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Publications (27)75.71 Total impact

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    ABSTRACT: In primary cultures of rat cerebral cortex, N-methyl-D-aspartate causes widespread neurotoxicity. Inhibitors of the nitric oxide generating the enzyme nitric oxide synthase has been shown to attenuate the effects of N-methyl-D-aspartate in a number of neuronal systems both in vivo and in vitro. In our experiments, the nitric oxide synthase inhibitor N-nitroarginine was ineffective at blocking neurotoxicity induced by N-methyl-D-aspartate. Cyclic guanine monophosphate, known to be synthesized in response to nitric oxide was demonstrably inhibited by identical treatments with N-nitroarginine in sister cultures. We conclude that although nitric oxide is produced in response to N-methyl-D-aspartate, it is neither necessary nor sufficient for neurotoxicity.
    Neuroreport 12/1993; 5(2):148-50. · 1.40 Impact Factor
  • Annals of the New York Academy of Sciences 06/1992; 648:355-7. · 4.38 Impact Factor
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    ABSTRACT: Quisqualate is a potent neurotoxin in cortical cultures of the rat. Unlike N-methyl-D-aspartate (NMDA), the toxicity of quisqualate is due to overstimulation of a membrane receptor after the agonist has been removed. This receptor appears to be the 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor since 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) are potent antagonists when added to the post incubation media. NBQX and DNQX are ineffective when present only during quisqualate exposure, indicating the AMPA receptor is not involved in the initial event. Transfer of culture media 30 min after quisqualate exposure to either neuronal or non-neuronal cells was found to cause toxicity in previously untreated neuronal cells. This effect could not be reproduced with NMDA. The neurotoxic chain of events could be interrupted during quisqualate exposure by removal of sodium from the incubation media, suggesting the involvement of a sodium-dependent plasma membrane uptake mechanism. Quisqualate may be continually recycled by internalization and release, causing neurotoxicity by persistent stimulation of the AMPA receptor.
    European Journal of Pharmacology 04/1992; 212(2-3):129-36. · 2.59 Impact Factor
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    ABSTRACT: Using fura-2 loaded neural tumour cells, SK-N-SH, we demonstrate that receptor-mediated activation of phosphoinositide hydrolysis not only causes the release of Ca2+ from intracellular stores but also causes a concomitant influx of extracellular Ca2+. Thapsigargin (TG), a sesquiterpene lactone, causes a sustained elevation of intracellular Ca2+ and depletion of the inositol 1, 4, 5-trisphosphate-sensitive intracellular Ca2+ stores. In the absence of extracellular Ca2+, the increase in intracellular Ca2+ concentration ([Ca2+]i) was transient, suggesting that thapsigargin activates both intracellular mobilization and the influx of Ca2+ from extracellular space. These results are consistent with the proposal that the depletion of the inositol 1, 4, 5-trisphosphate-sensitive intracellular Ca2+ pool serves as a signal for Ca2+ influx.
