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Biomedical subjects

B Martin

Publications and source records attributed to B Martin.

At least 163 records · Page 9Linked to original sources
PubMed1997

Magnesium kinetics in adolescent girls determined using stable isotopes: effects of high and low calcium intake.

Magnesium kinetics were measured in five adolescent girls who were participating in a calcium balance study. Two calcium levels were fed in a randomized crossover design. After an acclimation period, 26Mg was consumed orally and 25Mg was given intravenously, and then blood, urine, and feces were collected for 14 days. Total magnesium and percent enrichment were determined, and data were fitted to a eight-compartment model. There was no significant difference between high and low calcium intakes for any of the parameters examined. Mean values for control (800 mg/day) and high (1,800 mg/day) calcium intake were as follows: Mg intake, 305 +/- 30 and 286 +/- 9 mg/day; absorption (percent), 44 +/- 7 and 39 +/- 9; absorption (mg/day), 134 +/- 35 and 110 +/- 28; urinary excretion, 96 +/- 22 and 101 +/- 31 mg/day; fecal excretion, 175 +/- 32 and 200 +/- 11 mg/day; and magnesium balance, 13 +/- 35 and -34 +/- 48 mg/day, respectively. In conclusion, high calcium intake did not alter magnesium kinetics or balance in adolescent girls.

Absorption↗
PubMed1997

Glomus tumor of the plantar arch: a case report with magnetic resonance imaging findings.

A 55-year-old woman with a 12-year history of a painful nodule in the subcutaneous fat layer of the plantar arch was evaluated with magnetic resonance imaging, followed by excisional biopsy. Pathology revealed a glomus tumor, which is extremely rare in the plantar surface of the foot. The magnetic resonance imaging studies are presented. The literature on glomus tumors in the foot is reviewed. This entity should be considered in the differential diagnosis of solitary plantar nodules when marked sensitivity to temperature or pressure is exhibited.

Diagnosis, Differential↗
PubMed1997

At least three subdomains of v-erbA are involved in its silencing function.

Several members of the thyroid hormone receptor (TR) family are able to switch from a transcriptional repressor to a transcriptional activator upon binding of their ligand. The oncogene v-erbA is a variant form of the TR unable to bind hormone and thus acts as a constitutive repressor. We demonstrate, using fusion proteins between the DNA-binding domain of the yeast factor GAL4 and the silencing domains of v-erbA and TR beta, that point mutations in three different regions severely affect their repression function. Furthermore, the three regions, each as an inactive fusion protein with the GAL4 DNA-binding domain, restore silencing activity when assembled on the same promoter. These observations define at least three silencing subdomains, SSD1-SSD3, which are involved in the silencing function of v-erbA. We propose a model in which full silencing activity is brought about by the combined interaction of each silencing subdomain with corepressors and/or basal transcription factors.

Amino Acid Sequence↗
PubMed1997

Stroke Belt initiative: the Tennessee experience.

African Americans have a higher rate of stroke than other U.S. population groups. As part of the 11-state "Stroke Belt" region, Tennessee has the fifth highest death rate from stroke in the country. In 1993, a two-year community-based project was initiated to reduce the incidence of stroke and its associated risk factors among African Americans. Three counties, Shelby (Memphis), Davidson (Nashville), and Hamilton (Chattanooga), were selected as project sites because of their large African American populations. Specific objectives of the project were to promote risk factor awareness in African Americans, assist African American churches and community groups in developing and implementing intervention programs, and build the capacity for intervention programs within African American communities by collaborating with a variety of community organizations. This article describes the program's approach, which included using both adults and youth as mentors. In addition, it presents major accomplishments and lessons learned in project implementation.

Adolescent↗
PubMed1997

Nocturnal ophthalmic arterial hemodynamics in primary open-angle glaucoma.

