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Biomedical subjects

V Kumar

Publications and source records attributed to V Kumar.

At least 991 records · Page 55Linked to original sources
PubMedDate not supplied

Effects of melatonin in blocking the response to a skeleton photoperiod in the blackheaded bunting.

This investigation examined whether a long-day photoperiodic response induced in an interrupted-night (skeleton) photoschedule could not be induced if a short-day melatonin signal was maintained by exogenous melatonin. Three experiments, lasting for 30 days, were performed using photosensitive adult male birds. In Experiment 1, two groups (n = 12 each) were exposed to a skeleton photoperiod (6L:6D:1.5L:10.5D) and received daily either melatonin (10 micrograms bird-1 day-1) or saline (controls) in between 0.5 and 0.25 h prior to the onset of 1.5 h light pulse. Experiments 2 and 3 were similar to the Experiment 1, except in that the duration of the light break was reduced to 1 h (i.e., 6L:6D:1L:11D) and the dose of melatonin was increased to 25 micrograms bird-1 day-1 (Exp. 2) or 100 micrograms bird-1 day-1 (Exp. 3). In addition, one group of 12 birds was maintained on 6L:18D and served as noninjected controls. Although all melatonin treatments reduced fattening and weight gain (p < 0.05, compared to vehicle-treated controls), and the suppressive effects progressively increased with increasing dose of melatonin, in none of the groups were these reduced to the values found in short-day controls. Gonadal growth occurred in all groups but in birds that received 100 micrograms of melatonin photostimulated testes were significantly smaller than the vehicle-treated controls. In buntings exogenous melatonin, which encounters the suppressive effects of mid-night light pulse on melatonin peak (elevated nocturnal melatonin levels), seems not to completely block the inductive effects of light pulse. It is suggested that melatonin may not be involved in the circadian system regulating photoperiodic responses in birds, but may have peripheral effects on the neuroendocrine circuitry.

Animals↗
PubMedDate not supplied

Use of agraphia in subtyping of Alzheimer's disease.

Agraphia, the inability to write a sentence, was studied in 46 Alzheimer's disease (AD) patients to explore the potential usefulness of this measure in the subtyping of AD. In this sample there was significant correlation between the agraphia and the severity of the cognitive impairment. However, there was no correlation between agraphia and the patients' age, age at onset, duration of the illness, presence of family history of AD, cerebrospinal fluid choline and acetylcholinesterase levels. Agraphia does not seem to help in the subtyping of Alzheimer disease.

Journal Article↗
PubMedDate not supplied

Molecular characterization of the rat NK cell receptor 2B4.

2B4 (CD244) is a cell surface glycoprotein of the immunoglobulin superfamily involved in the regulation of natural killer and T lymphocyte function. It is the high affinity counter-receptor for CD48. In mouse and human NK cells, crosslinking of 2B4 with a specific monoclonal antibody or with CD48 can trigger cell-mediated cytotoxicity, IFN-gamma secretion, phosphoinositol turnover and NK cell invasiveness. Recent reports of defective 2B4 signaling and NK cell function in X-linked lymphoproliferative syndrome suggest that this may contribute to the progression of this human disease. Here we describe the molecular characterization of the rat 2B4 gene. The cDNA encodes a protein of 395 amino acid residues that contain two Ig domains in the extracellular region and three unique tyrosine motifs (TxYxxV/I/A) in the cytoplasmic region. The predicted protein has 81 and 68% similarity with mouse 2B4 and human 2B4, respectively. Additionally, it has 94 and 89% similarity at the protein level with the recently reported rat 2B4 related genes, r2B4R-tm and r2B4R-se respectively. Northern blot analysis indicated the presence of multiple transcripts in rat LAK cells and RNK-16 cells. Immunoprecipitation and deglycosylation studies showed that rat 2B4 is glycosylated to similar extent as that of mouse and human 2B4. The cloning of r2B4 in the light of the availability of rat NK cell lines should facilitate in vitro and in vivo experiments to decipher the functional role of 2B4 in NK cell biology.

Amino Acid Sequence↗
PubMedDate not supplied

Advances in Alzheimer therapy: cholinesterase inhibitors.

