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Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20 kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20 kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204-362 kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry allowed to conclude that H2O2 is formed from non-excited OH (X(2)Π) and HO2 radicals. Finally, it was shown that at the studied conditions the efficiency of ultrasonic degassing is hardly influenced by frequency., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The thalamic centre median-parafascicular complex (CM/Pf), a main input and output station of the basal ganglia, is attracting increasing interest in the field of movement disorders, including Parkinson's disease (PD). CM/Pf undergoes partial neurodegeneration in PD patients and some rodent models. Cellular evidence has been provided in experimental animals that thalamic degeneration may not aggravate but rather counteract the effects of dopamine lesion. But functional changes in the circuits involving the spared neurons could play a detrimental role. This view fits with converging anecdotic and recent direct experience in patients that stress the potential of CM/PF deep brain stimulation (DBS) to alleviate motor disorders, notably tremor and dyskinesias. As a preclinical contribution to the characterization of this target, we investigated the functional impact of CM/Pf-DBS in the 6-hydroxydopamine hemiparkinsonian rat model of PD. When testing different frequencies (25, 60, 130 Hz), only high frequency stimulation (HFS) had significant antiakinetic action as evidenced by alleviation of limb use asymmetry in the cylinder test. Although less efficient than HFS of the subthalamic nucleus in the latter task, CM/PF-HFS completely corrected lateralized neglect in the corridor task. Unlike subthalamic nucleus, CM/Pf-HFS did not induce per se dyskinesias. Finally, the benefits provided by CM/Pf-HFS were associated with widespread impact on the changes in neuronal metabolic activity induced by the dopamine depletion in the basal ganglia. These data point to own particular outcome of CM/Pf-DBS that may be of interest in currently developing multi-target strategies.

There is accumulating evidence that the centre median-parafascicular (CM/Pf) complex of the thalamus is implicated in basal ganglia-related movement disorders and notably in Parkinson's disease. However, the impact of the changes affecting CM/Pf on the pathophysiological functioning of basal ganglia in parkinsonian state remains poorly understood. To address this issue, we have examined the effects of excitotoxic lesion of CM/Pf and of 6-hydroxydopamine-induced lesion of nigral dopamine neurons, separately or in association, on gene expression of markers of neuronal activity in the rat basal ganglia (striatal neuropeptide precursors, GAD67, cytochrome oxidase subunit I) by quantitative in situ hybridization histochemistry. CM/Pf lesion prevented the changes produced by the dopamine denervation in the components of the indirect pathway connecting the striatum to the output structures (striatopallidal neurons, globus pallidus, subthalamic nucleus), and among the output structures, in the entopeduncular nucleus. Preliminary data on the effects of deep brain stimulation of CM/Pf in rats with nigral dopamine lesion show that this surgical approach produces efficient anti-akinetic effect associated with partial reversal of the dopamine lesion-induced increase in striatal preproenkephalin A mRNA levels, a marker of the striatopallidal neurons. These data, which provide substrates for the potential of CM/Pf surgery in the treatment of movement disorders, are discussed in comparison with the effects of lesion or deep brain stimulation of the subthalamic nucleus, the currently preferred target for the surgical treatment of PD.