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PubMed1980

Uptake, intra-axonal transport and fate of horseradish peroxidase in embryonic spinal neurons of the chick.

Horseradish peroxidase (HRP) was injected in ovo into the ventral muscle mass of the hind limb of 5- to 7-day-old chick embryos or into the gastrocnemius muscle of 8- to 18-day embryos and localized histochemically. HRP is extensively incorporated via endocytosis into axonal growth cones or presynaptic terminals in the proximity of the injection site. Much of the tracer is taken up in vesicles and small vacuoles. Most of these are smooth-surfaced and only a few are bristle-coated. A small amount of the tracer is also incorporated into the axon terminal through the openings between the axolemma and an intricate membrane channel. The majority of the tracer-laden vesicles and vacuoles rapidly fuse with one another to become large vacuoles, some of which are transformed into multivesicular bodies (MVBs). In axon shafts, many labeled vacuoles and MVBs are transferred to tubule-like organelles, which appear to be the primary carrier for transporting the tracer back to the cell bodies in the lumbar spinal cord. HRP arrives in the sensory ganglia about 0.5-1 hour earlier than in the motoneurons of the lateral motor column. The maximal rate of the retrograde axoplasmic transport is about 3.5 mm/hour. After arriving in the cell bodies, HRP is transferred from tubule-like organelles to discrete vacuoles of various sizes and appearance. Lysosomal dense bodies and HRP-labeled vacuoles can be distinguished ultrastructurally. A fusion of HRP-labeled vacuoles with lysosomal dense bodies or Golgi vesicles was occasionally observed and the density of HRP-labeled vacuoles diminished after 2 to 3 days. Most of the HRP-labeled organelles were found to contain acid phosphatase activity. Therefore, the complete disappearance of HRP by 4 days postinjection is most likely related to lysosomal degradation. Neuronal cell bodies diffusely labeled with HRP were only observed prior to day 6. After day 6, despite various attempts to injure the peripheral axons, only granularly labeled cell bodies were found. This difference may imply that "mature" neurons have a more efficient mechanism for the sequestration of "free" HRP in the cytoplasmic matrix into membrane-bounded organelles. A mature-like retrograde transport mechanism appears to exist at the earliest stages of axonal growth in vivo.

Animals↗
PubMed1983

Differences in the kinetics of axonal transport for individual lipid classes in rat sciatic nerve.

Lipid precursors ([2-3H]glycerol for phospholipids and [3H]acetate for cholesterol) were injected into the L-5 dorsal root ganglion of adult rats. At various times, animals were killed, the ganglion and consecutive 5-mm segments of sciatic nerve were dissected, and lipids were extracted and analyzed by TLC. Individual lipid classes exhibited markedly different transport patterns. The crest of radioactive phosphatidylcholine moved as a sharply defined front at about 300 mm/day, with a relatively flat plateau behind the moving crest. Although some radioactive phosphatidylethanolamine also moved at the same rate, the crest was continually attenuated as it moved so that a gradient of radioactive phosphatidylethanolamine along the axon was maintained for several days. Transported diphosphatidylglycerol exhibited a defined crest, as did phosphatidylcholine, but moved at about half the rate. Labeled cholesterol was transported at a rapid rate similar to that for phosphatidylcholine and phosphatidylethanolamine, but like phosphatidylethanolamine, the initial moving crest of radioactivity was continually attenuated. Relative to the phospholipids, cholesterol showed a more prolonged period of accumulation in the axons and was more metabolically stable. We propose that most labeled phosphatidylcholine, phosphatidylethanolamine, and cholesterol is transported in similar (or the same) rapidly moving membranous particles. Once incorporated into these particles, molecules of phosphatidylcholine tend to maintain associated with them during transport. In contrast, molecules of phosphatidylethanolamine and cholesterol in these transported particles exchange extensively with unlabeled molecules in stationary axonal structures. Diphosphatidylglycerol, localized in a specialized organelle, the mitochondrion, is transported at a slower rate than other phospholipids, and does not exchange with other structures.

Acetates↗
PubMed1974

Axonal transport of newly synthesized glycoproteins in a single identified neuron of Aplysia californica.

Increasing amounts of glycoprotein synthesized from L-[(3)H]fucose injected into the cell body of R2, an identified Aplysia neuron, were found in the right pleuro-abdominal connective. Autoradiography revealed that the glycoproteins were localized in the axon of R2. Glycoproteins appearing in the axon presumably were synthesized in the cell body, since no significant incorporation was observed when [(3)H]fucose was injected directly into the axon. [(3)H]glycoproteins were detected in the connective after a delay of 1 h after intrasomatic injection. Thereafter, transport from the cell body was rapid, and by 10 h after injection, 45% of the total neuronal [(3)H]glycoprotein had appeared in the axon. By analysing the radioactivity in cell body and connective 4, 10, and 15 h after injection, we found that [(3)H]glycoproteins were transported selectively compared to nonmacromolecular material. Sequential sectioning of the connective revealed that [(3)H]glycoproteins were transported in discrete waves. The population of membrane-associated [(3)H]glycoproteins in the axon differed from that in the cell body. Two of the five somatic components appeared to be transported preferentially. In addition a new component appeared in the axon 10 h after injection.

Animals↗
PubMed1985

Localization and axonal transport of immunoreactive cholinergic organelles in rat motor neurons--an immunofluorescent study.

Antisera produced in rabbits against pure fractions of cholinergic vesicles from Narcine brasiliensis were used to study cholinergic organelles in rat motor neurons. The indirect immunofluorescence method was used on perfusion-fixed material. The rats were surgically sympathectomized to remove sympathetic adrenergic and cholinergic nerves from the sciatic nerve. In the intact animal immunoreactive material, likely to represent cholinergic vesicles, was observed in motor endplates, identified by labelling with rhodamine-conjugated alpha-bungarotoxin or with subsequent acetylcholinesterase staining. The motor perikarya contained very little immunoreactive material. Non-terminal axons were virtually devoid of immunofluorescence in the intact animal. After crushing the sciatic nerve, immunoreactive material (likely to represent axonal cholinergic organelles) accumulated rapidly on both sides of the crush, indicating a rapid bidirectional transport. The transport was sensitive to local application of mitotic inhibitors. The axons which accumulated immunoreactive organelles were motor axons, as demonstrated by various procedures: Cutting of ventral roots prevented accumulation of immunoreactive material in the nerve. Deafferentation did not notably influence accumulations of immunoreactive material. Ligated axons with immunoreactive material were acetylcholinesterase positive when identification was made on the same section; the intra-axonal distribution of immunoreactive material and acetylcholinesterase was not identical, however, and the Narcine antisera did not cross-react with bovine acetylcholinesterase in a solid phase immunoassay. Most axons in ventral roots, but not in dorsal roots, accumulated strongly fluorescent immunoreactive material, while axons in dorsal roots contained weakly fluorescent material. On the other hand, substance P-like immune reactivity was present in many dorsal root axons, but only very rarely in ventral roots. It is suggested that the antisera against Narcine cholinergic vesicles can be used as a marker for cholinergic organelles in the motor neuron, and may be an important tool for studying the axonal cholinergic vesicles. It cannot, however, be used to identify cholinergic structures in unknown locations because it recognizes common antigenic determinants in transmitter organelles of other nerves, e.g. adrenergic nerves. The axonal cholinergic organelles may carry important molecules, other than acetylcholine to the nerve endings.

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