Search PubMed⌕ Search

Biomedical subjects

J L Brown

Publications and source records attributed to J L Brown.

At least 73 records · Page 4Linked to original sources
PubMed1997

Psychroserpens burtonensis gen. nov., sp. nov., and Gelidibacter algens gen. nov., sp. nov., psychrophilic bacteria isolated from antarctic lacustrine and sea ice habitats.

Psychrophilic, yellow-pigmented, seawater-requiring bacteria isolated from the pycnocline of meromictic Burton Lake and from sea ice cores obtained in the Vestfold Hills (68 degrees S, 78 degrees E) in eastern Antarctica were characterized. Phenotypic analysis showed that the strains isolated formed two distinct taxa. The first taxon included nonmotile, nutritionally fastidious strains that were isolated from the pycnocline of Burton Lake. The cells of these strains were morphologically variant, ranging from vibrioid to ring shaped to coiled and filamentous; in addition, the strains were unable to metabolise carbohydrates or polysaccharides and had DNA G + C contents of 27 to 29 mol%. The strains of the second taxon, which were isolated from sea ice cores and from ice aigal biomass, were saccharolytic, exhibited rapid gliding motility, were rodlike to filamentous, and had DNA G + C contents of 36 to 38 mol%. A 16S ribosomal DNA (rDNA) sequence analysis revealed that the two Antarctic taxa formed related but distinct lineages within the [Flexibacter] maritimus rRNA branch of the family Flavobacteriacrae. The levels of 16S rDNA sequence similarity between the taxa were 90.5 to 91.3%, while the levels of similarity to other members of the [F.] maritimus rRNA branch were 85 to 90%. The whole-cell lipid profiles of the Antarctic strains were mainly comprised of branched and unbranched monounsaturated C15 to C17 fatty acids. The presence of significant levels of the lipids a 15:1 omega 10c and a17:1 omega 7c appeared to be useful biomarkers for the new Antarctic taxa and for differentiating these organisms from other members of the family Flavobacteriaceae. On the basis of polyphasic taxonomic data we propose that the new taxa are novel bacterial species designated Psychroserpens burtonensis gen. nov., sp. nov. (type strain, ACAM 188) and Gelidibacter algens gen. nov., sp. nov. (type strain, ACAM 536).

Antarctic Regions↗
PubMed1997

Arginine vasopressin secretion with mutants of wild-type and Brattleboro rats AVP gene.

Defects in peptide processing are associated with several disorders, including central diabetes insipidus (CDI). In the Brattleboro (BB) rat with CDI, the mRNA and protein of arginine vasopressin (AVP) are present in the hypothalamus, but no circulating AVP is detectable, thus suggesting a processing defect. The present study examined AVP secretion in cultured COS cells transfected with various constructs from wild-type and mutated Brattleboro AVP gene precursors. The precursor contains three exons encoding for vasopressin (VP), neurophysin (NP), and glycopeptide (GP). The Brattleboro rat has a deletion of a single base, guanine (G), in the NP coding region that leads to a frameshift, resulting in the loss of normal stop codon. The wild-type pcVP (22.0 +/- 5.2 pg/10[-2] U beta-galactosidase [beta-gal]), but not the mutated BB AVP gene pcBB (1.2 +/- 0.4 pg/10[-2] U beta-gal), was associated with AVP secretion from the COS cells as measured by RIA. The wild-type AVP gene without the GP coding region was associated with AVP release greater (47.4 +/- 13.5 pg/10[-2] U beta-gal, n = 5, P < 0.05, versus pcVP) than the pcVP with intact VP, NP, and GP coding regions. However, the wild-type AVP gene with VP coding region alone was not processed and secreted. Normalizing the pcBB total length with the insertion of a stop codon at the site of the normal stop codon was not associated with AVP secretion (3.0 +/- 1.4 pg/10[-2] U beta-gal). However, insertion of a stop codon so that the pcBB length equaled the length of VP and NP coding regions of the wild type was associated with AVP secretion (13.5 +/- 4.0 pg/10[-2] U beta-gal). When a stop codon was inserted into the wild-type NP coding region at the same site as the G deletion in the pcBB, the AVP secretion was significantly lower (15.1 +/- 5.0 pg/10[-2] U beta-gal) than pcVP with VP + NP but no GP coding regions (47.4 +/- 13.5 pg/10[-2] U beta-gal, n = 5, P < 0.05). In summary, (1) both VP and intact NP, but not GP, coding regions are necessary for AVP processing and secretion; (2) decreasing the length of the NP coding region diminishes but does not abolish AVP processing and secretion; and (3) shortening of the pcBB length with a stop codon at a site comparable to wild-type VP + NP allows AVP secretion, albeit less than with wild-type gene precursor. Thus, the CDI in BB rats is caused by the G deletion in NP coding region. This defect leads to abnormalities that contribute to the abnormal AVP processing. Specifically, the frameshift and absence of a stop codon cause a mutated extended C terminus, which, along with the mutated NP, contribute to the abnormal steps of AVP processing, transport, and secretion in the BB rat. These defects no doubt impair the folding and configuration necessary for normal processing of the AVP gene precursor.

