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D L Gilbert

Publications and source records attributed to D L Gilbert.

At least 55 records · Page 3Linked to original sources
PubMed1996

Location-dependent artifact for no measurement using multiwell plates.

The Griess reaction is widely used to measure the cellular production of NO by detecting the supernatant levels of nitrite. Ordinarily, background levels of nitrite in the media are subtracted from the levels of nitrite produced by the cells by preparing a "blank" during the determination of the standard curve. Although this method is adequate for most experimental conditions, it cannot be used when cell supernatants are collected from multiwell dishes, particularly when low amounts of NO are produced and when long incubation periods are required to induce NO production. Our data show that a highly variable level of nitrite is found in the absence of cells in the media from wells at the edges of the 96-well plate while media from interior wells shows no detectable nitrite accumulation. The most likely source of this noncellular NO is from nitric oxides (NOx) found in the ambient air and reduction of air exchange or regulation of the gaseous environment eliminates this "border effect."

Analysis of Variance↗
PubMed1995

Protection from oxidation enhances the survival of cultured mesencephalic neurons.

Oxidative stress has been linked to the destruction of dopaminergic neurons in the substantia nigra and may be a significant factor in both Parkinson's disease and MPTP toxicity. Using primary cultures of embryonic rat mesencephalon and standard immunocytochemical techniques, we have examined the survival of tyrosine hydroxylase-containing (TH+) neurons cultured in the presence of antioxidants and/or in an environment of low oxygen partial pressure. The number of TH+ neurons increased approximately twofold if superoxide dismutase, glutathione peroxidase (GP), or N-acetyl cysteine (NAC) were added to the culture media. Exposure of the neurons to a 5% oxygen environment (38 torr, i.e., 38 mm Hg) also increased the survival of TH+ neurons by about twofold. A dramatic enhancement of survival, however, was seen when NAC was used in combination with the 5% oxygen environment. In this case, the number of TH+ neurons increased fourfold from nontreated controls. Morphological changes were also noted. GP increased the average neurite length while NAC increased the average area of the cell body in the TH+ neuron. These results suggest that manipulation of oxidative conditions by changing the ambient O2 tension or the level of antioxidants promotes survival of TH+ neurons in culture and may have implications for transplantation therapies in Parkinson's disease.

Acetylcysteine↗
PubMed1994

K+ modulation of microglial superoxide production: involvement of voltage-gated Ca2+ channels.

A variety of cytoactive factors produced during injury and inflammation are known to activate the central nervous system (CNS) macrophage, the microglia. Since extracellular potassium levels are known to rise rapidly at sites of injury in the CNS, we examined the possibility that changes in extracellular potassium could mediate changes in microglial function. The effect of an increase in potassium concentration on microglial superoxide anion production was studied in cultured neonatal rat microglia. Rather than directly inducing superoxide anion production, exposure to media containing 25 and 55 mM potassium enhanced the production of superoxide induced by phorbol 12-myristate 13-acetate. This potentiation was blocked by nifedipine, a voltage-gated calcium channel blocker. Treatment of the microglia with BAY K 8644, an agonist for voltage-gated calcium channels, produced an enhancement of superoxide levels similar to that of potassium. Because these data indicated the presence of a voltage-gated calcium channel, we also examined whole cell current in cultured microglia. A small, voltage-dependent inward calcium current was seen that was increased by exposure of the microglia to BAY K 8644. The presence of a small but finite calcium influx via these channels may be an important factor in the regulation of intracellular microglial events such as activation of the NADPH oxidase and the consequent production of superoxide anion.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1992

Oxygen dependency of synaptic transmission at the squid Loligo pealei giant synapse.

1. Synaptic transmission at the squid giant synapse was blocked in 45 min by exposure to 0.02 atm oxygen but was maintained for more than 90 min in air (0.21 atm oxygen) or pure oxygen (1 atm). 2. Excitatory post-synaptic potential amplitude decreased in 0.02 atm oxygen but did not change in either 1 or 0.21 atm oxygen. Fast facilitation was increased in 0.02 atm oxygen only. 3. Post-synaptic resting membrane potential (Vm) and input resistance (Ro) remained unchanged in 1 or 0.21 atm oxygen but Ro was increased in 0.02 atm oxygen. 4. Our results suggest that severe hypoxia decreased the release of transmitter from the pre-synaptic terminal.

