PROCESSING OF COLOR-CODED AND NON-COLOR-CODED SIGNALS IN THE GOURAMI
RETINA. I. HORIZONTAL CELLS
Sakai, H. M., Machuca, H., and Naka, K.-I.
From.
APStracts 4:0074, 1997.
ABSTRACT
There are two types of horizontal cells, the luminosity and the chromaticity
cells, in the retina of the kissing gourami, Helostoma rudolfi. Luminosity
cells occupy the outermost layer proximal to the receptor terminals, while
chromaticity cells form a layer proximal to the layer of luminosity cells.
Neither type of cell has axons. Responses were evoked by light from red and
green light-emitting diodes. The two stimuli were modulated either by a
pulsatile or a white-noise signal. The luminosity cell always produced a
hyperpolarizing response. The chromaticity cell produced a hyperpolarizing
response when stimulated by only one color. However, in the presence of a
steady or modulated green input, a red stimulus produced a depolarizing
response. Such chromaticity cells were similar to the (spectral) biphasic
chromaticity horizontal cells observed in other retinae. The depolarizing
phase of the red response was produced by the balance of intensity of the two
inputs, red and green. We used white-noise methodology to identify the
dynamics of the horizontal cell's modulation response by taking advantage of
the fact that a Wiener kernel is a measure of a cell's incremental
sensitivity, which includes its response dynamics. Under all conditions, a
steady-state modulation response by both luminosity and chromaticity cells was
always linearly related to the input modulation. The average mean square error
(MSE) of the model predicted by the first-order kernel was about 8% for both
luminosity (n=116) and chromaticity (n=23) cells. In some cases, the MSE was a
few % even when the peak-to-peak response amplitude was nearly 30 mV. The
ratio of inputs from red and green cones to both types of horizontal cells was
variable; the major input for luminosity cells came from red cones, whereas
the major input for chromaticity cells came from green cones. First-order
kernels generated by the major input were robust in terms of waveform in the
sense that the waveform remained unchanged whether or not there was a steady
or modulated illumination by the opposing color. The results reported here do
not address the question of the neural circuitry that generates horizontal-
cell responses, in particular, the depolarizing response. However, whatever
that circuitry might be, the high degree of linearity of the modulation
response by both types of cell under various stimulus conditions imposes
restrictions on the performance of any proposed model, as well as on
mechanisms that underlie the generation of the horizontal-cell response.
Received 1997 May 1; accepted in final form 1997 May 7.
APS Manuscript Number J301-6
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997