Direct role of hydrogen in the Staebler-Wronski effect in hydrogenated amorphous silicon.

We report a hydrogen-related defect that establishes the direct role of hydrogen in stabilizing the silicon dangling bonds created in the Staebler-Wronski effect in hydrogenated amorphous silicon. A specific NMR signal due to paired hydrogen atoms occurs only after optical excitation, exists at an intensity that is consistent with the density of optically induced silicon dangling bonds, and anneals at temperatures that are consistent with the annealing of the optically induced silicon dangling bonds. At this defect the hydrogen atoms are 2.3+/-0.2 A apart.

Trisomy 21. Second-trimester ultrasound.

Not every aspect of sonographic examination reveals karyotypic abnormalities. Ultrasound examination of a fetus with trisomy 21 generally reveals normal amniotic fluid, normal placentation, and normal fetal growth. In addition, other chromosomal abnormalities have many of the same sonographic findings as Down syndrome, and many findings have a large overlap with phenotypically normal fetuses. The importance of second-trimester ultrasound screening for Down syndrome has remained great because of its ease of use and relative effectiveness. Trained sonographers can adjust the relative risk for trisomy 21 and alter the need for genetic amniocentesis. It is important that parents understand the limitations of a screening test and the risks and benefits of possible subsequent confirmatory testing. If a major structural abnormality is identified on ultrasound, karyotype determination should be considered. Nuchal thickness in the first or second trimester remains the most clinically useful marker for trisomy 21. The predictive value of all the markers depends on the population studied and can be modified by a host of biochemical markers and historical factors. If fetal karyotype analysis could be performed without sampling through the uterus, prenatal diagnosis could be offered to all pregnant women, and screening would be unnecessary. Despite its limitations, ultrasound will have an important role in prenatal diagnosis at least until isolating and testing fetal cells from maternal blood or other sources becomes practical and widely available. Whether used alone or in conjunction with additional biochemical or molecular serum markers, ultrasound is an important and powerful tool in prenatal genetic evaluation.

Post-surgical recovery and time-of-day mask potentiated responses of ACTH to repeated moderate hemorrhage in conscious rats.

We determined how changes in the responsiveness of the hypothalamo-pituitary-adrenal (HPA) system that accompany experimentation affect facilitation of HPA responses to hemorrhage. Hemorrhage (10 ml/kg over 3 min) was performed in conscious, chronically prepared rats. Blood was sampled over 1 h followed by reinfusion of shed blood. Hemorrhage was performed either once or twice separated by 24 h in different groups of animals. To test the effect of the circadian variation in responsiveness, rats were hemorrhaged on days 4 and 5 after surgery either in the morning (AM) or in the afternoon (PM). The response of ACTH to hemorrhage on day 4 was greater in the PM than in the AM (P<0.01). The ACTH response to the second hemorrhage on day 5 was greater than that to hemorrhage on day 4 only in the AM group (P<0.01). Thus, facilitation of ACTH responses by prior hemorrhage was evident only in the AM. To determine the effects of surgical recovery, additional experiments were done in the AM either early (days 3 and 4) or later (days 6 and 7) after surgery. In these experiments, hemorrhage was performed in all rats on days 4 and 7 and either hemorrhage or blood sampling alone was performed on day 3 and 6. ACTH did not increase in rats with sampling and no hemorrhage. ACTH increased more after an initial hemorrhage on day 3 than on day 6 (P<0.01). ACTH response to hemorrhage on day 4 was greater when preceded by hemorrhage vs sampling on day 3 (P<0.01). ACTH response to hemorrhage in rats bled twice did not differ on day 3 and day 4. On day 7, the response of ACTH in rats that had hemorrhage on day 6 was greater than both their own response on day 6 and the response of a control group with sampling on day 6 (P<0.01). These results demonstrate potentiation of ACTH responses to hemorrhage by an earlier similar hemorrhage, but clearly indicate that enhanced sensitivity of the HPA to hemorrhage either by circadian factors or by surgery can mask this effect.

Potentiated response of corticotropin (ACTH) to repeated moderate hemorrhage requires amygdalar neuronal processing.

