Biomedical subjects

Murray K Clayton

Publications and source records attributed to Murray K Clayton.

8 recordsLinked to original sources

PubMed2006

A cluster model for space-time disease counts.

Modelling disease clustering over space and time can be helpful in providing indications of possible exposures and planning corresponding public health practices. Though a considerable number of studies focus on modelling spatio-temporal patterns of disease, most of them do not directly model a spatio-temporal clustering structure and could be ineffective for detecting clusters. In this paper, we extend a purely spatial cluster model to accommodate space-time clustering. Inference is performed in a Bayesian framework using reversible jump Markov chain Monte Carlo. This idea is illustrated using data on female breast cancer mortality from Japan. A hierarchical parametric space-time model for mapping disease is used for comparison.

Adult↗

PubMed2006

Road development, housing growth, and landscape fragmentation in northern Wisconsin: 1937-1999.

Roads remove habitat, alter adjacent areas, and interrupt and redirect ecological flows. They subdivide wildlife populations, foster invasive species spread, change the hydrologic network, and increase human use of adjacent areas. At broad scales, these impacts cumulate and define landscape patterns. The goal of this study was to improve our understanding of the dynamics of road networks over time, and their effects on landscape patterns, and identify significant relationships between road changes and other land-use changes. We mapped roads from aerial photographs from five dates between 1937 and 1999 in 17 townships in predominantly forested landscapes in northern Wisconsin, U.S.A. Patch-level landscape metrics were calculated on terrestrial area outside of a 15-m road-effect zone. We used generalized least-squares regression models to relate changes in road density and landscape pattern to concurrent changes in housing density. Rates of change and relationships were compared among three ecological regions. Our results showed substantial increases in both road density and landscape fragmentation during the study period. Road density more than doubled, and median, mean, and largest patch size were reduced by a factor of four, while patch shape became more regular. Increases in road density varied significantly among ecological subsections and were positively related to increases in housing density. Fragmentation was largely driven by increases in road density, but housing density had a significantly positive relationship with largest patch area and patch shape. Without protection of roadless areas, our results suggest road development is likely to continue in the future, even in areas where road construction is constrained by the physical environment. Recognizing the dynamic nature of road networks is important for understanding and predicting their ecological impacts over time and understanding where other types of development are likely to occur in the future. Historical perspectives of development can provide guidance in prioritizing management efforts to defragment landscapes and mitigate the ecological impacts of past road development.

Ecosystem↗

PubMed2005

Hypoenergetic high-carbohydrate or high-fat parenteral nutrition induces a similar metabolic response with differential effects on hepatic IGF-I mRNA in dexamethasone-treated rats.

The optimal level of energy for critically ill patients who require parenteral nutrition (PN) is unclear. Our objective was to determine whether 50% energy (50%E) restriction due to a reduction in carbohydrate or fat, with provision of adequate protein and micronutrients, ameliorates the detrimental effects of dexamethasone (Dex) on body protein catabolism, insulin resistance, and insulin-like growth factor-I (IGF-I) responses in rats administered PN. The experiment included 6 PN groups, adequate energy (AE) +/- Dex, 50% AE with high carbohydrate (50%E CHO) +/- Dex and 50% AE with high fat (50%E FAT) +/- Dex. There was a significant interaction between energy level and Dex such that the increase in body catabolism due to 50%E from CHO or FAT was reduced by approximately 50%, although the amount of body weight and nitrogen lost over 7 d was significantly greater with 50%E than with AE. AE+Dex induced a 60% increase in liver mass, whereas 50%E+Dex reduced the increase to 26%. AE+Dex induced a 5-fold increase in serum insulin level, whereas 50%E+Dex normalized the insulin to glucose ratio. Serum IGF-I levels were reduced 14-18% by Dex and 30% by 50%E. Hepatic immunoreactive IGF-I was significantly correlated with serum IGF-I and nitrogen balance. 50%E CHO and 50%E FAT had differential effects on hepatic IGF-I mRNA with a 40% decrease in IGF-I mRNA due to 50%E FAT+Dex. In summary,CHO or FAT hypoenergetic PN with adequate protein had similar effects in normalizing hyperinsulinemia, attenuating hepatomegaly, and reducing the increment, but not the total amount of body protein catabolism, induced by glucocorticoid excess.

