Sodium regulates clock time and output via an excitatory GABAergic pathway.

The suprachiasmatic nucleus (SCN) serves as the body's master circadian clock that adaptively coordinates changes in physiology and behaviour in anticipation of changing requirements throughout the 24-h day-night cycle1-4. For example, the SCN opposes overnight adipsia by driving water intake before sleep5,6, and by driving the secretion of anti-diuretic hormone7,8 and lowering body temperature9,10 to reduce water loss during sleep11. These responses can also be driven by central osmo-sodium sensors to oppose an unscheduled rise in osmolality during the active phase12-16. However, it is unknown whether osmo-sodium sensors require clock-output networks to drive homeostatic responses. Here we show that a systemic salt injection (hypertonic saline) given at Zeitgeber time 19-a time at which SCNVP (vasopressin) neurons are inactive-excited SCNVP neurons and decreased non-shivering thermogenesis (NST) and body temperature. The effects of hypertonic saline on NST and body temperature were prevented by chemogenetic inhibition of SCNVP neurons and mimicked by optogenetic stimulation of SCNVP neurons in vivo. Combined anatomical and electrophysiological experiments revealed that osmo-sodium-sensing organum vasculosum lamina terminalis (OVLT) neurons expressing glutamic acid decarboxylase (OVLTGAD) relay this information to SCNVP neurons via an excitatory effect of γ-aminobutyric acid (GABA). Optogenetic activation of OVLTGAD neuron axon terminals excited SCNVP neurons in vitro and mimicked the effects of hypertonic saline on NST and body temperature in vivo. Furthermore, chemogenetic inhibition of OVLTGAD neurons blunted the effects of systemic hypertonic saline on NST and body temperature. Finally, we show that hypertonic saline significantly phase-advanced the circadian locomotor activity onset of mice. This effect was mimicked by optogenetic activation of the OVLTGAD→ SCNVP pathway and was prevented by chemogenetic inhibition of OVLTGAD neurons. Collectively, our findings provide demonstration that clock time can be regulated by non-photic physiologically relevant cues, and that such cues can drive unscheduled homeostatic responses via clock-output networks.

Effect of Hypertonic Saline Solution on the Ventilatory Mechanics of Lungs Donated After Brain Death.

INTRODUCTION: Brain death (BD) compromises the viability of the lung for donation. Hypertonic saline solution (HSS) induces rapid intravascular volume expansion and immunomodulatory action. We investigated its role in ventilatory mechanics (VMs) and in the inflammatory activity of the lungs of rats subjected to BD. METHODS: Wistar rats were divided into four groups: control, n = 10: intact rats subjected to extraction of the heart-lung block; BD, n = 8 (BD): rats treated with isotonic saline solution (4 mL/kg) immediately after BD; hypertonic saline 0 h, n = 9 (Hip.0'): rats treated with HSS (4 mL/kg) immediately after BD; and hypertonic saline 1 h, n = 9 (Hip.60'), rats treated with HSS (4 mL/kg) 60 min after BD. The hemodynamic characteristics, gas exchange, VMs, inflammatory mediators, and histopathological evaluation of the lung were evaluated over 240 min of BD. RESULTS: In VMs, we observed increased airway resistance, tissue resistance, tissue elastance, and respiratory system compliance in the BD group (P < 0.037), while the treated groups showed no impairment over time (P > 0.05). In the histological analysis, the BD group showed a greater area of perivascular edema and a higher neutrophil count than the control group and the Hip.60' group (P < 0.05). CONCLUSIONS: Treatment with HSS was effective in preventing changes in the elastic and resistive pulmonary components, keeping them at baseline levels. Late treatment reduced perivascular and neutrophilic edema in lung tissue.

Hypertonic Saline Versus Other Intracranial-Pressure-Lowering Agents for Patients with Acute Traumatic Brain Injury: A Systematic Review and Meta-analysis.

