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D Curtin

Publications and source records attributed to D Curtin.

6 recordsLinked to original sources
PubMed2004

Distribution of residence times in bistable noisy systems with time-delayed feedback.

We analyze theoretically and experimentally the residence time distribution of bistable systems in the presence of noise and time-delayed feedback. We explain various nonexponential features of the residence time distribution using a two-state model and obtain a quantitative agreement with an experiment based on a Schmitt trigger. The limitations of the two-state model are also analyzed theoretically and experimentally using a semiconductor laser with optoelectronic feedback.

Journal Article↗
PubMed2001

Androgen suppression of GnRH-stimulated rat LHbeta gene transcription occurs through Sp1 sites in the distal GnRH-responsive promoter region.

Steroids may regulate LH subunit gene transcription by modulating hypothalamic GnRH pulse patterns or by acting at the pituitary gonadotrope to alter promoter activity. We tested direct pituitary effects of the androgen dihydrotestosterone (DHT) to modulate the rat LHbeta promoter in transfected LbetaT2 clonal gonadotrope cells and in pituitaries of transgenic mice expressing LHbeta-luciferase. The LHbeta promoter (-617 to +44 bp)-luciferase construct was stimulated in LbetaT2 cells 7- to 10-fold by GnRH. Androgen treatment had little effect on basal promoter activity but suppressed GnRH stimulation by approximately 75%. GnRH stimulation of LHbeta was also suppressed by DHT in isolated pituitary cells from male or female mice with functional nuclear ARs, but not in male littermates with mutant AR. GnRH stimulation of the LHbeta promoter requires interactions between a complex distal response element containing two specificity protein-1 (Sp1) binding sites and a CArG box, and a proximal element with two bipartite binding sites for steroidogenic factor-1 and early growth response protein-1 (Egr-1). DHT effectively suppressed promoter constructs with an intact distal response element. The distal response element does not bind AR, but AR reduces Sp1 binding to this region. Glutathione-S-transferase pull-down studies demonstrated direct interactions of AR with Sp1, which requires the DNA-binding domain of AR, and weaker interactions with Egr-1. We conclude that androgen suppression of the rat LHbeta promoter occurs primarily through direct interaction of AR with Sp1, with some possible role through binding to Egr-1. These interactions result in interference with GnRH-stimulated gene transcription by reducing cooperation between the distal and proximal GnRH response elements.

Animals↗
PubMed2000

Plasmodium vivax polymorphs and Plasmodium falciparum circumsporozoite proteins in Anopheles (Diptera: Culicidae) from Belize, Central America.

Eight species of Anopheles mosquitoes from indoor/outdoor human landing collections in Belize, Central America, were examined for human Plasmodium circumsporozoite protein (CSP) using an enzyme-linked immunosorbent assay (ELISA). A total of 14 of 9,104 females tested were positive from general surveys throughout Belize and three of 11,966 were positive from a longitudinal study in Caledonia, northern Belize. ELISA results, using pooled head-thorax preparations and species-specific monoclonal antibodies directed against the circumsporozoite proteins of Plasmodium falciparum and two Plasmodium vivax polymorphs (210 and VK247), found four species reactive: Anopheles vestitipennis (3 pools), Anopheles darlingi (2 pools), Anopheles albimanus (10 pools), and Anopheles gabaldoni (2 pools). The minimum field infection rates (MFIR) for combined Plasmodium species from the general survey were 0.282% for An. vestitipennis, 0.271% for An. darlingi, 0.126% for An. albimanus, and 0.395% for An. gabaldoni. MFIRs for combined Plasmodium species from the longitudinal study in the village of Caledonia were 0.018% for both An. vestitipennis and An. albimanus and 1.66% for An. gabaldoni. Positive CSP pools were collected from the Cayo, Corozal, Orange Walk, Stann Creek, and Toledo political districts. No CSP positive pools were detected from collections in the Belize District. The study provides valuable information on the spatial distribution and species type of Plasmodium positive mosquitoes. This information, in combination with other vector data, suggest that An. vestitipennis and An. darlingi are commonly involved in malaria transmission. Additionally, these species appear to be much more efficient vectors than An. albimanus in Belize.

Animals↗
PubMed1992

Assessment of Pediococcus acidilactici as a Potential Silage Inoculant.

Eighteen Pediococcus strains were screened for their potential as silage inoculants. Pediococcus acidilactici G24 was found to be the most suitable, exhibiting a short lag phase on both glucose and fructose, a rapid rate of acid production, a high sugar-to-lactate conversion efficiency, no detectable breakdown of proteins or lactic acid, and the ability to grow within a broad range of pH and temperature. When tested in laboratory silos using grass with a water-soluble carbohydrate content of 24 g/kg of aqueous extract, P. acidilactici G24 stimulated the natural Lactobacillus plantarum population and accelerated the rates of lactic acid production and pH decrease. After 6 days of fermentation, the inoculated silage exhibited a 12% decrease in ammonia nitrogen and an 11% increase in crude protein levels compared with uninoculated controls. The use of an L. plantarum inoculant at a rate of 10 bacteria per g of grass in conjunction with P. acidilactici G24 produced no additional beneficial effect. Inoculation of grass with a water-soluble carbohydrate level of 8 g/kg of aqueous extract with P. acidilactici G24 led to no acceleration in the rate of L. plantarum growth or pH decrease. However, after 7 days of fermentation the inoculated silage had a 14% lower ammonia nitrogen protein content than did uninoculated controls. The results suggest that P. acidilactici G24 may be useful as a silage inoculant for crops with a sufficiently high water-soluble carbohydrate level.

Journal Article↗