IMMUNOHISTOCHEMICAL LOCALIZATION OF ENDOGENOUS NERVE GROWTH-FACTOR

Nerve growth factor (NGF) has been proposed as a trophic molecule essential for the development of sympathetic and primary sensory neuron. In newborn mice and rats, administration of nerve growth factor results in an increase in the number of surviving neurons, whereas administration of antiserum to NGF decreases neuronal survival. It was proposed that the factor is produced and secreted by the relevant target tissues to provide trophic support for the ingrowing nerves. The site of synthesis of nerve growth factor is still unknown; a precise physiological role for the molecule cannot be ascribed until the cell types that produce it are known. Immunohistochemistry was used to localize endogenous NGF in the rat iris, a tissue in which there is sound biochemical evidence for the production of NCG activity. NGF was readily detected in Schwann cells, but not in smooth muscle cells of the iris when it is sympathetically denervated or cultured.