Search PubMed⌕ Search

Biomedical subjects

J Black

Publications and source records attributed to J Black.

At least 217 records · Page 12Linked to original sources
PubMed1991

In vitro comparison of Thoroughbred and Standardbred racehorses with regard to local fatigue failure of the third metacarpal bone.

In vitro local fatigue testing of the third metacarpal bone from Thoroughbred and Standardbred racehorses was performed, using fully reversed cyclic bending. Strain number of cycle data were accumulated and indicated that significant difference did not exist between the 2 breeds. It was concluded that the marked difference in the incidence of fatigue failure in the third metacarpal bone (bucked shins, dorsal metacarpal disease) seen in Thoroughbreds and Standardbreds was not related to any differences between the 2 breeds in mechanical properties of the bone.

Animals↗
PubMed1991

Hypomagnesaemia in elderly hospital admissions: a study of clinical significance.

Serum magnesium estimations carried out on 1576 consecutive elderly patients at the time of hospital admission revealed that 10.7 per cent had a serum magnesium level below 0.7 mmol/l, with 4.4 per cent of the total having a serum level less than 0.65 mmol/l. Hypokalaemia was frequently associated with hypomagnesaemia, for which diuretic therapy was the most commonly found predisposing factor. Outcome of illness, measured at six months in terms of mortality, duration of hospital stay and percentage of patients discharged from hospital, was no worse in patients admitted with hypomagnesaemia than in normomagnesaemic controls.

Aged↗
PubMed1990

Morphological evidence for an apparent lysosomotropic activity by unsaturated putrescine analogues.

Treatment of cultured L1210 cells with the putrescine analogue, 2,5-diamino-3-hexyne, at 0.5 nM resulted in the rapid (1-2 h) appearance of numerous cytoplasmic vacuoles which were highly visible by light microscopy. Ultrastructural examination revealed that the vacuoles contained numerous membrane vesicles and electron-dense structures resembling endosomal elements. Other cellular organelles were unaffected by the drug. The overall morphological effect by 2,5-diamino-3-hexyne was nearly identical to that produced in the same cells by the known lysosomotropic agent, chloroquine. Since the putrescine analogue, 1,4-diamino-2-butyne at 1.2 mM, also produced comparable cytoplasmic vacuolation, and putrescine itself failed to do so at concentrations as high as 5 mM, it was concluded that the apparent lysosomotropic activity of the putrescine analogues was probably due to their weaker basicity related to the presence of an internal triple bond. Although it is uncertain whether the effect of the analogues on the endosomal system is related to the natural function of polyamines, the finding points out the previously unrecognized potential for certain polyamine analogues to act in this manner.

Animals↗
PubMed1990

Learning-induced afterhyperpolarization reductions in hippocampus are specific for cell type and potassium conductance.

Hippocampal slices were prepared from rabbits trained in a trace eye-blink conditioning task and from naive and pseudoconditioned controls. Measurements of the post-burst afterhyperpolarization (AHP), action potential, and other cellular properties were obtained from intracellular recordings of CA1 pyramidal (N = 49) and dentate gyrus granule cells (N = 52). A conditioning-specific reduction in the amplitude of the AHP was found in CA1 cells but not in dentate granule cells. This reduction in the AHP was apparent at 50 ms after the end of a depolarizing current pulse, and was maintained for at least 650 ms. Other measured cell characteristics (input resistance, resting membrane potential, action potential shape, inward rectification, spike threshold) were not affected by training, in either CA1 pyramidal or dentate granule cells. Time-course measures indicate that both the medium, Ca2(+)-independent AHP and the slow, Ca2(+)-dependent AHP are reduced by conditioning. The slow AHP largely reflects the Ca2(+)-dependent K+ current, IAHP. Rising and falling slopes, peak amplitude, and width of individual action potentials were not changed by learning. This contrasts with observations from invertebrates in which action potential broadening was reported following learning. We conclude that the reduction in AHP that follows hippocampally-dependent associative learning occurs in specific hippocampal cell types and not others, and is mediated by changes in a Ca2(+)-independent AHP and a particular Ca2(+)-dependent K+ current, IAHP.

Action Potentials↗
PubMed1990

The antiphospholipid syndrome: prevalence among patients with stroke and transient ischemic attacks.

