Biomedical subjects

P Skolnick

Publications and source records attributed to P Skolnick.

At least 91 records · Page 5Linked to original sources

PubMed1994

The putative anti-addictive drug ibogaine is a competitive inhibitor of [3H]MK-801 binding to the NMDA receptor complex.

Ibogaine is a putative anti-addictive drug with potential efficacy for the treatment of opiate, stimulant, and alcohol abuse. We now report ibogaine is a competitive inhibitor (Ki, 1.01 +/- 0.1 microM) of [3H]MK-801 binding to N-methyl-D-aspartate (NMDA) receptor coupled cation channels. Since MK-801 can attenuate the development of tolerance to morphine and alcohol as well as sensitization to stimulants in preclinical studies, the reported ability of ibogaine to modify drug-seeking behavior in man may be attributable to a blockade of NMDA receptor coupled cation channels.

Animals↗

PubMed1994

The potential for safer anaesthesia using stereoselective anaesthetics.

The molecular mechanisms by which inhalational agents produce anaesthesia remains a subject of controversy, despite a history of clinical use spanning two centuries. The demonstration of a significant difference in the anaesthetic potencies of (+)- and (-)-isoflurane provides compelling evidence for the hypothesis that proteins, rather than lipids, are the primary sites of anaesthetic action. Moreover, the optically active isomers of volatile anaesthetics provide new tools to discriminate among putative molecular targets of anaesthesia. A difference in the anaesthetic potencies of (+)- and (-)-isoflurane, together with an apparent lack of stereoselectivity in their myocardial suppression, raises the possibility that an optically active volatile agent may have clinical advantages over currently available racemic mixtures.

Anesthesia, Inhalation↗

PubMed1994

Sex differences, weapon focus, and eyewitness reliability.

Two aspects of eyewitness identification were tested: sex differences in eyewitness reliability and an explanation of the weapon focus effect that is based on object salience. One hundred ninety-one male and female American college students watched a slide sequence that depicted a male or female target person enacting a simple behavioral progression while holding various objects. Afterward, the subjects attempted to identify the target person in a photospread and to recall physical details about him or her on a questionnaire. The results confirmed a predicted own-sex identification bias effect (p < .001) but did not support the object salience hypothesis. An interaction between subject sex and object indicated that men and women attended to and were distracted by different types of objects (p < .009).

Female↗

PubMed1994

Inhibition of [3H]isradipine binding to L-type calcium channels by the optical isomers of isoflurane. Lack of stereospecificity.

BACKGROUND: The dose-dependent myocardial depression of volatile general anesthetics such as isoflurane has been linked to blockade of L-type Ca2+ channels. The effects of (+)- and (-)-isoflurane on the inhibition of [3H]isradipine binding to L-type Ca2+ channels in membranes prepared from mouse heart were examined. In addition, because there is a stereo-specific effect of these isomers on sleep time in mice, the potential contribution of L-type Ca2+ channels to isoflurane-induced sleep was assessed by determining whether a similar stereoselectivity would be manifested at these sites in cerebral cortical membranes. METHODS: The effects of isoflurane stereoisomers on the binding of an L-type Ca2+ channel ligand ([3H]isradipine) were studied in cardiac and brain cortical membranes. Their potencies and effects on the Kd and Bmax of [3H]isradipine were measured. RESULTS: Pharmacologically relevant concentrations of (+)- and (-)-isoflurane inhibited [3H]isradipine binding. The IC50 values for (+)-isoflurane were 0.48 +/- 0.02% and 0.40 +/- 0.01% in heart and brain membranes, respectively. The values for (-)-isoflurane were not significantly different from the respective values for the (+)-isomer. Saturation analysis demonstrated (+)- and (-)-isoflurane inhibited [3H]isradipine binding by significantly reducing Bmax and increasing Kd, but there were no significant differences between these isomers in either tissue. CONCLUSIONS: The stereoisomers of isoflurane are equipotent as inhibitors of [3H]isradipine binding to L-type Ca2+ channels. This lack of stereoselectivity between (+)- and (-)-isoflurane indicates that the [3H]isradipine site on L-type Ca2+ channels in brain does not contribute to the differences in isoflurane-induced sleep time reported for these stereoisomers. Taken with a lack of stereoselectivity at L-type Ca2+ channels in heart, an optically resolved isomer of isoflurane may have clinical advantages compared to the current racemic mixture.

