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Biomedical subjects

D A Nelson

Publications and source records attributed to D A Nelson.

At least 37 records · Page 2Linked to original sources
PubMed1999

Whole body bone mass and body composition in a girl with achondroplasia, at ages 9 through 12.

A 9-yr-old white female with achondroplasia was one of a group of 773 children who were recruited for a study of the accumulation of whole body skeletal mass during four annual measurements. Measurements of bone, fat, and lean mass were obtained with a Hologic 1000W instrument. The following variables are used to compare the subject with the 130 healthy white girls who participated in the study: bone mineral content (BMC), bone mineral density (BMD), and bone mineral apparent density (BMAD). Ratios of BMC to weight or BMC to height, and BMD to weight or height, were also calculated. We found that the BMC of the subject was lower when compared to the reference group, but the ratios of BMC to weight or BMC to height were similar in both. BMD was also lower in the patient, but, when expressed in relation to height and weight, the ratios were similar or slightly higher in the case. BMAD was higher in the subject with achondroplasia at all ages. The subject had a lower percentage fat and higher percentage lean mass than the reference children. We conclude that the accumulation of bone mass in this subject with achondroplasia is appropriate for her reduced body size.

Achondroplasia↗
PubMed1999

Training psychiatric residents for Part II of the American Board of Psychiatry and Neurology Examination.

Of the physicians who took the American Board of Psychiatry and Neurology (ABPN) Examination, Part II, in 1995, 41% failed. The Accreditation Council for Graduate Medical Education (ACGME) requires that residency psychiatry programs conduct an organized evaluation of residents' clinical skills at least twice during the 4 years of training. At the University of Oklahoma Health Science Center-Tulsa, the residents attend formal didactic instruction on conducting a psychiatric interview. Having gained this didactic foundation, they then participate in actual patient interviews. First- and 3rd-year residents are mock examiners, paired with an experienced board-certified psychiatrist. Second- and 4th-year residents examine an actual patient. A survey evaluating this curriculum was rated as very good to excellent by the participants.

Curriculum↗
PubMed1998

Brain temperature and limits on transcranial cooling in humans: quantitative modeling results.

Selective brain cooling (SBC) of varying strengths has been demonstrated in a number of mammals and appears to play a role in systemic thermoregulation. Although primates lack obvious specialization for SBC, the possibility of brain cooling in humans has been debated for many years. This paper reports on the use of mathematical modeling to explore whether surface cooling can control effectively the temperature of the human cerebrum. The brain was modeled as a hemisphere with a volume of 1.33 1 and overlying layers of cerebrospinal fluid, skull, and scalp. Each component was assigned appropriate dimensions, physical properties and physiological characteristics that were determined from the literature. The effects of blood flow and of thermal conduction were modeled using the steady-state form of the bio-heat equation. Input parameters included core (arterial) temperature: normal (37 degrees C) or hyperthermic (40 degrees C), air temperature: warm (30 degrees C) or hot (40 degrees C), and sweat evaporation rate: 0, 0.25, or 0.50 l x m(-2) x h(-1). The resulting skin temperatures of the model ranged from 31.8 degrees C to 40.2 degrees C, values which are consistent with data obtained from the literature. Cerebral temperatures were generally insensitive to surface conditions (air temperature and evaporation rate), which affected only the most superficial level of the cerebrum (< or =1.5 mm) The remaining parenchymal temperatures were 0.2-0.3 degrees C above arterial temperatures, regardless of surface conditions. This held true even for the worst-case conditions combining core hyperthermia in a hot environment with zero evaporative cooling. Modeling showed that the low surface-to-volume ratio, low tissue conductivity, and high rate of cerebral perfusion combine to minimize the potential impact of surface cooling, whether by transcranial venous flow or by conduction through intervening layers to the skin or mucosal surfaces. The dense capillary network in the brain assures that its temperature closely follows arterial temperature and is controlled through systemic thermoregulation independent of head surface temperature. A review of the literature reveals several independent lines of evidence which support these findings and indicate the absence of functionally significant transcranial venous flow in either direction. Given the fact that humans sometimes work under conditions which produce face and scalp temperatures that are above core temperature, a transcranial thermal link would not necessarily protect the brain, but might instead increase its vulnerability to environmentally induced thermal injury.

