Nerve cell death resulting from stroke, head injury and a range of degenerative disorders is a major cause of mortality and also has devastating effects on the lives of survivors. Understanding the mechanisms of this cell death is an important goal, since development of successful treatments could greatly minimize the subsequent social cost of these conditions. A common triggering event in neurodegeneration is widely held to be the excessive release of the excitatory transmitter glutamate, and subsequent massive Ca2+ influx. This process has been termed """"""""excitotoxicity."""""""" We have investigated excitotoxic mechanisms in restricted regions of nerve dendrites, and shown that glutamate receptor agonists initiate sustained Ca2+ elevations at these sites, and that these """"""""secondary Ca2+ responses"""""""" then spread very slowly throughout neurons and lead to cell death. Our hypothesis is that fine dendrites, being richly endowed with Ca2+ -permeable glutamate receptors and channels, act as initiation sites of excitotoxic Ca2+ signals, and that procedures to prevent the initiation and/or spread of secondary Ca2+ responses will provide important new approaches to limiting cell death. We have exploited differences in excitotoxic vulnerability between inbred murine strains (C57B1/6 and C57B1/10) to clearly demonstrate the involvement of these responses in excitotoxic cell death in intact slice preparations. As well as implicating secondary responses as key determinants of excitotoxic vulnerability, this work has resulted in novel preparations that permit the first rigorous investigations of 1) mechanisms underlying secondary response initiation, 2) mechanisms by which secondary responses spread through dendritic processes and 3) how secondary responses trigger cellular damage. Acute murine hippocampal slices will be studied using combined electrophysiological and single-cell Ca2+ imaging approaches. Secondary responses will be initiated using glutamate receptor agonists, and pharmacological approaches used to identify the routes of Ca2+ entry involved in triggering, and progression of these events. Studies to determine the basis for murine strain differences in secondary response generation will be complemented by immunohistochemical approaches. A further set of mechanistic studies will test the hypothesis that mitochondrial Ca2+ loading is a key event linking secondary responses to cellular damage, using imaging methods to assess mitochondrial function, Ca2+ loading and production of reactive oxygen species. In the long term, results from these studies should provide a basis for novel interventions designed at preventing cell death following excitotoxic stimulation at sites remote from neuronal somata. such as might occur in a very wide range of neurological disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS043458-02
Application #
6623510
Study Section
Special Emphasis Panel (ZRG1-MDCN-2 (01))
Project Start
2002-04-01
Project End
2006-03-31
Budget Start
2003-04-01
Budget End
2004-03-31
Support Year
2
Fiscal Year
2003
Total Cost
$248,041
Indirect Cost
Name
University of New Mexico
Department
Neurosciences
Type
Schools of Medicine
DUNS #
868853094
City
Albuquerque
State
NM
Country
United States
Zip Code
87131
Vander Jagt, Thomas A; Connor, John A; Shuttleworth, C William (2008) Localized loss of Ca2+ homeostasis in neuronal dendrites is a downstream consequence of metabolic compromise during extended NMDA exposures. J Neurosci 28:5029-39
Brennan, A M; Connor, J A; Shuttleworth, C W (2007) Modulation of the amplitude of NAD(P)H fluorescence transients after synaptic stimulation. J Neurosci Res 85:3233-43
Hoskison, M M; Yanagawa, Y; Obata, K et al. (2007) Calcium-dependent NMDA-induced dendritic injury and MAP2 loss in acute hippocampal slices. Neuroscience 145:66-79
Dietz, Robert M; Kiedrowski, Lech; Shuttleworth, C William (2007) Contribution of Na(+)/Ca(2+) exchange to excessive Ca(2+) loading in dendrites and somata of CA1 neurons in acute slice. Hippocampus 17:1049-59
Chinopoulos, Christos; Connor, John A; Shuttleworth, C William (2007) Emergence of a spermine-sensitive, non-inactivating conductance in mature hippocampal CA1 pyramidal neurons upon reduction of extracellular Ca2+: dependence on intracellular Mg2+ and ATP. Neurochem Int 50:148-58
Azimi-Zonooz, Aryan; Shuttleworth, C William; Connor, John A (2006) GABAergic protection of hippocampal pyramidal neurons against glutamate insult: deficit in young animals compared to adults. J Neurophysiol 96:299-308
Hoskison, M M; Shuttleworth, C William (2006) Microtubule disruption, not calpain-dependent loss of MAP2, contributes to enduring NMDA-induced dendritic dysfunction in acute hippocampal slices. Exp Neurol 202:302-12
Brennan, Angela M; Connor, John A; Shuttleworth, C William (2006) NAD(P)H fluorescence transients after synaptic activity in brain slices: predominant role of mitochondrial function. J Cereb Blood Flow Metab 26:1389-406
Xing, Hong; Azimi-Zonooz, Aryan; Shuttleworth, C William et al. (2004) Caffeine releasable stores of Ca2+ show depletion prior to the final steps in delayed CA1 neuronal death. J Neurophysiol 92:2960-7
Hoskison, M M; Connor, J A; Shuttleworth, C W (2004) GABA(B)-receptor modulation of short-term synaptic depression at an excitatory input to murine hippocampal CA3 pyramidal neurons. Neurosci Lett 365:48-53

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