The development of a non-invasive behavioral model of thermal heat stress in laboratory mice (Mus musculus).

BACKGROUND: Many behavioral and physiological studies of laboratory mice employ invasive methods such as radio telemetry to measure key aspects of behavior and physiology. Radio telemetry requires surgical implants, which may impact mouse health and behavior, and thus reduce the reliability of the data collected. NEW METHOD: We developed a method to measure key aspects of thermoregulatory behavior without compromising animal welfare. We examined the thermoregulatory response to heat stress in a custom-built arena that permitted the use of simultaneous and continuous infrared thermography (IRT) and video capture. This allowed us to measure changes in surface body temperature and determine total distance traveled using EthoVision XT animal tracking software. RESULTS: Locomotor activity and surface body temperature differed between heat-stressed mice and mice kept within their thermal comfort zone. The former had an increase in surface body temperature and a decline in locomotor activity, whereas the latter had a stable surface body temperature and showed greater activity levels. METHODS: Surface body temperature and locomotor activity are conventionally quantified by measurements taken at regular intervals, which limit the use and accuracy of the data. We obtained data of high resolution (i.e., recorded continuously) and accuracy that allowed for the examination of key physiological measurements such as energy expenditure and peripheral vasomotor tone. CONCLUSIONS: This novel experimental method for studying thermoregulatory behavior in mice using non-invasive tools has advantages over radio-telemetry and represents an improvement in laboratory animal welfare.

Impacts of climate change and climate variability on the competitiveness of wheat and beef cattle production in Emerald, north-east Australia.

Emerald, north-east Queensland, is at the northern margin of the wheat cropping region of Australia. The Emerald region was previously used predominantly for grazing beef cattle; however, cropping has developed in importance over the past 30 years. We use historical climate records (1890-1998) to simulate and compare wheat yields, grass production and live-weight gain (LWG) over time. The cropping expansion from the 1970s to the early 1990s has occurred in a unique period in the 108-year record with the highest average wheat yields, lowest wheat yield variability and the greatest relative productivity of wheat production against grass production. If this window of opportunity is a result of long-term climate variability, then cropping is likely to decline in the region as conditions return to those experienced earlier in the record. If this increase is related to climate change, then cropping is likely to persist in the region with productivity maintained at current levels particularly through the yield-enhancing effects of increased atmospheric CO2 concentrations. However, this persistence will be influenced by the frequencies of El Niño conditions that may increase with global warming. The high relative productivities experienced over the past few decades have probably biased producers' expectations, and applications for drought support need to take into account the longer-term perspective provided by this analysis. Nevertheless, the last 6 years have the lowest simulated mean LWG production on the record. The identification of poor production periods depended on the production element being addressed and the timescale involved.

An evaluation of the time dependence of the anisotropy of the water diffusion tensor in acute human ischemia.

We have performed MRI examinations to determine the water diffusion tensor in the brain of six patients who were admitted to the hospital within 12 h after the onset of cerebral ischemic symptoms. The examinations have been carried out immediately after admission, and thereafter at varying intervals up to 90 days post admission. Maps of the trace of the diffusion tensor, the fractional anisotropy and the lattice index, as well as maps of cerebral blood perfusion parameters, were generated to quantitatively assess the character of the water diffusion tensor in the infarcted area. In patients with significant perfusion deficits and substantial lesion volume changes, four of six cases, our measurements show a monotonic and significant decrease in the diffusion anisotropy within the ischemic lesion as a function of time. We propose that retrospective analysis of this quantity, in combination with brain tissue segmentation and cerebral perfusion maps, may be used in future studies to assess the severity of the ischemic event.

Buprenorphine: an alternative to methadone for heroin dependence treatment.