    Neuroreport 04/1991; 2(3):124-6. · 1.40 Impact Factor
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    ABSTRACT: The effects of inhibitors of voltage-sensitive calcium channels (VSCC) on K(+)-evoked [3H]D-aspartate release from rat hippocampal slices and the K(+)-evoked increase in intracellular calcium in neocortical neurons in primary culture were examined. K+ caused a concentration-dependent release of [3H]D-aspartate that was approximately 85% dependent on the presence of extracellular calcium. Neither the marine snail toxin, omega-conotoxin GVIA, nor the dihydropyridine VSCC antagonist, nitrendipine, had any effect on K(+)-evoked release of [3H]D-aspartate. omega-Conotoxin GVIA and nitrendipine caused a relatively small (20-30%) inhibition of K(+)-evoked increase in intracellular calcium in neocortical neurons in primary culture. This suggests that K(+)-evoked [3H]D-aspartate release is not dependent on L- or N-type VSCC, whereas K(+)-evoked neuronal calcium influx was only partially dependent on L- and N-type VSCC. Verapamil, dextromethorphan and diltiazem caused a concentration-dependent inhibition of K(+)-evoked release of [3H]D-aspartate with IC50 values of 30, 100 and 120 microM, respectively. The K(+)-evoked increase in intracellular calcium was inhibited with essentially the same rank order of potency, but with slightly greater potencies (IC50 values for verapamil, diltiazem and dextromethorphan were 20, 50 and 50 microM, respectively). At 300 microM, neither verapamil, diltiazem nor dextromethorphan inhibited [3H]D-aspartate release evoked by the calcium ionophore ionomycin, suggesting that these compounds are not acting intracellularly to inhibit the ability of free cytosolic calcium to evoke release.(ABSTRACT TRUNCATED AT 250 WORDS)
    European Journal of Pharmacology 02/1991; 192(1):9-17. · 2.59 Impact Factor
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    ABSTRACT: Using primary neuronal cultures we have examined the role of extracellular Ca2+ in a receptor-regulated phosphoinositide turnover. We report that receptor (glutamic acid and acetylcholine)-activated phosphoinositide turnover requires the presence of extracellular Ca2+ (EC50 = 21.1 microM). The requirement for Ca2+ appears to be at an intracellular level and is highly selective for Ca2+. We also found that several inorganic and organic Ca2+ channel blockers, including La3+ and verapamil, inhibit phosphoinositide turnover. However, the pharmacological profile of these agents in this regard was distinct from their actions at the voltage-sensitive Ca2+ channels. To explain the above requirement for extracellular Ca2+ in agonist-stimulated phosphoinositide turnover and its sensitivity to Ca(2+)-channel blockers, we propose a hypothetical model suggesting that Ca2+, following IP-3-mediated mobilization, exerts a facilitatory action on the activity of receptor-phospholipase C complex. We further propose that in the absence of extracellular Ca2+ or in the presence of certain Ca(2+)-channel blockers, refilling of calciosomes is ineffectual or inhibited, causing its depletion and subsequent inactivation of agonist-stimulated phosphoinositide turnover.
    Journal of Molecular Neuroscience 02/1991; 3(1):19-27. · 2.89 Impact Factor
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    ABSTRACT: HA-966 (1-hydroxy-3-aminopyrrolidone-2) is an antagonist at the glycine allosteric site of the N-methyl-D-aspartate receptor ionophore complex. Unlike presently known glycine antagonists, HA-966 is chiral. We report stereoselectivity for the (R)-enantiomer at the glycine antagonist site. In [3H]glycine binding, the (R)-enantiomer has an IC50 of 4.1 +/- 0.6 microM. The racemic mixture has an IC50 of 11.2 +/- 0.5 microM, whereas (S)-HA-966 has an IC50 greater than 900 microM. In glycine-stimulated [3H]1-[1-(2- thienyl)cyclohexyl]piperidine binding, the (R)-enantiomer inhibits with an IC50 of 121 +/- 61 microM, whereas the racemic mixture has an IC50 of 216 +/- 113 microM and (S)-HA-966 is inactive. The inhibition by (R)-HA-966 can be prevented by the addition of glycine. (R)-HA-966 and racemic HA-966, but not (S)-HA-966, also prevent N-methyl-D-aspartate cytotoxicity in cortical cultures. The (R)-enantiomer and, less potently, the (S)-enantiomer inhibit N-methyl-D-aspartate-evoked [3H]norepinephrine release from rat hippocampal slices (IC50 values of about 0.3 mM and 1.6 mM, respectively), but only the inhibition by (R)-HA-966 is reversed by added glycine. In glutamate-evoked contractions of the guinea pig ileum, (R)-HA-966 causes a glycine-reversible inhibition (IC50 of about 150 microM), whereas (S)-HA-966 is much less potent (IC50 of greater than 1 mM). These results demonstrate stereoselectivity of the glycine antagonist site of the N-methyl-D-aspartate receptor complex in a variety of tissues and assays. The stereoselectivity also confirms the specificity of N-methyl-D-aspartate receptors in glutamate-evoked contractions of the guinea pig ileum, and supports their similarity to central N-methyl-D-aspartate receptors.
