Capacity for consciousness under ketamine anaesthesia is selectively associated with activity in posteromedial cortex in rats.

It remains unclear how specific cortical regions contribute to the brain's overall capacity for consciousness. Clarifying this could help distinguish between theories of consciousness. Here, we investigate the association between markers of regionally specific (de)activation and the brain's overall capacity for consciousness. We recorded electroencephalographic responses to cortical electrical stimulation in six rats and computed Perturbational Complexity Index state-transition (PCIST), which has been extensively validated as an index of the capacity for consciousness in humans. We also estimated the balance between activation and inhibition of specific cortical areas with the ratio between high and low frequency power from spontaneous electroencephalographic activity at each electrode. We repeated these measurements during wakefulness, and during two levels of ketamine anaesthesia: with the minimal dose needed to induce behavioural unresponsiveness and twice this dose. We found that PCIST was only slightly reduced from wakefulness to light ketamine anaesthesia, but dropped significantly with deeper anaesthesia. The high-dose effect was selectively associated with reduced high frequency/low frequency ratio in the posteromedial cortex, which strongly correlated with PCIST. Conversely, behavioural unresponsiveness induced by light ketamine anaesthesia was associated with similar spectral changes in frontal, but not posterior cortical regions. Thus, activity in the posteromedial cortex correlates with the capacity for consciousness, as assessed by PCIST, during different depths of ketamine anaesthesia, in rats, independently of behaviour. These results are discussed in relation to different theories of consciousness.

General Anesthesia Disrupts Complex Cortical Dynamics in Response to Intracranial Electrical Stimulation in Rats.

The capacity of human brain to sustain complex cortical dynamics appears to be strongly associated with conscious experience and consistently drops when consciousness fades. For example, several recent studies in humans found a remarkable reduction of the spatiotemporal complexity of cortical responses to local stimulation during dreamless sleep, general anesthesia, and coma. However, this perturbational complexity has never been directly estimated in non-human animals in vivo previously, and the mechanisms that prevent neocortical neurons to engage in complex interactions are still unclear. Here, we quantify the complexity of electroencephalographic (EEG) responses to intracranial electrical stimulation in rats, comparing wakefulness to propofol, sevoflurane, and ketamine anesthesia. The evoked activity changed from highly complex in wakefulness to far simpler with propofol and sevoflurane. The reduced complexity was associated with a suppression of high frequencies that preceded a reduced phase-locking, and disruption of functional connectivity and pattern diversity. We then showed how these parameters dissociate with ketamine and depend on intensity and site of stimulation. Our results support the idea that brief periods of activity-dependent neuronal silence can interrupt complex interactions in neocortical circuits, and open the way for further mechanistic investigations of the neuronal basis for consciousness and loss of consciousness across species.

Avoiding the formation of vesicles by patch excision from Xenopus oocytes.

BACKGROUND: The patch-clamp technique is well-established to investigate the function of ion channels. Several patch configurations have been described, including the inside-out patch configuration providing the unique advantage of having free access to the patch from the cytosolic side. An inside-out patch is predominantly built from a cell-attached patch by pulling the patch pipette back. However, when using pipettes with high resistance (>8 MΩ), often a vesicle is formed instead of the desired inside-out patch, preventing proper recording of ion currents. NEW METHOD: Using quartz pipettes with high resistance we studied the benefit of a simple alternative excision manoeuvre that significantly enhances the efficiency to obtain an inside-out patch from Xenopus oocytes. RESULTS: We show that the formation of vesicles depends on the direction of patch excision: after a cell-attached patch has formed, pushing the patch pipette first into the depth of the oocyte and exposing the patch only then to the bath solution generated a success rate of 89% (16 out of 18) for a proper inside-out patch, as evaluated by the current flowing through HCN2 channels which were heterologously expressed in the oocytes. COMPARISON WITH EXISTING METHOD: In contrast, with the same type of pipettes and oocytes only 22% (4 out of 18) of the patches developed HCN2 currents when pulling the pipette in the backward direction as usual. CONCLUSION: The difference in the success rate favours the idea to use "pushed inside-out patches" instead of "pulled inside-out patches" when studying ion channels expressed in Xenopus oocytes.

