Further development of a transcervical technique for artificial insemination in sheep using previously frozen semen

A transcervical technique (the Guelph System for transcervical AI) was used to inseminate 2060 ewes on 65 farms (average 31 ewes, range 5 to 107) in Ontario, Canada, from October 1990 to September 1992, using previously frozen semen. Estrus was synchronized using progestagen pessaries and PMSG with median inseminations done at 54 h from pessary removal. Maiden ewes were not included. Only ewes in which the cervix could be penetrated were inseminated with 150 million spermatozoa per insemination. A total of 1809 were penetrated and inseminated (penetration rate 87.8%). Success of penetration increased from 76.3% in the first 500 ewes to 97.9% in the last 500 (P=0.01). Cervical penetration was more successful in ewes in the accelerated lambing program (92.3%, average 3.1 mo since the previous lambing) than those in the annual lambing program (82.4%, average 7.0 mo since the previous lambing; P=0.06). The lambing rate for ewes bred during the combined traditional breeding seasons (Fall of 1990, 1991, 1992) was 50.7% compared to 24.4% for ewes bred at other periods (P=0.00001). The average time required for handling and insemination decreased from 8.62 min in the first 500 ewes to 3.62 min in the last 500 ewes. The Guelph System for Transcervical AI was found to be successful for cervical penetration in most ewes. Penetration success was affected by period since the last lambing and by inseminator experience. The lambing rate was higher for ewes bred during the traditional Fall breeding seasons than during other times of the year.     

Volatile anesthetics inhibit NMDA-stimulated45Ca uptake by rat brain microvesicles

We have previously shown that volatile anesthetics inhibit glutamate-stimulated [³H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated⁴⁵Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated⁴⁵Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC₅₀ of 1.4±0.5 M. The NMDA-stimulated⁴⁵Ca uptake was inhibited by MK-801 and D-AP-5 with IC₅₀'s of 10 M. Enflurane and halothane inhibited⁴⁵Ca uptake stimulated by 100 M NMDA by as much as 60–80% with IC₅₀'s of 0.2–0.3 mM, concentrations achieved during routine clinical use. Basal⁴⁵Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated⁴⁵Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated⁴⁵Ca uptake, with a t_1/2 of 20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state.     

Chiral copper(I)—thiolate clusters in metallothionein and glutathione

Metallothionein (MT) is a ubiquitous mammalian protein comprising 61 or 62 nonaromatic amino acids of which 20 are cysteine residues. The high sulfhydryl content imparts to this protein a unique and remarkable ability to bind multiple metal ions in structurally significant metal–thiolate clusters. MT can bind seven divalent metal ions per protein molecule in two domains with exclusive tetrahedral metal coordination. The domain stoichiometries for the M₇S₂₀ structure are M₄(S_cys)₁₁ (α domain) and M₃(S_cys)₉ (β domain). Up to 12 Cu(I) ions can displace the 7 Zn²⁺ ions bound per molecule in Zn₇–MT. The incoming Cu(I) ions adopt a trigonal planar geometry with domain stoichiometries for the Cu₁₂S₂₀ structure of Cu₆(S_cys)₁₁ and Cu₆(S_cys)₉ for the α and β domains, respectively. The circular dichroism (CD) spectra recorded as Cu⁺ is added to Zn₇–MT to form Cu₁₂–MT directly report structural changes that take place in the metal binding region. The spectrum arises under charge transfer transitions between the cysteine S and the Cu(I); because the Cu(I)–thiolate cluster units are located within the chiral binding site, intensities in the CD spectrum are directly related to changes in the binding site. The CD technique clearly indicates stoichiometries of several Cu(I)–MT species. Model Cu(I)–thiolate complexes, using the tripeptide glutathione as the sulfhydryl source, were examined by CD spectroscopy to obtain transition energies and the Cu(I)–thiolate coordination geometries which correspond to these bands. Possible structures for the Cu(I)–thiolate clusters in the α and β domains of Cu₁₂–MT are proposed. © 1994 Wiley-Liss, Inc.     

