Fig. 2. Effects of intraocular colchicine on the survival of neurons in the ION between embryonic day 11.5 (E11.5) and 5 d posthatch (P5). A, Nissl-stained section through the ION atE17. Most ION neurons die after injection of colchicine at E15. B, Section through the ION at P3. Very few neurons are affected by colchicine injections at P1. Scale bar (shown in A): 10 μm. C, Developmental profile of sensitivity of ION neurons to colchicine. The survival of ION neurons was assessed 48 hr after injection of colchicine. The percentage of surviving neurons (relative to the ipsilateral control ION) is plotted as a function of age. Note the gradual increase in sensitivity between E12 and E16, and the abrupt loss of sensitivity after injections at E19. The following average number of neurons was counted in the experimental ION of each age group: E13.5–14.0 (n = 2), 10,121; E15 (n = 1), 7167; E16 (n = 2), 3813; E17 (n = 1), 751; E18.5–19.0 (n = 3), 1142; E20 (n = 1), 1440; E20.5-P1 (n = 3), 3401; P2 (n = 1), 11,350; P3–P4 (n = 2), 8476; P5 (n = 2), 9864.