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Biomedical subjects

L Davis

Publications and source records attributed to L Davis.

At least 235 records · Page 13Linked to original sources
PubMed1982

Characterization of a cold-sensitive hisW mutant of Salmonella typhimurium.

Previous studies of hisW mutants of Salmonella typhimurium have led to the suggestion that such strains are defective in tRNA maturation. (J. E. Brenchley and J. Ingraham, J. Bacteriol. 114:528-536, 1973). In this study, we report that one hisW strain is defective in the accumulation of all stable RNA species. Polyacrylamide gel electrophoresis of radiolabeled RNA indicated tha at the nonpermissive temperature (20 degrees C) all stable RNa species in the cold-sensitive hisW3333 mutant were synthesized and rapidly degraded. We propose that the cold sensitivity of this strain is caused by such a restriction in stable RNA accumulation at low temperature. In vitro and in vivo studies demonstrated that the RNA degraded in this strain was synthesized de novo and was not preexisting RNA. Furthermore, physiological and genetic recovery from the cold-sensitive hisW phenotype resulted in relatively normal RNA synthesis and accumulation. Thus, the RNA alterations observed in this strain were not explained by defects in a tRNA modification enzyme. Rather, these findings suggest the existence of defective RNA processing and that a control mechanism for the overall synthesis or accumulation of stable RNA species is altered in the hisW3333 mutant.

Gene Expression Regulation↗
PubMed1982

Decerebrate rigidity in humans.

Decerebrate rigidity (DR) in humans results from a midbrain lesion and is manifested by an exaggerated extensor posture of all extremities. It is characterized by shortening and lengthening reactions and can be modified by tonic neck, labyrinthine (Magnus-de Kleijn), and phasic spinal reflexes. These criteria, and not extensor posture alone, reflect the observations of Sherrington and should form the basis of the clinical examination; however, the experimental-anatomical lesion and physiological findings can never be reproduced exactly in humans. "Tonic and cerebellar fits" are not the equivalent of DR, but are forms of muscle spasm that result in an extensor attitude. They are caused by irritation and excitation of the brain stem. The most common cause of DR in humans is trauma. The incidence of DR in head-injured patients may be as high as 40%, resulting in an average mortality rate of 80%; the presence of an extensor posture increases the mortality from 20 to 70%. The surgical removal of an intracranial lesion does not improve the high mortality rate in patients with craniocerebral trauma who are decerebrate. Although the Glasgow coma scale (GCS) does not consider the specific type of central nervous system abnormality caused by trauma, it is an accurate and accepted assessment of outcome after coma lasting longer than 6 hours. DR is a factor in the best motor response of the GCS and should be assigned major importance in the prognosis of comatose head-injured patients.

Brain Injuries↗
PubMed1981

Friend murine leukemia virus-induced leukemia is associated with the formation of mink cell focus-inducing viruses and is blocked in mice expressing endogenous mink cell focus-inducing xenotropic viral envelope genes.

In these studies, we have shown data that are consistent with the hypothesis that mink cell focus-inducing viruses (MCF) play an important role in the generation of an erythroproliferative disease developing after injection of certain strains of newborn mice with ecotropic Friend murine leukemia virus (F-MuLV). Resistance to this disease is correlated with the endogenous expression of an MCF/xenotropic virus-gp70-related protein that may interfere with the replication or spread of MCF viruses. These ideas are supported by the following observations: (a) after infection with F-MuLV, only 6/13 strains of mice-developed disease, and studies with crosses between susceptible and resistant strains indicated that resistance was dominant. Although F-MuLV was shown to replicate equally well in all strains tested, viruses coding for MCF-specific viral envelope proteins could be detected only in the spleens of mice from strains that were resistant to F-MuLV-induced disease and not in the spleens of mice from strains that were resistant to F-MuLV-induced disease; (b) a Friend MCF (Fr-MCF) virus isolated from the spleen of an F-MuLV-infected mouse from a susceptible strain induced the same erythroproliferative disease when injected as an appropriate pseudotype into mice from susceptible but not resistant strains of mice; and (c) resistant but not susceptible strains of mice endogenously express MCF/xenotropic virus-related envelope glycoproteins that may be responsible for resistance by blocking receptors for MCF viruses. These results not only indicate that Fr-MCF virus is a crucial intermediate in the induction of disease by F-MuLV, but also suggest that a novel gene, either an MCF/xenotropic virus-related envelope gene or a gene controlling its expression, is responsible for resistance to erythroleukemia induced by F-MuLV.

