Malin Jonsson Fagerlund

Resolving postoperative neuroinflammation and cognitive decline

Cognitive decline accompanies acute illness and surgery, especially in the elderly. Surgery engages the innate immune system that launches a systemic inflammatory response that, if unchecked, can cause multiple organ dysfunction. We sought to understand the mechanisms whereby the brain is targeted by the inflammatory response and how this can be resolved.

Current concepts in neuromuscular transmission

The neuromuscular junction (NMJ) is structured and powered to transduce electrical activity from the distal nerve terminal of a motor neurone via the neuromuscular cleft to the post-junctional muscle membrane to ultimately generate muscle contraction. Our understanding of this complex function has expanded over many years, and the NMJ has served as a prototype for how different synapses operate in the peripheral and central nervous systems. The NMJ has a presynaptic part which is synonymous with the distal nerve ending, being responsible for neurotransmitter synthesis, packaging into vesicles, and subsequent vesicle transportation to active release sites where vesicle docking, fusion, and release of acetylcholine and other co-released transmitters finally take place. The synaptic cleft, filled with large molecular complexes that guarantee ultrastructural NMJ arrangement and signal transduction, allows for rapid diffusion and degradation of the neurotransmitter. The postsynaptic part consists of a folded muscle membrane into which nicotinic acetylcholine receptors (nAChRs) directly opposite the presynaptic active release sites are mounted and fixed by a cytoskeleton. This specialized postsynaptic region is closely associated with the perijunctional zone where a high density of sodium channels promote and amplify the signal in order to guarantee the propagation of the electrical activity to generate muscle contraction. The transduction process is maintained at load (i.e. high stimulus frequency) by a presynaptic mechanism allowing for sustained transmitter release over time at high demand. This positive feedback mechanism relies on neuronal nAChRs present on the distal nerve terminal, whereas the continuation of the transduction process at the postsynaptic part relies on the classical muscle type nAChR. In this review, we will focus on recent findings of potential clinical importance that will advance our understanding of the effects of neuromuscular blocking agents and neuromuscular monitoring and also our management of disorders of the neuromuscular system within anaesthesia and intensive care.

The human carotid body transcriptome with focus on oxygen sensing and inflammation – a comparative analysis

•  The carotid body (CB) is the key oxygen sensor and governs the ventilatory response to hypoxia. •  CB oxygen sensing and signalling gene expression is well described in animals whereas human data are absent. •  Here we have characterized the human CB global gene expression in comparison with functionally related tissues and mouse CB gene expression. •  We show that the human CB expresses oxygen sensing genes in common with mice but also differs on key genes such as certain K+ channels. There is moreover increased expression of inflammatory response genes in human and mouse CBs in comparison with related tissues. •  The study establishes similarities but also important differences between animal and human CB gene expression profiles and provides a platform for future functional studies on human CBs.

Pharmacological Characteristics of the Inhibition of Nondepolarizing Neuromuscular Blocking Agents at Human Adult Muscle Nicotinic Acetylcholine Receptor

Background:Nondepolarizing neuromuscular blocking agents (NMBAs) are classic competitive-inhibitors at the muscle nicotinic acetylcholine receptor (nAChR). Although the fetal subtype muscle nAChR has been extensively studied at a molecular level, less is known about the interaction between nondepolarizing NMBAs and the human adult muscle nAChR. The aim of this study was to investigate the effect of clinically used nondepolarizing NMBAs at human adult muscle nAChRs and the mechanisms behind the inhibition. Methods:Human subunits for the adult &agr;1&bgr;1Δϵ muscle nAChR were cloned and expressed into Xenopus oocytes and thereafter studied with two-electrode voltage clamp. The effect of the clinically used nondepolarizing NMBAs, including atracurium, cis-atracurium, mivacurium, pancuronium, rocuronium, vecuronium, and d-tubocurarine, on acetylcholine-induced and dimethylphenylpiperazinium-induced currents were investigated. Results:All nondepolarizing NMBAs tested inhibited acetylcholine- and dimethylphenylpiperazinium-induced currents in human adult &agr;1&bgr;1Δϵ muscle nAChRs, and no receptor activation was seen. Interestingly, acetylcholine desensitized the human adult &agr;1&bgr;1Δϵ muscle type receptor and attenuated the inhibition caused by nondepolarizing NMBAs, as evident by lack of increase in IC50 values for the nondepolarizing NMBAs with increased concentrations of acetylcholine. In contrast, dimethylphenylpiperazinium-induced currents were competitively inhibited by the nondepolarizing NMBAs. Conclusions:This study demonstrates that nondepolarizing NMBAs inhibit human adult muscle nAChRs expressed in Xenopus oocytes by mixed mechanisms. When using the nondesensitizing agonist dimethylphenylpiperazinium, inhibition by the NMBA is competitive, whereas activation with high concentrations of acetylcholine in combination with NMBA induces a noncompetitive inhibition, which the authors speculate can involve receptor desensitization similar to that observed in the neuromuscular junction.

