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Tim Green

Publications and source records attributed to Tim Green.

14 recordsLinked to original sources
PubMed2006

Interface interactions modulating desensitization of the kainate-selective ionotropic glutamate receptor subunit GluR6.

Ionotropic glutamate receptors from the AMPA and kainate subfamilies share many functional and structural features, but it is unclear whether this similarity extends to the molecular mechanisms underlying receptor desensitization. The current model for desensitization in AMPA receptors involves the rearrangement of dimers formed between subunit agonist binding domains. Key evidence for this has come from a single point mutant (from leucine to tyrosine) that abolished desensitization and that was shown to stabilize the binding domain dimer. However, the desensitization of kainate receptors appears to differ from that of AMPA receptors in several key respects. Although the kinetics of AMPA receptor gating and desensitization are consistent with channels formed from two dimers, similar evidence for the functional involvement of dimers has not been found in kainate receptors. Furthermore, despite the homolog of the nondesensitizing tyrosine in AMPA subunits also being a tyrosine in wild-type kainate subunits, these receptors desensitize rapidly and completely. Using mutagenesis based on the crystal structure of the glutamate receptor subunit GluR6 S1S2 domain in complex with domoate, we identified four residues neighboring this tyrosine that differ between AMPA and kainate subunits and that contribute to the different desensitization kinetics of these receptors. Detailed analysis of the effects of mutations at these sites confirms that there is in fact a common general mechanism for desensitization in non-NMDA receptors, dependent on the stability of the binding domain dimer interface, and reveals the existence of potential agonist-specific desensitization pathways.

Amino Acid Sequence↗
PubMed2006

Nurse-led management of carpal tunnel syndrome: an audit of outcomes and impact on waiting times.

INTRODUCTION: This article describes the outcome of a nurse-led service developed to manage patients referred with a presumptive diagnosis of carpal tunnel syndrome. PATIENTS AND METHODS: We developed a rapid-access service in response to unacceptable waiting times for patients with carpal tunnel syndrome. The service was developed around the role of a nurse practitioner providing a single practitioner pathway from first clinic appointment, through surgery to discharge. RESULTS: Waiting times improved considerably whilst the standard and quality of care was maintained. CONCLUSIONS: There is a role for nurses to perform certain surgical procedures within a well-defined environment.

Carpal Tunnel Syndrome↗
PubMed2005

New heterocyclic analogues of 4-(2-chloro-5-methoxyanilino)quinazolines as potent and selective c-Src kinase inhibitors.

A series of 5,7-disubstituted quinazolines, bearing 4-heteroaryl substituents such as 2-pyridinylamine or 2-pyrazinylamine, has been synthetised and evaluated as c-Src kinase inhibitors. Highly potent inhibition, high selectivity and physical properties suitable for oral dosing were achieved within this series: 23d and 42 were identified as sub-0.1muM inhibitors in a c-Src-driven cell proliferation assay and displayed adequate rat pharmacokinetics after oral administration.

Aniline Compounds↗
PubMed2005

Structure of the kainate receptor subunit GluR6 agonist-binding domain complexed with domoic acid.

We report the crystal structure of the glycosylated ligand-binding (S1S2) domain of the kainate receptor subunit GluR6, in complex with the agonist domoate. The structure shows the expected overall homology with AMPA and NMDA receptor subunit structures but reveals an unexpected binding mode for the side chain of domoate, in which contact is made to the larger lobe only (lobe I). In common with the AMPA receptor subunit GluR2, the GluR6 S1S2 domain associates as a dimer, with many of the interdimer contacts being conserved. Subtle differences in these contacts provide a structural explanation for why GluR2 L483Y and GluR3 L507Y are nondesensitizing, but GluR6, which has a tyrosine at that site, is not. The structure incorporates native glycosylation, which has not previously been described for ionotropic glutamate receptors. The position of the sugars near the subunit interface rules out their direct involvement in subunit association but leaves open the possibility of indirect modulation. Finally, we observed several tetrameric assemblies that satisfy topological constraints with respect to connection to the receptor pore, and which are therefore candidates for the native quaternary structure.

Amino Acid Sequence↗
PubMed2005

Positron emission tomography in the investigation of pediatric inflammatory bowel disease.

