Laser Synthesis and Spectroscopy of Ligand-Coated Chromium Oxide Nanoclusters.

Ultra-small chromium oxide nanoclusters produced by laser vaporization in a fast flow tube reactor are ligand-coated by gas-phase reactions with acetonitrile vapor and then captured in a cold trap and transferred to solution. The resulting clusters are characterized with mass spectrometry, UV-visible absorption and emission spectroscopy, infrared spectroscopy, and surface-enhanced Raman spectroscopy. According to mass spectrometry, clusters of the form Cr xO y(MeCN) z are produced in the size range of x ≤ 10 and y < 25. The ligand-coated clusters in solution exhibit a limited number of prominent sizes, with the same preferences for specific stoichiometries seen in earlier gas-phase studies of ligand-free clusters. Computational studies provide structures and predicted spectra for these systems. The intrinsic stability of these clusters is confirmed by their production under different laser ablation conditions and by their significant shelf lives (several months) without aggregation or decomposition. UV-visible spectra indicate that these clusters contain highly oxidized chromium. Theory and previous experiments indicate that compact cages are favored for ligand-free clusters. However, infrared and Raman spectra suggest that ring and chainlike structures become prominent for ligand-coated clusters. Consistent with these observations, theory also indicates that these more open structures are energetically favored for ligated clusters. Apparently, ligand binding induces a structural transformation of the compact oxide core clusters, producing more extended ring and chain structures.

Novel mutations in PTH1R associated with primary failure of eruption and osteoarthritis.

Autosomal dominant mutations in PTH1R segregate with primary failure of eruption (PFE), marked by clinical eruption failure of adult teeth without mechanical obstruction. While the diagnosis of PFE conveys a poor dental prognosis, there are no reports of PFE patients who carry PTH1R mutations and exhibit any other skeletal problems. We performed polymerase chain reaction-based mutational analysis of the PTH1R gene to determine the genetic contribution of PTH1R in 10 families with PFE. Sequence analysis of the coding regions and intron-exon boundaries of the PTH1R gene in 10 families (n = 54) and 7 isolated individuals revealed 2 novel autosomal dominant mutations in PTH1R (c.996_997insC and C.572delA) that occur in the coding region and result in a truncated protein. One family showed incomplete penetrance. Of 10 families diagnosed with PFE, 8 did not reveal functional (nonsynonymous) mutations in PTH1R; furthermore, 4 families and 1 sporadic case carried synonymous single-nucleotide polymorphisms. Five PFE patients in 2 families carried PTH1R mutations and presented with osteoarthritis. We propose that the autosomal dominant mutations of PTH1R that cause PFE may also be associated with osteoarthritis; a dose-dependent model may explain isolated PFE and osteoarthritis in the absence of other known symptoms in the skeletal system.

Photodissociation of cobalt and nickel oxide cluster cations.

Cobalt and nickel oxide cluster cations, Co(x)O(y)(+) and Ni(x)O(y)(+), are produced by laser vaporization of metal rods in a pulsed nozzle cluster source and detected using time-of-flight mass spectrometry. The mass spectra show prominent stoichiometries of x = y for Co(x)O(y)(+) along with x = y and x = y - 1 for Ni(x)O(y)(+). The cluster cations are mass selected and multiphoton photodissociated using the third harmonic (355 nm) of a Nd:YAG laser. Although various channels are observed, photofragmentation exhibits two main forms of dissociation processes in each system. Co(x)O(y)(+) dissociates preferentially through the loss of O(2) and the formation of cobalt oxide clusters with a 1:1 stoichiometry. The Co(4)O(4)(+) cluster seems to be particularly stable. Ni(x)O(y)(+) fragments reveal a similar loss of O(2), although they are found to favor metal-rich fragments with stoichiometries of Ni(x)O(x-1). The Ni(2)O(+) fragment is produced from many parent ions. The patterns in fragmentation here are not nearly as strong as those seen for early or mid-period transition-metal oxides studied previously.

Detection of reflux esophagitis on double-contrast esophagrams and endoscopy using the histologic findings as the gold standard.

