Biomedical subjects

H Davis

Publications and source records attributed to H Davis.

At least 19 recordsLinked to original sources

PubMed2005

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.

Journal Article↗

PubMed2005

Frisby Davis distance stereoacuity values in visually normal children.

AIMS: To establish the range of normal distance stereoacuity in young children using the Frisby Davis distance stereo test (FD2). METHODS: Children passing preschool vision screening assessments underwent measurement of distance stereoacuity with the FD2 using a standard testing protocol. RESULTS: 59 visually normal children aged between 36 months and 68 months were recruited to this study. All 59 were able to understand the test requirements and were examined with the FD2 stereo test. Four (6.8%) had no measurable stereoacuity; 13 (24%) had stereoacuity measurable only at a 3 metre testing distance (mean 92.3 seconds of arc; SD 52.6). These children were significantly younger than the remaining 42 (76%) who demonstrated a stereoacuity response at a 6 metre testing distance (mean 29.6 seconds of arc; SD 13.1, p=0.008). CONCLUSION: The FD2 stereo test enables the measurement of distance stereoacuity in young children. There appears to be a maturational effect with distance stereoacuity improving between 36 months and 68 months. The data on age related normal values will provide a baseline from which to compare outcomes in clinical populations.

Aging↗

PubMed2005

Transgenic overexpression of neuromedin U promotes leanness and hypophagia in mice.

Recent work has shown that neuromedin U (NmU), a peptide initially identified as a smooth muscle contractor, may play a role in regulating food intake and energy homeostasis. To further evaluate this putative function, we measured food intake, body weight, energy expenditure and glucose homeostasis in transgenic mice that ubiquitously overexpress murine proNmU. NmU transgenic mice were lighter and had less somatic and liver fat, were hypophagic, and had improved insulin sensitivity as judged by an intraperitoneal insulin tolerance test. Transgenic mice had higher levels of hypothalamic NPY, POMC and MCH mRNA. There was no difference in O2 consumption between genotypes; however, NmU transgenic mice displayed a modest increase in respiratory quotient during food deprivation and refeeding. There were no behavioral disturbances in the NmU transgenic mice that could account for the results (e.g. changes in locomotor activity). When placed on a high-fat diet, transgenic mice remained lighter than wild-type mice and ate less, but gained weight at a rate similar to wild-type mice. Despite the increased weight gain with high-fat feeding, glucose tolerance was significantly improved in the transgenic mice. These findings support the hypothesized role of NmU as an endogenous anorexigenic peptide.

Animals↗

PubMed2004

Developmental neurotoxicity of ketamine: morphometric confirmation, exposure parameters, and multiple fluorescent labeling of apoptotic neurons.

Ketamine is a widely used pediatric anesthetic recently reported (C. Ikonomidou et al., 1999, Science 283, 70-74) to enhance neuronal death in neonatal rats. To confirm and extend these results, we treated four groups of PND 7 rats with seven sc doses, one every 90 min, of either saline, 10 mg/kg ketamine, 20 mg/kg ketamine, or a single dose of 20 mg/kg ketamine. The repeated doses of 20 mg/kg ketamine increased the number of silver-positive (degenerating) neurons in the dorsolateral thalamus to a degree comparable to previous results (Ikonomidou et al., 1999, Science 283, 70-74), i.e., 28-fold vs. 31-fold respectively. However, blood levels of ketamine immediately after the repeated 20 mg/kg doses were about 14 micrograms/ml, about seven-fold greater than anesthetic blood levels in humans (J. M. Malinovsky et al., 1996, Br. J. Anaesth. 77, 203-207; R. A. Mueller and R. Hunt, 1998, Pharmacol. Biochem. Behav. 60, 15-22). Levels of ketamine in blood following exposure to the multiple 10 mg/kg doses of ketamine or to a single 20 mg/kg dose ranged around 2-5 micrograms/ml; although these blood levels are close to an anesthetic level in humans, they failed to produce neurodegeneration. To investigate the mode of ketamine-induced neuronal death, coronal sections were stained with both Fluoro-Jade B (a green fluorescent stain selective for neurodegeneration) and DAPI (a blue DNA stain), as well as for caspase-3 (using an antisera labeled red with rhodamine). These histochemical results confirmed the developmental neurotoxicity of ketamine, demonstrated that Fluoro-Jade B (FJ-B), like silver methods, successfully stained degenerating neurons in neonatal rats, and indicated that ketamine acts by increasing the rate of neuronal apoptosis.

