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Biomedical subjects

A H Meyer

Publications and source records attributed to A H Meyer.

14 recordsLinked to original sources
PubMed2003

Cerebellar granule cell Cre recombinase expression.

The cerebellum maintains balance and orientation, refines motor action, stores motor memories, and contributes to the timing aspects of cognition. We generated two mouse lines for making Cre recombinase-mediated gene disruptions largely confined to adult cerebellar granule cells. For this purpose we chose the GABA(A) receptor alpha6 subunit gene, whose expression marks this cell type. Here we describe mouse lines expressing Cre recombinase generated by 1) Cre knocked into the native alpha6 subunit gene by homologous recombination in embryonic stem cells; and 2) Cre recombined into an alpha6 subunit gene carried on a bacterial artificial chromosome (BAC) genomic clone. The fidelity of Cre expression was tested by crossing the mouse lines with the ROSA26 reporter mice. The particular alpha6BAC clone we identified will be valuable for delivering other gene products to cerebellar granule cells.

Animals↗
PubMed2000

Quantitative evidence for global amphibian population declines.

Although there is growing concern that amphibian populations are declining globally, much of the supporting evidence is either anecdotal or derived from short-term studies at small geographical scales. This raises questions not only about the difficulty of detecting temporal trends in populations which are notoriously variable, but also about the validity of inferring global trends from local or regional studies. Here we use data from 936 populations to assess large-scale temporal and spatial variations in amphibian population trends. On a global scale, our results indicate relatively rapid declines from the late 1950s/early 1960s to the late 1960s, followed by a reduced rate of decline to the present. Amphibian population trends during the 1960s were negative in western Europe (including the United Kingdom) and North America, but only the latter populations showed declines from the 1970s to the late 1990s. These results suggest that while large-scale trends show considerable geographical and temporal variability, amphibian populations are in fact declining--and that this decline has been happening for several decades.

Amphibians↗
PubMed1998

Analysis of three amphibian populations with quarter-century long time-series.

Amphibians are in decline in many parts of the world. Long tme-series of amphibian populations are necessary to distinguish declines from the often strong fluctuations observed in natural populations. Time-series may also help to understand the causes of these declines. We analysed 23-28-year long time-series of the frog Rana temporaria. Only one of the three studied populations showed a negative trend which was probably caused by the introduction of fish. Two populations appeared to be density regulated. Rainfall had no obvious effect on the population fluctuations. Whereas long-term studies of amphibian populations are valuable to document population declines, most are too short to reveal those factors that govern population dynamics or cause amphibian populations to decline.

Animals↗
PubMed1997

Regulation of cyclin-dependent kinase inhibitor p21(WAF1/Cip1/Sdi1) gene expression in hepatic regeneration.

WAF1/Cip1/Sdi1 (p21) is the prototype of a family of proteins that inhibit cyclin-dependent kinases and regulate cell cycle progression in eukaryotic cells. In addition to normal cell cycle progression, p21 is involved in growth suppression mediated by p53 and transforming growth factor beta (TGFbeta), differentiation, and apoptosis. To gain insight into the possible involvement of p21 in liver cell growth, the expression and regulation of the p21 gene was evaluated in rodent models of liver regeneration and specimens of human liver diseases. Little p21 mRNA was detected in normal liver tissue. After growth stimulation in vivo by 70% partial hepatectomy (PH), the p21 transcript was upregulated in a biphasic manner, with enhanced expression during G1 phase and following S phase. The induction of p21 after PH was regulated primarily at the post-transcriptional level and was due to enhanced mRNA stability. Inhibition of protein synthesis with cycloheximide rapidly induced p21 expression, primarily by post-transcriptional stabilization of the transcript. Hepatic p21 mRNA was also induced by dietary protein deprivation in normal mice. Expression of the p21 gene after PH was similar in p53-deficient (p53 -/-) and wild-type mice, but was p53-dependent following protein deprivation. Primary hepatocytes in culture demonstrated increased p21 expression after treatment with hepatocyte growth factor, TGFbeta, and activin A. p21 mRNA was upregulated in human liver diseases, suggesting a possible role in hepatic growth regulation in pathologic states. The present study demonstrates that p21 is regulated by p53-dependent and -independent pathways in the liver, and is influenced by both mitogenic and growth inhibitory stimuli.

