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Biomedical subjects

A R Walker

Publications and source records attributed to A R Walker.

At least 109 records · Page 6Linked to original sources
PubMed1996

Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism.

The plant hormone auxin regulates various developmental processes including root formation, vascular development, and gravitropism. Mutations within the AUX1 gene confer an auxin-resistant root growth phenotype and abolish root gravitropic curvature. Polypeptide sequence similarity to amino acid permeases suggests that AUX1 mediates the transport of an amino acid-like signaling molecule. Indole-3-acetic acid, the major form of auxin in higher plants, is structurally similar to tryptophan and is a likely substrate for the AUX1 gene product. The cloned AUX1 gene can restore the auxin-responsiveness of transgenic aux1 roots. Spatially, AUX1 is expressed in root apical tissues that regulate root gravitropic curvature.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1996

Amblyomma tick feeding in relation to host health.

The tick Amblyomma variegatum has been shown by field and controlled laboratory experiments to have a direct causal relationship with severe clinical dermatophilosis. The tick does not transmit the pathogen in the usual sense, either biologically or mechanically. The tick suppresses the immune system of the host, for unknown reasons, and this appears to enable the existing dermatophilosis to become a severe disease. There are other factors involved with the progression of dermatophilosis to clinical disease, such as malnutrition. However, the role of ticks is so distinct that it is likely that appropriate tick control using acaricide, when combined with other measures to improve the husbandry of the cattle, will reduce the incidence and severity of dermatophilosis.

Africa, Western↗
PubMed1996

Formulation of integrated control of Boophilus microplus in Paraguay: analysis of natural infestations.

A 3-year study into the seasonal variation in the numbers of Boophilus microplus ticks infesting three breeds of beef cattle in Paraguay was carried out to provide the basic data necessary to formulate tick control recommendations. The effect of tick burden on weight gain was also analysed. Economic parameters for tick control were calculated. Half body counts of standard female B. microplus were carried out every 2 weeks, at the same time engorged female ticks were placed in the field to observe time to oviposition, larval hatching and 50% survival time. Cattle were weighed every 2 months. Peak tick burdens were encountered in late autumn, with a winter low. Observations of the non-parasitic cycle of the tick suggested that four generations year-1 were possible. High tick burdens were well correlated to low weight gains or weight losses, depending on the breed of cattle. Compensatory weight gains were seen in all three breeds at the end of winter when tick burdens decreased. The economic threshold for tick treatment was calculated at 53 and 54 ticks per animal in 2 separate years of the study. Recommendations for tick control programmes are given.

Animals↗
PubMed1996

Integument and sensillum auriforme of the opisthosoma of Rhipicephalus appendiculatus (Acari:Ixodidae).

The opisthosomal integument and sensilla auriformia of Rhipicephalus appendiculatus Neumann larvae, nymphs, females and males, both unfed, fed, and during molt, were examined by light and electron microscopy in relation to semiochemical production. The integument consists of epidermis, endocuticle, exocuticle, epicuticle, a superficial wax layer and a variable additional deposit. The integument of immature instars and females grows greatly during feeding. The integument is traversed by pore canals from the epidermis to the outer wax canals. The epidermis can secrete material to the exterior by way of the pore canals and wax canals. The sensillum auriforme is a common disk-shaped organ, with a complex internal chamber open to the exterior by way of a pore. It has no apparent secretory capacity and is of presumed sensory function. It is located in the integument of scutum and alloscutum of all instars.

Animals↗
PubMed1996

Integumental glands of the tick Rhipicephalus appendiculatus (Acari:Ixodidae) as potential producers of semiochemicals.

The opisthosomal integument and associated secretory organs of Rhipicephalus appendiculatus Neumann larvae, nymphs, females and males, both unfed and fed were examined by light and electron microscopy. Type 1 dermal glands were found on the alloscutum and scutum of all ticks. They were undeveloped in unfed ticks and reached full development in engorging ticks. They produced secretory granules from 2 glandular cells but without accumulation of a reservoir of secreted material. Type 2 dermal glands were found in all ticks, with pores on the alloscutum, edge of scutum, and on anal plates. These glands produced secretion during feeding and accumulated large reservoirs of secreted material that were present in engorging, recently detached and questing ticks. Spiracular glands were found in all ticks below the spiracle plate. They produced small amounts of secretion and had pores to the exterior by way of spiracle goblets. No obvious cycle of secretory activity was recorded. Foveal glands were present and produced secretions in nymphs, females, and males. They were largest in females with an accumulation of secretory vesicles in feeding ticks. The potential function of these glands is discussed in the context of the chemical ecology of this tick.

Animals↗
PubMed1996

Emergency department management of house fire burns and carbon monoxide poisoning in children.

Fires continue to be a major killer of children, accounting for as many as 34% of fatal injuries in those younger than 16 years of age. Recent advances in burn care have improved to the extent that attention is being refocused on the initial resuscitation period as a time when significant improvements in mortality and morbidity may be achieved. Early invasive monitoring in selected patients may help children survive very severe burn injury. Carbon monoxide poisoning remains a common and controversial problem. Although it is clear that venous carboxyhemoglobin levels are similar to arterial levels, the treatment of children with significant poisoning has not been well studied. Hyperbaric oxygen therapy may be helpful in preventing serious central nervous system injury, but studies in children are lacking. Prevention of burns is far superior to treatment of burns.

Adolescent↗
PubMed1996

Some thoughts on the influence of attitude on health and ageing.

Morbidity and longevity among the middle-aged and elderly are affected by a variety of factors including genetics, social class, diet, smoking practice, alcohol consumption, and physical activity. Additionally, in some individuals and communities, the factors of attitude, regularity of life and religiosity appear important. In this contribution, some behavioural and metabolic ramifications of adverse attitude are discussed, and some examples are given of benefits conferred in populations, past and present, marked by regularity of life and religiosity. Comments are made on the possibility of persons making changes in the traits described.

Adaptation, Psychological↗