Animals↗
PubMed1997

Predicting the extension of equivalence classes from primary generalization gradients: the merger of equivalence classes and perceptual classes.

In Experiment 1, 6 college students were given generalization tests using 25 line lengths as samples with a long line, a short line, and a "neither" option as comparisons. The neither option was to be used if a sample did not go with the other comparisons. Then, four-member equivalence classes were formed. Class 1 included three nonsense words and the short line. Class 2 included three other nonsense words and the long line. After repeating the generalization test for line length, additional tests were conducted using members of the equivalence classes (i.e., nonsense words and lines) as comparisons and intermediate-length lines as samples. All Class 2 comparisons were selected in the presence of the test lines that also evoked the selection of the long line in the generalization test that had been given before equivalence class formation. Class 1 yielded complementary findings. Thus, the preclass primary generalization gradient predicted which test lines acted as members of each equivalence class. Regardless of using comparisons that were nonsense words or lines, the post-class-formation gradients overlapped, showing the substitutability of class members. Experiment 2 assessed the discriminability of the intermediate-length test lines from the Class 1 (shortest) and Class 2 (longest) lines. The test lines that functioned as members of an equivalence class were discriminable from the line that was a member of the same class by training. Thus, these test lines also acted as members of a dimensionally defined class of "long" or "short" lines. Extension of an equivalence class, then, involved its merger with a dimensionally defined class, which converted a close-ended class to an open-ended class. These data suggest a means of predicting class membership in naturally occurring categories.

Conditioning, Operant↗
PubMed1997

Dimethylarsinic acid treatment alters six different rat biochemical parameters: relevance to arsenic carcinogenesis.

In a previous study, we found that sodium arsenite increased hepatic ornithine decarboxylase (ODC) activity and hepatic heme oxygenase (HO) activity, but did not cause any DNA damage in adult female rat liver or lung, suggesting that arsenite may be a promoter of carcinogenesis. In this study sodium arsenate, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) were administered orally in equitoxic doses to adult female rats at 21 and 4 h prior to sacrifice. DNA damage (DD), cytochrome P450 content (P450), glutathione content (GSH), ODC, serum alanine aminotransferase (ALT) and HO were measured in liver and/or lung tissue. At 60 mg/kg in rat liver, sodium arsenate increased hepatic HO fivefold. MMA decreased ALT at 226 mg/kg, decreased ALT and GSH at 679 mg/kg and also increased P450 at 679 mg/kg in rat liver. DMA decreased ALT and hepatic GSH and increased hepatic HO at 387 mg/kg. In the lung, DMA decreased ODC at both 129 and 387 mg/kg. DD in lung tissue was significantly higher at 387 mg/kg DMA, demonstrating organ specific DNA damage. The biochemical effects and the inferred oncologic potential of the four major forms of arsenic (arsenate, arsenite, MMA and DMA) differ dramatically. The inorganic forms (arsenate and arsenite) are similar to each other (both good HO inducers); the methylated organic forms of arsenic (MMA and DMA) also share a similar pattern of biochemical effects (decreased GSH and ALT, increased P450). All six of the biochemical parameters studied were altered by DMA in either rat liver or lung.

