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Biomedical subjects

F C Davis

Publications and source records attributed to F C Davis.

At least 55 records · Page 3Linked to original sources
PubMed1985

Development of hamster circadian rhythms: prenatal entrainment of the pacemaker.

Individual hamster pups were maintained in constant dim light from just prior to birth, and their circadian wheel-running activity rhythms were recorded beginning at 18 days of age. Records of the postweaning free-running activity rhythm were used to determine the phase of a pup's rhythm on the day of weaning. Two groups of pups (LD and DL) were born to mothers that had been entrained before birth to light-dark cycles 12 hr out of phase. Both groups of pups were raised in constant dim light by foster mothers that had been entrained to only one of the prenatal cycles (LD). Thus pups born to mothers from different cycles were exposed to identical rhythmic environments postnatally. Despite the similar postnatal treatment, the two groups of pups showed activity rhythms at weaning with very different phases. The LD pups, born to and raised by LD mothers, were approximately synchronous with one another and with their foster mothers. The DL pups, born to DL mothers, but raised by LD mothers, were not synchronous with one another or with their foster mothers. Half of the DL pups showed phases predicted by their prenatal treatment, but the other half showed scattered phases. The results demonstrate that phase at weaning is affected by prenatal rhythmicity, and suggest that the circadian pacemaker underlying the activity rhythm is already functional and entrained at, or before, birth.

Animals↗
PubMed1985

Sexually dimorphic regions in the medial preoptic area and the bed nucleus of the stria terminalis of the guinea pig brain: a description and an investigation of their relationship to gonadal steroids in adulthood.

Sexually dimorphic regions are described in two areas of the guinea pig brain: the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST). The volume of a darkly staining portion of the MPOA is approximately 4-fold larger in male than in female guinea pigs, and the volume of a darkly staining portion of the BNST is approximately 36% larger in male than in female animals. The sex differences in both of these areas are present in animals that have been gonadectomized as adults as well as in intact animals, suggesting that they result from differences between the sexes in the hormonal environment during early development. Both the MPOA and the BNST bind high levels of gonadal steroids early in life, during the period when functional differentiation occurs. It is possible that dramatic morphological sex differences characterize such steroid-binding areas. Furthermore, these sexually dimorphic areas may form an anatomically and functionally interrelated system. Attention to these possibilities may help elucidate more precisely the neural basis for sexually dimorphic functions, as well as the basic mechanisms underlying sexual differentiation of behavior and the brain.

Animals↗
PubMed1983

Regulation of histone synthesis during early Urechis caupo (echiura) development.

The histones present in mature oocytes and embryos of Urechis caupo and their pattern of synthesis during early development have been characterized. Acid-soluble proteins extracted from mature oocyte germinal vesicles and from embryonic nuclei were analyzed by two-dimensional polyacrylamide gel electrophoresis. Histones are accumulated in the mature oocytes in amounts sufficient to provide for the assembly of chromatin through the 32- to 64-cell stage of embryogenesis. Two H1 histones, which appear to be variants, were found. Germinal vesicles and cleavage-stage nuclei are enriched in H1M (maternal). During late cleavage a faster-migrating H1, H1E (embryonic), appears among the nuclear histones and, as embryogenesis continues, replaces H1M as the predominant H1. No new core histone variants are detected during early development. Examination of [3H]lysine-labeled histones from germinal vesicles and embryonic nuclei reveals stage-specific patterns of histone synthesis. H1M is the major H1 species synthesized in mature oocytes. After fertilization, a switch to the predominant synthesis of H1E occurs. Comparison of the [3H]lysine incorporated into H1E and core histones indicates that H1E synthesis is disproportionately high from midcleavage through the midblastula stage. By the gastrula stage, a balanced synthesis of H1E and each core histone is established. The results indicate that there is noncoordinate regulation of H1 and core histone synthesis during Urechis development.

Animals↗
PubMed1983

Sex differences in the circadian control of hamster wheel-running activity.

The circadian pacemaker that underlies the wheel-running activity of hamsters was studied in males and females. Sex differences were found in the mechanism by which the pacemaker entrains to light-dark cycles and in the timing of activity onset. When exposed to a light-dark cycle with a period of 24.75 h (with 1 h of light/cycle), males show a greater ability to maintain entrainment than do females. This difference in the upper limit of entrainment appears due to a sex difference in the magnitude of light-induced phase shifts. A small difference in free-running period may also contribute to the sex difference in entrainment. Two weeks after castration of adults, the sex difference in entrainment is not affected, indicating that the difference does not depend on circulating gonadal steroids or on estrous cyclicity of the female. However, castration of females at an early age increases their ability to entrain, whereas long-term castration of males seems to reduce entrainment ability. During entrainment to a 24-h light-dark cycle (LD 14:10), females were found to begin their daily activity before males and before castrated females. This difference is consistent with a sex difference in the magnitude of light-induced phase shifts and in entrainment of the pacemaker. However, evidence is given that the sex difference in activity onset might also be caused by a sex difference in the relationship of locomotor activity to the pacemaker in intact males and females.

