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Biomedical subjects

A Roberts

Publications and source records attributed to A Roberts.

At least 235 records · Page 13Linked to original sources
PubMed1990

Effects of sex, race and year in college on self-reported drinking-related problem behaviors.

This research was conducted to study the effects of sex, race, and year in college on self-reported drinking-related problem behaviors. It was hypothesized that men would report more problem behaviors than women, white students would report more than Hispanic or black students, and an interaction of sex and race would be observed. The study was conducted at a middle-sized eastern college, where 181 students anonymously filled out a 17-item questionnaire. The design was a 3 (race) x 2 (sex) x 2 (year in college) factorial. The hypotheses for sex and race were confirmed. Investigation of whether these self-reported drinking-related problem behaviors are congruent with actual behaviors requires study.

Adult↗
PubMed1990

How does a nervous system produce behaviour? A case study in neurobiology.

The behaviour and nervous systems of most adult animals are extremely complex so to achieve analysis down to the cellular level we have studied a very simple animal, the hatchling clawed-toad tadpole. Even if the brain is removed these tadpoles can swim when touched showing that this behaviour can be co-ordinated in the spinal cord. The use of neuroanatomical and electrophysiological techniques to discover what nerve cells are present in the spinal cord is described and how they interact to generate swimming behaviour is explored. We now have a working hypothesis for spinal cord network operation which is being tested using computer simulations and which suggests general principles on how nervous systems may work. Our study also provides a bird's-eye view of current approaches to investigating nervous systems at the cellular level.

Animals↗
PubMed1989

Obesity and breast disease. The role of the female sex hormones.

An Australian study of 513 women evaluated associations between obesity and both benign and malignant breast disease, and in particular investigated the role of female sex hormones. Women who gained more than 10 kg from early womanhood had a two-fold increase in risk of developing breast cancer, whereas lean women had a greater risk of being treated for benign breast disease. Obese women with breast cancer were more likely to have Stage II tumors but there was no significant association between obesity and tumor size or estrogen and progesterone receptor status. Obesity was strongly associated with the proportions of nonprotein-bound and albumin-bound estradiol, and inversely associated with sex hormone binding globulin (SHBG) levels and the proportion of SHBG-bound estradiol. In addition, age at menarche was inversely associated, and age at menopause directly associated with recalled weight at those time periods. These data demonstrate weight gain as a risk factor for breast cancer, and suggest a possible mechanism supporting its development.

Adolescent↗
PubMed1989

The metabolism and testicular toxicity of cyclohexylamine in rats and mice during chronic dietary administration.

Cyclohexylamine hydrochloride has been given in the diet to mice and to Wistar and DA rats for 13 weeks, to provide a constant intake of 400 mg of the base/kg/day. Significantly decreased food intake and body weight gain were found in both strains of rats but not mice. The metabolism of [14C]cyclohexylamine was widely different in Wistar and DA rats and in rats and mice, and these differences were not altered appreciably by chronic intake for 13 weeks. The differences in metabolism resulted in marked and persistent differences in the concentrations of the hydroxylated metabolites in the plasma and testes of treated animals with Wistar much greater than DA much greater than mice. After 7 and 13 weeks testicular atrophy was demonstrated in both strains of rats given cyclohexylamine diet by a decrease in organ weight and by histological changes. DA rats appeared more sensitive to testicular toxicity from cyclohexylamine than Wistar rats, while mice showed no evidence of testicular damage. These data show that the development of testicular toxicity is not related to the extent of hydroxylation. The concentrations of cyclohexylamine in the plasma and testes of the treated animals were lower in mice than in either strain of rats despite a similar daily intake. This suggests that species differences in pharmacokinetics may contribute to the apparent difference in sensitivity to testicular toxicity.

Animals↗
PubMed1989

The pharmacokinetics and tissue concentrations of cyclohexylamine in rats and mice.

