RNA content of normal and axotomized retinal ganglion cells of rat and goldfish

Abstract

The responses of rat and goldfish retinal ganglion cells to axotomy were examined by a quantitative cytochemical method for RNA and by morphometric measurement 1–60 (rat) and 3–90 (goldfish) days after interruption of one optic nerve or tract intracranially. Unoperated control animals were studied also. The RNA content of axotomized neurons of rat fell 7–60 days postoperatively. Additionally, atrophy of the axotomized somas occurred. Over time, neuronal atrophy approximately paralleled the loss of RNA, and mean cell area and RNA content were reduced by about 25% 60 days after axotomy. Incorporation of ³H‐uridine by axotomized neurons declined also. Axotomized retinal ganglion cells of goldfish behaved differently from those of the rat and showed increases in RNA content, most conspicuously 14–60 days postoperatively. Enlargement of axotomized fish neurons occurred but was less proportionately than concomitant increases in RNA content. The nonaxotomized ganglion cells of goldfish displayed statistically significant increases in size and RNA content 14–49 days after unilateral optic nerve or tract lesions. In contrast, alterations in rat retinal ganglion cells contralateral to interruption of one optic nerve were of limited and questionable significance. The contrasting reactions to axotomy by the retinal ganglion cells of these two vertebrates, one of which regenerates optic axons and one of which does not, may support the proposition that the somal response to axon injury has an important bearing upon the success or failure of CNS regeneration. Although mammalian intrinsic neurons commonly undergo regressive changes after axotomy, they may remain viable for long periods during which they may yet prove to be stimulable by pharmacologic or other means to the mounting of a restitutive response to axon injury.