Environmental and developmental controls over the seasonal pattern of isoprene emission from aspen leaves

Isoprene emission from plants represents one of the principal biospheric controls over the oxidative capacity of the continental troposphere. In the study reported here, the seasonal pattern of isoprene emission, and its underlying determinants, were studied for aspen trees growing in the Rocky Mountains of Colorado. The springtime onset of isoprene emission was delayed for up to 4 weeks following leaf emergence, despite the presence of positive net photosynthesis rates. Maximum isoprene emission rates were reached approximately 6 weeks following leaf emergence. During this initial developmental phase, isoprene emission rates were negatively correlated with leaf nitrogen concentrations. During the autumnal decline in isoprene emission, rates were positively correlated with leaf nitrogen concentration. Given past studies that demonstrate a correlation between leaf nitrogen concentration and isoprene emission rate, we conclude that factors other than the amount of leaf nitrogen determine the early-season initiation of isoprene emission. The late-season decline in isoprene emission rate is interpreted as due to the autumnal breakdown of metabolic machinery and loss of leaf nitrogen. In potted aspen trees, leaves that emerged in February and developed under cool, springtime temperatures did not emit isoprene until 23 days after leaf emergence. Leaves that emrged in July and developed in hot, midsummer temperatures emitted isoprene within 6 days. Leaves that had emerged during the cool spring, and had grown for several weeks without emitting isoprene, could be induced to emit isoprene within 2 h of exposure to 32°C. Continued exposure to warm temperatures resulted in a progressive increase in the isoprene emission rate. Thus, temperature appears to be an important determinant of the early season induction of isoprene emission. The seasonal pattern of isoprene emission was examined in trees growing along an elevational gradient in the Colorado Front Range (1829–2896 m). Trees at different elevations exhibited staggered patterns of bud-break and initiation of photosynthesis and isoprene emission in concert with the staggered onset of warm, springtime temperatures. The springtime induction of isoprene emission could be predicted at each of the three sites as the time after bud break required for cumulative temperatures above 0°C to reach approximately 400 degree days. Seasonal temperature acclimation of isoprene emission rate and photosynthesis rate was not observed. The temperature dependence of isoprene emission rate between 20 and 35°C could be accurately predicted during spring and summer using a single algorithm that describes the Arrhenius relationship of enzyme activity. From these results, it is concluded that the early season pattern of isoprene emission is controlled by prevailing temperature and its interaction with developmental processes. The late-season pattern is determined by controls over leaf nitrogen concentration, especially the depletion of leaf nitrogen during senescence. Following early-season induction, isoprene emission rates correlate with photosynthesis rates. During the season there is little acclimation to temperature, so that seasonal modeling simplifies to a single temperature-response algorithm.     

Advanced techniques in abdominal surgery.

Almost every abdominal organ is now amenable to laparoscopic surgery. Laparoscopic appendicectomy is a routine procedure which also permits identification of other conditions initially confused with an inflamed appendix. However, assessment of appendiceal inflammation is more difficult. Almost all colonic procedures can be performed laparoscopically, at least partly, though resection for colonic cancer is still controversial. For simple patch repair of perforated duodenal ulcers laparoscopy is ideal, and inguinal groin hernia can be repaired satisfactorily with a patch of synthetic mesh. Many upper abdominal procedures, however, still take more time than the open operations. These techniques reduce postoperative pain and the incidence of wound infections and allow a much earlier return to normal activity compared with open surgery. They have also brought new disciplines: surgeons must learn different hand-eye coordination, meticulous haemostasis is needed to maintain picture quality, and delivery of specimens may be problematic. The widespread introduction of laparoscopic techniques has emphasised the need for adequate training (operations that were straight-forward open procedures may require considerable laparoscopic expertise) and has raised questions about trainee surgeons acquiring adequate experience of open procedures.     