Animals↗

PubMed1994

Chronic exposure to benzodiazepine receptor ligands uncouples the gamma-aminobutyric acid type A receptor in WSS-1 cells.

Chronic exposure to benzodiazepines can result in an "uncoupling" of gamma-aminobutyric acid (GABA) receptors and benzodiazepine receptors (BzR) both in primary neuronal cell cultures and in vivo. The effect of chronic exposure to BzR ligands was examined in an engineered cell line (WSS-1) stably expressing "type I" GABAA receptors. Chronic exposure to flurazepam produced a concentration- (EC50, approximately 1.1 microM after a 48-hr exposure) and time-dependent (t1/2, approximately 3 hr at 100 microM) reduction in the efficacy (Emax) of GABA to enhance [3H]flunitrazepam binding to BzR, a characteristic of uncoupling in native GABAA receptor isoforms. Uncoupling of GABAA receptors and BzR without concomitant changes in BzR density was also produced by chronic exposure to other, structurally diverse, BzR ligands, including Ro 15-1788 and methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, but was not manifested after exposure to the 5-hydroxytryptamine reuptake blocker fluoxetine. Chronic (12-48-hr) exposure to flurazepam did not remarkably alter levels of alpha 1 and gamma 2 mRNAs, which constitute GABAA receptors in this cell line. Based on these findings, it is hypothesized that uncoupling of GABAA receptors and BzR in this engineered cell line can proceed without the elaboration of additional novel subunits and could involve either post-translational modification of GABAA receptor proteins or changes in subunit stoichiometry.

Cell Line↗

PubMed1994

Differential effects of compounds that act at strychnine-insensitive glycine receptors in a punishment procedure.

The anxiolytic and memory-impairing effects of compounds that act at strychnine-insensitive (SI) glycine receptors were examined and compared with those of a competitive N-methyl-D-aspartate antagonist, 2-amino-7-phosphonoheptanoic acid (AP7); a use-dependent channel blocker, dizocilpine; and a benzodiazepine agonist, diazepam (DZP). Mice were trained to avoid a dark compartment and their latencies to step through were measured either within 1 hr after training in the presence of the drug (to assess the anxiolytic effects) or 24 hr after pre- or post-training treatment (to assess the effects on learning and memory). Post-training administration of the glycinergic compounds 1-aminocyclopropanecarboxylic acid, 7-chlorokynurenic acid and D-cycloserine reduced step-through latencies when testing was performed 30 min after drug treatment and within 1 h after training. Latencies were unaltered by these glycinergic compounds when testing was performed 24 hr later. Similar results were obtained with AP7 and DZP. In contrast, an amnesic dose of pentylenetetrazole reduced latencies both within 1 and 24 hr after training. Pretreatment with glycine abolished the reduction in latencies observed with SI glycine receptor ligands 1 hr after training but did not antagonize the reduction produced by AP7. Pretraining administration of SI glycine receptor ligands did not alter step-through latencies measured 24 hr later. In contrast, under these same conditions, AP7, dizocilpine and DZP produced a significant reduction in latencies. These results demonstrate that compounds that act at SI glycine receptors do not impair learning and memory at doses that are anxiolytic in a single-trial punishment paradigm.

2-Amino-5-phosphonovalerate↗

PubMed1994

Adaptation of the N-methyl-D-aspartate receptor complex following chronic antidepressant treatments.

