PubMed Health⌕ Search

Biomedical subjects

John F Cooper

Publications and source records attributed to John F Cooper.

4 recordsLinked to original sources
PubMed2006

Immunolabeling demonstrates the interdependence of mouse brain alpha4 and beta2 nicotinic acetylcholine receptor subunit expression.

Immunolabeling of beta2 and alpha4 subunits was quantitated in brain sections (14 mum) using [(125)I]mAb 270 and [(125)I]mAb 299, respectively. Specificity was demonstrated by signal loss in beta2(-/-) and alpha4(-/-) brain sections, respectively. Even mild paraformaldehyde fixation severely affected immunolabeling, so this study used unfixed sections. Immunolabeling autoradiography was used to map and quantitate the effects of beta2 and alpha4 subunit-null mutations on their putative partner subunits' protein expression. [(125)I]mAb 299 labeling was nearly eliminated in beta2(-/-) sections, although dorsal interpeduncular nucleus (IPN) retained a faint signal. Therefore, alpha4 subunit expression is almost universally beta2-dependent. In contrast, alpha4-null mutation effects on [(125)I]mAb 270 immunolabeling varied widely among brain regions. In corticothalamic regions, [(125)I]mAb 270 labeling was eliminated. However, in habenulopeduncular regions, alpha4 genotype had no effect. Other (predominantly dopaminergic and optic tract) nuclei also retained reduced [(125)I]mAb 270 labeling in alpha4(-/-) sections. Thus, although most beta2 subunit protein expression is alpha4-dependent, this dependence is not universal. Presumably, residual beta2 subunits are found in non-alpha4* subtypes. Together, these results show that immunolabeling is applicable to reliable, quantitative investigations of neuronal nAChRs, and that subunit-null mutants can be appropriate controls for such experiments. In situ mRNA hybridization was also performed to determine if altered mRNA transcription mediated the interdependence of alpha4 and beta2 subunit expression. alpha4-Null mutation did not affect beta2 mRNA expression, nor did beta2 genotype affect alpha4 mRNA expression. Consequently, it seems that the two subunits' effects on each other's expression are mediated at the protein, rather than gene expression level.

Acetylcholine↗
PubMed2006

Clathrate hydrates of oxidants in the ice shell of Europa.

Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes. The temperature and pressure environments of regions within the europan hydrosphere are expected to permit the formation of mixed clathrate compounds. The formation of carbon dioxide and sulfur dioxide clathrates has been examined in some detail. Here we add to this analysis by considering oxidants produced radiolytically on the surface of Europa. Our results indicate that the bulk ice shell could have a approximately 1.7-7.6% by number contamination of oxidants resulting from radiolysis at the surface. Oxidant-hosting clathrates would consequently make up approximately 12-53% of the ice shell by number relative to ice, if oxidants were entrained throughout. We examine, in brief, the consequences of such contamination on bulk ice shell thickness and find that clathrate formation could lead to substantially thinner ice shells on Europa than otherwise expected. Finally, we propose that double occupancy of clathrate cages by O2 molecules could serve as an explanation for the observation of condensed-phase O2 on Europa. Clathrate-sealed, gas-filled bubbles in the near surface ice could also provide an effective trapping mechanism, though they cannot explain the 5771 A (O2)2 absorption.

Ice↗