Animals↗

PubMed2003

Can tonic accommodation predict surgical performance?

BACKGROUND: Pilots undergo many visual tests for both selection and assessment, and we know that there are many similarities between pilots and surgeons. Hence, it would not be unreasonable to bring similar visual tests into surgery. Tonic accommodation (TA) is a stable parameter that is adopted by the eye in the absence of any stimulation. Over recent years, surgery has undergone change from traditional open surgery to minimally invasive procedures, bringing many advantages. However, not every surgeon has the ability to perform under conditions where the operative field is represented on a flat monitor. METHOD: We determined the TA values in medical students and then correlated this with their performance on a virtual reality surgical simulator. RESULTS: We found that TA values predicted the number of errors made with the dominant hand, accounting for 27% of the variance. CONCLUSION: The data suggest that TA may play a role in the individual differences that are noted when surgeons perform laparoscopic surgery. Further studies are needed to evaluate the exact role of TA in surgical performance.

Accommodation, Ocular↗

PubMed2003

Infant-mother interaction as a predictor of child's chronic health problems.

BACKGROUND: Psychological stress is associated with physical illnesses like asthma or infections. For an infant, situations perceived as stressful are highly dependent on the relationship with the caregiver. Constantly poor mother-infant interaction increases the child's vulnerability to stressful conditions and experiences. The aim of the study was to investigate the impact of the quality of early mother-infant interaction on the subsequent physical health of the child. Poor mother-infant interaction was hypothesized to be associated with chronic or recurrent health problems in the child. PARTICIPANTS: Fifty-seven mother-infant dyads from families at risk of psychosocial problems and 63 from non-risk families, altogether 120 dyads, participated in the study. Families were drawn from normal population, from well-baby clinics in the city of Tampere, Finland. Infants were full-term and healthy, families with severe risks like psychotic illnesses of the parents or a history of child protection concerns were excluded from the study. METHODS: After the initial interview with the mother, the mother-infant interaction was videotaped when the infants were 8-11 weeks of age and the interaction was assessed using the Global Rating Scale for Mother-Infant Interaction (Murray et al. 1996a). After the 2-year follow-up mothers were interviewed again and the health problems of the child were elicited. RESULTS: Poor dyadic mother-infant interaction and infant's poor interactive behaviour assessed at two months were separately associated with the physical health of the child during the two-year follow-up. After adjusting for other factors in the logistic regression analysis infant's poor interactive behaviour remained as a significant predictor of chronic or recurrent health problems in the child. Infant's health problems at the time of the initial interview and day care centre attendance were also significant predictors. CONCLUSIONS: The results suggest that interactional issues between a mother and her infant are related to the child's subsequent physical health. Children with recurrent or chronic health problems may have relationship difficulties with which they need help. Also, early avoidant behaviour of the infant should be regarded as an indicator of the infant's distress with possibly adverse outcomes in the child's physical health, among other consequences.

Adult↗

PubMed2003

Positive tensilon test and intracranial tumor: a case report.

PURPOSE: To report a case of intracranial tumor in a patient with positive tensilon test. METHODS: Interventional case report. A 19-year-old male presented with left 6th nerve palsy and had a tensilon test, which was highly positive and was diagnosed as having myasthenia gravis. RESULTS: The neurologist scanned the patient, which showed an intracranial tumor in the floor of the temporal fossa on the left side. The patient had surgery and a schwannoma was removed. The VIth nerve palsy did not improve up to two years after surgery. CONCLUSIONS: A patient with a positive tensilon test can also have an associated intracranial tumor.

