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D J McAdoo

Publications and source records attributed to D J McAdoo.

6 recordsLinked to original sources
PubMed1979

Anatomy and ultrastructure of the axons and terminals of neurons R3-R14 in Aplysia.

Using light and electron microscopy and autoradiography, we have traced the axons of neurons R3-R14 in the parietovisceral ganglion (PVG) of Aplysia to terminal fields associated with vascular tissue. The axons are identified by their large size (15-30 micrometer diameter), extensive glial infolding, characteristic dense core vesicles (DCV; approximately 180 nm diameter), and specific, rapid uptake of 3H-glycine. Each neuron in this homogeneous group sends an axon via the branchial nerve to the pericardial region surrounding the junction of the efferent gill vein and the heart. R14 also sends axons to major arteries near the PVG. The R3-R14 axons branch extensively; we estimate that there are at least several hundred per cell. Branches along axons in the branchial nerve exit the nerve, subdivide, and end blindly in the sheath which is bathed by hemolymph. Similar blind endings from R3R14 occur in the sheath of the PVG (Coggeshall, '67). Axonal branches in the pericardial region and the special R14 axons in the arterial walls form both varicose endings near and terminals in contact with vasvular smooth muscle. All R3-R14 endings are free of glia, packed with DCV, show occasional omega-shaped profiles and rapidly take up 3H-glycine. R3-R14 manufacture specific low molecular weight peptides (Gainer and Wollberg, '74), and both the cell bodies (Iliffe et al., '77) and the germinals contain unusually high concentrations of glycine. The presence of peptides as putative neurohormones and sheath endings (neurohormonal release areas) are consistent with R3-R14 being neurosecretory (Coggeshall et al., '66). While glycine could not be a circulating hormone due to its high circulating levels (Iliffe et al., '77), glycine could act as a local chemical messenger between R3-R14 and smooth muscle. The terminal morphology of R3-R14 is consistent with these neurons having both synaptic-type and neurosecretory-type functions.

Animals↗
PubMed1979

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.

Amino Acids↗
PubMed1978

Serotonin shifts the phase of the circadian rhythm from the Aplysia eye.

A putative neurotransmitter, serotonin, may be used to transmit temporal information in the eye of Aplysia, because it can shift the phase of the circadian rhythm of spontaneous optic nerve impulses from the eye and the eye contains a significant quantity of serotonin. Serotonin acts either directly on the cell, or cells, containing the circadian pacemaker or on cells electronically coupled to the pacemaker cells.

5-Hydroxytryptophan↗
PubMed1978

Specific glycine uptake by identified neurons of Aplysia californica. II. Biochemistry.

Glycine is taken up twice as rapidly by neurons R3-R14 as by other identified neurons in the Aplysia parietovisceral ganglion. Earlier studies had shown that R3-R14 have much higher glycine concentrations than other Aplysia neurons. Most of the glycine taken up by R3-R14 was biochemically untransformed for at least 1 h following its uptake. Glycine is actively transported into into R3-R14 and other Aplysia neurons by carrier-mediated processes. Glycine uptake by R3-R14 was markedly reduced in the absence of Na+ and in the presence of Hg2+, while these treatments had little effect on glycine uptake by other Aplysia neurons. There appears to be a special glycine uptake system present in R3-R14 and a general glycine uptake system common to all Aplysia neurons. The elevated glycine concentrations and special glycine uptake associated with R3-R14 may indicate that glycine is utilized as a neurotransmitter by those neurons.

Alanine↗