The purpose of our study was to determine the accuracy of double-contrast barium studies and endoscopy for detecting reflux esophagitis, using the endoscopic biopsy findings as the gold standard. A review of radiology, endoscopy, and pathology files showed 37 patients with reflux symptoms who underwent double-contrast barium studies and endoscopy with biopsy specimens from the esophagus. The radiographic images were reviewed in a blinded fashion and correlated with the endoscopic and histologic findings to determine the radiographic and endoscopic accuracies for detecting reflux esophagitis, using the endoscopic biopsy specimens as the gold standard. Double-contrast barium studies and endoscopy had low but comparable accuracies for detecting reflux esophagitis, with sensitivities of 35% and 39%, specificities of 79% and 71%, positive predictive values of 73% and 69%, and negative predictive values of 42% and 41%, respectively. When mucosa granularity was evaluated as an individual sign of esophagitis on double-contrast studies, this finding had a sensitivity of 35%, a specificity of 93%, a positive predictive value of 89%, and a negative predictive value of 46% for detecting reflux esophagitis. Our experience suggests that double-contrast barium studies and endoscopy have limited ability to detect reflux esophagitis, in particular mild esophagitis, when using the histologic findings as the gold standard. When radiographic abnormalities are detected, however, mucosal granularity is the single best sign of reflux esophagitis on double-contrast studies.

Patterning of olfactory sensory connections is mediated by extracellular matrix proteins in the nerve layer of the olfactory bulb.

In early rat embryos when axons from sensory neurons first contact the olfactory bulb primordium, lactosamine-containing glycans (LCG) are detected on neurons that are broadly distributed within the olfactory epithelium, but that project axons to a very restricted region of the ventromedial olfactory bulb. LCG(+) axons extend through channels defined by the coexpression of galectin-1 and beta2-laminin. These two extracellular matrix molecules are differentially expressed, along with semaphorin 3A, by subsets of ensheathing cells in the ventral nerve layer of the olfactory bulb. The overlapping expression of these molecules creates an axon-sorting domain that is capable of promoting and repelling subsets of olfactory axons. Specifically, LCG(+) axons preferentially grow into the region of the nerve layer that expresses high amounts of galectin-1, beta2-laminin, and semaphorin 3A, whereas neuropilin-1(+) axons grow in a complementary pattern, avoiding the ventral nerve layer and projecting medially and laterally. These studies suggest that initial patterning of olfactory epithelium to olfactory bulb connections is, in part, dependent on extracellular components of the embryonic nerve layer that mediate convergence and divergence of specific axon subsets.

Semaphorin 3A is required for guidance of olfactory axons in mice.

Semaphorin 3A (Sema3A) is a membrane-associated secreted protein that has chemorepulsive properties for neuropilin-1 (npn-1)- expressing axons. Although mice lacking the Sema3A protein display skeletal abnormalities and heart defects, most axonal projections in the CNS develop normally. We show here that Sema3A is expressed in the lamina propria surrounding the olfactory epithelium (OE) and by ensheathing cells in the nerve layer of the ventral olfactory bulb (OB) throughout development. Subsets of sensory neurons expressing npn-1 are distributed throughout the OE and extend fibers to the developing OB. In wild-type mice, npn-1-positive (npn-1(+)) axons extend to lateral targets in the rostral OB and medial targets in the caudal OB, avoiding regions expressing Sema3A. In Sema3A homozygous mutant mice, many npn-1(+) axons are misrouted into and through the ventral nerve layer, beginning as early as embryonic day 13 and continuing at least until birth. At postnatal day 0, npn-1(+) glomeruli are atypically located in the ventral OB of Sema3A(-/-) mice, indicating that aberrant axon trajectories are not corrected during development and that connections are made in inappropriate target regions. In addition, subsets of OCAM(+) axons that normally project to the ventrolateral OB and some lactosamine-containing glycan(+) axons that normally target the ventral OB are also misrouted in Sema3A mutants. These observations indicate that Sema3A expression by ensheathing cells plays an important role in guiding olfactory axons into specific compartments of the OB.

The role of international environmental agreements in metered-dose inhaler technology changes.

Introduced in the 1950s, metered dose inhalers (MDIs) became a revolutionary way to deliver medication directly to the lungs of patients with asthma and chronic obstructive pulmonary disease. Since their initial introduction, MDIs have used chlorofluorocarbons to propel the medication out of the canister into a patient's lungs. This article presents an overview of the global transition away from the use of chlorofluorocarbon propellants in MDIs to non-ozone-depleting substitutes including hydrofluoroalkane (outside of the pharmaceutical industry and in the context of Montreal Protocol and Kyoto Protocol discussions, these gases are referred to as hydrofluorocarbons; hydrofluoroalkane-134a, for example, is referred to as hydrofluorocarbon-134a) propellants, in accordance with the terms of the international environmental agreement the Montreal Protocol on substances that deplete the ozone layer (the Montreal Protocol). This article will also describe the environmental characteristics of chlorofluorocarbons and hydrofluoroalkanes when they are used as MDI propellants. Finally, the article will review key provisions of the pending Kyoto Protocol to the United Nations Framework Convention on Climate Change (the Kyoto Protocol) that may affect the future of hydrofluoroalkanes.