Animals↗
PubMed1981

Nutritional supplementation of pregnant adolescents.

Disadvantaged pregnant black teenagers have a higher proportion of low-birth-weight infants and their offspring have a lower mean birth weight. One hundred and fifty-seven pregnant adolescents enrolled in a Baltimore public school for pregnant teenagers were studied to determine the impact of a nutritional supplement on pregnancy outcome. Seventy-eight students voluntarily agreed to receive a nutritional supplement; 79 comparably matched students did not receive the supplement. The supplement Sustacal provided a mean intake of 8691 cal with 530 g of protein and additional vitamins and minerals over an average period of 15.1 weeks. This supplement was associated with a significant increase of 157 g in the mean infant birth weight (P less than 0.05). A significant increase in infant birth weight of 269 g was noted in the offspring of supplemented girls below 16 years of age compared with the nonsupplemented girls below this age (P less than 0.05). Significant differences in infant birth weight were also noted in the offspring of nonsmoking supplemented adolescents (P less than 0.05). The proportion of low-birth-weight infants was decreased in the supplemented subjects, but the difference was not significant.

Adolescent↗
PubMed1981

Veterans Administration cooperative study on aphasia: a comparison of individual and group treatment.

Five Veterans Administration Medical Centers participated in an investigation designed to compare individual with group treatment for aphasic patients who had suffered a left hemisphere cerebral vascular accident. Patients who met selection criteria were assigned randomly to either traditional, individual, stimulus-response type treatment of specific language deficits or group therapy designed to improve communication through group interaction and discussion with no direct treatment of specific language deficits. All patients received eight hours of therapy each week beginning at four weeks postonset and continuing until 48 weeks postonset or until they dropped out of the study. A battery of language measures and a clinical neurologic evaluation were administered at intake and every 11 weeks a patient was in the study. Results show both individually and group-treated patients made significant improvement in language abilities. Individual treatment resulted in significantly better overall performance on the Porch Index of Communicative Ability; however, no significant differences were observed between groups on the other language measures. If the traditional belief is correct that significant spontaneous recovery is complete by three to six months postonset, significant improvement in both groups beyond 26 weeks postonset indicates both individual and group treatment are efficacious methods for managing aphasic patients.

Adult↗
PubMed1981

Decerebrate rigidity in animals.

Decerebrate rigidity (DR) in animals is caused by a release of spinal neurons from supraspinal inhibition, which results in a caricature of reflex standing and includes tonic neck and labyrinthine reflexes. The reticular formation, cerebellum, vestibular complex, spinal cord, and muscle spindle system and their neurophysiological interaction are critical to DR. Its discovery and investigation were essential to Sherrington's concept of the integrative action of the nervous system. There are two types of DR with different anatomical and physiological bases. Intercollicular decerebration yields rigidity in extensor muscles that results from bilateral destruction of the central tegmental tracts, is abolished by posterior root section, and is due to a facilitation of gamma motoneuron discharge (gamma animal). Anemic decerebration is characterized by excessive extensor rigidity, depends upon the release of tonic labryinthine reflexes from cerebellar inhibition, is independent of posterior root section, and is caused by excessive alpha motoneuron discharge (alpha animal). DR has provided an insight into the mechanisms of posture and standing, but the correlation of laboratory observations and results from animals to humans must be made with caution.

Animals↗
PubMed1981

Fibronectin associated with Clq in a Clq isolation procedure.