Animals↗
PubMed1996

Localization of a gene coding for the phospholipase A2-L subtype (PLA2L) to human chromosome 8q24-qter.

Phospholipases A2 (PLA2) form an extended class of enzymes that play an important role in signal transduction. Phospholipase A2-like (PLA2L) belongs to the secreted forms of phospholipases A2, but constitutes a new subgroup. We have assigned the gene for this enzyme to human chromosome 8q24-qter using fluorescence in situ hybridization and radiation hybrid mapping techniques.

Animals↗
PubMed1991

Hyperpolarization of the cell membrane of mouse hepatocytes by metabolizable and nonmetabolizable monosaccharides.

The effect of metabolizable (D-glucose, D-fructose) and nonmetabolizable (2-deoxy-D-glucose, L-glucose) monosaccharides on the membrane potential (Vm) of mouse hepatocytes was investigated employing a superfused liver slice technique. D-Cellobiose was used as an osmotic control. All monosaccharides tested hyperpolarized the liver cell membrane. The short-term effects of D-glucose, D-fructose and 2-deoxy-D-glucose were similar, whereas the effect of L-glucose was less pronounced. The K+ channel blocker quinine reversed the effects of glucose and 2-deoxy-D-glucose on the Vm, suggesting that opening of K+ channels is involved in the hyperpolarizing effect of monosaccharides. The bearing of these findings with regard to hepatic control of food intake is discussed. The findings argue against a role of hepatocytes as glucoreceptors sensing glucose metabolism.

Animals↗
PubMed1991

Changes in feeding behavior and plasma vasopressin concentration during water deprivation in goats.

To further characterize the suppression of feeding that normally accompanies water deprivation and to test whether vasopressin contributes to this hypophagia, food intake, meal patterns and plasma vasopressin concentrations were measured during 24 h or 72 h of water deprivation in pygmy goats. The effects of exogenous vasopressin and of a V1-receptor antagonist on feeding during water deprivation were also assessed. The hypophagia during water deprivation was primarily due to decreases in meal size. The plasma vasopressin concentration increased about 2.5-fold and 10-fold after 24 and 72 h of water deprivation, respectively. Plasma osmolality also increased (measured only after 72 h of water deprivation). Intraperitoneally (ip) injected vasopressin (1.5 micrograms/kg b. wt.) that previously reduced food intake in goats with ad lib, access to water (Meyer et al., 1989), failed to affect cumulative food intake in water deprived goats, but led to a transient increase in meal size. The V1-receptor antagonist (2.5 micrograms/kg b. wt., ip) did not affect cumulative food intake or meal patterns either. These findings indicate that endogenous vasopressin is not crucially involved in the hypophagia during water deprivation. The results are in line with the hypothesis that an abnormal prandial increase in the osmolality of the ruminal fluid is a major contributor to the hypophagia during water deprivation.

Animals↗
PubMed1989

Vasopressin reduces food intake in goats.

The effect of arginine vasopressin (VP) on cumulative food intake and meal pattern was tested in pygmy goats. VP injected intraperitoneally (I.P.) (0.75, 1.5 and 3.0 micrograms kg-1 body weight) appeared to reduce food intake in a dose-dependent manner by reducing the size of the first meal and by increasing the first intermeal interval (IMI). The hypophagic effect of VP was reversed by both a V1-receptor antagonist and an alpha-adrenergic antagonist. Exogenous VP (0.75 and 1.5 microgram kg-1 body weight I.P.) produced increases in plasma VP concentration which also may occur in stressful situations. VP might therefore be related to stress-induced anorexia.

Animals↗
PubMed1976

Reduction mammaplasty followed by development of a bilateral non-synchronous carcinoma of the breast.

Case report of a woman who at the age of 26 underwent mammary reduction (strmbeck) for macromastia. A primary bilateral non-synchronous carcinoma of the breast was discovered 20 months and 5 years after the plastic surgery. On pathological examination lymph node metastases were not found in both instances. There was a positive family history of the occurrence of carcinoma. Mammography prior to mammary reduction is recommended.

Adult↗