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Biomedical subjects

R R Miller

Publications and source records attributed to R R Miller.

At least 91 records · Page 5Linked to original sources
PubMed1994

Styrene production, use, and human exposure.

Styrene is an extremely important commodity chemical used extensively in the manufacture of numerous polymers and copolymers, including polystyrene, acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), styrene-butadiene latex, and styrene-butadiene rubber. Styrene is a component of cigarette smoke and automobile exhaust, and it may occur naturally at low levels in various types of foods. The highest potential human exposures to styrene occur in occupational settings, particularly those involving the production of large glass-reinforced polyester products such as boats, which require manual lay-up and spray-up operations. Substantially lower occupational exposures occur in styrene monomer and polymer production facilities. The general public is exposed to very low concentrations of styrene in ambient air, indoor air, food, and drinking water.

Environmental Pollution↗
PubMed1994

Second-order conditioning and Pavlovian conditioned inhibition: operational similarities and differences.

Procedures for establishing second-order excitation (conditioned stimulus [CS] 1-unconditioned stimulus [US] trials followed by CS2-CS1 trials) are highly similar to those for Pavlovian conditioned inhibition (CS1-US trials interspersed with CS2-CS1 trials). Conditioned suppression in rats was used to identify the critical operational differences that result in second-order excitation as opposed to Pavlovian inhibition. No, few, or many CS2-CS1 trials were either interspersed with or given after CS1-US trials. CS2 proved excitatory only after few CS2-CS1 trials, either interspersed or sequential (Experiment 1). In contrast, CS2 proved inhibitory on both summation (Experiment 2) and retardation (Experiment 3) tests only after many CS2-CS1 trials, and then only when the excitatory status of CS1 was preserved. Apparently, the critical difference for establishing second-order excitation or Pavlovian inhibition is the number of CS2-CS1 pairings.

Animals↗
PubMed1994

Comparison of collagen synthesis in the peripheral and central region of the canine meniscus.

A comparison of collagen synthesis in the peripheral and central regions of the normal medial meniscus, the normal lateral meniscus, and the medial meniscus, three months after reconstruction of the anterior cruciate ligament (ACL), was performed in a canine model. Triangular-shaped explants were labeled in vitro with tritiated proline to compare collagen synthesis. Regional cellularity was also quantified. In the normal medial and lateral meniscus, cellularity was similar. Total collagen synthesis, as assessed by collagenase digestible material, was significantly elevated in the peripheral one-third of the medial meniscus versus the central region (paired t-test, p = 0.026). However, in the medial meniscus after ACL reconstruction, cellularity and total collagen synthesis were significantly higher in the peripheral one-third versus the contiguous central region. They were also elevated relative to the peripheral and central region of the normal medial and lateral meniscus (ANOVA, p < 0.05; Student-Neuman-Kuel test, p < 0.05). Thus, in the normal medial meniscus, the peripheral one-third may have an increased healing potential based on its increased ability to synthesize collagen. Furthermore, after ACL reconstruction, only the peripheral, and not the central, region of the canine meniscus responds to the altered mechanical and synovial environment by significantly increasing cellularity and collagen synthesis.

Analysis of Variance↗
PubMed1993

Primary culture of microvascular endothelial cells from canine meniscus.

Microvascular endothelial cells were isolated and cloned from canine knee menisci. Initially, the endothelial cell colonies in culture exhibited a cobblestone morphology. With passage and time, these cultures adopted a fibroblastic or fusiform morphology. The endothelial nature of the cells was demonstrated by positive immunostaining with antibodies to von Willebrand factor, laminin, and type-IV collagen and by capillary-like tube formation on Matrigel. These endothelial cells could be passaged as many as 10 times with retention of the endothelial characteristics. This population of meniscal microvascular endothelial cells will facilitate studies on the role of blood vessels in meniscal repair.

Animals↗
PubMed1993

Long-chain fatty acids and ethanol affect the properties of membranes in Drosophila melanogaster larvae.

The larval fatty acid composition of neutral lipids and membrane lipids was determined in three ethanol-tolerant strains of Drosophila melanogaster. Dietary ethanol promoted a decrease in long-chain fatty acids in neutral lipids along with enhanced alcohol dehydrogenase (EC 1.1.1.1) activity in all of the strains. Dietary ethanol also increased the incorporation of 14C-ethanol into fatty acid ethyl esters (FAEE) by two- to threefold and decreased the incorporation of 14C-ethanol into free fatty acids (FFA). When cultured on sterile, defined media with stearic acid at 0 to 5 mM, stearic acid decreased ADH activity up to 33%. In strains not selected for superior tolerance to ethanol, dietary ethanol promoted a loss of long-chain fatty acids in membrane lipids. The loss of long-chain fatty acids in membranes was strongly correlated with increased fluidity in hydrophobic domains of mitochondrial membranes as determined by electron spin resonance and correlated with a loss of ethanol tolerance. In the ethanol-tolerant E2 strain, which had been exposed to ethanol for many generations, dietary ethanol failed to promote a loss of long-chain fatty acids in membrane lipids.

