Comparison of benzodiazepine receptors in cerebellum and inferior colliculus

Reversible and irreversible binding of [3H]flunitrazepam was investigated in membranes from cerebellum and inferior colliculus of young and adult rats. Results indicate that in adult animals predominantly BZ1 receptors are enriched in both brain regions. In the brains of newborn animals, however, additional benzodiazepine receptor subtypes seem to exist in cerebellum as well as in inferior colliculus.

[Methodology and problems in the study of drugs of abuse in urine]

The analysis of drugs of abuse in urine is a valuable tool for the detection of illicit drug use and the treatment and rehabilitation of addicts. In order for the results to be conclusive, however, several precautions have to be taken during the collection, storage, mailing and analysis of the urinary specimen. Since immunological methods for the determination of drugs of abuse are not completely specific, all positive results on immunoassay should be confirmed, at least for forensic purposes, by a chromatographic technique. Although much more complicated and time-consuming, some chromatographic techniques such as gas chromatography-mass spectrometry offer the possibility of unambiguously identifying drugs of abuse. However, in some cases, even with this method it is not possible to decide whether the identified metabolite of a drug of abuse stems from food or illicit or elicit drug use. A single urinary analysis is, therefore, sometimes not sufficient to provide unambiguous proof of the use of illicit drugs. However, definite evidence of repeated drug abuse can be obtained if the person involved is carefully instructed as to which medicines or food must not be taken during the investigation period and yet the analysis of several urinary specimens taken at intervals of one or two days proves positive.

[Comparison of the bioavailability of two diazepam preparations. Clinical comparison between a new commercial preparation and a standard preparation after oral and intramuscular administration]

The following pharmacokinetic study was aimed at a comparison of the bioavailability of two different preparations of diazepam (Gewacalm and a further wellknown formulation). 40 healthy volunteers were subjected to a cross-over design in which plasma levels of diazepam were assayed after oral and intramuscular application of 10 mg of a preparation. In the comparison (N = 30) of oral bioavailability (rate and completeness of enteral absorption) no statistical difference between both preparations was observed. In the study of intramuscular bioavailability (N = 10), a trend of quicker and more complete resorption of Gewacalm was of statistical significance (p less than 0.05), however, because of the small number of subjects tested in the intramuscular study a replication study is advisable.

Light treatment in depressive illness. Polysomnographic, psychometric and neuroendocrinological findings

Objective and subjective quality of sleep and awakening as well as circadian rhythms in cortisol, temperature and well-being were investigated in 10 female hospitalized depressed patients diagnosed as major depressive disorders according to RDC criteria before (baseline), during (intervention) and after (recovery) treatment with biologically active or bright light (BL) and were compared with the findings in 10 normals. Polysomnographic evaluation demonstrated in depressed patients an increased sleep latency, decreased total sleep time, attenuated S4 and augmented REM sleep, as well as a shortened REM latency and a statistically significant increased average REM length as compared with normals. BL tended to shorten sleep onset, decrease number of awakenings, increase REM latency and significantly attenuated the average REM length. Subjective sleep quality tended to improve as did the subjective awakening quality after the recovery night. There was, however, a statistically significant improvement of the objectively evaluated quality of awakening and early morning behavior characterized by an improved attention, reaction time and performance in the reaction time task, while concentration and psychomotor activity tended to improve as as well. BL effects were also seen in hormonal secretion patterns: circadian cortisol secretion maxima occurred earlier in depressed patients than in normals before and after BL treatment, while during BL intervention this difference disappeared. Circadian temperature rhythms did not exhibit any significant findings with the exception of an earlier occurring minimum in depressed patients than in normals after treatment. Finally, subjective well-being as rated by means of an analogue scale was significantly worse in depressed patients than normals before but not during and after light treatment. The findings are discussed.

Postnatal development of proteins associated with different benzodiazepine receptors

The postnatal development of several proteins irreversibly labeled by [3H]flunitrazepam in membranes from rat cerebral cortex was investigated. It was demonstrated that in the early postnatal days proteins with apparent molecular weights 55,000 and 59,000 were predominantly labeled whereas irreversible labeling of a protein with apparent molecular weight 51,000 started to predominate only in the second postnatal week. Irreversible labeling of another protein with apparent molecular weight 62,000 was weak throughout development. All these proteins seem to be associated with central benzodiazepine receptors. Irreversible labeling at various time points after birth seems to parallel the postnatal development of these proteins, and the different time course of development and different binding properties of the individual proteins support the hypothesis that these proteins are associated with separate and distinct benzodiazepine receptor subtypes. The pharmacological properties of the individual receptor subtypes seem to be fully developed in the early postnatal days, and therefore newborn animals seem to be a good model system for the investigation of properties and function of these various benzodiazepine receptor subtypes.

Benzodiazepine receptors: multiple receptors or multiple conformations?