After a decade of intense study of cholinergic therapies for Alzheimer's disease, three conditions in this field are apparent: 1) The potential that cholinergic agents will ameliorate the memory dysfunction of Alzheimer patients (as 1-dopa benefits Parkinson patients) is still a stimulus for research. 2) Cholinergic neuropharmacology and its impact on the therapy of memory disorders associated with cholinergic dysfunction needs to be further characterized and understood. 3) While there is still a search for a symptomatic treatment for AD, the path to find a treatment for the Alzheimer disease process must first pass through a phase of basic research to find the cause of Alzheimer's disease. At the meeting, there was an undercurrent of concern that the cholinergic deficit is too severe to be treated, that the cholinergic systems are too complex to respond to a pharmacologic therapy and that too many other systems are involved in Alzheimer's disease for a cholinergic treatment to be successful. However, this concern was balanced by the evidence of basic scientific experiments which indicate that the central cholinergic system mediating memory can be positively manipulated in animal lesion preparations and Alzheimer tissue. Also there were reports that improved pharmacological approaches and psychological measures are being developed. It appears that Alzheimer therapy is at the stage that cancer chemotherapy was 20 years ago: the promising agents cause nausea without producing clear effects but the basic laboratory studies strongly suggest that substantial benefits are possible and several agents have shown encouraging results. Meanwhile, patients and scientists are becoming increasingly interested in the field.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗
PubMedDate not supplied

Human oestrogen receptor cDNA: sequence, expression and homology to v-erb-A.

We have cloned and sequenced the complete complementary DNA of the oestrogen receptor (ER) present in the breast cancer cell line MCF-7. The expression of the ER cDNA in HeLa cells produces a protein that has the same relative molecular mass and binds oestradiol with the same affinity as the MCF-7 ER. There is extensive homology between the ER and the erb-A protein of the oncogenic avian erythroblastosis virus.

Amino Acid Sequence↗
PubMedDate not supplied

Caspase-dependent apoptosis induced by telomere cleavage and TRF2 loss.

Chromosomal abnormalities involving telomeric associations (TAs) often precede replicative senescence and abnormal chromosome configurations. We report here that telomere cleavage following exposure to proapoptotic agents is an early event in apoptosis. Exposure of human and murine cancer cells to a variety of pro-apoptotic stimuli (staurosporine, thapsigargin, anti-Fas antibody, and cancer chemotherapeutic agents) resulted in telomere cleavage and aggregation, and finally their extrusion from the nuclei. Telomere loss was associated with arrest of cells in G2/M phase and preceded DNA fragmentation. Telomere erosion and subsequent large-scale chromatin cleavage were inhibited by overexpression of the anti-apoptotic protein, bcl-2, and two peptide caspase inhibitors (BACMK and zVADfmk), indicating that both events are regulated by caspase activation. The results demonstrate that telomere cleavage is an early chromatin alteration detected in various cancer cell lines leading to drug-induced apoptosis, and suggest that this event contributes to mitotic catastrophe and induction of cell death. Results also suggest that the decrease of telomeric-repeat binding factor 2 (TRF2) may be the earliest event in the ara-C-induced telomere shortening, induction of endoreduplication and chromosomal fragmentation leading to cell death.

Animals↗
PubMedDate not supplied

The effect of immunosuppressive therapy on the course of development of Dictyocaulus viviparus in guinea-pigs.

Three chemical immunosuppressive agents, viz. dexamethasone, methotrexate and cyclophosphamide, were administered to guinea-pigs two days prior to their infection with Dictyocaulus viviparus infective larvae and onward. The cell mediated immunity of these guinea-pigs was subdued under the influence of these immunosuppressive agents as evidenced by macrophage migration inhibition test but this could not prevent or postpone the rejection of majority of the worm population of guinea-pigs on day 15 post-infection. Methotrexate exerted, besides its cell mediated immunosuppressive action on the host, some inhibitory influence on the general biotic potentialities of the developing worms so that, on day eight post-infection, a reduced number of stunted worms was recovered.

Animals↗