    Journal of Neurochemistry 11/1990; 55(4):1346-51. · 3.97 Impact Factor
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    ABSTRACT: Based on radioligand binding and electrophysiological studies, quinoxalinediones such as 6,7-dinitroquinoxaline-2,3-dione (DNQX) have been shown to be potent competitive antagonists at the quisqualate and kainate subtypes of the glutamate receptor. In this report we have examined the effects of DNQX on excitatory amino acid neurotoxicity and evoked neurotransmitter release. DNQX was found to be a potent neuroprotective agent against glutamate and N-methyl-D-aspartate (NMDA) neurotoxicity. The data suggest that this neuroprotective activity of DNQX is due to its antagonism of the coagonist activity of glycine at the NMDA receptor-channel complex. The specificity of DNQX for the glycine site associated with the NMDA receptor-channel complex was confirmed in radioligand binding and neurotransmitter release studies. DNQX also prevented kainate neurotoxicity and kainate-evoked neurotransmitter release, presumably by direct competition for the kainate receptor. DNQX, however, did not prevent quisqualate neurotoxicity, suggesting that a novel quisqualate-preferring receptor insensitive to DNQX may mediate quisqualate toxicity.
    Journal of Neurochemistry 08/1990; 55(1):114-21. · 3.97 Impact Factor
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    ABSTRACT: Activation of phosphoinositide metabolism is an early event in signal transduction for a number of neurotransmitters and hormones. In primary cultures of rat neurocortical cells, various excitatory amino acids stimulate inositol phosphate production with a rank order of potency of quisqualate greater than ibotenate greater than glutamate greater than kainate, N-methyl-D-aspartate greater than alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate. This response to excitatory amino acids was insensitive to a variety of excitatory amino acid antagonists including 6-cyano-7-nitroquinoxaline-2,3-dione, 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphonate, and 2-amino-4-phosphonobutyrate. The individual responses of quisqualate-, ibotenate-, and kainate-stimulated inositol phosphate production were not additive. These results suggest that phosphoinositide metabolism activated by excitatory amino acids is mediated by a unique quisqualate-preferring receptor that is not antagonized by known N-methyl-D-aspartate and non-N-methyl-D-aspartate antagonists, and is relatively insensitive to alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate.
    Journal of Neurochemistry 06/1990; 54(5):1461-6. · 3.97 Impact Factor
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    ABSTRACT: Current evidence indicates that glutamate acting via the N-methyl-D-aspartate (NMDA) receptor/ion channel complex plays a major role in the neuronal degeneration associated with a variety of neurological disorders. In this report the role of glycine in NMDA neurotoxicity was examined. We demonstrate that NMDA-mediated neurotoxicity is markedly potentiated by glycine and other amino acids, e.g., D-serine. Putative glycine antagonists HA-966 and 7-chlorokynurenic acid were highly effective in preventing NMDA neurotoxicity, even in the absence of added glycine. The neuroprotective action of HA-966 and 7-chlorokynurenic acid, but not that of NMDA antagonists 3-(2-carboxypiperazine-4-yl)propylphosphonate and MK-801, could be reversed by glycine. These results indicate that glycine, operating through a strychinine-insensitive glycine site, plays a central permissive role in NMDA-mediated neurotoxicity.
