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Biomedical subjects

A L Lawrence

Publications and source records attributed to A L Lawrence.

At least 19 recordsLinked to original sources
PubMed2004

Molecular phylogeny in 3-D.

Molecular phylogenetic trees are constructed in three dimensions relative to the distribution of MW and pl classes and immunocrossreactivity against polyclonal antibodies to lens crystallins, as well as multiple sequence alignment between amino acid sequences, coding nucleotide sequences and the gene nucleotide sequences for beta-globin. Euclidian distances are estimated to position species in x, y, z space by multidimensional scaling and merged with bootstrap-tested branching pattern of Fitch & Margoliash plots to obtain 3-D phylogenetic tree. Compared to single attributes, phylogenetic trees based on multiple parameters allow significant repositioning of rodents, chiroptera and primates.

Animals↗
PubMed2001

Factors controlling the bioaccumulation of mercury and methylmercury by the estuarine amphipod Leptocheirus plumulosus.

The bioaccumulation of inorganic mercury (HgI) and monomethylmercury (MMHg) by benthic organisms and subsequent trophic transfer couples the benthic and pelagic realms of aquatic systems and provides a mechanism for transfer of sedimentary contaminants to aquatic food chains. Experiments were performed to investigate the bioavailability and bioaccumulation of particle-associated HgI and MMHg by the estuarine amphipod Leptocheirus plumulosus to further understand the controls on bioaccumulation by benthic organisms. HgI and MMHg are particle reactive and have a strong affinity for organic matter, a potential food source for amphipods. Microcosm laboratory experiments were performed to determine the effects of organic matter on Hg bioaccumulation and to determine the major route of Hg uptake (i.e. sediment ingestion, uptake from water/porewater, or uptake from 'food'). Amphipods living in organic-rich sediment spiked with Hg accumulated less Hg than those living in sediments with a lower organic matter content. Feeding had a significant impact on the amount of HgI and MMHg accumulated. Similarly, amphipods living in water with little organic matter accumulated more Hg than those living in water with a greater percentage of organic matter. MMHg was more readily available for uptake than HgI. Experimental results, coupled with results from a bioaccumulation model, suggest that accumulation of HgI and MMHg from sediment cannot be accurately predicted based solely on the total Hg, or even the MMHg, concentration of the sediment, and sediment-based bioaccumulation factors. All routes of exposure need to be considered in determining the accumulation of HgI and MMHg from sediment to benthic invertebrates.

Animals↗
PubMed2000

Early direct and transneuronal effects in mice with targeted expression of a toxin gene to D1 dopamine receptor neurons.

The neurochemical profile was examined at postnatal day 3-4 in mutant mice generated by in vivo Cre mediated activation of an attenuated diphtheria toxin gene inserted into the D1 dopamine receptor gene locus. An earlier study of this model had shown that D1 dopamine receptor, substance P and dynorphin were not expressed in the striatum. Quantitative in situ hybridization analysis showed an increase in D2 dopamine receptor and enkephalin messenger RNA expression. The nigrostriatal pathway in the mutant pups was intact with a normal number of dopaminergic neurons in the substantia nigra and the ventral tegmental area in addition to a normal pattern of striatal dopamine transporter and tyrosine hydroxylase immunoreactivity. Quantitative analysis of striatal dopamine transporter density using [3H]mazindol showed a reduction of 26% suggesting a degree of transneuronal down-regulation. There was also a 49% reduction of striatal GABA receptor binding and a 36% reduction of striatal muscarinic receptor binding in mutant pups. The number of healthy striatal neuropeptide Y-containing interneurons was also substantially down-regulated in the mutant striatum. In contrast, there was an increase in the number of striatal cholinergic interneurons. Down-regulated cortical GABA receptor and muscarinic receptor binding was also observed in addition to subtle morphological changes in the neuropeptide Y-expressing population of cortical neurons. The changes reflect the early cascade of events which follows the ablation of D1 dopamine receptor-positive cells. Although extensive changes in a number of striatal and cortical neurons were demonstrated, only subtle transneuronal effects were seen in the nigrostriatal pathway.