Body Temperature↗
PubMed1998

Anterior forebrain pathway is needed for stable song expression in adult male white-crowned sparrows (Zonotrichia leucophrys).

The anterior forebrain pathway of the avian song system is involved in juvenile song learning, but its function in adult song behavior is not known. This report uses lesions to study the role of a particular forebrain nucleus, IMAN, in the seasonal regeneration of song in adult white-crowned sparrows (Zonotrichia leucophrys oriantha). White-crowned sparrows, even when acoustically isolated as juveniles, crystallize a single song which they maintain throughout adulthood. The lateral portion of the magnocellular nucleus of the anterior neostriatum (1MAN) was lesioned bilaterally in adult males maintained on short days (8 h of light). Daylength was increased to 16 h following the surgeries, and all birds were recorded in the post-lesion singing season. Lesioned birds showed a large decrease in song note frequency following the lesions, significantly larger than did intact, age-matched controls. Further changes were seen in the post-lesion songs of seven of 11 successfully lesioned males. These changes included variability in song pattern, loss of frequency control and addition of new notes, some of which had been practiced during juvenile song development. These changes seemed especially large in birds that had either been acoustically isolated or had not fully copied a tape-tutor song during juvenile song development. These results are the first to indicate that the motor memories for song elements that had been practiced and discarded early in life are retained, and they suggest that 1MAN affects seasonal song expression by selectively reinforcing a particular song pattern.

Animals↗
PubMed1998

Overt and relational aggression in Russian nursery-school-age children: parenting style and marital linkages.

Maternal and paternal parenting styles and marital interactions linked to childhood aggressive behavior as described in Western psychological literature were measured in an ethnic Russian sample of 207 families of nursery-school-age children. Results corroborated and extended findings from Western samples. Maternal and paternal coercion, lack of responsiveness, and psychological control (for mothers only) were significantly correlated with children's overt aggression with peers. Less responsiveness (for mothers and fathers) and maternal coercion positively correlated with relational aggression. Some of these associations differed for boys versus girls. Marital conflict was also linked to more overt and relational aggression for boys. When entered into the same statistical model, more marital conflict (for boys only), more maternal coercion, and less paternal responsiveness were found to be the most important contributors to overt and relational aggression in younger Russian children.

Adult↗
PubMed1998

Double esterase staining and other neutrophilic granule abnormalities in 237 patients with the myelodysplastic syndrome studied by the cancer and leukemia group B.

We investigated double (specific and nonspecific) esterase (DE) staining in marrow cells of 237 patients with the myelodysplastic syndromes (MDS). Additional abnormalities of neutrophilic granules were examined cytochemically and immunocytochemically for myeloperoxidase activity and antigen elastase, lactoferrin and CD15 granule-membrane glycoproteins. Abnormal DE staining (>/=3% of all nucleated marrow cells) was present in 27% of patients with no difference among different MDS subtypes. However, the prevalence of high abnormal DE staining (>/=10%) was significantly lower in refractory anemia with excess blasts in transformation (1%) compared to other MDS subtypes (12-15%; p = 0.004). The prevalence of other granule abnormalities was not statistically different in the DE normal and DE abnormal groups. Abnormal DE staining is relatively common among all MDS subtypes. High DE staining may identify a subgroup of patients with a lower grade MDS.

Bone Marrow Cells↗
PubMed1998

Prevalence of osteoporosis in women referred for bone density testing: utility of multiple skeletal sites.

