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Biomedical subjects

T J Nelson

Publications and source records attributed to T J Nelson.

At least 19 recordsLinked to original sources
PubMed1995

Alzheimer and beta-amyloid-treated fibroblasts demonstrate a decrease in a memory-associated GTP-binding protein, Cp20.

The two proteins most consistently identified in the brains of patients with Alzheimer disease (AD) have been beta-amyloid and tau, whose roles in the physiology or pathophysiology of brain cells are not fully understood. To identify other protein(s) involved in AD that have been implicated in physiological contexts, we undertook to analyze a specific memory-associated protein, Cp20, in fibroblasts from AD and control donors. Cp20, a GTP-binding protein that is a member of the ADP-ribosylation factor family, was significantly decreased in fibroblasts from AD patients. Normal control fibroblasts exposed to 10 nM beta-amyloid, the same concentration that induced AD-like K+ changes in control fibroblasts, showed a similar decrease in Cp20. Since it has been previously demonstrated that Cp20 is a potent regulator of K+ channels, these findings suggest that changes in this memory-associated protein may explain previously observed differences in AD K+ channels and suggest a pathophysiologic involvement linked to soluble beta-amyloid metabolism that could contribute to the characteristic memory loss of AD.

Alzheimer Disease↗
PubMed1995

Phosphorylation of the conditioning-associated GTP-binding protein cp20 by protein kinase C.

The phosphorylation state of cp20, a low molecular weight membrane-associated GTP-binding protein, was previously shown to increase two- to threefold 24 h after associative conditioning. Here, cp20 is shown to be phosphorylated by protein kinase C (PKC) in vitro. Pronounced differences in activity were observed with the three major isoforms of PKC, whereas casein kinase, calcium/calmodulin-dependent protein kinase II, and cyclic AMP-dependent protein kinase produced no detectable phosphorylation of cp20. Phosphorylation of cp20 had no effect on its GTPase or GTP-binding activity but caused a translocation of cp20 from cytosol to the nuclei/mitochondrial particulate fraction. These results suggest that the increase in phosphorylation of cp20 after conditioning may be due to PKC.

Animals↗
PubMed1995

The assigned protection factor of 10 for half-mask respirators.

A number of researchers have published or presented papers on workplace protection factor (WPF) studies involving halfmask respirators. Individually, each study contains a relatively small amount of data, generally less than 25 data points for any single respirator. Because of the small amount of data, any attempt to quantify the result statistically does not provide useful information on the low end of the distribution of WPFs. Several studies on half-mask respirators were combined to yield a data set with 390 observations. Of these WPF data, 1.5% were less than 10, the best estimate of the 5th percentile was 13, with a 95% confidence interval of 10 to 18. Differences between the mean WPF based on the type of filter were found, but no difference was found between the mean performance of elastomeric and disposable respirators equipped with dust/mist and dust/fume/mist filters.

Evaluation Studies as Topic↗
PubMed1994

Characterization of a GTP-binding protein implicated in both memory storage and interorganelle vesicle transport.

The phosphorylation state of cp20, a low molecular weight GTP-binding protein that is a high-affinity substrate for protein kinase C, was previously shown to change after associative conditioning of molluscs and mammals and to induce many of the biophysical and structural modifications that accompany memory retention. Here, cp20 was purified from squid optic lobes and biochemically characterized. A monoclonal antibody prepared against squid cp20 reacted with Hermissenda cp20 and a 20-kDa protein in rabbit hippocampus, while a polyclonal antibody also cross-reacted with Sar1p and ADP-ribosylation factor (ARF). A partial peptide sequence of squid cp20 was 50% identical (23/46 amino acids) with Sar1p, a yeast GTP-binding protein involved in vesicle transport, indicating that cp20 is probably a new member of the ARF family. This classification is consistent with our recent demonstration that cp20 affects retrograde movement of intraaxonal organelles or particles and suggests a possible role for particle traffic between intraneuronal organelles in memory acquisition.

Amino Acid Sequence↗
PubMed1994

Internal Ca2+ mobilization is altered in fibroblasts from patients with Alzheimer disease.

The recent demonstration of K+ channel dysfunction in fibroblasts from Alzheimer disease (AD) patients and past observations of Ca(2+)-mediated K+ channel modulation during memory storage suggested that AD, which is characterized by memory loss and other cognitive deficits, might also involve dysfunction of intracellular Ca2+ mobilization. Bombesin-induced Ca2+ release, which is inositol trisphosphate-mediated, is shown here to be greatly enhanced in AD fibroblasts compared with fibroblasts from control groups. Bradykinin, another activator of phospholipase C, elicits similar enhancement of Ca2+ signaling in AD fibroblasts. By contrast, thapsigargin, an agent that releases Ca2+ by direct action on the endoplasmic reticulum, produced no differences in Ca2+ increase between AD and control fibroblasts. Depolarization-induced Ca2+ influx data previously demonstrated the absence of between-group differences of Ca2+ pumping and/or buffering. There was no correlation between the number of passages in tissue culture and the observed Ca2+ responses. Furthermore, cells of all groups were seeded and analyzed at the same densities. Radioligand binding experiments indicated that the number and affinity of bombesin receptors cannot explain the observed differences. These and previous observations suggest that the differences in bombesin and bradykinin responses in fibroblasts and perhaps other cell types are likely to be due to alteration of inositol trisphosphate-mediated release of intracellular Ca2+.

