[Abstract Title]. - Society for Neuroscience

Support: NIH Grant EY11850
HHMI
Title: Light stimuli alters the balance of two components of synaptic inhibition received by
primate ON parasol ganglion cells
Authors: J. P. CAFARO, *F. M. RIEKE;
HHMI/Dept Physiol & Biophysics, Univ. Washington, Seattle, WA
Abstract: The retina provides an excellent opportunity to examine the relationship between
synaptic input and action potential generation because of the ability to record synaptic inputs
elicited by physiological stimuli. We are exploring how excitatory and inhibitory synaptic input
shape the spike output of primate ON parasol retinal ganglion cells. Consistent with work on
other retinal ganglion cells, an increase in light intensity produced a rapid increase in excitatory
synaptic input followed by a slower increase in inhibitory input. The timing of the inhibitory
input was consistent with feedforward inhibition. Surprisingly, a decrease in light intensity
produced a slow decrease in excitatory input and a rapid increase in inhibitory input. Thus ON
parasol cells apparently receive inhibitory input through both ON and OFF pathways. Consistent
with this idea, application of the mGluR6 agonist, L-APB, abolished excitatory synaptic input
but had a modest impact on the inhibitory synaptic input elicited by decreases in light intensity.
The kinetics and timing of the ON and OFF inhibitory components suggest that synaptic
inhibition may play two distinct roles in shaping spike output - i.e. the ON component of
synaptic inhibition follows excitation closely and may thus abbreviate the duration of the
resulting depolarization, while the OFF component operates in a push-pull fashion with
excitation. The relative contribution of the ON and OFF components of synaptic inhibition were
not fixed, but instead depended on both mean light level and contrast. The ON component of
synaptic inhibition was relatively stronger at rod light levels than cone light levels. Similarly,
increasing contrast at either rod or cone light levels caused a decrease in the contribution of the
ON component of synaptic inhibition relative to the OFF component. We are currently
investigating how this shift in the timing and kinetics of synaptic inhibition alters the cell‟s spike
output.
Disclosures: J.P. Cafaro, None; F.M. Rieke , None.
Poster
237. Synaptic Integration II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 237.20/D45