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Biomedical subjects

P Sen

Publications and source records attributed to P Sen.

At least 19 recordsLinked to original sources
PubMed2001

Simulation of flux lines with columnar pins: bose glass and entangled liquids.

Using path integral Monte Carlo we simulate a 3D system of up to 1000 magnetic flux lines by mapping it onto interacting bosons in (2+1)D. With increasing temperatures we find first order melting from an ordered solid to an entangled liquid signaled by a finite entropy jump and sharp discontinuities of the defect density and the structure factor S(G). For a particular density of strong columnar pins the crystal is transformed into a Bose glass phase with patches of crystalline order disrupted by the trapped vortices at the pinning sites but with no overall positional or orientational order. This glassy phase melts into a defected entangled liquid through a continuous transition.

Journal Article↗
PubMed2001

Quantum-fluctuation-induced spatial stochastic resonance at zero temperature.

We consider a model in which the quantum fluctuation can be controlled and show that the system responds to a spatially periodic external field at zero temperature. This signifies the occurrence of spatial stochastic resonance where the fluctuations are purely quantum in nature. Various features of the phenomenon are discussed.

Journal Article↗
PubMed2001

Selective impairment of protein kinase C isotypes in murine macrophage by Leishmania donovani.

Leishmania donovani, an obligate intracellular parasite resides and multiplies within macrophage of the reticuloendothelial system. The intracellular signalling mechanism involved in the impaired oxidative response in leishmaniasis has not yet been clearly established. Generation of superoxide anion (O2-) is supposed to be the first line of host defence during microbial invasion. We found a substantial inhibition of superoxide anion generation in parasitized macrophages, which was just the reverse in case of macrophages challenged with Lipophosphoglycan (LPG) deficient attenuated leishmanial parasite UR-6. The generation of O2- essentially needs the prior activation of protein kinase C (PKC) mediated phosphorylation events. Our study proposed that phosphorylation of 67, 54, 47 and 36 kDa proteins was attenuated during infection. This was supported by PKC activity study, where Ca-dependent PKC activity was inhibited but, Ca-independent PKC activity was enhanced. This result was further confirmed by using isotype specific pseudosubstrate inhibitors of Ca-dependent PKC beta and Ca-independent PKC zeta. Application of beta-pseudosubstrate could not alter the Ca-dependent PKC activity but zeta-pseudosubstrate inhibited the Ca-independent PKC activity in infected macrophages. Our immunoblot analysis with specific antibody against PKC beta and PKC zeta isotypes showed down regulation of PKC beta-II expression with concomitant induction of PKC zeta. Such inhibition of Ca-dependent PKC beta was reversed in macrophages treated with UR-6. Taken together, our observations revealed that infection with L. donovani selectively attenuates both the expression and activity of Ca-dependent PKC beta.

Animals↗
PubMed2000

Quantum phase transitions in the Ising model in a spatially modulated field.

The phase transitions in the transverse field Ising model in a competing spatially modulated (periodic and oscillatory) longitudinal field are studied numerically. There is a multiphase point in absence of the transverse field where the degeneracy for a longitudinal field of wavelength lambda is [(1+sqrt[5])/2](2N/lambda) for a system with N spins, an exact result obtained from the known result for lambda=2. The phase transitions in the Gamma (transverse field) versus h(0) (amplitude of the longitudinal field) phase diagram are obtained from the vanishing of the mass gap Delta. We find that for all the phase transition points obtained in this way, Delta shows finite size scaling behavior signifying a continuous phase transition everywhere. The values of the critical exponents show that the model belongs to the universality class of the two dimensional Ising model. The longitudinal field is found to have the same scaling behavior as that of the transverse field, which seems to be a unique feature for the competing field. The phase boundaries for two different wavelengths of the modulated field are obtained. Close to the multiphase point at h(c), the phase boundary behaves as (h(c)-h(0))(b), where b is also lambda dependent.

Journal Article↗
PubMed2000

A benign parathyroid cyst presenting with hoarse voice.

Parathyroid tumours and cysts are rare and, when presenting as neck masses, can be clinically misdiagnosed as thyroid lesions. Symptoms may be caused by compression of the surrounding structures or hormonal overactivity. This paper describes a patient with recurrent hoarseness owing to the pressure effects of a parathyroid cyst on the recurrent laryngeal nerve.

Adult↗
PubMed1999

Immunoprophylaxis and immunotherapy against experimental visceral leishmaniasis.

The ability of the Leishmanial parasite, UR6 (MHOM/IN/1978/UR6) to act as a immunoprophylactic and immunotherapeutic agent against experimental visceral leishmaniasis in a hamster model was tested. The Leishmanial parasite, UR6, lacked LPG but possessed abundant message for kinetoplastid membrane protein-11 (KMP-11), and failed to induce visceral infection when given through the intracardiac route, unlike the virulent Leishmania donovani, AG83 (MHOM/IN/1983/AG83), the causative agent of Kala-azar. Priming of macrophage with UR6 in vitro, induced superoxide (O2-) generation whereas a similar experiment with virulent AG83 inhibited O2- generation. This observation prompted us to test the efficacy of UR6 as a immunoprophylactic and immunotherapeutic agent. It was observed that priming of hamsters with either live or sonicated UR6 in the absence of any adjuvant provided strong protection against subsequent virulent challenge. The UR6 mediated protection was also observed in hamsters having established infection. Furthermore, UR6 primed infected hamsters displayed a greatly extended life span as compared to infected hamsters. To our knowledge, this is the first report concerning the use of an atypical Leishmanial parasite, UR6 in immunoprophylaxis and immunotherapy in the absence of any adjuvant.

Animals↗
PubMed1999

Using focus groups to evaluate an education program.

