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Biomedical subjects

M S Roy

Publications and source records attributed to M S Roy.

At least 19 recordsLinked to original sources
PubMed2004

Phylogeography of a high-dispersal New Zealand sea-star: does upwelling block gene-flow?

New Zealand's (NZ) geographical isolation, extensive coastline and well-characterized oceanography offer a valuable system for marine biogeographical research. Here we use mtDNA control region sequences in the abundant endemic sea-star Patiriella regularis to test the following literature-based predictions: that coastal upwelling disrupts north-south gene flow and promotes population differentiation (hypothesis 1); and that an invasive Tasmanian population of the species was introduced anthropogenically from southern New Zealand (hypothesis 2). We sequenced 114 samples from 22 geographical locations, including nine sites from North Island, nine from South Island, one from Stewart Island and three from Tasmania. Our analysis of these sequences revealed an abundance of shallow phylogenetic lineages within P. regularis (68 haplotypes, mean divergence 0.9%). We detected significant genetic heterogeneity between pooled samples from northern vs. southern New Zealand (FST = 0.072; P = 0.0002), consistent with the hypothesis that upwelling disrupts gene flow between these regions (hypothesis 1). However, we are currently unable to rule out the alternative hypothesis that Cook Strait represents a barrier to dispersal (North Island vs. South Island; FST = 0.031; P = 0.0467). The detection of significant spatial structure in NZ samples is consistent with restricted gene flow, and the strong structure evident in northern NZ may be facilitated by distinct ocean current systems. Four shared haplotypes and nonsignificant differentiation (FST = 0.025; P = 0.2525) between southern New Zealand and Tasmanian samples is consistent with an anthropogenic origin for the latter population (hypothesis 2).

Animals↗
PubMed2003

Confirmation of low genetic diversity and multiple breeding females in a social group of Eurasian badgers from microsatellite and field data.

The Eurasian badger (Meles meles) is a facultatively social carnivore that shows only rudimentary co-operative behaviour and a poorly defined social hierarchy. Behavioural evidence and limited genetic data have suggested that more than one female may breed in a social group. We combine pregnancy detection by ultrasound and microsatellite locus scores from a well-studied badger population from Wytham Woods, Oxfordshire, UK, to demonstrate that multiple females reproduce within a social group. We found that at least three of seven potential mothers reproduced in a group that contained 11 reproductive age females and nine offspring. Twelve primers showed variability across the species range and only five of these were variable in Wytham. The microsatellites showed a reduced repeat number, a significantly higher number of nonperfect repeats, and moderate heterozygosity levels in Wytham. The high frequency of imperfect repeats and demographic phenomena might be responsible for the reduced levels of variability observed in the badger.

Animals↗
PubMed2002

Evidence of a human-mediated invasion of the tropical western Atlantic by the 'world's most common brittlestar'.

Approximately three million years ago the Isthmus of Panama formed an impenetrable land barrier between the tropical eastern Pacific Ocean and the tropical western Atlantic Ocean. Since this time, isolated geminate species have evolved from once contiguous populations, either side of the barrier. One such organism whose distribution is divided by the Isthmus is the tropical brittlestar Ophiactis savignyi, once suggested to be the most common brittlestar in the world. Rather than showing a genetic pattern consistent with a history of isolation, we show that this species has recently dispersed between the Pacific Ocean and the western Atlantic Ocean. This conclusion is based upon a phylogenetic analysis using sequences of the COI mitochondrial DNA gene from these populations. Identical haplotypes between oceans, and a genetic signature of population expansion, provide compelling evidence that the western Atlantic contains at least one cluster of haplotypes recently derived from the Indo-Pacific. Inadvertent human-aided translocation of individuals, presumably in ballast water or fouling communities, is strongly implicated as a mechanism for dispersal between oceans. We believe that cryptic marine invasions are likely to be common and our awareness of them will rapidly increase as systematic and phylogeographic knowledge of marine taxa grow.

