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S C Singh

Publications and source records attributed to S C Singh.

13 recordsLinked to original sources
PubMed2006

Seismic reflection images of the Moho underlying melt sills at the East Pacific Rise.

The determination of melt distribution in the crust and the nature of the crust-mantle boundary (the 'Moho') is fundamental to the understanding of crustal accretion processes at oceanic spreading centres. Upper-crustal magma chambers have been imaged beneath fast- and intermediate-spreading centres but it has been difficult to image structures beneath these magma sills. Using three-dimensional seismic reflection images, here we report the presence of Moho reflections beneath a crustal magma chamber at the 9 degrees 03' N overlapping spreading centre, East Pacific Rise. Our observations highlight the formation of the Moho at zero-aged crust. Over a distance of less than 7 km along the ridge crest, a rapid increase in two-way travel time of seismic waves between the magma chamber and Moho reflections is observed, which we suggest is due to a melt anomaly in the lower crust. The amplitude versus offset variation of reflections from the magma chamber shows a coincident region of higher melt fraction overlying this anomalous region, supporting the conclusion of additional melt at depth.

Journal Article↗
PubMed2002

RP-LC determination of oleane derivatives in Terminalia arjuna.

A rapid sensitive and reproductive reversed phase high performance liquid chromatographic method with photo diode arrray detection is described for the simultaneous quantification of major oleane derivatives: arjunic acid (4), arjunolic acid (3), arjungenin (2) and arjunetin (1) in Terminalia arjuna extract. The method involves the use of a Waters Spherisorb S10 ODS2 column (250 x 4.6 mm, I.D., 10 microm) and binary gradient mobile phase profile. The various other aspects of analysis viz. Extraction efficiency, peak purity and similarity were validated using a photo diode array detector.

Calibration↗
PubMed2001

New naphthoquinones from Arnebia hispidissima roots.

Besides shikonin and arnebifuranone, two new shikonin esters isolated from the roots of Arnebia hispidissima have been characterized as butylshikonin and 2'-methyl-hexa-1',3'-dienoylshikonin by physicochemical methods. Arnebifuranone is the first report from this species.

Food Coloring Agents↗
PubMed1999

Persistency of bioactive fractions of Indian plant, Polygonum hydropiper as an insect feeding deterrent.

An improved extraction procedure resulted into a six-fold yield of bioactive fraction than the usual extraction method with a high per cent of feeding deterrence against 3rd instar larvae of Spilarctia obliqua and Spodoptera litura. The effective concentration (EC50) of PH-2 was 4321 and 4155 ppm against the two insects. No loss in feeding deterrency was recorded when the bioactive ether fraction, PH-2 was exposed to sunlight for 6 h.

Animals↗
PubMed1999

Wide spectrum antibacterial and antifungal activities in the seeds of some coprophilous plants of north Indian plains.

In a survey at Lucknow, India, the seedlings of plant species which are prescribed in the Indian traditional system of medicine for a variety of infectious diseases were found to predominate on fresh or decomposing cattle dung, a harsh medium for plant growth due to high microbial load and other abiotic factors. Plants of most of the common species did not occur on the cattle dung heaps. It was hypothesized that plant species which are able to grow on cattle dung may have antimicrobial compounds in their seeds to protect them from microbial attack. In confirmation, the seeds of 15 of the coprophilous (kopros--dung, philein--to love) plant species, identified as occurring most frequently on fresh/decomposing cattle dung were directly tested against eight bacterial and three fungal strains. Interestingly, seeds of all the examined species exhibited antimicrobial activity. The seeds of the species found more frequently on the cattle dung heaps possessed higher levels of antimicrobial activities.

Animals↗
PubMed1981

The short-term toxicity of ethanol to neurons in rat cerebral cortex tested by topical application in vivo, and a note on a problem in estimating ethanol concentrations in tissue.

In rats anesthetized with ethanol 4.0 g/kg i.p. the dura overlying the parietal cortex was exposed and superfused with 100% ethanol for 1 h. After 6 days survival the underlying cortex was stained with a silver method that is selective for degenerating axons and their terminals. No degeneration was found in the superfused cortex, although heat-lesioned tissue stained concurrently showed axonal degeneration and so validated the technique. Electron microscopy after 3-20 days survival did not show any degeneration, and synapses of normal appearance were present immediately beneath the cortical surface. In other rats the ethanol concentration in the superfused tissue was assayed in 0.4 mm thick discs sectioned with a vibratome from a 4-mm diameter core cut with a trocar from the cortex immediately after 1 h of superfusion. The ethanol was eluted in 2% TCA, and an aliquot assayed enzymatically. A second elution of the tissue disc contributed a further 5% of the ethanol content indicating a partition coefficient for ethanol between wet brain tissue and 2% TCA of about 10. The total concentration of ethanol in the superficial cortex was found to be about 0.82 M or 3.8%. This estimation was confirmed by superfusion with 14C-labelled ethanol and scintillation counting. Thus neurons in the cerebral cortex did not degenerate after exposure for 1 h to a concentration of ethanol that was 3 times greater than the concentration that causes death in a rat by paralysis of the respiratory centre (1.2%).

Administration, Topical↗
PubMed1980

Evaluation of xylazine in camels.