Acute traumatic brain injury (TBI) is a major cause of mortality and disability worldwide. Intracranial pressure (ICP)-lowering is a critical management priority in patients with moderate to severe acute TBI. We aimed to evaluate the clinical efficacy and safety of hypertonic saline (HTS) versus other ICP-lowering agents in patients with TBI. We conducted a systematic search from 2000 onward for randomized controlled trials (RCTs) comparing HTS vs. other ICP-lowering agents in patients with TBI of all ages. The primary outcome was the Glasgow Outcome Scale (GOS) score at 6 months (PROSPERO CRD42022324370). Ten RCTs (760 patients) were included. Six RCTs were included in the quantitative analysis. There was no evidence of an effect of HTS on the GOS score (favorable vs. unfavorable) compared with other agents (risk ratio [RR] 0.82, 95% confidence interval [CI] 0.48-1.40; n = 406; 2 RCTs). There was no evidence of an effect of HTS on all-cause mortality (RR 0.96, 95% CI 0.60-1.55; n = 486; 5 RCTs) or total length of stay (RR 2.36, 95% CI - 0.53 to 5.25; n = 89; 3 RCTs). HTS was associated with adverse hypernatremia compared with other agents (RR 2.13, 95% CI 1.09-4.17; n = 386; 2 RCTs). The point estimate favored a reduction in uncontrolled ICP with HTS, but this was not statistically significant (RR 0.52, 95% CI 0.26-1.04; n = 423; 3 RCTs). Most included RCTs were at unclear or high risk of bias because of lack of blinding, incomplete outcome data, and selective reporting. We found no evidence of an effect of HTS on clinically important outcomes and that HTS is associated with adverse hypernatremia. The included evidence was of low to very low certainty, but ongoing RCTs may help to the reduce this uncertainty. In addition, heterogeneity in GOS score reporting reflects the need for a standardized TBI core outcome set.

Initial Diagnosis and Management of Acutely Elevated Intracranial Pressure.

Acutely elevated intracranial pressure (ICP) may have devastating effects on patient mortality and neurologic outcomes, yet its initial detection remains difficult because of the variety of manifestations that it can cause disease states it is associated with. Several treatment guidelines exist for specific disease processes such as trauma or ischemic stroke, but their recommendations may not apply to other causes. In the acute setting, management decisions must often be made before the underlying cause is known. In this review, we present an organized, evidence-based approach to the recognition and management of patients with suspected or confirmed elevated ICP in the first minutes to hours of resuscitation. We explore the utility of invasive and noninvasive methods of diagnosis, including history, physical examination, imaging, and ICP monitors. We synthesize various guidelines and expert recommendations and identify core management principles including noninvasive maneuvers, neuroprotective intubation and ventilation strategies, and pharmacologic therapies such as ketamine, lidocaine, corticosteroids, and the hyperosmolar agents mannitol and hypertonic saline. Although an in-depth discussion of the definitive management of each etiology is beyond the scope of this review, our goal is to provide an empirical approach to these time-sensitive, critical presentations in their initial stages.

Successful blood transfusion in a Holstein cow experiencing hemorrhagic shock under general anesthesia.

A 2-year-old Holstein cow weighing 530 kg at 2 mo gestation was scheduled for a paracostal laparotomy and abomasotomy following diagnosis of a reticular foreign body causing obstruction and abomasal impaction. Hemorrhagic shock occurred during surgery, with a rapid, approximately 60% decrease in arterial blood pressure, and reflex tachycardia with a 2-fold increase in heart rate. Following identification of hemorrhagic shock, arterial blood pressure was supported by reducing the inhalant anesthetic requirement, positive inotropic support (IV dobutamine infusion), and IV fluid therapy. Hypertonic saline was administered IV for initial resuscitation of arterial blood pressure, followed by a whole blood transfusion to replenish red blood cells, support oxygencarrying capacity, and provide intravascular volume to maintain cardiac output and tissue perfusion. A gradual increase in arterial blood pressure and a decrease in heart rate were observed in response to treatment. This case report demonstrates the physiologic compensatory response to hemorrhagic shock and the treatment to stabilize cardiovascular parameters in an anesthetized cow. Key clinical message: This case illustrates the physiological reponses to acute hemorrhage under general anesthesia and the effects of various treatment interventions.

