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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The interactions of the atypical benzodiazepine 4′-chlorodiazepam (Ro 5-4864) with functionally expressed human GABAA receptor cDNAs were determined. Cotransfection of human α2, β1, and γ2 subunits was capable of reconstituting a 4′-chlorodiazepam recognition site as revealed by a dose-dependent potentiation of t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to the GABA-activated chloride channel. This site is found on GABAA receptor complexes containing sites for GABA agonist-like benzodiazepines and neuroactive steroids. The importance of the α subunit was further demonstrated as substitution of either α1 or α3 for the α2 subunit did not reconstitute a 4′-chlorodiazepam recognition site that was capable of modulating [35S]TBPS binding under the same experimental conditions. The 4′-chlorodiazepam modulatory site was shown to be distinct from the benzodiazepine site, but the phenylquinolines PK 8165 and PK 9084 produced effects similar to 4′-chlorodiazepam, consistent with the previous analysis of the 4′-chlorodiazepam site in brain homogenates. Further analysis of the subunit requirements revealed that coexpression of α2 and β1 alone reconstituted a 4′-chlorodiazepam recognition site. It is interesting, however, that the 4′-chlorodiazepam site was found to inhibit [35S]TBPS binding to the GABA-activated chloride channel. Thus, the 4′-chlorodiazepam site may be reconstituted with only the α and β polypeptides.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: : Neuroactive steroids, in particular 3α-hydroxypregnanes, are allosteric modulators of the γ-aminobutyric acidA (GABAA) receptor. Regionally selective expression of receptor subunit subtypes may account for differential responsiveness of tissues to GABAergic inhibition and ncurosteroid modulatory effects. the effect of 5α-pregnan-3α-ol-20-one (epiallopregnanolone) on heterotropic cooperativity on the GABAA receptor complex has been studied in three subtypes of expressed recombinant human receptors and in cat brain and spinal cord. Steroid potentiation of [3H]flunitrazepam binding was greatest for the α1β1γ2 receptor complex, whereas α1β1γ2 and α2β1γ2 complexes showed 〈 100% enhancement in binding. Previous studies suggest that the spinal cord is devoid of α1, whereas cerebellum is rich in α1 subunits. Correspondingly, a differential enhancement of [3H]flunitrazepam binding in spinal cord (51%) versus cerebellum (28%) was also observed. The structure of neuroactive steroids is important in determining the extent of neuromodulatory activity. The 5β-pregnanes, 5β-pregnan-3α-ol-20-one (epipregnanolone) and 5β-pregnan-3α,21-diol-20-one (5β-tetrahydrodeoxycorticosterone), were both less potent than their corresponding 5α derivatives. A 3α-hydroxyl group is essential for neuromodulatory activity in the expressed receptors, as demonstrated by the observation that 5α-preg-nan-3β-ol-20-one (allopregnanolone) and 4-pregnen-3,20-dione (progesterone) were both inactive. The ability to screen synthetic molecules using expressed human receptors that selectively contain individual subunit subtype combinations may prove to be a powerful tool in the development of therapeutic agents that act as allosteric modulators of the GABAA receptor and other neurotransmitter receptors as well.