When xylazine was given intramuscularly to 12 apparently healthy adult camels (Camelus dromedarius) at the rate of 0.4 mg/kg of body weight, mean values for onset of weak time, down time, and time until recovery were 8.6 +/- 1.1, 10.5 +/- 0.6, and 150 +/- 56.9 minutes, respectively. Mild salivation, drooping of lower lips, and relaxation of neck were observed at meant times of 15.3 +/- 4.9, 11.0 +/- 1.7, and 22.7 +/- 3.9 minutes, respectively. Analgesic effects remained for 60 to 90 minutes. Hemocytologic changes were not statistically significant. Marked hyperglycemia was observed at 30 minutes after xylazine administration. Hypotension from 30 to 60 minutes after xylazine administration was not correlated with elevated central venous pressure or with bradycardia. Electrocardiography revealed 1st-degree atrioventricular block, sinoatrial block, sinus arrhythmia, and wandering pacemaker in sinoatrial node, which were attributed to vagal stimulation. Primary T-wave changes and ST segment elevation also were observed. When xylazine was used at the same dosage in 13 clinical cases involving surgery of short duration, it proved to be a satisfactory sedative, analgesic, and muscle relaxant.

Analgesia↗
PubMed1980

Deformed dendrites and reduced spine numbers on ectopic neurones in the hippocampus of rats exposed to methylazoxymethanol-acetate. A Golgi-Cox study.

Clusters of ectopic neurones appeared in the hippocampus of rat offspring which were exposed to the alkylating neurotoxin methylazoxymethanol-acetate (MAMac) during foetal development. The offspring were 30 and 60 days old when their brains were removed and prepared by the Golgi-Cox procedure outlined by Sholl (1953). Reductions in the number of dendritic branches, changes in apical dendritic lengths, abnormalities in the shapes of the dendritic shafts, and significant diminution in spine numbers were observed in ectopic neurones. The significance of these pathological alterations in dendritic morphology is discussed with special reference to the findings of an earlier study which revealed that afferent axons terminate upon ectopic neurones in an abnormal way.

Animals↗
PubMed1978

Redirected perforant and commissural of connections of eutopic and ectopic neurons in the hippocampus of methylazoxymethanol-acetate treated rats.

In an earlier study, it was reported that clusters of ectopic neurons developed postnatally in the hippocampus of rats which were exposed to Methylazoxymethanol acetate (MAMac) during fetal development (Singh, 1977b). This paper describes the perforant tract and commissural connections of hippocampal eutopic and ectopic neurons. These connections were traced with a reduced-silver method (Eager, 1970). Two observations of significance were made: (i) Ectopic neurons misplaced in stratum radiatum received terminals from axons in the perforant tract. The upper boundary for these redirected fibers was stratum pyramidale--approximately 350 mu outside the normal boundary which is situated near the hippocampal fissure. (ii) Ectopic neurons received a dramatically reduced commissural projection, compared with eutopic pyramidal neurons in Ammon's horn. Eutopic neurons in the hippocampus were found to receive afferent perforant tract and commissural fibers in the same way--i.e., density and distribution, as in control rats.

Animals↗
PubMed1977

Ectopic neurones in the hippocampus of the postnatal rat exposed to methylazoxymethanol during foetal development.

Ectopic neurons have been detected in the hippocampus of postnatal hooded rats aged 5-24 days. These rats were exposed to methylazoxymethanol acetate (MAMac) during foetal development by injecting the mother rats with this neurotoxin. At birth, the hippocampus of rats exposed to MAMac showed a normal cytoarchitecture; ectopic neurones became prevalent from 5 days onwards. These ectopic neurones were restricted to subfields CA 1-2 of Ammon's horn, and evidence is presented which suggests that these ectopic sites are formed by neuronal emigration from stratum pyramidale. Ectopic neurones have been shown to occur in genetic abnormalities of man, and in the mutant mouse 'reeler'. MAMac is a powerful methylating agent especially for guanine which is present in DNA and RNA. It is postulated that viable cells with an altered DNA-RNA state may in some way be predisposed to the formation of ectopic cell clusters after a latent period. The movement of neurones from stratum pyramidale provides a convenient animal model for investigating the mechanisms by which ectopic neuronal sites are formed by abnormal migratory patterns.

Age Factors↗
PubMed1977

The development of olfactory and hippocampal pathways in the brain of the rat.

The temporal order of development of olfactory, hippocampal and thalamocortical connections has been determined by light microscopy. Scalpel lesions were made to interrupt these connections and the resulting terminal degeneration was stained by Eager's method (1970). A post-operative survival time of one to four days was used. Evidence of the development of these connections was first obtained at the following ages: Olfactory mucosa to olfactory bulb: axon fascicles by 16 days of gestation and terminals in glomeruli at birth; Olfactory bulb to prepyriform cortex at birth; Prepyriform to entorhinal cortex at 13 days after birth; Entorhinal cortex to hippocampus (the perforant path) at 9 days; Hippocampal dentate-Ammonic mossy fibres at 9 days; Hippocampal efferent projection to the septum at birth; Subicular projections to the anterior thalamus at birth and to the mammillary body at 6 days; Hippocampal commissural connections at birth; Corticothalamic and thalamocortical connections by 2 days. These results are discussed in relation to the question of how the development of brain connections is programmed.

Animals↗
PubMed1977

Comparison of electron microscopy and silver staining for the detection of the first entorhinal synapses to develop in the dentate gyrus.

The development of the projection from the entorhinal cortex to the dentate gyrus (perforant path) has been studied with the electron microscope. The projection was lesioned in baby rats 5--13 days old and the dentate gyrus examined after 6--72 hr. Degenerating synapses first appeared in small numbers in the dentate neuropile at 7 days and in greater numbers in progressively older animals. There was a sixteen-fold increase in the number of synapses undergoing degeneration between 7 and 13 days. This investigation provides a calibration for the reduced silver method which has been used to trace developing axons (Singh, 1977). By this method the first signs of Wallerian degeneration, after cutting axons in the perforant path, were seen in the dentate neuropile at 9 days.

Animals↗