Bidirectional axonal transport of free glycine in identified neurons R3--R14 of Aplysia.
The axonal transport of 3H-amino acids was studied in the axons of identified neurons R3--R14 in the parietovisceral ganglion (PVG) of the mollusc Aplysia. The PVG was incubated (3--24 hr) in media containing physiological concentrations of single 3H-amino acids while the isolated nerve was superfused with plain or chemically altered media. The nerve was then sliced into sequential segments for biochemical analyses or fixed for autoradiography. 3H-glucine was transported at 70 mm/day in 6X greater quantities than other amino acids which were transported at less than 40 mm/day. In the 3H-glycine experiments, greater than 80% of the label transported into the nerve remained as free glycine, comigrating with glycine in thin-layer chromatographs. In autoradiographs of sections 4 mm from the ganglion-nerve barrier, greater than 50% of the silver grains were over R3--R14 axons which occupy less than 10% of the nerve cross-sectional area. EM autoradiographs confirmed that grains were within R3--R14 and not in surrounding glia. The selective transport of glycine was inhibited by Hg2+, by vinblastine and Nocodazole, and by low Ca2+ media. Autoradiographs of vinblastine-treated nerves showed a drastic reduction in label over R3--R14 and other axons. Label was also transported retrogradely; this transport rate was similar to the orthograde rate, but 5--10 times less label moved retrogradely. Autoradiographs showed that the retrograde label was localized to R3--R14 axons. This report clearly demonstrates the rapid, selective, and bidirectional transport of a free amino acid and provides further evidence that glycine may be used as a neurochemical messenter by neurons R3--R14.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001048:Aplysia / Q000502:physiology; D001345:Autoradiography; D001370:Axonal Transport / Q000187:drug effects; D003078:Colchicine / Q000494:pharmacology; D005724:Ganglia / Q000166:cytology*; D005998:Glycine / Q000378:metabolism*; D008628:Mercury / Q000494:pharmacology; D008870:Microtubules / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010070:Oxalates / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
D000596:Amino Acids; D010070:Oxalates; D014747:Vinblastine; D008628:Mercury; D003078:Colchicine; D005998:Glycine