REGENERATIVE AND OTHER RESPONSES TO INJURY IN THE RETINAL STUMP OF THE OPTIC-NERVE IN ADULT ALBINO-RATS - TRANSECTION OF THE INTRACRANIAL OPTIC-NERVE

The response to injury of the proximal (retinal) stump of the intracra nially transected optic nerve in adult rats has been studied by electr on microscopy. The central part of the retinal stump of the optic nerv e underwent severe ischaemic damage resulting in the formation by 3 da ys postoperation (dpo) of a cone-shaped region of necrotic tissue whic h extended from a base occupying most of the cross-sectional area of t he nerve at the cut end to an apex within the intraorbital part of the nerve and only 2-3 mm from the eyeball. A mixture of apparently viabl e and dead or dying cells and axons was present in anl intermediate zo ne surrounding the ischaemic core. Apparently intact nerve fibres occu pied most of the periphery of the optic nerve. Small bundles of sprout -like axons were seen in the intermediate zone at 3 dpo, and by 5 dpo such sprouts were present at the periphery of the degenerative core. B y 7 dpo, the sprouts were also found in the centre of the degenerative core, accompanied by astrocyte processes. The number, of axonal sprou ts present in the degenerative core and intermediate zone was much hig her at 2 and 4 wk postoperation (wpo) than at 7 dpo, then declined gra dually by 6 and 8 wpo. These results show that intracranial transectio n of the rat optic nerve produces extensive degeneration in the proxim al stump and effectively produces an intraorbital axotomy of many reti nal ganglion cells. Nevertheless, surviving axons display the ability to produce regenerative sprouts which persist for considerably longer than those produced after intraorbital injury.