Administration, Oral↗
PubMed1997

Simultaneous purification of human albumin and hemoglobin for use as environmental biomarkers.

A combination of known biochemical techniques (binding of bromocresol green to human albumin, nondenaturing electrophoresis and electroelution) have been utilized in a novel purification of human albumin. This paper reports (a) purification of intact, nondenatured human albumin, (b) simultaneous purification of albumin and hemoglobin from a human plasma and red blood cell lysate mixture, (c) development of a purification method for the two most commonly employed protein biomarkers in human environmental epidemiology and (d) demonstration of the general technique of protein purification of colored ligand-protein complexes by nondenaturing electrophoresis. The noncovalent binding between a protein (albumin) and a colored ligand (bromocresol green) is the biochemical characteristic exploited in this novel purification scheme. This general purification method may be useful for other colored ligand or fluorescent ligand binding proteins. For small-scale electrophoresis, the amount of protein isolated, percentage yield and protein purity (estimated by SDS-PAGE) were 270 micrograms, 80% yield and > 99% purity for albumin and 217 micrograms, 54% yield and > 99% purity for hemoglobin, respectively. For large-scale electrophoresis the comparable data was 38.3 mg, 57% yield and 98% purity for albumin and 17.2 mg, 57% yield and 99% purity for hemoglobin, respectively.

Biomarkers↗
PubMed1997

An eight-month evaluation of prehospital 12-lead electrocardiogram monitoring in Baltimore County.

The purpose of this evaluation was to determine if a prehospital 12-lead electrocardiogram (ECG) led to a delay in transportation when compared to non-12-lead ECG, and if it led to improved "door to drug" time. A quasi-experimental design was used to compare on-scene times for suspected acute myocardial infarction (AMI) patients; a comparison was made between advanced life support (ALS) units without 12-lead ECG and those who were augmented by equipped EMS district officer units. Our control group had an on-scene time of 22.05 minutes; the mean on-scene time for the experimental group was 21.85 minutes. The results of this study indicated that 12-lead ECG acquisition by district officers did not extend the on-scene time.

Electrocardiography↗
PubMed1996

Dose-response relationship for rat liver DNA damage caused by 1,2-dimethylhydrazine.

An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis, using DNA damage as a biomarker. Female rats were give 13 different doses of 1,2-dimethylhydrazine (from 1.4 to 135,000 micrograms/kg) and the subsequent hepatic DNA damage was determined by the alkaline elution technique. DMH doses below 450 micrograms/kg did not significantly damage DNA; all DMH doses of 1000 micrograms/kg or higher damaged rat hepatic DNA (P < 0.05). In this study the x values (dose) ranged over five orders of magnitude and the y values (DNA damage) ranged 30-fold. Ten different regression models (linear, quadratic, cubic, power, and six nonlinear transition models) were compared in their ability to fit the experimental data. With respect to log transformed dose, the six nonlinear transition equations fit the data considerably better than the four power type of equations. A sigmoid model fit to the log transformed dose of 1,2-dimethylhydrazine had an r2 of 0.9979, a degree of freedom adjusted r2 of 0.9969, a F-statistic of 1,457, and a fit standard error of 0.50. With respect to untransformed dose, only three equations (sigmoid, cascade and gaussian cumulative) could creditably fit the DMH data. The experimental results are interpreted with respect to hormesis, use of log transformed dose, sigmoid dose-response models, thresholds of biological response and cancer risk assessment.

1,2-Dimethylhydrazine↗
PubMed1996

The KNH1 gene of Saccharomyces cerevisiae is a functional homolog of KRE9.

The KNH1 gene from Saccharomyces cerevisiae was identified as an open reading frame on the right arm of chromosome IV. The product encoded by the KNH1 gene, Knhlp, shares 46% overall identity with Kre9p, a protein required for cell surface beta 1,6-glucan synthesis. While disruption of the KNH1 locus had no effect on cell growth, killer toxin sensitivity or beta 1,6-glucan levels, overexpression of KNH1 was found to suppress the severe growth defect of a kre9 delta mutant and restored the level of alkali-insoluble beta 1,6-glucan to almost wild-type levels. Knhlp, like Kre9p, can be found in the extracellular culture medium as an O-glycoprotein, with a molecular mass of 45-61 kDa. Disruption of both KNH1 and KRE9 is lethal, and unlike single kre9 delta mutants, could not be rescued by overproducing SKN7, a putative transcription factor involved in the regulation of extracellular matrix assembly. Transcription of KNH1 was found to be carbon-source and kre9 delta dependent, but SKN7 independent, suggesting that KNH1 is subject to alternative transcriptional control.