The human carotid body: expression of oxygen sensing and signaling genes of relevance for anesthesia.

Background:Hypoxia is a common cause of adverse events in the postoperative period, where respiratory depression due to residual effects of drugs used in anesthesia is an important underlying factor. General anesthetics and neuromuscular blocking agents reduce the human ventilatory response to hypoxia. Although the carotid body (CB) is the major oxygen sensor in humans, critical oxygen sensing and signaling pathways have been investigated only in animals so far. Thus, the aim of this study was to characterize the expression of key genes and localization of their products involved in the human oxygen sensing and signaling pathways with a focus on receptor systems and ion channels of relevance in anesthesia. Methods:Six CBs were removed unilaterally from patients undergoing radical neck dissection. The gene expression and cell-specific protein localization in the CBs were investigated with DNA microarrays, real-time polymerase chain reaction, and immunohistochemistry. Results:We found gene expression of the oxygen-sensing pathway, heme oxygenase 2, and the K+ channels TASK (TWIK-related acid sensitive K+ channel)-1 and BK (large-conductance potassium channel). In addition, we show the expression of critical receptor subunits such as &ggr;-aminobutyric acid A (&agr;2, &bgr;3, and &ggr;2), nicotinic acetylcholine receptors (&agr;3, &agr;7, and &bgr;2), purinoceptors (A2A and P2X2), and the dopamine D2 receptor. Conclusions:In unique samples of the human CB, we here demonstrate presence of critical proteins in the oxygen-sensing and signaling cascade. Our findings demonstrate similarities to, but also important differences from, established animal models. In addition, our work establishes an essential platform for studying the interaction between anesthetic drugs and human CB chemoreception.

The Immune Response of the Human Brain to Abdominal Surgery

Surgery launches a systemic inflammatory reaction that reaches the brain and associates with immune activation and cognitive decline. Although preclinical studies have in part described this systemic‐to‐brain signaling pathway, we lack information on how these changes appear in humans. This study examines the short‐ and long‐term impact of abdominal surgery on the human brain immune system by positron emission tomography (PET) in relation to blood immune reactivity, plasma inflammatory biomarkers, and cognitive function.

The human carotid body releases acetylcholine, ATP and cytokines during hypoxia

What is the central question of this study? Data on human carotid body (CB) function are limited. The aim of this study was therefore to investigate whether the human CB releases acetylcholine, ATP or cytokines during hypoxia. What is the main finding and its importance? Using human CBs, we demonstrate hypoxia‐induced acetylcholine and ATP release, suggesting that these neurotransmitters, as in several experimental animal models, play a role in hypoxic signalling also in the human carotid body. Moreover, the human CB releases cytokines upon hypoxia and expresses cytokine receptors as well as hypoxia‐inducible factor proteins HIF‐1α and HIF‐2α in glomus cells, indicating their role in immune signalling and oxygen sensing, respectively, in accordance with previous animal data.

Presence of nicotinic, purinergic and dopaminergic receptors and the TASK-1 K+-channel in the mouse carotid body.