BACKGROUND: Endoscopic and radiologic studies are frequently required in inflammatory bowel disease (IBD) to determine disease activity, extent of disease, and delineating disease type. Positron emission tomography (PET) using fluorine-18-fluoro-deoxyglucose to identify metabolically active tissues may offer a simple noninvasive alternative to conventional studies in identification and localization of active intestinal inflammation in children with IBD. The aim of this study was to assess the value of PET in identifying active intestinal inflammation compared with conventional endoscopic and radiologic studies, including small bowel follow-through and colonoscopy. METHODS: Sixty-five children were enrolled in the study. This included 55 children (mean age, 13.3 yr; range, 7-18 yr; 20 girls) with newly diagnosed IBD (37) or symptoms suggestive of recurrent disease (18) and 10 children with recurrent abdominal pain (mean age, 12.7 yr; range, 8-15 yr; 7 girls) who were studied with PET, and the results were compared with small bowel follow-through with pneumocolon and/or colonoscopy. Thirty-eight patients had Crohn's disease (17 ileal, 12 ileocolic, 5 pancolonic, 3 left-sided disease, 1 right-sided disease), and 17 had ulcerative colitis (15 pan-colitis, 2 left-sided colitis). Mean time interval between PET and other studies was 30 +/- 17.6 days. RESULTS: PET correctly identified active inflammatory disease in 80% of children with IBD (81.5% with Crohn's disease; 76.4% with ulcerative colitis) and correctly showed no evidence of inflammation in children with recurrent abdominal pain. Gluorine-18-fluoro-deoxyglucose accumulated at sites that corresponded with active disease at colonoscopy in 83.8% of patients and with small bowel follow-through with pneumocolon 75.0% of the time. CONCLUSION: This study suggests that PET offers a noninvasive tool for identifying and localizing active intestinal inflammation in children with IBD. PET may not be able to replace conventional studies; however, it may be useful when conventional studies cannot be performed or fail to be completed.

Abdominal Pain↗
PubMed2005

Enhancement of temporal periodicity cues in cochlear implants: effects on prosodic perception and vowel identification.

Standard continuous interleaved sampling processing, and a modified processing strategy designed to enhance temporal cues to voice pitch, were compared on tests of intonation perception, and vowel perception, both in implant users and in acoustic simulations. In standard processing, 400 Hz low-pass envelopes modulated either pulse trains (implant users) or noise carriers (simulations). In the modified strategy, slow-rate envelope modulations, which convey dynamic spectral variation crucial for speech understanding, were extracted by low-pass filtering (32 Hz). In addition, during voiced speech, higher-rate temporal modulation in each channel was provided by 100% amplitude-modulation by a sawtooth-like wave form whose periodicity followed the fundamental frequency (F0) of the input. Channel levels were determined by the product of the lower- and higher-rate modulation components. Both in acoustic simulations and in implant users, the ability to use intonation information to identify sentences as question or statement was significantly better with modified processing. However, while there was no difference in vowel recognition in the acoustic simulation, implant users performed worse with modified processing both in vowel recognition and in formant frequency discrimination. It appears that, while enhancing pitch perception, modified processing harmed the transmission of spectral information.

Adult↗
PubMed2004

Inhibition of SRC tyrosine kinase as treatment for human pancreatic cancer growing orthotopically in nude mice.

PURPOSE: The Src family comprises a family of nonreceptor intracellular tyrosine kinases that mediate a variety of cellular pathways. Src kinases are overexpressed in a variety of human tumors, including cancer of the colon, breast, and pancreas, and they are an integral part of tumor cell signaling pathways associated with migration, proliferation, adhesion, and angiogenesis. EXPERIMENTAL DESIGN: We investigated whether the blockade of Src kinase by daily oral administration of the novel Src tyrosine kinase inhibitor AZM475271 [kindly provided by AstraZeneca (Macclesfield, United Kingdom)], alone or in combination with intraperitoneal gemcitabine, can inhibit growth and metastasis of orthotopically implanted human pancreatic carcinoma cells in nude mice. RESULTS: Treatment with AZM475271 alone reduced the primary pancreatic tumor volume by approximately 40%, whereas AZM475271 plus gemcitabine reduced tumor volume by 90%. Furthermore, treatment with AZM475271 and gemcitabine significantly reduced metastasis: none of eight animals who received the combination treatment had lymph node or liver metastases, compared with five of five and three of five animals, respectively, in the control group (P = 0.001). Src inhibition by AZM475271 (alone or with gemcitabine) was associated with significantly reduced tumor cell proliferation, decreased tumor microvessel density, and increased apoptosis in vivo. Moreover, these effects were all significantly increased when gemcitabine was combined with AZM475271 compared with gemcitabine alone. CONCLUSIONS: Src inhibition by AZM475271, either alone or in combination with gemcitabine, demonstrated significant antitumor and antimetastatic activity in an orthotopic nude mouse model for human pancreatic cancer. The combination of AZM475271 with gemcitabine sensitized tumor cells to the cytotoxic effect of gemcitabine.