Predicting therapeutic response and degree of pituitary tumour shrinkage during treatment of acromegaly with octreotide LAR

BACKGROUND/AIMS: The efficacy of transsphenoidal surgery in the treatment of patients with acromegaly is largely dependent on tumour size. A reduction in pituitary tumour volume by medical therapy might therefore improve subsequent surgical cure rates. This study prospectively determined the effects of the depot somatostatin analogue octreotide LAR on pituitary tumour size, GH and IGF-I levels and clinical symptoms in a cohort of previously untreated patients with acromegaly. METHODS: Six patients newly diagnosed with acromegaly (mean age 53 years; range 42-76 years) received intramuscular octreotide LAR every 28 days for 6 months. The initial dose of LAR was 20 mg, but increased to 30 mg after the initial 3 injections if mean GH levels were >5 mU/l. Prior to commencing LAR therapy, each patient received 3 injections of subcutaneous octreotide (50, 100 and 200 mug) in a randomized order on separate days, and the serum GH response was measured. Pituitary tumour volume was calculated from MRI or computed tomography scans at baseline, then 3 and 6 months after initiation of treatment, and assessed by a 'blinded' radiologist in random order. At baseline, 4 patients had a macroadenoma and 2 patients had a microadenoma. For the latter, the whole gland volume was measured. RESULTS: Serum GH levels decreased from 29.6 +/- 19.2 mU/l (mean +/- SD) at baseline to 12.1 +/- 10.5 mU/l at 3 months and 10.4 +/- 9.3 mU/l at 6 months. Three patients achieved a mean serum GH level of <5 mU/l. In these patients, the serum GH had declined to <5 mU/l in response to a single 100 mug subcutaneous octreotide injection. Serum IGF-I levels decreased by a mean of 45 +/- 7.4%. Tumour volume decreased in all patients: mean baseline volume 2,175 mm(3) (range 660-6,998) decreasing to 1,567 mm(3) (range 360-4,522) at 3 months (p < 0.05) and 1,293 mm(3) (range 280-4,104) at 6 months (p < 0.002). The mean percentage decrease in size was 29% (range -54 to +4%) at 3 months (p < 0.02) and 47% (range 21-97%) at 6 months (p < 0.002). There was no statistically significant correlation between GH response and tumour shrinkage. CONCLUSIONS: A single test dose of subcutaneous octreotide may be useful in predicting the subsequent efficacy of octreotide LAR. Octreotide LAR results in significant shrinkage of pituitary tumours of newly diagnosed patients with acromegaly. Whether its administration to such patients for 6-12 months can improve the efficacy of subsequent transsphenoidal surgery will require further study.     

Cloning and characterization of SK2 channel from chicken short hair cells

In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74±0.17 M. The expressed channels were blocked by apamin (IC₅₀=73.3±5.0 pM) and d-tubocurarine (IC₅₀=7.6±1.0 M), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates.     

Quality of life assessment of growth hormone deficiency in adults (QoL-AGHDA): comparison of normative reference data for the general population of England and Wales with results for adult hypopituitary patients with growth hormone deficiency

BACKGROUND/AIM: Age- and gender-specific reference values for the quality of life (QoL) measures used in assessing the impact of growth hormone deficiency (GHD) are important. The objective of this study was to develop such data for the QoL-AGHDA instrument for the population of England and Wales and to demonstrate the QoL deficit in patients with GHD. METHODS: For the purpose of this study, a questionnaire was developed that contained the EurQoL EQ-5D, QoL-AGHDA, questions recording an individual's general situation and social functioning, and a self-reported five-point rating scale of general health. The questionnaire was mailed out to a sample of 1,190 individuals drawn from the general population of England and Wales. Corresponding data for 836 patients were retrieved from KIMS (Pfizer International Metabolic Database). The postal survey data were weighted to ensure that they were representative of the general population. RESULTS: The mean weighted QoL-AGHDA scores for the general population were 6.2 and 7.1 for men and women, respectively, compared with 13.6 and 15.7 for patients. For both males and females the differences in mean QoL-AGHDA scores between the general population and patients were statistically significant for all age categories (p < 0.01). In the general population the mean QoL-AGHDA score for each category of self-assessed health status increased progressively, indicating a poorer QoL as health status declined. CONCLUSIONS: This study reports QoL-AGHDA normative values for the population of England and Wales and confirms the extent of QoL impairment in patients with GHD in comparison with the general population.     

