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Biomedical subjects

R K Clark

Publications and source records attributed to R K Clark.

At least 55 records · Page 3Linked to original sources
PubMed1991

Polymorphonuclear leukocyte infiltration into cerebral focal ischemic tissue: myeloperoxidase activity assay and histologic verification.

Two different techniques were utilized to identify the infiltration of polymorphonuclear leukocytes (PMN) into cerebral tissue following focal ischemia: histologic analysis and a modified myeloperoxidase (MPO) activity assay. Twenty-four hours after producing permanent cortical ischemia by occluding and severing the middle cerebral artery of male spontaneously hypertensive rats, contralateral hemiparalysis and sensory-motor deficits were observed due to cerebral infarction of the frontal and parietal cortex. In hematoxylin-and-eosin-stained histologic sections, PMN, predominantly neutrophils, were identified at various stages of diapedesis from deep cerebral and meningeal vessels at the periphery of the infarct, into brain parenchyma. When MPO activity in normal brain tissue was studied initially, it could not be demonstrated in normal tissues extracted from non-washed homogenates. However, if tissue was homogenized in phosphate buffer (i.e., washed), MPO activity was expressed upon extraction. Utilizing this modified assay, MPO activity was significantly increased only in the infarcted cortex compared to other normal areas of the brain. This was observed in non-perfused animals and after perfusion with isotonic saline to remove blood constituents from the vasculature prior to brain removal. The increased PMN infiltration and MPO activity were not observed in forebrain tissue of sham-operated control rats. Also, MPO activity was not increased in the ischemic cortex of MCAO rats perfused immediately after middle cerebral artery occlusion, indicating that blood was not trapped in the ischemic area. By using a leukocyte histochemical staining assay, activity of peroxidases was identified within vascular-adhering/infiltrating PMN in the infarcted cortex 24 hr after focal ischemia. An evaluation of several blood components indicated that increased MPO activity was selective for PMN. The observed increase of approximately 0.3 U MPO/g wet weight ischemic tissue vs. nonischemic cerebral tissues probably reflects the increased vascular adherance/infiltration of approximately 600,000 PMN/g wet weight infarcted cortex 24 hr after focal ischemia. This combined biochemical and histological study strongly suggests that PMN adhere within blood vessels and infiltrate into brain tissue injured by focal ischemia and that the associated inflammatory response might contribute to delayed progressive tissue damage in focal stroke. This modified MPO assay is a useful, quantitative index of PMN that can be utilized to elucidate the potential deleterious consequences of neutrophils infiltrating into the central nervous system after cerebral ischemia, trauma, or other pro-inflammatory stimuli.

Animals↗
PubMed1991

Reproducibility of natural head position.

The orientation of the head, when the natural head position was adopted, was measured relative to the true vertical on standardized black and white profile photographs. Two methods of obtaining the natural head position were compared and their reproducibility tested. No statistically significant difference was found between the two different methods or at different sittings.

Adult↗
PubMed1991

Quantitative comparison of magnetic resonance imaging (MRI) and histologic analyses of focal ischemic damage in the rat.

Hemispheric swelling and area of infarction, two parameters of cerebral focal ischemic damage, were identified and quantified from T2-weighted magnetic resonance imaging (MRI) two days after occlusion of the middle cerebral artery (MCAO) in spontaneously hypertensive rat (SHR) brains. Results were compared with these measures quantified from 2,3,5-triphenyltetrazolium hydrochloride (TTC)- and hematoxylin and eosin (H&E)-stained histologic sections in the same brains. The degree of hemispheric swelling and infarct size determined by MRI were highly correlated to the measurements as determined in the TTC- and H&E-stained tissues. These results demonstrate that the focal ischemic damaged area and associated tissue swelling identified by MRI is quantitatively similar to, and thus, is representative of actual tissue damage/changes that can be identified by gross or histologic examination.

Animals↗
PubMed1991

The N-terminal 31 amino acids of human immunodeficiency virus type 1 envelope protein gp120 contain a potential gp41 contact site.

We have compared the expression of full-length gp160 envelope protein from human immunodeficiency virus type 1 with that of a deletion mutant lacking the N-terminal 31 amino acids of the mature protein (gp160 delta 32). The gp160 and gp160 delta 32 proteins are processed to yield gp41 and gp120 or gp120 delta 32, respectively. In contrast to full-length gp120, gp120 delta 32 failed to associate with gp41 at the cell surface, despite conformational integrity as judged by soluble CD4 binding. Thus, the N-terminal 31 amino acids of gp120, which contain hyperconserved sequences, are likely involved in forming a contact site for gp41.

Amino Acid Sequence↗
PubMed1991

Antiserum to a novel peptide sequence reacts selectively with epithelial subpopulations.

