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Biomedical subjects

S Sawyer

Publications and source records attributed to S Sawyer.

49 records · Page 3Linked to original sources
PubMed1981

A continuous migration model with stable demography.

A probability model of a population undergoing migration, mutation, and mating in a geographic continuum R is constructed, and an integro-differential equation is derived for the probability of genetic identity. The equation is solved in one case, and asymptotic analysis done in others. Individuals at x, y epsilon R in the model mate with probability V(x, y) dt in any time interval (t, t + dt). In two dimensions, if V(x, y) = V(x - y) where V(x) approximately V(x/beta)/beta2 approaches a delta function, the equilibrium probability of identity vanishes as beta Leads to 0. The asymptotic rate at which this occurs is discussed for mutation rates u = u0 Greater than 0 and for beta approximately cua, alpha Greater than 0, and u Leads to 0.

Animals↗
PubMed1980

A simple method for the isolation of platelet-free lymphocyte suspensions from rat whole blood.

A simple technique for obtaining platelet-free lymphocyte suspensions from rat whole blood for use in complement-dependent microcytotoxicity assays is presented. Rat lymphocytes were purified by filtering buffy coat preparations containing thrombin over nylon fiber columns prior to Ficoll-Hypaque centrifugation. The addition of thrombin to buffy coat preparations significantly (P < 0.001) enhanced platelet retention on the nylon fiber columns. This procedure yielded lymphocyte suspensions which had a 98% mean reduction in platelet contamination compared to lymphocyte preparations which were purified using only Ficoll-Hypaque centrifugation. The thrombin-nylon fiber filtration method produced lymphocyte suspensions containing an average of 98% lymphocytes, and the total yield of lymphocytes isolated from 2 ml of blood averaged 2.85 X 10(6) cells. The sensitivity of complement-dependent microcytotoxicity assays was increased by the use of the thrombin-nylon fiber-filtered platelet-free lymphocyte preparations compared to the use of platelet-contaminated lymphocyte suspensions.

Animals↗
PubMed1980

Neostriatal dopamine and sensory inattention.

Damage to the mesotelencephalic dopamine-containing projection of rats results in a sensory inattention, characterized by impairments in orientation toward somatosensory, visual, and olfactory stimuli. The present experiments were performed to establish which branch of this dopaminergic system is responsible for these sensorimotor deficits. Two approaches were used. In the first, individual dopamine-innervated forebrain sites were damaged by localized 6-hydroxydopamine injection into, or by electrolytic lesions of, these regions. In the second, rats were given tegmental 6-hydroxydopamine injections that damaged the entire mesotelencephalic projection and subsequently received intracerebral injections of the dopamine agonist apomorphine into specific forebrain sites in an attempt to reinstate orientation. The results demonstrate that dopaminergic terminals in the neostriatum are critical for orientation. Unilateral neostriatal 6-hydroxydopamine injections or electrolytic lesions reduced orientation to contralateral touch, whereas similar damage to other dopamine-innervated forebrain structures did not. Further, the results suggest that dopaminergic terminals in the anterior neostriatum are especially important for orientation to touch of the rostral body surface while those in the posterior neostriatum are most critical for orientation to caudal touch. After damage to all branches of the mesotelencephalic dopaminergic system, orientation to touch was reinstated by injection of apomorphine into the neostriatum but not by injection into the other dopamine-innervated forebrain regions tested.

Animals↗
PubMed1979

Maximum geographic range of a mutant allele considered as a subtype of a Brownian branching random field.

A rare allelic type is modeled as a field of individuals diffusing independently in d-dimensional space (d = 1,2,...), in which individuals are replaced by random numbers of offspring at a constant rate. In an infinite-allele model with selectively identical alleles, the offspring distribution would have mean 1 - u, in which u is the mutation rate; otherwise mean (1 - u)w, in which w is the relative fitness of the allele. Let p(x) be the probability that some descendent of an individual initially at zero diffuses unilaterally as far as x(d = 1), or else the probability that some descendent of an individual at x diffuses within a > 0 of the origin (d >/= 2). A nonlinear differential equation is found for p(x) that is solvable for d = 1 and related to Emden's equation for d >/= 2. For p(x) >/= 10(-4) and u </= 10(-5), genetic drift is more important than mutation in the behavior of p(x) (d = 1). If u = 0 and w = 1, p(x) approximately C/x(2) as x --> infinity for d </= 3. As a mathematical application, it is shown that if the initial distribution is uniform Poisson, a bounded open set K is visited by individuals in the field at arbitrarily large times if d >/= 2 but not if d = 1.

Journal Article↗
PubMed1979

Genetic drift in sex-linked lethal disorders.

A model is considered to calculate effects of genetic drift on the expected proportion of new mutants amongst males affected by a sex-linked recessive lethal. We show how to relate the number of cases of the disorder in males to the expected deviations from the deterministic value of the proportion of new mutants. For small values of alpha (= 3N mu), where N is the size of the female population, and mu is the mutation rate from wild-type to lethal allele, the standard deviation (SD) of the proportion of new mutants is large. However, if alpha more than 50, the potential effect of genetic drift is probably less important than the many other sources of error and bias.

Gene Frequency↗
PubMed1976

Role of activated macrophages in resistance of mice to infection with Trypanosoma cruzi.

The role of the activated macrophage in resistance of mice to infection with Trypanosoma cruzi was investigated with use of mice that had not been infected with T. cruzi but whose macrophages were activated by Toxoplasma gondii or Besnoitia jellisoni. Mice with activated macrophages were significantly more resistant to intra-peritoneal challenge with the Tulahuen strain of T. cruzi than were controls. The role of serum factors in resistance to T. cruzi was excluded by the demonstration of no difference between survival of T. cruzi in serum from mice with activated macrophages and in that from controls. As the only modality of resistance to T. cruzi in this in vivo model appeared to be the activated macrophage, this cell was investigated in vitro. Activated macrophages were shown to be able to inhibit completely multiplication of T. cruzi, whereas significant multiplication of the parasite occurred in control macrophages. Both in vivo and in vitro data suggest that the activated macrophage may play a major role in resistance to infection with T. cruzi.

Animals↗
PubMed1969

Specificity of the induced bactericidin of the West Indian spiny lobster, Panulirus argus.

To investigate the specificity of an inducible hemolymph bactericidin, West Indian spiny lobsters were immunized with a variety of antigens. Bactericidal assays were conducted with strain EMB-1, a gram-negative bacillus isolated from normal lobster intestine. Animals given saline solution with or without 0.3% Formalin exhibited only a slight response similar to sham controls. Injections of type 2 pneumococci or bovine albumin produced slightly higher responses. These were much less pronounced than the homologous response to EMB-1. Formalin exhibited an adjuvant-like effect with EMB-1.

Animals↗
PubMedDate not supplied

Introducing an analgesic prescription chart.

The report of the working party on pain after surgery states that the 'failure to relieve pain is morally and ethically unacceptable' (Working Party of the Commission on the Provision of Surgical Services, 1990). The report's recommendations include: A patient's pain should be assessed and recorded along with other observations; The level of care and monitoring is appropriate both to the clinical condition of the patient and the technique employed, with training for staff to include programmes for the diagnosis and management of the complications and hazards of particular forms of treatment.

Audiovisual Aids↗