INCORPORATION OF 14C‐LABELLED LEUCINE INTO SYNAPTOSOMES FROM RAT CEREBRAL CORTEX IN VITRO

PROTEINS in the axon and axon terminal may be spatially far removed from the neuron nucleus. If nuclear control is exerted over protein synthesis in the axon, problems of supply of essential components for the synthetic mechanism must be overcome by the system. Several authors postulate that protein is synthesized in the perikaryon and is supplied to the axon by a process of axonal flow (WEISS and HISCOE, 1948; SAMUELS, BOYARSKY, GERARD, LIBET and BRUST, 1951; MIANI, 1960; DROZ and LEBLOND, 1963; AUSTIN, BRAY and YOUNG, 1966). However, none of these authors demonstrate that all axonal proteins are supplied from the perikaryon, and evidence has been produced by CLOUET and WAELSH (1961), KOENIG and KOELLE (1961) and KOENIG (19650) to demonstrate that at least one enzyme, acetylcholinesterase, is synthesized locally within the axon. The absence of ribonucleoprotein granules from the axoplasm (PALAY and PALADE, 1955) and the inability of NURNBERGER, ENGSTROM and LINDSTROM (1952) to demonstrate nucleic acids in axons by U.V. absorption analysis suggest at first sight that protein synthetic mechanisms are lacking from within the axon. More recently, however, low concentrations of RNA have been demonstrated as axonal components of axons of Mauthner cells of the gold fish (EDSTROM, EICHNER and EDSTROW, 1962; EDSTROM, 1964) of lobster sensory stretch receptor, (GRAMPP and EDSTROW, 1963) and the Xlth cranial nerve root of the cat (KOENIG, 196%). The development of techniques for the isolation of nerve ending components from brain by GRAY and WHITTAKER (1962) and DE ROBERTIS, PELLEGRINO DE IRALDI, RODRfCUEZ DE hREs ARNAIZ and SALGANICOFF (1962) has provided a new approach to the investigation of the problem of the site of synthesis of axonal proteins, particularly those contained within membranous structures in the synaptosome. The results reported here show the distribution of newly formed protein within subcellular structures of chopped rat brain cortex after incubation with isotopicallylabelled leucine and the effect of some inhibitors of protein synthesis on this incorporation. '