Inhibition of neurogenesis impairs contextual fear memory in rats. A, B, E, F, Young, DCX+, neurons were numerous in the dentate gyrus of control rats (A) and mice (E) but were absent from irradiated rats (B) and mice (F). C, Rats irradiated 4 weeks earlier showed decreased 24 h fear memory upon reexposure to the conditioned context compared with controls, as reflected by reduced freezing behavior (F
(4,104) = 2.3, p < 0.05 for treatment × time interaction in 2-way repeated-measures ANOVA). D, Rats irradiated 8 weeks earlier showed greater memory impairment (F
(1,72) = 5.6, p < 0.05 for main effect of treatment). G, H, However, irradiation did not affect freezing behavior in mice upon reexposure to the conditioned context at either the 4 week (G) or 8 week (H) time points. Scale bar, 200 μm; hil, hilus; gcl, granule cell layer; mol, molecular layer; #
p < 0.05 in post hoc tests.