    Journal of Neurochemistry 04/1990; 54(3):849-54. · 3.97 Impact Factor
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    ABSTRACT: Glycine caused a concentration-dependent evoked release of [3H]norepinephrine from rat hippocampal brain slices. Other amino acids evoked [3H]norepinephrine release with a rank order of potency: L-serine greater than or equal to glycine greater than beta-alanine greater than D-serine. Strychnine inhibited [3H]norepinephrine release evoked by both glycine and L-serine, but was less effective in inhibiting the release evoked by N-methyl-D-aspartate (NMDA) and kainic acid. Inhibitors of the NMDA receptor/ionophore complex, MK-801, CPP and Mg++, as well as the strychnine-insensitive glycine receptor antagonist, HA-966, caused an incomplete inhibition (maximum approximately 60%) of glycine-evoked [3H]norepinephrine release. The potencies with which MK-801, CPP and Mg++ inhibited glycine- and NMDA-evoked [3H]norepinephrine release were very similar. The combination of MK-801 plus kynurenic acid, a nonselective glutamate receptor antagonist, caused no greater inhibition of glycine-evoked release than MK-801, alone. omega-Conotoxin GVIA, an inhibitor of neuronal L- and N-type voltage-sensitive calcium channels, inhibited glycine-evoked [3H]norepinephrine release by approximately 50%, whereas the L-channel inhibitor PN 200-110 had no significant effect. The combination of MK-801 plus omega-conotoxin GVIA caused only a slightly greater inhibition (P greater than .05) of glycine-evoked release than MK-801 alone. Tetrodotoxin inhibited glycine-evoked release of [3H]norepinephrine by approximately 75%. The inhibitory effects of tetrodotoxin and omega-conotoxin GVIA suggest that voltage-sensitive sodium channels and N-type voltage-sensitive calcium channels are important mediators of glycine-evoked release of [3H]norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)
    Journal of Pharmacology and Experimental Therapeutics 03/1990; 252(2):574-80. · 3.89 Impact Factor
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    ABSTRACT: ICI 198,256, a member of the cinnoline series, was shown to be a potent anxiolytic agent in several species of animals. In addition, ICI 198,256 exhibited potent activity as an antagonist of both metrazole and bicuculline-induced convulsions. The salient features of ICI 198,256 are that it possesses minimal sedative liability, lower ethanol interaction and possibly lower dependence liability than benzodiazepines (e.g., diazepam). Neurochemically, this structurally novel anxiolytic compound is potent and selective for the Type 1 (cerebellar) BZ receptors in vivo as well as ex vivo, and in addition shows an agonist BZ-like profile in a variety of systems. Thus, ICI 198,256 may offer several significant advantages in the treatment of anxiety in humans than existing benzodiazepines.
    Progress in clinical and biological research 02/1990; 361:483-8.
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    ABSTRACT: A series of 1-substituted 4-amino-1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid esters and amides were synthesized and screened for anxiolytic activity in the shock-induced suppression of drinking (SSD) test. The compounds were also tested for their ability to displace [3H]flunitrazepam (FLU) from brain benzodiazepine (BZ) binding sites. Many compounds were active in these screens and, additionally, demonstrated a selectivity for the type 1 BZ (BZ1) receptor over the type 2 BZ (BZ2) receptor as indicated by Hill coefficients significantly less than unity and by analysis of [3H]FLU binding results from different brain regions. Based on the results of structure-activity studies of these compounds, a hypothesis was proposed to explain the structural features necessary for optimal interaction with brain BZ receptors. A detailed pharmacological evaluation of one of the most potent behaviorally active compounds (27) demonstrated it to be BZ1 selective; also, in comparison to diazepam, 27 showed minimal sedative and alcohol interactive properties at therapeutically effective doses.
