Biomedical subjects

P Skolnick

Publications and source records attributed to P Skolnick.

At least 109 records · Page 6Linked to original sources

PubMed1993

MK-801 is neuroprotective but does not improve survival in severe forebrain ischemia.

The effects of MK-801 on postischemic recovery, survival and neuronal preservation in the cortex, hippocampus and striatum were studied in Mongolian gerbils. The drug was administered 30 min prior to 20 of min forebrain ischemia induced by bilateral ligation of the carotids. Neurological recovery and survival were monitored for 7 days. At the end of the monitoring period neuronal damage was analyzed in the brains of the survivors in both groups. Treatment with MK-801 did not improve either neurological recovery or end-point survival. However, significant (P < 0.01) neuronal protection was observed in the hippocampi and striata of the drug treated animals while cortical neurons were not significantly protected. These findings demonstrate that protection against ischemic neuronal damage can be observed without concomitant improvement in either postischemic neurological recovery or survival. Protection of selectively vulnerable brain regions, often used as the predictor of the therapeutic potential of an agent, does not appear to correlate well with postischemic survival in this animal model of ischemia.

Animals↗

PubMed1993

Desensitization of the NMDA receptor complex by glycinergic ligands in cerebellar granule cell cultures.

Glutamate neurotoxicity was examined in cultured cerebellar granule neurons following both prolonged (20-24 h) and brief (45 min) exposure to compounds acting at strychnine-insensitive glycine receptors. Glutamate neurotoxicity was reduced in a concentration-dependent fashion by brief exposure to the glycine partial agonists 1-aminocyclopropanecarboxylic acid (ACPC) and (+-)-3-amino-1-hydroxy-2-pyrrolidone (HA-966) and the competitive antagonist, 7-chlorokynurenic acid (7-CK) with a rank order efficacy: 7-CK > HA-966 > ACPC. Neither D-cycloserine (D-CS) nor glycine affected neurotoxicity produced by maximum glutamate concentrations, while glycine but not D-CS augmented the effects of submaximum glutamate concentrations. Prolonged exposure of cultures to either full (glycine) or partial agonists (ACPC, D-CS, HA-966) abolished the neuroprotective effects of ACPC and significantly diminished the neuroprotective effects of HA-966. In contrast, the neuroprotective effects of 7-CK were only marginally reduced by prolonged exposure to glycinergic ligands, while the neuroprotection afforded by compounds acting at other loci on the NMDA receptor complex (e.g. 2-amino-5-phosphonopentanoate (APV) and dizocilpine (MK-801)) were unaltered. These effects may represent homologous desensitization of the NMDA receptor complex at its strychnine-insensitive glycine receptor induced by prolonged exposure to glycinergic agonists and partial agonists. Nonetheless, levels of the NMDA receptor subunit zeta 1 mRNA were unaffected by prolonged exposure to ACPC, indicating the apparent desensitization could involve a post-translational modification of the NMDA receptor complex.

2-Amino-5-phosphonovalerate↗

PubMed1993

Synthesis and structure-activity relationships of 3,5-disubstituted 4,5-dihydro-6H-imidazo[1,5-a][1,4]benzodiazepin-6-ones at diazepam-sensitive and diazepam-insensitive benzodiazepine receptors.

A series of imidazobenzodiazepin-6-ones possessing varying substituents at the 3- and 5-positions were synthesized and evaluated for their affinities at diazepam-sensitive (DS) and diazepam-insensitive (DI) benzodiazepine receptors (BzR) in rat cortical and cerebellar membranes. Replacement of an ester substituent at the 3-position with a carbamate, acetylamino, formylamino, isothiocyanato, 2-oxazolinyl, 2-benzoxazolyl, or p-tolylsulfonyl groups lead to > 100-fold reductions in affinity at both DS and DI BzR. Replacement of a methyl group on the nitrogen at the 5-position with propyl, allyl, or phenethyl groups also led to significant reductions in affinity at both BzR isoforms. However, incorporation of a benzyl group yields ligands (11f,h,i and 14a-c) with moderate to high affinities at DS BzR, suggesting the presence of a hydrophobic pocket at the receptor site. Introduction of chlorine at the 7-position enhances ligand affinity at DS BzR while chlorine at the 8-position decreases affinity (IC50: 11f, 9.3 nM; 11h, 2.4 nM; 11i, 37.8 nM). In contrast, chlorine substitution at the 7- as well as the 8-position increases affinity at DI BzR (Ki: 11f, 112 nM; 11h, 20.2 nM; 11i, 10.9 nM). Compound 11 is among the few described high affinity DI-site ligands with a selectivity comparable to that of Ro 15-4513. Despite their in vitro affinities, compounds 11f, 11h, and 11i exhibit low in vivo activities that may be attributable to unfavorable metabolic or pharmacokinetic properties.