Transfusion sanguine réussie chez une vache Holstein en état de choc hémorragique sous anesthésie générale. Une vache Holstein de 2 ans pesant 530 kg à 2 mois de gestation devait subir une laparotomie paracostale et une abomasotomie à la suite du diagnostic d'un corps étranger réticulaire provoquant une obstruction et une impaction abomasale. Un choc hémorragique est survenu pendant la chirurgie, avec une diminution rapide d'environ 60 % de la pression artérielle et une tachycardie réflexe avec une augmentation du double de la fréquence cardiaque. À la suite de l'identification d'un choc hémorragique, la pression artérielle a été soutenue en réduisant le besoin d'anesthésique inhalé, un soutien inotrope positif (perfusion de dobutamine IV) et une thérapie avec des fluides IV. Une solution saline hypertonique a été administrée par voie intraveineuse pour la restauration initiale de la pression artérielle, suivie d'une transfusion de sang total pour rétablir la quantité de globules rouges, soutenir la capacité de transport d'oxygène et fournir un volume intravasculaire pour maintenir le débit cardiaque et la perfusion tissulaire. Une augmentation progressive de la pression artérielle et une diminution de la fréquence cardiaque ont été observées en réponse au traitement. Ce rapport de cas démontre la réponse physiologique compensatoire au choc hémorragique et le traitement pour stabiliser les paramètres cardiovasculaires chez une vache anesthésiée.Message clinique clé :Ce cas illustre les réponses physiologiques à une hémorragie aiguë sous anesthésie générale et les effets de diverses interventions thérapeutiques.(Traduit par Dr Serge Messier).

Intravital imaging of mucus transport in asthmatic mice using microscopic optical coherence tomography.

Asthma is one of the most common chronic diseases. Mucus overproduction is consistently linked to asthma morbidity and mortality. Despite the knowledge of the importance of mucus, little data exist on how mucus is transported in asthma and the immediate effects of therapeutic intervention. We therefore used microscopic optical coherence tomography (mOCT) to study spontaneous and induced mucus transport in an interleukin-13 (IL-13)-induced asthma mouse model and examined the effects of isotonic (0.9% NaCl) and hypertonic saline (7% NaCl), which are used to induce mucus transport in cystic fibrosis. Without intervention, no bulk mucus transport was observed by mOCT and no intraluminal mucus was detectable in the intrapulmonary airways by histology. Administration of ATP-γ-S induced mucus secretion into the airway lumen, but it did not result in bulk mucus transport in the trachea. Intraluminal-secreted immobile mucus could be mobilized by administration of isotonic or hypertonic saline but hypertonic saline mobilized mucus more reliably than isotonic saline. Irrespective of saline concentration, the mucus was transported in mucus chunks. In contrast to isotonic saline solution, hypertonic saline solution alone was able to induce mucus secretion. In conclusion, mOCT is suitable to examine the effects of mucus-mobilizing therapies in vivo. Although hypertonic saline was more efficient in inducing mucus transport, it induced mucus secretion, which might explain its limited benefit in patients with asthma.

Brain edema after oocyte retrieval: a case report.

BACKGROUND: Brain edema is a rare and serious complication of assisted reproductive technology (ART). The increased intracranial pressure and injured brain parenchyma are life-threatening and may even result in death. The pathogenesis may involve increased vascular permeability mediated by vascular endothelial growth factor and other vasoactive substances, including interleukin 6, interleukin 1ß, angiotensin II, insulin-like growth factor 1, transforming growth factor ß, and the renin-angiotensin system. CASE PRESENTATION: We presented a unique case report of a 29-year-old woman developed sudden irritability, blurred consciousness, and vomiting 8 h after oocyte retrieval. Blood examinations showed hyponatremia and cranial computed tomography showed swelling of the brain parenchyma. After therapeutic use of hypertonic saline and mannitol infusion, the patient's consciousness recovered and her neurological state improved. CONCLUSIONS: Brain edema is a rare and serious complication of ART. Quick infusion of hypertonic salt solution and mannitol is a key treatment. A good prognosis can be achieved after prompt treatment.

Induction of renal tumor necrosis factor-α and other autacoids and the beneficial effects of hypertonic saline in acute decompensated heart failure.

Although administration of hypertonic saline (HSS) in combination with diuretics has yielded improved weight loss, preservation of renal function, and reduction in hospitalization time in the clinical setting of patients with acute decompensated heart failure (ADHF), the mechanisms that underlie these beneficial effects remain unclear and additional studies are needed before this approach can be adopted on a more consistent basis. As high salt conditions stimulate the production of several renal autacoids that exhibit natriuretic effects, renal physiologists can contribute to the understanding of mechanisms by which HSS leads to increased diuresis both as an individual therapy as well as in combination with loop diuretics. For instance, since HSS increases TNF-α production by proximal tubule and thick ascending limb of Henle's loop epithelial cells, this article is aimed at highlighting how the effects of TNF-α produced by these cell types may contribute to the beneficial effects of HSS in patients with ADHF. Although TNF-α produced by infiltrating macrophages and T cells exacerbates and attenuates renal damage, respectively, production of this cytokine within the tubular compartment of the kidney functions as an intrinsic regulator of blood pressure and Na+ homeostasis via mechanisms along the nephron related to inhibition of Na+-K+-2Cl- cotransporter isoform 2 activity and angiotensinogen expression. Thus, in the clinical setting of ADHF and hyponatremia, induction of TNF-α production along the nephron by administration of HSS may attenuate Na+-K+-2Cl- cotransporter isoform 2 activity and angiotensinogen expression as part of a mechanism that prevents excessive Na+ reabsorption in the thick ascending limb of Henle's loop, thereby mitigating volume overload.

