Fifteen-year experience with screening for phenylketonuria with an automated fluorometric method.

An automated fluorometric method, rather than the Guthrie test, has been used in North Carolina for neonatal screening for phenylketonuria (PKU). Although there is no testing law, 97% of newborn infants are screened. Twelve children with PkU, not referred for dietary management, were born before the screening program was established, were born elsewhere, or were successfully identified at birth but not referred for treatment. None was missed because of laboratory error or because of the lack of a testing law. Positive skewing was noted among initial blood phenylalanine levels of 49 infants with PKU and severe hyperphenylalaninemia. Log transformations caused the values to be normally distributed and permitted the calculation of tolerance and confidence limits. These provided estimates of the percentage of phenylketonuric infants whose initial blood levels might fall below any given cutoff value.     

Restricted Ig H chain V gene usage in the human antibody response to Haemophilus influenzae type b capsular polysaccharide

The mechanisms that govern the content of the human antibody repertoire are poorly understood. To investigate the antibody response to a clinically relevant Ag, we have produced heterohybridomas secreting human antibodies directed against the capsular polysaccharide of Haemophilus influenzae type b (Hib PS). Immune lymphocytes were harvested 7 days after immunization with either of two vaccine formulations, a plain polysaccharide vaccine (Hib PS) or a polysaccharide-protein conjugate of Hib PS and diphtheria toxoid (Hib PS-D). H chain V region gene nucleic acid sequences were determined for five stable hybridomas. All use members of the VHIII gene family and are 83% to 98% homologous to two candidate germ-line sequences. A variety of D and JH segments are used. Thus the Ig H chain repertoire appears to be restricted to a limited group of VHIII family members. The previously reported expression of homologous sequences in the human fetal repertoire suggests that the inability of young children to respond to this Ag is not caused by deficiencies of these important elements early in development. The restricted use of VHIII gene segments suggests that this gene family plays a pivotal role in the immune response to this important childhood pathogen.     

RELATIVE IMPORTANCE OF CHOLINE TRANSPORT TO SPONTANEOUS AND POTASSIUM DEPOLARIZED RELEASE OF ACh

—The importance of extracellular choline transport to spontaneous and K⁺ depolarized release of ACh was studied using mouse brain cortex minces. The results suggest that extracellular choline transport is not essential to spontaneously released ACh but is essential to K⁺ depolarized ACh release. Similar cumulative amounts of choline and ACh were found in the incubation media following incubation of minces in either Krebs or 35 mm -K⁺ Krebs suggesting the same production of free choline during both conditions. Double reciprocal plots of choline accumulation by non-depolarized cortex minces yield high and low affinity components. Conversely, similar analysis of choline accumulation by depolarized minces yields a single Michaelis constant (68 μm ) similar to the low affinity (50 μm ) Michaelis constant determined for choline accumulation by non-depolarized minces. Kinetic analysis of ACh release as a function of extracellular choline concentration during K⁺ depolarization also yields a Michaelis constant of 68 μm These data suggest a link between choline transport and ACh release during K⁺ depolarization.     

REGIONAL DIFFERENCES IN HIGH AFFINITY CHOLINE TRANSPORT VELOCITY IN GUINEA-PIG BRAIN

The kinetic parameters of choline accumulation by synaptosomes prepared from different regions of guinea-pig brain (cortex, brainstem, and cerebellum) were determined. Choline was accumulated by a high affinity transport process for all regions tested and the apparent Michaelis constants were similar. However, the apparent maximal velocities of choline accumulation for the brain regions differed; the differences were related to the amount of acetylcholine formed by the respective regions. The results suggested that the maximal velocity of the high affinity transport process may reflect the density of cholinergic nerve endings within brain regions.     

Snow depth manipulation and its influence on soil frost and water dynamics in a northern hardwood forest

Climate change will likelyresult in warmer winter temperatures leading toless snowfall in temperate forests. Thesechanges may lead to increases in soil freezingbecause of lack of an insulating snow cover andchanges in soil water dynamics during theimportant snowmelt period. In this study, wemanipulated snow depth by removing snow for twowinters, simulating the late development of thesnowpack as may occur with global warming, toexplore the relationships between snow depth,soil freezing, soil moisture, and infiltration.We established four sites, each with two pairedplots, at the Hubbard Brook Experimental Forest(HBEF) in New Hampshire, U.S.A. and instrumentedall eight plots with soil and snow thermistors,frost tubes, soil moisture probes, and soillysimeters. For two winters, we removed snowfrom the designated treatment plots untilFebruary. Snow in the reference plots wasundisturbed. The treatment winters (1997/1998 and1998/1999) were relatively mild, withtemperatures above the seasonal norm and snowdepths below average. Results show the treatedplots accumulated significantly less snow andhad more extensive soil frost than referenceplots. Snow depth was a strong regulator ofsoil temperature and frost depth at all sites.Soil moisture measured by time domainreflectometry probes and leaching volumescollected in lysimeters were lower in thetreatment plots in March and April compared tothe rest of the year. The ratio of leachatevolumes collected in the treatment plots tothat in the reference plots decreased as thesnow ablation seasons progressed. Our data showthat even mild winters with low snowfall,simulated by snow removal, will result inincreased soil freezing in the forests at theHBEF. Our results suggest that a climate shifttoward less snowfall or a shorter duration ofsnow on the ground will produce increases insoil freezing in northern hardwood forests.Increases in soil freezing will haveimplications for changes in soil biogeochemicalprocesses.     

Understorey plant community assemblage of Australian Eucalyptus woodlands under elevated CO2 is modulated by water and phosphorus availability

水分和磷调控的澳大利亚桉树林林下植物群落组合对二氧化碳浓度升高的响应 鉴于林下植物群落具有的关键性功能作用和全球范围内巨大的森林覆盖面积,研究林下群落对 CO₂浓度升高(eCO₂)的响应以及土壤资源在这些响应中的作用,对于了解CO₂浓度升高对森林生态系统造成的影响非常重要。本研究评估了在澳大利亚东部磷有限的桉树林林下群落中,两种限制性的资源(即水分和磷)在发芽、物候、覆盖率、群落组成和叶片性状等方面对eCO₂响应的作用。我们收集了含有当地土壤种子库的土壤,在温室条件下种植实验性的林下植物群落。研究结果表明,添加磷提高了植物的总体覆盖率,特别是在生长期的最初4 周以及水分含量高的条件下,而且该响应是由植物群落中的类禾本科植物所驱动。然而,随着实验的进行,不同处理方法之间的差异逐渐减小,所有处理在大约11周后均达到了80%左右的植物覆盖率。相反,植物覆盖率并未受到eCO₂ 的影响。多元分析结果反映出植物群落组成随时间的变化,盆栽从以裸土为主变为以高覆盖率的多样化群落为主。但是在实验过程中,磷的添加以及水分可利用性和CO₂之间的相互作用都对植物群落随时间的变化轨迹有所影响。CO₂浓度的升高也增加了群落水平的比叶面积,这表明植物群落对eCO₂的功能适应可能发生在成分响应开始之前。鉴于我们用种子库培育的林下群落对eCO₂ 的响应随着时间的推移而有 所变化,并且受到与磷和水分可利用性的相互作用的调节。我们的结果表明,在水分含量有限的系统中, 特别是在土壤养分可利用性低所导致的生产力响应受限的情况下,CO₂浓度的升高在塑造植物群落方面作用有限。