Animals↗

PubMed1993

Immunocompetence in the long sleep and short sleep mouse lines: baseline versus primed responses.

Two lines of mice which were selectively bred for high (Long Sleep; LS) and low (Short Sleep; SS) reactivities to a sedative dose of ethanol, are also differentiated by agents that act at the GABAA-receptor complex. Since this supramolecular complex may also modulate immune function, measures of immunity have been examined in these lines. In the present study the immune responsiveness before and after an allogeneic priming stimulus was investigated. Lower mitogen-induced T-cell proliferation, mixed leukocyte reaction, and cytotoxic T lymphocyte activity were found in unprimed LS compared to unprimed SS mice. In contrast, the LS line exhibited a marked augmentation of these responses after priming, while the SS mice appeared unresponsive to this challenge. Addition of splenocytes or cell-free splenic cultures from primed mice to cultures from unprimed mice suggested that differences in priming-induced cell-to-cell interactions, rather than the release of a soluble helper factor(s) into the medium, are responsible for the marked augmentation of the secondary response in LS, compared to SS mice. Fewer T-helper and T-suppressor/cytotoxic cells were found in LS compared to SS mice, and this was unaffected by priming. These results extend previous findings demonstrating a higher natural killer cell activity and rate of tumor rejection in LS mice and suggest that these lines may be useful in studying the regulatory role of the GABAA complex in immune function.

Animals↗

PubMed1993

Differences in fear motivated behaviors among inbred mouse strains.

The behavioral performance of inbred mouse strains was examined in animal models of anxiety to evaluate the potential contribution of genetic factors to fear-motivated behaviors. The preference that randomly bred mice and rats exhibit for the enclosed as opposed to the open arms of an elevated maze has been considered a fear-motivated behavior. Pronounced differences were observed in this measure among 16 inbred mouse strains. An estimate of the proportion of the variance attributable to between-strain differences, eta 2, revealed that 78% and 69% of the variance in time and number of entries in the open arms of an elevated maze, respectively, can be attributed to genetic factors. In contrast, only 27% and 42% of the variance could be attributed to between-strain differences in ambulatory activity in the open field and elevated maze, respectively. Furthermore, performance in the elevated maze was predictive of behavior in other animal models of anxiety. Thus, significant negative correlations were observed among inbred mouse strains between the percent time spent in the open arms of the elevated maze and amplitude of an acoustic startle response (rs = -0.88m P < 0.01) or latency to initiate chow consumption in a hyponeophagia paradigm (rs = -0.71, P < 0.05). These results indicate that genetic factors substantially contribute to fear motivated behaviors in these animal models of anxiety. The use of such inbred mouse strains may provide a novel approach to investigate the biochemical and genetic bases of fear.

Animals↗

PubMed1993

Sigma receptors modulate nicotinic receptor function in adrenal chromaffin cells.