A synthetic peptide corresponding to a novel protein sequence isolated from bovine kidney was used to immunize rabbits. When applied to Western blots of bovine kidney extracts, antiserum to this peptide recognizes proteins with molecular weights of 23 and 18 KD. Immunohistochemical examination of a variety of bovine and rat tissues with this antiserum revealed a unique distribution of immunoreactivity with the intermediate layers of a variety of stratified epithelia, in addition to renal glomeruli. The pattern of reactivity differed from previously described epithelial markers such as cytokeratins. These results indicate that this antiserum may be useful as a tool for the identification of cells of the intermediate layer of stratified epithelia and, as such, may aid in the study of this differentiating/proliferating tissue compartment.

Amino Acid Sequence↗
PubMed1991

Serodiagnostic antibody responses to Psoroptes sp. infestations in bighorn sheep.

The antibody responses of bighorn sheep (Ovis canadensis) infected with Psoroptes sp. mites were investigated by enzyme linked immunosorbent assay on western blots of P. cuniculi antigens. Serum from 20 Psoroptes sp.-infested bighorn sheep (O. canadensis mexicana, O. canadensis nelsoni, O. canadensis canadensis) from New Mexico, Nevada, California, and Idaho reacted strongly with mite antigens ranging from 12 to 34 kd. Serum from 35 Psoroptes sp.-free bighorn sheep of unknown tick infestation status and from three Psoroptes sp.-free bighorn sheep infested with Dermacentor hunteri ticks did not react with these antigens. Psoroptes sp.-specific antibody responses were present throughout a 16 mo period in one infected bighorn sheep, but were not detectable 8 mo following successful treatment. These results demonstrate that specific serodiagnosis of Psoroptes sp. infestation is feasible in bighorn sheep and suggest that antibody responses are indicative of current or recent infestation.

Animals↗
PubMed1991

Kinetic ELISA for detection of antibodies to Psoroptes sp. (Acari: Psoroptidae) in bighorn sheep (Ovis canadensis).

A kinetic enzyme-linked immunosorbent assay (ELISA) was developed using antigenic extracts prepared from Psoroptes cuniculi mites and sera from 37 Psoroptes sp.-infested and 43 uninfested bighorn sheep (Ovis canadensis). Serial dilutions of these serum samples, representing 3 bighorn sheep subspecies and 9 geographic areas, gave parallel responses when plotted as log dilution versus log kinetic rate. Therefore, all 80 samples were run at a single dilution (1:100) and positive/negative cutoff values were established as the mean kinetic rate of all negative sera plus either 2, 3, or 4 standard deviations. The resulting ELISA was highly reproducible and accurate with sensitivities and specificities of 100% and 97.7%, 94.6% and 97.7%, and 94.6% and 100%, respectively. This immunoassay will be useful for prospective and retrospective studies assessing the distribution and prevalence of Psoroptes sp. infestations in bighorn sheep.

Animals↗
PubMed1989

Immunohistochemical analysis of antiserum from rhesus monkeys immunized with human colon carcinoma.

In an attempt to generate antibodies which recognize novel tumor-associated antigens we have immunized Rhesus monkeys (Macaca mulatta) with human colon carcinoma cells prepared from freshly excised tumors. Immunohistochemical characterization of polyclonal antisera from one monkey (DF6) revealed preferential reactivity with primary and metastatic colon carcinoma tissue, and a general lack of recognition of nonneoplastic mucosa. Immunoreactivity was localized to the luminal contents of glandular structures and to the apical surfaces of cells lining these glands. Immunoreactivity was not observed with any normal tissue examined. Examination of neoplastic tissues revealed reactivity with two gastric carcinoma specimens (n = 2) and one breast carcinoma (n = 7). In reactive colon carcinoma tissues, the pattern of staining with DF6 was similar to that of several other antibodies including anti-carcinoembryonic antigen, B72.3, anti-Le(x) and anti-Le(y). However, the panel of tissues recognized by these antibodies and DF6 differed significantly, suggesting that the DF6-reactive epitopes are unique. Human colon carcinoma cell lines maintained in vitro also expressed antigens recognized by DF6 in a pattern similar to that of surgically excised tissue. This preliminary characterization of DF6 antiserum suggests that immunization of Rhesus monkeys is a potentially useful protocol for identifying antigens preferentially expressed by human colon carcinoma.

Animals↗
PubMed1989

9.4-T NMR microimaging studies of hepatic metastases of human colorectal tumors in nude mice.

We have applied NMR microimaging at 9.4 T to detect metastatic deposits in the liver of nude mice noninvasively, using an animal model for metastatic colon cancer that mimics several aspects of the human disease. Images were obtained with a resolution of 100 x 100 x 900 microns and the tumor deposits were clearly distinguished from the normal liver tissue with excellent contrast. Comparison of NMR images with corresponding histologic sections indicates that lesions as small as 900 microns were detected.

Adenocarcinoma↗
PubMed1987

Capture methods in five subspecies of free-ranging bighorn sheep: an evaluation of drop-net, drive-net, chemical immobilization and the net-gun.