Animals↗
PubMed1991

Membrane bilayer assembly in neural tissue of rat and squid as a critical phenomenon: influence of temperature and membrane proteins.

Cell membrane bilayers have been reconstructed in vitro utilizing total lipid extracts from rat neural tissue (forebrain, cerebellum, brainstem and spinal cord) and from the optic lobe and fin nerve of the squid Loligo pealei. In agreement with the critical state theory of bilayer assembly (Gershfeld, N.L. 1986. Biophys. J. 50:457-461; Gershfeld, NL.L. 1989. J. Phys. Chem. 93:5256-5261), these lipid extracts spontaneously formed purely unilamellar structures in aqueous dispersion, but only at a critical temperature, T*, which was species dependent. For all the rat tissues T* = 37 +/- 1 degrees C; for squid neural extracts T* = 15.5 +/- 1.4 degrees C. These values correspond to 'physiological' temperatures for both organisms, implying that their lipid metabolism is geared to permit spontaneous assembly of unilamellar membranes at the ambient temperature in the tissues. Membrane protein composition had little or no effect on critical bilayer formation.

Animals↗
PubMed1991

The Pariacaca or Tullujuto story: political realism?

The first documented description of acute altitude sickness was published by Father Acosta in 1590. Acosta described this sickness when he traveled through a pass across the Andean divide in central Peru near the mountain Pariacaca. Almost all the maps of modern Peru do not name this mountain. We present evidence that mountaineers who have climbed this mountain know it as Tullujuto. This change in name is the reason why physiologists have found it difficult to locate Acosta's route; consequently the altitude where Acosta experienced this sickness could not be determined until recently. Further, we speculate that political pressures in the late 18th century caused the place name of Pariacaca either to be obliterated or else to be changed to Tullujuto.

Altitude Sickness↗
PubMed1990

Macromolecular release from collagen monolithic devices.

Collagen monolithic devices varying in crosslinking density, collagen structure, and crosslinker were fabricated. In vitro release rates of a model macromolecule, inulin, were found to be linear with t1/2 and were affected by crosslinking density, nature of crosslinker, and collagen structure. The biodegradation of the collagen matrix was also examined. Proteolytic enzymes did not degrade the collagen devices; the degradation rate with collagenase was dependent on collagen structure, crosslinker, crosslinking density, and enzyme concentration. In vivo biocompatibility, degradation, and 14C-inulin release rates were evaluated subcutaneously in rats. After 3 weeks, none of the collagen discs induced any severe cellular response. Dacron induced a stronger fibroblast response but fewer inflammatory cells as compared to the collagen discs. No significant degradation of the collagen discs occurred within 3 weeks. In vivo release of 14C-inulin from collagen monolithic devices was diffusion controlled.

Animals↗
PubMed1990

Chemotaxis by a CNS macrophage, the microglia.

Microglia demonstrate many characteristics similar to those seen in monocytes and tissue-specific macrophages, including phagocytosis, production of oxygen radicals, and growth factors and expression of MHC antigens. We have examined the ability of microglia, cultured from the cerebral cortices of neonatal rats, to demonstrate another important functional characteristic of monocytic-derived cells, that is, chemotaxis. Our results show that cultured rat microglia demonstrate chemotaxis to complement dependent chemoattractants such as recombinant C5a, zymosan activated serum, and to rat serum as well as to transforming growth factor-beta, a chemoattractant produced by platelets. Microglia fail to migrate to bacterial dependent chemoattractants such as the N-formyl peptides. The failure to respond is not dependent on maturational state of the microglia. Treatment with DMSO or casein, agents known to induce morphological and functional changes in cultured microglia reminescent of a "resting" and an "activated" macrophage, respectively, do not alter the response to fMet-Leu-Phe. In addition, the chemotactic response to serum in DMSO or casein-treated cells is the same as the response seen in untreated day 10 cultured microglia or untreated age-matched controls. The ability of microglia to migrate in response to inflammatory mediators suggests that these cells can move to sites of injury, thereby enabling them to participate in an inflammatory response.

Animals↗
PubMed1987

Production of superoxide anions by a CNS macrophage, the microglia.

Microglia have been implicated in both physiological and pathological processes of the brain. Their possible roles have been compared to those of macrophages and granulocytes. Here we demonstrate that specific ability of microglia to secrete the superoxide radical ion in response to a complement activated agent, opsonized zymosan, and to phorbol myristate acetate. As in other organs, this endogenously produced reactive oxygen intermediate could have both beneficial and deleterious effects.