Neither the physiological function of sigma (sigma) receptors nor the cellular mechanism responsible for the pharmacological effects of sigma receptor ligands is known. We now report that sigma receptor ligands noncompetitively inhibit nicotine-stimulated catecholamine release from bovine adrenal chromaffin cells in a concentration-dependent and reversible manner. The rank order of potency of ligands to inhibit nicotine-stimulated catecholamine release is significantly correlated (P < 0.005) with that observed in radioligand binding assays selective for the sigma 1 receptor subtype. This naltrexone-insensitive effect is paralleled by an inhibition of nicotine-stimulated increases in [Ca2+]i. Sigma ligands were without effect on catecholamine release or [Ca2+]i in the absence of nicotine. In addition, nicotine accelerated the association of the sigma receptor selective radioligand, [3H](+)pentazocine, to adrenal medullary homogenates while having no effect on the rate of ligand dissociation, consistent with a sigma ligand binding site closely associated with and allosterically modulated by the nicotinic acetylcholine receptor. Thus, the actions of agonists at the nicotinic acetylcholine receptor in bovine chromaffin cells are modulated by sigma 1 receptor selective ligands.

Adrenal Medulla↗

PubMed1993

Adaptive changes in the N-methyl-D-aspartate receptor complex after chronic treatment with imipramine and 1-aminocyclopropanecarboxylic acid.

Chronic (14 daily injections) treatment of mice with the prototypic tricyclic antidepressant imipramine significantly alters ligand binding to the N-methyl-D-aspartate (NMDA) receptor complex. These effects were compared to a chronic regimen of 1-aminocyclopropanecarboxylic acid, a high-affinity partial agonist at strychnine-insensitive glycine receptors which mimics the effects of imipramine in preclinical models predictive of antidepressant action. Changes in the NMDA receptor complex after chronic, but not acute treatment with imipramine were manifested as: 1) a reduction in the potency of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding to strychnine-insensitive glycine receptors; 2) a decrease in the proportion of high-affinity glycine sites inhibiting [3H]CGP 39653 binding to NMDA receptors; and 3) a decrease in basal [3H]MK-801 binding (under nonequilibrium conditions) to sites within NMDA receptor-coupled cation channels which was reversible by the addition of glutamate. These effects were observed in cerebral cortex, but not in hippocampus, striatum or basal forebrain. Chronic treatment with 1-aminocyclopropanecarboxylic acid resulted in changes which paralleled those of imipramine on ligand binding to the NMDA receptor complex, but the reduction in basal [3H]MK-801 binding did not achieve statistical significance. These findings indicate that adaptive changes in the NMDA receptor complex could be a feature common to chronic treatment with structurally unrelated antidepressants.

2-Amino-5-phosphonovalerate↗

PubMed1993

Neurochemical actions of inhalational anesthetics at the GABAA receptor complex.

Pharmacologically relevant concentrations of inhalational anesthetics such as halothane, enflurane and isoflurane enhance [3H]flunitrazepam (FLU) binding to benzodiazepine receptors prepared from well-washed membranes of murine cerebral cortex and cerebellum. These effects were concentration dependent and markedly enhanced by addition of chloride to the incubation medium. Using halothane as a prototype inhalational agent, it was observed that like barbiturates, increases in [3H]FLU binding were effected through an increase apparent in the apparent affinity of this radioligand with no accompanying change in the maximum number of binding sites. Although previous reports have demonstrated barbiturates augment gamma-aminobutyric acid-enhanced [3H]benzodiazepine binding, halothane exerts an additive effect in the nominal absence of chloride. Isoflurane produces a significant reduction in the EC50 of pentobarbital-augmented [3H]FLU binding. Halothane modestly reduced the binding of a benzodiazepine receptor inverse agonist, [3H]Ro 15-4513. Significant differences were also observed in the potencies and efficacies of both isoflurane and enflurane to enhance [3H]FLU binding to benzodiazepine receptors in cerebellar and cortical membranes. These findings provide a possible molecular basis for the clinical observation that benzodiazepines and barbiturates augment the anesthetic properties of inhalational agents. Moreover, the regional differences in anesthetic potency and efficacy reported here suggest a differential interaction of these inhalational agents among gamma-aminobutyric acidA receptor isoforms.

Administration, Inhalation↗

PubMed1993

Transduction of a discriminative stimulus through a diazepam-insensitive gamma-aminobutyric acidA receptor.