    Journal of Medicinal Chemistry 01/1990; 32(12):2561-73. · 5.61 Impact Factor
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    ABSTRACT: : HA-966 (1-hydroxy-3-aminopyrrolidone-2) is an antagonist at the glycine allosteric site of the N-methyl-d-aspartate receptor ionophore complex. Unlike presently known glycine antagonists, HA-966 is chiral. We report stereoselectivity for the (R)-enantiomer at the glycine antagonist site. In [3H]glycine binding, the (R)-enantiomer has an IC50 of 4.1 ± 0.6 μM. The racemic mixture has an IC50 of 11.2 ± 0.5 μM, whereas (S)-HA-966 has an IC50 greater than 900 μM. In glycine-stimulated [3H]l-[1-(2-thienyl)cyclohexyl] piperidine binding, the (R)-enantiomer inhibits with an IC50 of 121 ± 61μM, whereas the racemic mixture has an IC50 of 216 ± 113 μM and (S)-HA-966 is inactive. The inhibition by (R)-HA-966 can be prevented by the addition of glycine. (R)-HA-966 and racemic HA-966, but not (S) HA-966, also prevent N-methyl-d-aspartate cytotoxicity in cortical cultures. The (R)-enantiomer and, less potently, the (S)-enantiomer inhibit N-methyl-d-aspartate-evoked [3H]norepinephrine release from rat hippocampal slices (IC50 values of about 0.3 mM and 1.6 mM, respectively), but only the inhibition by (R)-HA-966 is reversed by added glycine. In glutamate-evoked contractions of the guinea pig ileum, (R)-HA-966 causes a glycine-reversible inhibition (IC50 of about 150 μM), whereas (S)-HA-966 is much less potent (IC50 of greater than 1mM). These results demonstrate stereoselectivity of the glycine antagonist site of the N-methyl-d-aspartate receptor complex in a variety of tissues and assays. The stereoselectivity also confirms the specificity of N-methyl-d-aspartate receptors in glutamate-evoked contractions of the guinea pig ileum, and supports their similarity to central N-methyl-d-aspartate receptors.
    Journal of Neurochemistry 01/1990; 55(4):1346-1351. · 3.97 Impact Factor
  • J B Patel, R E Giles
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    ABSTRACT: The proconvulsive tendency of the novel carbapenem, meropenem was compared to that of imipenem, alone and in combination with cilastatin. The potentiation of metrazole-induced convulsions in mice was measured. Both imipenem and imipenem/cilastatin caused significant potentiation of metrazole-induced convulsions at a dose of 200 mg/kg, i.v. In contrast, meropenem (50-400 mg/kg, iv) failed to exhibit any significant potentiation of metrazole-induced seizures.
    Journal of Antimicrobial Chemotherapy 10/1989; 24 Suppl A:307-9. · 5.34 Impact Factor
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    ABSTRACT: The role of endogenous glycine in supporting N-methyl-D-aspartate (NMDA)-evoked neurotransmitter release was investigated. HA-966 (1-hydroxy-3-aminopyrrolidone-2) inhibited NMDA-evoked release of [3H]norepinephrine from rat hippocampal brain slices, but was much less effective in inhibiting [3H]norepinephrine release evoked by kainic acid (KA). Glycine (1 mM) reversed the HA-966 (1 mM) antagonism of NMDA-evoked release of [3H]norepinephrine. Strychnine (10 microM) had no effect on the ability of glycine to reverse HA-966 antagonism of NMDA-evoked neurotransmitter release. Other amino acids were also capable of reversing the HA-966 antagonism of NMDA-evoked [3H]norepinephrine release with a rank order of potency: D-serine greater than or equal to glycine much greater than L-serine approximately beta-alanine. These same compounds inhibited strychnine-insensitive [3H]glycine binding to rat cortical membrane fragments with a rank order of potency: glycine greater than D-serine much greater than L-serine greater than or equal to beta-alanine. In addition, HA-966 inhibited [3H]glycine binding (IC50 = 8.5 microM). The results suggest that HA-966 antagonism of NMDA-evoked neurotransmitter release is due to the inhibition of endogenous glycine acting at a strychnine-insensitive modulatory glycine site associated with the NMDA receptor/ionophore complex.
    European Journal of Pharmacology 09/1989; 166(3):393-400. · 2.59 Impact Factor
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    ABSTRACT: Physical dependence was rapidly induced in mice by administering diazepam intraperitoneally twice daily using an incremental dosing regimen (50 to 450 mg/kg) for nine consecutive days. Withdrawal was induced (24 hr after the last dose) by administration of a benzodiazepine antagonist, RO-15-1788 (10 mg/kg, IP). All of the mice exhibited clear-cut withdrawal symptoms (i.e., convulsions) within minutes of antagonist treatment. This method offers a simple, reliable, high throughput procedure for the assessment of benzodiazepine-like physical dependence liability and withdrawal, and it would be useful for screening purposes.