Adult↗
PubMed1993

GABA-mediated synaptic interaction between the visual and vestibular pathways of Hermissenda.

The synaptic convergence of the eyes and the vestibular hair cells in the nudibranch mollusc Hermissenda has been shown previously to mediate the learning of simple visual-vestibular associations. The neurotransmitter mediating this interaction between the visual and vestibular organs was characterized. HPLC chromatography, confirmed by mass spectroscopic analysis, demonstrated endogenous GABA in the statocysts, in a concentration approximately 150 times greater than in the whole CNS. Additional confirmation was provided by immunocytochemical localization of GABA in hair cell axons and branches that converge with photoreceptor terminal branches. Depolarization of the hair cells in the caudal region of the statocyst in response to positive current injection or vibratory stimulation caused a hyperpolarization and a cessation of the type B photoreceptor impulse activity. The inhibition of the B cell was unaffected by addition to the artificial sea water bath of the adrenergic antagonist yohimbine (250 microM), the cholinergic antagonist atropine (250 microM), and the serotonergic antagonist imipramine (50 microM). In contrast, the GABAA antagonist bicuculline (250 microM) significantly reduced the inhibitory interaction. Moreover, the GABA reuptake inhibitor guvisine (250 microM) increased the hyperpolarization. Pressure microapplication of GABA (12.5 or 25 microM) onto the terminal branches of the B cell resulted in a concentration-dependent hyperpolarization and cessation of spikes in the B cell. Depolarization of the caudal hair cell, or direct GABA application, decreased input resistance across the B cell soma membrane. Moreover, removal of chloride from the extracellular solution reduced inhibition of the B cell induced by GABA application or hair cell stimulation. Furthermore, application of the GABAB agonist baclofen hyperpolarized the type B cell and reduced or eliminated spontaneous impulse activity at the resting membrane potential. The reversal potentials for inhibition induced in all three procedures ranged from -70 to -80 mV and were consistent with mixed Cl- and K+ conductances. These results implicate GABA as the endogenous neurotransmitter mediating visual-vestibular interactions in this animal, and suggest a possible role of GABA in visual-vestibular associative learning.

Animals↗
PubMed1992

Rapid isoelectric focusing of proteins in hydrolytically stable capillaries.

Three new types of capillary coatings for capillary isoelectric focusing that avoid siloxane chemistry, resulting in hydrolytically stable coatings, are described and tested: phenyl-silica, acrylamide-reacted vinyl-silica, and pure PTFE. Capillaries of these three types were compared using standard proteins and a biological mixture of proteins similar to what might be encountered in actual use. Of these, the acrylamide-coated capillary produced the highest-quality results. In contrast to capillaries prepared using siloxane reactions, the capillaries described herein exhibited greatly enhanced stability at high pH.

Acrylamides↗
PubMed1991

Deconvolution method for accurate determination of overlapping peak areas in chromatograms.

A method is described for deconvoluting chromatograms which contain overlapping peaks. Parameters can be selected to ensure that attenuation of peak areas is uniform over any desired range of peak widths. A simple extension of the method greatly reduces the negative overshoot frequently encountered with deconvolutions. The deconvoluted chromatograms are suitable for integration by conventional methods.

Chromatography↗
PubMed1991

GTP-binding proteins and potassium channels involved in synaptic plasticity and learning.

Inhibition of potassium channels is possibly the first step in the sequence of biochemical events leading to memory formation. These channels appear to be regulated directly or indirectly by GTP-binding proteins (G proteins), which may themselves be affected by phosphorylation and dephosphorylation in response to elevated calcium levels or other phenomena resulting from the blockage of the potassium channels. A wide variety of cellular phenomena, from transcriptional changes to axonal transport, are thus capable of being initiated by these events.

Animals↗
PubMed1991

Classical conditioning-induced changes in low-molecular-weight GTP-binding proteins in rabbit hippocampus.

Classical conditioning of Hermissenda, involving paired light-rotation events, results in a 30-35% decrease in the levels of a 20-kDa G protein (cp20). To test whether a similar protein exists in vertebrates, rabbits were trained to associate a tone with periorbital electrical stimulation and G proteins were analyzed by photoaffinity labeling with [alpha-32P]GTP-azidoanilide. A 20-kDa G protein similar to cp20 decreased by 36% in the hippocampus of rabbits subjected to paired tone and electrical stimulation, but not in unpaired controls. Learning-specific decreases were also found in the amount of ras protein.

Acoustic Stimulation↗
PubMed1990

Specificity of molecular changes in neurons involved in memory storage.

