Regulation of neurotransmitter release
Dr Talvinder Sihra
|Reader in Cellular and Molecular Neuroscience|
|Tel: +44 (0)20 7679 3296/3385|
RESEARCH | TEACHING
Dr Talvinder S. Sihra obtained his BSc in Biochemistry and Physiology at the University of Sheffield (1982) and his PhD in Biochemistry at the Department of Biochemistry, University of Dundee (1985). He was Postdoctoral Associate at the Rockefeller University in New York until 1990, when he returned to the University of Dundee with an MRC Fellowship. As a Wellcome Trust Lecturer, he established his laboratory at the Royal Free Hospital School of Medicine (Department of Pharmacology) in 1993. In April 1997, he relocated to the Pharmacology Department at UCL where he is a Reader in Cellular and Molecular Neuroscience. He is a current member of the Signal Transduction Theme Panel of the Biochemical Society and has formerly held positions as secretary of Neuroscience Group, member of the Meetings Board and member (elected) of Council at the Society. He is an Editor for the British Journal of Pharmacology.
The basic interests of the laboratory centre around the mechanisms by which neurotransmitter release is regulated at central nervous system (CNS) synapses.
1) Presynaptic receptors, through ionotropic and metabotropic mechanisms, represent a fundamental means for regulating neurotransmitter release. One of our interests is to identify and characterize presynaptic receptors that modulate the release of the neurotransmitters glutamate and GABA. The model system we use for these studies is the isolated nerve terminal preparation (synaptosomes). Nerve terminal depolarization leads to Ca2+-influx and exocytosis, followed by endocytosis and recycling of transmitter containing small synaptic vesicles (SSVs). To delineate the loci at which presynaptic receptor activation impinge, we use membrane potential-sensitive dyes to assay nerve terminal excitability and depolarization, fura-2 to monitor Ca2+-influx and on-line enzymatic assays or HPLC to determine the release of glutamate and GABA by the exocytosis of small synaptic vesicles (SSVs).
Post-translational modification of the proteins involved in the cascade of events leading to neurotransmitter release offers a powerful means of mediating presynaptic plasticity. Thus, one way that presynaptic receptor activation can potentially modulate the properties of proteins involved in neurotransmitter release is through the stimulation of second messenger cascades that lead to protein phosphorylation or dephosphorylation. Using synaptosomes labelled with 32P-orthophosphate, we can ascertain presynaptic receptor-mediated activation of specific protein and lipid kinases and phosphatases employing identified intraterminal substrates for these enzymes. Currently, we are characterising the nerve terminal modulatory roles of mitogen-activated protein kinases and lipid kinases leading to the production of polyphosphoinositides.
2) The second major focus of the laboratory is to determine the role of specific protein kinases or phosphatases in the cascade of events leading to SSV exocytosis and endocytosis. For these studies, we have taken the approach of altering enzyme expression in neuronal cell lines and primary cell cultures that are amenable to molecular biological procedures. Currently, we are evaluating the effects of altered expression of the major Ca2+-dependent protein phosphatase, protein phosphatase 2B (calcineurin, CN) and its associated proteins. We wish to characterize of the role of CN in: (a) controlling voltage-dependent Ca2+-influx and, (b) the exocytotic/endocytotic cycling of SSVs and control thereof by the CN substrates, synapsin I and dynamin. We examine VDCC activity using whole-cell patch-clamping and Ca2+-influx, either spectrophometrically or by Ca2+-imaging of single cells, using Ca2+-sensitive fluorophors. Effects of phosphorylation/dephosphorylation on SSV-associated proteins are elucidated using styryl SV-probes (e.g. FM1-43, FM2-10) to image endocytosis/exocytosis.
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- Negrete-Diaz JV, Sihra TS, Delgado-Garcia JM, Rodriguez-Moreno A (2007) Kainate receptor-mediated presynaptic inhibition converges with presynaptic inhibition mediated by Group II mGluRs and long-term depression at the hippocampal mossy fiber-CA3 synapse. J Neural Transm.
- Xu X, Muller-Taubenberger A, Adley KE, Pawolleck N, Lee VW, Wiedemann C, Sihra TS, Maniak M, Jin T, Williams RS. (2007) Attenuation of phospholipid signaling provides a novel mechanism for the action of valproic acid. Eukaryot Cell 6(6):899-906.