From Creutzfeldt-Jakob disease to the mad cow epidemic.

Hans-Gerhard Creutzfeldt and Alfons Jakob independently authored clinical and pathologic descriptions of a new syndrome in the 1920s. This syndrome, which subsequently came to be named after them, was characterized by dementia, motor and coordination abnormalities, a fatal course, and pathologic findings of diffuse spongiform neuronal degeneration. Although it appeared for many years to be little more than a medical curiosity, Creutzfeldt-Jakob disease attained widespread attention by its pathologic similarity to kuru and bovine spongiform encephalopathy, "mad cow disease." Because there are sporadic, familial, and iatrogenic forms of Creutzfeldt-Jakob disease, it is considered to have both genetic and infectious aspects. Although its causation has for some time been ascribed to "slow viruses," the etiology of Creutzfeldt-Jakob disease is currently thought to be due to prions, small proteinaceous infectious particles that have genetic encoding. The debate regarding whether the appearance of atypical Creutzfeldt-Jakob disease can be linked to the epidemic of "mad cow disease" is currently unresolved.

Willy Burgdorfer: Lyme disease.

The documented history of erythema migrans dates to 1909, when Arvid Afzelius described a case of this skin lesion at a dermatologic meeting in Sweden. He felt that the eruption was likely produced by the bite of a tick. The initial description of Lyme arthritis appeared in 1977, and a number of the patients described in this series developed a rash thought to be erythema migrans. Four years later, Burgdorfer discovered the presence of spirochetes (subsequently named Borrelia burgdorferi) in ticks from an endemic locus of Lyme arthritis and determined this to be the causative organism of the disease. Lyme disease is the most common tickborne infection in the United States. Its natural course has been divided into three clinical stages. The infection begins with a rash and flulike symptoms and may progress after days to weeks to a disseminated stage and in months to years to a late stage. There is little information (except erythema migrans) about the clinical features of the illness that is specific for Lyme disease. There are a number of effective antibiotic treatment regimens, and although acute infection generally responds well to treatment, management of chronic illness with antibiotics has been less consistently successful. With respect to antibiotic prophylaxis, the few studies performed have led to the conclusion that, even in endemic areas, the risk of infection is so low that routinely instituting treatment following a tick bite is not warranted.

Transcriptional activation of the c-myc proto-oncogene in murine keratinocytes enhances the response to epidermal growth factor.

To investigate the relationship between activation of the c-myc proto-oncogene and the controls of cellular growth and differentiation of epidermal cells, a transcriptionally activated c-myc gene (DM-myc) was introduced into the established murine keratinocytes, BALB/MK. Exponential growth rates of myc-transfectants were not significantly different from that of parental BALB/MK cells. C-myc RNA transcripts were not detectable in confluent, mitogen-deprived cultures of parental BALB/MK cells, whereas four out of five clones expressed elevated levels of myc mRNA under these conditions. All of the cell lines, however, displayed density-dependent growth arrest in the G0/1 phase of the cell cycle. Maximal stimulation of quiescent BALB/MK cells with epidermal growth factor (EGF) caused a 70- to 100-fold increase of [methyl-3H]-thymidine incorporation into DNA. In the four subclones that expressed the myc gene, the peak thymidine incorporation into DNA was significantly higher than in BALB/MK cells, ranging from 340- to 650-fold control levels. This increased sensitivity to EGF was not due to autocrine mitogenic activity or to a change of EGF binding. Type beta transforming growth factor strongly inhibited the EGF-induced DNA synthesis in BALB/MK cultures as well as in each of the five transfectants (IC50 4-40 pM). Furthermore, both BALB/MK cells and the transfected subclones could be induced to form cornified cell envelopes by increasing the extracellular concentration of calcium. Thus, the constitutive expression of c-myc in BALB/MK appears to affect predominantly the reinitiation of DNA synthesis by EGF.

Down-regulation of glucocorticoid binding sites by retinoic acid in squamous carcinoma cells resistant to the induction of keratinization by hydrocortisone.