Adult↗

PubMed2001

Randomised controlled trial of an interactive multimedia decision aid on hormone replacement therapy in primary care.

OBJECTIVE: To determine whether a decision aid on hormone replacement therapy influences decision making and health outcomes. DESIGN: Randomised controlled trial. SETTING: 26 general practices in the United Kingdom. PARTICIPANTS: 205 women considering hormone replacement therapy. INTERVENTION: Patients' decision aid consisting of an interactive multimedia programme with booklet and printed summary. OUTCOME MEASURES: Patients' and general practitioners' perceptions of who made the decision, decisional conflict, treatment choice, menopausal symptoms, costs, anxiety, and general health status. RESULTS: Both patients and general practitioners found the decision aid acceptable. At three months, mean scores for decisional conflict were significantly lower in the intervention group than in the control group (2.5 v 2.8; mean difference -0.3, 95% confidence interval -0.5 to -0.2); this difference was maintained during follow up. A higher proportion of general practitioners perceived that treatment decisions had been made "mainly or only" by the patient in the intervention group than in the control group (55% v 31%; 24%, 8% to 40%). At three months a lower proportion of women in the intervention group than in the control group were undecided about treatment (14% v 26%; -12%, -23% to -0.4%), and a higher proportion had decided against hormone replacement therapy (46% v 32%; 14%, 1% to 28%); these differences were no longer apparent by nine months. No differences were found between the groups for anxiety, use of health service resources, general health status, or utility. The higher costs of the intervention were largely due to the video disc technology used. CONCLUSIONS: An interactive multimedia decision aid in the NHS would be popular with patients, reduce decisional conflict, and let patients play a more active part in decision making without increasing anxiety. The use of web based technology would reduce the cost of the intervention.

Decision Making, Computer-Assisted↗

PubMed2001

Randomised controlled trial of an interactive multimedia decision aid on benign prostatic hypertrophy in primary care.

OBJECTIVE: To determine whether a decision aid on benign prostatic hypertrophy influences decision making, health outcomes, and resource use. DESIGN: Randomised controlled trial. SETTING: 33 general practices in the United Kingdom. PARTICIPANTS: 112 men with benign prostatic hypertrophy. INTERVENTION: Patients' decision aid consisting of an interactive multimedia programme with booklet and printed summary. OUTCOME MEASURES: Patients' and general practitioners' perceptions of who made the decision, decisional conflict scores, treatment choice and prostatectomy rate, American Urological Association symptom scale, costs, anxiety, utility, and general health status. RESULTS: Both patients and general practitioners found the decision aid acceptable. A higher proportion of patients (32% v 4%; mean difference 28%, 95% confidence interval 14% to 41%) and their general practitioners (46% v 25%; 21%, 3% to 40%) perceived that treatment decisions had been made mainly or only by patients in the intervention group compared with the control group. Patients in the intervention group had significantly lower decisional conflict scores than those in the control group at three months (2.3 v 2.6; -0.3, -0.5 to -0.1, P<0.01) and this was maintained at nine months. No differences were found between the groups for anxiety, general health status, prostatic symptoms, utility, or costs (excluding costs associated with the video disc equipment). CONCLUSIONS: The decision aid reduced decisional conflict in men with benign prostatic hypertrophy, and the patients played a more active part in decision making. Such programmes could be delivered cheaply by the internet, and there are good arguments for coordinated investment in them, particularly for conditions in which patient utilities are important.

Aged↗

PubMed2001

An HIV-1 transgenic rat that develops HIV-related pathology and immunologic dysfunction.