Six hundred thirty-four bighorn sheep (Ovis canadensis) were captured in the western United States between 1980 and 1986, using four different methods: drop-net (n = 158), drive-net (n = 249), chemical immobilization (n = 90) and net-gun (n = 137). The net-gun was found to have considerable advantages over the use of ground nets and chemical immobilization methods for capturing bighorn sheep. Evaluation of specific outcome categories for individual sheep, including normal, compromised (stress-induced), mortality from capture myopathy (CM), and accidental mortality, revealed significant differences in these rates between capture groups (P less than 0.05). The use of the net-gun resulted in the lowest proportion of compromised sheep at 11% (15/137), had no CM mortality, and resulted in a 2% (2/137) accidental mortality. The use of drop-nets resulted in 15% compromised sheep (24/158), a CM mortality rate of 2% (3/158), and an accidental mortality rate of 1% (2/158). A similar proportion of sheep were compromised with the drive-nets (16%, 39/249). This method also had the highest CM mortality rate at 3% (7/249), and an accidental mortality rate of less than 1% (2/249). Chemical immobilization resulted in the most compromised sheep at 19% (17/90), had a CM mortality rate of 2% (2/90), and caused the most accidental deaths at 6% (5/90). Drop-nets and drive-nets were comparable when combining total mortality with rates for compromised bighorn sheep, 18% and 19%, respectively (29/158 and 48/249). Chemical immobilization had the highest combined measure of risk at 27% (24/90) and net-gun lowest at 12% (17/137).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Effects of capture on biological parameters in free-ranging bighorn sheep (Ovis canadensis): evaluation of drop-net, drive-net, chemical immobilization and the net-gun.

Blood samples and physiological data were collected from 634 bighorn sheep captured between 1980 and 1986 in the western United States. Bighorn sheep were evaluated for physiological parameters (temperature, pulse and respiration), selected biochemical parameters (cortisol, creatine phosphokinase (CPK), serum glutamic oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH), alkaline phosphotase (AP), potassium, sodium, chloride, creatinine, blood urea nitrogen (BUN), selenium, glucose, total protein, plasma pH and plasma PCO2), and selected hematological parameters (packed cell volume (PCV), hemoglobin (HB), red blood cell count (RBC), and white blood cell count (WBC]. These parameters were compared among bighorn sheep captured by four different methods: drop-net (n = 158), drive-net (n = 249), chemical immobilization (n = 90) and the net-gun (n = 137). Biological parameters affected by stress, including temperature, respiration, cortisol, CPK, SGOT, potassium, glucose and WBC revealed significant differences among capture methods (P less than 0.05). Some blood parameter differences, including temperature, respiration, cortisol, glucose and WBC could be explained partially by the distribution of age and sex within capture method groups. Drop-net and net-gun methods of capture appeared to produce the least amount of alteration to biological parameters related to capture stress or compromise and capture mortality. Drive-net was similar to the former methods while chemical immobilization caused the greatest changes in the above physiological, biochemical and hematological parameters.

Animals↗
PubMed1987

Effects of capture on biological parameters in free-ranging bighorn sheep (Ovis canadensis): evaluation of normal, stressed and mortality outcomes and documentation of postcapture survival.

Blood samples and physiological data were collected from 634 bighorn sheep (Ovis canadensis) captured by four different methods between 1980 and 1986 in the western United States. These parameters were evaluated for selected physiological, biochemical and hematological values. Postcapture biological parameters were compared among bighorn sheep according to four different outcomes; normal, stressed or compromised, capture myopathy (CM) mortality, and accidental mortality. Significant differences (P less than 0.05) were noted between outcome groups relative to certain parameters: temperature, respiration, creatinine phosphokinase (CPK), lactic dehydrogenase (LDH), serum glutamic oxaloacetic transaminase (SGOT), blood urea nitrogen (BUN), glucose, white blood cell count (WBC) and plasma pH. Such differences between groups may help in evaluating the clinical status of bighorn sheep at capture, enabling one to predict those animals that might develop CM at a later date, indicate candidates for preventive medical treatment prior to release, and/or which should be followed closely to determine long-term survival. Evaluation of follow-up data (n = 77) related to outcome status and long-term survival of bighorn sheep indicated that less than 4% (3 of 77) were dead within 1 mo of capture (one of these had been classified as normal and two as stressed or compromised at capture); less than 3% (3 of 77) were dead greater than 1 mo, and less than 6 mo after capture two were classified in the stressed outcome and one as diseased. Eighty-eight percent (68 of 77) were alive from 1 mo to 5 yr after capture (53 were classified as normal, 12 as stressed or compromised and 3 as diseased), and 2% (1 of 77) had chronic CM but was still alive (this animal had been classified as normal). Of 77 sheep in the follow-up group, less than 3% (2 of 77) were not observed following capture (one was classified as normal and one as stressed and diseased). Of the fatalities, less than 3% (2 of 40) had been captured by the net-gun and less than 4% (1 of 27) by drive-net. Those two unobserved in the follow-up group also had been caught with the net-gun, 5% (2 of 40). The single surviving CM case had been captured by the net-gun. Although the net-gun appears to be one of the safest methods of capturing individual bighorn sheep, based on evaluation of capture data and biological parameters, it may not be associated with the best long-term survival in some bighorn sheep.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