The complement component Clq, prepared by euglobulin precipitation of serum to which EDTA or EGTA had been added, contained fibronectin (FN) as detected by radioimmunoassay and immunodiffusion methods. The FN contents of the Clq preparations varied between 3 and 29% by weight of the Clq contents. Adsorptions of sera with polymerized IgG (an absorbent for Clq) in the presence or absence of EDTA removed all detectable Clq and between 12 and 95% of the FN. In a similar manner, adsorptions of sera and Clq preparations with insolubilized gelatin (to which FN will bind) reduced greatly or removed completely the FN component but also strikingly reduced the Clq contents. High salt concentration or the addition of EDTA did not alter the gelatin absorption results indicating that the association was not sensitive to high ionic condition and that Clq was equally bound as Clq or as the Cl complex. The results suggest that FN and Clq bind individually to both gelatin and IgG or that FN and Clq co-associate, accounting for removal of one component when the other is bound to its expected adsorbent.

Antigen-Antibody Reactions↗
PubMed1981

Fibronectin in von Willebrand's disease and thrombasthenia: role in platelet aggregation.

Fibronectin is involved in cell-cell and cell-substratum adhesion processes. Since von Willebrand's disease and thrombasthenia are characterized, respectively, by platelet-substratum and platelet-platelet adhesion anomalies, we investigated the state of fibronectin in platelets and plasma of these two disorders as well as the role of plasma fibronectin in platelet aggregation. The levels of platelet and plasma fibronectin in three cases of von Willebrand's disease and in three cases of thrombasthenia did not show statistically significant differences as compared with the normal controls. Immunofluorescent staining intensity and patterns of disease-derived and normal platelets, studied with anti-fibronectin antibodies, were similar. Furthermore, 125I-labeled protein A binds to anti-fibronectin-treated platelets from the two diseases investigated in the same fashion as in normal controls. No role for plasma fibronectin was detected in platelet aggregation induced by ADP, thrombin, collagen, epinephrine, and arachidonic acid. Thus our results do not indicate a direct quantitative role of fibronectin in the adhesion anomalies encountered in these diseases. However, fibronectin may still be important to platelet adhesion and normal hemostasis processes through interactions with the plasma von Willebrand factor and the membrane glycoproteins IIb and III, which have been shown to be deficient in von Willebrand's disease and thrombasthenia, respectively.

Blood Platelets↗
PubMed1981

Electrodiagnostic study of carpal tunnel syndrome after Colles fracture.

Thirty-three patients with unilateral Colles fracture were evaluated by clinical and electrodiagnostic methods to determine the frequency of concomitant ipsilateral carpal tunnel syndrome. Four cases were documented, an incidence of 12.1%; this is two to four times greater than the incidence previously reported in the orthopaedic literature. Four other cases showed bilateral carpal tunnel syndrome, on of which was more more severe on the fracture side. Although electrodiagnosis was not found to be a more sensitive diagnostic indicator than was careful history and physical examination is these patients, it was useful in objectively confirming the clinical impression and assessing the severity of involvement. Recovery of hand function was not adversely affected by the presence of carpal tunnel syndrome in our cases. In view of the rather frequent occurrence of this complication, it is recommended that all patients with Colles fracture be carefully evaluated for the presence of symptoms or signs suggesting median nerve compression, and that all suspected cases by referred for early electrodiagnostic evaluation.

Adult↗
PubMed1980

Reisolation of immunoreactive radioiodinated antigens using glutaraldehyde-insolubilized antibody preparations.

Radioiodination of antigens for use in radioimmunoassay can result in substantial losses of antigenic reactivity with the corresponding antibody and antisera preparations. We describe a method whereby antigens iodinated with the chloramine-T procedure are bound to and eluted from glutaraldehyde-insolubilized antibody. Unfractionated antisera, an ammonium sulfate precipitated fraction or the IgG fraction of antisera may be used as insolubilized immunoadsorbents. The method has been applied for the reisolation of a radioiodinated peptide, a low molecular weight protein and the fibronectin molecule. The total binding of 125I-antigens to antibody in radioimmunoassays can be increased from such low amounts before reisolation that the assay is not feasible, to 85% above background binding, after adsorption and elution from the insolubilized antibody preparations.

Adsorption↗