Terminal nerve sprouting at the frog neuromuscular junction induced by prolonged tetrodotoxin blockade of nerve conduction

Brain Cell Biology - The effects of a prolonged blockade of nerve conduction by tetrodotoxin on frog motor innervation were studied in the cutaneous pectoris muscle ofRana esculenta. Prolonged...     

Serotypes and antibiotic resistance of Verotoxigenic (VTEC) and Necrotizing (NTEC) Escherichia coli strains isolated from calves with diarrhoea

Serotypes and antibiotic resistance of 51 Verotoxigenic (VTEC) and 33 Necrotizing (NTEC) bovine Escherichia coli strains were determined and compared with those shown by 205 non-VTEC non-NTEC strains isolated from the same batch of calves. E. coli untypable for O-antigen represented 47% of the VTEC, 12% of the NTEC and 8.8% of the non-VTEC non-NTEC. Typable VTEC belonged to serotypes 02:K?, 0103:K-, 0104:K?, 0128:K?, 0153:K- and O157:K-:H7, whereas typable NTEC were of serotypes 08:K87, 015:K14, 015:K-, 054:K?, 076:K-, 078:K(80), 088:K?, 0123:K-, 0139:K- and 0153:K-. Non-VTEC non-NTEC showed a wide variety of serotypes which were generally unrelated to those found in VTEC and NTEC. VTEC were resistant to antibiotics at higher rates than NTEC and non-VTEC non-NTEC, and showed also the highest multidrug-resistant pattern. Our results show that bovine VTEC strains belonged to O-groups usually found in human VTEC causing sporadic diarrhoea, haemorrhagic colitis and/or haemolytic uraemic syndrome, such as 02, 0103, 0104, 0153 and especially 0128 and O157. In contrast, bovine NTEC strains belonged to serotypes different from those previously found in necrotizing E. coli strains of human origin.     

The role of secreted acid hydrolases in the utilization of complex nutrients byTetrahymena

In an attempt to extend our knowledge of the biology of feeding of the ciliateTetrahymena thermophila, this organism was grown axenically on complex organic material. The nutrient substrate was based on autoclaved wheat grains and adjusted to either pH 5.5 or 7.5. In wild type cultures the cells grew and multiplied only under acidic conditions. In cultures of a mutant cell line blocked in the secretion of acid hydrolases the cells did not grow at either pH value. Thus released acid hydrolases may play a key role in the utilization of complex nutrients in combination with uptake of small organic molecules. Mechanisms in the feeding biology ofTetrahymena thermophila andParamecium tetraurelia are compared.     

Zinc protection against delayed development produced by cadmium

The protective effect of zinc against slight teratogenical action, exerted by low cadmium concentrations, was evaluated inBufo arenarum embryos treated simultaneously with both cations or preincubated with Zn before Cd treatment. Data on survival, malformations, and delay in development pointed out that Zn could prevent the-deleterous effects of Cd in previous and simultaneous treatments with that heavy metal.     

One step shoot tip multiplication and rooting of Digitalis thapsi L.

Shoot tips from seedlings of Digitalis thapsi L. were cultured on Murashige and Skoog's medium and the effect of various auxins (2,4-D, NAA and IAA) were analyzed alone or in combination with cytokinis (BA and kinetin). Shoot multiplication and direct rooting of the new shoots were obtained after four weeks of culture in MS medium without hormones, but callus formation and the appearance of abnormal phenotypes were frequent. The addition of auxins to the cultures prevented the formation of callus but not the appearance of variant phenotypes. Both drawbacks could be avoided by combination of NAA or IAA with BA or kinetin. The best results for shoot multiplication and direct rooting were obtained with 0.5 mg l^-1 NAA and 0.1 or 0.5 mg l^-1 kinetin.Abbreviations BA 6-benciladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - Kin kinetin - NAA naphtalene acetic acid - MS Murashige and Skoog     

Phenology of Festuca pallescens in relation to topography in north-western Patagonia

Abstract. The phenological changes in populations of Festuca pallescens (St. Yves) Parodi at different topographic positions and exposure along an altitudinal gradient (600 - 1100 m) were investigated during two growing seasons in northwestern Patagonia. Stepwise multiple regression analysis was used to describe the relationship between phenology and environment during the entire growing season. Analysis of variance was also performed at each sample date to detect significant environmental factors influencing phenology at different sites. The sum of maximum air temperatures was identified as the environmental variable best correlated with the seasonal variation of phenological events of Festuca pallescens over the period of two growing seasons, explaining 93.2 % of the total variance. Significant differences between sites were observed at each sample date. Main effects of altitude and topographic position and two-way interactions between altitude and topographic position, and topographic position and exposure were also detected as significant. Phenology was delayed at increased altitude. Differences in phenology between topographic sites at the same altitude were not detected during the entire growing season and were only observed in the reproductive phase. At this time, the phenology was significantly delayed at high topographic positions on the slopes as compared with low and mid positions. At high altitudes in the valley (950 m a. s. 1.), where steep slopes and humid conditions prevail, phenology was delayed on western exposures and low positions. The results adequately summarize and quantify the effect of spatial and temporal environmental variation on the phenological development of Festuca pallescens in northwestern Patagonia.     