Several lines of evidence from reversible binding studies seem to indicate there are at least two "central" benzodiazepine receptor subtypes, the BZ1 and BZ2 receptors. Irreversible binding studies, using 3H-flunitrazepam as a photoaffinity label for benzodiazepine receptors, not only are in perfect agreement with the data from reversible binding studies but extend these studies by identifying P51, a protein with apparent molecular weight 51,000, as a protein associated with the BZ1 receptor and by suggesting that the BZ2 receptor might actually consist of several different benzodiazepine receptors associated with different and distinct proteins irreversibly labeled by 3H-flunitrazepam. Other reversible binding studies have accumulated indicating the existence of several different conformations of benzodiazepine receptors. Irreversible binding studies support this conclusion and in addition suggest the existence of four different benzodiazepine binding sites within the GABA-benzodiazepine receptor complex. It is therefore hypothesized that there are several different GABA-benzodiazepine receptor subtypes all of which have four distinct benzodiazepine binding sites which can exist in at least three different but freely interconvertible conformations. This hypothesis can account for all experimental observations obtained so far and might partially explain the distinct clinical effects of structurally similar benzodiazepines.

Comparison of benzodiazepine receptor binding in membranes from human or rat brain

Specific high affinity binding of [3H]flunitrazepam to membranes from human brain was stimulated by gamma-aminobutyric acid (GABA), pentobarbital, 1-ethyl-4-(isopropylidene-hydrazino)-1H-pyrazolo[3,4b]pyridine-5-carboxy lic acid ethyl ester hydrochloride (SQ 20009) and avermectin B1a and was unaffected by 2 microM 4'-chlorodiazepam (Ro 5-4864) indicating that [3H]flunitrazepam in human brain as well as in rat brain predominantly binds to benzodiazepine receptors specific to brain, which was associated with a GABA receptor and several modulatory binding sites for drugs. The potency of several selective and non-selective ligands for benzodiazepine receptors for inhibition of the binding of [3H]flunitrazepam was compared in membranes from human or rat brain cerebellum, hippocampus and cerebral cortex. It was demonstrated that all these compounds, derived from different chemical structures, had a remarkably similar potency for inhibition of the binding of [3H]flunitrazepam in the corresponding regions of the human or rat brain. However, irreversible labelling of benzodiazepine binding sites with [3H]flunitrazepam and subsequent SDS-polyacrylamide gel electrophoresis and fluorography revealed more photolabelled protein bands in human than in rat cerebellum and hippocampus. The results seem to indicate that, although the pharmacological properties of reversible binding of [3H]flunitrazepam are remarkably similar in membranes from rat or human brain, the molecular heterogeneity of benzodiazepine binding sites is even greater in human than in rat brain.

Differential degradation of different benzodiazepine binding proteins by incubation of membranes from cerebellum or hippocampus with trypsin

When rat brain membranes were incubated with [3H]flunitrazepam in the presence of UV light, predominantly one protein (P51) was irreversibly labeled in cerebellum and at least two proteins (P51 and P55) were labeled in hippocampus. On digestion of membranes with increasing concentrations of trypsin up to 40% of radioactivity irreversibly bound to proteins was removed from the membranes. In addition, P51 was nearly completely degraded to a peptide with apparent molecular weight 39,000 and this peptide was further degraded to a peptide with apparent molecular weight 25,000. In contrast, protein P55 was only partially degraded by trypsin and yielded two proteolytic peptides with apparent molecular weights 42,000 and 45,000 which seemed to be rather stable against further attack by trypsin. Membranes treated with trypsin still had the capacity to bind [3H]-flunitrazepam reversibly with an affinity similar to that of membranes not previously treated with trypsin. When these membranes were irradiated with UV light, the same proteolytic peptides were detected as in membranes first photolabeled and then digested with trypsin. These results suggest a close association between reversible and irreversible benzodiazepine binding sites and indicate that membrane-associated proteins P51 and P55 are differentially protected against degradation by trypsin.

Affinity of various ligands for benzodiazepine receptors in rat cerebellum and hippocampus

The structure-affinity relationship of benzodiazepine receptor ligands for binding to their receptors was investigated by measuring the potency of 41 benzodiazepines or benzodiazepine analogues and of 9 non-benzodiazepines for inhibition of [3H]flunitrazepam binding to cerebellar or hippocampal membranes. It was found that a chloro or a fluoro substitutent in position 2' enhanced whereas substituents in position 3 and substituents larger than a methyl group in position 1 of the benzodiazepine ring system reduced the potency of benzodiazepines for inhibition of [3H]flunitrazepam binding in cerebellum or hippocampus. In addition, several benzodiazepines could be identified which have a higher affinity for benzodiazepine receptors in cerebellum than for those in hippocampus. A selectivity of benzodiazepines for their receptors in cerebellum seems to be caused not only by certain substituents in position 1 but also by a chloro group in position 2' and together with this substituent by a hydroxy group in position 3.

