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PubMed1993

GTP gamma S inhibits organelle transport along axonal microtubules.

Movements of membrane-bounded organelles through cytoplasm frequently occur along microtubules, as in the neuron-specific case of fast axonal transport. To shed light on how microtubule-based organelle motility is regulated, pharmacological probes for GTP-binding proteins, or protein kinases or phosphatases were perfused into axoplasm extruded from squid (Loligo pealei) giant axons, and effects on fast axonal transport were monitored by quantitative video-enhanced light microscopy. GTP gamma S caused concentration-dependent and time-dependent declines in organelle transport velocities. GDP beta S was a less potent inhibitor. Excess GTP, but not GDP, masked the effects of coperfused GTP gamma S. The effects of GTP gamma S on transport were not mimicked by broad spectrum inhibitors of protein kinases (K-252a) or phosphatases (microcystin LR and okadaic acid), or as shown earlier, by ATP gamma S. Therefore, suppression of organelle motility by GTP gamma S was guanine nucleotide-specific and evidently did not involve irreversible transfer of thiophosphate groups to protein. Instead, the data imply that organelle transport in the axon is modulated by cycles of GTP hydrolysis and nucleotide exchange by one or more GTP-binding proteins. Fast axonal transport was not perturbed by AlF4-, indicating that the GTP gamma S-sensitive factors do not include heterotrimeric G-proteins. Potential axoplasmic targets of GTP gamma S include dynamin and multiple small GTP-binding proteins, which were shown to be present in squid axoplasm. These collective findings suggest a novel strategy for regulating microtubule-based organelle transport and a new role for GTP-binding proteins.

Animals↗
PubMed1972

Retrograde axonal transport in the central nervous system.

When horseradish peroxidase is injected into the optic tectum of a chick, axons of ganglion cells transport it centripetally to their cell bodies in the retina at a rate of about 72 millimeters per day. After intraocular injections in the young chick, the peroxidase is transported centripetally along efferent axons, and is concentrated in cell bodies within the isthmo-optic nucleus. This retrograde movement of protein from axon terminal to cell body suggests a possible mechanism by which neurons respond to their target areas.

Animals↗
PubMed1984

Axonal transport of receptors: coexistence with neurotransmitter and recycling.

Receptor sites move along the axon of neurones by means of fast transport mechanisms. In rat sciatic nerves, the accumulation of muscarinic receptors above a ligature was linear up to 24 hr after the operation and exactly paralleled that of dopamine-beta-hydroxylase. After 6-hydroxydopamine treatment, there was a marked reduction of these receptor sites in the rat sciatic nerve and the spleen. Fractionation of dog splenic nerves by differential and isopycnic centrifugation enabled us to show that the muscarinic receptors in sympathetic nerves are associated with noradrenaline and dopamine-beta-hydroxylase in synaptic vesicles. Receptor and neurotransmitter may thus coexist in the same subcellular organelle. Opiate receptors measured in vitro and in vivo with 3H-lofentanil in the rat vagus nerve were found to accumulate on both sides of the ligature. After capsaicin treatment this accumulation was markedly reduced suggesting that the opiate receptors in the vagus are mainly associated with substance P neurones. Double ligature experiments suggest the existence of a recycling phenomenon in the perikaryon for vesicles containing muscarinic receptors and dopamine-beta-hydroxylase. This may represent a pathway to convey informational molecules from the extracellular to the intracellular compartment of a neurone.

Animals↗