Chronic (14 day) but not acute (1 day) treatment of mice with clinically active antidepressants produces a significant (approximately 1.8-4.3 fold) reduction in the potency of glycine to inhibit [3H]-5,7-dichlorkynurenic acid (5,7-DCKA) binding to strychnine-insensitive glycine receptors in neocortical membranes. Moreover, these effects were not observed following chronic treatment with a variety of nonantidepressant drugs such as D-deprenyl, chlorpromazine, salbutamol, scopolamine and chlordiazepoxide. The time course and dose-response relationships for this effect were examined after treatment with two representative antidepressant drugs (imipramine and citalopram) and electriconvulsive shock (ECS). Increases in the IC50 of glycine to inhibit [3H]-5,7-DCKA binding were observed after treatment for 7 days with ECS, 10 days with citalopram and 14 days with imipramine, respectively, and were no longer apparent by the 10th day after cessation of treatment. These findings indicate that the antidepressant-induced reduction in the IC50 of glycine to inhibit [3H]-5,7-DCKA binding is: 1) a slowly developing, adaptive phenomenon; 2) remarkably persistent after cessation of treatment; and 3) a significantly better predictor of antidepressant activity (22 of 23 drugs) than either beta adrenoceptor down-regulation (15 of 23 drugs) or efficacy in the forced swim test (13 of 23 drugs) [P < .01 vs. each measure, Fisher's Exact Test]. The ability of antidepressants drawn from every principal therapeutic class to effect adaptive changes in the N-methyl-D-aspartate receptor complex is consistent with the hypothesis that this ligand-gated ion channel serves as a final common pathway of antidepressant action and indicates that glutamatergic pathways may be involved in the pathophysiology of depression.

Adaptation, Physiological↗

PubMed1994

Verapamil is not an antidepressant in patients resistant to tricyclic antidepressants.

The effects of a calcium channel blocker (verapamil, 160-320 mg/day for 4 weeks) were studied in seven unipolar major-depressed patients resistant to treatment with tricyclic antidepressants. This regimen of verapamil did not alter either the Hamilton rating scales for depression and anxiety or the Beck depression inventory score in these patients. Thus, verapamil appears devoid of antidepressant properties in patients resistant to tricyclic antidepressants.

Adult↗

PubMed1993

Adaptation of the NMDA receptor in rat cortex following chronic electroconvulsive shock or imipramine.

Chronic (14 days) administration of either imipramine or electroconvulsive shock effected significant changes in the ligand binding properties of the NMDA (N-methyl-D-aspartate) receptor complex in rat cortex. These changes were manifested as: (1) a reduction in the potency of glycine to inhibit the binding of 5,7-dichloro[3H]kynurenic acid to strychnine-insensitive glycine receptors; and (2) a reduction in the proportion of high affinity, glycine-displaceable [3H]CGP-39653 binding to NMDA receptors. Chronic electroconvulsive shock, but not imipramine treatment also reduced the density of [3H]CGP-39653 binding sites in cortical membranes. These findings demonstrate that the ability of chronic antidepressant treatments to induce adaptive changes in the glycine and glutamate regulatory sites of the NMDA receptor is not species specific, since it obtains in rats as well as mice.

2-Amino-5-phosphonovalerate↗

PubMed1993

MK-801, but not drugs acting at strychnine-insensitive glycine receptors, attenuate methamphetamine nigrostriatal toxicity.

Repeated administration of methamphetamine (METH) results in damage to nigrostriatal dopaminergic neurons. Both competitive N-methyl-D-aspartate (NMDA) receptor antagonists and use-dependent cation channel blockers attenuate METH-induced damage. The objectives of the present study were to examine whether comparable reductions in METH-induced damage could be obtained by compounds acting at strychnine-insensitive glycine receptors on the NMDA receptor complex. Four injections of METH (5 mg/kg i.p.) resulted in a approximately 70.9% depletion of striatal dopamine (DA) and approximately 62.7% depletion of dihydroxyphenylacetic acid (DOPAC) content, respectively. A significant protection against METH-induced DA and DOPAC depletion was afforded by the use-dependent channel blocker, MK-801. The competitive glycine antagonist 7-chlorokynurenic acid (7-Cl-KA), the low efficacy glycine partial agonist (+)-3-amino-1-hydroxy-2-pyrrolidone ((+)-HA-966), and the high efficacy partial glycine agonist 1-aminocyclopropane-carboxylic acid (ACPC) were ineffective against METH-induced toxicity despite their abilities to attenuate glutamate-induced neurotoxicity under both in vivo and in vitro conditions. These results indicate that glycinergic ligands do not possess the same broad neuroprotective spectrum as other classes of NMDA antagonists.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1993