Amino Acid Sequence↗
PubMed1996

Human Ste20 homologue hPAK1 links GTPases to the JNK MAP kinase pathway.

BACKGROUND: The Rho-related GTP-binding proteins Cdc42 and Rac1 have been shown to regulate signaling pathways involved in cytoskeletal reorganization and stress-responsive JNK (Jun N-terminal kinase) activation. However, to date, the GTPase targets that mediate these effects have not been identified. PAK defines a growing family of mammalian kinases that are related to yeast Ste20 and are activated in vitro through binding to Cdc42 and Rac1 (PAK: p21 Cdc42-/Rac-activated kinase). Clues to PAK function have come from studies of Ste20, which controls the activity of the yeast mating mitogen-activated protein (MAP) kinase cascade, in response to a heterotrimeric G protein and Cdc42. RESULTS: To initiate studies of mammalian Ste20-related kinases, we identified a novel human PAK isoform, hPAK1. When expressed in yeast, hPAK1 was able to replace Ste20 in the pheromone response pathway. Chemical mutagenesis of a plasmid encoding hPAK1, followed by transformation into yeast, led to the identification of a potent constitutively active hPAK1 with a substitution of a highly conserved amino-acid residue (L107F) in the Cdc42-binding domain. Expression of the hPAK1(L107F) allele in mammalian cells led to specific activation of the Jun N-terminal kinase MAP kinase pathway, but not the mechanistically related extracellular signal-regulated MAP kinase pathway. CONCLUSIONS: These results demonstrate that hPAK1 is a GTPase effector controlling a downstream MAP kinase pathway in mammalian cells, as Ste20 does in yeast. Thus, PAK and Ste20 kinases play key parts in linking extracellular signals from membrane components, such as receptor-associated G proteins and Rho-related GTPases, to nuclear responses, such as transcriptional activation.

Alleles↗
PubMed1996

Identification of ASK10 as a multicopy activator of Skn7p-dependent transcription of a HIS3 reporter gene.

Recent evidence has demonstrated that the yeast Skn7p appears to act as a 'response regulator' in a eukaryotic 'two-component' signal transduction pathway. A search to identify possible regulators of the SKN7 mediated 'two-component' regulatory system has identified Ask10p as a novel potential transcription factor. The ASK10 sequence has been deposited in GenBank with Accession Number U27209.

Amino Acid Sequence↗
PubMed1996

Arsenite, but not cadmium, induces ornithine decarboxylase and heme oxygenase activity in rat liver: relevance to arsenic carcinogenesis.

Sodium arsenite and cadmium chloride, were administered orally to adult female rats at 21 and 4 h prior to sacrifice. Liver, lung, skin and urinary bladder were the tissues studied. DNA damage, cytochrome P450, glutathione content (GSH), ornithine decarboxylase (ODC), serum alanine aminotransferase and heme oxygenase activity were measured. Sodium arsenite increased rat hepatic ODC activity at 1.6 and 24.6 mg/kg and hepatic heme oxygenase activity at 8.2 and 24.6 mg/kg, but did not cause any DNA damage. Cadmium chloride did not affect any of the six parameters tested. These findings suggest that sodium arsenite may be a promoter rather than an initiator of carcinogenesis.

Alanine Transaminase↗
PubMed1996

Excretory fate of estradiol and progesterone in the African elephant (Loxodonta africana) and patterns of fecal steroid concentrations throughout the estrous cycle.

