Low-temperature muon spin rotation studies of the monopole charges and currents in Y doped Ho2Ti2O7.

In the ground state of Ho2Ti2O7 spin ice, the disorder of the magnetic moments follows the same rules as the proton disorder in water ice. Excitations take the form of magnetic monopoles that interact via a magnetic Coulomb interaction. Muon spin rotation has been used to probe the low-temperature magnetic behaviour in single crystal Ho2-xYxTi2O7 (x = 0, 0.1, 1, 1.6 and 2). At very low temperatures, a linear field dependence for the relaxation rate of the muon precession λ(B), that in some previous experiments on Dy2Ti2O7 spin ice has been associated with monopole currents, is observed in samples with x = 0, and 0.1. A signal from the magnetic fields penetrating into the silver sample plate due to the magnetization of the crystals is observed for all the samples containing Ho allowing us to study the unusual magnetic dynamics of Y doped spin ice.

Induced random fields in the LiHoxY1-xF4 quantum Ising magnet in a transverse magnetic field.

The LiHoxY1-xF4 magnetic material in a transverse magnetic field Bx x perpendicular to the Ising spin direction has long been used to study tunable quantum phase transitions in a random disordered system. We show that the Bx-induced magnetization along the x direction, combined with the local random dilution-induced destruction of crystalline symmetries, generates, via the predominant dipolar interactions between Ho3+ ions, random fields along the Ising z direction. This identifies LiHoxY1-xF4 in Bx as a new random field Ising system. The random fields explain the rapid decrease of the critical temperature in the diluted ferromagnetic regime and the smearing of the nonlinear susceptibility at the spin-glass transition with increasing Bx and render the Bx-induced quantum criticality in LiHoxY1-xF4 likely inaccessible.

Induction and regulation of nitric oxide synthase in airway epithelial cells by respiratory syncytial virus.

In this study, we evaluated the effects of respiratory syncytial virus (RSV) infection on nitric oxide (NO) production in human airway epithelial cells. In addition, we evaluated whether T-helper type 1 (Th1)- and Th2-type cytokines modulate the release of NO in response to RSV infection. To do this, we infected monolayers of A549 cells with RSV and determined nitrite levels in the supernatant fluids. We also measured nitrite levels in human small-airway epithelial cells (SAEC) in primary culture and in the bronchoalveolar lavage fluid (BALF) obtained from Balb/c mice after RSV infection. To further support our observations in these analyses, we performed immunocytochemistry and Western blot analysis for inducible nitric oxide synthase (iNOS) in A549 cells. To evaluate the regulation of NO production in response to RSV, we performed experiments in the absence and presence of the Th1 and Th2 type cytokines: interferon (IFN)-gamma, interleukin (IL)-4, and IL-13. In addition, we assessed the inhibitory effect of dexamethasone on iNOS in RSV infected A549 cells. Results were expressed in terms of nmol/mg protein and shown as percents of control values (mean +/- SE). RSV increased the release of nitrites in A549 cells, SAEC, and BALF. The increase in nitrite levels was supported by immunocytochemistry and Western blot analysis for iNOS protein in A549 cells, indicating activation of iNOS in response to RSV infection. IFN-gamma and IL-13 did not affect the RSV-induced increase in NO production. By contrast, IL-4 and dexamethasone suppressed the release of NO in response to RSV infection. These observations show that RSV infection leads to activation of iNOS within the airway epithelium and that IL-4 and dexamethasone inhibit the production of NO in response to RSV infection.

Phenotypic expression of the systemic toxicity of cocaine in genetically epilepsy-prone rats.

The purpose of the present investigation was to determine whether the sensitivity to systemic toxic effects of cocaine is altered in genetically epilepsy-prone rats (GEPRs). Moderate seizure (GEPR-3) and severe seizure (GEPR-9) rats, and the control strain, Sprague-Dawley rats, 10 weeks of age, were lightly anesthetized with halothane and nitrous oxide. Following surgical preparation and stabilization, the animals were given a constant intravenous infusion of cocaine (4 mg/kg per min) until death. Blood pressure, ECG, and EEG were monitored continuously throughout the experiment. Cocaine doses required to produce seizures (i.e., epileptiform activity on the EEG) were not significantly different between GEPRs and control rats (16.8+/-0.6 mg/kg in GEPR-3, 18.7+/-0.7 mg/kg in GEPR-9, and 14.7+/-1.3 mg/kg in Sprague-Dawley). Seizure duration, amplitude and the number of epileptiform bursts were also similar among the three strains. Additionally, there was no significant difference in cocaine doses that produced arrhythmias and cardiac asystole between GEPRs and control. The results indicate that genetically epilepsy-prone rats do not exhibit altered sensitivity to cocaine-induced seizures despite the marked susceptibility to sound-evoked seizures. Local anesthetic-induced seizures and acoustically-evoked seizures apparently have different underlying mechanisms.

The reversal of profound mivacurium-induced neuromuscular blockade.