Cyclohexylamine showed dose-dependent kinetics after administration of single oral doses up to 500 mg/kg in rats, with a reduction in plasma clearance, an increase in apparent half-life, and an increased area under the testicular concentration-time curve. Cyclohexylamine was absorbed and eliminated more rapidly by mice. Saturation of cyclohexylamine uptake by rat renal cortical slices in vitro and of renal tubular secretion in vivo occurred at concentrations and doses comparable to the oral dose studies. During chronic dietary administration the concentrations of cyclohexylamine in the plasma and testes showed a pronounced diurnal variation in rats which was not detected in mice. The steady-state plasma clearance in rats was approximately one-half that in mice. The concentrations of cyclohexylamine in the plasma and testes of rats, but not mice, showed a nonlinear relationship to dietary intake. Elevated concentrations were found at intakes greater than 200 mg/kg/day. The pharmacokinetics of cyclohexylamine make an important contribution to the difference in sensitivity to testicular atrophy in rats and mice and the dose-response relationship for this toxicity in rats.

Animals↗
PubMed1989

Development of early swimming in Xenopus laevis embryos: myotomal musculature, its innervation and activation.

The development of the axial musculature, its innervation and early locomotion in Xenopus laevis embryos are described. Between stages 17 and 40 some 45 myotomes are formed on each side of the body. During this period the animals develop from non-motile to free swimming embryos. Using fluorescein-conjugated bungarotoxin the acquisition of acetylcholine receptor-sites was studied. At stage 25 (early flexure stage) bound bungarotoxin was confined to the first seven intermyotomal clefts, in free swimming embryos (stage 33) to the first 20 clefts. Application of horseradish peroxidase to the intermyotomal clefts in embryos ranging from stages 25 to 37/38 revealed that primary motoneurons were usually situated 100-400 microns, i.e. 0.5-1.5 myotomes, rostral to the cleft they innervated. The motor axons left the spinal cord at the caudal side of each spinal segment where neural crest was present between the cord and the myotomes. At stage 25 ventral root activity could be recorded extracellularly from only the first three intermyotomal clefts, at stage 32/33 from the first 16 clefts. The first spontaneous rhythmic swimming-like activity could be recorded around stage 28. Between stages 27 and 32/33 the initial swimming frequency and the swimming episode duration increased at least three-fold. Comparable results were obtained with high-speed cinematography and measurements with a photoelectric transducer. Between stages 17 and 40 the number of myotomes increased by 0.9 myotome h, approximately 11.4 h later followed by the innervation of the myotomes at 0.7 cleft/h. About 3.6 h after this, ventral root activity appeared at the rate of 0.6 cleft h. This study shows that the early swimming pattern generating neuronal network, located within the rostral spinal cord, reaches a state of "critical mass" around stage 27, at which the first rhythmic swimming activity occurs. At least 6-10 functional spinal segments and adjacent myotomes are required for early swimming.

Animals↗
PubMed1989

Do big breasts disadvantage women with breast cancer?

The present study was undertaken in order to discover whether patients with breast cancer in large breasts experienced a delay in the detection of their cancer due to the bulk of the breast and consequently presented with more advanced tumours compared with women with small breasts. Mastectomy specimens were weighed and their dimensions measured, in particular recording breast mass and breast thickness (anterior-posterior depth). Tumour diameter, the number of involved lymph nodes and the oestrogen and progesterone receptor levels were measured as prognostic indices. Although there was no difference in receptor status of tumours from large and small breasts, on presentation, patients with big breasts had larger tumours and more involved lymph nodes than women with small breasts, whether breast size was assessed by weight or thickness. Women with large breasts may therefore be expected to fare worse than those with small breasts.

Breast↗
PubMed1989

Expression of pertussis toxin in Bordetella bronchiseptica and Bordetella parapertussis carrying recombinant plasmids.

Pertussis toxin is produced only by strains of Bordetella pertussis. Cloned genes encoding pertussis toxin from B. pertussis were transferred into Bordetella bronchiseptica and Bordetella parapertussis by conjugation. These transconjugants expressed pertussis toxin at levels comparable to those expressed by B. pertussis. The toxin made by these strains was biologically active in the Chinese hamster cell clumping assay, contained all five subunits, and was mostly periplasmic. Toxin expression appeared to be modulated in the same way as are the vir-regulated genes of B. pertussis. Introduction of these plasmids into B. pertussis failed to produce hypertoxigenic strains. Instead, these transconjugants underwent plasmid loss, gene deletions, or conversion to the avirulent phase.

