Prospective timing in pigeons: Isolating temporal perception in the time-left procedure.

In the time-left procedure, a task used to study prospective timing, animals choose between two stimuli that signal different delays to reinforcement. Trials begin with one stimulus signaling C seconds to reinforcement and, at different moments since its onset, another stimulus, signaling S seconds to reinforcement, with C>S, is introduced. Optimal performance consists in choosing the stimulus signaling the shorter time to reinforcement. Animals have been found to perform in this optimal way. However, this procedure is complex and variables other than time may be responsible for the results. In two experiments with pigeons we sought to improve the time-left procedure to better isolate the effect of time in the animals' behavior. We attempted to control for two confounding variables, the asymmetry in the time markers from training to testing and the cost of switching between the two response alternatives. We conclude that in the time-left task pigeons seem indeed to regulate their behavior based on time because, with our improved procedure, they still chose the stimulus associated with the shorter time to food. However, our version of the procedure created new interpretative difficulties, strengthening the idea that the time-left procedure may be too complex to study timing.

Expression of the major heat shock proteins DnaK and GroEL in Streptococcus pyogenes: a comparison to Enterococcus faecalis and Staphylococcus aureus.

One of the outstanding problems in the field of heat shock response has been to elucidate the mechanism underlying the induction of heat shock proteins (HSPs). In this work, we initiate an analysis of the expression of heat shock groEL and dnaK genes and their promoters in S. pyogenes. The synthesis of total cellular proteins was studied upon transfer of a log-phase culture from 37 degrees C to 42 degrees C by performing 5-min pulse-labeling experiments with (35)S-Met. The heat shock responses in the pathogenic Gram-positive cocci, Enterococcus faecalis and Staphylococcus aureus, were also analyzed.

Preliminary assessment of heavy metal levels in Mytella falcata (Bivalvia, Mytilidae) from Bacanga River estuary, São Luís, state of Maranhão, northeastern Brazil.

The concentrations of Cu, Zn, Pb, and Cd were determined in the mussel Mytella falcata from the Bacanga River estuary, in order to evaluate the potential role of domestic effluents released "in natura" on the quality of the estuarine environment with consequences to shellfish resources. Cu concentrations ranged from 5.2 mg.g-1 to 13.1 mg.g-1, while Zn concentrations ranged from 49.1 mg.g-1 to 76.3 mg.g-1. Pb and Cd showed concentrations lower than 2 mg.g-1. The results showed low concentrations of Cu, Pb and Cd in the filter-feeding Mytella falcata in the study area in comparison with the maximum values stablished to foods by the Brazilian Government (Decree Law No 55,871). Finally, Zn presented slightly higher values than the maximum ones stablished by the Brazilian government.

Surgical correction of aortic disease using intraluminal, crimped bovine pericardial graft.

We propose the use of a crimped bovine pericardial graft joined to a rigid and grooved ring for the treatment of aortic dissections and aneurysms. This device was developed to support common tubular vascular prostheses of any material, length, diameter, or form, transforming them into intraluminal ones during the surgical procedure. During March 1989 to May 1994, 74 patients underwent an operation on the aorta in which this intraluminal ring, prepared from a tubular prosthesis of bovine pericardium, was used. Twenty-seven patients had an acute type A aortic dissection, 6 had an acute type B aortic dissection, 10 had annuloaortic ectasia, 6 had a descending aortic aneurysm, 3 had a thoracoabdominal aneurysm, and 22 had an abdominal aneurysm. The global mortality rate of 10.8% in the immediate postoperative period cannot be related to the surgical technique or the type of prosthesis used. We conclude from our findings that this modification of the sutureless intraluminal graft, which allows it to be used to replace diseased segments of the aorta, affords the quickest and simplest means of repair and is attended by the least likelihood of anastomotic complications.

Extracellular deoxyribonucleases of streptococci: a comparison of their occurrence and levels of production among beta-hemolytic strains of various serological groups.

Production of extracellular deoxyribonuclease by 394 strains of beta hemolytic streptococci was examined employing a deoxyribonucleic acid-methyl green assay. Enzymatic activities were measured in supernatants of bacterial cultures. Of the strains tested, 316 (80%) produced the enzyme. Nuclease production was demonstrated in 100% of group A strains and in 85, 74 and 58% of groups B, C and G, respectively. Levels of nuclease activity were then evaluated statistically. The analysis of variance showed that group A strains produced more enzyme than did streptococci of groups B, C or G. Group B strains produced less nuclease than did isolates of groups C or G. There was no significant difference in the levels of nuclease produced by groups C and G or by the various serological types of group B streptococci. Human group C strains produced more enzyme than animal strains.

Effect of malathion on Bufo arenarum Hensel development--I. Esterase inhibition and recovery.

Newly fertilized Bufo arenarum Hensel embryos were exposed continuously or for a brief period (72-120 hr) to malathion (44 ppm) and then resuspended in amphibian Ringer's solution. Continuous exposure depressed acetylcholinesterase (EC 3.1.1.7), butyrylcholinesterase (EC 3.1.1.8) and carboxylesterase (EC 3.1.1.1) activities. The activities of the three enzymes in embryos treated for 72 hr recovered after a delay of 24 hr, but these enzymes showed different rates of recovery in embryos treated for 120 hr. Acrylamide disc electrophoresis showed several bands of esterase activity in control embryos. Continuous exposure to malathion abolished all esterase activity within 48 hr, but if the exposure continued new bands of esterase activity appeared at 120 hr of exposure. The zymograms of embryos exposed for 72 or 120 hr to malathion and then transferred to uncontaminated medium for 120 hr were similar to that of control embryos.

Correlation between growth in antibiotic-medium and hemolytic activity of group C and G streptococci.

The effect of a subminimal inhibitory concentration of penicillin on the production of bound and free hemolysins by streptococci was examined using sheep red blood cells. A marked decrease of a group C cell-free and bound activities was observed with penicillin at a concentration of 1/3 of the MIC whereas an increase was observed with those of a group G strain. Potassium ferricyanide and anti-streptolysin O (group A streptococcus) were strongly inhibitory for the free activities of both strains. The cell-bound activities were stimulated by addition of RNA during bacterial growth in control cultures and also in drug-containing media.