PURPOSE: Recent studies have found nocturnal reductions in systemic arterial blood pressure associated with progressive visual field loss in glaucoma. Although ocular ischemia has been hypothesized to link these two phenomena, it remains unknown if perfusion of the eye is reduced during the night in patients with glaucoma. PATIENTS AND METHODS: Nine patients with primary open-angle glaucoma (POAG) and stable visual fields who were free from systemic hypertension, as well as nine age- and gender-matched controls, were studied at 9:00 P.M., and then during sleep at 12:00, 3:00, and 6:00 A.M. Systemic blood pressure, intraocular pressure (IOP), and color Doppler imaging (CDI) of the ophthalmic artery were measured at each time. RESULTS: Arterial blood pressure and ophthalmic artery peak systolic and end-diastolic velocities were similar and were unchanged over time, in both groups. In contrast, the ophthalmic arterial resistance index decreased as the night progressed (p < 0.05), identically in controls and patients. In patients with glaucoma, CDI indices were independent of changes in arterial pressure, IOP, or calculated ocular perfusion pressure. CONCLUSION: Patients with POAG characterized by stable visual fields who were free from systemic hypertension exhibited normal ophthalmic arterial hemodynamics at night; there was no evidence of ocular ischemia or vasoconstriction.

Blood Pressure↗
PubMed1996

Mouse chromosome 9 involvement in beta-CCM-induced seizures.

Analysis of beta-CCM induced seizures in three inbred strains of mice, ABP/Le, C57BL/6J and C57BL/6ByJ, and their F1s and F2s progeny, allowed identification of a putative seizure susceptibility controlling locus on chromosome 9 near the short-ear locus. The involvement of a gene in the medial segment of this chromosome in both seizure activity and GABA-controlled behaviour is discussed.

Animals↗
PubMed1996

Cell death in the midbrain of the murine mutation weaver.

The midbrain of the adult homozygous weaver (wv/wv) mouse is notable for a reduction in the numbers of dopamine-containing cells in the substantia nigra (A9) and the retrorubral nucleus (A8). We have determined that the reduction in tyrosine hydroxylase (TH)-positive neurons in the ventral midbrain of the weaver is attributable to the loss of neurons after postnatal day 7 (P7). Because the number and spatial distribution of TH-positive mesencephalic neurons in wv/wv, heterozygous weavers (+/wv), and wild-type mice are not significantly different on P7, we conclude that the early developmental steps of proliferation and migration have taken place normally in the mutant. Although numbers and distribution of cells are normal in the wv/wv on P7, the appearance of the TH-stained ventral midbrain is abnormal because of the paucity of TH-stained dendritic processes. The ventrally extending TH-positive dendrites are largely absent in the young wv/wv. The wv/wv also can be distinguished from both homozygous normal (+/+) and wv/wv littermates on P7 based on the appearance of dendrites that are more numerous than in the wv/wv but thin, disorganized, and sparse compared with +/+. Most cell death seems to take place in wv/wv before P21. However, at least one subset of dopamine-containing neurons disappears later. The zone of densely packed TH-positive neurons in the substantia nigra that is likely to be the origin of innervation to striosomes in the caudoputamen disappears between P21 and adulthood. Despite the early pathology evident in the mesencephalic dopamine-producing neurons of the +/wv, no evidence for cell death was observed there even in the oldest +/wv weavers studied.

Aging↗
PubMed1996

The effect of systemically administered PDGF-BB on the rodent skeleton.

Platelet-derived growth factor (PDGF), an osteoblast mitogen, has been demonstrated to accelerate fracture healing and periodontal bone repair when applied locally in vivo. To explore whether PDGF could stimulate bone formation in intact bone, we administered it systemically to rats rendered acutely estrogen-deficient. Because PDGF may stimulate bone resorption in vitro, PDGF was administered with and without an antiresorptive agent (alendronate). All treatments were given by intravenous injection 3 times a week for 6 weeks. Spinal bone mineral density (BMD) decreased by 5% in the vehicle-treated ovariectomized (OVX) rats by the end of the study as determined by DXA. Treatment with PDGF prevented this bone loss and significantly (p < 0.05) increased the bone density in the spine (9%) and whole skeleton (5.8%). Combined treatment with PDGF and alendronate resulted in a greater increase at the spine (18%) and whole skeleton (12.8%) than either agent alone. Histomorphometric analysis demonstrated that treatment with PDGF increased the osteoblast number and osteoblast perimeter without consistent changes in osteoclast estimates. Biomechanical testing demonstrated that PDGF administration increased the vertebral body compressive strength and femoral shaft torsional stiffness and resulted in a trend for enhanced femoral head shearing strength. Coadministration of alendronate further increased these indices of bone strength. PDGF administration also caused premature closure of the growth plate, decreased body fat, and resulted in extraskeletal collagen deposition. We therefore demonstrate, for the first time, that systemic administration of PDGF can increase bone density and strength throughout the skeleton.

