Fig. 4.

Labeling of photoreceptors does not increase markedly during the 24 hr after a pulse of [³H]histidine. Preparations were incubated for 15 min in [³H]histidine and then maintained in normal saline for 1 (A), 5 (B), or 24 (C) hr before processing the preparation for autoradiography. Photomicrographs of axons at each time period show that even after 24 hr the glia were more heavily labeled than the photoreceptors. Labeling of neither the photoreceptor somata nor their axons increased significantly over the 24 hr. Scale bars, 20 μm.