Although there appear to be a large number of possible isoforms of the gamma-aminobutyric acid (GABA)A receptor, the relationship of a particular isoform to a specific behavior or behavioral process has not been identified. In the present study we describe a functional role for a diazepam-insensitive (DI) isoform of the GABAA receptor in the control of a complex discrimination. Pigeons were trained to discriminate the benzodiazepine antagonist flumazenil (100 micrograms/kg) from vehicle by requiring 30 keypeck responses on one key when flumazenil was given and on a different key when vehicle was given. Only ligands with high affinities for DI sites fully substituted for the discriminative stimulus effects of flumazenil. A significant positive correlation was observed between ligand affinities for DI sites and ED50 values for discriminative stimulus effects. These compounds mimicked the discriminative stimulus effects of flumazenil despite partial agonist, inverse agonist or antagonist actions at other diazepam-sensitive GABAA receptors. A specific role of DI GABAA receptors in the control of this behavior was confirmed further by the inability of either a high-affinity agonist (midazolam) or antagonist (ZK 93,426) at diazepam-sensitive receptors (that possess low affinities for DI sites) to block the discriminative stimulus effects of flumazenil. These findings establish a link between a GABAA receptor isoform and a specific behavior.

Animals↗

PubMed1992

Predictive binding of beta-carboline inverse agonists and antagonists via the CoMFA/GOLPE approach.

The synthesis and affinities of six new 3-substituted beta-carbolines (6-10, 12) for the benzodiazepine receptor (BzR) are described. These analogs were used both to probe the dimensions of the hydrophobic pocket in the benzodiazepine receptor and to test the predictive ability of a previously reported 3D-QSAR regression model. Of the new analogs synthesized, the gamma-branched derivatives (isobutoxy, 7, IC50 = 93 nM; isopentoxy, 9, IC50 = 104 nM) display significantly higher affinity for the BzR than either the beta-branched (sec-butoxy, 6, IC50 = 471 nM; tert-butyl ketone, 12, IC50 = 358 nM) or delta-branched (isopentoxy, 8, IC50 = 535 nM) analogs. An exception to this rule is the gamma-branched 3-benzyloxy derivative 10 (IC50 > 1000 nM) which appears to have a chain length that is too long to be accommodated by the BzR. The standard error of prediction for these six new beta-carbolines using the original regression model is significantly lower than the standard error estimate of the cross validation runs on the training set, hence the predictions made using this model are much better than expected. In order to obtain more credible predictions, a new procedure called GOLPE (generating optimal linear PLS estimates) was used to eliminate irrelevant electrostatic and steric descriptors from the regression equation. A substantial reduction in the standard error estimate resulted. The predictions from this new regression equation were somewhat less accurate than the ones obtained with the original regression equation; however the standard error of prediction and the standard error estimate are in much closer agreement. Finally, to probe the effect that the quality of the steric and electrostatic potentials has on 3D-QSAR analyses, the semiempirical MNDO parallel PRDDOE geometries and Mulliken charges used in the original analyses were replaced with ab initio 3-21G parallel 6-31G* geometries and electrostatic potential fit charges. A modest decrease in the standard error estimate and increase in cross validated R2 resulted.

Animals↗

PubMed1992

A novel treatment of global cerebral ischaemia with a glycine partial agonist.

Chronic treatment of gerbils with 1-aminocyclopropanecarboxylic acid (a high affinity, partial agonist at strychnine-insensitive glycine receptors) resulted in a 3-fold increase in survival, a significant improvement in neurological status, and an extensive protection of vulnerable brain regions following severe forebrain ischaemia. A bolus of 1-aminocyclopropanecarboxylic acid 30 min prior to ischaemia did not further improve outcome compared to gerbils receiving their last injection 24 h prior to ischaemia. These findings are consistent with the hypothesis that chronic treatment with a glycine partial agonist desensitizes the N-methyl-D-aspartate receptor complex. Pharmacological intervention at the strychnine-insensitive glycine receptor may be an effective means of ameliorating the consequences of neuronal degeneration caused by excitotoxic phenomena.

Amino Acids↗

PubMed1992

Isoflurane anesthesia is stereoselective.

