The morphological properties of cat retinal ganglion cells projecting to the suprachiasmatic nucleus (SCN) of the hypothalamus were studied by using retrograde labeling, in vitro intracellular injection, confocal optical section, and computer three-dimensional reconstruction techniques. A total of 218 stained cells were studied. Neither the dendritic fields nor soma diameters of SCN-projecting cells varied with eccentricity. Approximately 50% of cells were concentrated not in the area centralis, but rather in the visual streak. SCN-projecting cells showed large and symmetrical dendritic fields (596 +/- 159 microm) and medium to small sized somas (17.2 +/- 3.3 microm). The ramification patterns of SCN-projecting cells were similar. Most cells primarily ramify in either sublamina A or B. Evidence from quantitatively analyzed cells (n = 39) suggests that these cells ramified more frequently in sublamina A (n = 17) than in sublamina B (n = 8). A large number of cells, on the other hand, showed diffuse ramification (n = 14) throughout the inner plexiform layer (IPL). The functional roles of these cells and the corresponding retinal neurocircuitry in circadian entrainment remain to be studied.
Copyright 1999 Wiley-Liss, Inc.