Abstract
Purpose: :
The goals of this study are to determine the developmental profile of directional selectivity (DS) of retinal ganglion cells (RGCs), and the roles of visual stimulation in the maturation of DS.
Methods: :
Multielectrode array was used to record the action potentials of mouse RGCs evoked by moving bar stimuli. A white rectangular bar, which moves upon black background and perpendicularly to its long axis in 12 directions at 30º intervals, was used to evoke RGC light responses. The directional selectivity index (DSI) was defined as (Rpreferred–Rnull)/ (Rpreferred+Rnull), and was calculated for both the leading and trailing edge (ON and OFF) responses, respectively.
Results: :
To determine whether the DS of RGCs is developmentally regulated, we recorded RGCs light responses before and two weeks after eye–opening. The average DSI of ON–OFF RGCs increased from 0.246±0.008 (ON response) and 0.198±0.007 (OFF response) at P12 to 0.329±0.016 (ON response) and 0.307±0.015 (OFF response) at P30 (p<0.0001, for both ON and OFF response). However, the DSIs of ON and OFF RGCs have no significant change after eye–opening. To examine whether visual stimulation is required for the developmental change of DS, we compared the DSI of RGCs from mice raised in constant darkness from birth with age–matched controls. Our data showed that the average DSI of OFF response of ON–OFF RGCs in dark reared mice is smaller than that of age–matched controls (0.266±0.012 vs. 0.307±0.015, p<0.05), but larger than P12–aged mice raised under cyclic light/dark conditions. The DSIs of ON response of ON–OFF RGCs, ON RGCs and OFF RGCs are similar to that of age–matched controls.
Conclusions: :
The DS of ON–OFF RGCs continuously develops after eye–opening. Visual deprivation seems to selectively prevent the maturational changes of DS of OFF response in ON–OFF RGCs.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • retinal connections, networks, circuitry • retinal development