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Biomedical subjects

M C Osborne

Publications and source records attributed to M C Osborne.

6 recordsLinked to original sources
PubMed2007

Androgen regulates trkB immunolabeling in spinal motoneurons.

Neurotrophic factors and steroid hormones have been shown to have neuroprotective/neurotherapeutic effects, and it has been shown previously that brain-derived neurotrophic factor (BDNF) and testosterone have a combinatorial effect in the maintenance of motoneurons. Given that gonadal hormones regulate the BDNF receptor, tyrosine receptor kinase B (trkB), we hypothesized that such a regulatory effect could mediate the interactive effects of BDNF and testosterone. Using immunohistochemical methods, we examined the frequency of cells immunolabeled for trkB receptors in two populations of spinal motoneurons, the hormone-sensitive, sexually dimorphic motoneurons of the spinal nucleus of the bulbocavernosus (SNB) and the nondimorphic motoneurons innervating the muscles of the quadriceps. In both the highly androgen-sensitive SNB motoneurons and the more typical somatic motoneurons innervating the quadriceps, the frequency of motoneurons intensely immunolabeled for trkB receptors was regulated by the presence of testosterone. Castrated animals deprived of testosterone showed a reduced frequency of intensely labeled motoneurons compared with intact animals or castrated animals given testosterone replacement. This finding suggests that the combinatorial effect of BDNF and testosterone in the maintenance of motoneurons could occur at least in part through an androgen-mediated expression of the BDNF receptor.

Androgens↗
PubMed2005

Pharmacological profile of a novel, non-TZD PPARgamma agonist.

AIM: The purpose of this study was to characterize a novel, non-thiazolidinedione (TZD) peroxisome proliferator-activated receptor (PPAR)gamma agonist, RWJ-348260, via both in vitro and in vivo approaches. METHODS: The in vitro PPARgamma activities of RWJ-348260 were assessed in PPARgamma-GAL4 co-transfection assay, PPARgamma receptor binding assay, aP2 gene induction assay and preadipocyte differentiation assay. The in vivo efficacy of the compound was determined in rodent genetic diabetes models [ob/ob mouse, db/db mouse and Zucker diabetic fatty (ZDF) rat] following multiple days of oral administration. RESULTS: RWJ-348260 selectively activated PPARgammain vitro. In vivo, RWJ-348260 produced significant decreases in plasma glucose, HbA1c, insulin and triglyceride levels. RWJ-348260 also dose-dependently improved oral glucose tolerance. In db/db mice, the compound up-regulated PPARgamma target genes in white adipose tissues. RWJ-348260 produced a lower extent of hepatocyte lipid deposition and a smaller increase in liver weight compared to rosiglitazone in db/db mice. While RWJ-348260 effectively normalized hyperglycaemia and dyslipidaemia, it did not change haematocrit, transaminase, alkaline phosphatase, total bilirubin levels or liver weights in ZDF rats. CONCLUSIONS: RWJ-348260 is a potent PPARgamma agonist with efficacious antidiabetic activity in diabetic animal models. The compound has an improved side-effect profile compared to rosiglitazone.

Adipocytes↗
PubMed2002

Oomycete plant pathogens use electric fields to target roots.

Plant roots generate electrical currents and associated electrical fields as a consequence of electrogenic ion transport at the root surface. Here we demonstrate that the attraction of swimming zoospores of oomycete plant pathogens to plant roots is mediated in part by electrotaxis in natural root-generated electric fields. The zones of accumulation of anode- or cathode-seeking zoospores adjacent to intact and wounded root surfaces correlated with their in vitro electrotactic behavior. Manipulation of the root electrical field was reflected in changes in the pattern of zoospore accumulation and imposed focal electrical fields were capable of overriding endogenous signals at the root surface. The overall pattern of zoospore accumulation around roots was not affected by the presence of amino acids at concentrations expected within the rhizosphere, although higher concentrations induced encystment and reduced root targeting. The data suggest that electrical signals can augment or override chemical ones in mediating short-range tactic responses of oomycete zoospores at root surfaces.

Electricity↗
PubMed1999

A novel method for analysis of nuclear receptor function at natural promoters: peroxisome proliferator-activated receptor gamma agonist actions on aP2 gene expression detected using branched DNA messenger RNA quantitation.

Peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of the nuclear hormone receptor superfamily, plays an essential role in the mediation of the actions of antidiabetic drugs known as thiazolidinediones (TZDs). PPARgamma activates many target genes involved in lipid anabolism including the adipocyte fatty acid binding protein (aP2). In this study, induction of aP2 gene expression by PPARgamma agonists was examined in both cultured cells and diabetic mice using branched DNA (bDNA)-mediated mRNA quantitation. bDNA technology allows for the direct measurement of a particular mRNA directly within cellular lysate using a 96-well plate format in a time frame comparable to a reporter gene assay. In cultured human subcutaneous preadipocytes, the TZDs, troglitazone and BRL-49653, both rapidly induced aP2 mRNA as detected with the bDNA method. In these cells, the effect of BRL-49653 on aP2 mRNA levels was detectable as early as 30 min after treatment (47% increase) and was maximal after 24 h of treatment (12-fold increase). The effects of troglitazone on aP2 mRNA induction were similar to those of BRL-49653 except that the maximal level of induction was consistently lower (e.g. 24 h treatment = 4-fold increase). Dose-response relationships for both of the TZDs were also determined using the 24-h treatment time point. EC50s for both BRL-49653 and troglitazone were estimated to be 80 nM and 690 nM, respectively. A natural PPARgamma ligand, 15-deoxy-delta12,14-PGJ2, was also active in this assay with a maximal induction of aP2 mRNA of approximately 5-fold when tested at 1 microM. Since the PPARgamma:retinoid X receptor (RXR) heterodimer has been characterized as a permissive heterodimer with respect to RXR ligands, the ability of 9-cis-retinoic acid (9-cis-RA) to induce aP2 mRNA was examined. Although 9-cis-RA had very low efficacy (2-fold induction), the maximal effect was reached at 100 nM. No synergism or additivity in aP2 mRNA induction was detected when 9-cis-RA was included with either of the TZDs used in this study. Significant induction of aP2 mRNA in bone marrow of db/db mice treated with either troglitazone or BRL-49653 was also detected, indicating that the bDNA assay may be a simple method to monitor nuclear receptor target gene induction in vivo.

Adipocytes↗
PubMed1989

Potential regulatory role of inflammatory cells on local vascular smooth muscle tone.

A neutrophil-derived relaxing factor (NDRF) from oyster glycogen (OG)-elicited rat PMN, which causes an endothelium independent relaxation of rat aorta, and which is pharmacologically indistinguishable from endothelium-derived relaxing factor (EDRF) has been described. Experiments were designed to evaluate the presence of NDRF in PMN from rat -whole blood, -carrageenan pleurisy, -OG peritonitis, and guinea pig (GP) -OG peritonitis, as well as in OG-elicited rat macrophages (M phi). Significant vascular relaxing activity was found using rat PMN from OG peritonitis and carrageenan pleurisy, as well as from OG-M phi. Little or no activity was found in rat whole blood PMN or PMN from GP-OG peritonitis. These results suggest that NDRF activity may be expressed upon cellular migration to an inflammatory site in the rat, and may not be present in all species. Also, all inflammatory cells examined were capable of reversing EDRF-dependent relaxations when stimulated to produce superoxide anion suggesting a dual regulatory role for these cells on local vascular tone.

Animals↗