The objective of this study was to determine retrospectively the prevalence of osteoporosis in a referral population and to compare the effectiveness of measuring multiple skeletal sites for identifying osteoporosis. Although osteoporosis is considered to be a major public health problem in the United States, and there are reliable methods for diagnosis based on bone densitometry, fewer than 25% of cases are currently identified. There is no consensus about which skeletal site(s) should be measured for optimal results. In this study, bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) at the radius (proximal site), lumbar spine, femoral neck, and total proximal femur regions in 537 consecutive white females age 50 and older referred by community physicians for bone densitometry. The prevalence of osteopenia and osteoporosis (based on the World Health Organization definitions) was determined, as well as the incidence of misclassification of patients based on different skeletal sites. Overall, 53.3% had osteoporosis, an additional 37.7% had osteopenia, and only 8.7% had normal BMD at all measurement sites. The prevalence was similar at all measurement sites and the incidence of misclassification was low. Given the magnitude of undetected osteoporosis and the efficacy of bone densitometry at any skeletal site, these data have important implications for the optimal deployment of bone density measurement facilities.

Journal Article↗
PubMed1998

Peripheral bone densitometry: an old friend revisited.

The earliest assessments of bone "mass" involved metacarpal morphometry that provided insight into age-related changes, the effects of low habitual dietary calcium intake, and the effects of estrogen deficiency and replacement. Single photon absorptiometry (SPA) made quantitative mass measurement possible but this was intellectually unsatisfactory since osteoporotic fractures are more of a concern at the spine and hip than at the wrist. Necessity forced the development of axial bone mass measurement (dual photon absorptiometry--DPA, dual energy xray absorptiometry--DXA, quantitative computed tomography--QCT). Hip measurements provide a better prediction of hip fracture risk than measurements at any other skeletal site. For every standard deviation decrement of bone mass at the hip, relative risk of fracture is 3.0. At non-hip sites the relative risk is only 2.0 for each standard deviation decrement in bone mass. However measurement at non-hip sites provide a fracture risk prediction that is at least the equal of blood pressure measurement for predicting risk of CVA, and substantially better than the risk assessment of acute MI afforded by cholesterol measurement. An important caveat of the superiority of hip measurement is that the data are derived from short-term studies in older women (> 70 years). The relative risk data from phalangeal, forearm, and heel measurements have all been obtained from longer-term studies in younger women. From a community health perspective, bone density measurements, no matter how accurate, precise, and meaningful, have limited value if access to the technology is limited. Peripheral measurements can be obtained on existing radiographic equipment (phalanges), or small, portable, inexpensive dedicated equipment (forearm, heel). This technology is more likely to make it to the office of the primary care physician than the larger, more expensive, dedicated equipment needed for hip measurements. The peripheral measurement technology is also suitable for high traffic areas, just as blood pressure and cholesterol measurements are widely available. This presentation reviewed the scientific validity of peripheral bone mass measurement and explored the potential for making this technology available at non-traditional facilities such as pharmacies, shopping malls, health clubs, etc.

Absorptiometry, Photon↗
PubMed1998

Periarticular osteoporosis in osteoarthritis of the knee.

OBJECTIVE: To test the hypothesis that bone mineral density (BMD) in periarticular subchondral regions of the knee joint is abnormal in patients with osteoarthritis (OA). METHODS: Sixty-two knees from patients with relatively mild OA (primarily radiographic grades 0, 1, 2) of the knee were compared with 62 knees from normal subjects matched for age, sex, race, and body side (right or left). BMD of the lumbar spine, distal femoral shaft, and several periarticular subchondral regions of the knee were determined by dual energy x-ray absorptiometry (DXA). To facilitate increased accuracy of BMD values, lateral DXA of the knees was also performed and used to provide a third dimension to the usual two-dimensional anterior-posterior g/cm2, producing measurements as g/cm3. Subchondral bone regions included both superficial and deep regions of the medial femoral, medial tibial, and lateral tibial compartments. RESULTS: BMD (g/cm3) was lower than normal in 6 subchondral bone regions of the knees (n=43) of white female patients with OA (average decrease -13.3%), significant in all 6 subchondral regions (p=0.001 to p=0.047). Two-dimensional BMD (g/cm2) was lower than normal in 6 subchondral regions of the knees (n=43) of white female patients with OA (average decrease -7.3%), significant in only 2 of 6 subchondral regions (p=0.011 to p=0.014). BMD (g/cm3) was lower than normal in 6 subchondral regions of the knees (n=19) of African American female patients with OA (average decrease -9.1%), significant in only one of the 6 subchondral regions (p=0.016). There was no significant difference in spinal BMD (L1-L4) or femoral shaft BMD between normal and OA for either racial group. About 13% of the OA patients had osteoporosis at the spine. CONCLUSION: A significant decrease in periarticular subchondral BMD is present in female patients with relatively mild OA of the knee whether or not they had osteoporosis based on a spine BMD measurement.