PURPOSE: The prevalence of the antiphospholipid syndrome was determined prospectively in patients presenting with stroke and transient ischemic attacks. An attempt was made to define a subset of stroke patients at risk for this syndrome on the basis of their clinical features. PATIENTS AND METHODS: Fifty-one consecutive patients with stroke and transient ischemic attacks were assessed. Tests used for the laboratory diagnosis of the antiphospholipid syndrome included four phospholipid-dependent coagulation tests for detection of the lupus anticoagulant, and two enzyme-linked immunosorbent assays for antibodies to phospholipid. RESULTS: Three of 51 patients (6%, 95% confidence intervals 0% to 12.0%) had a lupus anticoagulant and the clinical features of the antiphospholipid syndrome. Seven patients had clinical features suggestive of the syndrome but negative laboratory tests. Those patients who were clinically unlikely to have this syndrome also had negative laboratory tests. CONCLUSION: In a series of 51 unselected patients presenting with stroke and transient ischemic attacks, three had the antiphospholipid syndrome. The clinical features of this syndrome are helpful in identifying this group of patients. The role of the lupus anticoagulant in the pathogenesis of stroke remains to be defined.

Adolescent↗
PubMed1990

Why do young infants fail to search for hidden objects?

Recent evidence indicates that infants as young as 3.5 months of age understand that objects continue to exist when hidden (Baillargeon, 1987a; Baillargeon & DeVos, 1990). Why, then, do infants fail to search for hidden objects until 7 to 8 months of age? The present experiments tested whether 5.5-month-old infants could distinguish between correct and incorrect search actions performed by an experimenter. In Experiment 1, a toy was placed in front of (possible event) or under (impossible event) a clear cover. Next, a screen was slid in front of the objects, hiding them from view. A hand then reached behind the screen and reappeared holding the toy. The infants looked reliably longer at the impossible than at the possible event, suggesting that they understood that the hand's direct reaching action was sufficient to retrieve the toy when it stood in front of but not under the clear cover. The same results were obtained in a second condition in which a toy was placed in front of (possible event) or behind (impossible event) a barrier. In Experiment 2, a toy was placed under the right (possible event) or the left (impossible event) of two covers. After a screen hid the objects, a hand reached behind the screen's right edge and reappeared first with the right cover and then with the toy. The infants looked reliably longer at the impossible than at the possible event, suggesting that they realized that the hand's sequence of action was sufficient to retrieve the toy when it stood under the right but not the left cover. A control condition supported this interpretation. Together, the results of Experiments 1 and 2 indicate that by 5.5 months of age, infants not only represent hidden objects, but are able to identify the actions necessary to retrieve these objects. The implications of these findings for a problem solving explanation of young infants' failure to retrieve hidden objects are considered.

Attention↗
PubMed1990

Influences of sensation seeking, gender, risk appraisal, and situational motivation on smoking.

The study evaluated the current relationship between the trait of sensation seeking and smoking as possibly mediated by gender, cognitive risk appraisal and situational-relevant motivation. Subject were 1071 male and female undergraduates of whom 279 indicated they were past or current smokers and completed a Smoking Questionnaire (SQ). All subjects took the Sensation Seeking Scale. Sensation seeking is significantly (p less than .001) related to the proportion smoking in both men and women, although more women at the university are now smoking. Sensation seekers inhaled more of the smoke than lows, perhaps an indication of stronger nicotine need. Smoking was seen as highly risky, but the degree of estimated risk was not related to sensation seeking. Women reported smoking more in emotional and social situations; men reported smoking more in situations requiring close attention to a task. Sensation seekers reported smoking more than lows in social situations. Research is needed on specific cognitive factors mediating smoking and how they are related to personality and gender.

Adult↗
PubMed1990

Distribution of substance P receptors in rabbit airways, functional and autoradiographic studies.