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Recently, it was proposed that β-carbolines interact with a subset of benzodiazepine (BZD) binding sites in mouse brain. This postulate was based upon evidence showing changes in binding properties of the BZD receptor following photoaffinity labeling of membranes with flunitrazepam (FLU). Under conditions in which 80% of specific [3H]diazepam binding was lost in photolabeled membranes, specific [3H]propyl β-carboline-3-carboxylate ([3H]PCC) binding was spared. In this study, the binding of the BZD antagonists [3H]PCC, [3H]Ro15 1788 and [3H]CGS 8216 was examined in rat brain membranes following photoaffinity labeling with FLU. No significant changes in the apparent KD and small reductions in the Bmax of 3H antagonist binding were observed. However, in the same membranes, up to 89% of specific [3H]FLU binding was lost. When [3H]PCC (0.05 nM) was used to label the receptors in control and photolabeled membranes, the ability of BZD receptor agonists to inhibit [3H]PCC binding was greatly diminished in the photolabeled membranes. In contrast, the potency of BZD antagonists remained the same in both control and treated membranes. Based upon PCC/[3H]Ro15 1788 competition experiments, the ability of PCC to discriminate between BZD receptor subtypes was unaffected by photoaffinity labeling of cortical membranes. Overall, these findings suggest that β-carbolines do not interact with a subset of BZD binding sites per se, but may be a consequence of the differential interaction of BZD agonists and antagonists with BZD binding sites that have been photoaffinity labeled with FLU. A possible mechanism underlying this phenomenon is discussed. The ability of photolabeled membranes to differentiate between BZD agonists and antagonists provides a potential screen for agonist and antagonist activity in compounds that interact with the BZD receptor.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The binding of the cage convulsant t-butylbicyclo phosphorothionate (TBPS) and 36CI- uptake by synaptoneurosomes were used to test the ability of progesterone metabolites to modulate allosterically the Ro 5–4864 (4′-chlorodiazepam) binding site that is functionally coupled to the γ-aminobutyric acid (GABA)/benzodiazepine receptor complex (GBRC) in rat brain. Dose-dependent enhancement of [35S]TBPS binding by Ro 5–4864 occurs in rat cerebral cortex in the presence of the progesterone metabolites 5αpregnan-3α-ol-20-one (3α-OH-DHP) and 5α-pregnan-3α, 20α-diol(pregnanediol). The pregnanediol effect is completely GABA dependent, whereas that of 3α-OH-DHP is not. Conversely, Ro 5–4864 opposed the action of 3α-OH-DHP by increasing the IC50 for 3α-OH-DHP inhibition of [35S]TBPS binding. In cortical snaptoneurosomes, Ro 5–4864 antag onized both 3α-OH-DHP and pregnanediol enhancement of GABA-stimulated 36CI- uptake. In both binding and functional studies, pregnanediol showed limited efficacy relative to 3α-OH-DHP, as previously reported. These findings provide the initial evidence that the GBRC-linked Ro 5–4864 binding site is allosterically coupled to the putative progesterone metabolite recognition site and confirm the GABA mimetic properties of 3α-OH-DHP and pregnanediol.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: t[3H]Butylbicycloorthobenzoate ([3H]TBOB; 22 Ci/mmol) was prepared by reductive dechlorination of its 4-chlorophenyl analog with tritium gas. This new radioligand binds reversibly to fresh washed rat brain P2 membranes in 500 mM NaCl plus 50 mM sodium-potassium phosphate buffer (pH 7.4) at 25°C, with 80–90% specific relative to total binding, a KD of 61 ± 15 nM, and a Bmax of 1.6 ± 0.5 pmol/mg of protein. [3H]TBOB association with its binding site(s) is monophasic, but its dissociation is biphasic. The binding characteristics of [3H]TBOB are essentially identical to those of t-[35S]butylbicyclophosphorothionate ([35S]TBPS) with respect to pH dependence, stimulation by anions, regional distribution in the brain, and pharmacological profile. Saturation analyses and dissociation studies further indicate that TBOB and TBPS have a common binding site. However, binding of the two radioligands differs in respect to temperature effects. In contrast to [35S]TBPS, which exhibits negligible binding at 0°C, [3H]TBOB binds to rat brain membranes at 0, 25, and 37°C with similar KD values. [3H]TBOB with its long radioactive half-life and temperature-independent KD is a valuable supplement to [35S]TBPS in further biochemical and pharmacological characterization of the γ-aminobutyric acid receptor-ionophore complex.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1546-170X
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Patients taking fluoroquinolone antibiotics such as norfloxacin exhibit a low incidence of convulsions and anxiety. These side effects probably result from antagonism of the neurotransmitter γ-aminobutyric acid (GABA) at the brain GABAA receptor complex (GRC). Modification of norfloxacin ...