Animals↗

PubMed2004

Density-dependent effects of multiple predators sharing a common prey in an endophytic habitat.

Multiple predator species feeding on a common prey can lead to higher or lower predation than would be expected by simply combining their individual effects. Such emergent multiple predator effects may be especially prevalent if predators share feeding habitat. Despite the prevalence of endophagous insects, no studies have examined how multiple predators sharing an endophytic habitat affect prey or predator reproduction. We investigated density-dependent predation of Thanasimus dubius (Coleoptera: Cleridae) and Platysoma cylindrica (Coleoptera: Histeridae) on a bark beetle prey, Ips pini (Coleoptera: Scolytidae), in a laboratory assay. I. pini utilize aggregation pheromones to group-colonize and reproduce within the stems of conifers. T. dubius and P. cylindrica exploit these aggregation pheromones to arrive simultaneously with the herbivore. Adult T. dubius prey exophytically, while P. cylindrica adults enter and prey within the bark beetle galleries. Larvae of both predators prey endophytically. We used a multiple regression analysis, which avoids confounding predator composition with density, to examine the effects of varying predator densities alone and in combination on herbivore establishment, herbivore reproduction, and predator reproduction. Predators reduced colonization success by both sexes, and decreased I. pini reproduction on a per male and per female basis. The combined effects of these predators did not enhance or reduce prey establishment or reproduction in unexpected manners, and these predators were entirely substitutable. The herbivore's net replacement rate was never reduced significantly below one at prey and predator densities emulating field conditions. Similar numbers of each predator species emerged from the logs, but predator reproduction suffered from high intraspecific interference. The net replacement rate of P. cylindrica was not affected by conspecifics or T. dubius. In contrast, the net replacement rate of T. dubius decreased with the presence of conspecifics or P. cylindrica. Combinations of both predators led to an emergent effect, a slightly increased net replacement rate of T. dubius. This may have been due to predation by larval T. dubius on pupal P. cylindrica, as P. cylindrica develops more rapidly than T. dubius within this shared habitat.

Analysis of Variance↗

PubMed2003

A hierarchical model for spatially clustered disease rates.

Maps of regional disease rates are potentially useful tools in examining spatial patterns of disease and for identifying clusters. Bayes and empirical Bayes approaches to this problem have proven useful in smoothing crude maps of disease rates. In recent years, models including both spatially correlated random effects and spatially unstructured random effects have been very popular. The spatially correlated random effects have been proposed in an attempt to capture a general clustering in the data. As an alternative, we propose replacing the spatially structured random effect with fixed clustering effects associated with particular areas. A reversible jump Markov chain Monte Carlo (RJMCMC) algorithm for posterior inference is described. We illustrate the model using the well-known New York leukaemia data.

Cluster Analysis↗

PubMed2003

Intraduodenal serotonin elicits non-propagating spike potentials in the small intestine of the rat.

Serotonin (5-hydroxytryptamine, 5-HT) is an endogenous signalling molecule capable of altering small intestinal motility. Serotonin is normally present in the intestinal lumen and released by enterochromaffin cells of the mucosal epithelium. We found that intraduodenal infusion of exogenous serotonin causes a dose-dependent myoelectric response in the smooth muscle of the small intestine in the conscious rat. The response consists of repetitive bursts of action potentials (RBAP) that are characterized as short bursts of non-propagative myoelectric spiking. RBAP occur intermittently and only during the first 15 min after intralumenal serotonin infusion. After the initial 15 min period, the frequency of RBAP declines, and the myoelectric pattern shifts to prolonged and continuous spiking, eliminating the interdigestive migrating myoelectric pattern. The effects of intralumenal serotonin are not replicated by parenteral or intraperitoneal infusion nor by intralumenal infusion of 5-hydroxytryptophan or 5-hydroxyindoleacetic acid. The response to intralumenal serotonin was eliminated by several specific 5-HT receptor antagonists. On repeated intralumenal administration of serotonin, the RBAP response decreased demonstrating a decreased sensitivity of the muscle contraction on re-exposure to serotonin. We conclude that intralumenal infusion of serotonin can temporarily initiate specific small intestinal muscle events that are not generated by serotonin from other non-lumenal administration sites. We speculate that an afferent neuro-pathway is necessary for the induction of RBAP, since RBAP are not observed from in vitro muscle preparations.