Eighty-five heroin addicts who were unwilling to receive methadone maintenance or enter therapeutic communities were assessed, single-blind, for the lowest sublingual dose of buprenorphine that blocked heroin craving (8.0 mg max). All doses were administered daily under observation. After maintenance for 4 to 12 weeks, abstinent subjects (confirmed by urine drug screens) entered a double-blind discontinuation trial and were randomly assigned to receive dose reductions (10% twice weekly for 5 weeks to zero dose, then placebo for 2 weeks) or a stable dose for 7 weeks. Subjects were terminated from discontinuation if heroin was used or they had increased craving/symptoms. Subjects completed the trial if they did not use heroin and had no increase in craving/symptoms. A wide dose range (1.5-8.0 mg/day) was effective in reducing heroin craving and use. Of 73 subjects who received buprenorphine for 4 to 52 weeks, 40 had no prior treatment, despite high levels (mean $/day heroin = 70.5 +/- 94.7) and many years (mean years = 10.7 +/- 8.6) of dependence. Subjects who received dose reductions developed abstinence symptoms, low energy most commonly, associated with drug-seeking behavior. Discontinuation trial outcome (n = 51) shows a highly significant difference between 29 subjects who received dose reductions (28 terminated, 1 completed) and 22 subjects who received no dose reductions (3 terminated; 19 completed) (chi-square = 36.08; p less than .00001). The findings suggest that buprenorphine could be an important medication for reducing demand for heroin by many heroin addicts who remain outside the present health-care system.(ABSTRACT TRUNCATED AT 250 WORDS)

Complications of ergometer exercise in children.

To determine the frequency of significant complications of exercise testing in children, we reviewed 1,730 studies performed over a 9-year period, 1973 to 1982. The protocol used a graded, continuous test to maximal effort on a cycle ergometer. The overall incidence of complications was 1.79%, similar to the 1.7% previously reported by Freed [4]. No deaths occurred. Complications were classified into 4 groups with their frequency of occurrence as follows: chest pain (0.69%), dizziness or syncope (0.29%), decreased blood pressure (0.35%), hazardous arrhythmias (0.46%). These data confirm that exercise testing in children has low morbidity and mortality. We believe that the safety of stress testing should encourage physicians to expand its use in the assessment of functional ability.

Responses to exercise in children with sickle cell trait.

To determine whether responses to exercise in children with sickle cell trait (AS) are different from those of normal children, we performed dynamic cycle ergometer stress testing in 48 children with AS, aged 4 to 21 years. We compared these data with those obtained from 184 healthy black children. No subject with AS demonstrated definite ischemia on the exercise ECG, but four (8.3%) had equivocal ischemia. Population statistics derived from Z score values showed that the subjects with AS had lower exercise values for heart rate and work load than the controls. The BP response to exercise was normal in subjects with AS. Since no ischemia or complications occurred, exercise in subjects with AS appears to be safe. Further studies are needed to define the mechanism for the impaired pulse rate and work load variables.

Responses to ergometer exercise in a healthy biracial population of children.

To determine normal values for the exercise variables heart rate, blood pressure, maximal workload, physical working capacity index, J point displacement, and ST segment slope, we stress tested 405 healthy children. We analyzed the data for four body surface area-determined groups, to discover whether there were any racial differences between healthy white children and black children. There were numerous racial differences in blood pressure, maximal workload, and physical working capacity index; there were no differences in the heart rate values. The incidence of false-positive J point displacement was less than or equal to 3% when the PR isoelectric line method was used. The ST segment slope in healthy children was always greater than zero at maximal exercise. Thus, norms for exercise variables must be expressed in relation to both sex and race. The nomograms presented in this report provide an easy-to-use set of normative data for cycle ergometer stress testing in children.

Automated blood pressure measurement during ergometer exercise in children.

The measurement of systolic and diastolic blood pressure during exercise is often difficult to perform due to patient motion and environmental noise. We evaluated an automated system of blood pressure determination in 121 children undergoing cycle ergometer stress testing. The system (Critikon Model 1165) utilized acoustic transduction, with electrocardiogram gating and microprocessor signal filtering. One observer measured the blood pressure values from the same arm as the automated system; this observer was blinded to the readout of the system. The correlation coefficients for systolic blood pressure at rest, during exercise, and during recovery were all greater than 0.91, and improved with the use of a stethophone adapter. This system can eliminate intraobserver variation as well as the necessity for the technician or physician to direct attention away from the electrocardiogram and patient during stress testing.