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Biomedical subjects

H A Armstrong

Publications and source records attributed to H A Armstrong.

7 recordsLinked to original sources
PubMed2001

Growth patterns in euconodont crown enamel: implications for life history and mode-of-life reconstruction in the earliest vertebrates.

Euconodonts were the first vertebrates to produce a mineralized skeleton. It is concluded that the minor increments in the crown enamels of Protopanderodus varicostatus and Drepanodus robustus are probable homologues of the cross striations in hominoid enamel, although they are much more variable in thickness and represent daily to weekly growth. Major increments are superficially similar to lines of Retzuis, but represent a check in growth that is likely to have occurred at monthly intervals. Periods of above- and below-average growth are likely to have been seasonally moderated. The growth of P. varicostatus' elements are characterized by two distinct phases: the production of a triangular, asymmetrical juvenile 'proto-element' followed, in a second phase, by the development of the curved and twisted geometry of the adult element. These fundamentally different morphologies imply that juvenile and adult animals had different modes of life and/or feeding strategies. In these animals the growth of the elements was indeterminate. The growth model for euconodonts is clearly different from that of hominoid teeth as the enamel organ must have reformed repeatedly throughout life.

Animals↗
PubMed1996

Effect of face context on recognition memory for voices.

Participants heard 10 voices and were given a 2-alternative recognition-memory test. Accuracy was higher when testing was intentional rather than incidental and when faces accompanying the original voices were re-presented during the test. Some support was found for an attention-allocation model, which predicted poorest performance with incidental testing and faces not reinstated. Reported confidence was higher for correct than for incorrect decisions, but more confident participants were not more accurate.

Adult↗
PubMed1992

Presence of the earliest vertebrate hard tissue in conodonts.

From histological investigations into the microstructure of conodont elements, a number of tissue types characteristic of the phosphatic skeleton of vertebrates have been identified. These include cellular bone, two forms of hypermineralized enamel homologs, and globular calcified cartilage. The presence of cellular bone in conodont elements provides unequivocal evidence for their vertebrate affinities. Furthermore, the identification of vertebrate hard tissues in the oral elements of conodonts extends the earliest occurrence of vertebrate hard tissues back by around 40 million years, from the Middle Ordovician (475 million years ago) to the Late Cambrian (515 million years ago).

Animals↗
PubMed1992

Linkage analysis of candidate loci in autosomal dominant myotonia congenita.

Electrophysiologic studies in patients with autosomal dominant myotonia congenita (ADMC) have implicated defects of both muscle membrane sodium and chloride channels. An adult skeletal muscle sodium channel (ASkM1) gene maps to chromosome 17q23-25, and defects in this gene are almost certainly responsible for at least three variants of hyperkalemic periodic paralysis (HPP)--myotonic HPP, nonmyotonic HPP, and paramyotonia congenita. A gene for a muscle chloride channel has not yet been mapped in humans, but has been identified in the mouse. The gene for the cystic fibrosis transmembrane regulator (CFTR), which has chloride channel properties, is located on chromosome 7q31. This region is syntenic with the area of mouse chromosome 6 that contains the muscle chloride channel gene, a defect in which is responsible for the ADR phenotype, a murine model of myotonia. We performed linkage analysis using chromosome 17q polymorphisms at D17S74, SCN4A, and GH1, two chromosome 7q31 restriction fragment length polymorphisms, and a dinucleotide repeat polymorphism within the CFTR gene (CFTR-DNR), in three pedigrees with ADMC. The lod scores obtained show that the locus for ADMC is not at ASkM1 and is excluded from a region of at least 24 cM on either side of the CFTR gene.

Chromosome Mapping↗
PubMed1986

Absence of antibody to HTLV I and III in sera of Canadian patients with multiple sclerosis and chronic myelopathy.

Recently, elevated titers of antibody to HTLV I have been demonstrated in patients with tropical spastic paraparesis and multiple sclerosis. We evaluated the possible role of human retroviruses HTLV I and III in Canadian patients with multiple sclerosis and chronic idiopathic myelopathy. Using sensitive enzyme immunoassays, we were unable to find antibody to either HTLV I or III in 201 patients with multiple sclerosis, 29 patients with chronic myelopathy, 51 patients with other neurological disorders, or 29 normal subjects. These data do not support a role for these viruses in the cause of sporadic multiple sclerosis and chronic myelopathy in a regionally based Canadian population, but do not exclude a role for other antigenically distinct retroviruses.

Antibodies, Viral↗
PubMed1985

Oligoclonal bands in multiple sclerosis: clinical-pathologic correlation.

Although oligoclonal banding is a characteristic feature of MS spinal fluid, some patients do not show this abnormality. Four of 18 consecutive patients with autopsy-proven MS had no oligoclonal bands (OB) in CSF during life or at postmortem. Patients with OB had numerous plasma cells in meninges and plaques (confirmed in sections stained for cytoplasmic immunoglobulin). The four patients without bands had few or no identifiable plasma cells. Therefore, lack of OB correlates with both inactivity of plaques and absence of plasma cells in plaques or meninges. This is another form of heterogeneity in MS.

Adult↗