Two evaluation studies were carried out in 1995 and 1997. The first evaluation assessed tile effectiveness of the Psychiatric Nurse Practitioner's education program and its impact on mental health and psychiatry in Belize. The second study was done to determine if the mental health services were sustained in the country. Interviews and focus groups were used for data collection. In this paper the focus is on the findings from the focus groups. The findings show that the PNP's role performance was adequate, they have made an impact on the mental health services and the services are sustained.

Attitude of Health Personnel↗
PubMed1999

Pharmacology of rosemary (Rosmarinus officinalis Linn.) and its therapeutic potentials.

The use of plants is as old as the mankind. Natural products are cheap and claimed to be safe. They are also suitable raw material for production of new synthetic agents. Rosemary (Rosmarinus officinalis Linn.) is a common household plant grown in many parts of the world. It is used for flavouring food, a beverage drink, as well as in cosmetics; in folk.medicine it is used as an antispasmodic in renal colic and dysmenorrhoea, in relieving respiratory disorders and to stimulate growth of hair. Extract of rosemary relaxes smooth muscles of trachea and intestine, and has choleretic, hepatoprotective and antitumerogenic activity. The most important constituents of rosemary are caffeic acid and its derivatives such as rosmarinic acid. These compounds have antioxidant effect. The phenolic compound, rosmarinic acid, obtains one of its phenolic rings from phenylalanine via caffeic acid and the other from tyrosine via dihydroxyphenyl-lactic acid. Relatively large-scale production of rosmarinic acid can be obtained from the cell culture of Coleus blumei Benth when supplied exogenously with phenylalanine and tyrosine. Rosmarinic acid is well absorbed from gastrointestinal tract and from the skin. It increases the production of prostaglandin E2 and reduces the production of leukotriene B4 in human polymorphonuclear leucocytes, and inhibits the complement system. It is concluded that rosemary and its constituents especially caffeic acid derivatives such as rosmarinic acid have a therapeutic potential in treatment or prevention of bronchial asthma, spasmogenic disorders, peptic ulcer, inflammatory diseases, hepatotoxicity, atherosclerosis, ischaemic heart disease, cataract, cancer and poor sperm motility.

Animals↗
PubMed1998

Epilepsies among twins born in families of Indian probands with epilepsy.

Twins have a high frequency of adverse perinatal events and have been reported to have an increased risk of seizures. Contrary to popular belief, a recent study reported that twins do not have an increased risk of seizures. We studied the relationship of twinning and epilepsy in India. The frequency of twinning in families of probands with epilepsy was compared with the frequency of twinning among hospital births in the same region of India. We also compared consecutively ascertained probands with epilepsy for their twin status and the occurrence of epilepsies in their twin and non-twin relatives. The frequency of twin births in families of 524 probands with epilepsy was comparable to the twin births among consecutive deliveries over a 3-year period in another government hospital in the same catchment area (1:99 vs. 1:75). Every 1 in 58 of probands with epilepsy was a twin while a twin was born in these families every 1 in 71 live births. The frequency of epilepsy in non-proband twin relatives was 1.5% compared with 2% among non-proband, non-twin relatives. This data suggests that twin birth is not a major risk factor for seizures even in families of Indian probands with epilepsy. Family data such as ours can be used to study the contribution by genetic factors in the pathogenesis of complex genetic diseases such as human epilepsies.

Adult↗
PubMed1996

SKP1 connects cell cycle regulators to the ubiquitin proteolysis machinery through a novel motif, the F-box.

We have identified the yeast and human homologs of the SKP1 gene as a suppressor of cdc4 mutants and as a cyclin F-binding protein. Skp1p indirectly binds cyclin A/Cdk2 through Skp2p, and directly binds Skp2p, cyclin F, and Cdc4p through a novel structural motif called the F-box. SKP1 is required for ubiquitin-mediated proteolysis of Cin2p, Clb5p, and the Cdk inhibitor Sic1p, and provides a link between these molecules and the proteolysis machinery. A large number of proteins contain the F-box motif and are thereby implicated in the ubiquitin pathway. Different skp1 mutants arrest cells in either G1 or G2, suggesting a connection between regulation of proteolysis in different stages of the cycle.

Amino Acid Sequence↗
PubMed1996

The effects of an RNA synthesis inhibitor on the survival and regeneration of rat motoneurones injured at birth.

This preliminary study aimed to test the proposal that neuronal death is triggered by expression of specific genes. In rat pups, the sciatic nerve was injured unilaterally on the first day after birth and actinomycin D, an RNA synthesis inhibitor, was administered 3 days later in a lower and higher dose to rat pups just prior to onset of motoneurone death induced by the lesion. Four weeks later, sciatic motoneurones from operated and contralateral pools were counted and their size measured. Significantly fewer motoneurones (16.7% +/- 2.9 SD) survived when the animals were treated with a lower dose of the inhibitor compared to saline treated controls (36.6% +/- 12.7 SD). Experiments recording tension generated in soleus muscle in response to sciatic nerve stimulation, at different ages following nerve crush, suggested that the treatment with the RNA synthesis inhibitor may have delayed regeneration of motor axons back to the muscle. However, survival of motoneurones after treatment with the higher dose did not differ significantly from controls (27.5% +/- 1.3 SD). Nevertheless, the higher dose significantly reduced growth of motoneurones after 4 weeks. Therefore, the higher dose, although impeding normal development of motoneurones, is less neurotoxic than a lower dose. This suggests that a balancing of conflicting effects may have occurred. The neurodegenerative effects of delayed reinnervation induced by RNA synthesis inhibition may be balanced by some neuroprotective effects at a higher dose. More extensive studies are required to validate these pilot findings.

Animals↗