We examined the role of the amygdala in the potentiation of the corticotropin (ACTH) response to a 10 mg/kg hemorrhage by a 1-hour episode of equivalent hypovolemia done 24 h earlier. Unanesthetized rats were studied on the fourth (D1) and fifth (D2) day after chronic implantation of arterial and venous catheters. Immunocytochemistry for Fos protein indicated that neurons in the central and medial nuclei of the caudal amygdala were activated by hemorrhage. We then tested the effect of excitotoxic destruction of the neurons in these areas by bilateral injections of ibotenic acid 10 days prior to catheter placement. In rats that were hemorrhaged on both D1 and D2, the responses of ACTH and corticosterone increased significantly from the first (H1) to the second hemorrhage (H2) in a control group injected with saline (p < 0.05) and in lesioned groups without bilateral damage of the Fos-responsive areas (p < 0.01). In the group with bilateral damage to these sites, the responses to H1 and H2 did not differ. Additional rats had H1 on D2 to control for the long-term effects of the chronic cannulation. The responses of ACTH to H1 on either D1 or D2 did not differ between the saline-injected controls and any of the lesioned groups. In contrast, the response of ACTH to H2 on D2 in rats with bilateral damage of the caudal amygdala was not significant and was less than the response of ACTH to H2 in both rats with unilateral damage of this area (p < 0.05) and those injected with saline (p < 0.05). We conclude that bilateral neuronal processing within the caudal amygdala is required for the potentiation of the response of ACTH to H2 by H1.

Fetal echogenic bowel: parameters to be considered in differential diagnosis.

OBJECTIVES: To evaluate the extent that associated findings aid in the differential diagnosis and/or prognosis of fetal echogenic bowel. METHODS: Medical history, obstetric records and outcome details were examined for 131 consecutive pregnancies with fetal hyperechogenic bowel. RESULTS: In 62 (47%) cases, there were no visible anomalies other than hyperechogenic bowel and no evidence of growth restriction. This group included four (7%) pregnancies with Down syndrome, 15 (24%) with infection or a recent episode of influenza and eight (13%) with blood staining of amniotic fluid. In the remaining 69 (53%) cases, hyperechogenic bowel was accompanied by hydrops or nuchal edema (n = 16, 12.2%), growth restriction (n = 9, 6.9%), other markers for chromosome anomalies (n = 33, 25.2%) or multiple structural anomalies (n = 11, 8.4%). In this group, the prevalence of Down syndrome was 12%, infection or influenza was reported in 14 (20%) cases and there was blood staining of amniotic fluid in seven (10%). Cystic fibrosis screening was performed in 65 (50%) pregnancies; the results were negative in all cases and clinical assessment did not indicate cystic fibrosis in any of the 91 infants who were born alive. Maternal serum screening was performed in 41 (31%) pregnancies. High alpha-fetoprotein levels were associated with multiple abnormalities or severe growth restriction. CONCLUSIONS: In many pregnancies with fetal hyperechogenic bowel, there are multiple factors that may explain these findings. Thus identification of one potential underlying cause should not preclude further testing. Once chromosome defects, cystic fibrosis, structural abnormalities, infection and growth restriction have been excluded, parents can be counseled that the prognosis is good, irrespective of the presence or absence of blood stained amniotic fluid.

Chronic/subacute total occlusion of the left main coronary artery--a case report and review of literature.

Total occlusion of the left main coronary artery is rare. Acute occlusion is invariably fatal; however, survival is possible if the patient reaches the hospital in time. Patients usually present with acute myocardial infarction, cardiogenic shock, and sudden cardiac death. Chronic total occlusion presents with angina, myocardial infarction, or congestive heart failure. The authors describe complete occlusion of the left main coronary artery in a patient who presented with recent-onset angina. They review the clinical and angiographic features of 60 cases described in the literature.

Baroreceptor-mediated compensation for hemodynamic effects of positive end-expiratory pressure.

The roles of the carotid arterial baroreceptor reflex and of vagally mediated mechanisms during positive end-expiratory pressure (PEEP) were determined in pentobarbital-anesthetized dogs with isolated carotid sinuses. Spontaneously breathing dogs were placed on PEEP (5-10 cmH2O) with the carotid sinus pressure set to the systemic arterial pressure (with feedback) or to a constant pressure (no feedback). Right atrial volume was measured with a conductance catheter. With carotid baroreceptor feedback before bilateral cervical vagotomy, total peripheral resistance increased (P < 0.01) and mean arterial pressure decreased (-9.8 +/- 4.3 mmHg) in response to PEEP. With no feedback after vagotomy, mean arterial pressure decreased to a greater extent (-45 +/- 6 mmHg, P < 0.01), and total peripheral resistance decreased (P < 0.05) in response to PEEP. In contrast, cardiac index decreased similarly during PEEP (P < 0.01) for all baroreceptor and vagal inputs. This response comprised a decrease in the passive phase of right ventricular filling (P < 0. 01) that was not matched by the estimated increase in active right atrial output. Although the carotid baroreceptor reflex and vagally mediated mechanisms elicit vasoconstriction to compensate for the effects of PEEP on the arterial pressure, these processes fail to defend cardiac output because of the profound effect of PEEP on the passive filling of the right ventricle.