We have studied systematically the distribution of receptors for substance P in the airway smooth muscle of the rabbit using both functional studies and light-microscopic autoradiography. Four areas of the respiratory tract were examined: the midtrachea (T1) and proximal, middle and distal portions of the right main bronchus (B1, B2 and B3, respectively). The magnitude of the contractile response to substance P in preparations from six to eight animals was location-dependent, increasing significantly from proximal to distal areas. Maximal tension expressed as a function of tissue weight +/- S.E.M. was 24.8 +/- 3 for T1, 39 +/- 10 for B1, 108 +/- 31 for B2 and 160 +/- 42 for B3. The potency of substance P in B2 and B3 was significantly greater (EC50 = 4.8 x 10(-7) M; 2.8 x 10(-7) M, respectively) than that in T1 (2.5 x 10(-6) M). After inhibition of endogenous enkephalinase by phosphoramidon there was an increase in sensitivity to substance P in both T1 (EC50 = 2.3 x 10(-7) M, n = 5) and B3 (2.6 x 10(-9) M, n = 5). There was remarkable agreement in the results obtained with autoradiography. No binding sites (0) were visualized to Bolton Hunter substance P in T1. Sparse but specific binding (+) was seen in B1, whereas it was marked ( ) in B2 and very dense ( ++) in B3. Thus, our results have shown that receptors for substance P are more numerous in the distal than proximal airways of the rabbit. This may indicate a physiological role for substance P in the regulation of airway smooth muscle tone in the distal airways.

Animals↗
PubMed1990

A comparison of the antimalarial activity of the cinchona alkaloids against Plasmodium falciparum in vitro.

The effects of four major cinchona alkaloids: (-) quinine, (+) quinidine, (-)cinchonidine, and (+)cinchonine against Plasmodium falciparum FCQ-27/PNG were studied. The alkaloids were tested in vitro as either single alkaloids, racemic mixtures of stereoisomers, or as an equimolar combination of all four alkaloids. Results indicate (+)quinidine to be most effective and both (+)stereoisomers were more potent than the (-)stereoisomers. Inhibitory concentrations 50% (Ki) of racemic mixtures of stereoisomers were similar to those of the (+)stereoisomers alone. The Ki of four alkaloids in equimolar combination were similar to that of the (-) cinchonidine/(+)cinchonine racemic mixture. A total alkaloidal extract of Cinchona sp. was tested and compared with the pure alkaloids. HPLC analysis indicated that (+)cinchonine, (-)cinchonidine and (-)quinine were present in a ratio of approximately 1:1:2, respectively. The total alkaloid extract, with (-)stereoisomers predominating, was less effective than the four alkaloids in combination. The nature of the interaction between stereoisomers was investigated and appears to be one of addition.

Animals↗
PubMed1989

Drugs from emasculated hormones: the principle of syntopic antagonism.

This lecture illustrates the early stages in the planning and discovery of propranolol, an adrenaline beta-adrenergic receptor antagonist, and cimetidine, a histamine H2-receptor antagonist--the first examples of clinically useful drugs from each of these classes. The significance of selective agonists, partial agonists, and syntopic antagonists and the importance of the bioassay and the use of molar models in the drug discovery process are discussed. For the future, an outline of potential developments in hormone-receptor concepts is offered leading to the conclusion that progress may depend on improvements in bioassays and related molar modeling.

Adrenergic beta-Antagonists↗
PubMed1989

Traumatogenicity: effects of self-reported noncombat trauma on MMPIs of male Vietnam combat and noncombat veterans treated for substance abuse.

A recent review of the literature on Post-Traumatic Stress Disorder (PTSD) and the MMPI has shown that all previously published studies have been limited to clinical groups whose trauma occurred in Vietnam combat. The purpose of this study was to test hypotheses that predict higher MMPI and PTSD scale scores among combat veterans who differ in degrees of noncombat traumas. Results support predictions. Those who reported more noncombat traumas attain significantly higher MMPI scores for scales F, Hypochondriasis, Hysteria, Psychopathic Deviate, Psychasthenia, Schizophrenia, Mania, Social Introversion, and an MMPI PTSD score (Keane, Malloy, & Fairbank, 1984). Moreover, noncombat effects are manifested differentially: Combat veterans with higher noncombat trauma evidence greater social withdrawal, whereas noncombat veterans who report higher noncombat trauma are characterized by higher anxiety. MMPI elevations were progressively higher as groups increased in degrees of combat and noncombat trauma: noncombat and low combat trauma veterans were the better adjusted, and combat veterans with higher noncombat trauma were the worst adjusted. Results provide descriptive validity for PTSD as a construct and underscore the importance of assessing frequency and intensity, as well as types of traumas and stresses, in the background histories of substance abusers and other clinical groups as well.

Adult↗