(A) Control HB afferent input (red) projects to the proximal (medial) region of the tectal neuropil, RGC afferent input (green) projects to the distal (lateral) region of the tectal neuropil. In the merged image, notice the gap, indicated by the white bracket, between two sets of sensory input, and the corresponding gap in peak axon fluorescence shown in the corresponding fluorescent intensity profile (far right). (B) HB and RGC axons innervating the tectum of a tadpole exposed to MK801 at stage 39 (‘early’) and corresponding fluorescent profile (far right). There appears to be a less distinct gap between the two inputs, suggesting less segregation. (C) HB and RGC axons of a tadpole exposed to MK801 at stage 45 (‘late’), and corresponding fluorescent profile (far right). The merged image and fluorescent profile suggest that MK-801 rearing at stage 45 does not disrupt the segregation along the tectal neuropil at stage 49. Notice the gap between the two sets of input. (D) Bar graph summarizing the distance between peak HB and RGC axon fluorescence. (E) Bar graph summarizing the amount of overlap between HB and RGC axons. R: rostral, C: caudal, L: lateral, M: medial.