The isolated choroid plexus cyst.

OBJECTIVE: To describe the karyotypes of a population of fetuses with choroid plexus cysts and compare affected fetuses with and without additional ultrasonographic findings. METHODS: The study population included all patients undergoing second-trimester ultrasound examination in a prenatal diagnostic program between January 1993 and October 1995. The records of all cases in which a choroid plexus cyst was found were reviewed, and information was abstracted regarding the fetal karyotype and the presence of other sonographic abnormalities. RESULTS: Two hundred ten cases of choroid plexus cysts were identified among 7617 patients (2.8%) who underwent second-trimester ultrasound examination. The majority of the cases (181, or 86%) involved isolated choroid plexus cysts and the remaining 29 (14%) were associated with additional ultrasonographic findings. Autosomal aneuploidy was found in one patient with an isolated choroid plexus cyst (trisomy 21) and in another with additional findings (trisomy 18); the mothers of both of these patients were at least 35 years old. For those fetuses with known outcome, the risk of aneuploidy with isolated choroid plexus cyst (one in 180) was not statistically significantly different from that associated with choroid plexus cyst accompanied by other sonographic findings (one in 26). More than 1000 fetuses with choroid plexus cysts would have to be studied to determine whether such a difference was real. CONCLUSION: Because of the rarity of aneuploidy, the reported risk for a fetus with an isolated choroid plexus cyst must be interpreted cautiously and should include the baseline risk.

Three-dimensional ultrasonography in obstetrics and gynecology: preliminary experience.

OBJECTIVE: Technologic advances in ultrasonographic imaging have revolutionized the management of women's health care. We recently began to evaluate the clinical applications of three-dimensional ultrasonography. STUDY DESIGN: This study prospectively evaluated 161 obstetric and gynecologic patients. Both two- and three-dimensional imaging data were acquired from real-time ultrasonography. Three orthogonal planes were displayed on a monitor and were used to create the rendered three-dimensional images. RESULTS: To date, 201 three-dimensional ultrasonographic studies have been performed, 165 transabdominally and 36 transvaginally. Transabdominally, an average of eight acquisitions per patient were obtained. Of the clinically suspected abnormalities, 29 of 32 (91%) were confirmed by three-dimensional imaging. Three of 32 (9%) improved the diagnostic capabilities or changed the diagnosis. Of the 36 transvaginal studies, an average of four acquisitions per patient were done. Thirty (83%) of these patients had suspected abnormalities and all were confirmed. CONCLUSIONS: Three-dimensional ultrasonographic imaging appears to be highly promising in the clinical setting.

Cervical teratoma: prenatal diagnosis and long-term follow-up.

Cervical teratomas are rare tumours which are the result of abnormal prenatal development. They are usually detected at birth, but can occasionally remain silent until adulthood. Obstruction of the airway is the major challenge in the neonatal period. Prenatal diagnosis allows for early consultation with paediatric surgical specialists, so that the time and place of delivery can be addressed, and planning for resuscitative efforts can be organized in advance. If the airway is quickly stabilized and resection of the tumour is not delayed, the prognosis is good. Cervical teratomas in neonates are usually benign; however, malignant transformation and metastasis can occur as a rare event, influencing long-term survival and prognosis. We present two cases of neonatal cervical teratoma detected prenatally by ultrasound. In one case, termination of the pregnancy was elected. In the other case, the child was delivered at 36 weeks' gestation, an airway was secured, and subtotal resection of the tumour was performed. No developmental or neurological deficit has been detected on long-term follow-up at 5 years of age. We present a review of the literature, with attention to outcome and potential for malignancy in neonatal cervical teratomas, in order to provide help in decision-making, once prenatal diagnosis is made.

