Electrical stimulation of human tibialis anterior: (A) contractile properties are stable over a range of submaximal voltages; (B) high- and low-frequency fatigue are inducible and reliably assessable at submaximal voltages

OBJECTIVES: To investigate the validity and reliability of submaximal voltage stimulation for assessing the 'fresh' contractile properties of human tibialis anterior muscle (TA) and the efficacy of such stimulation in inducing and assessing high- and low-frequency fatigue. INTERVENTIONS: (A) Contractile properties of fresh TA were assessed in six normal volunteers using multifrequency stimulation trains (comprising 2 seconds at each of 10, 20 and 50 Hz, arranged contiguously) over a range of submaximal voltages. (B) On three separate occasions, fatigue was induced in the TA of 10 normal volunteers by means of a 3-minute unbroken sequence of the described multifrequency stimulation trains, delivered at a 'standardized' submaximal voltage. This fatiguing protocol was preceded by discrete multifrequency stimulation trains, at the same standardized voltage, but followed by discrete multifrequency trains delivered over a range of submaximal voltages (which included the standardized voltage). OUTCOME MEASURES: In experiment A the 10:50 Hz and 20:50 Hz force ratios were analysed for between-voltages variability using coefficients of variation (CVs), and for trends using Friedman tests and post-hoc Wilcoxon tests. In experiment B low-frequency fatigue was detected using 10:50 Hz and 20:50 Hz force ratios derived from the discrete multifrequency trains. High-frequency fatigue was calculated from the decline in high-frequency force which occurred during the fatiguing protocol itself. Each parameter was assessed for between-days repeatability using CVs. RESULTS: In experiment A the 'fresh' 10:50 Hz force ratio was clearly unreliable at voltages which generated <10% of maximal voluntary contractile force (MVC) (CV< or =29.7%), but was reasonably reliable at voltages which generated 20-30% of MVC (CV < or = 11.5%; p = 0.847). The 'fresh' 20:50 Hz force ratio was,in contrast, extremely reliable throughout the tested voltage range (CV< or =5.8%; p = 0.636) in fresh muscle. In experiment B paired t-tests indicated that the fatiguing protocol induced significant high-frequency fatigue (p <0.0037) and low-frequency fatigue (p <0.0008 for 'fresh' versus 'fatigued' 10:50 Hz force ratio; p <0.0001 for 'fresh' versus 'fatigued' 20:50 Hz force ratio). In muscle thus fatigued, the 20:50 Hz force ratio was extremely reliable in the 20-33% of MVC range (CV < or =7.3%; p = 0.847). Between-days repeatability was poor for the 10:50 Hz force ratio in both fresh and fatigued muscle (CV < or =23.8 and 44.4% respectively), but was highly acceptable for both voluntary and stimulated fatigue indices and for the 20:50 Hz force ratio, the latter in both fresh and fatigued muscle. CONCLUSIONS: These results confirm the validity and reliability of submaximal voltages in assessing contractile properties (including low-frequency fatiguability) and inducing fatigue of human TA.     

Xenobiotic metabolism in rat, dog, and human precision-cut liver slices, freshly isolated hepatocytes, and vitrified precision-cut liver slices

