Dacey, Dennis, Ph.D. Professor dmd@u.washington.edu I-419A 543-3315 It is now well accepted that the vertebrate retina contains on the  order of 50-60 distinct neural cell types.  Why does the retina,  situated at the earliest stage of the visual process, require so many   cell types?  One hypothesis is that the photoreceptor responses to  light are channelled into a number of parallel signal pathways that  separately encode various aspects of a visual image and play   different roles in visual perception.  In the retina each of these  visual pathways would be composed of a set of interneurons linked to  an output neuron, the ganglion cell, whose axon projects to a target   in the brain.  To test this hypothesis we are attempting to identify  each of the retinal ganglion cell types and their associated  interneurons.  Work in the lab has recently focused on the retina of   the human and macaque monkey.  In the primate we know that some  ganglion cell types receive excitatory input from red, green, or blue  cone photoreceptors and therefore show color selective light   responses; other ganglion cell types are excited equally by all of  the cone types and are non-color selective.  The neural organization  that gives rise to these distinct signal pathways is unknown.   To  approach the problem we are using intracellular recording and  staining in in vitro preparation of the macaque retina to identify  the color-coding light responses of morphologically identified  ganglion  cell types. References Dacey, D.M., and Brace, S.  (1992)  A coupled network for parasol but  not midget ganglion cells in the primate retina. Visual Neuroscience  9: 279-290. Dacey,  D.M., and Petersen, M.  (1992)  Dendritic field size and  morphology of midget parasol ganglion cells of the human retina.   Proc. Natl. Acad Sci. USA.  89: 9666-9670. Milam, A.H., Dacey,  D.M., and Dizhoor, A.M.  (1993)  Recovering  immunoreactivity in mammalian cone bipolar cells. Visual Neuroscience  10: 1-12. Dacey, D.M.  (1993)  Morphology of a small-field  bistratified  ganglion cell type in the macaque and human retina.   Visual Neuroscience 10: 1081-1098. Dacey, D.M.  (1993)  The mosaic of midget ganglion cells in the human  retina.   The Journal of Neuroscience 13:5334-5355. Dacey, D.M., and Lee, B.B.  (1994)  The blue-ON opponent pathway in  primate retina originates from a distinct bistratified ganglion cell  type.  Nature  367: 731-735. Dacey DM, Peterson BB, Robinson FR, Gamlin PD (2003) Fireworks in the  primate retina: in vitro photodynamics reveals diverse LGN-projecting  ganglion cell types. Neuron 37(1):15-27 Lee BB, Dacey DM, Smith VC, Pokorny J (2003) Dynamics of sensitivity  regulation in primate outer retina: the horizontal cell network. Journal  of Vision 3:513-26 Dacey DM, Packer OS (2003) Colour coding in the primate retina: diverse  cell types and cone-specific circuitry. Current Opinion in Neurobiology  13: 421-427. Diller LC, Packer OS, Verweij J, McMahon MJ, Williams DR, Dacey DM  (2004) L- and M-cone contributions to the midget and parasol ganglion  cell receptive fields of macaque monkey retina. Journal of Neuroscience  24(5):1079-1088 McMahon MJ, Packer OS, Dacey DM (2004) The classical receptive field  surround of primate parasol ganglion cells is mediated primarily by a  non-GABAergic pathway. Journal of Neuroscience, 24(15):3736-3745. Dacey DM, Liao H-W, Peterson BB, McDougal DH, Robinson FR, Smith VC,  Pokorny J, Yau K-W, Gamlin PD (2005) Melanopsin-expressing ganglion  cells in primate retina project to the LGN and signal both color and  irradiance. Nature 433:749-754. Packer, OS, Dacey DM (2005) Synergistic center-surround receptive field  model of monkey H1 horizontal cells. Journal of Vision, 5(11): 1038-1054. Gamlin PD, McDougal DH, Smith VC, Dacey DM, Pokorny J, Yau K-W. Human  and macaque pupil responses driven by intrinsically photoreceptive  retinal ganglion cells. Submitted.