Journal of Neuroscience, Vol 13, 1543-1550, Copyright © 1993 by Society for Neuroscience
The spectral sensitivity of dark- and light-adapted cat retinal ganglion cells
E Guenther and E Zrenner
Department of Pathophysiology of Vision and Neuroophthalmology, University Eye Hospital, Tubingen, Germany.
The spectral sensitivity of cat retinal ganglion neurons (RGNs) was
determined by means of extracellular recordings under scotopic and photopic
conditions, in both receptive field center and surround. Test stimuli were
presented either as square-wave single flashes or as flicker stimuli.
Chromatic adaptation was achieved by a large steady monochromatic
background field. In the dark-adapted state the spectral sensitivity of the
majority of ganglion cells (92%) was rod mediated (peak sensitivity at 501
nm). Under photopic conditions all neurons received input from a
long-wavelength-sensitive (L-cone) system with a peak sensitivity of 550
nm. Input from a short-wavelength-sensitive (S- cone) system (peak
sensitivity at 450 nm), however, was found only in 15% of the ganglion
cells. A small cell population (8%) located within the area centralis
revealed a different receptive field organization. In these cells, spectral
sensitivity in the field center peaked at 520 nm in the dark-adapted state
and response threshold was about 1 log unit higher than in cells with a
peak sensitivity of 501 nm. Critical flicker fusion was reached at 60-70
Hz, a frequency that usually is mediated by cones. We therefore postulate
an additional input of a midspectral receptor system (M-system) other than
rods in cat retinal ganglion cells. This input was found only in the
receptive field center of some ganglion cells in the dark-adapted state,
whereas the surround sensitivity was mediated in all cells by rod signals
under scotopic and predominantly by L-cone signals under photopic
conditions.