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Biomedical subjects

S C Sharma

Publications and source records attributed to S C Sharma.

At least 271 records · Page 15Linked to original sources
PubMed1982

Retinofugal pathways in juvenile and adult channel catfish, Ictalurus (Ameiurus) punctatus: an HRP and autoradiographic study.

The retinal projections of the juvenile and adult channel catfish, Ictalurus (Ameiurus) punctatus, were studied by using horseradish peroxidase (HRP) and autoradiography. The contralateral optic tract sends fibers to the suprachiasmatic nucleus (SCN) and divides into lateral (LOT) and medial optic tracts (MOT). In the adult fish, the former is thicker than the latter, whereas in the juvenile form, the reverse is true. The MOT curves laterally and divides into eight to 15 medial fascicles of the optic tract (MFOT). The contralateral optic fibers project to the nucleus opticus dorsolateralis, nucleus of the posterior commissure, nucleus geniculatus lateralis, pretectal nuclear complex, nucleus corticalis, stratum fibrosum et griseum superficiale (SFGS), and a few optic fibers extend into the stratum griseum centrale. The tractus opticus accessorius arises from the posterodorsal margin of the LOT and extends ventromedially to project to the nucleus opticus accessorius. At the optic chiasm a few fibers do not decussate, and these fibers project to almost all ipsilateral sites similar to those of the contralateral side, including the optic tectum. The autoradiographic observations substantiated the analysis of optic fiber projections provided by the HRP technique.

Animals↗
PubMed1982

Dosimetric analysis of stereo and orthogonal reconstruction of interstitial implants.

We have evaluated the performance of stereo and orthogonal computerized three-dimensional implant reconstruction algorithms. Sets of orthogonal and stereo radiographs of a simulated interstitial seed implant were taken. Computer reconstructed coordinates of each source were compared with their measured positions in order to assess the geometric accuracy of the two methods. We find that the effect of random measurement errors on reconstructed coordinates from stereo films is 3-5 times that of the orthogonal method. Although relative individual seed positions may be in error by as much as 1 cm, these errors do not significantly change the shape or area of isodose curves surrounding the implant periphery.

Brachytherapy↗
PubMed1982

Methods for routine calibration of brachytherapy sources.

Two types of routine geometry calibrators, the nuclear medicine dose calibrator and a Lucite jig holding a 30-ml external beam ion chamber with the source in a rigid geometry, were compared with open-air measurements for 137Cs, 192Ir, and 226Ra brachytherapy sources. The proximity of scattering surfaces in the second apparatus resulted in significant distortion of the buildup effect and deviation from the inverse square law (5% to 15%). For the dose calibrator, the response/Roentgen was found to be dependent not only on source energy, but on source capsule thickness as well. Approximately one half of the observed variation (27%) in calibration factors was accounted for by differences in filtration among sources. A mathematical logarithm that corrects for these geometric and filtration effects is presented. In addition, the activity assay procedure provided by the manufacturer of the dose calibrator is shown to be unsuitable for brachytherapy sources. Steps to overcome these problems are discussed.

Brachytherapy↗
PubMed1982

Axonal transport and transcellular transfer of nucleosides and polyamines in intact and regenerating optic nerves of goldfish: speculation on the axonal regulation of periaxonal cell metabolism.