Mosaic trisomy 16 ascertained through amniocentesis: evaluation of 11 new cases.

Trisomy 16, once thought to result uniformly in early pregnancy loss, has been detected in chorionic villus samples (CVS) from on-going pregnancies and was initially ascribed to a second, nonviable pregnancy. Prenatally detected trisomy 16 in CVS and its resolution to disomy has led to the reexamination of the viability of trisomy 16. This study evaluates 11 cases of mosaic trisomy 16 detected through second trimester amniocentesis. In 9 of the 11 cases, amniocenteses were performed in women under the age of 35 because of abnormal levels of maternal serum alpha-fetoprotein (MSAFP) or maternal serum human chorionic gonadotropin (MShCG). The other two amniocenteses were performed for advanced maternal age. Five of the 11 pregnancies resulted in liveborn infants, and six pregnancies were electively terminated. The liveborn infants all had some combination of intrauterine growth retardation (IUGR), congenital heart defects (CHD), or minor anomalies. Two of them died neonatally because of complications of severe congenital heart defects. The three surviving children have variable growth retardation, developmental delay, congenital anomalies, and/or minor anomalies. In the terminated pregnancies, the four fetuses evaluated by ultrasound or autopsy demonstrated various congenital anomalies and/or IUGR. Cytogenetic and fluorescent in situ hybridization studies identified true mosaicism in 5 of 10 cases examined, although the abnormal cell line was never seen in more than 1% of cultured lymphocytes. Placental mosaicism was seen in all placentas examined and was associated with IUGR in four of seven cases. Maternal uniparental disomy was identified in three cases. Mosaic trisomy 16 detected through amniocentesis is not a benign finding but associated with a high risk of abnormal outcome, most commonly IUGR, CHD, developmental delay, and minor anomalies. The various outcomes may reflect the diversity of mechanisms involved in the resolution of this abnormality. As 80% of these patients were ascertained because of the presence of abnormal levels of MSAFP or MShCG, the increased use of maternal serum screening should bring more such cases to clinical attention.

Role of endotoxin in the response to experimentally induced bacteremia in chronically prepared rats.

Chronically prepared rats were injected intravenously with live Escherichia coli in doses from approximately 10(5) to approximately 10(9) colony-forming units (CFU). Significant dose-related increase in plasma adrenocorticotropin and corticosterone occurred after approximately 10(7) CFU. Fever occurred after approximately 10(7) CFU but not after approximately 10(9) CFU. These responses changed significantly but were not blocked completely when > 94% of the viable E. coli was removed from the inoculates. The remaining endotoxin activity in the inoculates resembled lipopolysaccharide (LPS) extracted from the same strain of E. coli on electrophoretic gels. Plasma endotoxin increased for > or = 240 min to 5.1 +/- 0.9 endotoxin units (EU)/ml after approximately 10(7) CFU and to 440 +/- 59 EU/ml after approximately 10(9) CFU. Endotoxin at approximately 10(9) CFU caused death within 24 h that was not predicted by the total activity of endotoxin that was injected. In contrast, extracted LPS with its strain and total activity matched to approximately 10(7) CFU mimicked the responses to this nonfatal dose. The total endotoxin activity of the injected bacteria appears to account for the effects of nonfatal doses of E. coli but not for the effects of fatal doses.

Adrenocorticotropin correlates strongly with endotoxemia after intravenous but not after intraperitoneal inoculations of E. coli.

To determine the influence of the site of infection on circulating endotoxin and hormonal release, male rats were prepared with arterial catheters and with either intravenous (i.v.) or intraperitoneal (i.p.) catheters under pentobarbital. Four days later, they were injected either i.v. or i.p. with Escherichia coli suspended in saline. Plasma was assayed for adrenocorticotropin (ACTH), corticosterone, and endotoxin activity. After approximately 10(9) colony-forming units (CFU) of E. coli, plasma endotoxin in i.v. rats (496 +/- 96 EU/mL) differed from that in i.p. rats (12.6 +/- 3.6 EU/mL, p < .01). However, ACTH and corticosterone increased to the same extent in both groups. After approximately 10(7) CFU, plasma endotoxin in i.v. rats (9.15 +/- 2.09 EU/mL) was greater than in i.p. rats (2.56 +/- .42 EU/mL, p < .05), and ACTH and corticosterone increased more at 1 h in i.v. rats than in i.p. rats (p < .01). Additional rats given approximately 0.3 x 10(9) CFU i.p. had plasma endotoxin that did not differ from values measured after either approximately 10(9) CFU i.p. or approximately 10(7) CFU i.v. However, the ACTH responses in these three groups differed from one another (p < .01). ACTH was more strongly correlated to plasma endotoxin in i.v. rats (r = .915) than in i.p. rats (r = .528, p < .01 for difference from i.v. group). The weak relationship between plasma endotoxin and ACTH after i.p. inoculations suggests that peritoneal infections activate important pathways that are independent of the circulation.