Physiologic concentrations of retinoic acid strongly inhibit the in vitro maturation of human squamous carcinoma cells in serum-free medium. Differentiation, as measured by the capacity to synthesize cornified cell envelopes, could be induced by hydrocortisone in retinoic acid-treated SqCC/Y1 and CE-81T cells. However, two other cell lines (C4-1 and A431) were less competent to spontaneously form cornified cell envelopes and resistant to the induction of envelope competence by hydrocortisone in the presence of retinoic acid. To investigate the mechanism underlying the resistance of these two lines to hydrocortisone, the characteristics of glucocorticoid receptors were analyzed. Whole cell dexamethasone binding sites ranged from 1300 to 9000 sites per cell for the four cell lines. The binding affinity for dexamethasone was similar in all four squamous carcinoma cell lines (1.32 to 4.75 nM). During retinoic acid-treatment, the binding of dexamethasone by intact SqCC/Y1 and CE-81T cells increased 1.5- to 3.0-fold over 48 h. In contrast, the number of dexamethasone binding sites were decreased by 80% in retinoic acid-treated A431 and C4-1 cells. In each case, the regulation of dexamethasone binding was dependent on the concentration of retinoic acid, with maximal effects being observed at 10(-6) M. Thus, the manner in which retinoic acid regulates the availability of dexamethasone binding sites might explain, in part, the effects of glucocorticoids on differentiation of retinoic acid-treated squamous carcinoma cell lines.

Reinitiation of DNA synthesis in quiescent mouse keratinocytes; regulation by polypeptide hormones, cholera toxin, dexamethasone, and retinoic acid.

Cloned mouse keratinocytes (MK-1 cells) display density-dependent growth arrest when reaching confluency in a serum-free medium with a calcium concentration less than 0.1 mM, supplemented only with insulin and transferrin. In this quiescent state, greater than 95% of the cell population is in the Go/1 phase of the cell cycle. Treatment of quiescent MK-1 cells with 1 to 10 ng/ml epidermal growth factor (EGF) resulted in a sharp burst of DNA synthetic activity. Both insulin and cholera toxin potentiated the mitogenic effect of EGF, but neither agent was necessary or sufficient to induce thymidine incorporation into DNA. Dexamethasone abolished the effect of insulin, but not the mitogenic effect of EGF alone. In contrast, retinoic acid (RA) did not possess any mitogenic effect for quiescent MK-1 cells, nor did it modulate the actions of EGF or dexamethasone. A number of commercially available crude extracts of bovine brain and pituitary were also capable of initiating DNA synthesis in resting MK-1 cells. Finally, transforming growth factor type beta (TGF beta) proved to be a potent inhibitor of the mitogen-induced DNA synthesis in MK-1 cells (IC50:10 pM). This defined culture system is eminently suited to study the regulation of DNA synthesis of epidermal cells. In addition, it can be used as a sensitive bioassay for the detection of epidermal mitogens, as well as inhibitors of DNA synthesis such as TGF beta.

Effect of pregnancy on diabetic retinopathy.

The incidence of progression of diabetic retinopathy during pregnancy is unknown and its proper management uncertain. In this study, 55 insulin-dependent diabetic patients under strict glucose control were followed throughout pregnancy with serial retinal examinations by ophthalmoscopy and photographs. Nineteen patients had minimal or background retinopathy and 7 had untreated proliferative changes. Six patients had been treated before pregnancy with photocoagulation for proliferative retinopathy. A positive correlation was found between progressive proliferative diabetic retinopathy and the duration of diabetes mellitus independent of glucose control. During gestation 3 of 19 patients (16%) with minimal or background retinopathy and 6 of 7 patients (86%) with untreated proliferative retinopathy experienced deterioration of their eye disease. In 4 patients with proliferative retinopathy, progression of retinal disease was arrested with photocoagulation during pregnancy. Only 1 of 6 who had received laser treatment prior to pregnancy experienced progression of her retinopathy. These results suggest that photocoagulation prior to pregnancy may protect against rapidly progressive proliferative retinopathy and that aggressive treatment during pregnancy can prevent progression of proliferative retinopathy and visual impairment.

Mortality rate in strabismus surgery.

Strabismus surgery has been viewed as being associated with a high degree of mortality. Many past studies have used small surgical samples and have stressed the various theoretical causes of the deaths rather than view the procedure from a statistical and scientific standpoint. We present here a large series of surgical cases collected nationwide showing that strabismus surgery is a relatively safe procedure associated with a mortality less than that of a tooth extraction.

Reliability of fixation disparity curves.

Fixation disparity curves were recorded in three normal subjects once per week over a period of 10 weeks. Results indicate that measurements of fixation disparity are reliable within limited ranges of forced convergence and forced divergence. Increases in the demand to maintain fusion lead to increases in observed variability of fixation disparity. It is suggested that variability of fixation disparity might be related to the ease with which the two eyes are used as a team.