Physiological response properties of cat retinal ganglion cells projecting to suprachiasmatic nucleus.

The aim of this experiment was to characterize the physiological properties of cat retinal ganglion cells that project to the suprachiasmatic nucleus (SCN). Retrogradely labeled SCN-projecting ganglion cells were recorded extracellularly in vitro. For the first time, this study provides crucial information on visual response properties of ganglion cells in the entrainment circuitry. All recorded cells gave sustained responses (n = 9). Although most of the cells (n = 8) had an "on" center receptive field, one cell showed "on-off" center receptive field properties. The range of receptive field sizes was 2 to 5 deg. For most of the cells tested, the spectral wavelength that evoked peak responses was 500 nm (3 out of 5 cells). All recorded cells (n = 9) preferred still or extremely slow-moving stimuli (3.3 deg/s). These results indicate that cat SCN-projecting cells receive inputs from conventional photoreceptors. The hypothesis that both conventional and cryptochromic photoreceptors are involved in transferring photic signals is discussed.