We report, to our knowledge, the first HIV type 1 (HIV-1) transgenic (Tg) rat. Expression of the transgene, consisting of an HIV-1 provirus with a functional deletion of gag and pol, is regulated by the viral long terminal repeat. Spliced and unspliced viral transcripts were expressed in lymph nodes, thymus, liver, kidney, and spleen, suggesting that Tat and Rev are functional. Viral proteins were identified in spleen tissue sections by immunohistochemistry and gp120 was present in splenic macrophages, T and B cells, and in serum. Clinical signs included wasting, mild to severe skin lesions, opaque cataracts, neurological signs, and respiratory difficulty. Histopathology included a selective loss of splenocytes within the periarterial lymphoid sheath, increased apoptosis of endothelial cells and splenocytes, follicular hyperplasia of the spleen, lymphocyte depletion of mesenteric lymph nodes, interstitial pneumonia, psoriatic skin lesions, and neurological, cardiac, and renal pathologies. Immunologically, delayed-type hypersensitivity response to keyhole limpet hemocyanin was diminished. By contrast, Ab titers and proliferative response to recall antigen (keyhole limpet hemocyanin) were normal. The HIV-1 Tg rat thus has many similarities to humans infected with HIV-1 in expression of viral genes, immune-response alterations, and pathologies resulting from infection. The HIV-1 Tg rat may provide a valuable model for some of the pathogenic manifestations of chronic HIV-1 diseases and could be useful in testing therapeutic regimens targeted to stages of viral replication subsequent to proviral integration.

Animals↗

PubMed2001

Impact of Transcendental Meditation on cardiovascular function at rest and during acute stress in adolescents with high normal blood pressure.

OBJECTIVE: This study examined the impact of the Transcendental Meditation (TM) program on cardiovascular (CV) reactivity in adolescents with high normal BP. METHOD: Thirty-five adolescents [34 African Americans (AAs), 1 Caucasian American (CA); ages 15-18 years] with resting systolic blood pressure (SBP) between the 85th and 95th percentile for their age and gender on three consecutive occasions, were randomly assigned to either TM (n=17) or health education control (CTL, n=18) groups. The TM group engaged in 15-min meditation twice each day for 2 months including sessions during school lunch break. Primary CV outcome measures were changes in blood pressure (BP), heart rate (HR), and cardiac output (CO) at rest and in response to two laboratory stressors, a simulated car driving stressor and an interpersonal social stressor interview. RESULTS: The TM group exhibited greater decreases in resting SBP (P<.03) from pre- to postintervention, compared to the CTL group. The TM group exhibited greater decreases from pre- to postintervention in SBP, HR, and CO reactivity (P's<.03) to the simulated car driving stressor, and in SBP reactivity (P<.03) to the social stressor interview. CONCLUSION: The TM program appears to have a beneficial impact upon CV functioning at rest and during acute laboratory stress in adolescents at-risk for hypertension.

Adolescent↗

PubMed2001

Cardiovascular (CV) responsivity and recovery to acute stress and future CV functioning in youth with family histories of CV disease: a 4-year longitudinal study.

Blood pressure (BP) and heart rate (HR) data obtained during supine rest, in response to and recovery from four laboratory stressors in a baseline year were used to predict supine resting BP and HR values obtained during each of four consecutive annual follow-up evaluations. Subjects were 385 normotensive youth [95 African American (AA) males, 106 AA females, 92 European American (EA) males, 92 EA females] (mean age 12.7+/-2.6 at baseline year) with a positive family history of cardiovascular disease (CVD). During the baseline evaluation subjects were presented with four laboratory stressors (namely, postural change, video game challenge, social competence interview, and parent--child conflict discussion). The BP and HR values taken during each of the laboratory stressors and during the post stressor recovery periods were converted to z-scores which were averaged to yield aggregate measures for systolic and diastolic BP and HR responsivity and recovery. The data obtained during the baseline evaluation were subsequently used to predict the follow-up values of supine resting BP and HR. The prediction models were fairly consistent across each of the 4 follow-up years. Responsivity or recovery accounted for up to 6% of the total variance after accounting for baseline values. Within the prediction models responsivity or recovery accounted for 4--56% of the variance. The predictive value of the derived models did not decline from one annual evaluation to the next over the length of the study. CV recovery may supplement resting and responsivity in the prediction of future development of CVD

Adolescent↗

PubMed2001

Activation of central melanocortin receptors by MT-II increases cavernosal pressure in rabbits by the neuronal release of NO.