Real-time confocal microscopy imaging of corneal cytoarchitectural changes induced by different stresses.

Maintenance of the corneal refractive power and tissue transparency is essential for normal vision. Real-time characterization of changes in corneal cells during suffering stresses or wound healing may provide a way to identify novel targets, whose therapeutic manipulation can improve the outcome of this response induced by injury. Here we describe a novel user friendly and effective confocal real-time confocal microscopy attachment that monitors the effects of anisoosmotic stress on cell morphology and corneal thickness in situ. Corneal epithelial nuclei gradually became highly reflective in the isotonic group and the corneal stroma was slightly thickened as compared with that seen prior to 60 min exposure to a hypotonic solution. After 30 min of exposure to hypertonic stress, the corneal stromal cells became crenate and shriveled. The hyper-reflective area of the corneal stroma in the hypo-osmotic group was significantly larger than that in the other two groups, as demonstrated by 3D reconstruction imaging. The hypotonic fresh chlorinated pool water was observed to cause atrophy of corneal epithelial nuclei, while the isosmotic bee venom solution caused high reflection of the corneal stroma layer and corneal endothelial cell damage. With the microscopic attachment, the inward movement of corneal epithelial cells toward the denuded central region was detected in the serum-treated group. The microscopy attachment is an effective system for obtaining a more detailed understanding of the time dependent losses in the corneal cell structure and tissue architecture of full thickness corneas induced by osmotic stress or cytotoxic agents.

Rheological effects of hypertonic saline and sodium bicarbonate solutions on cystic fibrosis sputum in vitro.

BACKGROUND: Cystic fibrosis (CF) is a life-threatening multiorgan genetic disease, particularly affecting the lungs, where recurrent infections are the main cause of reduced life expectancy. In CF, mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein impair transepithelial electrolyte and water transport, resulting in airway dehydration, and a thickening of the mucus associated with abnormal viscoelastic properties. Our aim was to develop a rheological method to assess the effects of hypertonic saline (NaCl) and NaHCO3 on CF sputum viscoelasticity in vitro, and to identify the critical steps in sample preparation and in the rheological measurements. METHODS: Sputum samples were mixed with hypertonic salt solutions in vitro in a ratio of either 10:4 or 10:1. Distilled water was applied as a reference treatment. The rheological properties of sputum from CF patients, and the effects of these in vitro treatments, were studied with a rheometer at constant frequency and strain, followed by frequency sweep tests, where storage modulus (G'), loss modulus (G″) and loss factor were determined. RESULTS: We identified three distinct categories of sputum: (i) highly elastic (G' > 100,000 Pa), (ii) elastic (100,000 Pa > G' > 1000 Pa), and (iii) viscoelastic (G' < 1000). At the higher additive ratio (10:4), all of the added solutions were found to significantly reduce the gel strength of the sputum, but the most pronounced changes were observed with NaHCO3 (p < 0.001). Samples with high elasticity exhibited the greatest changes while, for less elastic samples, a weakening of the gel structure was observed when they were treated with water or NaHCO3, but not with NaCl. For the viscoelastic samples, the additives did not cause significant changes in the parameters. When the lower additive ratio (10:1) was used, the mean values of the rheological parameters usually decreased, but the changes were not statistically significant. CONCLUSION: Based on the rheological properties of the initial sputum samples, we can predict with some confidence the treatment efficacy of each of the alternative additives. The marked differences between the three categories suggest that it is advisable to evaluate each sample individually using a rheological approach such as that described here.

Hypertonic Sodium Lactate to Alleviate Functional Deficits Following Diffuse Traumatic Brain Injury: An Osmotic or a Lactate-Related Effect?