Animals↗
PubMed2001

Molecular systematics and evolutionary history of kalats (genus Sheppardia): a pre-Pleistocene radiation in a group of African forest birds.

The African forest robins (akalats) of the genus Sheppardia are represented by eight forest-dwelling species with restricted distributions in tropical Africa. All but three are strictly montane, inhabiting isolated highland areas in eastern and western Africa. Due to their subtle plumage variation and almost wholly allopatric distribution, determining systematic relationships based upon morphology has proven difficult. However, akalats, due to their distribution, offer an ideal opportunity to test models of speciation within tropical forests. We therefore investigated the phylogeny of species of this genus from presently sampled regions of their distribution using mtDNA sequence analysis. We found that the monophyly of described species, even from disjunct populations, is well supported. However, relationships among species is generally poorly resolved, with support given only to the paired relationships S. montana/S. lowei, S. bocagei/S. gunningi, and S. aequatorialis/S. cyornithopsis. This dataset lent support to S. montana and S. lowei representing a superspecies. All species appear to have evolved rapidly from a common ancestor around the Miocene/Pliocene transition, a time of the last uplift of East Africa's montane region. Surprisingly, intraspecific radiations suggest a far more recent population expansion in the upper Pleistocene, concordant with major climatic variation and vegetational changes. We discuss the implications of our results in the light of previous discussions of the montane speciation model.

Africa↗
PubMed2001

Contrast dependency of VEPs as a function of spatial frequency: the parvocellular and magnocellular contributions to human VEPs.

The present study investigated the contrast dependency of visual evoked potentials (VEPs) elicited by phase reversing sine wave gratings of varying spatial frequency. Sixty-five trials were recorded for each of 54 conditions: 6 spatial frequencies (0.8, 1.7, 2.8, 4.0, 8.0 and 16.0 c deg(-1)) each presented at 9 contrast levels (2, 4, 8, 11, 16, 23, 32, 64 and 90%). At the lowest spatial frequency, the waveform contained mainly one peak (P1). For spatial frequencies up to 8 c deg(-1), P1 had a characteristic magnocellular contrast response: it appeared at low contrasts, increased rapidly in amplitude with increasing contrast, and saturated at medium contrasts. With increasing spatial frequency, an additional peak (N1) gradually became the more dominant component of the waveform. N1 had a characteristic parvocellular contrast response: it appeared at medium to high contrasts, increased linearly in amplitude with increasing contrast, and did not appear to saturate. The data suggest the contribution of both magnocellular and parvocellular responses at intermediate spatial frequencies. Only at the lowest and highest spatial frequencies tested did magnocellular and parvocellular responses, respectively, appear to dominate.

Adult↗
PubMed2001

Macular edema and retinal hard exudates in African Americans with type 1 diabetes: the New Jersey 725.

OBJECTIVE: To determine frequency and associated risk factors for macular edema and retinal hard exudates in hospitalized African Americans with type 1 diabetes. SUBJECTS AND METHODS: Included were 725 African Americans with type 1 diabetes who participated in the New Jersey 725. Clinical evaluations consisted of a structured clinical interview, ocular examination, stereoscopic fundus photographs, and blood pressure measurements. Presence of macular edema and hard exudates was determined via masked grading of fundus photographs. Biological evaluations included blood and urine assays. RESULTS: Of the 725 patients, 89 (12.3%) had macular edema and 149 (20.6%) had retinal hard exudates in at least 1 eye. The presence of macular edema and hard exudates was significantly associated with older age at examination, longer duration of diabetes, and severity of diabetic retinopathy. Presence of proteinuria, missing insulin injections at least once a week, and longer duration of diabetes were significantly and independently associated with macular edema. Presence of proteinuria, male sex, higher low-density lipoprotein cholesterol levels, and longer duration of diabetes were significantly and independently associated with severity of retinal hard exudates. CONCLUSION: Macular edema and hard exudates are common in African Americans with type 1 diabetes, particularly in patients with evidence of renal disease.

