Figure 1

Developmental epochs in the rat neural retina and superior colliculus. Cytogenesis in the rat retina occurs from E9 through to P12, with distinct and overlapping waves of cell birth and differentiation [48]-[51]. Death of differentiated retinal ganglion cells (RGCs) is predominantly perinatal; starting at E20, peaking between birth and P3, falling sharply at P5 and continuing on until around P10 [52]-[57]. Astrocyte apoptosis is observed from P0, peaking between then and P5, and is associated with vasculature development [51],[58]. Bipolar and amacrine cell apoptosis occurs concurrently with different peaks, from P5 until P13/P14 [54]. Synapse generation in the inner plexiform layer (IPL) starts at P2 with amacrine cells [59],[60], and from P12 in bipolar cells [59], both peaking around the time of eye opening [54],[59]. Outer plexiform layer (OPL) synaptogenesis begins at P4 [59]-[62] and, while its time-course in the rat is not certain, in the mouse continues until about P12 [63]. Neurogenesis in the rat superior colliculus (SC) occurs from E12 to E17 [64],[65]. Apoptosis in the visual layers of the rat SC (stratum griseum superficiale; SGS) occurs from birth, peaking at between P4 and P7, and lasting until P13 [66],[67]. Circuit maturation in the SGS, as judged by synapse density and composition, is mostly postnatal [68],[69] in three stages: P0-P12/P14 (eye opening), P12-P24 increasing number of synapses, P21-P30/P40 increasing ratio of inhibitory to excitatory terminals [70]. Retinal axons first enter the SC at E16/E17 [71], and continue to arrive until P5/P6 [52],[72]. Cortico-tectal innervation starts at P3, with marked ingrowth between P6 and P12, and adult-like innervation observable from P18 [73]. Scale: downwards ticks mark 5 days, upwards ticks mark time points in this study; IPL: inner plexiform layer; OPL: outer plexiform layer; RGC: retinal ganglion cell; SGS: stratum griseum superficiale.