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Biomedical subjects

C J Gibson

Publications and source records attributed to C J Gibson.

79 records · Page 5Linked to original sources
PubMed1972

Phenotypic suppression of methicillin resistance in Staphylococcus aureus by mutant noninducible penicillinase plasmids.

Methicillin (intrinsic) resistance of Staphylococcus aureus was suppressed almost completely by regulatory gene (penI(1)) mutations of penicillinase plasmids that made penicillinase production strictly noninducible. Methicillin resistance was restored by secondary regulatory gene mutations that altered the noninducible phenotype or by complementation with a compatible plasmid that did not bear the noninducible mutation. No evidence was obtained for genetic linkage between a penicillinase plasmid and the gene for methicillin resistance. We suggest, therefore, that the mutant noninducible repressor acted in trans by binding to a site on the methicillin resistance determinant. This hypothesis would imply an appreciable degree of homology between penicillinase plasmids and methicillin resistance genes.

Anti-Bacterial Agents↗
PubMedDate not supplied

Tyrosine for depression.

The catecholamine hypothesis of affective disorders postulates that depression reflects inadequate norepinephrine activity at unspecified brain centers that regulate mood. In light of experimental data showing that the oral administration of tyrosine, precursor of the catecholamine series of neurotransmitters, can increase brain norepinephrine concentrations and activity, we have conducted preliminary trials of tyrosine in depressed outpatients. Initial results are encouraging, and we are now conducting a double-blind, parallel-group trial comparing tyrosine to the tricyclic antidepressant imipramine and to placebo in non-bipolar outpatients with major depression.

Brain Chemistry↗
PubMedDate not supplied

Nefiracetam improves Morris water maze performance following traumatic brain injury in rats.

Nefiracetam, a pyrrolidone derivative, is a nootropic agent that has facilitated cognitive function in a wide variety of animal models of cognitive dysfunction. The purpose of this study was to investigate the efficacy of the chronic postinjury administration of nefiracetam (DM-9384) in improving cognitive performance following central fluid percussion brain injury in rats. Twenty-four hours following surgical preparation, a sham injury or a moderate fluid percussive injury (2.1 atm) was delivered. Nefiracetam was administered chronically (0 or 9 mg/kg, po, for sham animals and 0, 3, or 9 mg/kg for injured animals) on postinjury days 1-15. Cognitive performance was assessed using the Morris water maze (MWM) on postinjury days 11-15. Chronic administration of 3 and 9 mg/kg nefiracetam attenuated MWM deficits produced by central fluid percussive brain injury. Importantly, the MWM performance of the injured animals treated with 9 mg/kg did not significantly differ from uninjured, sham animals. The 9-mg/kg dose of nefiracetam did not have a positive or negative effect on MWM performance of uninjured animals. The results of the present experiment suggest that a nootropic such as nefiracetam may be an appropriate treatment for trauma-induced cognitive dysfunction.

Animals↗
PubMedDate not supplied

Memory for temporal order of new and familiar spatial location sequences: role of the medial prefrontal cortex.

Rats with medial prefrontal cortex or sham control lesions were tested on an eight-arm radial maze task to examine memory for the temporal order of a variable and a constant sequence of spatial locations as a function of temporal distance. During the study phase of each trial, rats were allowed to visit each of eight arms once in an order that was randomly selected or fixed for that trial. The test phase required the rats to choose which of two arms occurred earlier in the sequence of arms visited during the study phase. The arms selected as test arms varied according to temporal distance (0, 2, 4, or 6) or the number of arms that occurred between the two test arms in the study phase. For the variable sequences based on new information, control rats showed an increasing temporal distance function. Relative to control rats, medial prefrontal cortex-lesioned rats displayed a temporal order memory deficit across all distances. For the constant sequence based on familiar information, control rats performed well across all distances. Relative to controls, the medial prefrontal cortex-lesioned rats displayed a performance deficit. The results support the idea that the medial prefrontal cortex contributes to mnemonic operations associated with temporal order for new and familiar spatial location information.

Analysis of Variance↗
PubMedDate not supplied

Acute myocardial and plasma catecholamine changes in experimental stroke.

Focal cerebral ischemia in humans increases the incidence of cardiac arrhythmias, and serum cardiac enzyme and plasma norepinephrine levels. In addition, systemic administration of catecholamines causes myocardial damage. This suggests that cerebral ischemia may cause myocardial damage as a consequence of elevated plasma norepinephrine levels. Therefore, experiments were done in 23 chloralosed, paralyzed and artificially ventilated cats to investigate the effects of occluding (n = 17) or sham-occluding (n = 6) the left middle cerebral artery on the myocardium and on circulating levels of plasma catecholamines. After occlusion of the middle cerebral artery for 12-22 hr, 41% (7/17) of the hearts had either acute myocardial necrosis (3/7), focal hemorrhage (3/7), or both (1/7). In animals with acute myocardial damage the levels of plasma norepinephrine and epinephrine were significantly increased compared to pre- middle cerebral artery occlusion values (+46 +/- 18% and +142 +/- 45%, respectively). As well, in cats with acute myocardial damage, changes from initial levels of plasma norepinephrine and epinephrine were significantly increased over those of experimental cats without acute myocardial damage. In animals which did not have acute myocardial damage (10/17) the circulating plasma levels of catecholamines were not significantly different from pre-occlusion values. Similarly, sham occlusion did not alter plasma catecholamine levels. These data demonstrate that a percentage of animals subjected to middle cerebral artery occlusion have myocardial damage and an increase in plasma concentration of norepinephrine and epinephrine. This suggests that a rise in plasma catecholamine levels, due to increased sympathetic activity after middle cerebral artery occlusion, may cause myocardial damage.

Acute Disease↗
PubMedDate not supplied

Evaluation of shading algorithms for surface display: depth information, surface orientation, colour and transparency.

When interpreting a shaded surface image the observer must infer a three-dimensional shape from a two-dimensional image. The principal monocular cues used in this process are surface orientation and apparent depth. Four shading algorithms were compared, ranging from pure depth to pure surface orientation with two intermediates. Eight observers assessed these algorithms using 40 sets of images showing test objects derived from emission computed axial tomograms, X-ray computed tomograms and simulated data. The results demonstrated a highly significant preference (p less than 0.01) for surface orientation over depth information for all observers and both imaging modalities. The coefficient of concordance showed that the observers were in good agreement as to the rank order of the algorithms, with significant agreement (p less than 0.05) for 37 of the 40 sets of images. The overall preferred algorithm was based on a local polynomial fitting procedure and contained primarily surface information. This shading algorithm was extended to include colour, which was used both as an arbitrary surface property to identify parts of a complex object and as a means of conveying temporal information. Further extension of the algorithm to the display of transparent surfaces was facilitated by an illumination model based on purely isotropic light. This enabled even irregular surfaces to be displayed as transparent objects, and was combined with opaque shading for displaying nested surfaces in nuclear magnetic resonance data.

Algorithms↗