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  • 7
    ISSN: 1573-6903
    Keywords: GABAA Receptor ; pregnane steroids ; Benzodiazepines ; chloride channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Conclusion Based on the pharmacological and biochemical evidence to date, especially that derived from the recombinantly expressed receptor studies, the suggestion that a novel GBRC-linked steroid recognition site exists becomes a cogent argument. The high affinity of the steroid site for certain naturally occurring metabolites of progesterone and glucocorticoids favors a physiologic role for these steroids in the regulation of brain excitability. Clearly, investigations of such a regulatory role is warranted. If present, it provides an important example of endocrine control of a major inhibitory neurotransmitter in the CNS. Moreover, as we gain a greater understanding of the molecular organization of the GBRC, the putative steroid site provides a novel target for the rational design of therapeutic agents for the treatment of anxiety, epilepsy, and insomnia.
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  • 8
    ISSN: 1432-2072
    Keywords: Key words Neurosteroid ; Neuroactive steroid ; Anxiolytic ; Anticonvulsant ; GABAA receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Endogeneously occurring neuroactive steroids, metabolites of progesterone and deoxycorticosterone, have been shown previously to interact with the GABAA receptor with great specificity in vitro and to have anticonvulsant, anxiolytic and sedative activity in vivo. However, these endogenously occurring steroids are not useful as therapeutic agents due to their potential metabolism to hormonally active steroids and their poor oral bioavailability. In an attempt to develop therapeutic agents which would maintain the pharmacological profiles of endogeneous neuroactive steroids but with increased oral bioavailability and reduced metabolic liability, we explored simple substitutions at the 3β-position of the endogenous neuroactive steroid, 3α-hydroxy-5α-pregnan-20-one (3α,5α-P). This report describes part of the in vitro and in vivo pharmacological profile of a 3β-substituted analog, 3β-ethenyl-3α-hydroxy-5α-pregnan-20-one (Co 3-0593). The compound exhibited anticonvulsant activity against pentylenetrazol-induced seizures in mice and rats (ED50 = 5.6 and 11. 5 mg/kg, IP, respectively). Co 3-0593 showed robust anxiolytic effects, comparable to benzodiazepines in the Geller-Seifter test after both SC and oral administration. Furthermore, the anxiolytic activity was maintained after chronic administration suggesting an absence of tolerance. The compound did not affect the acquisition of a learned response at both anticonvulsant and anxiolytic doses. However, at higher doses the compound showed roto-rod deficit which was further enhanced by ethanol. In summary, 3β-ethenyl-substituted 3α,5α-P appeared to maintain the pharmacological activities of the endogenous neuroactive steroid with apparent oral activity.
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  • 9
    ISSN: 1432-2072
    Keywords: Key words Allopregnanolone ; Pregnanolone ; Neurosteroid ; Neuroactive steroid ; Motor behavior ; Ethanol interaction ; Benzodiazepine ; Triazolam ; Diazepam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Endogenous pregnane steroids, such as allopregnanolone (3α-hydroxy-5α-pregnan-20-one; 3α, 5α-P) and pregnanolone (3α-hydroxy-5β-pregnan-20-one; 3α,5β-P), allosterically modulate GABAA receptor function and exhibit behavioral effects similar to benzodiazepines, though acting at a distinct recognition site. Inasmuch as some positive allosteric modulators of GABAA receptor function exhibit profound interactions with ethanol, the effects of 3α,5α-P and 3α,5β-P were compared to those of two benzodiazepines, triazolam and diazepam, on the motor function of mice and rats when administered either alone or in combination with ethanol. All four test compounds exhibited dose-related impairment of motor function in the horizontal wire task in mice and the rotorod task in rats. Ethanol caused a marked enhancement of triazolam- and diazepam-induced motor impairment. In contrast, ethanol enhanced to a lesser extent the motor impairment induced by both neurosteroids in mice and not at all in rats. All four compounds increased ethanol-induced behavioral sleep time in mice, although the benzodiazepines did so at a much smaller fraction of their ataxic doses as compared to the neurosteroids. As one of the undesired side-effects of therapeutic use of benzodiazepines is their interaction with ethanol, development of neuroactive steroids as drugs may offer therapeutic advantages.
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