PURPOSE: Mivacurium is metabolized by plasma cholinesterase catalyzed ester hydrolysis. Acetylcholinesterase antagonists used in the reversal of muscle relaxation may also inhibit plasma cholinesterase and, therefore, delay the hydrolysis of mivacurium. The clinical interaction between acetylcholinesterase antagonists and mivacurium induced neuromuscular blockade was studied. METHOD: Intraoperative muscle relaxation was maintained with a mivacurium infusion to achieve a constant intense block (first twitch, T1, 2-3% of control). Patients were randomly divided into three groups. Patients in Group 1 received no anticholinesterase, in Group 2 neostigmine 0.07 mg.kg-1, and in Group 3 edrophonium 1 mg.kg-1. The times between termination of the mivacurium infusion (Group 1) or the administration of the anticholinesterase (Groups 2 and 3) to 25%, 50%, 75% and 95% T1 recovery, and to 50%, 70% and 90% recovery in the ratio, T4/T1 (TR) were recorded. RESULT: In the neostigmine Group, T1 recovery to 25%, 50% and 75% (2.32 +/- 1.41, 3.90 +/- 1.85 and 6.88 +/- 2.66 min) was accelerated compared with control (3.36 +/- 1.34, 5.78 +/- 2.22, and 8.58 +/- 3.60, and), but recovery to 95% (18.53 +/- 9.09 vs 13.29 +/- 5.24 min) was delayed. Also, TR recovery to 50%, 70%, and 90% was slower (14.47 +/- 8.73, 21.25 +/- 11.06 and 31.37 +/- 12.11 min vs 11.75 +/- 3.74, 13.78 +/- 4.39 and 17.86 +/- 6.44 min). However, all T1 and TR recovery times were decreased in the edrophonium group (0.88 +/- 0.51, 2.00 +/- 1.50, 4.97 +/- 2.96, and 9.35 +/- 5.24 min for T1 and 6.86 +/- 3.93, 9.05 +/- 4.51 and 12.24 +/- 6.66 min for TR). CONCLUSION: Neostigmine reversal of intense mivacurium neuromuscular block should be avoided, as this may result in prolongation of the block.

Cerebral metabolism during propofol anesthesia in humans studied with positron emission tomography.

BACKGROUND: Although the effects of propofol on cerebral metabolism have been studied in animals, these effects have yet to be directly examined in humans. Consequently, we used positron emission tomography (PET) to demonstrate in vivo the regional cerebral metabolic changes that occur in humans during propofol anesthesia. METHODS: Six volunteers each underwent two PET scans; one scan assessed awake-baseline metabolism, and the other assessed metabolism during anesthesia with a propofol infusion titrated to the point of unresponsiveness (mean rate +/- SD = 7.8 +/- 1.5 mg.kg-1.h-1). Scans were obtained using the 18fluorodeoxyglucose technique. RESULTS: Awake whole-brain glucose metabolic rates (GMR) averaged 29 +/- 8 mumoles.100 g-1.min-1 (mean +/- SD). Anesthetized whole-brain GMR averaged 13 +/- 4 mumoles.100 g-1.min-1 (paired t test, P < or = 0.007). GMR decreased in all measured areas during anesthesia. However, the decrease in GMR was not uniform. Cortical metabolism was depressed 58%, whereas subcortical metabolism was depressed 48% (P < or = 0.001). Marked differences within cortical regions also occurred. In the medial and subcortical regions, the largest percent decreases occurred in the left anterior cingulate and the inferior colliculus. CONCLUSION: Propofol produced a global metabolic depression on the human central nervous system. The metabolic pattern evident during anesthesia was reproducible and differed from that seen in the awake condition. These findings are consistent with those from previous animal studies and suggest PET may be useful for investigating the mechanisms of anesthesia in humans.

A new method to evaluate cardiovascular response in anesthetized rats. Hypertension after variable intensity, brief electrical stimuli.

To establish and standardize a nociceptive response in anesthetized rats, the hypertensive responses to defined electrical and mechanical stimuli were studied. Rats (n = 7) were given etomidate, 3.8 mg/kg/hr intravenously (i.v.) 2 hr following carotid artery and jugular vein cannulation. At 15 min after beginning the infusion, four types of noxious stimuli were administered sequentially at 1-min intervals (14 stimuli total): Type 1: Square electrical waves, 125 cps, 1.6 msec, 2-sec train duration, varying current from 0.4 to 12 mA (11 stimuli); Type 2: A single 10-mA electrical stimulus, 5-sec train duration; Type 3: Tail clamping; and, Type 4: Skin incision. After each stimulus, maximum change in systolic blood pressure (delta SBP) was measured. delta SBP after the most intense stimuli was as follows: Type 1 (12 mA, 2 sec), 32.1 +/- 2.14 mmHg; Type 2 (10 mA 5 sec), 42.9 +/- 2.4 mmHg; Type 3 (tail-clamping), 34.3 +/- 3.3 mmHg; Type 4 (skin incision), 14.2 +/- 2.8 mmHg. For the multiple Type-2 stimuli, a relationship between current and delta SBP was present. The authors believe that characterized graded electrical stimulation will allow a more quantitative evaluation of the hypertensive response to noxious stimuli in etomidate anesthetized rats, as compared to observing a single response to a single stimulus. The characterization of the electrical stimulation by amplitude, frequency, and wave form makes research work on nociception under anesthesia easily reproducible.