Parturition following transfer of embryos produced in two media under two oxygen concentrations

In vitro-produced blastocysts were transferred singly to 99 Angus crossbred recipients. Culture treatments were a 2 x 2 factorial of medium (KSOM or SOF) and oxygen concentration (5 or 20%). At parturition, birth weight and frame measurement before colostrum intake were recorded. Fetal membranes were collected; distribution and diameter of cotyledons was recorded. Cotyledon surface area was calculated. Culture with 5% O2 tended to yield smaller birth weights than culture with 20% O2 (39.7+/-1.3 kg versus 43.1+/-1.4 kg; P < 0.1); this effect was pronounced in KSOM, suggesting a medium by oxygen interaction (P < 0.1). When expressed on a body weight basis, calves born following culture with 20% O2 had consistently smaller skeletal measurements than those from culture with 5% O2. Culture with 20% O2 significantly increased individual cotyledon areas both overall and in the fetal horn and cotyledon surface area in the fetal horn. Overall, individual cotyledons were 32% larger when culture involved 20% O2 versus 5% O2; in the fetal horn the increase was 49%. Cotyledon surface area was greater for 20% compared to 5% O2 culture, though a medium by oxygen interaction was also significant (P < 0.05). Cotyledon surface area in the nonfetal horn was greater for KSOM fetal membranes than those from culture in SOF. There was a significant medium by oxygen interaction for total cotyledon number. These data demonstrate culture system-specific effects on calf and fetal membrane traits.     

Induction of poplar leaf nitrate reductase: a test of extrachloroplastic control of isoprene emission rate

Several recent studies have suggested that control of isoprene emission rate is in part exerted by supply of extrachloroplastic phosphoenolpyruvate to the chloroplast. To test this hypothesis, we altered PEP supply by differential induction of cytosolic nitrate reductase (NR) and PEP carboxylase (PEPC) in plants of Populus deltoides grown with NO3- or NH4+ as the sole nitrogen source. Growth with 8 mM NH4+ produced a high leaf nitrogen concentration, compared with 8 mM NO3-, as well as slightly elevated rates of photosynthesis and significantly enhanced rates of isoprene emission and content of dimethylallyl diphosphate (DMAPP, a precursor to isoprene biosynthesis), chlorophyll (a+b) and carotenoids. Growth with 8 mM NO3- resulted in parallel reductions in both leaf isoprene emission rate and DMAPP. The differential effects of growth with NH4+ or NO3- were not observed when plants were grown with 4 mM nitrogen. The effects of reduced DMAPP availability were specific to isoprene emission and were not propagated to higher isoprenoids, as the correlations between nitrogen content and either leaf chlorophyll (a+b) or total carotenoids were unaffected by nitrogen source. Biochemical analysis revealed significantly higher levels of NR and PEPC activity in leaves of 8 mM NO3- -grown plants, consistent with their fundamental roles in nitrate assimilation. Taken together, these results support the hypothesis that foliar assimilation of NO3- reduces isoprene emission rate by competing for carbon skeletons (mediated by PEPC) within the cytosol and possibly reductant within the chloroplast. Cytosolic competition for PEP is a major regulator of chloroplast DMAPP supply, and we offer a new "safety valve" hypothesis to explain why plants emit isoprene.     

A Distinct Class of Antibodies May Be an Indicator of Gray Matter Autoimmunity in Early and Established Relapsing Remitting Multiple Sclerosis Patients

We have previously identified a distinct class of antibodies expressed by B cells in the cerebrospinal fluid (CSF) of early and established relapsing remitting multiple sclerosis (RRMS) patients that is not observed in healthy donors. These antibodies contain a unique pattern of mutations in six codons along V_H4 antibody genes that we termed the antibody gene signature (AGS). In fact, patients who have such B cells in their CSF are identified as either having RRMS or developing RRMS in the future. As mutations in antibody genes increase antibody affinity for particular antigens, the goal for this study was to investigate whether AGS⁺ antibodies bind to brain tissue antigens. Single B cells were isolated from the CSF of 10 patients with early or established RRMS. We chose 32 of these B cells that expressed antibodies enriched for the AGS for further study. We generated monoclonal full-length recombinant human antibodies (rhAbs) and used both immunological assays and immunohistochemistry to investigate the capacity of these AGS⁺ rhAbs to bind brain tissue antigens. AGS⁺ rhAbs did not recognize myelin tracts in the corpus callosum. Instead, AGS⁺ rhAbs recognized neuronal nuclei and/or astrocytes, which are prevalent in the cortical gray matter. This pattern was unique to the AGS⁺ antibodies from early and established RRMS patients, as AGS⁺ antibodies from an early neuromyelitis optica patient did not display the same reactivity. Prevalence of CSF-derived B cells expressing AGS⁺ antibodies that bind to these cell types may be an indicator of gray matter-directed autoimmunity in early and established RRMS patients.