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Biomedical subjects

D Spencer

Publications and source records attributed to D Spencer.

At least 145 records · Page 8Linked to original sources
PubMed1969

Studies on a Maize Mutant Sensitive to Low Temperature II. Chloroplast Structure, Development, and Physiology.

In the Zea mays L. mutant M11 grown in the dark at 15 degrees , the ultrastructure of the etioplast is abnormal. The pigment content of the etioplasts is reduced but the in vivo absorption characteristics suggest that the normal protochlorophyll (ide)-holochrome is present. The lowered synthetic ability of the etioplasts is not primarily due to a reduced complement of plastid ribosomes. The plastids of mutant M11 grown in the light at 15 degrees contain little pigment, are markedly deficient in ribosomes and their ultrastructure is abnormal. In mutant M11 grown at 15 degrees , an extreme sensitivity of the plastid membranes to light was observed.

Journal Article↗
PubMed1968

A model of blebbing in mitotic tissue culture cells.

A preliminary study of blebbing in tissue cultures has been made. The tubal epithelium of fetal mouse oviduct was cultured at 37 degrees C in Rose chambers. A cinematographic record was obtained of phase microscope observations of mitotic cells. Measurements of the size of both cells and blebs were made on the film using a "traveling" microscope. The duration and the rise and decay times of blebs were determined simply by counting frames on the film. Detailed observations are reported on blebbing in four cells undergoing mitosis. The results indicate that the frequency of blebbing as well as the duration of individual blebs exhibits a maximum during telophase. A model is proposed to account for blebbing in mitotic cells. The model attributes to local regions of the cell membrane the property of constant tension independent of stretch over some restricted range of stretch. This property implies that the cell membrane is locally unstable. Further assumptions stated explicitly in the model are that (i) cell division occurs at constant volume, (ii) the cell membrane stretches during cleavage, (iii) there is a positive pressure drop across the cell membrane. Evidence is cited in support of these assumptions as well as independent evidence that the cell membrane may be locally unstable. A physical model is described which would be expected to exhibit blebbing given the above assumptions.

Animals↗
PubMedDate not supplied

Epidemic AIDS-related Kaposi's sarcoma in southern Africa: experience at the Johannesburg General Hospital (1980-1990).

Epidemic acquired immune deficiency syndrome-related Kaposi's sarcoma (AKS) in tropical and southern Africa is a highly varied neoplastic disease, characterized by multifocal mucocutaneous, lymphatic and visceral involvement. It follows a clinical course similar to AKS in Europe and the USA. However, lack of adequate medical facilities in many African countries hampers successful palliation of this fatal disease. In this retrospective analysis, we summarize our experience with 52 patients with AKS treated at Johannesburg General Hospital, South Africa, between 1980 and 1990. Radiation therapy can provide good to excellent palliation with only minimal side-effects, producing a lesser impact on the haematological and immunological system than chemotherapy.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

High rate of Bartonella henselae infection in HIV-positive outpatients in Johannesburg, South Africa.

The emerging opportunistic pathogen Bartonella henselae has a wide range of clinical presentation, which includes, particularly, bacillary angiomatosis. This non-random pilot survey of outpatients attending HIV clinics in Johannesburg, South Africa, sampled 188 patients, in whom there was a 10% prevalence of Bartonella bacteraemia, as determined by nested polymerase chain reaction.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Trunk strengths in structurally normal girls and girls with idiopathic scoliosis.

Maximum voluntary isometric strengths of the trunk were measured in 93 girls who had mild idiopathic scoliosis and 109 girls who had structurally normal spines. Subject ages ranged from 10 to 16 years, and the mean Cobb measurement in the girls with scoliosis was approximately 22 degrees. Strengths were measured in attempted trunk flexion, attempted extension, ad attempted left and right lateral bending. No consistent differences appeared in performance between the girls with scoliosis and the structurally normal girls.

Adolescent↗
PubMedDate not supplied

Trunk muscle myoelectric activities in idiopathic scoliosis.

Twenty adolescent girls with mild-to-moderate cases of idiopathic scoliosis and twelve adolescent girls with structurally normal spines performed 15 exercises isometrically while standing. The exercises included resisting flexion, extension, and lateral bending moments imposed on the trunk. Myoelectric activities in 12 trunk muscle groups were measured during these performances, using surface electrodes. For one set of comparisons, the patients were divided into those whose clinical records documented curve progression and those with no documented progression. No significant differences were noted in mean myoelectric activities between these two patient groups. For a second set of comparisons, the subjects were divided into patients with curves of more than 25 degrees, patients with curves of 25 or fewer degrees and normals. No significant differences in mean myoelectric activities were noted between the patients with the smaller curves, while the patients with the larger curves had significantly larger convex side myoelectric activities in their anterior, lateral and posterior muscles at lumbar levels compared to the normal girls. The findings of this study, along with biomechanical model analyses, suggest that the asymmetries in muscle actions evidenced by myoelectric measurements result from scoliosis. Scoliosis progression seems not to be caused by asymmetry in muscle contractions; rather it may be caused by a lack of adequate asymmetry.

Abdominal Muscles↗
PubMedDate not supplied

Interictal spikes and hippocampal somatostatin levels in temporal lobe epilepsy.

We investigated the relationship between somatostatin-like immunoreactivity (SSLI) and interictal spikes (IIS) in human temporal lobe epileptic tissue. IIS counted manually from depth electrode recordings obtained preoperatively were expressed as spike frequency in anterior, middle, and posterior portions of hippocampus. SSLI was determined by radioimmunoassay (RIA). An inverse relationship between SSLI in the entorhinal cortex (EC) and IIS frequency in hippocampus was present (r = -0.55, p = 0.06). No correlation between IIS and SSLI in CA4, CA3, CA1, or the dentate was evident. This finding suggests a role of the EC in generation, regulation, or expression of interictal paroxysmal electrical activity in temporal lobe epilepsy (TLE), for which somatostatin may be a marker.

Electroencephalography↗
PubMedDate not supplied

Morphological patterns of seizures recorded intracranially.

We analyzed the frequency and morphological characteristics of the initial EEG manifestations of spontaneous seizures recorded from depth and subdural electrodes in 26 patients for whom pathological analysis of the area of seizure onset was available after resective surgery. Pathological features considered to be positive findings included well-defined structural lesions (hamartoma, neoplasm) or strictly defined mesial temporal sclerosis. Seizure onset was characterized by the frequency of the rhythmic discharge greater than 2 Hz in the first second and by the presence or absence of periodic low-frequency spikes (less than 2 Hz) preceding this stable change in background frequency. These features were correlated with the presence or absence of pathologic abnormalities in temporal and extratemporal locations. Although all patterns and frequencies of seizure onset were recorded in both medial temporal and extratemporal locations, medial temporal seizure onset was significantly more likely to have high frequency (greater than 13 Hz, p less than 0.00001) and tended to show periodic spikes prior to the seizure when it was associated with medial temporal sclerosis compared to when it was not. Extratemporal seizure onset associated with abnormal pathological substrate was significantly more likely to have a lower frequency (less than 13 Hz, p less than 0.05) and no periodic spikes before seizure onset (p less than 0.00001) than extratemporal seizure onset recorded from areas without pathological findings. Variability of seizure onset frequency was a characteristic of temporal, but not extratemporal, seizures (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Diseases↗