Elementary functional properties of single HCN2 channels.

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels are tetramers that evoke rhythmic electrical activity in specialized neurons and cardiac cells. These channels are activated by hyperpolarizing voltage, and the second messenger cAMP can further enhance the activation. Despite the physiological importance of HCN channels, their elementary functional properties are still unclear. In this study, we expressed homotetrameric HCN2 channels in Xenopus oocytes and performed single-channel experiments in patches containing either one or multiple channels. We show that the single-channel conductance is as low as 1.67 pS and that channel activation is a one-step process. We also observed that the time between the hyperpolarizing stimulus and the first channel opening, the first latency, determines the activation process alone. Notably, at maximum hyperpolarization, saturating cAMP drives the channel to open for unusually long periods. In particular, at maximum activation by hyperpolarization and saturating cAMP, the open probability approaches unity. In contrast to other reports, no evidence of interchannel cooperativity was observed. In conclusion, single HCN2 channels operate only with an exceptionally low conductance, and both activating stimuli, voltage and cAMP, exclusively control the open probability.

Dynamic Trap Formation and Elimination in Colloidal Quantum Dots.

Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping.

[Frequency of polyphasic health-care-associated outbreaks is highest in surgical departments - results of a systematic literature search]. / Chirurgen sind am häufigsten von mehrphasischen nosokomialen Ausbrüchen betroffen - Ergebnisse einer systematischen Literaturrecherche.

BACKGROUND: So-called polyphasic nosocomial outbreaks describe a situation in which additional infections occur after a certain case-free interval - despite the detection of the outbreak's source. This article summarises the results of a systematic search of the medical literature on polyphasic outbreaks. MATERIALS AND METHODS: For this purpose, the Outbreak Worldwide-Database, PubMed and reference lists of relevant articles were screened. RESULTS: A total of 124 polyphasic outbreaks (median duration of 50 weeks) was included in the analysis and then compared to 2089 monophasic nosocomial outbreaks. Surgical departments were significantly more often involved in polyphasic outbreaks than they were in monophasic events (33.9 % vs. 24.5 %; p < 0.05). Hepatitis B virus outbreaks were significantly more often seen as poly-phasic events. Either there had been more than one source initially, or a new source developed during the first phase of the outbreak and led to additional cases thereafter. CONCLUSIONS: Up to now, only little is known about polyphasic nosocomial outbreaks. Thus, there is a further need to close this gap of information in the future. Personnel on the ward as well as -infection control staff should always consider the possibility of the existence of more than one -source when investigating a nosocomial outbreak.

Prophylactic endovascular placement of internal iliac occlusion balloon catheters in parturients with placenta accreta: a retrospective case series.

BACKGROUND: Endovascular occlusion balloon catheters can be placed preoperatively in internal iliac vessels of patients perceived to be at risk of major obstetric haemorrhage during caesarean section. Their safety and efficacy remains undefined, and we report our experience of 14 patients over four years. METHODS: We undertook a chart review of all patients who had undergone prophylactic internal iliac balloon catheters before caesarean section in our institution. RESULTS: Balloon catheters were placed in 14 and inflated in 11 (78.6%) patients. Five of the 14 patients (35.7%) underwent emergency balloon catheter placement before unscheduled caesarean section. Surgeons reported that balloon inflation provided favourable surgical conditions in six of 11 cases (54.5%), no improvement in four and was not required in one due to lack of pathology. Within the balloon-inflated group, nine patients underwent a hysterectomy: two electively, the remaining seven because of perioperative confirmation of placenta accreta or for control of bleeding. One patient suffered massive haemorrhage leading to three perioperative hypovolaemic cardiac arrests. Four patients required intervention to avoid complications related to balloon catheters: three minor and one related to catheter displacement and prolonged resuscitation. CONCLUSION: Internal iliac balloon catheters can be inserted electively or in an emergency in patients at risk of major obstetric haemorrhage. Although useful in some, they are not universally effective; patients are still at risk of significant blood loss and at high risk of requiring a hysterectomy. In our experience, catheters can be placed electively or in an emergency but have been associated with adverse outcomes. These lessons have been important learning points in perioperative management.