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Biomedical subjects

W W Anderson

Publications and source records attributed to W W Anderson.

At least 55 records · Page 3Linked to original sources
PubMed1986

Membrane currents underlying bursting pacemaker activity and spike frequency adaptation in invertebrates.

Invertebrate systems have proved to be quite useful for the development of an understanding of some processes in the central nervous system (CNS). An understanding of the basic mechanisms of epilepsy will result from understanding not only how populations of neurons interact but also how the physiological processes in individual neurons are altered in epileptogenesis. Because invertebrate neurons have been so accessible to experimentation, it has been possible to explore in detail the basic mechanisms controlling neuronal excitability using these cells and to make some useful predictions about electrophysiological mechanisms that may be present in central neurons. This chapter deals with two electrophysiological processes that have been observed in invertebrate neurons and that may have some relevance to understanding the basic mechanisms of epilepsy. We review first the past and current studies of invertebrate burst firing neurons. It appears that the electrophysiological mechanisms producing burst firing may be present in CNS neurons participating in epileptogenesis. With caution, the information gleaned from invertebrate studies may be applicable to higher systems. The second process we consider is the phenomenon of spike frequency adaptation seen in invertebrates. Spike frequency adaptation is the process by which the firing rate of the neuron declines despite the maintenance of a constant stimulus. This process is not so thoroughly studied as burst firing, but it appears to represent a cellular mechanism designed to suppress prolonged periods of repetitive firing. Clearly, the suppression of such a process would produce excessive neuronal excitability, while its enhancement might have some anticonvulsant effects. The extreme sensitivity of spike frequency adaptation to barbiturates suggests such a possibility. These two electrophysiological processes are interesting in themselves and also because they may underlie the genesis or control of seizures. However, the greater significance is that, to understand the basic mechanisms of epilepsy, we may be well advised to examine neuronal processes in systems not considered to have seizure susceptibility.

Action Potentials↗
PubMed1982

Homozygosity and patch structure in plant populations as a result of nearest-neighbor pollination.

The population genetic consequences of nearest-neighbor pollination in an outcrossing plant species were investigated through computer simulations. The genetic system consisted of two alleles at a single locus in a self-incompatible plant that mates by random pollen transfer from a neighboring individual. Beginning with a random distribution of genotypes, restricted pollen and seed dispersal were applied each generation to 10,000 individuals spaced uniformly on a square grid. This restricted gene flow caused inbreeding, a rapid increase in homozygosity, and striking microgeographic differentiation of the populations. Patches of homozygotes bordered by heterozygotes formed quickly and persisted for many generations. Thus, high levels of inbreeding, homozygosity, and patchiness in the spatial distribution of genotypes are expected in plant populations with breeding systems based on nearest-neighbor pollination, and such observations require no explanation by natural selection or other deterministic forces.

Journal Article↗
PubMed1982

Clinical features of pruritus among patients undergoing maintenance hemodialysis.

Patients undergoing maintenance hemodialysis were asked to complete a questionnaire to define further the nature of uremic pruritus. Of the 237 respondents, 87 (37%) reported "prolonged bothersome itchiness" at the time surveyed, and an additional 97 (41%), not affected at that time, had experienced this problem in the past. Of the 184 patients who reported pruritus in either the past or present, discomfort occurred only during or soon after dialysis in 46 (25%) patients and was most severe at those times in an additional 78 (42%) patients. Topical emollients and orally administered antipruritic agents provided relief in only 33 (18%) and 31 (17%) patients, respectively. These data provide the first statistical basis for certain clinical impressions concerning uremic pruritus and suggest it is not as common among patients who are undergoing dialysis as has been previously implied.

Adult↗
PubMed1981

Synaptic mechanisms that generate network oscillations in the absence of discrete postsynaptic potentials.

Synaptic mechanisms were examined in the pyloric network of the lobster stomatogastric which generate network oscillations in the absence of discrete postsynaptic potentials (PSPs). In normal saline, the unstimulated pyloric network underwent weak bursting in only a few cells. Stimulation of the input nerve, or bath application of the input neurotransmitter dopamine, produced similar vigorous bursting in many pyloric neurons. In saline-containing tetrodotoxin (TTX) plus dopamine, action potentials and corresponding discrete PSPs were blocked, but the underlying slow wave oscillations in network neurons continued. No oscillations occurred in TTX-saline without dopamine. The generation of these nonspiking network oscillations can be explained by the interaction between two synaptic mechanisms which do not produce discrete PSPs: neurotransmitter activation of bursting pacemaker oscillations in a single network neuron, and graded inhibition between network neurons.

