Abstract
Purpose: :
Characterization of diverse ganglion cell structure and function in primate is ongoing (Szmajda, et al. J Comp Neurol 510; 251 2008; Yamada, et al. Vis Neurosci 22; 383 2005; Rodieck, & Watanabe, J.Comp.Neurol. 338, 289 1993; Dacey, D M, in The Cognitive Neurosciences, MIT Press, 2004; Crook, et al., J Neurosci 28, 12654 2008) but an overall synthesis has not yet been achieved. Our goal is a complete description of primate visual pathway origins, providing an anatomical basis for targeted physiological analysis, dissection of underlying circuitry and for making trans-species comparisons most notably with the mouse, for which transgenic technology offers increasing access to retinal pathways.
Methods: :
To observe ganglion cell dendritic morphology we used retrograde photostaining (Dacey et al., 2003) from tracer injections made into either the lateral geniculate nucleus (LGN; n = 16) or the superior colliculus-pretectum (SC; n = 8). This method had the advantage of providing complete staining of the dendritic tree for large numbers of retrogradely labeled ganglion cells, permitting measurements of relative density and inner retina stratification depth derived from the mosaic organization of overlapping dendritic trees.
Results: :
In addition to previously well-described midget, parasol, smooth monostratified and melanopsin-expressing inner-outer cell pairs, and the single small bistratified-blue-ON cell type, 6 additional low-density populations have been clearly established. These include a large-field bistratified blue-ON cell that precisely costratifies with the small bistratified blue-ON cell, an inner-outer pair of narrowly stratified (30/75% IPL depth), highly branched ‘thorny’ cells and possible primate correlates of the mammalian local edge detector (ON-OFF; broad thorny) and the ON- and ON-OFF-direction selective cells (‘recursive’ mono- and bistratified types).
Conclusions: :
Density estimates derived from mosaic coverage suggest that the 15 types quantified thus far account for only 85% of all macaque ganglion cells and a number of additional very low density populations remain to be clearly identified.
Keywords: retina • ganglion cells