Requirements for high affinity binding of glycine analogs to the glycine site of the NMDA receptor complex.

Correlation of the isopotential contours of the optimized conformations of a series of alpha-amino acids, in their neutral and zwitterionic forms, with their potencies to inhibit [3H]glycine binding and to enhance [3H]10,11-dihydro-5-methyl-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) binding, leads to the following conclusions: (a) steric congestion at the amino group is detrimental to binding potency; (b) a zwitterionic amino acid is required for high affinity to the receptor; (c) a conformation in which the carboxylate group is at a 90 degrees dihedral angle to the ammonium nitrogen is preferred for high affinity; and (d) placing the carbon backbone of the zwitterionic alpha-amino acid, in its preferred conformation, above the plane defined by the ammonium nitrogen and the carboxylate oxygen atoms, and viewing the molecule along the nitrogen to carboxylate carbon axis, there is a space forbidden to the ligand (receptor-required-space) to the left.

Animals↗

PubMed1993

Labelling of diazepam-sensitive and -insensitive benzodiazepine receptors with [3H]tert-butyl-8-chloro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-a][1,4]benzodiazepine 3-carboxylate (ZG-63).

A diazepam-insensitive subtype of benzodiazepine receptor has been identified in the cerebella of several species, including man. t-Butyl-8-chloro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4] benzodiazepine 3-carboxylate (ZG-63) was recently described as a selective, high affinity ligand at diazepam-insensitive benzodiazepine receptors. This compound was tritiated, and its properties as a radioligand evaluated in rat brain membranes. Consistent with the high affinity and selectivity described for the non-radioactive form of this compound, saturation analyses of [3H]ZG-63 binding to cerebellar diazepam-insensitive and other, diazepam-sensitive benzodiazepine receptors revealed Kd values of 2.6 +/- 0.2 nM and 10.6 +/- 1.4 nM, respectively. The density (Bmax) of cerebellar diazepam-insensitive receptors labelled with [3H]ZG-63 was not significantly different from values obtained with the prototypical diazepam-insensitive receptor ligand [3H]Ro 15-4513, representing approximately 30% of total cerebellar benzodiazepine receptors. [3H]ZG-63 also labelled cortical diazepam-sensitive benzodiazepine receptors, with Bmax values that were not significantly different from those obtained with [3H]flunitrazepam. Diazepam-insensitive benzodiazepine receptors in rat cerebral cortex could be detected with [3H]ZG-63, but the densities of these sites are a very minor component (< or = 5%) of total benzodiazepine receptors. In the presence of GABA, [3H]ZG-63 behaved as a 'gamma-aminobutyric acid (GABA) -positive', 'GABA-negative', and 'GABA-neutral' ligand at cortical diazepam-sensitive receptors, cerebellar diazepam-sensitive receptors, and cerebellar diazepam-insensitive benzodiazepine receptors, respectively. This profile differs from the prototype diazepam-insensitive receptor ligand, [3H]Ro 15-4513. Competition studies demonstrated a very high correlation (r2 = 0.98; P < 0.002) between the potencies of a series of benzodiazepine receptor ligands to inhibit [3H]ZG-63 and [3H]Ro 15-4513 binding to cerebellar diazepam-insensitive receptors. The high affinity and selectivity of [3H]ZG-63 for diazepam-insensitive receptors (diazepam-insensitive/diazepam-sensitive ratio of approximately 0.25) together with a GABA-shift profile which differs from Ro 15-4513 suggests that this compound may be useful in elucidating the function(s) of this benzodiazepine receptor subtype.