Action Potentials↗

PubMed2002

Fatigue microdamage in the radial predilection site for osteosarcoma in dogs.

OBJECTIVE: To evaluate whether body size and anatomic site influence the quantity of bone microdamage in dogs without osteosarcoma (OS). SAMPLE POPULATION: Pairs of radii were collected from 10 small dogs (< 15 kg) and 10 large dogs (> 25 kg). PROCEDURE: Specimens were stained in basic fuchsin for bone microdamage. Transverse sections were cut from each proximal and distal radial metaphysis at 15 and 85% of bone length. The following variables were determined for each region: mean microcrack length (CrLe, microM), microcrack density (CrDn, microcracks/mm2), microcrack surface density (CrSDn, microm/mm2), and estimated activation frequency (Acf, microcracks/mm2/y). RESULTS: Metaphyseal region did not significantly influence CrDn, CrLe, and CrSDn. The CrDn and CrSDn were influenced by body size, with microdamage being increased in large dogs, compared with small dogs. However, mean CrLe was not significantly influenced by body size. Acf significantly decreased with age and was significantly decreased in large dogs and in the distal radial metaphysis, compared with small dogs and the proximal radial metaphysis, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Our data did not reveal an increase in microdamage or remodeling at the OS predilection site (ie, the distal metaphysis of the radius), suggesting that induction of microdamage and an associated increase in bone remodeling are unlikely to be an important risk factor for induction of OS.

Animals↗

PubMedDate not supplied

Quantification of Staphylococcus aureus adhesion to equine bone surfaces passivated with Plasmalyte and hyperimmune plasma.

OBJECTIVE: To quantify the adhesion of Staphylococcus aureus to 4 equine bone surfaces passivated in a balanced polyionic solution (Plasmalyte) or hyperimmune equine plasma (Polymune plasma). STUDY DESIGN: In vitro comparative study. SAMPLE POPULATION: Third metacarpal bone (MC3) surface explants from 9 equine cadavers. METHODS: Approximately 1 cm(2) sections of periosteum were removed from MC3 and stapled to sterile stainless steel screens. Three bone surface explants were cut using a surgical saw to present 1 cm(2) surfaces of subperiosteal bone, cut cortical bone, or endosteum. Duplicate explants of each surface were immersed for 1 hour in Plasmalyte or hyperimmune equine plasma. Each explant was then placed in a well of a 6-well sterile tissue culture plate with the surface of interest exposed. Each surface was inoculated with approximately 100 colony-forming units of S. aureus in 10 microL of Mueller Hinton broth and incubated for 6 hours at 37 degrees C. After gentle rinsing to remove non-adherent bacteria, samples were sonicated for 5 minutes at 60 kHz to loosen adhered bacteria. The number of adherent bacteria was determined by serial dilutions and incubation of the sonicate. Scanning electron microscopy (SEM) was performed on samples identically treated from an additional horse to confirm bacterial removal by sonication from all surfaces and support quantitative culture results. RESULTS: Less S. aureus adhered to periosteum than to cortical bone, cut cortical bone, and endosteal surfaces, which were all similar. Exposure of all surfaces to hyperimmune plasma reduced S. aureus adherence compared with Plasmalyte exposure; SEM supported these conclusions. CONCLUSION: Less bacteria adhere to periosteum than other bone surfaces. Hyperimmune plasma reduces bacterial adhesion to all bone tissue surfaces. CLINICAL RELEVANCE: Understanding the factors that affect bacterial adhesion to bone will facilitate development of improved intraoperative lavage solutions to reduce the morbidity and mortality associated with postoperative infection.

Animals↗