1. Melanotan-II had been reported to cause penile erections in men with erectile dysfunction. In the present study, we investigated the mechanisms by which systemic administration of MT-II increases intracavernosal pressure in anaesthetized rabbits. 2. MT-II (10 microM) had no effect on electrical field stimulation-evoked relaxations of rabbit corpus cavernosal strips in vitro. 3. Intravenous injection of MT-II (66 and 133 microg kg(-1) elicited dose-related increases in cavernosal pressure. SHU 9119 (3 microg kg(-1), i.v.), a non-selective antagonist of MC(3) and MC(4) receptors did not significantly affect either cavernosal pressure or systemic blood pressure but abolished the MT-II-induced increases in cavernosal pressure. SHU 9119 also inhibited the depressor response produced by MT-II. 4. Intracavernosal injection 100 microl of the cocktail containing phentolamine mesylate (1 mg ml(-1)), papaverine (20 mg ml(-1)) and PGE1 (20 microg ml(-1)) increased the cavernosal pressure by about 4 fold. 5. The role of NO-cyclic GMP dependent pathway to MT-II-induced increases in cavernosal pressure was investigated by bilateral transection of the pudendal nerves and by inhibition of NO synthase with L-NAME (20 mg kg(-1), i.v. over 30 min). Ablation of the pudendal nerves or pretreatment with L-NAME abolished the MT-II-induced increases in intracavernosal pressure in anaesthetized rabbits. 6. The data suggest that activation of central melanocortin receptors by MT-II increases cavernosal pressure by the neuronal release of NO.

Alprostadil↗

PubMed2001

Discrimination between individual humans by domestic fowl (Gallus gallus domesticus).

1. We demonstrate that Barred-Rock and Isa-Brown hens can discriminate between the presence of 2 different humans and use this information as a cue for whether or not to make an operant response. 2. This demonstration in domestic fowl, the first of its kind in any avian subject, is consistent with a growing body of evidence that many species, including agricultural animals, are surprisingly adept at differentiating between humans. 3. Such a discriminative ability carries considerable implications for issues related to husbandry, production and welfare.

Animal Husbandry↗

PubMed2001

Effects of position and speed on joint torques and knee shear after ACL injury.

PURPOSE: The purpose of this study was to assess the effect of joint position and movement speed on hip (HT) and knee (KT) extensor torque, HT/KT ratio (HKR), and anterior tibial shear (S) in presurgical-ACL deficient (PRE; N = 15), post-ACL reconstructed (POST; N = 15), and uninjured controls (CON; N = 15). METHODS: Measurements were recorded on a semirecumbent variable resistance, closed-chain dynamometer. Tests were conducted at 1 and 1.5 Hz and maximum speed at 33% and 50% 1RM. HT, KT, and S were recorded during the extension phase of the cycle (85 degrees -25 degrees of knee flexion). RESULTS: KT was greatest when the knee was more flexed, whereas HT dominated when it was more extended. This suggests that the hamstrings, as a component of the hip extensors, may generate considerable propulsive force during knee extension, which may help counter anterior tibial shear. S increased whereas KT decreased, suggesting that the quadriceps continue to generate shear force despite the decreasing mechanical advantage producing KT. Increasing knee extension speed significantly decreased S in the POST and CON groups. The correlations between KT and S changed from significantly negative to significantly positive as the knee extended from 85 degrees to 25 degrees in the POST and CON groups. This may be related to the orientation of the patellar tendon, relative to the tibial longitudinal axis that shifts from a posterior to anterior direction, as the knee extends. CONCLUSIONS: Joint position and movement speeds affect the magnitude of hip and knee torques and anterior tibial shear. Reducing the magnitude of S during heavy loads may be a normal phenomenon, and POST surgical subjects may retain or regain this function by 1 yr after surgery.

