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Biomedical subjects

D A Barnes

Publications and source records attributed to D A Barnes.

At least 19 recordsLinked to original sources
PubMed1992

Selection for high-level chloroquine resistance results in deamplification of the pfmdr1 gene and increased sensitivity to mefloquine in Plasmodium falciparum.

A chloroquine resistant cloned isolate of Plasmodium falciparum, FAC8, which carries an amplification in the pfmdr1 gene was selected for high-level chloroquine resistance, resulting in a cell line resistant to a 10-fold higher concentration of chloroquine. These cells were found to have lost the amplification in pfmdr1 and to no longer over-produce the protein product termed P-glycoprotein homologue 1 (Pgh1). The pfmdr1 gene from this highly resistant cell line was not found to encode any amino acid changes that would account for increased resistance. Verapamil, which reverses chloroquine resistance in FAC8, also reversed high-level chloroquine resistance. Furthermore, verapamil caused a biphasic reversal of chloroquine resistance as the high-level resistance was very sensitive to low amounts of verapamil. These data suggest that over-expression of the P-glycoprotein homologue is incompatible with high levels of chloroquine resistance. In order to show that these results were applicable to other chloroquine selected lines, two additional mutants were selected for resistance to high levels of chloroquine. In both cases they were found to deamplify pfmdr1. Interestingly, while the level of chloroquine resistance of these mutants increased, they became more sensitive to mefloquine. This suggests a linkage between the copy number of the pfmdr1 gene and the level of chloroquine and mefloquine resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Normal variations of the posterior corneal surface.

Measurements of the sphero-cylindrical components of the rear corneal surface were taken from 80 healthy right eyes in order to determine normal variations. Dimensions of this surface were strongly influenced by the front corneal surface with the exception that the rear surface exhibited more toricity. Both surfaces tended to be flatter in males compared to females and in myopes compared to hyperopes. The corneal surfaces were also found to be flatter in younger eyes compared to older eyes, but this finding was most likely due to the preponderance of myopes in the young and hyperopes in the older group. The influence of the ratio of anterior: posterior corneal surface radius upon the estimation of total corneal power as required for intraocular lens implant calculations was also considered.

Adult↗
PubMed1992

A chromosome 9 deletion in Plasmodium falciparum results in loss of cytoadherence.

Many lines of Plasmodium falciparum undergo a deletion of the right end of chromosome 9 during in vitro culture accompanied by loss of cytoadherence and gametocytogenesis. Selection of cytoadherent cells from a mixed population co-selects for those with an undeleted chromosome 9 and the selected cells produce gametocytes. The deletion also results in loss of expression of PfEMP1, the putative cytoadherence ligand, suggesting that PfEMP1 or a regulatory gene controlling PfEMP1 expression and gametocytogenesis may be encoded in this region. We have isolated several markers for the deleted region and are currently using a YAC-P. falciparum library to investigate this region of the genome in detail.

Animals↗
PubMed1991

Posterior corneal surface toricity and total corneal astigmatism.

The influence of posterior corneal surface toricity upon total corneal astigmatism was investigated in 60 young subjects (mean age 22.04 +/- 3.24 years). Both surfaces were found to be flatter horizontally than vertically. Astigmatism arising from the anterior corneal surface was therefore reduced by astigmatism of the opposite sign arising from the posterior surface. Had the toricity of the posterior corneal surface been purely governed by that of the anterior surface this reduction would have amounted to about 5%. However, the posterior surface was found to exhibit additional toricity bringing about a greater reduction of total corneal astigmatism amounting to approximately 14%.

Adult↗
PubMed1991

Effect of iris displacement on oblique astigmatism in aphakic eyes.

Aphakic eyes possess considerably less oblique astigmatism than phakic eyes. The possibility that posterior iris displacement after lens extraction accounts for the observed reduction in oblique astigmatism is tested in this study. Oblique astigmatism was calculated for a phakic and an aphakic schematic eye. With no iris displacement little reduction of oblique astigmatism occurred contrary to experimental findings. However, introduction of varying levels of iris displacement reduced this aberration to values found experimentally. Posterior iris displacement (mean = 1.19 mm) was confirmed in vivo by pre- and postoperative anterior chamber pachometry in eight patients.

Adult↗
PubMed1991

Osteomyelitis of the talus: an unusual cause of limping in childhood.

Hematogenous osteomyelitis of the talus is a rare and infrequently considered cause of limping in children. We describe five children younger than 2 years of age with osteomyelitis of the talus who had a limp and a paucity of constitutional symptoms. Conventional radiography and scintigraphy were the imaging techniques used. The usual radiologic features include soft-tissue swelling and an osteolytic defect in the talus without sequestrum formation of periosteal reaction. Bone scans were positive in all cases and led to the localization of the lesion in two patients. Definitive diagnosis was made in all cases only after needle aspiration or open biopsy and curettage. Increased awareness of this unusual lesion and its subtle early radiologic manifestations will allow prompt diagnosis and treatment.

Gait↗
PubMed1990

Bloodstream and metacyclic variant surface glycoprotein gene expression sites of Trypanosoma brucei gambiense.

