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T F Murray

Publications and source records attributed to T F Murray.

At least 55 records · Page 3Linked to original sources
PubMed1996

Synthesis and cannabinoid receptor binding activity of conjugated triene anandamide, a novel eicosanoid.

A polyenoic fatty-acid isomerase (PFI) from a red marine alga was used to convert anandamide (5Z,8Z,11Z,14Z-eicosatetraenoyl-N-ethan olamide) to the 5Z,7E,9E,14Z-eicosatetraenoyl-N-ethanol amide isomer. This novel eicosanoid, termed conjugated triene anandamide (CTA), was assessed for its ability to bind to the cannabinoid receptor in rat brain membrane preparations. CTA is a high affinity cannabimimetic substance whose novel structure provides new insight into structure-activity relationships of cannabinoid receptor ligands. These experiments illustrate the utility of enzymes isolated from marine organisms in the development of pharmacological probes.

Animals↗
PubMed1996

Characterization of glutamate toxicity in cultured rat cerebellar granule neurons at reduced temperature.

We have defined conditions whereby glutamate becomes toxic to isolated cerebellar granule neurons in a physiologic salt solution (pH 7.4). In the presence of a physiologic Mg++ concentration, acute glutamate excitotoxicity manifests only when the temperature was reduced from 37 degrees C to 22 degrees C. In contrast to glutamate, N-methyl-D-aspartate (NMDA) was nontoxic at either temperature at concentrations as high as 1 mM. Glycine strongly potentiated both the potency and efficacy of glutamate but revealed only a modest NMDA response. The non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxalinedione (CNQX), potently protected against glutamate challenge, although the contribution of antagonism at strychnine-insensitive glycine sites could not be excluded. To further characterize the non-NMDA receptor contribution to the excitotoxic response, the promiscuity of glutamate interaction with ionotropic receptors was simulated by exposing neurons to NMDA in the presence of non-NMDA receptor agonists. NMDA toxicity was potentiated four- to sevenfold when non-NMDA receptors were coactivated by a subtoxic concentration of AMPA, kainate, or domoate. These results suggest that non-NMDA receptor activation participates in the mechanism of acute glutamate toxicity by producing neuronal depolarization (via sodium influx), which in turn promotes the release of the voltage-dependent magnesium blockade of NMDA receptor ion channels.

Animals↗
PubMed1996

Characterization of [3H]MK-801 binding to N-methyl-D-aspartate receptors in cultured rat cerebellar granule neurons and involvement in glutamate-mediated toxicity.

The conditions required for growth and survival of cerebellar granule neurons in vitro are known to alter the developmental regulation of NMDA receptor subunit mRNA. In the present report, we have examined the functional and pharmacological characteristics of NMDA receptors on cerebellar granule neurons at 12 days in culture (12 DIC). Under open-channel conditions in extensively washed membranes, [3H]MK-801 labeled a uniform population of sites (Kd = 3.2 +/- 0.3 nM) in a saturable manner (Bmax = 416 +/- 18 fmol/mg); however, biexponential association and dissociation kinetics indicated the possible existence of at least two NMDA receptor populations that differ in pharmacological properties. The kinetically derived equilibrium dissociation constants for the high- and low-affinity binding components were 0.56 and 771 nM, respectively. The equilibrium competition analysis of MK-801 and other channel-blocking compounds as displacers of [3H]MK-801 revealed the presence of high- and low-affinity binding sites with relative apportionments of 70% and 30%, respectively. The rank-order potency profile of competitor binding at the high-affinity site was (+)-MK-801 > TCP > dextrorphan > dextromethorphan > (+)-ketamine. When tested for the ability to protect 12 DIC cerebellar granule neurons from acute glutamate-induced toxicity, the neuroprotective rank-order potency of these compounds was MK-801 > TCP > dextrorphan > (+)-ketamine > dextromethorphan, which correlated significantly with the high-affinity competition binding profile and thus established the role of NMDA receptors in glutamate toxicity. The findings of these experiments indicate that NMDA receptors on 12 DIC cerebellar granule neurons are a heterogenous population that functionally mediate glutamate-induced neurotoxicity. The heterogenous [3H]MK-801 binding sites may represent NMDA receptor channels composed of different subunits.