Evidence implicating molecular steps in memory storage is discussed, particularly with reference to molecular specificity and uniqueness and the possible relevance of these steps to other types of long-lasting transformations such as those of development, regeneration, and tumorigenesis. The role of protein kinase C-mediated phosphorylation of identified protein subtrates, such as a 20,000-dalton GTP-binding protein, is described for associative memory of the snail Hermissenda, associative conditioning of the rabbit, and long-term potentiation. Cyclic AMP-mediated phosphorylation during sensitization of the snail Aplysia is also examined.

Animals↗
PubMed1990

Isolation of a G protein that is modified by learning and reduces potassium currents in Hermissenda.

In Hermissenda crassicornis conditioned to associate light and rotation, type B photoreceptor neurons exhibit pairing-specific decreases in the potassium currents IA and IK-Ca, which account for many of the behavioral changes elicited by associative conditioning. To determine which proteins are involved in storage of this memory, high-performance liquid chromatography was used to examine proteins from Hermissenda eyes. Conditioning-specific changes in four phosphoproteins were observed 24 hours after conditioning. One of these proteins, cp20, was purified to apparent homogeneity and found to be a G protein. When injected back into Hermissenda type B cells, cp20 reduced IK and IK-Ca in a manner indistinguishable from the reduction caused by conditioning, suggesting that this protein may play a crucial role in memory acquisition or retention.

Animals↗
PubMed1990

GYN implant orthogonal film holder.

An orthogonal film holder has been developed for the use of implants in the O.R. This film holder provides both AP and lateral films that are truly 90 degrees apart from each other. Placement of the GYN applicators must be checked before completion of the procedure. Traditionally, orthogonal films have been used for positioning and for the dose calculations. Therefore it is critical to have good quality radiographs. The AP film holder is placed beneath the patient and the lateral film holder slides into the side of the AP film holder, providing accurate placement and reproducibility in relation to each other. After the films have been approved, the lateral film holder bolts on top of the AP film holder. The system then looks like a briefcase and has a carrying handle for easy transportation and storage. This newly designed system has been used successfully and has proved its ease of use and accuracy.

Brachytherapy↗
PubMed1990

Specific high molecular weight mRNAs induced by associative learning in Hermissenda.

Associative conditioning of Hermissenda crassicornis has been demonstrated to result in long-term changes in the potassium currents IA and ICa2(+)-K+ in photoreceptor neurons in the eye and to increase mRNA levels in the eye 2- to 3-fold. mRNA isolated from Hermissenda trained with paired light and rotation stimuli was labeled with [3H]acetic anhydride, while mRNA from naive animals or from animals subjected to random light and rotation stimuli was labeled with [14C]acetic anhydride. The labeled RNA was combined and separated by agarose gel electrophoresis. The overall size distribution of labeled mRNA was shifted to longer chain lengths in the paired group. In addition, the 3H/14C ratios were markedly increased for 21 distinct size bands, indicating increased mRNA of specific chain lengths in the paired group. Increases in the same size bands were also observed with mRNA labeled in vivo with 32Pi. This indicates that associative learning in Hermissenda results in a specific induction of a distinct set of at least 21 mRNAs, rather than in a generalized increase in synthesis of all mRNA, thus resembling in some respects a differentiation-like response.

Animals↗
PubMed1989

Biteblock-head immobilizer system.

To accurately deliver high doses of radiation to the head and neck region one must be able to achieve three primary goals: reproduce the patient set-up or position, immobilize the patient, and most importantly, position the treatment field on the patient in the same exact location on a daily basis. Many patient positioning devices are available commercially but none address the concept of positioning the treatment field on the patient. The system presented in this paper accomplishes all 3 goals. Using a biteblock and a coordinate system, it has decreased the daily set-up time and improved the accuracy of the treatment field placement on the patient. Five hundred port films were reviewed retrospectively from previously treated patients who were treated without this new system (66% of those films were approved, and 34% needed some sort of adjustment). Using the new system the accuracy of 107 port films was determined (91% were approved, while only 9% needed any type of adjustment). This newly developed system provides the extra step, treatment accuracy, that no other device has done.

Dental Impression Technique↗
PubMed1988

Irradiating with a prosthesis or metal pin in the radiation treatment field.

This is a case study of a patient who had a liposarcoma of the tibia and also had a titanium pin directly in the treatment field. A total midline dose of 63 Gy was prescribed. The effects of the pin in the treated area was examined. Four different methods were used to examine and verify the delivered dose: (1) Treatment planning computerized isodose curves, (2) A parallel plate ion chamber and polystyrene phantom, (3) TLD, and (4) Film dosimetry. The results from all four methods of dose examination are compiled and are used to make a decision on what to do about the dose non-uniformity due to the dense titanium pin. If a prosthesis or metal pin is in the treatment area, one must determine the composition of the pin. Then one should verify or examine the results of the dose perturbations produced. One may or may not want to change the original dose prescription but the dose throughout the irradiated volume will be changed due to the metal pin. It is important to evaluate these effects, as discussed in this article, to accurately deliver a prescribed dose.

Bone Nails↗