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Biomedical subjects

E Garcia

Publications and source records attributed to E Garcia.

13 recordsLinked to original sources
PubMed1979

Associative transfer and stimulus selection in classical conditioning of the rabbit's nictitating membrane response to serial compound CSs.

Four experiments were conducted to determine whether in conditioning to a serial compound, CS1-CS2-UCS, there are (a) associative mechanisms operating to extend conditioning beyond the bounds of a CS-UCS contiguity gradient and (b) stimulus selection processes acting to attenuate the potency of CS-UCS contiguity. In Experiments 1 and 2, the CS2-UCS interval was held at .35 sec while the CS1-UCS interval was varied across groups from .75 to 2.75 sec. CS1 test trials revealed substantial CR acquisition at all CS1-UCS intervals. Moreover, Experiment 2 indicated that when the contribution of cross-modal generalization from CS2 to CS1 was factored out, there still remained a substantial level of conditioning, which Experiment 3 indicated was attributable to an associative mechanism like higher-order or sensory conditioning. The observation of CR acquisition at CS1-UCS intervals of 4.75, 8.75, and 18.75 sec in Experiment 4 suggested that serial compound training yields conditioning to CSs located well beyond the single CS contiguity gradient for the rabbit's nictitating membrane response. Experiments 1 and 2 also indicated the presence of stimulus selection processes because, at the shorter CS1-UCS intervals (.75 and 1.25 sec), the levels of test-trial responding to CS2 fell below those observed to the less contiguous CS1.

Animals↗
PubMed1979

Nitrogen control in Salmonella: regulation by the glnR and glnF gene products.

The product of the glnR gene is required for nitrogen regulation of the synthesis of glutamine synthesis (Gln synthetase) [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] and two periplasmic transport proteins that are subject to nitrogen control in Salmonella. Strains with mutations to loss of function of the glnR product [e.g., a strain with a Tn10 insertion or one with an ICR-induced (frameshift) mutation in glnR] have about 3% as much Gln synthetase as a fully derepressed wild-type strain and are unable to increase synthesis of this enzyme or periplasmic transport proteins in response to nitrogen limitation. The structural gene for Gln synthetase, glnA, and those for the periplasmic transport proteins are unlinked on the chromosome; thus, glnR appears to encode a diffusible positive regulatory element. Consistent with this, the mutant glnR allele is recessive to the wild-type allele with regard to expression of glnA (synthesis of Gln synthetase). Although glnR is closely linked to glnA, strains with mutations to complete loss of function of the glnR product can be distinguished from glnA strains by their ability to produce detectable Gln synthetase and to grow in the absence of glutamine. To demonstrate unequivocally that glnR is distinct from glnA, we have purified and characterized Gln synthetase from a strain with a Tn10 insertion in glnR. Because the properties of Gln synthetase from the insertion mutant, most importantly the carboxyl-terminal sequence of amino acids, are the same as those of synthetase from wild type, the Tn10 insertion cannot be in glnA (if it were, the carboxyl terminus of Gln synthetase would have to be altered); therefore we conclude that the Tn10 insertion is in a regulatory gene, glnR, which is distinct from glnA. A model for the function of the glnR product together with the previously defined glnF product in mediating nitrogen control is discussed.

Carrier Proteins↗
PubMed1979

Effect of a physical conditioning program upon left ventricular ejection fractions determined serially by a noninvasive technique.

6 clinically normal subjects underwent a 3-month physical conditioning program with the ejection fractions determined before and after physical conditioning using a scintillation probe. All subjects achieved a conditioning effect as evidenced by increased treadmill test duration after conditioning (mean duration before conditioning: 658 vs. 715 sec after conditioning; p less than 0.02). All 6 subjects increased resting ejection fractions after conditioning (mean ejection fraction before conditioning: 54.5 +/- 5.4%; mean ejection fraction after conditioning: 67.0 +/- 9.0%; p less than 0.01). Thus, an aerobic physical conditioning program appears to increase resting ejection fractions in normal subjects.

Adult↗
PubMed1978

Early stages in Bacillus subtilis transformation: association between homologous DNA and surface structures.

The addition of ethylenediaminetetraacetate to competent cultures of Bacillus subtilis irreversibly inhibited the transformability as well as the cellular binding of DNA. Our results show that the inhibition of DNA binding by ethylenediaminetetraacetate in whole cells, protoplasts, and membrane vesicles is mainly due to a permanent alteration of the DNA receptors. Transformation absolutely requires free magnesium ions, whereas DNA binding is a magnesium-independent step. In contrast to ethylenediaminetetraacetate, the absence of Mg2+ does not irreversibly affect the capacity of the competent cells to be transformed DNA-binding receptors located at the cell surface remain associated with the plasma membrane after protoplasting and after isolation of membrane vesicles. A Mg2+-dependent endonucleolytic activity associated with the membrane appears to be responsible for the lower levels of binding by protoplasts in the presence of this ion.

Bacillus subtilis↗
PubMed1977

The product of a newly identified gene, gInF, is required for synthesis of glutamine synthetase in Salmonella.

The product of a newly identified gene, glnF, which is distinct from the glutamine synthetase structural gene (glnA), is required for synthesis of glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2[ in Salmonella typhimurium and probably in Escherichia coli. Salmonella strains with ICR (2-chloro-6-methoxy-9-[3-(2-chloroethyl)aminopropylamino]acridine dihyodrochloride)-induced (frameshift) mutations in glnF are glutamine auxotrophs; they have less than 10% oof wild-type glutamine synthetase activity or antigen and are unable to derepress the synthesis of the enzyme. The mutant allele is recessive to the wild-type allele, indicating that the glnF gene encodes a diffusible product. Mutant glnF strains have normal activities of all proteins involved in covalent modification of glutamine synthetase: adenylyltransferase (EC 2.7.7.42), PII, uridylyltransferase, and uridylyl removing enzyme. In addition, they have glutamate synthase (EC 1.4.1.13) and glutamate dehydrogenase (EC 1.4.1.4) activities. Thus, glnF does not encode the structure of any of these proteins. The above evidence suggests that the product of the glnF gene is (or produces) a positive regulatory factor that is required for synthesis of glutamine synthetase; it indicates that auto-regulation cannot account for control of the synthesis of glutamine synthetase in Salmonella.

Antigens, Bacterial↗
PubMed1976

Influence of several nucleotides on the competence development of Bacillus subtilis.

The influence of adenosine-3',5'-cyclic monophosphate (cAMP) and other nucleotides on the competence development of Bacillus subtilis was studied. The stimulation of competence which can be achieved by exposing physiologically low-competent cells to supernatants from highly competent cultures can be inhibited with different cAMP doses. When the same cells were suspended in a minimal medium with cAMP, varying degrees of stimulatin- of competence were observed depending on the time of addition of the drug. This effect is not specific for cAMP. It appears to be correlated to an increase of the amount of DNA bound to the competent cells. cAMP activities were antagonized by equimolar doses of adenosine-triphosphate (ATP) and guanosine-triphosphate (GTP).

Adenosine Triphosphate↗
PubMed1975

Evaluation of different antibiotic actions combined with rifampicin. In vitro synergism against Pseudomonas and Proteus.

Associations of penicillin, streptomycin, tetracycline and polymyxin B with rifampicin were tested for synergism against Pseudomonas and Proteus pathological strains. The combination of rifampicin and polymyxin B was clearly synergistic for all strains as it was evaluated by isobolograms and killing curvesmthe bactericidal action of this association, without any cross-resistance between its components, may eradicate gram-negative bacteria infections with marked polyvalent drug resistances.

Drug Synergism↗