H]tryptamine binding sites was observed. On concanavalin A and wheat germ agglutinin affinity chromatography, no [3H]tryptamine binding activity was found to be specifically bound. Therefore, the [3H]tryptamine binding protein appears to be devoid of lectin binding carbohydrate residues.

Loss of muscarinic and benzodiazepine neuroreceptors from hippocampus of alcohol abusers

Thiamine deficiency (Wernicke-Korsakoff's disease) may not be the only mechanism whereby chronic alcohol abuse affects the brain and not all alcohol-related changes may be evident morphologically. The purpose of this study was to determine if alcohol abuse affects muscarinic cholinergic and benzodiazepine receptors in the hippocampus of histologically normal brains obtained at autopsy in a general hospital population. Because patients were excluded who had significant brain atrophy and/or dementia severe enough to require institutionalization, the reported findings are presumed to be early changes in the development of an alcohol encephalopathy. In addition, patients were excluded from this study if they had clinical brain diseases (including Wernicke's disease), died in coma, had liver disease, or received medications that could potentially alter receptor binding. The reported changes in receptor binding were therefore presumed to be related to alcohol abuse per se and not an alcohol-associated condition. We found that muscarinic cholinergic synaptic receptor density determined with 3[H] quinuclidinyl benzilate was decreased by 30% in homogenates of the hippocampus of 25 alcohol abusers compared with 25 matched nonalcoholic controls. Similarly, densities of benzodiazepine receptors determined with 3[H] flunitrazepam were also decreased by approximately 30% in alcohol abusers. The affinities of both receptor types were not affected by alcohol abuse. Age and death-autopsy time interval had no significant effects on either wet tissue protein concentrations, yields of protein after centrifugation, or receptor binding. The contributions of age and time interval were each less than 2% of the total variance of protein concentrations and receptor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Laudanosine does not displace receptor-specific ligands from the benzodiazepinergic or muscarinic receptors

The present study was designed to investigate whether D,L-laudanosine (a breakdown product of the neuromuscular relaxant atracurium besylate) interacts with benzodiazepinergic receptors or muscarinic receptors, both of which are involved in epilepsy and other types of seizures. The ability of D,L-laudanosine (10(-10) to 5 X 10(-5) M) to displace ligands specific for these receptors from their binding sites was tested. D,L-Laudanosine failed to inhibit the binding of [3H]flunitrazepam to central benzodiazepine receptors in the cerebral cortex, the binding of [3H]PK 11195 to peripheral benzodiazepine binding sites in the cerebral cortex and kidney, the binding of [3H]Ro 5-4864 to peripheral benzodiazepine binding sites in the kidney, or the binding of [3H]quinuclidinyl benzilate to muscarinic receptors in the cerebral cortex. These results suggest that laudanosine does not exert its convulsive effect via interaction with benzodiazepinergic or muscarinic receptors.

Lorazepam administration during embryonic development alters GABAA receptor binding and function

Prenatal exposure to diazepam has been reported to lead to behavioral alterations in young and mature animals, but the neurochemical basis of this effect is uncertain. To examine effects of embryonic benzodiazepine exposure on the gamma-aminobutyric acidergic (GABA)ergic) system, we assessed binding and function at the GABAA receptor complex in chick embryos treated with lorazepam, 2 mg/kg, for 2-10 days. There was no change in benzodiazepine receptor binding in cortex after lorazepam administration, but a decrease in the number of chloride channel sites was observed. Overall function at the GABAA receptor complex as assessed by chloride uptake into cortical synaptoneurosomes was decreased after 10 days of lorazepam, and possibly increased after 4 days of lorazepam. Similar results were obtained when embryos were treated for 2- and 4-day periods beginning on day 8. These results indicate that chronic lorazepam administration to embryos alters binding and function in the GABA system measured soon before hatching. These alterations, if persistent, may contribute to the behavioral changes seen in animals exposed prenatally.