Rapid transport of protein in the optic system of the goldfish.

Several amino acids, particularly [3H]proline and [3H]asparagine specifically and efficiently labelled rapidly transported proteins in the goldfish optic nerve and tectum after intraocular injection. Studies with these amino acids showed that the rapidly transported proteins moved as a discrete band at a rate which was temperaturedependent, and was equal to 70-100 mm per day at 20°C. Transported protein in the optic tectum was 80 per cent particulate and was found in synaptosomal, mitochondrial, and myelin fractions, but not in purified nuclei or ribosomes. STUDIES on various mammalian and sub-mammalian species have demonstrated that protein is transported in axons at rates ranging from less than 1 mm per day to several hundred mm per day (LUBINSKA, 1964; WEISS, 1967; KARLSON and SJOSTRAND, 1968; LASEK, 1968; LIVETT, G E F F E N ~ ~ ~ A U S T I N , 1968; OCHS and JOHNSON, 1969; Blisnuw, 1969). Protein is reportedly transported in the optic nerve of the goldfish with at least two discrete rates, about 40 mm per day and 0.4 mm per day (MCEWEN and GRAFSTEIN, 1968). The rapidly transported protein was detected after injection of ['HIleucine into one eye by observing that within 6-12 h the radioactivity in the protein of the contralateral optic tectum was approximately double that of the ipsilateral optic tectum. Since free leucine apparently does not traverse the optic nerve, the excess of label in the contralateral tectum was presumably in protein transported from retinal ganglion cells in the injected eye to their corresponding nerve endings in the tectum. In the goldfish, the optic tracts are completely crossed and the tectum is a well-defined and easily removable brain area. These factors facilitate the study of transported protein in the nerve ending region. A complicating factor in such experiments is the high background labelling, as represented by the labelled non-transported protein in the ipsilateral tectum. This complication means that all calculations of transported radioactivity require the subtraction of one large number (ipsilateral radioactivity) from another large number (contralateral radioactivity). In the present study this complication was largely overcome by the use of amino acids which favourably label the transported protein, Studies on the kinetics of transport and subcellular distribution of protein labelled in this manner are presented. METHODS Fish storage undinjecrions. Goldfish (Curussius uurutus), 6-7 cm in body length, were obtained and stored as described previously KIM and AGRANOFF, 1969). Unless otherwise noted, fish-tank temperatures ranged from 18 to 23°C. In controlled temperature experiments the fish tanks were suspended This work was supported by grant MH 12506 of the National Institute of Mental Health and ' Interdisciplinary fellow, supported by Training Grant MH 07417 from the National InstitUte Abbreviutionr used: INT, 2-(piodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazol~um chloride. GB-5125X of the National Science Foundation.