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Patrick McDonald

Publications and source records attributed to Patrick McDonald.

6 recordsLinked to original sources
PubMed2006

Can sterile neutrinos be the dark matter?

We use the Ly-alpha forest power spectrum measured by the Sloan Digital Sky Survey and high-resolution spectroscopy observations in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter scenario. Such a neutrino would be created in the early Universe through mixing with an active neutrino and would suppress structure on scales smaller than its free-streaming scale. We ran a series of high-resolution hydrodynamic simulations with varying neutrino masses to describe the effect of a sterile neutrino on the Ly-alpha forest power spectrum. We find that the mass limit is m(s) >13 keV at 95% C.L. (9 keV at 99.9%), which is above the upper limit allowed by x-ray constraints, excluding this candidate from being all of the dark matter in this model.

Journal Article↗
PubMed2005

Calcium chelation improves spatial learning and synaptic plasticity in aged rats.

Impaired regulation of intracellular calcium is thought to adversely affect synaptic plasticity and cognition in the aged brain. Comparing young (2-3 months) and aged (23-26 months) Fisher 344 rats, stratum radiatum-evoked CA1 field EPSPs were smaller and long-term potentiation (LTP) was diminished in aged hippocampal slices. Resting calcium, in presynaptic axonal terminals in the CA1 stratum radiatum area, was elevated in aged slices. Loading the slice with the calcium chelator, BAPTA-AM, depressed LTP in young slices, but enhanced this plasticity in old slices. Forty-five minutes following LTP-inducing high frequency stimulation, resting calcium levels were significantly increased in both young and old presynaptic terminals, and significantly reduced by pretreatment with BAPTA-AM. In vivo, intraperitoneal administration of BAPTA-AM prior to training in the reference memory version of the Morris water maze test, significantly improved the acquisition of spatial learning in aged animals, without a significant effect in young rats. These results support the hypothesis that increasing intracellular neuronal buffering power for calcium in aged rats ameliorates age-related impaired synaptic plasticity and learning.

Aging↗
PubMed2002

Interleukin-15 inhibits spontaneous apoptosis in human eosinophils via autocrine production of granulocyte macrophage-colony stimulating factor and nuclear factor-kappaB activation.

Prolonged eosinophil survival, i.e., reduced apoptosis, is implicated in the pathogenesis of chronic allergic inflammation. Here we demonstrate that interleukin (IL)-15, in the presence or absence of tumor necrosis factor (TNF)-alpha, reduces spontaneous apoptosis in freshly isolated human eosinophils. The prosurvival effect of IL-15 was abrogated by neutralizing antibody to granulocyte macrophage-colony stimulating factor (GM-CSF), although GM-CSF was not detected in conditioned media by ELISA. Additionally, the effect of IL-15 on spontaneous eosinophil apoptosis appeared to require nuclear factor-kappaB (NF-kappaB) activation based on evidence for NF-kappaB nuclear translocation and abrogation of the effect by the NF-kappaB inhibitor, Bay 11- 7082. Finally, the data demonstrate that IL-15 expression is higher in the submucosa of endobronchial tissues from subjects with moderate to severe asthma when compared with control subjects. Thus, our results suggest that IL-15, either alone or in combination with TNF-alpha, may perpetuate allergic inflammation by reduction of spontaneous eosinophil apoptosis through autocrine production of GM-CSF and NF-kappaB activation.

Adolescent↗