Animals↗
PubMed1981

Processing of the ribonucleic acid in the large ribosomal subunits of Urechis caupo.

Ribosomal subunits were isolated from eggs or embryos of Urechis caupo, and the ribonucleic acid (RNA) was characterized by electrophoresis under denaturing conditions. The small ribosomal subunit contains a single 17S RNA sequence with a molecular weight of 6.20 X 10(5). The large ribosomal subunit contains four polynucleotide sequences. The 5S RNA has a molecular weight of 4.09 X 10(4). The 26S RNA complex isolated under nondenaturing conditions dissociates in the presence of formamide to yield a 5.8S RNA, molecular weight 5.46 X 10(4), and two approximately 17S and 17.5S RNA sequences with molecular weights of 6.04 X 10(5) and 6.61 X 10(5). The 17S and 17.5S RNAs of the large ribosomal subunits are formed in vivo from a 26S RNA precursor after assembly of the large ribosomal subunit. Large ribosomal subunits are transferred from the nucleus to the cytoplasm with the 26S RNA precursor intact. The hidden break to form the 17S and 17.5S RNAs is introduced in the cytoplasm. No intact 26S RNA could be detected in polysomes; this indicates that the conversion of the 26S RNA to the 17S and 17.5S RNAs may be required to produce large ribosomal subunits capable of participating in protein synthesis.

Animals↗
PubMed1980

Hamsters through time's window: temporal structure of hamster locomotor rhythmicity.

The temporal patterns of running-wheel locomotor activity of a group of 15 golden hamsters (Mesocricetus auratus) are described in detail. The temporal patterns of activity and the behavior of activity bouts in these animals provide the basis for a hypothetical multioscillator framework underlying locomotor activity. The framework consists of a pacemaker that controls the transitions between two continuous states, activity time and rest time, each composing approximately half of the circadian cycle. Activity time appears as a "window" during which the expression of locomotor bouts controlled by additional circadian oscillators is permitted. In our model, whether or not locomotor activity is expressed as well as its detailed temporal pattern are functions of the phase relationships between the window pacemaker and bout oscillators.

Animals↗
PubMed1976

Paediatric candidates' attitudes to computerized patient management problems in a certifying examination.

In September 1974 candidates who had taken a computerized patient managment problem examination (CPMP), as part of the certification process in paediatrics required by the Royal College of Physicians and Surgeons of Canada, completed a questionnaire designed to elicit their reactions to CPMPs. The results indicated that respondents were favourable to CPMPs, that there was little distraction caused by the equipment, logic or semantics of the problems, and that CPMPs were an acceptable examination technique. It was recommended that, in the future, CPMP examinees be allowed practice time to familiarize themselves with the equipment, that pre-examination instructions should be clarified, and that problems judged inadequate by candidates be revised.

Attitude of Health Personnel↗
PubMed1975

Unique sequence DNA transcripts present in mature oocytes of Urechis caupo.

DNA - DNA reannealing of sheared Urechis caupo DNA indicates that the genome is composed of two major repetitive sequence families. The repetitive sequence DNA families compose 8 and 7% of the DNA and are repeated in the genome on an average of 2.0 - 10-6 and 6.0 - 10-3 times, respectively. The unique sequence DNA composed a minimum of 75% of the genome and the rate of reannealing indicates a complexity of 2.6 - 10-8 nucleotide pairs per genome. Hybridization of isolated 3-H-labeled unique sequence DNA with an excess of unlabeled mature oocyte RNA provides a minimum estimate of the genetic diversity of the RNA present in the mature oocytes. The apparent saturation level of unique sequence DNA with RNA indicates that about 8.6% of the unique sequence DNA is expressed. Based on the fraction of the DNA that forms a stable hybrid and the complexity of the unique sequence DNA the RNA present in the mature oocyte is a complementary with 2.2 - 10-7 nucleotide pairs of unique sequence DNA.

Animals↗
PubMed1968

Ribosome biogenesis: nonrandom addition of structural proteins to 50S subunits.

Assemblage of structural proteins into 50S subunits was examined in Escherichia coli recovering fromt chloramphenicol treatment. Cells previously labeled with H3-leucine for three generations were incuibated for 30 minutes with chloramnlphenicol. Proteins synthesized during the initial 5 minuites of recovery from chlorarmphenicol treatmnent were labeled with C(14)-leucine. Marked variation in the ratios of C(14)- to H(3)-leucine in ribosomal protein occurred in cells that had been treated with chloramphenicol; luntreated cells displayed little variation. Thle resuilts sliggest that ribosomal proteins are assenmbled into 50S subunits in a nonrandom manner.

Bacterial Proteins↗