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D L Barker

Publications and source records attributed to D L Barker.

10 recordsLinked to original sources
PubMed1990

Autoradiography using storage phosphor technology.

We describe the application of photostimulable storage phosphor imaging plates to autoradiography of samples labeled with 32P, 14C and 35S. Imaging plates can detect a 32P-labeled sample at an exposure level of 1 disintegration/mm2, and 14C and 35S at 25 disintegrations/mm2. Compared to X-ray film, imaging plates offer increased sensitivity of 15- to 250-fold for 32P and 20- to 100-fold for 14C and 35S. Resolution is in the 0.3 mm range and is therefore suitable for any gel or blot application.

Autoradiography↗
PubMed1988

Muscarinic antagonist enhances one-trial food-aversion learning in the mollusc Pleurobranchaea.

One hour before training, in two replicate studies on the sea slug Pleurobranchaea californica, all animals (N = 114) received body-cavity injections of scopolamine, oxotremorine, or the equivalent volume of the saline/seawater vehicle that was used to inject the drugs. The low drug doses (2 mumol/kg) were near the threshold for generating observable neurophysiological responses, but did not affect feeding thresholds arising to a stimulus derived from beer (Sbr) and to one derived from squid (Ssq). Before training, the animals did not discriminate between Sbr and Ssq, as indicated by similar thresholds to both stimuli. During training, experimental animals in each injection group received Sbr alone for 10 sec and then paired with electric shocks for 50 sec; control animals received shocks 1 hr after Sbr. Postconditioning tests began 12 hr after training and were repeated once daily thereafter. After training, all experimental groups exhibited the expected aversive behavior to Sbr, as indicated by 100- to 1000-fold increases in feeding thresholds, and retained low thresholds to Ssq, but the scopolamine animals were better able to discriminate between Sbr and Ssq than either of the other experimental groups. The aversive responses to Sbr increased over a 3-day period, but there appeared to be no difference between injection groups on such a long-duration "consolidation" phase. Of the control groups, only the scopolamine animals exhibited low feeding thresholds to both Sbr and Ssq. The other control groups exhibited similar behavior as the experimental animals, indicating that associative factors relating to the 1-hr separation between Sbr and shocks may have produced the behavior in these control animals. Thus, by comparison to the other injections, scopolamine 1) increased the ability of the experimental animals to make the discrimination between Sbr and Ssq, and 2) prevented learning to avoid Sbr in the control animals. An accompanying paper provides a detailed characterization of muscarinic receptor pharmacology in Pleurobranchaea.

Animals↗
PubMed1988

Migration and differentiation of neural crest and ventral neural tube cells in vitro: implications for in vitro and in vivo studies of the neural crest.

During vertebrate development, neural crest cells migrate from the dorsal neural tube and give rise to pigment cells and most peripheral ganglia. To study these complex processes it is helpful to make use of in vitro techniques, but the transient and morphologically ill-defined nature of neural crest cells makes it difficult to isolate a pure population of undifferentiated cells. We have used several established techniques to obtain neural crest-containing cultures from quail embryos and have compared their subsequent differentiation. We confirm earlier reports of neural crest cell differentiation in vitro into pigment cells and catecholamine-containing neurons. However, our results strongly suggest that the 5-HT-containing cells that develop in outgrowths from thoracic neural tube explants are not neural crest cells. Instead, these cells arise from ventral neural tube precursors that normally give rise to a population of serotonergic neurons in the spinal cord and, in vitro, migrate from the neural tube. Therefore, results based on previously accepted operational definitions of neural crest cells may not be valid and should be reexamined. Furthermore, the demonstration that cells from the ventral (non-neural crest) part of the neural tube migrate in vitro suggests that the same phenomenon may occur in vivo. We propose that the embryonic "neural trough," as well as the neural crest, may contribute to the PNS of vertebrates.

Animals↗
PubMed1986

Characterization of muscarinic cholinergic receptors in the crab nervous system.

The selective muscarinic antagonist L-[3H]-quinuclidinyl benzilate (L-[3H]QNB) binds reversibly and with high affinity (KD = 0.3 nM) to a single population (Bmax = 105 fmol/mg protein) of specific sites in nervous tissue of the crab Cancer magister. The binding site is stereoselective; (-)QNB is over 200 times more potent than (+)QNB as an inhibitor of specific L-[3H]QNB binding. The muscarinic antagonists scopolamine and atropine are over 10,000 times more potent inhibitors of L-[3H]QNB binding than the nicotinic antagonists decamethonium and d-tubocurarine. The muscarinic agonists oxotremorine, pilocarpine, arecoline, and carbachol also compete effectively for the L-[3H]QNB binding site. This pharmacological profile strongly suggests the presence of classical muscarinic receptors in the crab nervous system. These receptors are localized to nervous tissue containing cell bodies and neuropil, whereas specific L-[3H]QNB binding is low or absent in peripheral nerve, skeletal muscle, and artery.