Absorptiometry, Photon↗
PubMed1997

Fast synaptic signaling by nicotinic acetylcholine and serotonin 5-HT3 receptors in developing visual cortex.

Cholinergic and serotonergic fiber systems invade the developing visual cortex several weeks before eye opening; both transmitters have been implicated in plasticity of neocortical circuits. These transmitters have been presumed to act predominantly through second messenger-coupled receptors, because fast cholinergic or serotonergic neurotransmission has never been observed in neocortex. However, acetylcholine and serotonin also act on ligand-gated ion channels; the nicotinic acetylcholine receptor and the serotonin 5-HT3 receptor, respectively. Here, using whole-cell patch-clamp techniques in developing ferret visual cortex, we pharmacologically isolated fast, spontaneous, and evoked cholinergic and serotonergic synaptic events in pyramidal cells and interneurons of all cortical layers. The number of cells receiving such inputs increased with the ingrowth of thalamic afferents, and the frequencies of the spontaneous events increased at eye opening. Thus, both acetylcholine and serotonin can mediate fast synaptic transmission in the visual cortex; the early onset of these mechanisms suggests a role during initial stages of circuit formation and during subsequent experience-dependent remodeling of cortical connections.

Acetylcholine↗
PubMed1997

Characterization of the mitotic phase pRb-directed protein phosphatase activity.

We have previously reported on the M-phase specific dephosphorylation of pRb and identified a type 1 serine/threonine protein phosphatase (PP1) as the enzyme mediating pRb dephosphorylation. In this report, we have characterized the pRb-directed phosphatase activity found in mitotic cells with respect to dose dependence and demonstrate that the pRb isoform conversion detected in vitro mirrors the pRb isoform conversion which occurs during mitosis of intact cells. Cell fractionation and PP1 catalytic subunit isolation studies support the notion that the pRb-directed phosphatase activity involves subpopulations of PP1 catalytic subunits. Coprecipitation studies revealed that PP1 can form a complex with hypophosphorylated pRb which was converted from the hyperphosphorylated form in mitotic cell extracts. Taken together with data from previous reports in the literature, a model for the regulation of PP1 activity towards pRb during mitotic exit is proposed.

Animals↗
PubMed1997

High molecular weight protein phosphatase type 1 dephosphorylates the retinoblastoma protein.

pRb controls cell proliferation by restricting inappropriate entry of cells into the cell division cycle. As dephosphorylation of pRb during mitotic exit activates its growth suppressive function, identification of the protein phosphatase that dephosphorylates pRb, and characterization of the mechanism of its regulation, are essential to elucidating the mechanisms of cell growth control. By fractionating mitotic CV-1P cell extracts, we identify the protein phosphatase which dephosphorylates pRb as a type 1 serine/threonine phosphoprotein phosphatase (PP1). Molecular sizing analyses indicate that the catalytic enzyme (PP1c) is present in a high molecular weight complex, with a predicted molecular mass of 166 kDa. PP1-interacting proteins in the mitotic cell extracts are identified. Two PP1-interacting proteins (41 and 110 kDa) are shown to form distinct complexes with PP1c from fractions of separated mitotic cell extracts containing phosphorylase phosphatase activity. However, only the 110-kDa PP1-interacting protein is present in fractions containing pRb-directed phosphatase activity, identifying this protein as a putative activator of PP1 function toward pRb during mitosis.

Animals↗