Inelastic response of silicon to shock compression.

The elastic and inelastic response of [001] oriented silicon to laser compression has been a topic of considerable discussion for well over a decade, yet there has been little progress in understanding the basic behaviour of this apparently simple material. We present experimental x-ray diffraction data showing complex elastic strain profiles in laser compressed samples on nanosecond timescales. We also present molecular dynamics and elasticity code modelling which suggests that a pressure induced phase transition is the cause of the previously reported 'anomalous' elastic waves. Moreover, this interpretation allows for measurement of the kinetic timescales for transition. This model is also discussed in the wider context of reported deformation of silicon to rapid compression in the literature.

Acoustic startle eyeblink response after acute exercise.

The acoustic startle eyeblink response (ASER) is a useful probe for investigating central nervous system activity associated with emotional responses to aversive and appetitive stimuli. Though the ASER is sensitive to change in emotional arousal, the effect of acute physical exertion on ASER has not been reported. We examined changes in ASER amplitude and latency in 26 healthy young men (24+/-5 yr) after 20 min of cycling at light and hard intensities (40% and 75% VO2peak) and after 20 min of quiet rest. Mixed model ANCOVA, controlling precondition scores, indicated no effects for ASER amplitude or latency in either sedentary or active participants (p>.10). Our findings indicate that possible effects of acute exercise on potentiated startle or ASER responses elicited by positive or negative foreground stimuli should not be expected to be confounded by an altered baseline acoustic startle eyeblink response when measured in healthy young men.

Bradycardia during baroreflex stimulation and active or passive stressor tasks: cardiorespiratory fitness and hostility.

We examined whether the resting bradycardia associated with cardiorespiratory fitness extends to lowered heart rate (HR) and mean arterial pressure during novel passive or active laboratory stressors and to a longer heart period during stimulation of the carotid-cardiac vagal baroreflex, independently of the Type A behavior pattern (TABP) and hostility. Forty-four normotensive Caucasian men (18-35 years of age) completed the Structured Interview for TABP, the Cook-Medley Hostility Scale, and a peak oxygen uptake (Vo2peak) test. Vo2peak was inversely related to HR prior to, during, and after each stressor and was positively related to heart period during baroreflex testing. Hostility was inversely related to heart period during baroreflex testing. TABP had no effects. Our findings indicate that cardiorespiratory fitness and low hostility are independently associated with a bradycardia during stimulation of the carotid-cardiac baroreflex, consistent with a possible enhancement of cardiac vagal tone.

Does body temperature mediate anxiolytic effects of acute exercise?

We tested the thermogenic hypothesis that reductions in blood pressure and self-reported state anxiety and altered brain electrocortical (electroencephalographic, EEG) activity after acute exercise are due to increased body temperature. Eleven fit [cycle peak O2 consumption (VO2peak) = 57 +/- 5.8 ml.kg-1 x min-1] males (26 +/- 5.8 yr) were randomly assigned to four 20-min conditions in a within-subjects counterbalanced design: 1) thermoneutral (32-35 degrees C) or 2) cold (18-23 degrees C) cycling at 70% VO2peak, 3) passive warm water exposure (39-41 degrees C), and 4) quiet rest (60 dB below ambient; 22 +/- 1 degrees C). All exercise testing was conducted in shoulder-deep water. Esophageal temperature increased equally during thermoneutral cycling (+1.45 +/- 0.05 degrees C) and passive heating (+1.51 +/- 0.06 degrees C), was blunted during cold cycling (+0.40 +/- 0.12 degrees C), and was unchanged at rest. Mean radial arterial pressure (MAP), self-reported state anxiety (State-Trait Anxiety Inventory, STAI), and spontaneous occipital (O1 + O2) and photostimulated temporal (T5 + T6) surface EEG activity (10-20 system) in theta (4-8 Hz), alpha (9-13 Hz), and beta (14-40 Hz) frequency bands were assessed 5 min pre- and 10-15 and 20-25 min postcondition and analyzed in 4- (condition) by-3 (time) repeated-measures analysis of variance (P < 0.05). Results showed a condition-by-time interaction for MAP, which decreased from pre- to 15 min postcondition for thermoneutral cycling (81 +/- 2 to 73 +/- 2.7 mmHg) and passive heating (86 +/- 2.5 to 74 +/- 1.4 mmHg) and persisted at 25 min postcondition.(ABSTRACT TRUNCATED AT 250 WORDS)

Feeding regime affects activity-stress ulcer production.

Rats were divided into either an active group housed in activity wheels or a control group housed in stationary laboratory cages. Both active and control groups were further divided into groups receiving 1, 2, 3, or 4 meals daily for a total feeding time of 1 hr. Control rats were food-yoked to active animals. Results indicated that active rats fed 1 meal daily developed significantly more ulceration, lost more weight, and consumed less food and water than other groups. The number of daily meals had no effect on the amount of activity. No control animals developed ulcers, although they received the same amount of food. These results suggest that frequent feedings mitigate gastric peptic ulcer formation in rats placed in the activity-stress ulcer paradigm.

Kainic acid stimulation of the lateral septum elicits tachycardia.

Electrical stimulation of the lateral septum results in a transient cardiodeceleration which may represent parasympathetic rebound to a brief sympathetic activation. Kainic acid (KA) is a potent neuronal excitant. Stimulation of the lateral septum by KA produced a short-latency tachycardia. Vehicle injections, as well as KA administration to adjacent structures, did not effect significant changes in heart rate. Intraventricular KA, however, did result in a significant tachycardia. Knife cuts of the fornix, interrupting the glutamatergic innervation of the septum, completely blocked the cardiovascular response to KA. Pharmacological treatments reducing sympathetic activity prevented or reversed KA-elicited tachycardia. Thus, it appears that septal administration of KA produces sympathetic activation. KA may serve as a useful tool in studies assessing central regulation of the autonomic nervous system, and the interrelationship between autonomic activity and seizure-induced neuronal loss.

Conditioned taste aversion as a function of age in mature male rats.

Experimental groups of young mature (90-120 days), mature (365-395 days), and aged (730-760 days) Fischer-344 rats were allowed to drink a saccharin solution followed by lithium chloride toxicosis initiated at one of three intervals, either 15, 60, or 240 minutes. Control groups were given saline placebos according to the same schedule. In a preference test conducted 48 hours after conditioning, there was little evidence of age differences in the acquisition of a saccharin aversion. Age differences were noted in the extinction of the aversion which was tested by monitoring preference over a period of 32 days of continuous access to saccharin and water. Older animals tended to show greater resistance to extinction.