Spatial and temporal asymmetries that underlie the neural computation of image motion in the retina. Stuart Mangel, Ph.D., Dept. of Neuroscience, OSU College of Medicine
Dept of Neuroscience, The Ohio State University
(December 6, 2005 4:30 PM - 5:30 PM)
The neural coding of the direction of stimulus motion, which is a classic example of local neural computation, is a common feature of the nervous system. In the vertebrate retina, the mechanisms that underlie the computation of the direction of image motion remain unresolved. Recent evidence indicates that directionally-selective light responses occur first in the dendrites of a retinal interneuron, 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. By measuring the GABA reversal potential in different starburst dendritic compartments a nd by mapping NKCC2 and KCC2 antibody staining on these dendrites, we have recently found that the localization of NKCC2 and KCC2 in different dendritic compartments results in a GABA-evoked depolarization and hyperpolarization at the NKCC2 and KCC2 compartments, respectively, and underlies the directionally-selective responses of starburst dendrites. Computational analysis of light-evoked voltage changes at the starburst cell body and dendritic tip suggest that directionally-selective light responses similar to those we have observed experimentally can be generated if there is a chloride gradient along starburst dendrites due to the differential compartmentalization of the chloride cotransporters and if the GABA-evoked increase in the chloride conductance is relatively long-lasting. Experimental measurements indicate that GABA produces long-lasting responses from starburst cells. The functional compartmentalization of interneuron dendrites may be an important means by which the nervous system computes complex information at the subcellular level.