Animals↗
PubMed1996

High level expression of the NMDAR1 glutamate receptor subunit in electroporated COS cells.

The rat N-methyl-D-aspartate (NMDA) glutamate receptor subunit NR1-1a was transiently expressed in COS cells using the technique of electroporation, which was fivefold more efficient than the calcium phosphate precipitation method of transfection. The glycine site antagonist 5,7-[3H]dichlorokynurenic acid labeled a single high-affinity site (KD = 29.6 +/- 6 nM; Bmax = 19.4 +/- 1.6 pmol/mg of protein) in membranes derived from COS cells electroporated with NR1-1a. In contrast to previous reports using transiently transfected human embryonic kidney 293 cells, binding of the noncompetitive antagonist (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine ([3H]MK-801) was not detected in NR1-1a-transfected COS cells. Although immunofluorescent labeling of electroporated COS cells demonstrated that the NR1-1a protein appears to be associated with the cell membrane, neither NMDA nor glutamate effected an increase in intracellular calcium concentration in fura-2-loaded cells, suggesting that homomeric NR1-1a receptors do not act as functional ligand-gated ion channels. Therefore, COS cells appear to differ from Xenopus oocytes with respect to the transient expression of functional homomeric NR1 receptors. Although expression of NR1-1a is sufficient to reconstitute a glycine binding site with wild-type affinity for antagonists in COS cells, recombinant homomeric NR1-1a receptors do not display properties that are characteristic of native NMDA receptors, such as permeability to Ca2+ and channel occupancy by MK-801, when expressed in this mammalian cell line.

Animals↗
PubMed1996

Chronic exposure to adenosine receptor agonists and antagonists reciprocally regulates the A1 adenosine receptor-adenylyl cyclase system in cerebellar granule cells.

Chronic treatment with the adenosine receptor antagonist caffeine evokes an up-regulation of A1 adenosine receptors and increased coupling of the receptor to G proteins in rat brain membranes. However, chronic agonist exposure has not been explored. Primary cultures of cerebellar granule cells were exposed chronically to A1 adenosine receptor agonists and antagonists. Exposure to the A1 adenosine receptor agonist N6-cyclopentyladenosine resulted in (1) a time- and concentration-dependent reduction in the density of receptors labeled by 1,3-[3H]dipropyl-8-cyclopentylxanthine, (2) an enhanced ability of guanyl nucleotides to decrease the fraction of A1 adenosine receptor sites displaying high affinity for 2-chloroadenosine, and (3) a functional uncoupling of receptors from adenylyl cyclase (EC 4.6.1.1). The adenosine antagonists caffeine and 8-p-sulfophenyltheophylline produced alterations in A1 adenosine receptor homeostasis that were antipodal to those associated with agonist treatment. Antagonist exposure (1) increased the density of A1 adenosine receptors in cerebellar granule cell membranes, (2) blunted the effect of guanyl nucleotides on receptor coupling to G proteins, and (3) increased the functional coupling of receptors to adenylyl cyclase inhibition. Forskolin treatment of cerebellar granule cells did not affect receptor density, suggesting that cyclic AMP is not involved in the regulation of A1 adenosine receptor expression.

2-Chloroadenosine↗
PubMed1996

Regional distribution and characterization of [3H]dextrorphan binding sites in rat brain determined by quantitative autoradiography.

