Localization of axonally transported 125I-wheat germ agglutinin beneath the plasma membrane of chick retinal ganglion cells.

Abstract

The distribution of 125I-wheat germ agglutinin (WGA) transported by axons of chick retinal ganglion cells to layer d of the optic tectum was studied by EM autoradiography. Of the radioactivity, 52% was located in axons and axon terminals in the contralateral optic tectum 22 h after intravitreal injection of affinity-purified 125I-WGA. Axons comprised 43% of the volume of layer d. Dendrites, glial cells and neuron cell bodies contained 20, 17 and 3% of the label, whereas these structures comprised 24, 21 and 2% of the tissue volume, respectively. The distances between the autoradiographic Ag grains and the plasma membranes of these profiles, and observed distributions of grains were compared to theoretical distributions computed for band-shaped sources at various distances from the plasma membranes. The radioactive sources within axons was distributed in a band of cytoplasm extending in from the plasma membrane a distance of 63 nm. Because WGA binds to specific membrane glycoconjugates, at least some glycoconjugates may be concentrated within an annular region of cytoplasm just beneath the axonal plasma membrane after axoplasmic transport from the neuron cell body.