We have characterized the mouse carotid body (CB) with special attention to nicotinic, purinergic and dopaminergic receptors as well as the TASK-1 K(+)-channel. Mouse CB sections were stained immunohistochemically and visualized using fluorescent and confocal microscopy. The CB type 1 cells contained the alpha3 (n=8), alpha4 (n=7), alpha7 (n=4) and beta2 (n=3) nicotinic acetylcholine receptor (nAChR) subunits, the ATP-receptors P2X(2) (n=15) and P2X(3) (n=9), the dopamine D(2) receptor (n=9) and the TASK-1 K(+)-channel (n=7). Here we report the presence of alpha3, alpha4, alpha7 and beta2 nAChR subunits, the D(2) receptor and the TASK-1 K(+)-channel in the mouse CB. Also, we confirm the presence of the P2X(2) and P2X(3) receptors in mouse CB. Thus, we have localized nicotinergic, purinergic and dopaminergic receptors and the TASK-1 K(+)-channel on a protein level in one species. Our data are in line with the theory that the CB chemoreceptor cell hosts an orchestra of receptor systems that ultimately modulate the response to hypoxia.

Sedation with Dexmedetomidine or Propofol Impairs Hypoxic Control of Breathing in Healthy Male Volunteers: A Nonblinded, Randomized Crossover Study.

Background:In contrast to general anesthetics such as propofol, dexmedetomidine when used for sedation has been put forward as a drug with minimal effects on respiration. To obtain a more comprehensive understanding of the regulation of breathing during sedation with dexmedetomidine, the authors compared ventilatory responses to hypoxia and hypercapnia during sedation with dexmedetomidine and propofol. Methods:Eleven healthy male volunteers entered this randomized crossover study. Sedation was administered as an intravenous bolus followed by an infusion and monitored by Observer’s Assessment of Alertness/Sedation (OAA/S) scale, Richmond Agitation Sedation Scale, and Bispectral Index Score. Hypoxic and hypercapnic ventilatory responses were measured at rest, during sedation (OAA/S 2 to 4), and after recovery. Drug exposure was verified with concentration analysis in plasma. Results:Ten subjects completed the study. The OAA/S at the sedation goal was 3 (3 to 4) (median [minimum to maximum]) for both drugs. Bispectral Index Score was 82 ± 8 and 75 ± 3, and the drug concentrations in plasma at the sedation target were 0.66 ± 0.14 ng/ml and 1.26 ± 0.36 &mgr;g/ml for dexmedetomidine and propofol, respectively. Compared with baseline, sedation reduced hypoxic ventilation to 59 and 53% and the hypercapnic ventilation to 82 and 86% for dexmedetomidine and propofol, respectively. In addition, some volunteers displayed upper airway obstruction and episodes of apnea during sedation. Conclusions:Dexmedetomidine-induced sedation reduces ventilatory responses to hypoxia and hypercapnia to a similar extent as sedation with propofol. This finding implies that sedation with dexmedetomidine interacts with both peripheral and central control of breathing.

Pronounced depression by propofol on carotid body response to CO2 and K+-induced carotid body activation

Propofol is a commonly used anesthetic agent, and it attenuates hypoxic ventilatory response in humans. Propofol reduce in vivo and in vitro carotid body responses to hypoxia as well as to nicotine in experimental animals. In the present study we examined the effects of propofol on carotid body responses to hypercapnia and K(+)-induced carotid body activation and compared these effects with hypoxia in an in vitro rabbit carotid body preparation. Hypoxia, hypercapnia and potassium increased the carotid sinus nerve activity and propofol attenuated the chemoreceptor responses to all three stimuli. However, the magnitude of propofol-induced attenuation was greater for hypercapnic and K(+)-induced carotid body activation compared to the hypoxic response. These observations suggest that propofol-induced attenuation of the hypoxic response is partly secondary to depression of chemoreceptor response to hypercapnia inhibiting the synergistic interactions between O(2) and CO(2) and may involve CO(2)/H(+) sensitive K(+) channels.