We developed and validated a noninvasive method to quantify fecal estrogens and progestins as a tool for monitoring long-term ovarian activity in free-ranging African elephants. The lag times between iv injection of [(3)H]estradiol and [(14)C]progesterone and peak excretion of radioactivity in urine and feces were approximately 4 hr and 48 hr, respectively. The majority of progesterone metabolites recovered was excreted in feces (55%) versus urine (45%), whereas comparatively little of the recovered estradiol metabolites were excreted in feces (5%) compared to urine (95%). Intrasample variation in fecal hormone concentrations was extremely high but could be substantially reduced by extracting well-mixed fecal powder from freeze-dried samples, taken from the central or premixed portion of the wet sample. This method resulted in a close correspondence between matched serum and fecal progestins (mean correlation = 0.81, range 0.61-0.94) collected from five nonpregnant adult females over a 7-month period. Fecal estrogen profiles were more ambiguous, tending to overlap with those of fecal progestins. We conclude that analyses of fecal progestins can provide an effective, noninvasive means of characterizing ovarian activity in free-ranging African elephants.

Animals↗
PubMed1996

Spinal cord substance P receptor immunoreactivity increases in both inflammatory and nerve injury models of persistent pain.

Numerous studies have implicated the primary afferent derived neuropeptide, substance P, which exerts its effects via the neurokinin-1/substance P receptor, in the transmission of nociceptive messages at the level of the spinal cord. Immunocytochemical studies demonstrate that the substance P receptor is concentrated in neurons of lamina I of the superficial dorsal horn. Since alterations in the number and distribution of the receptor may underlie persistent pain conditions, we have used immunocytochemistry to study the distribution of the receptor in two very different rat models of persistent pain: chronic inflammation, which is associated with increased levels of substance P, and sciatic nerve section, which is associated with decreased levels of substance P in the dorsal horn. Inflammation was produced by unilateral hindpaw injection of complete Freund's adjuvant. We report that there is an up-regulation of substance P receptor immunoreactivity in the superficial laminae of the dorsal horn in both injury models. The increase was found at all time points studied (up to one week after induction of inflammation and up to two weeks after sciatic nerve section). The increase in substance P receptor immunoreactivity was not only present in the medial part of the dorsal horn at segment L4, which is the region of input of the afferents from the hindpaw, but also in the lateral parts of the dorsal horn, and at segments rostral (L1) and caudal (S1) to the afferent input from the hindpaw. These results indicate that the up-regulation of the receptor is not predictable merely by the change in the concentration of substance P in the dorsal horn. Furthermore, the non-topographic up-regulation of substance P receptor in these different conditions may contribute to the central sensitization of dorsal horn nociceptors under conditions of persistent pain.

Animals↗
PubMed1996

A double blind, placebo-controlled study to assess the effect of famciclovir on virus replication in patients with chronic hepatitis B virus infection.

This is the first double-blind controlled study of famciclovir, an oral antiviral agent, as potential therapy for chronic hepatitis B virus (HBV) carries. A fall of more than 90% in HBV DNA levels was noted in six of 11 evaluable patients treated with a 10 day course of oral famciclovir. Further studies with more prolonged therapy are ongoing.

2-Aminopurine↗
PubMed1996

Responsiveness of ovaries to exogenous gonadotrophins and laparoscopic artificial insemination with frozen-thawed spermatozoa in ocelots (Felis pardalis).

Adult female ocelots (Felis pardalis) were treated with one of four dosages of equine chorionic gonadotrophin (eCG) and human chorionic gonadotrophin (hCG) (100 iu eCG/75 iu hCG, n = 3; 200 iu eCG/150 iu hCG, n = 4; 400 iu eCG/150 iu hCG, n = 5; 500 iu eCG/225 iu hCG, n = 5); hCG was administered 80 h after eCG. Ovaries of each animal were evaluated by laparoscopy 39-43 h after hCG, and blood was collected for progesterone and oestradiol analysis. With progressive increases in gonadotrophin dosage, female ocelots produced more (P < 0.05) unovulated follicles (> or = 2 mm in diameter), ranging from 1.3 +/- 0.7 (mean +/- SEM) follicles per female at the lowest dosage to 8.8 +/- 2.8 follicles per female at the highest dosage. Similarly, ocelots produced more (P < 0.05) corpora lutea with increasing gonadotrophin dosages, with mean values ranging from 0-5.0 +/- 1.2 corpora lutea. However, across treatment groups, a similar proportion (P > 0.05) of females ovulated in response to each dosage. At laparoscopy, serum concentrations of oestradiol (overall mean, 330.2 +/- 62.2 pg ml-1) and serum concentrations of progesterone (overall mean, 18.5 +/- 6.4 ng ml-1) in ovulating females did not differ (P > 0.05) across treatment groups. Ten ovulating ocelots were laparoscopically inseminated with fresh (4.7 +/- 0.2 x 10(6); n = 2 females) or frozen-thawed (10.7 +/- 1.8 x 10(6); n = 8 females), motile spermatozoa. One female treated with 500 iu eCG/225 iu hCG and inseminated with 7.5 x 10(6) motile, frozen-thawed spermatozoa conceived and gave birth to a healthy male kitten after a gestation of 78 days. We conclude that ocelots are relatively insensitive to exogenous gonadotrophins, requiring much higher dosages (on a per body mass basis) to elicit an appropriate ovarian response than do any other felid species studied to date. Nonetheless, the gonadotrophin-treated female can become pregnant and carry offspring to term after laparoscopic intrauterine insemination with frozen-thawed spermatozoa.