The anesthetic effects of the (+) and (-) isomers of isoflurane were determined in mice. Like the clinically important racemate, both isomers produced dose-dependent increases in anesthetic sleep time. A statistically significant (P less than 0.005, ANOVA) difference in the potencies of these isomers ((+) greater than (-)) was observed. To our knowledge, this is the first demonstration of a stereospecific action of a volatile anesthetic in vivo.

Analysis of Variance↗

PubMed1992

High-performance liquid chromatographic assay for 1-aminocyclopropanecarboxylic acid from plasma and brain.

A reversed-phase high-performance liquid chromatographic method for the analysis of 1-aminocyclopropanecarboxylic acid (ACPC) from plasma or brain tissue is described. Samples were deproteinized with perchloric acid, centrifuged, alkalinized with potassium hydroxide and recentrifuged. The supernatants were derivatized with o-phthaldialdehyde and injected onto a C18 3-microns column (100 mm x 4 mm I.D.) pumped with 1 ml/min methanol-acetonitrile-0.1 M sodium phosphate buffer pH 6.0 (28:5:67, v/v). The retention times for ACPC and the internal standard were 15 and 31 min, respectively. The minimum detectable amount of ACPC was 0.08 nmol. The extraction recovery of ACPC (2.7-270 nmol) from spiked plasma or brain tissue ranged from 88 to 109%. The intra- and inter-day coefficients of variation for 27 nmol ACPC were 3.9 and 4.9%, respectively. This method was utilized to obtain preliminary pharmacokinetic parameters following ACPC administration to mice.

Amino Acids↗

PubMed1992

Immunoenhancing effects of alprazolam, a benzodiazepine receptor agonist.

The effects of alprazolam (ALP), a triazolobenzodiazepine with high affinity for "central" benzodiazepine receptors, were examined on several parameters of immune function in mice. NK, MLR, and mitogen-induced lymphocyte proliferation were all significantly increased 2 hr after administration of low doses (0.02-1.0 mg/kg) of ALP. Twenty four hr later, similar but less robust immunoenhancing effects were observed. These measures of immune functions were not affected by higher doses of ALP (5-10 mg/kg). The immunoenhancing effects of ALP did not appear related to serum corticosterone levels. These and other findings demonstrate that the GABA/benzodiazepine receptor chloride channel complex can bidirectionally modulate immune function.

Alprazolam↗

PubMed1992

Nitric oxide does not mediate the neurotrophic effects of excitatory amino acids in cultured cerebellar granule neurons.

Excitatory amino acids, such as N-methyl-D-aspartate (NMDA) and kainate, promote neuritogenesis and viability in primary cultures of cerebellar granule cells. In view of the recent demonstration that excitatory amino acids activate the synthesis of nitric oxide, the present study examined a potential role of nitric oxide in mediating the neurotrophic effects of excitatory amino acids. NMDA enhanced the viability of 8-day-old cerebellar granule cell cultures in a concentration-dependent fashion, whereas kainate showed a concentration-dependent biphasic effect. A specific inhibitor of nitric oxide synthase, NG-nitroarginine (0.5 mM), did not antagonize the neurotrophic effects of NMDA (0.5 mM) or kainate (0.05 mM). The concentration of NG-nitroarginine was sufficient to inhibit NMDA or kainate stimulated nitric oxide synthesis and was stable in the culture media throughout the 8-day culture period. Using a specific chemiluminescence detection method, endogenous nitric oxide was directly measured in the headspace gas phase of homogenized cultured cerebellar granule cells, and was not detected when homogenates were incubated with NG-nitroarginine (0.5 mM). Furthermore, addition of a nitric oxide precursor, S-nitroso-N-acetylpenicillamine (1-200 microM), was not neurotrophic, but rather, was neurotoxic in granule cells. These findings indicate that nitric oxide is not a neurotrophic factor in primary cultures of cerebellar granule cells.

Animals↗

PubMed1992

Synthesis of novel 2-phenyl-2H-pyrazolo[4,3-c]isoquinolin-3-ols: topological comparisons with analogues of 2-phenyl-2,5-dihydropyrazolo[4,3-c]quinolin-3(3H)-ones at benzodiazepine receptors.