Animals↗
PubMed1987

In vitro and in vivo characterization of synthetic polymer/biopolymer composites.

Collagen, extracted from rat tail tendons using dilute acetic acid, was fabricated into films for subsequent characterization and biocompatibility testing. The reconstituted collagen was characterized with infrared spectroscopy, solution viscosity, contact angle, and tensile testing techniques and was found to be pure with molecular and physical properties consistent with findings of previous researchers. Composites composed of collagen coated on urethane and Silastic Rubber films were fabricated to give improved tear resistance. The biocompatibility of the composites and individual polymers was evaluated by discs implanted in the paravertebral muscle of rabbits. After four weeks none of the materials induced any gross changes in the muscle. Histopathological evaluation revealed a fibrous capsule around all of the materials. Collagen and collagen composites exhibited a stronger reaction as evidenced by a larger fibroblast layer and a variety of inflammatory cells, lymphocytes, eosinophils, and macrophages. The urethane was rated with a response index of 1.5 versus 3.25 for the urethane/collagen composite; Silastic Rubber rated a response index of 1.67 versus 3.12 for the Silastic Rubber/collagen composite; collagen rated a response index of 3.3. The polyester sutures also induced a reaction with a larger fibrous capsule but fewer inflammatory cells as compared to collagen and collagen composites.

Animals↗
PubMed1986

Changes in synaptic transmission produced by hydrogen peroxide.

The effect of hydrogen peroxide (H2O2) on excitatory and inhibitory synaptic transmission was studied at the lobster neuromuscular junction. H2O2 produced a dose dependent decrease in the amplitude of the junction potential (Vejp). This decrease was due to changes in both presynaptic transmitter release and the postsynaptic response to the neurotransmitter. Observed presynaptic changes due to exposure to H2O2 were a decrease in the amount of transmitter released, that is, quantal content, as well as a decrease in the fast facilitation, that is, the amplitude increase of successive excitatory junction potentials at a rate of 3 Hz. To discern postsynaptic changes, glutamate, the putative excitatory neurotransmitter for this preparation was applied directly to the bathing medium in order to bypass the presynaptic release process. H2O2 produced a decreased response of the glutamate receptor/ionophore. The action of H2O2 was not selective to excitatory (glutamate-mediated) transmission because inhibitory (GABA-mediated) transmission was also depressed by H2O2. This effect was primarily presynaptic since H2O2 produced no change in the postsynaptic response to applied GABA.

Animals↗
PubMed1983

The first documented report of mountain sickness: the China or Headache Mountain story.

This article gives the probable location within 65 km of the Big Headache Mountain where mountain sickness was first reported by Too Kin, a Chinese official, in 37-32 B.C. We believe that traveling over the western edge of the Himalayan Karakoram Range or in the Pamirs caused the major difficulties, probably when travelers crossed the Kilik Pass at an altitude of 4827 m or 15837 ft or within 60 km of this pass and at an altitude of at least 4500 m or 14750 ft. We theorize that the route Too Kin described is from Kashi, an important center in Sinkiang or Chinese Turkestan, to Kabul in Afghanistan. This particular route has two other altitude maxima; one at the Ulagh Rabat Pass in Sinkiang about 15 km west of the Muztagata peak where the elevation is 4250 m or 14000 ft, and the other at the Shandur Pass over the Hindu Kush in Pakistan where the elevation is 3734 m or 12250 ft.

Altitude Sickness↗
PubMed1983

The first documented description of mountain sickness: the Andean or Pariacaca story.

We describe here for the first time the actual route that Acosta took when he described mountain sickness so vividly in the sixteenth century. We have shown that when Acosta mentioned Pariacaca as the geographical site where he experienced high altitude sickness, this referred not only to the modern peak of Pariachaca, but to the snow covered mountains by this Cerro, and the Central Maritime Andean Range in Peru. In addition, the name Pariacaca also referred to a tambo or inn located on the plateau or Puno of Pariacaca. The location of this route has been obtained by locating primary descriptions on maps from the sixteenth to the eighteenth centuries. Using twentieth century maps, we have been able to identify the described sites along the road and the trail which still exists by them. In addition, using detailed topographical maps, an altitude profile of the trail was obtained. The maximum altitude on this trail or old road reached 4800 m (15750 ft), about the same elevation as the summit of Mt. Blanc, the highest mountain in western Europe.

Altitude Sickness↗