Alcohol Dehydrogenase↗
PubMed1993

Dietary ethanol reduces phosphatidylcholine levels and inhibits the uptake of dietary choline in Drosophila melanogaster larvae.

1. Low to moderate concentrations of dietary ethanol (200 mM to 600 mM) significantly increased the level of phosphatidylethanolamine (PE), while phosphatidylcholine (PC) levels decreased in third instar larvae. This was seen in both ethanol tolerant and intolerant strains of Drosophila melanogaster, indicating that the reduction of PC is not associated with a high level of ethanol tolerance. 2. The phospholipid changes were not ethanol-specific. Larvae fed ethanol, n-butanol, isopropanol, methanol, and n-propanol exhibited similar changes. 3. At 200 mM concentrations, dietary ethanol acted as a competitive inhibitor for the larval uptake of dietary choline. At higher concentrations, dietary ethanol acted as a noncompetitive inhibitor. This ethanol-induced inhibition of dietary choline uptake can only partially explain the ethanol-induced reductions in larval PC.

Alcohols↗
PubMed1993

Dietary ethanol stimulates the activity of phosphatidylcholine-specific phospholipase D and the formation of phosphatidylethanol in Drosophila melanogaster larvae.

When administered in the diet to third instar Drosophila melanogaster larvae, short chain primary alcohols reduce phosphatidylcholine (PC) levels. The ethanol-induced reductions in larval PC may be in part due to an increase in the activity of PC-specific phospholipase D (PC-specific PLD, EC 3.1.4.4). PC-specific PLD not only hydrolyzes PC, but it also apparently catalyzes the formation of phosphatidylethanol. PC-specific PLD activity was also stimulated by 200 mM ethanol, methanol, isopropanol, n-butanol, and n-propanol. In vitro studies indicated that Drosophila PC-specific PLD activities were enhanced by submicromolar concentrations of Ca2+ and by GTP-gamma S. In vivo studies utilizing [14C]lyso-palmitoyl phosphatidylcholine indicated that dietary ethanol promoted the flux of label into triacylglycerol, 1,2 diacylglycerol, and fatty acid ethyl esters, while the label in PC decreased.

Animals↗
PubMed1993

Temporal encoding as a determinant of blocking.

A blocking paradigm with rats was used to evaluate whether different temporal information is encoded in simultaneous rather than forward associations. During Phase 1, the blocking conditioned stimulus (CS) was simultaneously or forward paired with an unconditioned stimulus (US). During Phase 2, the pretrained CS occurred in compound with a novel target CS that was paired in a simultaneous or forward manner with the US. Forward pretraining resulted in more blocking of a forward than a simultaneously trained target CS, and simultaneous pretraining resulted in more blocking of a simultaneously than a forward trained target CS. Thus, greater blocking occurred when the blocking and blocked CSs had the same temporal relation to the US. The results support the temporal coding hypothesis and question the necessity of predictive information in blocking.

Animals↗
PubMed1993

Pulmonary talcosis: CT findings in three cases.

The authors describe the computed tomographic (CT) appearances in three patients with pulmonary talcosis resulting from chronic intravenous drug abuse. There was widespread ground-glass attenuation in one case and an appearance similar to that of progressive massive fibrosis in two cases. In the latter cases, there were confluent perihilar masses with areas of high attenuation. While the CT appearances may be suggestive of pulmonary talcosis, tissue sampling is required for definitive diagnosis.

Adult↗
PubMed1993

T1 lung cancer: prevalence of mediastinal nodal metastases and diagnostic accuracy of CT.

To determine the prevalence of mediastinal lymph node metastases in T1 non-small cell lung cancer and assess the sensitivity and specificity of computed tomography (CT) in detection of such metastases, the CT scans and surgical findings in 104 patients with T1 lesions were reviewed. Nodes longer than 10 mm on the short or long axis were considered abnormal. All patients underwent thorough mediastinal lymph node dissection at mediastinoscopy or thoracotomy. A total of 362 lymph nodes were sampled. Nodal metastases were present in 22 patients (21%). The sensitivity of CT for metastases to individual nodal stations was 41% for nodes measured on the short axis and 55% for those measured on the long axis. The specificity was 93% and 86%, respectively. When the adjacent nodal stations were included in the analysis, the sensitivity of CT was 59% for nodes measured on the short axis and 77% for those measured on the long axis; the specificity was 91% and 73%, respectively. T1 lung cancer has a higher prevalence of lymph node metastasis than previously reported, and CT is recommended in the preoperative staging of this disease.

