Experimental study on high-purity hydrogen generation from synthetic biogas in a 10 kW fixed-bed chemical looping system.

The utilization of locally available renewable resources is crucial for the creation of a sustainable energy system in the future. Biogas, a product of the anaerobic digestion of biogenic residues, exhibits great potential as feedstock to generate hydrogen for fuel cell mobility applications. A 10 kW fixed-bed chemical looping research system, to-date the largest in the world, was operated to prove the applicability of this versatile process for synthetic biogas utilization. In this experimental study, the focus was laid on examining the influence of different operating parameters (biogas composition, steam co-feeding, process temperature) on the attainable hydrogen purity and system efficiency. The generated hydrogen, between 90 to 230 g per cycle, was characterized online by ppm-range gas analysis and exhibited a product gas quality between 99.8% and 99.998%. The difference observed is attributed to carbon deposition if synthetic biogas with an increased share of carbon dioxide was supplied. This study involved the longest uninterrupted period of operation of a lab prototype system for fixed-bed chemical looping with 250 hours of time-on-stream, four months of discontinuous service and 50 consecutive experimental cycles.

Dose-dependent effects of erythropoietin in propofol anesthetized neonatal rats.

Exposure to Gamma-aminobutyric-acid (GABA)(A)-receptor agonists and N-Methyl-D-Aspartate (NMDA)-antagonists has been demonstrated to induce neurodegeneration in newborn rats. Exogenous erythropoietin (EPO) protects against NMDA antagonist-mediated neuronal death. In this study we evaluated whether EPO is also effective in limiting neurodegeneration of the GABA(A)-mimetic agent propofol in newborn rats. 6 day old rats were randomized to one of four groups and treated with intraperitoneal applications of 3 x 30 mg/kg propofol at 0, 90 and 180 min, propofol in combination with 5000 IU/kg rEPO, propofol in combination with 20,000 IU/kg rEPO or sham injections of PAD II solution as controls. After 24h, brains of the animals were histopathologically examined and a summation score of degenerated cells was calculated for every brain. Propofol increased neuronal degeneration scores from 16,090+/-4336 to 28,860+/-6569 (p<0.01). This effect was completely abolished by low-dose rEPO (14,270+/-4542, p<0.001 versus propofol only; p>0.05 versus controls). In contrast, high-dose rEPO was not protective (23 930+/-8896, p>0.05 versus propofol only). Propofol may cause neuronal death in newborn rat brains, which is prevented by low-dose rEPO but not high-dose rEPO.

Effects of sevoflurane on primary neuronal cultures of embryonic rats.

BACKGROUND AND OBJECTIVE: Commonly used anaesthetics can cause neurodegeneration in the developing brain. Sevoflurane, a widely used substance in paediatric anaesthesia, has not been analysed thus far. This study was carried out to investigate the effects of sevoflurane on neuronal cell viability. METHODS: Primary cortical neuronal cultures were prepared from Wistar rat embryos (E18), kept in 100 microl Gibco-Neurobasal-A medium and exposed to 4 and 8 Vol.% sevoflurane for up to 48 h. Cell viability was assessed using the methyltetrazolium assay and was related to untreated controls. To evaluate the role of gamma-aminobutyric acid type A receptors, untreated cells were preincubated with the receptor antagonists gabazine or picrotoxin and were subsequently exposed to 8 Vol.% sevoflurane and the receptor antagonist. Cell viability was assessed and compared with that of sevoflurane-treated controls. RESULTS: Up to 6 (8 Vol.%) and 12 h (4 Vol.%) of exposure to sevoflurane, cell viability was equal when compared with untreated controls. Only longer exposure times led to significantly lowered cell viability. After 12 h of exposure, no significant differences in cell viability were found between these two series. Cell viability of cultures treated with sevoflurane and the receptor antagonists showed no significant differences when compared with sevoflurane-exposed controls. CONCLUSION: These results suggest that sevoflurane does not cause neurodegeneration in primary cortical neurons of the rat following clinically relevant exposure times and concentrations.

Microglia express GABA(B) receptors to modulate interleukin release.

gamma-Aminobutyric acid (GABA) can act as a neuroprotective agent besides its well-established role as the main inhibitory neurotransmitter in the CNS. Here we report that microglial cells express GABA(B) receptors indicating that these prominent immunocompetent cells in the brain are a target for GABA. Agonists of GABA(B) receptors triggered the induction of K(+) conductance in microglial cells from acute brain slices and in culture. Both subunits of GABA(B) receptors were identified in cultured microglia by Western blot analysis and immunocytochemistry, and were detected on a subpopulation of microglia in situ by immunohistochemistry. In response to facial nerve axotomy, we observed an increase in GABA(B) receptor expressing microglial cells in the facial nucleus. We activated microglial cells in culture with lipopolysaccharide (LPS) to induce the release of interleukin-6 and interleukin-12p40. This release activity was attenuated by simultaneous activation of the GABA(B) receptors indicating that GABA can modulate the microglial immune response.

Purinergic receptors on microglial cells: functional expression in acute brain slices and modulation of microglial activation in vitro.

Microglial cells are the pathologic sensors in the brain. ATP released from damaged cells is a candidate for signalling neural injury to microglia. Moreover, ATP is an extracellular messenger for propagating astrocyte activity in the form of Ca2+ waves. To test for the functional expression of purinoreceptors in microglial cells we employed the patch-clamp technique in acute slices of adult mouse brain. ATP triggered a nonselective cationic and a K+ current. Pharmacological screening with purinergic ligands indicated the presence of P2Y1 and P2Y2/4 receptors linked to the activation of a K+ current and P2X receptors, including P2X7, linked to the activation of a nonselective cationic current. These findings suggest that microglial cells in situ express different purinergic receptors with distinct sensitivity and functional coupling. To test for the involvement of purinoreceptors in microglial activation, we stimulated cultured microglial cells with lipopolysaccharide and measured the release of tumour necrosis factor alpha, interleukin-6, interleukin-12 and macrophage inflammatory protein 1alpha, induction of K+ outward currents and nitric oxide release. All these parameters were reduced in the presence of purinergic ligands, indicating that purinergic receptor activation attenuated indicators of microglial activation.