Animals↗

PubMed1993

Ca2+ antagonists effect an antidepressant-like adaptation of the NMDA receptor complex.

Chronic, but not acute treatment of mice with nimodipine and diltiazem produce significant increases in the IC50 of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding in cerebral cortex. Such adaptive changes in the ligand binding properties of the NMDA receptor complex are also manifested following chronic treatment with antidepressants from every principal therapeutic class. These findings indicate voltage-dependent calcium channel antagonists would be strong candidates for rigorous clinical trials in depressive disorders.

Animals↗

PubMed1993

Polyamine-like actions of peptides derived from conantokin-G, an N-methyl-D-aspartate (NMDA) antagonist.

Conantokins-T and -G are highly conserved polypeptides derived from Conus venoms. The N-methyl-D-aspartate (NMDA) antagonist properties of these compounds have been attributed to a potent noncompetitive inhibition of polyamine responses. Substitution of the highly conserved gamma-carboxyglutamate residues as well as modification of the N and C termini of conantokin-G abolished the inhibition of polyamine responses at the NMDA receptor complex. However, several of these modified polypeptides closely mimicked the neurochemical profile of polyamines at the NMDA receptor complex. One of these derivatives, Tyr0-conantokin-G, was found to be the most potent compound exhibiting polyamine-like actions at the NMDA receptor complex described to date, approximately 7-fold more potent than spermine. Circular dichroism studies demonstrate a significant alpha-helical content in conantokin-G (27% in aqueous medium). However, this alpha-helicity is not sufficient for the NMDA antagonist action of the parent peptide and is neither necessary nor sufficient for the polyamine-like behavior of several conantokin-G analogs. The modified conantokin-G derivatives described in this report should be useful probes for examining the role of both polyamines and the polyamine recognition site in the operation of the NMDA receptor complex.

Amino Acid Sequence↗

PubMed1993

Stereospecific actions of the inhalation anesthetic isoflurane at the GABAA receptor complex.

The inhalation anesthetic isoflurane stereoselectively modulates ligand binding to the GABAA receptor complex. The (+)-isomer of isoflurane was more potent and efficacious than the (-)-isomer in enhancing [3H]flunitrazepam binding to benzodiazepine receptors. For example, concentration effect curves for Cl- enhancement of [3H]flunitrazepam binding were significantly different (P < 0.001) in the presence of (+)- and (-)-isoflurane (0.44 and 0.88 mM). At the higher anesthetic concentration, they potency of Cl- to increase [3H]flunitrazepam binding was increased 3.2- and 1.45-fold by (+)- and (-)-isoflurane, respectively (P < 0.05). Likewise, concentration-effect curves for (+) isoflurane-enhanced [3H]flunitrazepam binding were significantly different (P < 0.05-P < 0.001) from the (-)-isomer in the presence of 0-200 mM Cl-. Stereoselectivity was not observed with respect to the potencies of these enantiomers as inhibitors of [35S]t-butylbicyclophosphorothionate (TBPS) binding to sites within the Cl- ionophore. In this measure, the isomers had similar potencies (P > 0.05), although at higher concentrations (> 0.1 mM) (+)-isoflurane produced significantly more inhibition than (-)-isoflurane. While the absolute potency differences between isomers were modest (< or = 2-fold) and measure dependent, these effects were manifested at clinically relevant concentrations of isoflurane and are consistent with in vivo studies demonstrating (+)-isoflurane is a more effective anesthetic than the (-)-isomer. This is the first demonstration of an inhalation anesthetic producing a stereoselective perturbation of the GABAA receptor complex.

Animals↗

PubMed1993

Synthetic and computer-assisted analysis of the structural requirements for selective, high-affinity ligand binding to diazepam-insensitive benzodiazepine receptors.

