Biomedical subjects
Publications and source records attributed to B M Davis.
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Enkephalin peptides are present in the retina of several vertebrate species. In the avian retina, enkephalin immunoreactivity is primarily localized to a population of amacrine cells. In the present study, we determined the localization of cells expressing preproenkephalin (PPE) mRNA, which encodes the precursor of enkephalin peptides, in adult as well as in embryonic chicken retinas. The localization of PPE mRNA-expressing cells to the proximal inner nuclear layer (INL) in the adult chicken retina is similar to that of enkephalin-immunoreactive cells observed in previous studies, indicating that amacrine cells expressing PPE mRNA synthesize Met5- and Leu5-enkephalin peptides and related extended forms. Specific hybridization signal is absent in retinas at embryonic day (E) 11, but it is detected in retinas at E 15 and at hatching. PPE mRNA-expressing cells at these ages are located in the proximal INL, and they can be classified as amacrine cells on the basis of their soma size and laminar position. These findings confirm and extend previous observations on the presence of opioid peptides in amacrine cells of the chicken retina. The presence of PPE mRNA at embryonic ages, together with the evidence that enkephalins influence developmental processes, suggests that these peptides modulate retinal maturation in birds.
Naturally occurring radon in ground water can potentially be used as an in situ partitioning tracer to characterize dense nonaqueous phase liquid (DNAPL) saturations. The static method involves comparing radon concentrations in water samples from DNAPL-contaminated and noncontaminated portions of an aquifer, while the push-pull method involves the injection (push) and extraction (pull) of a radon-free test solution from a single well. In the presence of DNAPL, radon concentrations during the pull phase are retarded, with retardation manifested in greater dispersion of radon concentrations relative to a conservative tracer. The utility of these methods was investigated in the laboratory using a physical aquifer model (PAM). Static and push-pull tests were performed before and after contamination of the PAM sediment pack with trichloroethene (TCE), and after alcohol cosolvent flushing and pump-and-treat remediation. Numerical simulations were used to estimate the retardation factor for radon in push-pull tests. Radon partitioning was observed in static and push-pull tests conducted after TCE contamination. Calculated TCE saturations ranged up to 1.4% (static test) and 14.1% (push-pull test). Post-remediation tests showed decreases in TCE saturations. The results show that radon is sensitive to changes in DNAPL saturation in space and time. However, the methods are sensitive to DNAPL saturation heterogeneity, test location, sample size, and test design. The influence of these factors on test results, as well as the apparent overestimation of the retardation factor in push-pull tests, warrant further investigation.