Trypanosoma brucei gambiense is the causative agent of chronic human sleeping sickness. Previous studies have indicated that T. b. gambiense isolates expressed the antigens U1 or L2 in both the metacyclic and early bloodstream form of the parasite life cycle. These studies suggested that L2 and U1 were likely to be metacyclic variant surface glycoproteins (mVSG). The basic copies of the genes encoding the VSGs L2 and U1 are present in single copy in non-expressing isolates of T. b. gambiense. Furthermore, they have been found to be maintained stably in a large number of stocks isolated from a wide geographic area over a 30-year period. The genomic DNA comprising the upstream 5' flanking regions of the U1 and L2 putative mVSG gene expression sites have been cloned from bloodstream forms of T. b. gambiense. The L2 expression site clone, containing 12.5 kb of sequences 5' to the VSG gene, was found to lack the 72/76-bp repeat unit generally found in the 'barren' region upstream of bloodstream form expression sites. The U1 expression site clone, containing 13.5 kb of the 5' flanking region, appeared to have the repeats, which were localized to 2 kb of DNA immediately 5' to the U1 mVSG gene. Neither the U1 nor the L2 clone was found to have ESAG2 or ESAG3 gene sequences, but both were found to have ESAG1 genes. The ESAG1 genes from the putative metacyclic expression sites and from the U1 and L2 bloodstream form expression sites (in the form of cDNA clones) were sequenced and compared to all other published ESAG1 sequences.

Amino Acid Sequence↗
PubMed1990

Measurement of posterior corneal surface toricity.

We describe a method in which posterior corneal surface toricity can be determined by photographing catoptric (Purkinje) images in three fixed meridians simultaneously using infrared light sources. Keratometry, the comparison of anterior and posterior corneal catoptric (Purkinje) images and pachometric results, are applied to three meridional analysis equations, allowing the posterior corneal surface to be described in spherocylindrical form. The technique is evaluated on five subjects with anterior corneal radii varying from 7.11 to 8.52 mm.

Cornea↗
PubMed1990

Measurement of the posterior corneal radius using slit lamp and Purkinje image techniques.

A method for measuring the radius of the posterior corneal surface using the first and second Purkinje images has recently been developed. Values for the posterior corneal radius in the vertical meridian obtained using this method are compared with those obtained using a more conventional slit lamp method. A good correlation was found between values obtained using the two methods.

Anthropometry↗
PubMed1989

Two variant surface glycoprotein genes distinguish between different substrains of Trypanosoma brucei gambiense.

Trypanosoma brucei gambiense differs from other T. brucei subspecies in the stability and conservation of its bloodstream form antigenic repertoire. Two variant surface glycoprotein (VSG) cDNA clones corresponding to the antigens U1 and L2 were isolated from T. b. gambiense bacteriophage lambda gt11 expression libraries and characterized. A third VSG cDNA clone, P1, was also examined. The L2 and U1 VSG genes are present in a large number of T. b. gambiense stocks isolated over a thirty-year period from different geographical areas of Africa, suggesting that they are stably maintained in the T. b. gambiense genome. These probes may be useful in epidemiological studies of Gambian sleeping sickness to differentiate between T. b. gambiense isolates.

Animals↗
PubMed1989

An evaluation of Bennett's method for determining the equivalent powers of the eye and its crystalline lens without resort to phakometry.

Refraction and optical components have been measured in 36 eyes using objective optometry, keratometry, ophthalmophakometry and A-scan ultrasonography. A computing scheme was used to confirm that the accumulated experimental errors for a phakometric technique tend to exceed the inherent errors of a new method which calculates the equivalent powers of the eye and its crystalline lens without resort to phakometry. Bennett's method was shown to be a valuable technique in biometric studies which obviates the need for lengthy experimental investigations.

Adult↗
PubMed1989

An analysis of three meridional keratometric measurement of the anterior corneal surface.

Analysis of measurements taken in three meridians of a toroidal optical surface can produce a spherocylindrical result without having to locate the principal meridians. This technique is assessed for the anterior corneal surface using keratometry. Good agreement is found with measurements taken in the principal meridians making this a suitable method for the assessment of the eye's optical surfaces by Purkinje image measurement.

Adult↗
PubMed1989

Calculation of crystalline lens radii without resort to phakometry.

A computing scheme was developed in 1988 to determine the equivalent powers of the eye and its crystalline lens without resort to phakometry. An adaptation to this scheme is described which allows calculation of the crystalline lens radii using an assumed average value for Q. The values obtained for lens radii using this method compare well with phakometric measurements made on 36 eyes (ocular refraction range -9.37 D to + 3.14 D) which suggests that the variations in Q for a large proportion of the population are small.

Accommodation, Ocular↗
PubMed1987

Effect of intrauterine iodine infusion on luteal function and blood PGF2a concentration in cycling goats.

Studies were conducted to determine the effect of iodine infusion on the luteal function of goats, as evident by blood progesterone concentration, and on plasma PGF2a levels. Ten cycling mixed breed goats were synchronized for estrus by PGF2a (5 mg) and given a single intrauterine iodine infusion on day 5 and on day 15 of the estrous cycle. Iodine infusion on day 5 (group II) resulted in shorter estrous length (8.2 days) and a 7-fold increase in plasma PGF2a concentration as compared to control animals (group I) given distilled water infusion. Similar infusion on day 15 (group III), on the other hand, failed to alter the estrous cycle length but induced a moderate increase in PGF2a concentration which lasted only for a brief period. The progesterone levels declined concomitantly as PGF2a levels rose after iodine infusion in group II animals but failed to decline until after 24 hours in group III animals. The studies indicate that the endometrium reacts to the chemical stimuli and releases PGF2a which, in turn, alters the luteal function.

Animals↗
PubMed1987

A method for raytracing through schematic eyes with off-axis components.

A linear algebraic method for tracing skew rays through aspheric surfaces is described. The advantage of this method is that the refracting surfaces can be translated and rotated with respect to each other. The method is used to investigate the optical factors affecting the location of Purkinje images.

Cornea↗