The pharmacologic specificity and anatomic distribution of [3H]dextrorphan recognition sites in the rat brain was characterized by quantitative autoradiography. Equilibrium saturation analysis indicated that [3H]dextrorphan labeled a single population of high affinity binding sites. These sites are heterogeneously distributed throughout rat forebrain with the following order of binding densities: hippocampal formation > cerebral cortex > thalamic nuclei > striatum. The association rate of [3H]dextrorphan with its binding site in area stratum radiatum of CA1 is accelerated by the addition of glycine and glutamate. [3H]Dextrorphan binding is, however, relatively insensitive to glycine and glutamate under equilibrium conditions, despite extensive prewashing procedures to deplete endogenous levels of these substances. The competitive N-methyl-D-aspartate (NMDA) antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) and the glycine site antagonist 7-chlorokynurenic acid completely inhibit specific [3H]dextrorphan binding. D-AP5 suppresses [3H]dextrorphan binding in a regionally distinctive manner; a population of binding sites is weakly inhibited by D-AP5 in the lateral thalamic regions, whereas D-AP5 potently inhibits [3H]dextrorphan binding in the cerebral cortex. The rank order of potencies of an array of noncompetitive antagonists to inhibit [3H]dextrorphan binding unambiguously displays the pharmacologic profile of the noncompetitive antagonist domain of the NMDA receptor-channel complex. Furthermore, the distribution of [3H]dextrorphan binding sites in slide-mounted tissue appears qualitatively similar to the distribution of NMDA receptors previously reported using NMDA-displacement of [3H]glutamate, [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne (MK-801) and [3H]1-[1-(2-thienyl)cyclohexyl]-piperidine (TCP) in most brain areas examined except the cerebellum. The molecular layer of the cerebellum displays a particularly high density of [3H]dextrorphan binding sites. The regional distribution of [3H]dextrorphan binding sites in rat brain does not correspond to the reported distributions of [3H]dextromethorphan or sigma binding sites.

Animals↗
PubMed1996

Arthroscopy of the foot and ankle in the athlete.

Ankle arthroscopy has evolved over the past decade to address many acute and chronic injuries in the athlete. Although similar outcomes are reported with established open procedures, arthroscopic intervention confers the advantages of decreased postoperative morbidity and earlier return to sports activity. Arthroscopic procedures for the foot are evolving; however, most are considered investigational at this time.

Ankle Injuries↗
PubMed1995

Synthesis and opioid activity of conformationally constrained dynorphin A analogues. 1. Conformational constraint in the "message" sequence.

A constrained analogue of the opioid peptide dynorphin A (Dyn A) cyclized in the "message" sequence was designed which may be compatible with the helical conformation proposed by Schwyzer (Biochemistry 1986, 25, 4281-4286) as the conformation Dyn A adopts at kappa opioid receptors. On the basis of molecular modeling with AMBER, we prepared the lactam cyclo-[D-Asp2,Dap5]Dyn A-(1-13)NH2 (1; Dap = alpha, beta-diaminopropionic acid) containing a four-atom bridge between positions 2 and 5 as a possible constraint compatible with an alpha-helix, along with the homologues with five-(2) and six-atom (3) bridges containing Dab (alpha, gamma-diaminobutyric acid) and Orn, respectively, in position 5. All of the cyclic peptide analogues exhibited high binding affinity for both kappa and mu receptors and high potency in the guinea pig ileum (GPI) assay. As ring size increased, a trend in receptor selectivity from slightly kappa selective (compound 1) to nonselective for kappa vs mu (compound 2) to slightly mu selective (compound 3) was observed in the radioligand binding assays. The results in the GPI for antagonism of these peptides by naloxone paralleled the results of the binding assays and indicated that compound 1 preferentially interacted with kappa receptors in this tissue. Novel byproducts were also obtained from the cyclization reactions with HBTU (2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate) and characterized as [D-Asp2,X(Tmg)5]Dyn A-(1-13)NH2 (where X = Dap, Dab, or Orn and Tmg = tetramethylguanidinium). All of the Tmg linear byproducts bound with high affinity to kappa and mu receptors and also exhibited potent agonist activity in the GPI. Circular dichroism spectra of compound 1 and the parent peptide Dyn A-(1-13)NH2 determined in 80% trifluoroethanol at 5 degrees C were consistent with some alpha-helical content in the peptides; comparison of the delta epsilon at 222 nm suggested that compound 1 possessed slightly higher helical content than Dyn A-(1-13)NH2 under these experimental conditions. The cyclic Dyn A analogues 1-3 described here represent the first Dyn A analogues constrained in the "message" sequence with demonstrated high affinity and potency at kappa receptors.