Antibodies, Monoclonal↗
PubMed1989

Pulsed-spray pharmacomechanical thrombolysis: preliminary clinical results.

Pulsed-spray pharmacomechanical thrombolysis was used to treat 41 patients with 47 complete thrombotic occlusions of hemodialysis grafts (n = 29), arterial bypass grafts (n = 10), or peripheral native arteries (n = 8). The procedure involves the use of small pulses of highly concentrated urokinase, which are forcefully sprayed throughout the thrombus during systemic heparinization. Virtually complete lysis was achieved in 46 of 47 occlusions. In the 46 thrombi that lysed, mean time for completion of lysis was 63 +/- 35 min and initial partial return of flow required 26 +/- 18 min. Complications included small peripheral emboli in one treated bypass graft (which cleared promptly after further pulse-spray therapy) and bleeding in three cases (one case of hematoma in the infused field at the site of recent surgery, one case of bilateral hematomas at the femoral puncture site, and one minor delayed self-limited gastrointestinal hemorrhage). Results to date suggest that the pulsed-spray pharmacomechanical method augments the speed, consistency, safety, and cost efficacy of clinical thrombolysis. Further study is warranted.

Arteriovenous Shunt, Surgical↗
PubMed1989

The management of severe erythroblastosis fetalis by fetal transfusion: survival of transfused adult erythrocytes in the fetus.

The survival of adult erythrocytes transfused into the fetus was measured after intravascular and/or intraperitoneal transfusion. We performed 80 fetal transfusions on 20 severely anemic fetuses, 18 of whom survived. The survival of adult erythrocytes in the fetal circulation was similar to that in the adult circulation and did not depend on the route of transfusion, gestational age, or presence of hydrops. Eighty percent of blood transfused into the fetal peritoneal cavity appeared in the fetal circulation.

Adult↗
PubMed1989

Concordance between different measures of small sensory and autonomic fibre neuropathy in diabetes mellitus.

This study presents concordance data from 3 different tests of small nerve-fibre function on the same diabetic patients and also examines the effects of hyperglycaemia. Thus the TTT-Glasgow automated thermal threshold test, EAR-Electrically evoked axon reflex flare, and GOE-Gastric emptying of a mixed sold/liquid meal and oesophageal emptying of a solid bolus were all measured on 25 diabetic patients. The TTT, EAR and GOE all gave values ranging from within the normal reference range for non-diabetics to markedly dysfunctional readings. Mean warm perception (WPT) on the foot dorsum averaged 0.73 degrees C +/- 0.93 for normal controls, but was 4.67 degrees C +/- 3.99 in the 25 diabetics. Cold perception thresholds (CPT) were 0.48 degrees C +/- 0.55 for normal subjects and 3.75 degrees C +/- 4.28 for diabetics. In the same normal subjects the mean EAR flare laser flux responses (for 8 and 16 noxious TENS pulses) was 2.8 V.min, while for diabetics the mean was 0.2 V.min. Solid and liquid gastric 50% emptying times and oesophageal emptying for non-diabetics were within normal range (mean 78 min and 18 min, 18 sec respectively) but for the 25 diabetics emptying times ranged from normal to very prolonged (mean 114 min and 30 min, 68 sec respectively). A plot of 3 measured variables (TTT, EAR and GOE) showed a high degree of correspondence between the gastro-oesophageal emptying delays and the presence of reduced electrical axon reflex and elevated thermal thresholds. Of 25 patients, 6 could be classed as within normal limits on all 3 variables, but 8 of 25 displayed objective evidence of C-fibre neuropathy--thermal perceptual impairment (C- and A-delta sensory fibres), reduced neurogenic inflammatory flare (peptidergic nociceptive afferents) and delayed gastro-oesophageal emptying (vagal afferent/efferent fibres).

Autonomic Nervous System↗
PubMed1988

A neuronal mechanism for sensory gating during locomotion in a vertebrate.

