Decreased duration of Ca 2+ -mediated plateau potentials in striatal neurons from aged rats. Dunia, Richard, Galen Buckwalter, Tony DeFazio, Fernando Dos Santos Villar, Thomas H. McNeill and John P. Walsh. Ethel Percy Andrus Gerontology Center, USC Program in Neuroscience, University of Southern California, Los Angeles, CA 90089-0191.
APStracts 3:0120N, 1996.
1. The influence of age on striatal neuron Ca 2+ physiology was studied through an analysis of intracellularly recorded Ca 2+ -mediated plateau potentials. In vitro brain slices from young and aged rats were treated with the K + channel blocker tetraethylammonium (TEA)(30 mM) to facilitate the expression of plateau potentials. A sample of neurons were also filled with biocytin and post-hoc correlations were performed between morphology and physiology. 2. Testing of sampling parameters in neurons from young rats revealed that tetrodotoxin (TTX) did not affect the amplitude or duration of plateau potentials. The membrane potential induced during plateau testing and the rate of plateau potential generation, however, had to be held constant since these variables affected plateau potential duration. 3. A significant age-related decrease was found in the duration of Ca 2+ -mediated plateau potentials that could not be explained by alterations in the activation or inactivation properties of the plateau potential. Investigation into relationships between cell morphology and plateau potential duration revealed a number of correlations. Soma size and dendritic length were correlated with plateau potential duration, independent of age (hierarchical regression), and an age-related decrease in dendritic length, but not soma size was found. Spine density and plateau potential duration were also correlated, but the significance depended upon the variance associated with age. These data indicate that the extent of soma-dendritic membrane (including spines) affects plateau potential duration in striatal neurons and dendrite and spine loss in aged animals may contribute to age-related decreases in plateau potential duration. 4. The response to replacement of Ca 2+ with Ba 2+ was age- dependent, with Ba 2+ causing a greater increase in the duration of plateau potentials in young neurons. These data rule out an increase in Ca 2+ - mediated inactivation of Ca 2+ channels as a primary cause for the shortening of plateau potentials in aged neurons. Our morphological findings suggest that dendritic regression in aged neurons may have reduced the number of Ca 2+ channels participating in plateau potential generation, but other mechanisms related to changes in the type of Ca 2+ channel expressed and possible differences in their inactivation kinetics may also contribute to the age- related change in plateau potential duration.

Received 29 January 1996; accepted in final form 20 May 1996.
APS Manuscript Number J64-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96