Amino Acid Sequence↗
PubMed1994

Steroid modulation of GABAA receptors in an amphibian brain.

Steroids can modulate gamma-aminobutyric acid (GABAA) receptor function in rat brains, but the physiological relevance of this mechanism is still unclear. To determine whether this phenomenon is widespread among vertebrates, we investigated steroid modulation of GABAA receptors in amphibian brain tissue. Equilibrium binding parameters for t-butylbicyclophosphorothionate ([35S]TBPS) and [3H]flunitrazepam were similar in Taricha granulosa and mammalian brains, as was the allosteric regulation of [35S]TBPS and [3H]flunitrazepam binding by GABA. The rank order and absolute potencies of steroids to inhibit [35S]TBPS binding and enhance [3H]flunitrazepam binding were also similar in Taricha and rat brains. As in mammalian studies, physiological concentrations of corticosterone had no effect on ligand binding or GABA-stimulated Cl- uptake. In autoradiographic studies, 3 alpha-hydroxy-5 alpha-pregnan-20-one inhibited [35S]TBPS binding sites in all brain regions examined, whereas corticosterone had no effect on [35S]TBPS binding. These studies suggest that the steroid recognition sites on GABAA receptors have been highly conserved through vertebrate evolution and thus portend physiologically important functions. However, the pharmacological profiles for the GABAA receptor and the high-affinity corticosteroid receptor are apparently different, suggesting there are multiple types of steroid recognition sites on neuronal membranes.

Animals↗
PubMed1994

Activation of adenosine A1 receptors underlies anticonvulsant effect of CGS21680.

Focal injection of the adenosine A2A receptor agonist CGS21680 (2-[p-(2-carboxyethyl)phenylethylamino]-5'-N-ethyl-carboxamidoaden osine) in the rat prepiriform cortex produced a reduction in the severity of bicuculline methiodide-induced motor seizures. The anticonvulsant effect of CGS21680 exhibited dose-dependency and modest potency (ED50 = 605 +/- 47 pmol/rat). Pharmacological characterization of the anticonvulsant response in the prepiriform cortex revealed a significant correlation between the potency of adenosine analogs as anticonvulsants and their respective affinities for adenosine A1 receptors in vitro. These results indicate that the low affinity of CGS21680 for adenosine A1 receptors is sufficient to account for the anticonvulsant activity of this compound in the rat prepiriform cortex.

Adenosine↗
PubMed1994

Effects of an aerobic exercise program on community-based adults with mental retardation.

Effects of a 10-week aerobic exercise program on maximal oxygen consumption (VO2max), oxygen pulse (O2 pulse), maximum ventilation (max vent), exercise stress test duration (max time), flexibility, weight and body composition (percentage body fat, percentage lean mass, and percentage body water) were investigated in 14 community-based adults with mental retardation. Supervised optional training sessions were held 4 days per week. Subjects were assessed for VO2 max, O2 pulse, max vent, and max time before and after the training program. Flexibility, weight, and body composition changes were assessed before, midway through, and after the training program. Subjects had a 91.3% attendance rate, and all safely completed the program. The treatment produced significant increases in VO2 max, O2 pulse, max vent, max time, and flexibility. However, no significant change was observed in weight or body composition changes.

Activities of Daily Living↗
PubMed1993

Species comparison of adenosine and beta-adrenoceptors in mammalian atrial and ventricular myocardium.