Action Potentials↗
PubMed1979

Evidence for selection by male mating success in natural populations of Drosophila pseudoobscura.

Gene arrangement frequencies were determined at two stages in the life history of Drosophila pseudoobscura taken from nature. Three populations in the central highlands of Mexico were each sampled twice during 1976. Gene arrangement frequencies were measured in adult males and in larvae that were the offspring of females collected at the same time. The adult males were in all likelihood a representative sample of those who fathered the larvae produced by the wild females. Differences in gene arrangement frequency between these two life stages should indicate the operation of natural selection. One-third of our comparisons of common gene arrangement frequencies in males and in larvae from the next generation were statistically significant, as were one-third of our comparisons of total frequency arrays in the two life stages. We consider the components of selection that could produce such frequency changes and reason that male mating success must be the major one. Gene arrangement frequencies in the Mexican populations fluctuate within wide bounds. Selection must act to retain the polymorphism in the face of this flux in gene arrangement frequencies, and we suggest that male mating success plays an important role.

Animals↗
PubMed1976

Selection for geotaxis in Drosophila melanogaster: heritability, degree of dominance, and correlated responses to selection.

Selection for geotaxis was carried out with flies from a natural population of Drosophila melanogaster; geotactic behavior was measured by means of a Hirsch classification maze. The population was initally almost neutral to gravity, and it responded to both positive (downward) and negative (upward) selection with a realized heritability of about 0.13. Stabilizing selection toward neutral gravity was carried out simultaneously. At generations 6, 9, and 10, all possibly hybrid crosses between pairs of the selected populations were generated and tested. The geotactic scores of hybrids in generations 6 and 9 were not significantly different from the midparent values, while the scores of hybrids in generation 10 deviated significantly from the midparent values in the direction of positive geotaxis. The frequencies of polymorphic inversions declined in every population during selection, but the population under neutral selection seemed to maintain a higher chromosomal polymorphism than those under positive or negative selection. There was no significant depression of productivity, measured as number of progeny, in any population during nine generations of selection.

Animals↗
PubMed1974

Selection by fertility in Drosophila pseudoobscura.

Fertility, the component of selection due to female fecundity and male mating success, differed significantly among the ST/ST, ST/AR, and AR/AR karyotypes in experimental populations and varied with karyotypic frequency. In relation to ST/AR, ST/ST females and males had higher fertilities at low frequency; AR/AR males and females were at a significant fertility disadvantage at intermediate frequency, while at low and at high frequencies their fertilities matched or exceeded that of the heterokaryotype. These fertility differences were comparable in size to viability differences previously reported for D. pseudoobscura karyotypes. Differential fertility seems likely to be an important element, perhaps just as important as differential viability, in the balancing selection that maintains the chromosomal polymorphism in this species.

Animals↗
PubMed1970

Age-specific selection.

A model is presented for age-specific selection on the genotypes in a population. Each genotype is assigned a life table that specifies the viability and fecundity of its age classes. Breeding and reproduction occur at regular intervals, and generations overlap. Examples were generated on a digital computer. Gene frequencies and the distribution of individuals among the various age classes may oscillate until equilibrium is reached. Moreover, age structure and gene frequencies are intimately related; a change in either factor alone may bring about a change in the other. In an extension of the basic model, the fecundities of the genotypes were regulated by population density. Under the joint action of logistic control and age-specific selection, the growth curve of the population can, for some schedules of selection, show plateaus in an otherwise sigmoid increase. The relevance of the growth patterns obtained in different types of environments to current ideas of "r" and "K" selection is discussed.

Age Factors↗
PubMed1969

Polymorphism resulting from the mating advantage of rare male genotypes.

An algebraic model is presented for selection by the mating advantage of rare genotypes. In accordance with the results of recent experiments, the selective advantage is formulated as inversely proportional to genotype frequency. The model applies to any number of alleles at an autosomal locus or at a sex-linked locus, and it provides for a different intensity of selection for each genotype in each sex. The frequency of an allele under this selection proceeds to a stable, nontrivial equilibrium when any one of the genotypes carrying the allele and any one of those carrying another allele possess some degree of the advantage which varies inversely with genotype frequency. The changes in gene frequency are not affected by the mating system, being, for instance, the same with random mating as with inbreeding. With low values for the selection parameters, genetic polymorphisms could be maintained with little selection apparent except at rather low or rather high gene frequencies. The rare genotype advantage may be a significant element among the mechanisms which maintain the extensive genetic polymorphisms of natural populations.

Animals↗