BACKGROUND: There has been growing interest in the use of hypertonic sodium lactate (HSL) solution following traumatic brain injury (TBI) in humans. However, little is known about the effects of HSL on functional deficits with respect to the hyperosmotic nature of HSL. METHODS: We have compared the effects of HSL solution and isotonic saline solution using sensorimotor and cognitive tests for 14 days post-trauma in animals. Thirty minutes after trauma (impact-acceleration model), anesthetized rats were randomly allocated to receive a 2-h infusion of isotonic saline solution (TBI-saline group) or HSL (TBI-HSL group) (n = 10 rats per group). In another series of experiments using a similar protocol, the effects of equiosmolar doses of HSL and hypertonic saline solution (HSS) were compared in TBI rats (n = 10 rats per group). Blood lactate and ion concentrations were measured during the 2-h infusions. RESULTS: Compared to the TBI-saline group, the TBI-HSL group had a reduced latency to complete the adhesive removal test: 6 s (5-9) (median [25-75th centiles]) versus 13 s (8-17) on day 7, and 5 s (5-9) versus 11 s (8-26) on day 14 (P < 0.05), respectively, and a shorter delay to complete the radial arm maze test on day 7: 99 s (73-134) versus 176 s (127-300), respectively (P < 0.05). However, no differences were found between the TBI-HSL and TBI-HSS groups in neurocognitive tests performance. Compared to the TBI-saline group, the HSL and HSS groups had higher serum osmolality: 318 mOsm/Kg (315-321) and 315 mOsm/Kg (313-316) versus 307 mOsm/Kg (305-309), respectively (P < 0.05), and the HSL group had a higher serum lactate concentration: 6.4 mmol/L (5.3-7.2) versus 1.5 mmol/L (1.1-1.9) and 1.6 mmol/L (1.5-1.7), respectively (P < 0.05). CONCLUSIONS: These results indicate that improvements in cognitive and sensorimotor tests with HSL infusion post-TBI could be related to elevation of serum osmolality, not to exogenous administration of lactate.

Mechanisms involved in the cardiovascular effects caused by acute osmotic stimulation in conscious rats.

Both the autonomic nervous system and the neuroendocrine system are activated by osmotic stimulation (OS) evoking cardiovascular effects. The current study investigated the mechanisms involved in the cardiovascular responses evoked by an acute osmotic stimulus with intraperitoneal (i.p.) injection of either isotonic (0.15 M NaCl) or hypertonic saline (0.6 M NaCl) in conscious rats. Hypertonic saline increased mean arterial pressure (MAP) and heart rate (HR) for 30 min, as well as plasma osmolality and sodium content. Urinary sodium and urinary volume were also increased. Pretreatment with the ganglion blocker pentolinium (i.v.) did not affect the pressor response, but significantly decreased the tachycardic response caused by OS. Pretreatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP (i.v.) reduced the pressor response, without affecting the tachycardic response evoked by the hypertonic OS. Neither the pressor nor the tachycardic response to OS was affected by pretreatment with either the oxytocin receptor antagonist atosiban or the α1-antagonist prazosin. Pretreatment with the ß1-antagonist atenolol had no effect on the pressor response, but markedly decreased the tachycardic response evoked by OS. Results indicate that i.p. hypertonic OS-evoked pressor response is mediated by the release of vasopressin, with a minor influence of the vascular sympathetic input.LAY SUMMARYIncreased plasma osmolality, such as that observed during dehydration or salt intake, is a potent stimulus yielding to marked cardiovascular and neuroendocrine responses. The intraperitoneal (i.p.) injection of hypertonic saline solution is a commonly used animal model to cause a sustained increase in plasma osmolality, leading to a cardiovascular response characterized by sustained blood pressure and heart increases, whose systemic mechanisms were presently studied. Our findings indicate that the pressor response to the i.p. osmotic stimulus (OS) is mediated mainly by the release of vasopressin into the blood circulation with a minor or even the noninvolvement of the vascular sympathetic nervous system, whereas activation of the sympathetic-cardiac system mediates the tachycardic response to OS.

Role of PKC and AMPK in hypertonicity-stimulated water reabsorption in rat inner medullary collecting ducts.