Animals↗
PubMed1996

Reproductive activity in captive female cheetahs (Acinonyx jubatus) assessed by faecal steroids.

Faecal oestradiol and progestogen metabolite excretion was monitored in adult, female cheetahs (Acinonyx jubatus) (n = 26) for 1-24 months. Increased faecal oestradiol excretion was associated with mating or equine chorionic gonadotrophin (eCG) administration for artificial insemination, whereas increased progestogen metabolites were observed during natural and human chorionic gonadotrophin (hCG)-induced pregnant and nonpregnant luteal phases. On the basis of oestradiol excretory patterns, duration of the oestrous cycle (mean +/- SEM) was 13.6 +/- 1.2 days with high oestradiol concentrations lasting for 4.1 +/- 0.8 days. In non-gonadotrophin-treated cheetahs, 75% showed evidence of oestrous cyclicity; however, none evaluated for 1 year or longer were continuously cyclic. Rather, cyclicity was interrupted by periods of anoestrus, often exceeding several months in duration. These inactive ovarian periods were unrelated to season and were not synchronous among females. Mean duration of gestation (breeding to parturition) was 94.2 +/- 0.5 days, whereas duration of faecal progestogen metabolite excretion during the nonpregnant luteal phase was 51.2 +/- 3.5 days. On the basis of progestogen metabolite evaluations, spontaneous ovulation (non-mating induced) occurred only once in two females (2 of 184 oestrous cycles; 1.1%). Peak eCG-stimulated, preovulatory oestradiol concentrations were similar to those associated with natural oestrus, whereas progestogen metabolite profiles after hCG resembled those during pregnant and nonpregnant luteal phases after natural mating. In summary, results confirm that the cheetah is polyoestrus and ovulation is almost always induced. However, new evidence suggests that many females inexplicably experience periods of anoestrus unrelated to season, while 25% of the cheetahs examined expressed no ovarian activity during the study period.

Acinonyx↗
PubMed1996

Genetic diversity affects testicular morphology in free-ranging lions (Panthera leo) of the Serengeti Plains and Ngorongoro Crater.

Reduced genetic variability is known to adversely affect ejaculate quality in inbred lions (Panthera leo) physically isolated in the Ngorongoro Crater compared with outbred lions inhabiting the adjacent Serengeti Plains in East Africa. This study compared the histomorphology of testicular biopsies from these two lion populations. Ngorongoro Crater lions had fewer (P < 0.05) seminiferous tubules with spermiogenesis and fewer (P < 0.05) spermatids per seminiferous tubular cross-section than Serengeti Plains lions, although seminiferous tubular diameter did not differ (P > 0.05) between populations. Interstitial areas were greater (P < 0.05) in Crater than in Plains lions, but no qualitative differences were evident, suggesting that proportionately less testicular area was occupied by seminiferous tubules in Crater lions. None of the lions in either population had evidence of testicular degeneration. Overall results suggest that inbred Crater lions have reduced spermiogenesis and less total seminiferous tubular area per testis. These data further support the premise that genetic homogeneity compromises reproductive traits in free-living, male African lions.

Africa↗