Absorptiometry, Photon↗
PubMed1996

A mouse mutant strain highly resistant to methyl beta-carboline-3-carboxylate-induced seizures.

The convulsant properties of methyl beta-carboline-3-carboxylate (beta-CCM) were evaluated in the TaT-fm/GncTa+/+Tfm strain carrying the tabby coat color (Ta) and/or the testicular feminization (Tfm) gene. When injected intraperitoneally within a 5-60 mg/kg dose range, beta-CCM-induced convulsions in less than 25% of the mice, thus providing evidence for a high resistance of this strain, as compared to classical strains of mice. However, this strain responds normally to the convulsant pentylenetetrazol (PTZ), suggesting a specific resistance to beta-CCM. Both the Ta gene and the TaTfm/Gnc genetic background were involved in the high resistance to beta-CCM. In addition, concentrations of neurosteroids and benzodiazepine binding, both modulating GABAA receptor efficacy, have been measured in order to elucidate the biological mechanisms of drug resistance.

Animals↗
PubMed1996

Manual performance and laterality in twins of known chorion type.

Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8-12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used; dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.

Child↗
PubMed1996

Vocalizations in newborn mice: genetic analysis.

Two kinds of vocalizations are produced by newborn mice: whistles (between 50 and 150 ms in length), having a narrow bandwidth in each strain that ranges from 30 to 90 kHz; and clicks, which are shorter (about 1 ms) and have a larger bandwidth. These vocalizations were individually recorded in 1-day-old pups from seven inbred strains of laboratory mice, at two temperatures (23 +/- 0.5 and 15 +/- 0.5 degrees C). The numbers of clicks and whistles were counted under these two conditions. Moreover, the length and frequencies at the beginning, apex, and end of the whistles were measured during the 15 degrees C condition. Correlations, including several components-additivity, epistasis (between homozygous loci), and maternal environment-were calculated between the characteristics of the whistles during the 15 degrees C condition. Clicks and whistles were also counted from 1 to 8 days of age during the 15 degrees C condition. The numbers of clicks and whistles were age dependent, with a decrease from day 1 to day 8 for the clicks and a consistent production of whistles. A quantitative genetic analysis was also performed on the 1-day-old pups from the Mendelian generations produced by the inbred strains most contrasting for the number of whistles produced in the cold condition: NZB/BINJ and CBA/H. The heterozygous genotype of the mother induced an increment of the number of whistles. Moreover, a significant part of the additive variance was suspected from the first design, and found with the second one, for this variable. Quantitative genetic analysis showed significant dominance and epistasis between homozygous loci and homozygous and heterozygous loci. This points to multigenic correlates for the number of whistles in this population. The significant additive values for all the variables recorded during the 15 +/- 0.5 degrees C condition and for the number of whistles produced during the 23 +/- 0.5 degrees C condition are compatible with an effect that indicates neither directional nor stabilizing selection. This result is examined in the light of the multichannel sensorial process implicated in maternal behavior in mice.

Animals↗
PubMed1996

Retinal blood flow during dynamic exercise.

BACKGROUND: Exercise acutely lowers intraocular pressure (IOP) and raises arterial pressure. We wondered whether the resultant increase in ocular perfusion pressure would alter retinal blood flow. METHODS: To investigate this question, 11 healthy volunteers each performed progressive cycle ergometer exercise until exhaustion was reached in 5-10 min. Immediately after exercise, retinal blood flow and arteriovenous passage time were determined by video fluorescein angiography. Ten other volunteers performed repeated episodes of cycle ergometer exercise at approximately 60% of the maximal aerobic capacity, immediately prior to estimates of macular leukocyte velocity and density via blue-field stimulation. RESULTS: Progressive exercise lowered IOP and elevated calculated ocular perfusion pressure. Within the retinal circulation, this exercise tended to raise mean dye velocity, as it significantly narrowed the superior temporal artery and vein; as a result, calculated retinal blood flow was unchanged. Simultaneously, retinal arteriovenous passage time was substantially shortened. Blue-field simulation showed that exercise increased macular leukocyte velocity while leaving leukocyte density unchanged. CONCLUSIONS: These results show that the normal retinal hemodynamic response to increases in perfusion pressure on dynamic exercise includes vasoconstriction that normalizes flow and faster capillary and overall retinal blood transit.

Adult↗