Accuracy of passive ankle joint positioning during quiet stance in young and elderly subjects

Age-related postural deficits elicit compensatory mechanisms such as ankle dorsiflexion in the elderly. To gain further insight into this problem, the ability to match an ankle angle during quiet stance was studied in 12 elderly and 12 young subjects. Following an initial single limb angular perturbation presented in the ±4° range, a subject had to return a tilt platform to level, as determined by the nonperturbed limb. Elderly subjects exhibited significant positive (0.9°) over-shoot of the level position, in contrast to young subjects who matched ankle angle with a mean error of −0.1°. The elderly group also exhibited an increase in positioning error for angular displacements in the range between −1 and +1°. The results document age-related postural changes in ankle positioning which might affect postural stability in older adults.     

Effects of the environment on the behavioural response of mice to non-ataxic doses of ethyl alcohol.

An ethological analysis was used to examine the effects of ethyl alcohol on social behaviour in mice which were placed in different social contexts. In encounters between unfamiliar males, alcohol-treated mice from a diverse environment showed more exploration on the bars of an unfamiliar cage and less social investigation than controls. In an encounter situation between males and females, male mice given alcohol showed a significant increase in frequency and duration of all forms of social and sexual investigation other than mounts and attempted mounts compared with untreated males. In a territorial situation, alcohol administration before territory establishment resulted, on each of four occasions, in the dominant mouse of the alcohol-treated group becoming despot over the whole enclosure, whereas after territory establishment this effect was not seen. The overall effect of alcohol was, therefore, to increase the type of behaviour that was already stimulated by the test situation. The significance of these findings in relation to the differential effects of alcohol on different areas of the nervous system is discussed.     

Rapid ATP assays in perfused mouse liver by 31P NMR.

31P NMR was used to continuously monitor ATP and inorganic phosphate levels in perfused mouse liver. Under "optimal" conditions, the time resolution of the technique was approximately 1 min. In the absence of any metabolic perturbations the ATP level remained constant for at least 2 hr and decreased by only approximately 20% in 18 hr. Both ATP and inorganic phosphate levels responded to alterations in the oxygen supply to the liver. The half-time for this response was approximately 1 min, and the response to short periods of hypoxia or ischemia was partially reversible. The addition of insulin caused only a minor decrease in the ATP level but significantly decreased the rate of response of ATP and phosphate levels to hypoxia and ischemia.     

Two-dimensional analysis of the redox state of the rat cerebral cortex in vivo by NADH fluorescence photography.

A photographic method for measuring two-dimensional changes in NADH fluorescence and hemoglobin distributions in the rat cerebral cortex in vivo has been developed. Intracellular NADH was excited by UV light peaking at 360 nm and the emission was observed through a window with the maximum transmission at 450 nm. The fluorescence photographs (360 leads to 450 nm) required 20-25 sec exposures at the aperture opening of f/5.6 and the reflectance photographs (360 leads to 360 nm) 10 sec exposures at f/32. The digitization of photographic images was achieved either by a PDP-8-controlled microdensitometer coupled to an A/D converter or by a combination of a manually operated microdensitometer and a computer-controlled digitizer. In the latter case, a photographic negative was scanned with a Joyce-Loebl microdensitometer in parallel lines 170 mum apart, and the densitometric tracings were digitized with a PDP-8-controlled TV digitizer. The digital data were processed by DEC PDP-10 computer and the results were displayed in 3-dimensional surfaces. Nitrogen anoxia caused increases in fluorescence at 450 nm ranging from 10 to 75% fo the normoxic fluorescence intensities (after correcting for the logarithmic characteristics of the photographic films) and decreases in reflectance intensities in the range of 10-30%. The spatial resolution of the present technique is limited to approximately 30 mum X 30 mum on the cortical surface and the time resolution to 10-25 sec. The optical properties of the cerebral cortex in vivo appear to be controlled primarily by blood vessel patterns and hemodynamic factors and secondarily by the redox state of the tissue. Evidence for a heterogeneous redox response of the cerebral cortex toward N2 anoxia was obtained.