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BIOLOGICAL SCIENCES / NEUROSCIENCE
Dendritic compartmentalization of chloride cotransporters underlies directional responses of starburst amacrine cells in retina
*Department of Neuroscience, Ohio State University College of Medicine, Columbus, OH 43210; and Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, MA 02118
Edited by John E. Dowling, Harvard University, Cambridge, MA, and approved October 23, 2006 (received for review June 1, 2006)
The mechanisms in the retina that generate light responses selective for the direction of image motion remain unresolved. Recent evidence indicates that directionally selective light responses occur first in the retina in the dendrites of an interneuron, i.e., the starburst amacrine cell, and that these responses are highly sensitive to the activity of Na-K-2Cl (NKCC) and K-Cl (KCC), two types of chloride cotransporter that determine whether the neurotransmitter GABA depolarizes or hyperpolarizes neurons, respectively. We show here that selective blockade of the NKCC2 and KCC2 cotransporters located on starburst dendrites consistently hyperpolarized and depolarized the starburst cells, respectively, and greatly reduced or eliminated their directionally selective light responses. By mapping NKCC2 and KCC2 antibody staining on these dendrites, we further show that NKCC2 and KCC2 are preferentially located in the proximal and distal dendritic compartments, respectively. Finally, measurements of the GABA reversal potential in different starburst dendritic compartments indicate that the GABA reversal potential at the distal dendrite is more hyperpolarized than at the proximal dendrite due to KCC2 activity. These results thus demonstrate that the differential distribution of NKCC2 on the proximal dendrites and KCC2 on the distal dendrites of starburst cells results in a GABA-evoked depolarization and hyperpolarization at the NKCC2 and KCC2 compartments, respectively, and underlies the directionally selective light responses of the dendrites. The functional compartmentalization of interneuron dendrites may be an important means by which the nervous system encodes complex information at the subcellular level.
direction-selective | GABAergic excitation | interneuron
The authors declare no conflict of interest.
This article is a PNAS direct submission.
To whom correspondence should be addressed at: Department of Neuroscience, Ohio State University College of Medicine, 333 West 10th Avenue, Columbus, OH 43210. E-mail: mangel.1{at}osu.edu
© 2006 by The National Academy of Sciences of the USA
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