Several 1,4-diazepines were recently reported to bind with high affinities to the "diazepam-insensitive" (DI) isoform of the benzodiazepine receptor (BzR) (Korpi, E.R.; Uusi-Oukari, M.; Wegelius, K. Eur. J. Pharm. 1992, 213, 323-329. Wong, G.; Skolnick, P. Eur. J. Pharmacol. Mol. Pharm. Sec. 1992, 225, 63-68). However, only the putative ethanol antagonist 1 (Ro 15-4513) displayed modest selectivity for the DI site compared to other "diazepam-sensitive" (DS) BzR isoforms. In order to probe the requirements for selective, high-affinity binding to the DI site, the affinities of 47 benzodiazepines have been determined at both DI and DS BzR sites. In addition, single X-ray crystallographic analyses for three of these derivatives, 5 (Ro 17-1812), 6 (Ro 16-6028), and 42 (Ro 14-5974), are reported. The radioligand binding studies reveal that modifications to the 3-, 7-, and 8-positions of 6-oxoimidazo[1,5-alpha] [1,4]benzodiazepines have a marked influence on the Ki(DI)/Ki(DS) ratios. In order to more precisely determine the structural requirements for both high affinity and selectivity at DI BzR relative to DS, 3D-QSAR analyses were carried out on ligand affinities at both of these BzR isoforms. This analysis was based, in part, on the new X-ray crystallographic data. Satisfactory cross-validated regression equations were obtained individually for the logarithms of ligand affinities at DI and DS as well as for the differences of the logarithms of their affinities at these two isoforms (cross-validated R2 > 0.70 for all three regression equations). The steric and electrostatic 3D-QSAR DI and DS maps are in qualitative accord with the structure-activity relationship (SAR) data. Furthermore, the DI and DI/DS maps may be useful in the design of ligands with enhanced DI affinity and DI/DS selectivity, respectively.

Animals↗

PubMed1993

Structure-activity relationship studies at the benzodiazepine receptor (BZR): a comparison of the substitutent effects of pyrazoloquinolinone analogs.

The synthesis of a series of 2-phenylpyrazolo[4,3-c]quinolin-3-one derivatives and their in vitro biological evaluation as ligands for the benzodiazepine receptor are described. The in vitro activities, as determined by an analysis of GABA shift ratios, and binding affinities of these compounds to BZR are compared in terms of the electronic, lipophilic, and steric effect changes of their substituents.

Animals↗

PubMed1993

Synthesis and evaluation of imidazo[1,5-a][1,4]benzodiazepine esters with high affinities and selectivities at "diazepam-insensitive" benzodiazepine receptors.

A series of imidazo[1,5-a][1,4]benzodiazepine esters have been synthesized with varying ester side chains and 8-position substituents. The affinities of these compounds were evaluated at both "diazepam-insensitive" (DI) and diazepam-sensitive (DS) subtypes of the benzodiazepine receptor (BZR). A profound steric effect of the 3-position ester side chain moiety was observed on ligand affinity at DI. In contrast, ester size had a less robust effect on ligand affinity at DS. The tert-butyl ester compound 8 displayed the highest affinity (Ki = 1.7 nM) for DI within a series of 8-chloro esters. Furthermore, halogens at the 8-position resulted in an enhancement of both ligand affinity and selectivity at DI among the series of tert-butyl esters examined. The 8-nitro derivative 23 and 8-isothiocyanato congener 25 had high affinities for both DI and DS but exhibited little subtype selectivity (10.8 and 2.7 nM at DI versus 14 and 3.7 nM at DS, respectively). The 8-azido tert-butyl ester 29 exhibited a significantly higher affinity (Ki = 0.43 nM) and selectivity (DI/DS ratio of 0.2) than the corresponding ethyl ester, the prototypic DI ligand 1 (Ro 15-4513). Among the compounds synthesized, 29 is the highest affinity ligand for DI described to date while its 8-bromo analog 18 is the most selective ligand (DI/DS ratio of 0.17) for this novel BZR subtype.

Animals↗