Harvard University
The vertebrate retina contains ganglion cell types that appear to be
specialized for detecting temporal changes. These cells typically
respond to a static stimulus with a transient burst of action
potentials only at the presentation and/or removal of the stimulus,
and show a vigorous sustained discharge to dynamic inputs, such as
moving stimuli. These transient and motion-senstive responses are
thought to be generated by interactions in the inner retina involving
amacrine cells, but the nature of these interactions is not known. One
way to examine them is to remove specific cells from the circuitry and
measure the effects on ganglion cell responses. Here we apply a
cell-ablation technique to explore the roles of one amacrine cell
subclass in the mouse retina. Ganglion cell spike trains were recorded
from the isolated mouse retina using an extracellular multi-electrode
array, while presenting stimuli displayed on a computer
monitor. Ablation of the amacrine cell class altered the response
dynamics of the ON-type ganglion cells: Their response to a step
increase in uniform illumination was greatly prolonged, from 
ms (time above 
of maximal firing rate) to 
ms. Thus, the ablated amacrine class may normally serve to truncate a
sustained excitatory input to the ON cell. To also examine
spatio-temporal integration, we stimulated the retina with moving
square wave gratings of 8 different orientations. In normal retinae,
the response of about 
of all ON-type ganglion cells showed a
significant dependence on the grating orientation, indicating
anisotropy in their receptive field structure. In the
amacrine-depleted retinae, that proportion increased about
3-fold. Thus this amacrine cell class makes strong contributions to
both temporal and spatio-temporal integration by retinal ganglion
cells.