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Biomedical subjects

J A Macdonald

Publications and source records attributed to J A Macdonald.

16 recordsLinked to original sources
PubMed1992

Antarctic fishes survive exposure to carbon monoxide.

The extensive in vivo conversion of haemoglobin to the carbon monoxide derivative has no discernible effect on the survival of the red-blooded Antarctic fish Pagothenia bernacchii. Analysis of caudally sampled blood of cannulated specimens revealed that reconversion of carbon-monoxy haemoglobin to oxyhaemoglobin was complete within 48 hours. Thus, under stress-free conditions, haemoglobin is not necessary for survival of P. bernacchii. Red-blooded Antarctic fishes can carry oxygen necessary for routine delivery dissolved in plasma, in a similar way to the haemoglobinless Channichthyidae, although they lack the morphological and physiological adaptations which allow the latter to prosper without any haemoglobin.

Animals↗
PubMed1991

Adaptation of sleep and circadian rhythms to the Antarctic summer: a question of zeitgeber strength.

Adaptation of sleep and circadian rhythms was examined in three temperate zone dwellers arriving in Antarctica during summer. Rectal temperature, wrist activity, and heart rate were monitored continuously, sleep timing and quality noted on awakening, and mood and fatigue rated every 2 h while awake. Sleep was poorer in 2/3 subjects in Antarctica, where all subjects reported more difficulty rising. Sleep occurred at the same clock times in New Zealand and Antarctica, however, the rhythms of temperature, activity, and heart rate underwent a delay of about 2 h. The subject with the most Antarctic experience had the least difficulty adapting to sleeping during constant daylight. The subject with the most delayed circadian rhythms had the most difficulty. The delay in the circadian system with respect to sleep and clock time is hypothesized to be due to differences in zeitgeber strength and/or zeitgeber exposure between Antarctica and New Zealand.

Activities of Daily Living↗
PubMed1990

Effects of temperature on nervous system: implications for behavioral performance.

Temperature change has a major impact on the function of the nervous system and its components, including altering synaptic gain and changing synaptic and conduction delays. Although many animals are subject to changes in body temperature, the degree of temperature change actually experienced by many poikilotherms is not well documented. The fact that many animals continue to exhibit coordinated sensorimotor function during changes in body temperature indicates that some form of temperature compensation has occurred within the nervous system. Compensations may occur automatically (opposing effects of temperature offsetting each other), they may be an inherent property of closed-loop systems, or they may be effected by more sophisticated control mechanisms such as those of the vertebrate cerebellum.

Action Potentials↗
PubMed1989

Theoretical principles of optical pachometry.

Various configurations have been suggested for the optical measurement of corneal thickness by slit beam doubling, and corresponding ray traces have been provided to relate actual thickness to apparent thickness. In this report, a set of equations is provided which apply to the general situation in which neither the angle of illumination nor the angle of observation are aligned with or symmetrical about the normal to the cornea. An explicit solution to these equations giving true corneal thickness in terms of apparent thickness cannot be established, and an iterative procedure is used to develop a relationship for a number of different pachometer configurations. The near linearity of these relationships suggests the existence of a simple equation to relate these entities. By making appropriate assumptions, a linear approximation relating the inverse of the true thickness to the inverse of the apparent thickness is developed. An equation for determining the location of measurements of peripheral corneal thickness is also derived. The equations presented here may be generally applied to all optical pachometer configurations, can be used to estimate the relative contributions of various sources of error in pachometry and provide a basis for obtaining uniform absolute derivations of corneal thickness.

Cornea↗
PubMed1986

Temperature dependence of neurotransmitter release in the antarctic fish Pagothenia borchgrevinki.

The quantal contents of endplate potentials from extraocular muscles of an antarctic fish Pagothenia borchgrevinki were measured over a range of temperatures. Quantal release was maximal at about 5 degrees C but showed little dependence on temperature between -2 degrees C and 10 degrees C. Above 10 degrees C quantal content declined until release ceased about 18 degrees C. In view of the fact that the ambient temperature at which these fish live is constant at -1.9 degrees C, the results suggest that Pagothenia borchgrevinki is only partially adapted to its environment despite 25 million years acclimatization.

Animals↗
PubMed1985

Oculomotor function at low temperature: antarctic versus temperate fish.

The peripheral oculomotor system can be modelled as a first order linear system (Montgomery, 1983), and hence specified by its characteristic frequency and 'd.c.' gain. These parameters can be determined by recording eye movements produced by stimulation of the abducens nerve with sinusoidally modulated pulse trains, and compare well with those independently derived from the relationship between motoneurone firing and spontaneous eye movement. Characteristic frequency and gain of the peripheral oculomotor system were determined for two species of antarctic teleost and one temperate species, to examine temperature compensation within a complete motor output pathway. Compared with low temperature function in temperate fish, the characteristic frequency is clearly temperature compensated in antarctic fish, which explains in part the observed temperature compensation of their rapid eye movement. The 'd.c.' gain of the peripheral oculomotor system is inversely related to temperature, providing an automatic compensation for possible reductions in central nervous system output and sensory gain at low temperature.

Animals↗
PubMed1976

Fistula formation complicating pancreatic abscess.

Internal fistula formation is a rare complication of pancreatic abscess or pseudocyst; a fairly extensive search of the literature has produced only 47 cases. Common factors in the aetiology, presentation and management are discussed, and a further case is reported which demonstrates many features of this unusual condition.

Abscess↗
PubMedDate not supplied

The inhibitory effect of testosterone on the development of metabolic tolerance to ethanol.

We have investigated the mechanism(s) of metabolic tolerance to ethanol in a rat strain (spontaneously hypertensive or SH) in which liver alcohol dehydrogenase (ADH) levels are very low due to a marked inhibitory effect of testosterone on ADH. Chronic ethanol administration resulted in marked increases in the rate of ethanol metabolism and in ADH activity (+65 to 90%). Oxygen consumption measured in the perfused livers of the ethanol-fed rats was also elevated (+40%). The administration of 6-n-propyl-2-thiouracil (PTU), which was previously found to reduce hepatic oxygen consumption and to increase ADH activity, resulted in no change in the rate of ethanol metabolism in the ethanol-fed rats and an increase in the sucrose-fed controls, suggesting that increased ADH activity is more important for the development of metabolic tolerance to ethanol, in the male SH rat, than increased oxygen consumption. The activity of the microsomal ethanol-oxidizing system (MEOS) in vitro was induced by chronic ethanol treatment (+95%), but it may only account for a small part (32%) of the increase in ethanol metabolism in vivo. Serum testosterone concentrations were lower in the ethanol-fed rats at peak blood ethanol levels, relative to those found in controls. Concurrent chronic administration of ethanol and testosterone abolished about one-third of the absolute increases in ethanol metabolism and in ADH activity in the ethanol-fed rats. In conclusion, most of the metabolic tolerance to ethanol, in the male SH rat, appears to occur mainly due to a testosterone-independent increase in ADH activity and to a lesser degree to an increase in ADH activity produced by a reduction in testosterone levels in the ethanol-fed rats.

Alcohol Oxidoreductases↗