Screening for HIV during pregnancy. Survey of physicians' practices.
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AIDS Serodiagnosis↗
Biomedical subjects
S E MacDonald
Publications and source records attributed to S E MacDonald.
Cholinesterases in cardiac ganglia and modulation of canine intrinsic cardiac neuronal activity.
Cholinergic neurotransmission plays a significant role in intrinsic cardiac ganglia with the action of acetylcholine being terminated by acetylcholinesterase (AChE, EC 3.1.1.7). Anatomical studies were performed to characterize neurons associated with AChE and a closely related enzyme, butyrylcholinesterase (BuChE, EC 3.1.1.8), in canine intrinsic cardiac ganglia. Histochemical staining for AChE and BuChE in canine right atrial neurons showed that there were four neuronal populations, namely, those that contained AChE only, BuChE only, both AChE and BuChE, and those that did not contain either enzymes. The neuronal activity of intrinsic cardiac neurons in response to substrates and inhibitors of cholinesterases were studied in anesthetized dogs. The activity of intrinsic cardiac neurons, as measured by changes in the number of action potentials, increased by local application of acetylcholine. However, local application of butyrylcholine led to a considerably greater increase in the activity of intrinsic cardiac neurons. In keeping with the neurochemical heterogeneity in intrinsic cardiac ganglia with respect to cholinesterases, the activity generated by most butyrylcholine-sensitive neurons was not influenced by acetylcholine and the activity generated by the most acetylcholine-sensitive neurons was not influenced by butyrylcholine. This suggests that these two agents preferentially influence different populations of intrinsic cardiac neurons. Enzyme kinetic studies demonstrated that canine AChE preferentially catalyzed the hydrolysis of acetylcholine while canine BuChE preferentially catalyzed the hydrolysis of butyrylcholine. Cholinesterase inhibitors Ro 2-1250 and Ro 2-0638 inhibited both canine cholinesterases, while huperzine A preferentially inhibited canine AChE and ethopropazine inhibited canine BuChE. The activity of neurons in the intrinsic cardiac ganglia significantly increased when Ro 2-1250 or Ro 2-0638 was administered locally. The activity of neurons was not affected when huperzine A or ethopropazine was administered, indicating that both cholinesterases must be inhibited to increase neuronal activity. In summary, these data show that in addition to AChE, intrinsic cardiac ganglia also contain distinct populations of neurons that are associated with BuChE, and the activity generated by these neurons is differentially influenced by their substrates. Because simultaneous inhibition of AChE and BuChE leads to increased neuronal activity, it is concluded that AChE- and BuChE-positive intrinsic cardiac neurons may act synergistically to influence the overall tonic activity of intrinsic cardiac ganglia.
Acetylcholine↗
Learning the configuration of a landmark array: I. Touch-screen studies with pigeons and humans.
Pigeons and humans searched on a touch-screen monitor for an unmarked goal located relative to an array of landmarks presented in varied screen locations. After training with the goal centered in various square arrays of 4 landmarks, humans, but not pigeons, transferred accurately to arrays with novel elements. Humans searched in the middle of expanded arrays, whereas pigeons preserved the distance and direction to a single landmark. When trained with the goal centered below 2 identical horizontally aligned landmarks, humans responded to horizontal expansions or contractions of the array by shifting their search vertically, preserving angles from landmarks to goal. Pigeons did not adjust their search vertically. Humans trained with a single landmark adjusted search distance when landmark size was changed. Both pigeons and humans use the configuration of a landmark array, but the underlying processes seem to differ.
Adult↗
Effects of cold storage and water stress on water relations and gas exchange of white spruce (Picea glauca) seedlings.
To determine the effects of lifting time and storage on water-stress resistance of nursery-grown white spruce (Picea glauca (Moench) Voss) seedlings, we compared gas exchange, water relations and mortality of 3-year-old seedlings lifted in October 1991 and stored at -2 degrees C for 3 months with seedlings lifted in January 1992. The seedlings were placed in nutrient solution and subjected to -1.1 or -2.7 MPa water stress induced by polyethylene glycol 3350 for 9 days. Water stress, but not lifting time, had a significant effect on seedling net assimilation, symplastic volume and turgor loss point. In a second experiment, seedlings lifted in October 1991 were stored at -2 degrees C for 7 months and compared with seedlings lifted in May 1992. The seedlings were planted in pots, and their gas exchange and water relation parameters measured in response to gradual water stress. The results suggest that prolonged cold storage retards photosynthetic recovery of seedlings after planting. Higher rates of net assimilation in seedlings lifted in May were not directly related to their water status. Nonstomatal limitations were the primary factor influencing photosynthetic rate. We conclude that the inferior ability of cold-stored seedlings to tolerate water stress was due to poor osmotic adjustment and a lag in recovery of photosynthesis.