Hypertonicity increases water permeability, independently of vasopressin, in the inner medullary collecting duct (IMCD) by increasing aquaporin-2 (AQP2) membrane accumulation. We investigated whether protein kinase C (PKC) and adenosine monophosphate kinase (AMPK) are involved in hypertonicity-regulated water permeability. Increasing perfusate osmolality from 150 to 290 mosmol/kgH2O and bath osmolality from 290 to 430 mosmol/kgH2O significantly stimulated osmotic water permeability. The PKC inhibitors chelerythrine (10 µM) and rottlerin (50 µM) significantly reversed the increase in osmotic water permeability stimulated by hypertonicity in perfused rat terminal IMCDs. Chelerythrine significantly increased phosphorylation of AQP2 at S261 but not at S256. Previous studies show that AMPK is stimulated by osmotic stress. We tested AMPK phosphorylation under hypertonic conditions. Hypertonicity significantly increased AMPK phosphorylation in inner medullary tissues. Blockade of AMPK with Compound C decreased hypertonicity-stimulated water permeability but did not alter phosphorylation of AQP2 at S256 and S261. AICAR, an AMPK stimulator, caused a transient increase in osmotic water permeability and increased phosphorylation of AQP2 at S256. When inner medullary tissue was treated with the PKC activator phorbol dibutyrate (PDBu), the AMPK activator metformin, or both, AQP2 phosphorylation at S261 was decreased with PDBu or metformin alone, but there was no additive effect on phosphorylation with PDBu and metformin together. In conclusion, hypertonicity regulates water reabsorption by activating PKC. Hypertonicity-stimulated water reabsorption by PKC may be related to the decrease in endocytosis of AQP2. AMPK activation promotes water reabsorption, but the mechanism remains to be determined. PKC and AMPK do not appear to act synergistically to regulate water reabsorption.

Hypertonic saline stimulates vagal afferents that respond to lung deflation.

In our present studies, we seek to determine whether increased osmolarity stimulates deflation-activated receptors (DARs). In anesthetized, open-chest, and mechanically ventilated rabbits, we recorded single-unit activities from typical slowly adapting receptors (SARs; responding only to lung inflation) and DAR-containing SARs (DAR-SARs; responding to both lung inflation and deflation) and identified their receptive fields in the lung. We examined responses of these two groups of pulmonary sensory units to direct injection of hypertonic saline (8.1% sodium chloride; 9-fold in tonicity) into the receptive fields. Hypertonic saline decreased the activity in most SAR units from 40.3 ± 5.4 to 34.8 ± 4.7 imp/s (P < 0.05, n = 12). In contrast, it increased the activity in DAR-SAR units quickly and significantly from 15.9 ± 2.2 to 43.4 ± 10.0 imp/s (P < 0.01, n = 10). Many units initially had increased activity, mainly in the deflation phase. DAR-SAR activities largely returned to the control level 30 s after injection. Since hypertonic saline stimulated DAR-SAR units but not SAR units, we conclude that hypertonic saline activates DARs.

Carotid bodies contribute to sympathoexcitation induced by acute salt overload.

NEW FINDINGS: What is the central question of this study? Does carotid body input contribute to the hyperosmotic responses? What is the main finding and its importance? The response to NaCl overload is sympathorespiratory excitation. Eliminating the carotid body input reduced sympathoexcitation but did not affect the increase in phrenic burst frequency, whereas eliminating the hypothalamus prevented the tachypnoea and sympathoexcitation. We conclude that the carotid body inputs are essential for the full expression of the sympathetic activity during acute NaCl overload, whereas the tachypnoea depends on hypothalamic mechanisms. ABSTRACT: Acute salt excess activates central osmoreceptors, which trigger an increase in sympathetic and respiratory activity. The carotid bodies also respond to hyperosmolality of the extracellular compartment, but their contribution to the sympathoexcitatory and ventilatory responses to NaCl overload remains unknown. To evaluate their contribution to acute NaCl overload, we recorded thoracic sympathetic (tSNA), phrenic (PNA) and carotid sinus nerve activities in decorticate in situ preparations of male Holtzman rats (60-100 g) while delivering intra-arterial infusions of hyperosmotic NaCl (0.17, 0.3, 0.7, 1.5 and 2.0 mol l-1 ; 200 µl infusion over 25-30 s, with a 10 min time interval between solutions) or mannitol (0.3, 0.5, 1.0, 2.7 and 3.8 mol l-1 ) progressively. The cumulative infusions of hyperosmotic NaCl increased the perfusate osmolality to 341 ± 5 mosmol (kg water)-1 and elicited an immediate increase in PNA and tSNA (n = 6, P < 0.05) in sham-denervated rats. Carotid body removal attenuated sympathoexcitation (n = 5, P < 0.05) but did not affect the tachypnoeic response. A precollicular transection disconnecting the hypothalamus abolished the sympathoexcitatory and tachypnoeic responses to NaCl overload (n = 6, P < 0.05). Equi-osmolar infusions of mannitol did not alter the PNA and tSNA in sham-denervated rats (n = 5). Sodium chloride infusions increased carotid sinus nerve activity (n = 10, P < 0.05), whereas mannitol produced negligible changes (n = 5). The results indicate that carotid bodies are activated by acute NaCl overload, but not by mannitol. We conclude that the carotid bodies contribute to the increased sympathetic activity during acute NaCl overload, whereas the ventilatory response is mainly mediated by hypothalamic mechanisms.