Adult↗
PubMed1993

Parenchymal opacification in chronic infiltrative lung diseases: CT-pathologic correlation.

To correlate areas of parenchymal opacification on thin-section computed tomographic (CT) scans with histologic findings in patients with chronic infiltrative lung disease, the CT and histologic findings were evaluated in 29 patients with 11 such diseases. Open-lung biopsy was performed after CT. The area of predominant involvement was classified as air space, interstitium, or a mixture of both. A pathologic score of disease activity was assigned, and the extent of fibrosis was assessed whenever fibrosis was present. Parenchymal opacification on CT scans corresponded to abnormalities that affected mainly the air spaces in three patients (10%), the interstitium in 13 patients (45%), or both to a similar degree in 13 patients (45%). In 25 of 29 patients (86%), parenchymal opacification was associated with potentially treatable or reversible disease. Abnormalities considered irreversible were seen in three patients with end-stage fibrosis and one patient with talcosis. Parenchymal opacification on thin-section CT scans is a nonspecific finding in diseases that affect the air spaces, interstitium, or both but usually indicates potentially treatable or reversible disease.

Adult↗
PubMed1993

Local time horizons in Pavlovian learning.

Responding to a conditioned stimulus (CS) is impaired if the CS is trained in the presence of excitatory local context cues. Four lick suppression experiments with rats explored whether this local context effect arises from the influence of excitatory cues that precede or that follow a reinforced target CS. Pretrained nontarget stimuli served as local context cues that occurred (a) immediately before and after the target CS trial, (b) immediately before or after the target CS trial, or (c) only before or after the target CS trial with varying intervals between the nontarget stimulus and target CS. Results indicated similar control over responding to the target CS by the preceding and following nontarget cues. This outcome implies a symmetrical window of memory integration (local time horizon) for a Pavlovian CS. Possible mechanisms underlying the detrimental effect of embedding a CS in an excitatory local context are discussed.

Animals↗
PubMed1992

Diseases of the trachea and main-stem bronchi: correlation of CT with pathologic findings.

This article presents the computed tomographic (CT) features of the most common abnormalities of the trachea and main-stem bronchi and correlates CT and pathologic findings. The abnormalities are classified into focal and diffuse. Focal disease tends to produce a decreased airway diameter, whereas diffuse diseases are divided into those that increase the airway diameter and those that decrease it. Conventional CT with 10-mm collimation was performed in 36 patients to assess their condition. Additional dynamic incremental thin-section (1.5-5.0-mm collimation) CT was performed in patients with focal abnormalities. Findings from conventional CT correlated closely with those from pathologic analysis of specimens from patients with diffuse disease, but dynamic thin-section scans are necessary for optimal assessment of focal abnormalities. CT demonstrates the location and extent of disease; helps characterize abnormal tissues; helps evaluate the thickness of the tracheal and bronchial walls; and helps determine the extent of extraluminal disease, including the presence of mediastinal extension and lymphadenopathy.

Bronchi↗
PubMed1992

Tuberculosis of the thymus.

Tuberculosis is increasing in prevalence in North America, mainly due to HIV infection. We describe an unusual case of TB of the thymus in a HIV sero-negative Filipino immigrant who preoperatively was thought to have a thymoma. We describe the clinical, radiologic and pathologic findings and review the literature on TB of the thymus.

Adult↗
PubMed1992

High-resolution CT of bronchioloalveolar carcinoma.

Bronchioloalveolar cell carcinoma has a wide spectrum of pathologic and radiologic appearances. Some of the radiologic features are characteristic enough to suggest the underlying pathologic changes. This article illustrates the various manifestations of bronchioloalveolar cell carcinoma on high-resolution CT (1.5-mm collimation reconstructed with a high-spatial-frequency algorithm). Correlations between the CT and pathologic findings are included.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1992

Responding to a conditioned stimulus depends on the current associative status of other cues present during training of that specific stimulus.

The comparator hypothesis is a response rule stating that responding to a Pavlovian conditioned stimulus (CS) reflects the associative strength of the CS relative to that of other cues (comparator stimuli) that were present during CS training. Thus, modulation of the associative strength of a CS's comparator stimulus should alter responding to that CS. These studies examined the stimulus specificity of this effect using within-subjects designs. Rats were trained on 2 CSs, each with a unique comparator stimulus, to determine the degree to which posttraining extinction of the comparator stimulus for one CS influences responding to the other CS. Using negative contingency (Experiments 1 and 2), overshadowing (Experiment 3), and local context (Experiment 4) preparations, stimulus specificity was observed. In each case, posttraining extinction of the comparator stimulus for one CS had greater impact on responding to that CS than on responding to the alternate CS.

Animals↗