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Biomedical subjects

C S Wallace

Publications and source records attributed to C S Wallace.

7 recordsLinked to original sources
PubMed1992

Finite-state models in the alignment of macromolecules.

Minimum message length encoding is a technique of inductive inference with theoretical and practical advantages. It allows the posterior odds-ratio of two theories or hypotheses to be calculated. Here it is applied to problems of aligning or relating two strings, in particular two biological macromolecules. We compare the r-theory, that the strings are related, with the null-theory, that they are not related. If they are related, the probabilities of the various alignments can be calculated. This is done for one-, three-, and five-state models of relation or mutation. These correspond to linear and piecewise linear cost functions on runs of insertions and deletions. We describe how to estimate parameters of a model. The validity of a model is itself an hypothesis and can be objectively tested. This is done on real DNA strings and on artificial data. The tests on artificial data indicate limits on what can be inferred in various situations. The tests on real DNA support either the three- or five-state models over the one-state model. Finally, a fast, approximate minimum message length string comparison algorithm is described.

Algorithms↗
PubMed1992

Increases in dendritic length in occipital cortex after 4 days of differential housing in weanling rats.

To assess the capacity for experience to induce rapid alterations in the dendritic fields of cortical neurons, male Long-Evans hooded rats aged 30-31 days were housed in either a complex environment (EC) or an individual cage (IC) for 4 days. The basilar dendrites of layer III pyramidal cells in area 17 of visual cortex were measured in Golgi-stained sections. EC rats exhibited significant increases in total dendritic length and total number of branches. This finding demonstrates that the structural modifications previously reported after 30 days in the complex environment are well underway after only 4 days.

Animals↗
PubMed1992

A flexible perforated microelectrode array for extended neural recordings.

A flexible and perforated 32-element planar microelectrode array has been fabricated and used to measure evoked potentials in brain slices. Electrodes are spaced 200 microns apart in a 4 x 8 array and are sandwiched between layers of insulating polyimide. The polyimide sandwich is lifted off its substrate, making it flexible so that it could shape to contoured tissues. Prior to lift off, holes are etched to expose recording sites 15 microns in diameter and to create perforations which allow increased circulation of artificial cerebrospinal fluid to the recording surface of the tissue and, hence, increased viability. Comparisons of evoked potentials measured over time showed an average increase of 10 h to the viability of the slice while using the perforated versus nonperforated arrays.

Animals↗
PubMed1992

Lovastatin-induced rhabdomyolysis in the absence of concomitant drugs.

OBJECTIVE: Presentation of a case of lovastatin-induced rhabdomyolysis in the absence of other medications known to potentiate this adverse effect. METHODOLOGY: Case report. RESULTS: A 60-year-old black man developed rhabdomyolysis after receiving lovastatin for 14 months. Rhabdomyolysis developed in the absence of other medications previously reported to cause this adverse effect when administered concomitantly with lovastatin. Adverse drug reaction causality algorithms categorized this reaction as either possible or probable. CONCLUSIONS: Rhabdomyolysis is an uncommon adverse effect associated with lovastatin therapy. Although reported cases of lovastatin-induced rhabdomyolysis were associated with the coadministration of cyclosporine, erythromycin, gemfibrozil, or nicotinic acid, this adverse effect may occur in the absence of these agents.

Humans↗
PubMed1989

Effects of complex experience on somatic growth and organ development in rats.

Rats kept in complex environments (EC) show an array of brain changes relative to animals housed individually (IC). These effects have been explained as due to (a) information storage, (b) chronic stress that causes brain damage, or (c) neuroendocrine effects on brain maturation. Complex experience also affects somatic growth and organ development, and these may be related to the EC/IC brain differences. We have compared somatic growth and internal organs of 315 weanling and adult rats with various histories. (a) Young EC rats showed slower skeletal and visceral growth, while many brain components expand. (b) Although thymus and spleen were lighter in young ECs, immunocompetence was nonsignificantly (p less than .07) higher than in ICs. (c) Somatic growth of adult rats was slow and not very responsive to experience, whereas studies have shown EC/IC brain effects similar to those in young rats. (d) Males had slightly greater EC/IC somatic and visceral differences. (e) The stress index, adrenal weight, varied across age and experience, so chronic stress can not explain EC/IC brain differences. Training paradigms show brain changes similar to those from complex experience, occurring specifically with learning and in brain regions using the information. Learning and memory, therefore remain the best explanation of the EC brain effects.

Adrenal Glands↗
PubMed1987

Experience and brain development.

This article considers how experience can influence the developing and mature brain and proposes a new categorization scheme based upon the type of information stored and the brain mechanisms that appear to be involved in storing it. In this scheme, experience-expectant information storage refers to incorporation of environmental information that is ubiquitous in the environment and common to all species members, such as the basic elements of pattern perception. Experience-expectant processes appear to have evolved as a neural preparation for incorporating specific information: in many sensory systems, synaptic connections between nerve cells are overproduced, and a subsequent selection process occurs in which aspects of sensory experience determine the pattern of connections that remains. Experience-dependent information storage refers to incorporation of environmental information that is idiosyncratic, or unique to the individual, such as learning about one's specific physical environment or vocabulary. The neural basis of experience-dependent processes appears to involve active formation of new synaptic connections in response to the events providing the information to be stored. Although these processes probably do not occur entirely independently of one another in development, the categories offer a new view more in accord with neural mechanisms than were terms like "critical" or "sensitive period."

Brain↗