SUMMARYIncubation of abdominal ganglia, obtained from Aplysia californica weighing 120-260 g, with octopamine or serotonin led t o marked increases in cAMP (cyclic adenosine 3',5'-monophosphate) levels after 10 min of incubation; these increases were blocked by phentolamine and methysergide, respectively. Incubation for 21 hr with octopamine also produced an elevation in cAMP levels but prolonged incubation with serotonin did not. Both these amines increased incorporation of a2P or 33P into a specific protein with apparent molecular weight of 118,000, upon incubation with the ganglion for 21 hr. The selective effect on this phosphoprotein was previously shown to be blocked by phentolamine (for octopamine effect) or methysergide (for serotonin effect) and could be mimicked by addition of dibutyryl cAMP to the medium.Incubation for more than 15 hr was required to generate a stable phosphoprotein pattern in which 5 phosphoprotein peaks could be reliably identified on polyacrylamide gels. With shorter incubations there was marked variability between ganglia with respect to the proteins which incorporated radioactive phosphate. The dibutyryl cAMP effect on phosphorylation of specific protein could not be demonstrated with incubations shorter than 15 hr.The specific effect on the phosphoprotein with molecular weight 118,000 was not observed in a number of large identified cells removed from the ganglion after 21 hr of incubation with radioactive phosphate and dibutyryl CAMP. The effect was also not observed in connective nerves and the bag cell clusters, but was consistently present in that portion of the ganglion remaining after these dissections. Upon subcellular fractionation the phenomenon was not observed in a crude nu-* Present address: Friedrich Meischer-Institut, Postfach 273, CH-4002 Basel, Switzerland.
SUMMARYThe transport of RNA from the ganglion cell bodies within the retina to the contralateral optic tectum has been studied in the chick following intraocular injection of radioactive uridine. By tracing the appearance of labeled RNA at the proximal end of the optic nerve as it leaves the eyeball and comparing this to the time of arrival of RNA within the optic tectum, the migratory velocity of axonal RNA has been calculated to be around 12 mm per day. The continuation of RNA migration to the optic tecturn in the presence of intracerebrally injected actinomycin-D but not in the presence of the intraocularly injected drug, suggests a retinal site of synthesis of the excess RNA found in the tectum innervated by the injected eye. A study of the rate of disppearance of radioactivity of the trans.-ported RNA in the optic lobes, suggested that this RNA turns over more rapidly than the bulk of tectal RNA. The destination of migrating RNA within the optic tectum has been autoradiographically examined. Most radioactive RNA is found in the outer tectal layers in which are found the afferent fibers of the optic tract and most of their synaptic terminations. Label is not confined to these areas however but is also present in the deeper layers of the optic tectum which are not known to contain any primary synapses of the axons from retinal ganglion cells.
Abstract— Several isotopic precursors have been monocularly injected into chick embryos and into day‐old or 15‐day‐old chicks. After various intervals, the incorporation of various isotopes into acid insoluble material within the retina of the injected eye and within the optic lobes, was determined. Radioactive proline and fucose were used as precursors of protein and glycoprotein respectively while uridine was used as an RNA precursor. The proportion of rapidly migrating proteins and glycoproteins was reduced during maturation. The extent of RNA migrating also appeared to decline during development. The proportion of synthesized protein that was transported was relatively constant and independent of the amino acid used. Around 30 per cent of retinally synthesized glycoprotein migrated distally and this migrating material appeared to contain very few sialic acid residues. A considerable amount of retinally synthesized gangliosides also appeared rapidly in the distal regions of the optic nerve.
SUMMARYThe development of axonal transport in the optic nerve of the developing chick has been investigated. Following monocular injection of radioactive fucose and proline, the specific activity of protein from paired optic lobes was determined in chick embryos and new-hatched chicks. In addition, the magnitude of the acid soluble precursor pool within lobes was assayed. The specific activity of protein in the optic lobe contralateral to (and innervated by) the injected eye relative to that of protein within the corresponding ipsilateral lobe (not innervated by the injected eye) was used as an index of axonal flow. In embryonic chicks from 8-12 days of age, four hours after injection of 3 H -f~~a~e into a single eye, this ratio was somewhat above unity. In the 13-day incubated embryo the ratio rose abruptly to over 10, and remained high throughout the period studied (up to one day after hatch). No similar sharp rise was found for the corresponding ratio for acid soluble radioactivity which remained under 2 in all ages of chicks examined. Parallel experiments with 14C-proline resulted in a smaller and more gradual development of asymmetry of specific activity of protein from paired optic lobes.These data suggest that, at the 13th day of incubation, specialized mechanisms develop for the rapid distal transport of glycoprotein synthesized within the retinal ganglion cells to terminations in the optic tectum. This phenomenon follows the major development of cerebral oxidative metabolism, but precedes the appearance of spontaneous or evoked potentials within the chick brain.
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