Administration, Oral↗
PubMed2004

Enhancing temporal cues to voice pitch in continuous interleaved sampling cochlear implants.

The limited spectral resolution of cochlear implant systems means that voice pitch perception depends on weak temporal envelope cues. Enhancement of such cues was investigated in implant users and in acoustic simulations. Subjects labeled the pitch movement of processed synthetic diphthongal glides. In standard processing, noise carriers (simulations) or pulse trains (implant users) were modulated by 400 Hz low-pass envelopes. In modified processing, carriers were modulated by two components: (1) Slow-rate (<32 Hz) envelope modulations, conveying dynamic spectral shape changes crucial for speech; (2) a simplified waveform (e.g., a sawtooth) matching the periodicity of the input diphthong. In both normal listeners and implant users performance was better with modified processing, though temporal envelope cues were less effective with higher F0. Factors contributing to the advantage for modified processing may include increased modulation depth and use of a modulation waveform featuring a rapid onset in each period, resulting in a clearer representation of F0 in the neural firing pattern. Eliminating slow-rate spectral dynamics, so that within-channel amplitude changes solely reflected F0, showed that dynamic spectral variation obscured temporal pitch cues. Though significant, advantages for modified processing were small, suggesting that the potential for developing strategies delivering enhanced pitch perception is limited.

Acoustic Stimulation↗
PubMed2003

Estimated folic acid intakes from simulated fortification of the New Zealand food supply.

AIM: To identify a folic acid food fortification programme that will maximise the percentage of women of child-bearing age receiving at least 400 microg folic acid/day, the amount shown to reduce the risk of neural tube defect-affected pregnancies, while not putting population groups at risk of excessive intakes. METHODS: 1997 New Zealand National Nutrition Survey data and a computer modelling programme were used to estimate folic acid intakes from simulated fortification scenarios. RESULTS: Breads fortified with folic acid at 150 microg/50 g, white flour at 100 microg/35 g and liquid milk at 200 microg/200 ml, were found to be the best fortification scenarios. Thirty one percent, 21% and 18% of women of child-bearing age received > or = 400 microg folic acid/day from the fortification of bread, white flour and milk respectively. CONCLUSIONS: The most effective scenario for folic acid fortification is bread fortified at 150 microg/50 g. However, it is impossible to fortify food at a level that ensures the majority of women of child-bearing age receive more than 400 microg folic acid/day without exposing some people to excessive amounts of folic acid. The current public health message encouraging women to select folic acid fortified foods and take folic acid supplements, needs to continue.

Adolescent↗
PubMed2002

Differential activation of individual subunits in heteromeric kainate receptors.

Neuronal kainate receptors are assembled from subunits with dissimilar specificities for agonists and antagonists. The composite biophysical behavior of heteromeric kainate receptors is determined by intersubunit interactions whose nature is unclear. Here we use dysiherbaine, a selective kainate receptor agonist, to show that GluR5 subunits assembled in heteromeric GluR5/KA-2 kainate receptor complexes can gate current without concomitant activation of their partner KA-2 subunits. A long-lasting interaction between dysiherbaine and GluR5 subunits elicits a tonic current from GluR5/KA-2 receptors; subsequent cooperative gating of KA-2 subunits can be elicited by both agonists, such as glutamate, and some classically defined antagonists, such as CNQX. This study demonstrates that each type of subunit within a heteromeric kainate receptor contributes a distinct conductance upon activation by agonist binding, and therefore provides insight into the biophysical function of ionotropic glutamate receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2002

Identification of a new site in the S1 ligand binding region of the NMDA receptor NR2A subunit involved in receptor activation by glutamate.