Adolescent↗
PubMed2001

Vectorial efficacy of Phlebotomus argentipes in Kala-azar endemic foci of Bihar (India) under natural and artificial conditions.

Ability of Phlebotomus argentipes to acquire Leishmania donovani the causative agent of Indian Kala-azar was evaluated in the laboratory. Flies were fed artificially on infected blood suspensions, using a chick-skin-membrane feeding apparatus, and naturally on Leishmania donovani infected mice. In addition flies collected from different endemic areas were dissected and examined for natural infection. Flies fed on infected mice showed significantly higher feeding rate (14.4%, p < 0.01) compared to that of other experiments (9%, 8.75%) but the percentage of infection was very low (2.43%). No Chi-square comparison was made between infection rate and feeding rate because of low value in infection rate (less than 5). Flies dissected for natural infection showed only 0.1% infection. Not much difference was observed in the intensity of Leishmania donovani infection in the mid gut of sandflies examined from any of these experiments. These observations have confirmed that Phlebotomus argentipes has ability to acquire infection and it provides the final piece of evidence that Phlebotomus argentipes is the vector of Leishmania donovani in Bihar State.

Animals↗
PubMed2000

Diabetic retinopathy in African Americans with type 1 diabetes: The New Jersey 725: II. Risk factors.

OBJECTIVE: To determine whether diabetic retinopathy in African Americans with type 1 diabetes is associated with the following 6 putative risk factors: duration of diabetes, glycemic control, systemic hypertension, renal disease, socioeconomic status, and male sex. METHODS: Patients in The New Jersey 725 study underwent detailed ocular evaluation, a structured clinical interview, blood pressure measurements, and assays of blood and urine samples. RESULTS: Glycemic control was poor; 89.8% of the patients had glycosylated hemoglobin values of more than 0.08. Renal disease and systemic hypertension were present in 49.8% and 34.3% of patients, respectively. Frequency and severity of retinopathy were significantly associated with longer duration of diabetes (P<.001). After adjusting for duration of diabetes and other confounding variables, on average, patients with total glycosylated hemoglobin values in the highest quartile were 3 times more likely to have any retinopathy than those in the lowest quartile; patients with renal disease, 3 times more likely to have any retinopathy and 10 times more likely to have proliferative retinopathy than patients without renal disease; and patients in the highest quartile of systolic sitting blood pressure, 3 times more likely to have proliferative retinopathy than patients in the lowest quartile. CONCLUSIONS: Risk factors for diabetic retinopathy in African Americans with type 1 diabetes include presence of renal disease, poor glycemic control, high systolic blood pressure, and long duration of diabetes.

Adolescent↗
PubMed2000

Diabetic retinopathy in African Americans with type 1 diabetes: The New Jersey 725: I. Methodology, population, frequency of retinopathy, and visual impairment.

OBJECTIVE: To determine the frequency and severity of diabetic retinopathy, as well as associated visual impairment, among African Americans with type 1 diabetes. METHODS: A total of 725 African Americans with type 1 diabetes were enrolled in the study (The New Jersey 725). Clinical evaluations included structured clinical interview, ocular examination, stereoscopic fundus photography, and blood pressure measurements. Severity of retinopathy was determined via masked grading of fundus photographs. Biological evaluations included blood and urine assays. RESULTS: Of the 725 patients, 463 (63.9%) presented with any diabetic retinopathy and 137 (18.9%) with proliferative diabetic retinopathy. The frequency and severity of retinopathy were both significantly associated with older age at examination. Visual impairment (visual acuity in the better eye < or =20/40) was present in 79 (11.0%) and legal blindness in 22 (3.1%) of the patients. Diabetic retinopathy was responsible for 90.9% of the blindness. Frequency of visual impairment was significantly associated with older age and female sex, and only weakly with lower education. CONCLUSIONS: Diabetic retinopathy in African Americans with type 1 diabetes is common, being found in almost two thirds of the patients studied. Its frequency and severity increase with age. Visual impairment is common, increasing with age and duration of diabetes and is more frequent in women than in men.