Photoaffinity labeling of different benzodiazepine receptors at physiological temperature

Irreversible labeling of benzodiazepine receptors in membranes from cerebellum or hippocampus was compared at 0 degrees C using [3H]flunitrazepam as a photoaffinity ligand. [3H]Flunitrazepam reproducibly and irreversibly labeled mainly one protein (P51) in cerebellum and at least two proteins (P51 and P55) in hippocampus at both temperatures. Differential inhibition at 37 degrees C of irreversible [3H]flunitrazepam binding to the individual proteins by several selective benzodiazepine receptor ligands supports the hypothesis that P51 and P55 are associated with different benzodiazepine receptors.

[35S]tert.-butylbicyclophosphorothionate and avermectin bind to different sites associated with the gamma- aminobutyric acid-benzodiazepine receptor complex

Low concentrations of avermectin B1a (AVM) stimulated the specific high affinity binding of [35S]tert.-butylbicyclophosphorothionate [( 35S]TBPT) to membranes from rat cerebral cortex in the absence or presence of chloride or bromide ions. In contrast, TBPT either weakly stimulaes or does not significantly influence the specific high affinity binding of [3H]AVM to the same membranes in the absence or presence of chloride ions, respectively. These results indicate that [3H]AVM and [35S]TBPT bind to different but closely associated binding sites.

Evidence for association of a high affinity avermectin binding site with the benzodiazepine receptor

Avermectin B1a concentrations corresponding to the KD value of a specific high affinity binding site for [3H]avermectin B1a are sufficient to stimulate the specific high affinity binding of [3H]flunitrazepam to its receptors. This stimulation of [3H]flunitrazepam binding by low concentrations of avermectin B1a was enhanced by chloride ions and picrotoxinin and reduced by the GABA agonists THIP and PSA. The similar modulation by chloride ions, GABA agonists and picrotoxinin and the resistance against washing of membranes of avermectin B1a bound to its specific high affinity binding site or to the site modulating [3H]flunitrazepam binding indicate a close association of the specific high affinity binding site for [3H]avermectin B1a with the GABA-benzodiazepine receptor complex.

Apparent identity of alpha-subunit of pyruvate dehydrogenase and the protein phosphorylated in the presence of glutamate in P2-fractions of rat cerebral cortex

Addition of L-glutamate or several citric acid cycle intermediates stimulated the phosphorylation of a protein with apparent molecular weight of 43,000 ( P43 ) in P2-fractions from rat cerebral cortex, and this phosphorylation was inhibited by dichloroacetic acid, a specific inhibitor of pyruvate dehydrogenase kinase. Comparison of several molecular properties of phosphorylated P43 and the phosphorylated alpha-subunit of pyruvate dehydrogenase indicated that both proteins are extracted by a similar procedure and have an identical apparent molecular weight and isoelectric point. Furthermore, digestion of both phosphorylated proteins by several different proteases in the presence of SDS yielded a similar pattern of phosphorylated peptides indicating that these proteins have a considerable sequence homology. Thus, various pieces of evidence indicate that P43 and the alpha-chain of pyruvate dehydrogenase are very similar if not identical. The possible implication of a glutamate stimulated phosphorylation of pyruvate dehydrogenase for long term potentiation and epilepsy is discussed.

Properties of a high affinity binding site for [3H]avermectin B1a

The specific high affinity binding of [3H]avermectin B1a was investigated in membranes from several rat brain regions. Binding occurred rapidly, was reversible and partially dependent on the presence of chloride ions in the incubation medium. Specific high affinity binding of [3H]avermectin B1a was partially inhibited by GABA receptor agonists and this effect was blocked by GABA receptor antagonists. Pentobarbital and etazolate inhibited, and picrotoxin, picrotoxinin and IPTBO stimulated high affinity binding of [3H]avermectin B1a. All these effects were influenced by the presence of chloride ions in the incubation medium. The results indicate that the high affinity binding site of [3H]avermectin B1a is associated with the GABA-benzodiazepine receptor-chloride ion channel complex.

Several new benzodiazepines selectively interact with a benzodiazepine receptor subtype

The potency of several new benzodiazepines as inhibitors of [3H]flunitrazepam binding was investigated in membranes from rat cerebellum or hippocampus. It was found that quazepam and two of its metabolites have a higher affinity for benzodiazepine receptors in cerebellum than for those in hippocampus, indicating a preferential interaction of these compounds with BZ1-receptors. Other experiments indicated that these compounds have benzodiazepines agonistic properties similar to diazepam or flunitrazepam. Thus for the first time, benzodiazepines have been identified with differentially interact with different benzodiazepine receptors.