Dexmedetomidine for Refractory Intracranial Hypertension.

Dexmedetomidine (DEX) is a selective α2 adrenergic agonist that is commonly used for sedation in the intensive care unit (ICU). The role of DEX for adjunctive treatment of refractory intracranial hypertension is poorly defined. The primary objective of this study was to determine the effect of DEX on the need for rescue therapy (ie, hyperosmolar boluses, extraventricular drain [EVD] drainages) for refractory intracranial hypertension. Secondary objectives included the number of intracranial pressure (ICP) excursions, bradycardic, hypotensive, and compromised cerebral perfusion pressure episodes. This retrospective cohort study evaluated patients admitted to the neurosurgical ICU from August 1, 2009, to July 29, 2015, and who received DEX for refractory intracranial hypertension. The objectives were compared between the 2 time periods-before (pre-DEX) and during therapy (DEX). Twenty-three patients with 26 episodes of refractory intracranial hypertension met the inclusion criteria. The number of hyperosmolar boluses was decreased after DEX therapy was initiated. Mannitol boluses required were statistically reduced (1 vs 0.5, P = .03); however, reduction in hypertonic boluses was not statistically significant (1.3 vs 0.9, P = .2). The mean number of EVD drainages per 24 hours was not significantly different between the time periods (15.7 vs 14.0, P = .35). The rate of ICP excursions did not differ between the 2 groups (24.3 vs 22.5, P = .62). When compared to pre-DEX data, there was no difference in the median number of hypotensive (0 vs 0), bradycardic (0 vs 0), or compromised cerebral perfusion pressure episodes (0.5 vs 1.0). Dexmedetomidine may avoid increases in the need for rescue therapy when used as an adjunctive treatment of refractory intracranial hypertension without compromising hemodynamics.

Effects of Osmotic Therapy on Pupil Reactivity: Quantification Using Pupillometry in Critically Ill Neurologic Patients.

BACKGROUND: Osmotic therapy is a critical component of medical management for cerebral edema. While up to 90% of neurointensivists report using these treatments, few quantitative clinical measurements guide optimal timing, dose, or administration frequency. Its use is frequently triggered by a qualitative assessment of neurologic deterioration and/or pupil size, and anecdotally appears to improve pupil asymmetry suggestive of uncal herniation. However, subjective pupil assessment has poor reliability, making it difficult to detect or track subtle changes. We hypothesized that osmotic therapy reproducibly improves quantitative pupil metrics. METHODS: We included patients at two centers who had recorded quantitative pupil measurements within 2 h before and after either 20% mannitol or 23.4% hypertonic saline in the neurosciences intensive care unit. The primary outcome was the Neurologic Pupil Index (NPi), a composite metric ranging from 0 to 5 in which > 3 is considered normal. Secondary outcomes included pupil size, percent change, constriction and dilation velocity, and latency. Results were analyzed with Wilcoxon signed-rank tests, Chi-square and multi-level linear regression to control for other edema-reducing interventions. RESULTS: Out of 72 admissions (403 paired pupil observations), NPi significantly differed within 2 h of osmotic therapy when controlling for other commonly used interventions in our whole cohort (ß = 0.08, p = 0.0168). The effect was most pronounced (ß = 0.57) in patients with abnormal NPi prior to intervention (p = 0.0235). CONCLUSIONS: Pupil reactivity significantly improves after osmotic therapy in a heterogenous critically ill population when controlling for various other interventions. Future work is necessary to determine dose-dependent effects and clinical utility.

Effect of experimental muscle pain on the acquisition and retention of locomotor adaptation: different motor strategies for a similar performance.