Selenite bioremediation potential of indigenous microorganisms from industrial activated sludge.

Ten bacterial strains were isolated from the activated sludge waste treatment system (BIOX) at the Exxon refinery in Benicia, California. Half of these isolates could be grown in minimal medium. When tested for selenite detoxification capability, these five isolates (members of the genera Bacillus, Pseudomonas, Enterobacter and Aeromonas), were capable of detoxifying selenite with kinetics similar to those of a well characterized Bacillus subtilis strain (168 Trp+) studied previously. The selenite detoxification phenotype of the Exxon isolates was stable to repeated transfer on culture media which did not contain selenium. Microorganisms isolated from the Exxon BIOX reactor were capable of detoxifying selenite. Treatability studies using the whole BIOX microbial community were also carried out to evaluate substrates for their ability to support growth and selenite bioremediation. Under the appropriate conditions, indigenous microbial communities are capable of remediating selenite in situ.

Consensus radiation protection practices for academic research institutions.

Under the auspices of the Howard Hughes Medical Institute, a set of consensus guidelines for Radiation Protection Practices has been developed for biomedical research using radioactive materials. The purposes of the guidelines are (1) to promote good radiation protection practices consistent with the needs of biomedical research, the ALARA principle, and regulatory requirements; (2) to establish common goals and consistent practices within radiation safety programs; and (3) to build a meaningful partnership between radiation safety professionals and the biomedical research community. These practices are intended to enhance radiation protection and the efficiency of the research staff. The consensus guidelines will lessen the variability in radiation safety practices that is evident among many academic research institutions and will encourage better acceptance and regulatory compliance by users of radioactive materials in biomedical research.

Bioavailability of selenium accumulated by selenite-reducing bacteria.

The bioavailability of selenium (Se) was determined in bacterial strains that reduce selenite to red elemental Se (SeO). A laboratory strain of Bacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Microbacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na2SeO3). After harvest, the washed, lyophilized B. Subtilis and M. arborescens samples contained 2.62 and 4.23% total Se, respectively, which was shown to consist, within error, entirely of SeO. These preparations were fed to chicks as supplements to a low-Se, vitamin E-free diet. Three experiments showed that the Se in both bacteria had bioavailabilities of approx 2% that of selenite. A fourth experiment revealed that gray SeO had a bioavailability of 2% of selenite, but that the bioavailability of red SeO depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray SeO and bacterial Se; when ascorbate was the reductant, bioavailability was twice that level (3-4%). These findings suggest that aerobic bacteria such as B. subtilis and M. arborescens may be useful for the bioremediation of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.

Impairment of blood volume restitution after large hemorrhage: a mathematical model.

A mathematical model tests possible mechanisms for the progressive failure of blood volume restitution seen after larger hemorrhages ( > 26%) with increasing changes in plasma osmolality. After 10% hemorrhage, the model requires a decrease in net hydrostatic capillary pressure, the release of solute into the extracellular space, and the release of Na+ and K+ from a bound pool in equilibrium with the interstitium to match the experimental data. The solute and released cations expand the interstitium to drive the restitution of volume and protein from 3 to 24 h. After 30% hemorrhage, the best prediction of the average experimental responses occurs when the Na(+)-K(+)-adenosinetriphosphatase (ATPase) in the cell membrane is inhibited by 38.7% from 0.8 to 3 h, and the proportionality between capillary pressure and blood volume is reduced by 68% from its value for 10% hemorrhage. When the change in plasma osmolality is doubled after 30% hemorrhage, an increase in the inhibition of the ATPase to 85% and extension of its duration to 24 h are necessary to match experimental findings. The associated defect in sodium transport may occur after large hemorrhage so that sodium and water move into cells. This response may oppose osmotically driven expansion of the interstitium and thus account for the failure of restitution.