Irreversible binding of [3H]flunitrazepam to different proteins in various brain regions

Irreversible photolabeling by [3H]flunitrazepam of four proteins with apparent molecular weights 51,000 (P51), 53,000 (P53), 55,000 (P55), and 59,000 (P59) was investigated in various rat brain regions by SDS-polyacrylamide gel electrophoresis, fluorography, and quantitative determination of radioactivity bound to proteins. On maximal labeling of these proteins, only 15-25% of [3H]flunitrazepam reversibly bound to membranes becomes irreversibly attached to proteins. Results presented indicate that for every [3H]flunitrazepam molecule irreversibly bound to membranes, three molecules dissociate from reversible benzodiazepine binding sites. This seems to indicate that these proteins are either closely associated or identical with reversible benzodiazepine binding sites, and supports the hypothesis that four benzodiazepine binding sites are associated with one benzodiazepine receptor. When irreversible labeling profiles of proteins P51, P53, P55, and P59 were compared in different brain regions, it was found that labeling of individual proteins varied independently, supporting previous evidence that these proteins are associated with distinct benzodiazepine receptors.

Properties of [3H]flunitrazepam binding to different benzodiazepine binding proteins

Membranes from cerebellum or hippocampus were incubated with various concentrations of [3H]flunitrazepam in the absence or presence of diazepam, Cl 218 872 or ethyl-beta-carboline-3-carboxylate (beta-CCE). After binding equilibrium of [3H]flunitrazepam had been established, the membranes were either filtered for determination of reversible binding or were irradiated with UV light for determination of irreversible binding. Irradiated membranes were then subjected to SDS-polyacrylamide gel electrophoresis and fluorography. Individual photolabeled proteins were identified, appropriate sections cut out of the gel, and the radioactivity in the gel pieces measured. The results indicate that [3H]flunitrazepam binding to individual benzodiazepine binding proteins and its inhibition by various drugs can be measured by the present technique and support previous evidence for the independent existence of various proteins irreversibly labeled by [3H]flunitrazepam and their possible association with different benzodiazepine receptors.

Postnatal development of proteins irreversibly labeled by [3H]flunitrazepam

The irreversible labeling by [3H]flunitrazepam of three proteins with apparent molecular weights of 51,000 (P51), 55,000 (P55) and 59,000 (P59) was investigated using hippocampal membranes isolated from rats at various timepoints after birth. The present results indicate that [3H]flunitrazepam predominantly labels P55 and P59 in the early days after birth whereas labeling of P51 starts to increase significantly in the second postnatal week. A possible association of P55 and P59 with type 2 and of P51 with type 1 benzodiazepine receptors is suggested.

Glutamate-stimulated phosphorylation of a specific protein in P2 fractions of rat cerebral cortex

Incubation of P2 fractions from rat cerebral cortex with 32Pi in the presence of L-glutamate caused an increased phosphorylation of a protein with apparent molecular weight of 43,000 (P43) as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. This glutamate-stimulated phosphorylation of P43 was already detectable 10 s after the addition of glutamate and was dependent on the concentrations of glutamate in the incubation medium. Other excitatory amino acids such as D-glutamate, L-aspartate, D,L-cysteic acid, L-cysteinesulfinic acid, and D,L-alpha-aminoadipic acid did not stimulate the phosphorylation of P43. In contrast, alpha-ketoglutarate and succinate stimulated the phosphorylation of this protein. Glutamate-stimulated phosphorylation of P43 seemed not to be mediated by either cAMP or cGMP and was inhibited by the presence of Ca2+ in the incubation medium. Experiments performed with metabolic inhibitors indicated that glutamate-stimulated protein phosphorylation is localized in mitochondria. This conclusion is supported by the occurrence of glutamate-stimulated phosphorylation of P43 in mitochondrial fractions from several peripheral tissues. The present results are consistent with the hypothesis that P43 is a component of the pyruvate dehydrogenase complex of mitochondria.

Sedimentation and release properties of P2 fractions derived from rat cerebral cortex slices incubated with radiolabeled GABA for a short or long time period

On homogenization of rat cerebral cortex slices previously incubated with [3H] GABA or [14C]GABA for 5 or 30 min, respectively, particles were recovered in P2 fractions which exhibited similar buoyant density, but different sedimentation velocity on linear sucrose density gradient centrifugation. The K+-evoked release of [3H]GABA from particles isolated from slices previously incubated for 5 min with [3H]GABA was increased in the presence of exogenous Ca2+. In contrast, the K+-evoked release from particles isolated from slices previously incubated for 30 min with [3H]GABA, was not influenced by the presence of exogenous Ca2+. These results suggest that, depending on the incubation time of slices, exogenously applied GABA can be detected in different pools. These pools not only seem to differ in their CA2+ dependency of K+-evoked release but also in their subcellular localization.