Adolescent↗
PubMed2000

Preservation of neural function in the perinate by high PGE(2) levels acting via EP(2) receptors.

Despite increasingly frequent and longer lasting hypoxic episodes during progressive labor, the neonate is alert and vigorous at birth. We investigated whether high levels of PGs during the perinatal period assist in preserving neural function after such "stressful" hypoxic events. Visual evoked potentials (VEPs) and electroretinograms (ERGs) were recorded before and 45 min after mild moderate asphyxic hypoxia (two 4-min asphyxic-hypoxic periods induced by interrupting ventilation at 8-min intervals) in newborn piglets <12 h old treated or not treated with inhibitors of PG synthase (ibuprofen or diclofenac) with or without PG analogs. At 45 min after the hypoxic episode, P2 and b-wave amplitudes were slightly decreased and latencies were delayed. These changes in the VEP and ERG returned to near normal by 120 min. Ibuprofen and diclofenac decreased brain and retinal PG levels and markedly intensified 45 min after hypoxia-induced changes in VEP and ERG, but cerebral and retinal blood flows improved. Combined treatment with PG synthase inhibitor in combination with 16,16-dimethyl-PGE(2) (a PGE(2) analog), but not with PGI(2) and PGF(2alpha) analogs, and in combination with the EP(2) receptor agonist butaprost (but not EP(1) or EP(3) agonists), prevented ibuprofen- and diclofenac-aggravated postasphyxia electrophysiological changes. In conclusion, high levels of PGE(2) in nervous tissue, via actions on EP(2) receptors, seem to contribute to preservation of neural function in the perinate subjected to frequent hypoxic events.

Animals↗
PubMed2000

An entomological field evaluation of larval biology of sandfly in Kala-azar endemic focus of Bihar--exploration of larval control tool.

Knowing the exact breeding places inside the habitat is very important to plan the larval control strategy. Information regarding larval biology in relation to different seasons will be more useful to organize insecticide spray schedule at a particular month of maximum immature density to bring down the adult sandfly density. In the present study, maximum number of soil samples were found positive in the month of January and minimum in the month of September. Maximum positive soil samples were collected from cattle sheds, minimum in mixed dwellings and in case of human dwellings all soil samples were negative. Comparison of two methods for the isolation of immature stages showed that direct microscopic observation is superior to sugar flotation technique.

Animals↗
PubMed1999

Molecular phylogeny and evolutionary history of the tit-tyrants (Aves: Tyrannidae).

Tit-tyrants of the genus Anairetes presently consist of six species; five inhabit various regions along the Andean cordillera of South America and one is endemic to the Juan Fernandez Islands off the coast of Chile. Data from mtDNA ND2 and Cyt b sequences were used to construct a phylogeny for all Anairetes species as well as Uromyias agilis, a closely related genus, and Stigmatura as an outgroup, to determine their relationships and history of radiation in South America. Results strongly supported the following paired relationships: A. nigrocristatus-A. reguloides, A. flavirostris-A. alpinus, and A. parulus-A. fernandezianus. This dataset, however, could not resolve basal nodes; therefore relationships among these pairs remains obscure. Moreover the genus Uromyias, controversially separated on morphological criteria from Anairetes, fell within the Anairetes clade, although its exact position could not be ascertained with confidence. The molecular data indicate that this group probably radiated within the past 2 million years, concomitant with highly accentuated cycles of global climatic change. Certain high altitude areas within the Andes may have been stable during global climatic changes and may have served as refugia during the Plio-Pleistocene.

Animals↗
PubMed1999

Effects of early reduced light exposure on central visual development in preterm infants.