Animals↗
PubMed1985

Sprouting and functional regeneration of an identified serotonergic neuron following axotomy.

An identified serotonergic neuron (C1) in the cerebral ganglion of Helisoma trivolvis sprouts following axotomy and rapidly (seven to eight days) regenerates to recover its regulation of feeding motor output from neurons of the buccal ganglia. The morphologies of normal and regenerated neurons C1 were compared. Intracellular injection of the fluorescent dye, Lucifer Yellow, into neuron C1 was compared with serotonin immunofluorescent staining of the cerebral and buccal ganglia. The two techniques revealed different and complimentary representations of the morphology of neuron C1. Lucifer Yellow provided optimal staining of the soma, major axon branches, and dendritic arborization. Immunocytochemical staining revealed terminal axon branches on distant targets and showed an extensive plexus of fine fibers in the sheaths of ganglia and nerve trunks. In addition to C1, serotonin-like immunoreactivity was localized in approximately 30 other neurons in each of the paired cerebral ganglia. Only cerebral neurons C1 had axons projecting to the buccal ganglia. No neuronal somata in the buccal ganglia displayed serotonin-like immunoreactivity. Observations of regenerating neurons C1 demonstrated: Actively growing neurites, both in situ and in cell culture, displayed serotonin-like immunoreactivity; severed distal axons of C1 retained serotonin-like immunoreactivity for up to 28 days; axotomized neurons C1 regenerated to restore functional control over the feeding motor program.

Animals↗
PubMed1985

Stereoselective L-[3H]quinuclidinyl benzilate-binding sites in nervous tissue of Aplysia californica: evidence for muscarinic receptors.

The muscarinic antagonist L-[3H]quinuclidinyl benzilate (L-[3H]QNB) binds with a high affinity (Kd = 0.77 nM) to a single population of specific sites (Bmax = 47 fmol/mg of protein) in nervous tissue of the gastropod mollusc, Aplysia. The specific L-[3H]QNB binding is displaced stereoselectively by the enantiomers of benzetimide, dexetimide, and levetimide. The pharmacologically active enantiomer, dexetimide, is more potent than levetimide as an inhibitor of L-[3H]QNB binding. Moreover, the muscarinic cholinergic ligands, scopolamine, atropine, oxotremorine, and pilocarpine are effective inhibitors of the specific L-[3H]QNB binding, whereas nicotinic receptor antagonists, decamethonium and d-tubocurarine, are considerably less effective. These pharmacological characteristics of the L-[3H]QNB-binding site provide evidence for classical muscarinic receptors in Aplysia nervous tissue. The physiological relevance of the dexetimide-displaceable L-[3H]QNB-binding site was supported by the demonstration of the sensitivity of the specific binding to thermal denaturation. Specific binding of L-[3H]QNB was also detected in nervous tissue of another marine gastropod, Pleurobranchaea californica. The characteristics of the Aplysia L-[3H]QNB-binding site are in accordance with studies of numerous vertebrate and invertebrate tissues indicating that the muscarinic cholinergic receptor site has been highly conserved through evolution.

Animals↗
PubMed1979

Synthesis of dopamine and octopamine in the crustacean stomatogastric nervous system.

The spiny lobster stomatogastric nervous system synthesizes dopamine and octopamine in vitro from exogenous [3H]tyrosine. Each amine accumulates with a specific distribution among 9 separately analyzed regions within the system. Synthesis of other catecholamines was not observed. [3H]Dopamine is found in nerves, ganglia, and identified commissural ganglion cell bodies in which catecholamine histofluorescence has been demonstrated. The biosynthetic and histochemical data together indicate that dopaminergic cells send axons from the commissural ganglia to the stomatogastric ganglion neuropil along the same pathway followed by fibers that activate the pylroic motor network. The results support the hypothesis that dopamine mediates activation of the pyloric system in vivo, as observed in vitro. [3H]Octopamine accumulates primarily in the commissural and stomatogastric ganglia, where it may modulate neuronal activity, but octopaminergic cells and release sites within the stomatogastric system have not been identified.

Animals↗
PubMed1975

Synthesis of octopamine by insect dorsal median unpaired neurons.

Dorsal unpaired median (DUM) neurons of locusts and grasshoppers inhibit the instrinsic rhythm of contraction of metathoracic extensor tibia muscle fibers. This physiological action is mimicked by very low concentrations of octopamine and by higher concentrations of dopamine and noradrenaline. We have examined the synthesis of biogenic amines from tritiated tyrosine by these neurons. DUM cell bodies and a peripheral nerve containing the DUM axon which terminates in the extensor tibia both produced octopamine, but neither noradrenaline nor dopamine synthesis was detected. The observations support the suggestion that the dorsal unpaired median neurons are octopaminergic.

Animals↗