The axonal transport, metabolism, and transcellular transfer of uridine, adenosine, putrescine, and spermidine have been examined in intact and regenerating optic nerves of goldfish. Following intraocular injection of labeled nucleosides, axonal transport was determined by comparing left-right differences in tectal radioactivity, and transcellular transfer was indicated by light autoradiographic analysis. The results demonstrated axonal transport, transcellular transfer, and periaxonal cell utilization of both nucleosides in intact axons and severalfold increases of all of these processes in regenerating axons. Experiments in which the metabolism of the nucleosides was studied resulted in data which suggested that uridine and adenosine, when delivered to the tectum by axonal transport, are protected from degradation and thus are relatively more available for periaxonal cell utilization than nucleosides reaching these cells via the blood. In intact axons, the majority of the nonmetabolized radioactivity was present as UMP, UDP, and UTP following [3H]uridine injections, whereas the majority of the radioactivity following [3H]adenosine injections was present as adenosine, with the phosphorylated derivatives constituting a smaller proportion. During nerve regeneration, the relative proportion of nucleosides to nucleotides was reversed, with uridine being the principal labeled compound in the first case, and AMP, ADP, and ATP being the major labeled compounds in the latter case. The nucleosides also were found to be different from each other in that adenosine, but not uridine, can be taken up by optic axons and transported retrogradely from the tectum to retinal ganglion cell bodies in the eye. Following intraocular injection of [3H]spermidine, radioactivity was transported to the optic tectum and transferred to tectal cells in the vicinity of the regenerating axons. Following [3H]putrescine injections, silver grains were found over periaxonal glia, but preliminary findings suggest that they are not present over tectal neurons nor over radial glial cells in the periependymal layers. Analysis of tectal radioactivity showed in each case that it was composed primarily of the injected compounds. These studies indicate that, following axonal transport, the polyamines do not remain within regenerating axons but are transferred to cells surrounding the axon. On the basis of these and previous findings, we speculate that the axonal transport and transcellular transfer of uridine, adenosine, polyamines, and perhaps other small molecules are means of communication between axons and periaxonal cells; that the axon can affect RNA and protein synthesis in periaxonal cells by regulating the availability of these small molecules; and that, during nerve regeneration, the increased metabolic needs of periaxonal cells are met by an increased axonal supply of precursors (adenosine and uridine) and other molecules (polyamines) critical for protein synthesis.

Adenosine↗
PubMed1982

In vivo and in vitro drug metabolism in patients with leprosy.

Plasma antipyrine and chloramphenicol clearance was studied in 23 patients of leprosy and 12 control subjects. Drug metabolising enzymes (aminopyrine N-demethylase and bilirubin UDP-glucuronyl transferase) were estimated in liver biopsy samples of twelve patients and ten controls. A significant decrease in drug clearance and drug metabolising enzymes was observed. However, no significant correlation could be obtained between drug half lives and drug metabolising enzymes or with any of the liver function tests in these patients. The findings indicate that drug metabolism is impaired in leprosy patients.

Adolescent↗
PubMed1982

Interactions of ascorbic acid with prostaglandins.

Samples of blood, urine and ovarian tissues of non-pregnant cycling guinea-pigs were obtained from day 3 before until day 2 after oestrus. In addition placental specimens were obtained from 49- to 62-day pregnant guinea-pigs. In a separate series of experiments blood samples of normally menstruating and dysmenorrhoeic women were collected daily during the last one week preceding and the first two days of the menstrual cycle. Plasma and tissue samples were analyzed simultaneously for ascorbic acid (AA) and prostaglandins (PGs) E2 and F2 alpha. The urine and leukocyte samples were estimated for AA only. The results demonstrate that the ovarian AA depletion at ovulation is not associated with a rise in urinary, plasma or leukocyte levels. From about the 8th week of pregnancy in the guinea-pig the placental levels of AA start to decline, while the concentrations of PGs start to rise. During the late luteal phase, the plasma of normally cycling women has a PGD2 alpha/PGE2 ratio of about 0.6. In the dysmenorrhoeic women this ratio varies from 0.9 to 1.3. In addition, the plasma and leukocyte levels of AA in the dysmenorrhoeic women are lower than the levels found in the normally cycling women. The results of both animal and human studies indicate that an inverse relationship exists between the levels of AA and the amount of PGF2 alpha synthesized and/or released in the body tissues. It is suggested that AA acts to control the ratio between PGF2 alpha and PGE2 and therefore forms an integral part of the adenyl/guanylate cyclase system. The mechanism for the fall in tissue ascorbic acid is however not known. The results suggest that this is due to increased break-down and/or rapid consumption of AA in the body tissues. In addition the reduction in placental tissue levels of AA near term could be due to its redistribution from maternal to foetal tissues.