    Pharmacology Biochemistry and Behavior 05/1988; 29(4):753-4. · 2.61 Impact Factor
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    ABSTRACT: Tracazolate is a pyrazolopyridine anxiolytic that enhances the binding of [3H]-flunitrazepam [( 3H]FLU) to brain tissue. The discovery that a metabolite of tracazolate, desbutyltracazolate, was a weak inhibitor of [3H]FLU binding led to the synthesis of a series of potent anxiolytics. From this series, ICI 190,622 emerged as a viable drug candidate, being a potent anxiolytic in rats and monkeys. This anxiolytic agent appears to produce only minimal sedation. Furthermore, ICI 190,622 appears less likely to potentiate the actions of ethanol than diazepam. ICI 190,622 is also a potent anticonvulsant (anti-metrazol ED50 = 1.1 mg/kg, PO) in rodents. Neurochemically, ICI 190,622 is similar to the benzodiazepine anxiolytics. In vitro, ICI 190,622 competitively inhibited [3H]FLU binding in cerebral cortex with an IC50 of 81 nM and was 4.3-fold more potent in the cerebellum (IC50 = 19 nM). This suggests a selectivity for the Type 1 benzodiazepine binding site. In contrast, diazepam showed similar affinities in both regions (cerebral cortex = 7 nM and cerebellum = 9 nM). Following oral administration, ICI 190,622 displaced [3H]FLU binding from cerebellar membranes more potently than diazepam (ED50 = 3 and 6 mg/kg, respectively, 1 hour after administration). Thus, ICI 190,622 should be an effective anxiolytic with significant advantages over benzodiazepines.
    Pharmacology Biochemistry and Behavior 05/1988; 29(4):775-9. · 2.61 Impact Factor
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    ABSTRACT: Pyrazolopyridines (PZP's) in general represent a chemically unique class of non-sedative anxiolytic agents. Tracazolate (ICI 136,753) is a member of pyrazolopyridine series that has shown anxiolytic properties in animal models. Tracazolate demonstrates a wider separation between sedative and therapeutic doses than do benzodiazepines. In addition, tracazolate appears to cause fewer adverse interactions than the benzodiazepines in combination with barbiturates and alcohol. In interaction studies, tracazolate potentiated both the antimetrazol and anticonflict effects of chlordiazepoxide. Pyrazolopyridines cause enhancement of both 3H-flunitrazepam (3H-FLU) and 3H-GABA to their binding sites in brain. The enhancement of 3H-FLU binding by PZP's and GABA are additive and reversed by bicuculline. The enhancement of 3H-GABA binding by PZP's and benzodiazepines are additive and reversed by picrotoxin. It is hypothesized that the action of PZP's, and particularly tracazolate, may be related to their effects upon a GABA-stimulated chloride ionophore site. Finally, benzodiazepine antagonists (e.g., RO-15 1788) fail to reverse either the anxiolytic properties of 3H-FLU enhancers or their 3H-GABA binding enhancement effects. In contrast, benzodiazepine antagonists readily reverse the anxiolytic effects of benzodiazepines and non-benzodiazepines which cause 3H-FLU displacement. These data suggest that tracazolate, a non-benzodiazepine, has a pharmacological profile suggestive of novel anxiolytic activity.
    Pharmacology Biochemistry and Behavior 11/1985; 23(4):675-80. · 2.61 Impact Factor
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    ABSTRACT: Using a new rat conflict test it was found that 30% of the subjects failed to respond to benzodiazepines and other anxiolytic agents. This value is similar to that reported using more classical procedures such as the Geller-Seifter and Vogel conflict tests. Biochemical analysis of various brain regions from responder (R) and non-responder (NR) subjects revealed no significant differences in 5-HT1, 5-HT2, GABA receptor binding or GABA-activated benzodiazepine binding. However, a small, but significant, increase in basal benzodiazepine binding was noted in the hippocampus of NR rats. These findings suggest that the insensitivity of these animals to anxiolytics is probably unrelated to an alteration in serotonin, GABA or benzodiazepine binding sites in brain.
    Life Sciences 07/1984; 34(26):2647-53. · 2.56 Impact Factor