Cell-substrate adhesion and metastatic potential of cultured mesothelioma cells induced by asbestos

Cell-substrate adhesion was quantified for two cultured mesothelioma cell lines (epitheliomatus and sarcomatous) on glass, fibronectin and laminin substrates. Interference reflection microscopy (IRM) was used to image the adhesion patterns of cells and a grey level analysis was employed to quantify adhesion. Sarcomatous cells demonstrated marked adhesion to glass and fibronectin-coated substrates but not to laminin-coated substrate, with the greatest adhesion occurring on the fibronectin-coated surface. This adhesion was accompanied by cytoplasmic spreading. By contrast, epitheliomatous cells showed little tendency to adhere to any of the substrates and only showed significant spreading when in contact with the laminin substrate (P < 0.01). A bioassay was used to determine the metastatic potential of each of the cell lines. Via the intravenous route, the sarcomatous cells killed the host rats in 24.7 ± 1.5 (S.D.) days compared to 27.3 ± 0.9 (S.D.) days for the epitheliomatous cells (P < 0.01). After subcutaneous inoculation of tumour cells, the sarcomatous cells killed the host rats in 54.7 ± 0.7 (S.D.) days compared to 48.5 ± 0.5 (S.D.) days for the epitheliomatous cells (P < 0.01). We conclude that the results of the metastasis bioassays were consistent with the predicted behavior of these cell lines based on their ability to adhere to substrates in the in vitro adhesion assays.     

Size structure of the metazoan community in a Piedmont stream

We characterized the size structure of virtually the entire metazoan community in a fourth order, sandybottomed Piedmont stream during late summer. Our study, the first to sample across all habitat types and sizes of metazoans in an aquatic ecosystem, indicates that at the community level, stream size spectra may be bimodal for the benthos or trimodal when fish are included. Animals spanning 10 orders of magnitude in dry mass (from gastrotrichs to fish) were quantitatively collected from nine habitat types. The bimodal benthic size spectrum was characterized by a meiofaunal component (mostly oligochaetes and micro-crustacea) and a macrobenthic component (mostly the introduced asiatic clam, Corbicula fluminea). Insects contributed little to overall standing crop. Size-specific contribution to whole-community metabolism was assessed using allometric equations for respiration, and we found a distinctly bimodal distribution across the entire metazoan size range, with peaks in the meiofaunal and benthic macrofaunal size ranges. Our bimodal benthic size spectrum is similar to that observed for marine benthos but not to other freshwater benthic systems, possibly because the entire range of habitat types and/or animal sizes were not sampled in the latter. Numerous factors may influence size spectra in stream ecosystems, including local geomorphic (habitat) conditions, water level fluctuations, species introductions, and predation processes.     

Liquid water and the origin of life

Liquid water has many peculiarities which confer special properties. The most important among them probably are the ability to establish hydrogen bonds, a high polarity and a high dielectric constant. In the presence of liquid water, large organic molecules have to manage the conflict between hydrophobic groups and hydrophilic groups. This duality can generate interesting prebiotic situations such as the stereoselective aggregation of short peptide sequences of alternating hydrophobic — hydrophilic residues into thermostable -sheets endowed with chemical acrivity. Liquid water is also a powerful hydrolytic agent. As such, it allows pathways which would have few chances to occur in an organic solvent.Presented at the Session Water in the Solar System and Its Role in Exobiology during the 26th General Assembly of the European Geophysical Society, 22–26 April 1991 in Wiesbaden, Germany.     

Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium

We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (V_max) of the system was 3.86 units (U) mg^–1 protein with arabinoxylan as substrate and the substrate concentration giving half V_max (S_0.5) was 0.52 mg ml^–1. At concentrations of arabinoxylan greater than 15 mg ml^–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components. Correspondence to: P. Broda