As individuals with musculoskeletal disorders often experience motor impairments, contemporary rehabilitation relies heavily on the use of motor learning principles. However, motor impairments are often associated with pain. Although there is substantial evidence that muscle pain interferes with motor control, much less is known on its impact on motor learning. The objective of the present study was to assess the effects of muscle pain on locomotor learning. Two groups (Pain and Control) of healthy participants performed a locomotor adaptation task (robotized ankle-foot orthosis perturbing ankle movements during swing) on two consecutive days. On day 1 (acquisition), hypertonic saline was injected in the tibialis anterior (TA) muscle of the Pain group participants, while Control group participants were pain free. All participants were pain free on day 2 (retention). Changes in movement errors caused by the perturbation were assessed as an indicator of motor performance. Detailed analysis of kinematic and electromyographic data provided information about motor strategies. No between-group differences were observed on motor performance measured during the acquisition and retention phases. However, Pain group participants had a residual movement error later in the swing phase and smaller early TA activation than Control group participants, thereby suggesting a reduction in the use of anticipatory motor strategies to overcome the perturbation. Muscle pain did not interfere with global motor performance during locomotor adaptation. The different motor strategies used in the presence of muscle pain may reflect a diminished ability to anticipate the consequences of a perturbation. NEW & NOTEWORTHY This study shows that experimental muscle pain does not influence global motor performance during the acquisition or next-day retention phases of locomotor learning. This contrasts with previous results obtained with cutaneous pain, emphasizing the risk of directly extrapolating from one pain modality to another. Muscle pain affected motor strategies used when performing the task, however: it reduced the ability to use increased feedforward control to overcome the force field.

Hypertonic saline regulates microglial M2 polarization via miR-200b/KLF4 in cerebral edema treatment.

BACKGROUND: Hypertonic saline (HS) has been used clinically for treatment of cerebral edema for decades. Previously we have demonstrated that HS alleviates cerebral edema via regulating water/ion channel protein and attenuating neuroinflammation. However, whether HS treatment triggers microglia polarization and its regulatory mechanism during this process is unclear. METHODS AND RESULTS: The Sprague-Dawley (SD) rats that underwent right-sided middle cerebral artery occlusion (MCAO) were used for assessment of neuroinflammation and microglia functions. Treatment of 10% HS not only significantly reduced infarct size and ipsilateral ischemic hemispheric brain water content (BWC) via attenuating ischemia-induction of TNF-α, IL-1ß, microglia M1 markers (iNOS, CD86) and miR-200b, but also increased neurotrophic factors such as IL-10 and IL-4, microglia M2 markers (Arg1, CD206) and Krüppel-like factor 4 (KLF4). Similar changes were confirmed in primary microglial cells subjected to hypoxia with/without HS in vitro. Importantly, overexpression of miR-200b was able to induce microglia M1 polarization via directly targeting KLF4. Restoring KLF4 expression abolished this effect. On the contrary, miR-200b inhibitor or KLF4 overexpression led to microglia M2 polarization. Mechanistically, KLF4 directly binds to promoter region of Agr1, thus inducing its transcription. Similar to treatment of HS, experimental overexpression of KLF4 in vivo exerted significant beneficial effects on ischemia-induced cerebral edema. However, knockdown of KLF4 abrogated the benefits of HS. CONCLUSIONS: Hypertonic saline regulates microglial M2 polarization via miR-200b/KLF4 during its treatment of cerebral edema. This study may provide new insights of HS-related therapy for cerebral edema.

The in vitro effect of nebulised hypertonic saline on human bronchial epithelium.

Inhaled hypertonic saline (HS) is an effective therapy for muco-obstructive lung diseases. However, the mechanism of action and principles pertinent to HS administration remain unclear.An in vitro system aerosolised HS to epithelial cells at rates comparable to in vivo conditions. Airway surface liquid (ASL) volume and cell height responses were measured by confocal microscopy under normal and hyperconcentrated mucus states.Aerosolised HS produced a rapid increase in ASL height and decrease in cell height. Added ASL volume was quickly reabsorbed following termination of nebulisation, although cell height did not recover within the same time frame. ASL volume responses to repeated HS administrations were blunted, but could be restored by a hypotonic saline bolus interposed between HS administrations. HS-induced ASL hydration was prolonged with hyperconcentrated mucus on the airway surface, with more modest reductions in cell volume.Aerosolised HS produced osmotically induced increases in ASL height that were limited by active sodium absorption and cell volume-induced reductions in cell water permeability. Mucus on airway surfaces prolonged the effect of HS via mucus-dependent osmotic forces, suggesting that the duration of action of HS is increased in patients with hyperconcentrated mucus.