Patterns of nucleotide change in mitochondrial ribosomal RNA genes and the phylogeny of piranhas

The patterns and rates of nucleotide substitution in mitochondrial ribosomal RNA genes are described and applied in a phylogenetic analysis of fishes of the subfamily Serrasalminae (Teleostei, Characiformes, Characidae). Fragments of 345 bp of the 12S and 535 bp of the 16S genes were sequenced for 37 taxa representing all but three genera in the subfamily. Secondary-structure models based on comparative sequence analysis were derived to characterize the pattern of change among paired and unpaired nucleotides, forming stem and loop regions, respectively. Base compositional biases were in the direction of A-rich loops and G-rich stems. Ninety-five percent of substitutions in stem regions were compensatory mutations, suggesting that selection for maintenance of base pairing is strong and that independence among characters cannot be assumed in phylogenetic analyses of stem characters. The relative rate of nucleotide substitution was similar in both fragments sequenced but higher in loop than in stem regions. In both genes, C-T transitions were the most common type of change, and overall transitions outnumbered transversions by a factor of two in 16S and four in 12S. Phylogenetic analysis of the mitochondrial DNA sequences suggests that a clade formed by the generaPiaractus, Colossoma, andMylossoma is the sister group to all other serrasalmins and that the generaMyleus, Serrasalmus, andPristobrycon are paraphyletic. A previous hypothesis concerning relationships for the serrasalmins, based on morphological evidence, is not supported by the molecular data. However, phylogenetic analysis of host-specific helminth parasites and cytogenetic data support the phylogeny of the Serrasalminae obtained in this study and provide evidence for coevolution between helminth parasites and their fish hosts.     

Linkage disequilibrium analysis in Machado-Joseph disease patients of different ethnic origins

Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar degeneration originally described in families of Portuguese-Azorean ancestry. The hypothesis that its present world distribution could result from the spread of an original founder mutation has been raised. To test this possibility we have conducted a linkage disequilibrium study of markers segregating with the MJD1 locus in a total of 64 unrelated families of different geographical origins. Significant association was detected between the MJD1 locus and marker alleles at loci D14S280, D14S1050 and D14S81. All affected individuals, except one Chinese family, had allele 3 (237 bp) at D14S280. This finding is consistent with a founder effect in our MJD population. However, distinct haplotypes were observed in patients originating from the two Azorean islands showing the highest disease prevalence; therefore, the possible existence of more than one founder mutation can not be excluded with the markers currently available. Received: 27 February 1996 / Revised: 4 June 1996     

A Familial Factor Independent of CAG Repeat Length Influences Age at Onset of Machado-Joseph Disease

Machado-Joseph disease (MJD) is a late-onset, progressive, neurodegenerative disorder caused by the expansion of an unstable trinucleotide (CAG) repeat sequence in a novel gene (MJD1) on chromosome 14. Previous studies showed that age at onset is negatively correlated with the number of CAG repeat units, but only part of the variation in onset age is explained by CAG repeat length. Ages at onset and CAG repeat lengths of 136 MJD patients from 23 kindreds of Portuguese descent were analyzed, to determine whether familial factors independent of CAG repeat length modulate age at onset of MJD. Correlation among sibs for onset age adjusted for CAG repeat length was .43, which indicates that an environmental or genetic factor common to sibs influences onset age. Positive correlations were also observed for avuncular (r = .22) and first-cousin pairs (r = .28), which supports the hypothesis that a genetic factor is influencing age at onset. Commingling analysis of onset ages adjusted for CAG repeat length identified three distributions in this population of affected individuals. Further studies of a much larger sample are needed to determine whether these distributions represent the influence of a genetic or environmental factor.     

Identification of two glutaminases inRhizobium etli

We present evidence thatRhizobium etli has two glutaminases differentiated by their thermostability and electrophoretic mobility. The thermostable glutaminase (B) is constitutive, in contrast with the thermolabile glutaminase (A), which is positively regulated by glutamine and negatively regulated by ammonium and by the carbon source. In distinction to glutaminase A, glutaminase B plays a minor role in the utilization of glutamine as a carbon source, but it may play a role in maintaining the balance of glutamine and glutamate. By complementation of theRhizobium etli LM16 mutant that lacks glutaminase A, we have cloned the gene that codes for this enzyme.