Animals↗
PubMed1982

Relationship of total ascorbic acid to prostaglandins F2 alpha and E2 levels in the blood of women during the 3rd trimester of normal pregnancy.

Concentrations of Prostaglandins E2 and F2 alpha in the peripheral venous blood of women during the third trimester of normal pregnancy have been estimated using radioimmunoassay techniques. These values have been related to the levels of total ascorbic acid in the blood. It appears that AA acts to control the ratio between PGE2 and PGF2 alphja in the body. This effect may in turn be mediated via its actions on histamine levels. We have already suggested that AA acts as a modulator to control the synthesis, release and/or breakdown of histamine in the body.

Ascorbic Acid↗
PubMed1982

Levels of total ascorbic acid, histamine and prostaglandins E2 and F2 alpha in the maternal antecubital and foetal umbilical vein blood immediately following the normal human delivery.

Concentrations of total ascorbic acid (AA), histamine and prostaglandins (PGs) E2 and F2 alpha in the maternal antecubital vein and the foetal umbilical vein blood immediately following the normal vaginal delivery have been estimated. The results demonstrate that umbilical blood contains 1.5 to 2.7 times higher values of AA than the maternal blood. The ratio between PGF2 alpha and PGE2 is also wide in the umbilical blood than the antecubital vein blood. In the maternal blood the mean ratio between the two PGs is 1 : 0.7. In the foetal umbilical blood the mean ratio between PGF2 alpha and PGE2 is 1:1.98.

Ascorbic Acid↗
PubMed1981

Retinal projection in a non-visual area after bilateral tectal ablation in goldfish.

If, in the adult goldfish, one optic tectum is ablated, the regenerating optic axons from the contralateral retina innervate the remaining tectum, where they form a retinotopically ordered map. The pathway for this induced ipsilateral projection coincides with many of the pathways which normally connect the two tecta, but early in regeneration the optic fibres also enter non-visual centres to which there are degenerating tectal efferent pathways to follow. We have therefore now investigated the fate of regenerating optic axons in goldfish from which both optic tecta have been removed; they are found to innervate non-visual centres, where again they generate a retinotopic map.

Animals↗
PubMed1981

Organization of extrinsic tectal connections in Goldfish (Caraccius auratus).

Nonretinal sources of tectal afferents, the laminar and regional organization of the inputs, and the relation of the tectum with primary and secondary visual and motor centers in goldfish were studied following HRP injections in the optic tectum, orbit of the eye, cerebellum, pretectal area, and dorsolateral mesencephalic tegmentum. Ipsilateral tectal afferents include the area dorsalis centralis of the forebrain, the nucleus dorsalis lateralis of the thalamus, the area pretectalis, the nucleus pretectalis, a nucleus in the rostral mesencephalic tegmentum, the torus longitudinales, the torus semicircularis, a dorsolateral tegmental nucleus, the nucleus isthmi, and a rostral cell group of the nucleus motorius tegmenti. Comparison of results in a series of tectal HRP injections which differed in depth, tangential extent, and location indicated that projections from the area pretectalis, nucleus pretectalis, and nucleus isthmi terminate in the stratum fibrosum et griseum superficiale of the tectum. Terminals of the forebrain and nucleus dorsolateralis and contralateral tectum are sparse and widely branching. Projections from the area and nucleus pretectalis tend to terminate in the rostral tectum, and those from the contralateral tectum, torus semicircularis, dorsolateral tegmental nucleus, and nucleus motorius tegmenti terminate preferentially in the caudal tectum. Cells of origin of extrinsic tectal efferents were also identified following HRP injections in the pretectal area and mesencephalic tegmentum. Proximal dendrites and axons of these cells were labeled sufficiently to allow comparison with morphological types characterized in Golgi studies. HRP injections in the cerebellum labeled cells bodies in the area pretectalis, nucleus pretectalis, and the nucleus of the posterior commissure. Double label experiments with intraocular injection of tritiated proline demonstrated direct retinal input to these three areas. No indications of direct connections between the tectum and cerebellum were found following tectal or cerebellar HRP injections.

Animals↗