Based on the topology of pyrazoloquinolinones 10-12, a series of 2-phenyl-2H-pyrazolo[4,3-c]isoquinolines 6a-d, 7a-d, 8, and 9 have been synthesized and evaluated for their ability to inhibit radioligand binding to benzodiazepine receptors (BzR). Modification of the hydrogen bonding donor and acceptor characteristics of the NH and C = O functionalities of the pyrazoloquinolinones 10-12 resulted in ligands with dramatically reduced affinities (IC50 much greater than 2 microM) for BzR. The low affinities of 6a-d, 7a-d, 8, and 9 are consistent with the involvement of the NH function present on diverse classes of inverse agonists (beta-carbolines, diindoles, and pyrazoloquinolinones) with a hydrogen bond acceptor site (A2) on the binding protein. Moreover, it supports the involvement of the carbonyl function of the pyrazoloquinolinones and the pyridine nitrogen atom of beta-carbolines and diindoles with a hydrogen bond donor site (H1). Finally, the results from this work indicate that a simultaneous interaction at both hydrogen bond donor (H1) and acceptor sites (A2) at BzR is required for high affinity binding of inverse agonists.

Animals↗

PubMed1992

Ontogeny of glycine-enhanced [3H]MK-801 binding to N-methyl-D-aspartate receptor-coupled ion channels.

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor is thought to play a critical role in neuronal development, differentiation and plasticity. A number of studies have shown an enhanced sensitivity to NMDA receptor ligands in neonatal animals. This study examined the ontogenetic changes in the glycinergic modulation of NMDA-coupled cation channels in the developing central nervous system of rat pups. The nonequilibrium binding of the specific channel ligand [3H]MK-801 was used as a measure of NMDA channel access. Glycine (10(-5) M) enhancement of [3H]MK-801 binding at 2 h in forebrain membranes from adult rats was significantly greater than that observed in tissues from 8- to 28-day-old rat pups. This difference was due to changes in the efficacy, but not potency of glycine. The observed ontogenetic changes in the efficacy of glycine-enhanced [3H]MK-801 binding were attributable to developmental changes in receptor site density, as determined by equilibrium [3H]MK-801 saturation isotherms. Kinetic studies revealed that glycine increased the association rate constants of [3H]MK-801 in 8-day and adult membranes by a similar magnitude (0.111 +/- 0.021 vs 0.094 +/- 0.009 nM-1 h-1, respectively). Similarly, the fractional amount of [3H]MK-801 bound (i.e., amount bound at time t normalized to amount bound at equilibrium) in the presence of glycine was relatively constant throughout neonatal development. These findings suggest that the allosteric modulation of the NMDA ionophore by glycine is similar in postnatal and adult rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

High affinity ligands for 'diazepam-insensitive' benzodiazepine receptors.

Structurally diverse compounds have been shown to possess high affinities for benzodiazepine receptors in their 'diazepam-sensitive' (DS) conformations. In contrast, only the imidazobenzodiazepinone Ro 15-4513 has been shown to exhibit a high affinity for the 'diazepam-insensitive' (DI) conformation of benzodiazepine receptors. We examined a series of 1,4-diazepines containing one or more annelated ring systems for their affinities at DI and DS benzodiazepine receptors, several 1,4-diazepinone carboxylates including Ro 19-4603, Ro 16-6028 and Ro 15-3505 were found to possess high affinities (Ki approximately 2.6-20 nM) for DI. Nonetheless, among the ligands examined, Ro 15-4513 was the only substance with a DI/DS potency ratio approximately 1; other substances had ratios ranging from 13 to greater than 1000. Ligands with high to moderate affinities at DI were previously classified as partial agonists, antagonists, or partial inverse agonists at DS benzodiazepine receptors, but behaved as 'GABA neutral' (antagonist) substances at DI. The identification of several additional high affinity ligands at DI benzodiazepine receptors may be helpful in elucidating the pharmacological and physiological importance of these sites.

Animals↗