Metabolism of glycoconjugates in hypothalamic neurons and glial cells: comparison of incorporation of [3H]fucose and [3H]N-acetylmannosamine by electron microscopic autoradiography.

Incorporation of two glycoconjugate precursors, [3H]fucose and [3H]N-acetylmannosamine, in the arcuate nucleus of the rat hypothalamus is compared 30 min after intraventricular administration. Electron microscopic autoradiographs were analyzed by a sampling technique which provides information about (i) the distribution of radioactivity in the tissue, (ii) the relative volumes, and (iii) the amount of radioactivity per unit volume of the various tissue compartments. With both precursors, the highest incorporation was found in glial cell bodies, being about five to six times that of neurons. This holds true for all three types of glia. The concentration of radioactivity in the neuropil consisting of neuronal and glial processes was exceedingly low, although, due to its large volume, it contained the highest fraction of total tissue radioactivity. The limitations imposed on the interpretation of the data in terms of synthesis of fucosyl- and sialoglycoconjugates are discussed. It is proposed that the observations support the concept that high rates of synthesis for glycoproteins (and possibly gangliosides) are a characteristic metabolic property of glial cells.