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Sarika Singh

Publications and source records attributed to Sarika Singh.

9 recordsLinked to original sources
PubMed2006

Nitric oxide synthase regulation and diversity: implications in Parkinson's disease.

Nitric oxide (NO) is a janus faced chemical messenger, which, in the recent years, has been the focus of neurobiologists for its involvement in neurodegenerative disorders in particular, Parkinson's disease (PD). Nitric oxide synthase, the key enzyme involved in NO production exists in three known isoforms. The neuronal and inducible isoforms have been implicated in the pathogenesis of PD. These enzymes are subject to complex expressional and functional regulation involving mRNA diversity, phosphorylation and protein interaction. In the recent years, mRNA diversity and polymorphisms have been identified in the NOS isoforms. Some of these genetic variations have been associated with PD, indicating an etiological role for the NOS genes. This review mainly focuses on the NOS genes - their differential regulation and genetic heterogeneity, highlighting their significance in the pathobiology of PD.

Gene Expression Regulation, Enzymologic↗
PubMed2005

Myeloperoxidase cytochemical negativity: an unexpected but intrinsic property of blasts of all phases of chronic myeloid leukemia.

Myeloperoxidase (MPO) cytochemical activity, recognized as a very important hallmark of myeloblasts, is generally negative in chronic myeloid leukemia (CML) blast crisis (BC). Because this finding is unexpected, being not in keeping with the myeloproliferative nature of CML, we tried to ascertain if MPO cytochemical negativity could be an intrinsic property of blasts of CML and hence present in the preblastic phases as well. Myeloperoxidase cytochemistry of peripheral blood blasts in 161 cases of CML, including 103 in chronic phase (CP) and 29 each in accelerated phase (AP) and BC, was assessed and compared with that of 30 cases of acute myeloid leukemia, AML-M2. Blasts of 97 (94.2%) of 103 cases of CP, 28 (96.6%) of 29 cases of AP, and 22 (75.9%) of 29 cases of BC were negative for MPO (<3% MPO-positive blasts). Compared with the strong MPO positivity, both in terms of intensity and proportion, in the AML-M2 cases, the positivity in the CML cases was generally weak and was seen in a small number of blasts (5-15%), except in one case of BC with 20% positive blasts. Absence or, at times, weak MPO cytochemical activity is an intrinsic property of blasts of all phases of CML, and use of the term myeloblast in CML should be understood to refer to a cell with this property. This also explains why MPO cytochemistry, despite its high reputation as a myeloid-lineage marker, generally does not help in CML BC. CML BC should therefore be considered as a possible diagnosis along with acute lymphoblastic leukemia, AML-M0, AML-M7, etc., in the setting of MPO-negative blasts. Similarity between MPO expression pattern in CML, i.e., negative in blasts and positive in the more mature cells, and that during maturation of normal myeloid series of cells shows the deranged myelopoiesis of CML to be undisturbed at least with respect to MPO expression. There is need for a more comprehensive study of blasts of preblastic phases.

Biomarkers, Tumor↗
PubMed2005

Involvement of nitric oxide in neurodegeneration: a study on the experimental models of Parkinson's disease.

The present study was undertaken to explore involvement of nitric oxide (NO) in the experimental models of Parkinson's disease. Neurodegeneration was induced by unilateral injections of 6-hydroxydopamine (6-OHDA) or lipopolysaccharide (LPS) in the right striatum. Lesions were functionally evaluated by amphetamine-induced asymmetrical behaviour and by decrease in the tyrosine hydroxylase (TH) immunostaining. An induction in the expression of iNOS and augmentation in nitrite content was observed in both the models. The extent of increase in iNOS expression was, however, different but the elevation in the nitrite content was comparable in both the models. The increase in iNOS expression inversely correlated with the tyrosine hydroxylase (TH) immunolabeling. Animals pretreated with a NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), exhibited complete protection against amphetamine induced rotations in both the models. Thus, augmented NO availability subsequent to iNOS induction seems to play an important role in the initial phase of neurodegeneration.

Animals↗
PubMed2004

Cold tolerance of Littorinidae from southern Africa: intertidal snails are not constrained to freeze tolerance.

All intertidal gastropods for which cold tolerance strategies have been assessed have been shown to be freeze tolerant. Thus, freeze tolerance is considered an adaptation to the intertidal environment. We investigated the cold tolerance strategies of three species of subtropical and temperate snails (Gastropoda: Littorinidae) to determine whether this group is phylogenetically constrained to freeze tolerance. We exposed 'dry' acclimated and 'wet' rehydrated snails to low temperatures to determine temperature of crystallisation (Tc), lower lethal temperature and LT(50) and to examine the relationship between ice formation and mortality. Tc was lowest in dry Afrolittorina knysnaensis (-13.6+/-0.4 degrees C), followed by dry Echinolittorina natalensis (-10.9+/-0.2 degrees C) and wet A. knysnaensis (-10.2+/-0.2 degrees C) . The Tc of both A. knysnaensis and E. natalensis increased with rehydration, whereas Tc of dry and wet Afrolittorina africana did not differ (-9.6+/-0.2 and -9.0+/-0.2 degrees C respectively). Wet snails of all species exhibited no or low survival of inoculative freezing, whereas dry individuals of A. knysnaensis could survive subzero temperatures above -8 degrees C when freezing was inoculated with ice . In the absence of external ice, Afrolittorina knysnaensis employs a freeze-avoidance strategy of cold tolerance, the first time this has been reported for an intertidal snail, indicating that there is no family-level phylogenetic constraint to freeze tolerance. Echinolittorina natalensis and A. africana both showed pre-freeze mortality and survival of some internal ice formation, but were not cold hardy in any strict sense.

Adaptation, Physiological↗