Journal Article↗
Gorillas' (Gorilla gorilla gorilla) spatial memory in a foraging task.
The spatial memory of 2 gorillas (Gorilla gorilla gorilla) was explored in a simulated foraging task. Trials consisted of 2 parts separated by a delay. In the 1st part, half of the total number of food sites were baited with a highly preferred food, and the subject was allowed to search, find, and consume these items (search phase). During the delay the same locations were again baited. After the delay the animal was reintroduced to the test enclosure and allowed to search through the sites again (re-search phase). In Experiment 1, an adult gorilla was very accurate in remembering locations that had previously contained food at delay intervals of 24 hr or more. In Experiment 2, a juvenile gorilla was also accurate in remembering locations that had previously contained food at delays up to 10 min. The adult gorilla appeared to use a counting strategy during the search phase to minimize the number of sites visited.
Animals↗
Marmoset (Callithrix jacchus jacchus) spatial memory in a foraging task: win-stay versus win-shift strategies.
The spatial memory of common marmosets (Callithrix jacchus jacchus) was explored in 3 experiments with a simulated foraging task. In Experiment 1, individual monkeys foraged among 8 baited food sites. They appeared to use spatial memory to accurately avoid revisiting previously depleted sites. There was no difference in accuracy between the adult monkeys and a juvenile monkey tested on the same task. In Experiment 2, a win-stay paradigm was used. The adult monkey subject very accurately remembered locations that had previously contained food. The monkey tended to visit adjacent correct sites when retrieving food and thus minimized the total distance travelled. In Experiment 3, a win-shift paradigm was used with 2 adult monkeys. Although both monkeys performed at above-chance levels of accuracy on the win-shift task, they made many errors. These results suggest that marmosets may prefer tasks that require a win-stay strategy.
Animals↗
Ecophysiology of shade needles of Picea glauca saplings in relation to removal of competing hardwoods and degree of prior shading.
We studied shade needles of Picea glauca (Moench) Voss saplings that were growing in 15, 45 or 90% shade from competing vegetation at northern boreal forest sites in Alberta and Saskatchewan. At each site, in late May or early June 1990, all hardwoods were removed within a 2-m radius of each of eight saplings in each shade treatment (released saplings), and eight saplings in each shade treatment were left as controls. Light-saturated net assimilation (NA), stomatal and mesophyll conductance and water use efficiency of one-year-old needles were measured four times during the 1990 growing season and in the spring of 1991. There was a trend of increased photosynthetic capacity within one week following release. By August 1990 and in the following spring, NA was higher in released trees than in controls. The increase in NA appeared to be related to increased stomatal conductance to water vapor and to increased foliar nitrogen and resulting increases in mesophyll conductance to CO(2). There was no measurable effect of degree of shading prior to release on NA following release. Foliage of the released saplings appeared capable of rapid acclimation to the open conditions.
Journal Article↗
A comparison of family physicians' and obstetricians' intrapartum management of low-risk pregnancies.
BACKGROUND: We hypothesized that family physicians' style of intrapartum management was less interventional than the management style of obstetricians, and that this would not adversely affect maternal or neonatal outcomes. METHODS: A retrospective, matched-pair study design was used to compare low-risk women cared for by community family physicians with those cared for by obstetricians at a small teaching hospital. The subjects were matched on the basis of age and parity. We compared the rates of intervention between family physicians and obstetricians. RESULTS: We studied 351 matched pairs of women. The demographic characteristics of patients were similar as were the rates for most labor and delivery procedures. Family physicians had lower rates for induction, external and internal fetal monitoring, narcotic analgesia use, and postpartum oxytocin use. Women cared for by family physicians spent less time in the hospital, both during labor and postpartum. CONCLUSION: This study supports the hypothesis that at our center family physicians intervene less than obstetricians in intrapartum management. Comparisons with similar studies conducted at other academic centers illustrate differences in styles of practice between institutions, not just between specialties.
Adult↗
Caffeine intoxication: a near fatality.
A 37-year-old woman ingested approximately 27 g caffeine in a suicide attempt. After initial presentation with supraventricular tachycardia, hypotension, and coma, she suffered repeated episodes of ventricular fibrillation. Resin hemoperfusion was performed, with prompt stabilization of the patient's cardiovascular status. Methylxanthine toxicity is briefly reviewed.
Adult↗