Human, rat, and dog phase I and phase II xenobiotic metabolism in precision-cut liver slices and freshly isolated hepatocytes was compared using a range of substrates. Carbamazepine (50 microM) and styrene (2 mM) were used as probes to study the maintenance of cytochrome P450 and epoxide hydrolase-mediated metabolism in male Sprague-Dawley rat, precision-cut liver slices and hepatocytes. Carbamazepine metabolism in both models resulted in the formation of the bioactive 10,11-epoxide (KM = 766 microM and Vmax = 2.5 pmol/min/mg protein in precision-cut slices). Epoxide formation was higher (2.4-fold) in hepatocytes than slices. Styrene was deactivated to styrene diol at a higher rate in hepatocytes (9.7-fold) than slices. The lower rate of metabolism in slices compared with hepatocytes confirms our previous observations using testosterone, 7-ethoxycoumarin, 1-chloro-2,4-dinitrobenzene and 2-(5'-chloro-2'-phosphoryloxyphenyl)-6-chloro-4-(3H)-quinazolinone in the rat. Testosterone 6 beta-hydroxylation in human liver slices was similar to cultured hepatocytes, but lower than in freshly isolated hepatocytes. 7-Ethoxycoumarin O-deethylation was higher in freshly isolated human hepatocytes, as was the ratio of glucuronide to 7-hydroxycoumarin. Testosterone hydroxylations, 7-ethoxycoumarin O-deethylation, and 1-chloro-2,4-dinitrobenzene conjugation were also lower in male beagle dog slices, compared with freshly isolated hepatocytes. Attempts at long-term preservation of dog liver slices using vitrification and storage for up to 9 days at -196 degrees C resulted in the retention of phase I and phase II metabolism, although conjugation was lower than in freshly prepared slices. Xenobiotic metabolism in short-term incubations is consistently lower in dog and rat precision-cut slices than in freshly isolated hepatocytes; whereas, in humans, this quantitative difference is partly hidden by the large interindividual variation.     

Animal, vegetable or cerebral: brains in agricultural production

Recent developments in brain research seem to have passed unnoticed in veterinary and agricultural circles. Yet they have transformed views on the subject and, Dr Cross argues, made study of the brain mandatory for future advance in animal health and production.     

Altered electrodermal responsivity associated with clinical pain

We used certain physiologic maneuvers to perturb the autonomic nervous system (ANS) in an attempt to detect a link between the ANS and pain. In the unperturbed state, we found no difference in the electrodermal response among normal controls, preoperative patients (increased stress without pain) and postoperative patients (increased stress and pain). The electrodermal response elicited by autonomic maneuvers was significantly attenuated in postoperative patients but not in preoperative patients or in normal control subjects.     

Polarization Switching in (100)/(001) Oriented Epitaxial Pb(Zr, Ti)O3 Thin Films

Thin films made of (100)/(001)-oriented Pb(Zr, Ti)O₃ (PZT) were deposited by liquid-delivery metal-organic chemical vapor deposition on Ir/MgAl₂O₄/SiO₂/Si(100) substrates. For comparison, PZT thin films were also deposited on Ir/MgO(100) substrates. The X-ray scan spectra for the (202) reflections revealed that the PZT films have four-fold symmetry. It indicates that the PZT films were epitaxially grown as a cube-on-cube structure on both substrates. The switchable polarization (Q_sw) of the PZT capacitors on the silicon substrate was only 23 C/cm² at 1.8 V; however, Q_sw of PZT capacitors on MgO was 99 C/cm². In the case of PZT films deposited on silicon, the volume fraction of (001)-oriented domains (which contribute to polarization switching) was 15.1% (calculated from an XRD pattern). This result is due to the lower Q_sw of PZT capacitors on silicon. By piezoresponse-force microscopy, switchable and unswitchable domains could be identified by imaging color contrast, namely, (001) and (100) domains, respectively. Consequently, domain distribution of the PZT film on a silicon substrate indicates that the (001) domain exists in the (100) domain matrix.     

Global analysis of the riverine transport of 90Sr and 37Cs

Atmospheric nuclear weapons explosions and large-scale nuclear accidents may contaminate large areas of land with the long-lived radionuclides 137Cs and 90Sr. The mobility and bioavailability of these radionuclides in the environment is dependent primarily on soil characteristics and changes significantly over time after fallout (1-4). Radioisotope concentrations in different rivers and at different times after fallout vary over 2-3 orders of magnitude. Many previous studies have concentrated on the interactions of radiocesium and radiostrontium with various environmental components, but there are currently no operative models fortheirtransport over large spatial areas. We collected time-series measurements of 90Sr and 137Cs in 25 major European and Asian rivers and (using digital data sets with global coverage) determined characteristics of each of the rivers' catchments. This work has established, for the first time, a quantitative link between riverine transport of these radioisotopes and catchment and soil characteristics at a global scale. A generalized predictive model accounting for time changes in river concentrations and variation in catchment characteristics is developed. This can be used to predict the long-term riverine transport of these radiologically important radionuclides following any large-scale nuclear incident in North America, Europe, or (European and Asian) Russia.