Dendritic Spikes And Their Influence On Extracellular Calcium Signaling. Michael C. Wiest, David M. Egelman, Richard D. King, and P. Read Montague. Division of Neuroscience, Center for Theoretical Neuroscience, Baylor College of Medicine, 1 Baylor Plaza, Houston, TX 77030.
APStracts 6:0541N, 1999.
Extracellular calcium is critical for many neural functions, including neurotransmission, cell adhesion, and neural plasticity. Experiments have shown that normal neural activity is associated with changes in extracellular calcium, motivating recent computational work employing such fluctuations in an information-bearing role. This possibility suggests a new style of computing taking place in the mammalian brain in addition to current 'circuit' models that use solely neurons and connections. Previous computational models of rapid external calcium changes have used only gross approximations of calcium channel dynamics to compute the expected calcium decrements in the extracellular space. Using realistic calcium channel models, experimentally measured back-propagating action potentials, and a model of the extracellular space, we compute the fluctuations in external calcium that accrue during neural activity. In this realistic setting, we show that rapid, significant changes in local external calcium can occur when dendrites are invaded by back-propagating spikes, even in the presence of an extracellular calcium buffer. We further show how different geometrical arrangements of calcium channels or dendrites prolong or amplify these fluctuations. Lastly, we compute the influence of experimentally measured synaptic input on peri-dendritic calcium fluctuations. Remarkably, appropriately timed synaptic input can boost significantly the decrement in external calcium. The model shows that the extracellular space and the calcium channels that access it provide a medium that naturally integrates coincident spike activity from different dendrites that intersect the same tissue volume.
Received 7 July 1999; accepted in final form 23 October 1999.
APS Manuscript Number J547-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999