Activation of N-methyl-d-aspartate (NMDA) receptors requires the binding of both glutamate and glycine to independent sites on the receptor. These ligands bind to NR2 and NR1 subunits respectively. Ligand binding residues are located in two non-contiguous domains, S1 and S2, which have been implicated in glutamate binding in other ionotropic glutamate receptor subunits. To further define the amino acids through which glutamate activates the receptor, we generated single-site mutations to the NR2A subunit, and expressed them with wild type NR1 in HEK 293 cells. Using calcium imaging and whole cell patch clamp we determined glutamate and glycine potencies. Of the eight residues mutated we identified five (E413, K484, A508, G685 and G688), whose mutation leads to a large reduction (from 4- to 1000-fold) in glutamate potency, consistent with a role for these residues in receptor activation by glutamate. The potency of glycine was largely unchanged by these mutations. Thus our results extend the knowledge base of residues involved in NMDA receptor function and identifies a new site in S1, in the region of A508, that has a role in receptor activation by glutamate.

Amino Acid Sequence↗
PubMed2002

Spectral and temporal cues to pitch in noise-excited vocoder simulations of continuous-interleaved-sampling cochlear implants.

Four-band and single-band noise-excited vocoders were used in acoustic simulations to investigate spectral and temporal cues to melodic pitch in the output of a cochlear implant speech processor. Noise carriers were modulated by amplitude envelopes extracted by half-wave rectification and low-pass filtering at 32 or 400 Hz. The four-band, but not the single-band processors, may preserve spectral correlates of fundamental frequency (F0). Envelope smoothing at 400 Hz preserves temporal correlates of F0, which are eliminated with 32-Hz smoothing. Inputs to the processors were sawtooth frequency glides, in which spectral variation is completely determined by F0, or synthetic diphthongal vowel glides, whose spectral shape is dominated by varying formant resonances. Normal listeners labeled the direction of pitch movement of the processed stimuli. For processed sawtooth waves, purely temporal cues led to decreasing performance with increasing F0. With purely spectral cues, performance was above chance despite the limited spectral resolution of the processors. For processed diphthongs, performance with purely spectral cues was at chance, showing that spectral envelope changes due to formant movement obscured spectral cues to F0. Performance with temporal cues was poorer for diphthongs than for sawtooths, with very limited discrimination at higher F0. These data suggest that, for speech signals through a typical cochlear implant processor, spectral cues to pitch are likely to have limited utility, while temporal envelope cues may be useful only at low F0.

Adult↗
PubMed2002

NMDA receptors formed by NR1 in Xenopus laevis oocytes do not contain the endogenous subunit XenU1.

Activation of N-methyl-D-aspartate-selective ionotropic glutamate receptors (NMDA receptors) requires two agonists, glutamate and glycine. These ligands are thought to bind to the NR2 and NR1 subunits, respectively, apparently ruling out the formation of functional homomeric receptors. However, NMDA-mediated currents are observed when the mammalian NR1 subunit is expressed alone in Xenopus laevis oocytes. These currents have been generally ascribed to a functional association between NR1 and the endogenous glutamate receptor subunit XenU1. To determine whether such a functional association does in fact occur, we have isolated cDNAs for both XenU1 and XenU1a, a presumed nonallelic counterpart. We investigated whether the coexpression of either XenU1 or XenU1a with NR1 in either X. laevis oocytes and human embryonic kidney (HEK) 293 cells had any effect on the observed NMDA receptor responses. In oocytes, coinjection of XenU1 with NR1 did not increase the observed currents compared with injection of NR1 alone; similarly, in HEK 293 cells, coexpression of XenU1 and NR1 did not result in the formation of functional channels. We also found no pharmacological or biochemical evidence for interaction between the two subunits. We conclude, therefore, that XenU1 does not associate with the NR1 subunit and that an alternative explanation must be sought for the channels observed when NR1 is expressed alone in oocytes.

Amino Acid Sequence↗