The response of the foot to touch during walking depends on whether it is in the air or on the ground. In most animals, reflex responses to external stimuli are similarly adapted to their timing in the locomotor cycle, but there is only fragmentary information about the neural mechanisms involved. In arthropods, reflex modulation can occur in the sensory receptors themselves and in neurons that discharge during locomotion. By recording with dye-filled microelectrodes from neurons in the spinal cord of frog embryos, we describe reflex modulation at the level of sensory interneurons. Sensory inputs from skin receptors excite a specific class of spinal sensory interneuron whose activity leads to reflex bending of the body away from the stimulus. During swimming, these inputs are gated by rhythmic postsynaptic inhibition, so that sensory drive reaches motor neurons only at phases in the locomotor cycle when the resulting contraction would likewise turn the embryo away from the stimulated side. Such gating of sensory pathways could be a general feature of all locomotor systems where responses to sensory stimuli need to be adapted to the phase of locomotion.

Action Potentials↗
PubMed1988

Prevalence of the 281 (Gly----Glu) mutation in hepatoerythropoietic porphyria and porphyria cutanea tarda.

The prevalence of the 281 (Gly----Glu) mutation in hepatoerythropoietic porphyria (HEP) was investigated by the use of hybridization with a synthetic oligonucleotide probe. The mutation was found in HEP-affected members of two unrelated families from Spain, but was absent in two other patients from Italy and Portugal who also had HEP. Moreover, this mutation was not detected in 13 unrelated cases of familial (type II) porphyria cutanea tarda.

Carboxy-Lyases↗
PubMed1988

The negative inotropic effect of acetylcholine on ferret ventricular myocardium.

1. The effects of acetylcholine (ACh) on developed tension and intracellular Ca2+ concentration (as measured with aequorin) were studied in ferret papillary muscles, and on twitch shortening, the action potential and membrane currents in ferret ventricular myocytes. 2. Addition of ACh to ferret papillary muscles resulted in decreases in developed tension and the intracellular Ca2+ transient, both of which then partially recovered in the continued presence of ACh ('fade' of the response). On wash-off of ACh both developed tension and the intracellular Ca2+ transient increased above control ('rebound') before returning to control values. 3. Addition of ACh to ferret ventricular myocytes resulted in a membrane hyperpolarization of 2 +/- 0.5 mV (mean +/- S.E.M.; n = 9), a decrease in action potential duration to 23 +/- 6% of control and a decrease in twitch shortening to 31 +/- 5% of control. In the continued presence of ACh these responses to ACh faded. Thirty seconds after the maximal effect of ACh, action potential duration had partially recovered to 34 +/- 6% of control and twitch shortening to 46 +/- 7% of control. 4. The effects of ACh on twitch shortening could be mimicked under voltage clamp by varying voltage clamp pulse duration to simulate the ACh-induced changes in action potential duration. 5. When ACh was applied during a train of voltage clamp pulses of constant duration, 81% of the cells showed less than a 20% decrease in Ca2+ current and twitch shortening. However in 19% of the cells twitch shortening and the apparent Ca2+ current decreased by more than 30%. 6. In the 81% of cells, the normal decrease in twitch shortening was wholly the result of the shortening of the action potential. This in turn was the result of an increase in an outward background current which increased the rate of repolarization during the action potential. The ACh-induced background current reversed at -89 +/- 2 mV and showed inward-going rectification; these properties suggest that it was carried by K+. 7. In the 19% of cells, the normal decrease in twitch shortening was only partly the result of the shortening of the action potential (due to both the increase in outward background current as well as the apparent decrease in Ca2+ current). In these cells the decrease in twitch shortening may also have been partly the direct result of the apparent decrease of Ca2+ current.

Acetylcholine↗
PubMed1988

Nature, incidence and prognosis of neurological involvement in the acquired immunodeficiency syndrome in central London.

Clinical neurological involvement at various times throughout the illness was recorded in 52% of 122 patients seen in central London who died from acquired immunodeficiency syndrome (AIDS). Various metabolic encephalopathies, dementias, focal encephalopathies, retinopathies and peripheral nerve pathology were the most frequent manifestations. Seven of 9 patients with a neurological presentation had no other major systemic illness. The median time from diagnosis of AIDS to death was 9 months and from onset of neurological symptoms to death 4 months. Human immunodeficiency virus dementia, central nervous system opportunistic infections, presence of Kaposi sarcoma, neurological presentations and minor symptoms were not associated with major change in survival time.

Acquired Immunodeficiency Syndrome↗