UPTAKE OF PROTEIN BY MAMMALIAN NEURONS

Although the uptake of macromolecules by neurons often figures in theories of function in the nervous system (see reference 18), such uptake has actually been demonstrated only in a few instances, usually under special circumstances. In general, exogenous tracer proteins have been shown either to be stopped by "barriers" between the circulation and the nervous system (see references 3, 29) or to enter nonneuronal cells of nervous tissue, such as Schwann cells and capsule (satellite) cells (see references 21, 34). However, Rosenbluth and Wissig (30) using organ-cultured ganglia or massive intraperitoneal injection, have demonstrated uptake of ferritin by perikarya of toad ganglia. Also, Brightman (6, 7), using ferritin and peroxidase, and Becker et al. (2), using peroxidase, have reported protein uptake by rat and mouse central nervous system neurons after injection of the protein directly into cerebrospinal fluid or into extracellular spaces in the brain. In these several studies coated vesicles, multivesicular bodies, and dense bodies were found to be the chief intraneuronal sites of exogenous protein. In addition, several authors (1, 21, 35) have interpreted morphological observations as indicating pinocytic vesicle formation at neuronal surfaces. The present report deals with the uptake of horseradish peroxidase demonstrable in the perikarya and axons of the autonomic system which are scattered through the rat adrenal gland (the perikarya are of the ganglion cells; see references 14, 33 for additional details and references) and in neurons of mouse dorsal root ganglia grown in culture.