- Wang SJ, Wang KY, Wang WC, Sihra TS (2007) Unexpected inhibitory regulation of glutamate release from rat cerebrocortical nerve terminals by presynaptic 5-hydroxytryptamine-2A receptors. Journal of Neuroscience Research, 84(7):1528-42. REPRINT REQUEST | DOWNLOAD PDF
- Negrete-Díaz, J, Sihra, TS, Delgado-García J, Rodríguez-Moreno A (2006) Kainate receptor-mediated inhibition of glutamate release involves protein kinase A in the mouse hippocampus. Journal of Neurophysiology 96(4):1829-37. REPRINT REQUEST | DOWNLOAD PDF
- Martin SW, Butcher A J, Berrow NS, Richards MW, Paddon RE, Turner DJ, Dolphin AC, Sihra TS, Fitzgerald EM (2006) Phosphorylation Sites on Calcium Channel α1 And β Subunits Regulate Erk-Dependent Modulation of Neuronal N-Type Calcium Channels. Cell Calcium 39(3):275-92. REPRINT REQUEST | DOWNLOAD PDF
- Rodríguez-Moreno A, Sihra TS (2004) Presynaptic kainate receptor facilitation of glutamate release involves protein kinase A in the rat hippocampus. Journal of Physiology 557(3):733-745). REPRINT REQUEST | DOWNLOAD PDF
- Wang SJ, Sihra TS (2004) The Non-Competitive mGlu5 Receptor Antagonist, 2-Methyl-6-Styryl-Pyridine (SIB1893), Depresses Glutamate Release through Inhibition of Voltage-Dependent Ca 2+ Entry in Rat Cerebrocortical Nerve Terminals (Synaptosomes). Journal of Pharmacology and Experimental Therapeutics 309(3):951-958. REPRINT REQUEST | DOWNLOAD PDF
- Wang SJ, Sihra TS (2003). Opposing facilitatory and inhibitory modulation of glutamate release elicited by cAMP production in cerebrocortical nerve terminals (synaptosomes). Neuropharmacology 44:686-697. REPRINT REQUEST | DOWNLOAD PDF
- Wang SJ, Coutinho V and Sihra TS (2002). Presynapatic Cross-talk of b-Adrenoreceptor and 5-Hydroxytryptamine Receptor Signalling Systems in the Modulation of Glutamate Release from Cerebrocortical Nerve Terminals. British Journal of Pharmacology 137: 1371-1379. REPRINT REQUEST | DOWNLOAD PDF
- Jovanovic JN, Sihra TS, Nairn AC, Hemmings Jr HC, Greengard P and Czernik AJ (2001). Opposing changes in phosphorylation of specific sites in synapsin I during Ca2+-dependent glutamate release in isolated nerve terminals. Journal of Neuroscience 21:7944-7953. REPRINT REQUEST | DOWNLOAD PDF
- Wang SJ, Sihra TS, Gean PW. (2001). Lamotrigine inhibition of glutamate release from isolated cerebrocortical nerve terminals (synaptosomes) by suppression of voltage-activated calcium channel activity. Neuroreport 12(10):2255-2258. REPRINT REQUEST | DOWNLOAD PDF
- Burley JR and Sihra TS (2000). A modulatory role for protein phosphatase 2B (calcineurin) in the regulation of Ca2+ entry. European Journal of Neuroscience, 12:2881-2991. REPRINT REQUEST | DOWNLOAD PDF
- Jovanovic JN, Czernik AJ, Fienberg AA, Greengard P, Sihra TS (2000). Synapsins as mediators of BDNF-enhanced neurotransmitter release. Nature Neuroscience, 3(4):323-329. REPRINT REQUEST | DOWNLOAD PDF
- Perkinton MS, Sihra, TS, Williams, RJ. (1999). Ca2+-permeable AMPA receptors induce phosphorylation of cAMP response element-binding protein through a phosphatidylinositol 3-kinase-dependent stimulation of the mitogen-activated protein kinase signalling cascade in neurons. Journal of Neuroscience, 19:5861-5874. REPRINT REQUEST | DOWNLOAD PDF
- Perkinton MS, Sihra TS (1999). A high affinity presynaptic kainate-type glutamate receptor facilitates glutamate exocytosis from cerebral cortex nerve terminals (synaptosomes). Neuroscience, 90(4), 1279-1290. REPRINT REQUEST
- Wiedemann C, Schäfer T, Burger MM, Sihra TS (1998). An Essential Role for a Small Synaptic Vesicle-Associated Phosphatidylinositol 4-Kinase in Neurotransmitter Release. Journal of Neuroscience 18:5594-5602. REPRINT REQUEST | DOWNLOAD PDF
- Perkinton MS, Sihra TS (1998). Presynaptic GABAB receptor modulation of glutamate exocytosis from rat cerebrocortical nerve terminals: receptor decoupling by protein kinase C. Journal of Neurochemistry 70:1513-1522. REPRINT REQUEST
- Lukyanetz EA, Piper TP, Sihra TS (1998). Calcineurin involvement in the regulation of high threshold Ca channels in NG108-15 (rodent neuroblastoma x glioma hybrid) cells. Journal of Physiology 510.2:371-385. REPRINT REQUEST
- Sihra TS (1997). Protein phosphorylation and dephosphorylation in isolated nerve terminals (synaptosomes). In: Posttranslational Modifications: Techniques and Protocols (Hemmings HC ed), pp 67-119. Totowa: Humana Press. REPRINT REQUEST
- Jovanovic JN, Benfenati F, Siow YL, Sihra TS, Sanghera JS, Pelech SL, Greengard P, Czernik AJ (1996). Neurotrophins stimulate phosphorylation of synapsin I by MAP kinase and regulate synapsin I-actin interactions. Proc.Natl.Acad.Sci.U.S.A. 93:3679-3683. REPRINT REQUEST | DOWNLOAD PDF