The aim of this study was to determine, in infants born at < or =29 weeks postmenstrual age until 32 weeks postmenstrual age, whether reduction to light stimulation by occlusion of eyes affected central visual development. The pattern visual-evoked potential responses at 41 and 51 weeks postmenstrual age and 3 y of age did not differ between infants subjected or not to ocular occlusion. Hence, an early marked reduction in light stimulation in preterm infants does not seem deleterious to visual development.

Age Factors↗
PubMed1998

Characterization of an abundant short interspersed nuclear element (SINE) present in Canis familiaris.

A short interspersed nuclear element (Can SINE) of approximately 130-150 bp was cloned and characterized from Canis familiaris. We demonstrate that this element is interspersed, present approximately every 5-8.3 kbp, and many are sufficiently close to allow IRS (interspersed repetitive DNA sequences) PCR. Sequence analysis of > 20 Can SINEs from the dog has identified a conserved region that was used to design oligonucleotides for IRS PCR. Since Can SINEs are not present in human or rodent genomes, IRS PCR using oligonucleotides directed to the conserved region of Can SINEs can be used to simplify analysis of canid DNA in somatic cell hybrids, as well as in large insert cloning vectors. We demonstrate that the canid IRS products are polymorphic and could be developed as genetic markers for filter-based genotyping in this organism.

Animals↗
PubMed1997

Hemiretinal contribution to the timing of the full-field PVEP as determined with the motor reaction time.

With the use of the simple motor reaction time (RT), we examined the contribution of the hemiretinas to the timing of the pattern reversal visual evoked potential (PVEP). RTs were obtained to the reversal of a progressively dimmer check falling either on the central, nasal, temporal, superior or inferior retina. Results were correlated with the peak time of the P1 wave evoked to the reversal of the entire checkerboard stimulus to the same luminance conditions as that used to generate the RT measurements. Our results clearly indicate that the time taken to trigger a manual response depends not only on the luminance of the stimulus, but also on where it falls on the retina. Comparing the above data with the peak time of the PVEP obtained to the reversal of the entire screen indicates that at brighter luminance the peak time of the P1 wave correlates with that measured from the most central retina, while at dimmer intensities it correlates with the mathematical average of all the retinal locations tested.

Adult↗
PubMed1997

Pattern electroretinogram and spatial contrast sensitivity in primary congenital glaucoma.

OBJECTIVE: The authors investigated the temporal and spatial characteristics of pattern electroretinogram (PERG) and spatial contrast sensitivity (CS) in primary congenital glaucoma (PCG) to determine whether the PERG and CS could be useful tools in the diagnosis of childhood glaucoma, especially PCG. PARTICIPANTS: The PERGs were evaluated in eyes from ten patients with PCG and nine age-matched visually normal subjects. INTERVENTION: All patients received complete ophthalmologic evaluations including visual field testing. MAIN OUTCOME MEASURES: The PERGs were recorded using phase-alternating (2, 4, and 16 reversals per second [rps]) checkerboard patterns (30' and 60' checks). RESULTS: The patients with PCG exhibited decreased CS when compared with that of control subjects. Significant PERG deficits also were detected in these patients. However, PERG amplitude in patients with PCG almost reached control subject levels at high (16 rps) temporal frequency. This was true for both 30' and 60' checks. Taken together, these observations on PERG amplitude suggest a more important deficiency of the neural response of the retinal cells at lower temporal frequency (rps) in patients with PCG. This is unlike primary open-angle glaucoma (POAG) in which significant PERG deficits are observed at high temporal frequencies. CONCLUSIONS: The PERG amplitude is reduced in patients with PCG, and this is consistent with a loss of CS and visual field changes in these patients. However, the spatiotemporal characteristics of the PERG deficits in PCG differ from those of POAG. This could suggest a difference in the mechanisms mediating retinal ganglion cell dysfunction in the two types of glaucoma.

Adolescent↗