Incorporation of sialic acid into gangliosides and glycoproteins of the optic pathway following an intraocular injection of [N-3H]acetylmannosamine in the chicken.

Following an intraocular (i.o.) injection of [N-3H]acetylmannosamine, low molecular soluble radioactive label is distributed rapidly along the optic pathway. At the same time glycoproteins and gangliosides were found radioactively labelled in the distal parts of the optic pathway. Negligible amounts of radioactivity were incorporated into the same structures via the blood. The present data confirm, that glycoproteins are transferred in the retinal ganglion cells by a rapid axonal transport mechanism towards the nerve endings. Unlike glycoproteins labelled gangliosides accumulated in the optic nerves up to 4 days after the precursor injection. Simultaneously radioactive material, soluble in TCA/PTA, disappeared from the optic nerves. The specific radioactivities (disint./min/mug NeuNAc) of the single ganglioside fractions of the optic lobes, which contain the nerve endings of the retinal ganglion cells, differed considerably. Especially one fraction, moving on TLC plates identically to 'GD1a', was up to 20 times higher labelled than the other gangliosides. After an intracerebral injection of the same precursor, radioactivity was incorporated into the ganglioside fractions of the optic lobes to the same extent.