The antagonist radioligand 1,3-[3H]dipropyl-8-cyclopentylxanthine ([3H]DPCPX) was used to characterize adenosine A1 receptors in membrane preparations from atrial and ventricular myocardium of rat, rabbit, guinea pig and pig. Kd values in crude membranes from guinea pig atria and ventricles (3.3 and 3.0 nM) were higher than those in the other species (ranges, 1.5-1.8 and 1.5-1.9 nM). Bmax values were greater in atria than in ventricles in all four species, and in atria and ventricles of guinea pig (76 and 34 fmol/mg), than in the other species (ranges, 15-17 and undetectable to 12 fmol/mg). In contrast, guinea pig Kd and Bmax values for beta-adrenoceptors, which were labelled with (-)3-[125I]iodocyanopindolol, fell within the range of values for the other three mammalian species. In semipurified membrane preparations from pig, [3H]DPCPX and the agonist radioligand [125I]-N6-4-aminobenzyladenosine appeared to label a similar population of receptors and gave comparable Kd values in atria (0.73 and 0.66 nM) and in ventricles (0.57 and 0.70 nM). In semipurified preparations from pig, the agonist R-(-)-N6-(2-phenylisopropyl)adenosine (R-PIA) displaced [3H]DPCPX in a manner consistent with the presence of both high- and low-affinity adenosine A1 receptors. The data from this study indicate that the density of adenosine A1 receptors in atria is greater than in ventricles, but similar Kd values suggest that the A1 receptor population is the same in the two cardiac tissues. Also, the data demonstrate that the [3H]DPCPX antagonist binding characteristics of guinea pig myocardium differ from those in rat, rabbit and pig.

Adenylyl Cyclases↗
PubMed1993

The sigma receptor ligand 1,3-di(2-tolyl)guanidine is anticonvulsant in the rat prepiriform cortex.

Unilateral focal injection of 1,3-di(2-tolyl)guanidine (DTG) caused a dose-dependent and potent (ED50 = 5.25 nmol, 95% confidence limits 1.1 to 25.0 nmol) suppression of generalized motor seizures induced by (-)-bicuculline methiodide in the rat prepiriform cortex. These findings indicate that DTG is equipotent to the noncompetitive NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate) as an anticonvulsant. This potent pharmacological effect of DTG distinguishes it from two other prototypic sigma ligands, haloperidol and (+)-pentazocine, which are ineffective as anticonvulsants. Pretreatment of animals with haloperidol failed to block the anticonvulsant effects of DTG. These data therefore document a novel anticonvulsant action of DTG in vivo by a mechanism that does not involve sigma receptors.

Animals↗
PubMed1993

Synthesis and opioid activity of dynorphin A-(1-13)NH2 analogues containing cis- and trans-4-aminocyclohexanecarboxylic acid.

It has been proposed that the "message" sequence of dynorphin A (Dyn A) exists in an extended conformation in aqueous solution (Schiller, P. W. Int. J. Pept. Protein Res. 1983, 21, 307-312). Molecular modeling suggested that trans-4-aminocyclohexanecarboxylic acid (trans-ACCA) might function as a conformationally constrained replacement for Gly2-Gly3 of Dyn A in such an extended conformation. ACCA was synthesized by catalytic hydrogenation of p-aminobenzoic acid, and the cis and trans isomers were separated by fractional recrystallization. Analogues of Dyn A-(1-13)-NH2 containing cis- and trans-ACCA were prepared by solid-phase peptide synthesis using the Fmoc chemical protocol. Results from radioligand binding assays indicated that the peptides have modest affinity for kappa opioid receptors (Ki's = 9.1 and 13.4 nM for [cis-ACCA2-3]- and [trans-ACCA2-3]Dyn A-(1-13)NH2, respectively) and modest kappa-receptor selectivity (Ki ratio (kappa/mu/delta) = 1/13/210 and 1/21/103, respectively). [cis-ACCA2-3]- and [trans-ACCA2-3]Dyn A-(1-13)-NH2 are the first reported Dyn A analogues constrained in the "message" sequence that are selective for kappa receptors. The cis-ACCA analogue showed very weak opioid activity (IC50 = 4.0 microM) in the guinea pig ileum.