Animals↗
PubMed1981

Sugar and amino acid transport from the rat uterine lumen: effects of estrogen and progesterone.

Sugar and amino acid transport and diffusion from the uterine lumen were evaluated in either castrated rats 4 or 24 h after iv injection of 17 beta-estradiol (0.1--10 microgram) or in estrogen-primed castrated rats 12 or 24 h after iv injection of progesterone (25--250 microgram). Uptake phenomena were evaluated by selectively exposing the uterine luminal surface to a Ringer's solution containing [U-14C]D-mannitol and [3H]3-O-methyl-D-glucose or [3H]alpha-aminoisobutyric acid for a 30-sec incubation. Diffusion (D-mannitol uptake) decreased significantly 4 h (but not 24 h) after estrogen and 12 and 24 h after progesterone treatment. [3H]3-O-methyl-D-glucose transport increased significantly both 4 h (120--380%) and 24 h (50--200%) after estrogen. Although [3H]3-O-methyl-D-glucose transport was not significantly changed from that in the vehicle-injected control 12 or 24 h after progesterone, comparison of the transport at 12 h (reduced) to that at 24 h (increased) revealed a significant difference in the responses to progesterone treatment at these two times. [3H]alpha-aminoisobutyric acid transport increased significantly 4 and 24 h after only a pharmacological dose of 17 beta-estradiol and was unchanged 24 h after progesterone administration. In summary, uterine luminal diffusion and transport phenomena are hormone sensitive, with estrogen exerting a more pronounced effect on transport than does progesterone. Thus, through modulation of luminal transport mechanisms, these hormones may regulate substrate levels and, hence, their availability to the developing conceptus during different reproductive states in the rat.

Aminoisobutyric Acids↗
PubMed1980

Metabolic profiles of penaied shrimp: dietary lipids and ovarian maturation.

The major impediment to the culture of penaeid shrimp in captivity in the United States has been an inability to obtain ovarian maturation and spawning. Lipid profiles of tissues (gonads, hepatopancreas, and tail muscle) of Penaeus setiferus caught at sea have shown that cholesterol is the dominant sterol and that polyunsaturated fatty acids known to be essential in man comprise a significant portion of the fatty acid fraction. A prioprietary marine ration contains cholesterol, but is devoid of polyunsaturated fatty acids. Ovarian maturation and spawning were obtained when the shrimp diet was supplemented with an annelid rich in lipids containing these compounds. The biochemical significance of these findings is discussed.

Animal Nutritional Physiological Phenomena↗
PubMed1972

The effect of carbohydrates on the intestinal potentials of Cryptochiton stelleri.

1. The effect of various monosaccharides on the potential difference across the intestine of the invertebrate, Cryptochiton stelleri, was studied using an everted sac technique.2. D-Glucose, when present in the mucosal solution, increased the transmural potential across the anterior intestine but had no effect on electrical potentials across the posterior intestine.3. D-Galactose, when present in the mucosal solution, increased the transmural potential across the posterior intestine but had no effect on electrical potentials across the anterior intestine.4. D-Fructose and D-mannose, metabolizable but non-transported sugars, increased anterior intestinal potentials but not posterior intestinal potentials.5. 3-O-methylglucose, an actively transported (across the anterior intestine) but non-metabolizable sugar, did not alter potentials across either the anterior or posterior intestine.6. The addition of D-glucose to the serosal solution increased anterior intestinal potentials, but the serosal addition of D-galactose did not affect posterior intestinal potentials.7. NaF, phlorizin and anoxia prevented the increase in potential across the anterior intestine and phlorizin (10(-4) but not 10(-6)M) and NaF but not anoxia prevented the increase in potential across the posterior intestine.8. It was suggested that the effect of glucose on anterior intestinal potentials was a metabolic effect, whereas the effect of galactose on posterior intestinal potentials was related to the active transport of that sugar from mucosa to serosa.

Animals↗