Adult↗

PubMed2001

Determination of twin zygosity: a comparison of DNA with various questionnaire indices.

This study examined cross-validation and test-retest reliability of questions and questionnaire indices commonly used for twin zygosity classification. Mothers of 58 monozygotic (MZ) and 52 dizygotic (DZ) same sex twin pairs were interviewed by telephone to answer questions regarding the similarity of their twins (mean age = 14.6 +/- 2.8 years). A logistic regression equation correctly classified 91% of both MZ and DZ twin pairs in our sample using 7 of the 12 zygosity questions. The internal consistency for the total questionnaire (Cronbach's alpha) was 0.88. The median two month temporal stability estimate for the individual questions was r = .56 and r = .79 for the test total. For the cross-validation, zygosity classification indices taken from 9 previous studies were applied to our sample and compared to classification according to DNA microsatellite analyses (agreement range = 44 to 100%). The accuracy of the classification indices was significantly lower than the original studies for 62% of the comparisons. If zygosity determination with DNA markers or blood group typing for all subjects is not feasible, rather than using classification indices based on other studies, an optimal classification scheme can be achieved by using a zygosity questionnaire of which the reliability and validity of the questions is established in a random subsample of the same twin cohort.

Adolescent↗

PubMed2001

[Vaginismus--a psychiatric perspective, "secrets" and other psychodynamic causes].

Vaginismus is a disorder involving both psychiatry and gynecology. Psychiatric help is sought in only a small proportion of cases, although it is probable that the psychological etiology of the disorder is more frequent than generally recognized. This article deals with the causes and psychological circumstances of the disorder. Five cases are presented. In the first three cases, primary vaginismus caused unconsummated marriage in young women of religious or traditional background. In these cases a "secret" was revealed relating to a previous sexually related experience. This provides the basis for therapy. The other cases describe secondary vaginismus which appeared in older women who developed the symptom after a number of years of marriage. This article discusses the different psychotherapeutic approaches for the two types of cases. In the former cases, therapy may be brief and the prognosis is favorable. In the second case type, there is often more significant personality or marital pathology requiring prolonged and extensive psychotherapy. The authors stress the need for physicians to be mindful of cases of vaginismus requiring psychiatric intervention rather than gynecological treatment.

Adult↗

PubMed2000

Schizophrenia patients demonstrate a dissociation on declarative and non-declarative memory tests.

Declarative memory refers to the recall and recognition of factual information. In contrast, non-declarative memory entails a facilitation of memory based on prior exposure and is typically assessed with priming and perceptual-motor sequencing tasks. In this study, schizophrenia patients were compared to normal comparison subjects on two computerized memory tasks: the Word-stem Priming Test (n=30) and the Pattern Sequence Learning Test (n=20). Word-stem Priming includes recall, recognition (declarative) and priming (non-declarative) components of memory. The schizophrenia patients demonstrated an impaired performance on recall of words with relative improvement during the recognition portion of the test. Furthermore, they performed normally on the priming portion of the test. Thus, on tests of declarative memory, the patients had retrieval deficits with intact performance on the non-declarative memory component. The Pattern Sequence Learning Test utilizes a serial reaction time paradigm to assess non-declarative memory. The schizophrenia patients' serial reaction time was significantly slower than that of comparison subjects. However, the patients' rate of acquisition was not different from the normal comparison group. The data suggest that patients with schizophrenia process more slowly than normal, but have an intact non-declarative memory. The schizophrenia patients' dissociation on declarative vs. non-declarative memory tests is discussed in terms of possible underlying structural impairment.

Adult↗