Amino Acids↗
PubMed1993

Manipulation of endogenous adenosine in the rat prepiriform cortex modulates seizure susceptibility.

A1 adenosine receptors in the rat prepiriform cortex play an important role in the inhibition of bicuculline methiodide-induced convulsions. In the present study we evaluated manipulation of endogenous adenosine in this brain area as a strategy to effect seizure suppression. All compounds evaluated were unilaterally microinjected into the rat prepiriform cortex. Administration of exogenous adenosine afforded a dose-dependent protection (ED50 = 48.1 +/- 8.4 nmol) against bicuculline methiodide-induced seizures, and these anticonvulsant effects were significantly potentiated by treatment with an adenosine kinase inhibitor, 5'-amino-5'-deoxyadenosine; by the adenosine transport blockers, dilazep or nitrobenzylthioinosine 5'-monophosphate; and by an adenosine deaminase inhibitor, 2'-deoxycoformycin. When administered alone, 5'-amino-5'-deoxyadenosine, 5'-iodotubercidin and dilazep were found to be highly efficacious as anticonvulsants with respective ED50 values of 2.6 +/- 0.8, 4.0 +/- 2.7 and 5.6 +/- 1.5 nmol. In contrast, 2'-deoxycoformycin was both less potent and less efficacious. These results suggest that accumulation of endogenous adenosine may contribute to seizure suppression, and that adenosine kinase and adenosine transport may play a pivotal role in the regulation of extracellular levels of adenosine in the central nervous system. The adenosine antagonist, 8-(p-sulfophenyl)theophylline, increased markedly the severity of bicuculline methiodide-induced seizures. Moreover, reduction of extracellular adenosine formation by a focal injection of an ecto-5'-nucleotidase inhibitor, alpha, beta-methyleneadenosine diphosphate, produced generalized seizures (ED50 = 37.3 +/- 22.7 nmol). Together the proconvulsant effect of an adenosine receptor antagonist and the convulsant action of an ecto-5'-nucleotidase inhibitor further support the role of endogenous adenosine as a tonically active antiepileptogenic substance in the rat prepiriform cortex.

Adenosine↗
PubMed1992

Effect of modification of the basic residues of dynorphin A-(1-13) amide on kappa opioid receptor selectivity and opioid activity.

A series of dynorphin A-(1-13) amide (Dyn A-(1-13)NH2) analogues containing lysine or N epsilon-acetyllysine (Lys(Ac)) was prepared by solid-phase peptide synthesis and evaluated for opioid receptor affinity in radioligand binding assays and for opioid activity in the guinea pig ileum (GPI). Substitutions were made at positions 6, 7, 9, 11, and 13, the basic amino acids in the C-terminus of the peptide, in order to assess the individual contributions of these residues to the kappa opioid receptor affinity and selectivity of Dyn A-(1-13)NH2. While substitutions of Lys(Ac) for Arg in position 6 did not affect kappa receptor affinity, it enhanced affinity for mu and delta receptors and therefore caused a loss of kappa receptor selectivity. When Lys(Ac) was substituted for Arg9, kappa opioid receptor affinity was enhanced and kappa receptor selectivity was retained. Replacement for Arg7, Lys11, or Lys13 by Lys(Ac) resulted in both decreased affinity and selectivity for kappa receptors. These results demonstrate the importance of Arg6 to the receptor selectivity profile of Dyn A-(1-13)NH2 and indicate that, of the five basic residues in the C-terminus, only Arg9 can be replaced by a nonbasic residue without substantial loss of kappa opioid receptor selectivity.

Amino Acid Sequence↗