Emotional Stress Induces Structural Plasticity in Bergmann Glial Cells via an AC5-CPEB3-GluA1 Pathway.

Stress alters brain function by modifying the structure and function of neurons and astrocytes. The fine processes of astrocytes are critical for the clearance of neurotransmitters during synaptic transmission. Thus, experience-dependent remodeling of glial processes is anticipated to alter the output of neural circuits. However, the molecular mechanisms that underlie glial structural plasticity are not known. Here we show that a single exposure of male and female mice to an acute stress produced a long-lasting retraction of the lateral processes of cerebellar Bergmann glial cells. These cells express the GluA1 subunit of AMPA-type glutamate receptors, and GluA1 knockdown is known to shorten the length of glial processes. We found that stress reduced the level of GluA1 protein and AMPA receptor-mediated currents in Bergmann glial cells, and these effects were absent in mice devoid of CPEB3, a protein that binds to GluA1 mRNA and regulates GluA1 protein synthesis. Administration of a ß-adrenergic receptor blocker attenuated the reduction in GluA1, and deletion of adenylate cyclase 5 prevented GluA1 suppression. Therefore, stress suppresses GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway, and reduces the length of astrocyte lateral processes. Our results identify a novel mechanism for GluA1 subunit plasticity in non-neuronal cells and suggest a previously unappreciated role for AMPA receptors in stress-induced astrocytic remodeling.SIGNIFICANCE STATEMENT Astrocytes play important roles in synaptic transmission by extending fine processes around synapses. In this study, we showed that a single exposure to an acute stress triggered a retraction of lateral/fine processes in mouse cerebellar astrocytes. These astrocytes express GluA1, a glutamate receptor subunit known to lengthen astrocyte processes. We showed that astrocytic structural changes are associated with a reduction of GluA1 protein levels. This requires activation of ß-adrenergic receptors and is triggered by noradrenaline released during stress. We identified adenylyl cyclase 5, an enzyme that elevates cAMP levels, as a downstream effector and found that lowering GluA1 levels depends on CPEB3 proteins that bind to GluA1 mRNA. Therefore, stress regulates GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway in astrocytes and remodels their fine processes.

WITHDRAWN. Surfactant therapy for bronchiolitis in critically ill infants.

BACKGROUND: Viral bronchiolitis is a common cause of respiratory failure in infants and children, and accounts for a significant portion of intensive care unit (ICU) admissions during seasonal epidemics. Currently there is no evidence to support the use of anything but supportive care for this disease. Surfactant is a potentially promising therapy; alterations in its composition have been described in bronchiolitis, and it may play a role in the host immunity for this disease. OBJECTIVES: To assess the efficacy of exogenous surfactant for the treatment of bronchiolitis in mechanically ventilated infants and children. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2006, issue 1) which contains the Acute Respiratory Infections Group's Specialized Register; MEDLINE (1966 to Week 1, February 2006); and EMBASE (1990 to September 2005). SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing surfactant with placebo or surfactant with no surfactant in mechanically ventilated infants and children with viral bronchiolitis. DATA COLLECTION AND ANALYSIS: Two authors independently extracted data and assessed trial quality. Unpublished data were requested from trial authors when necessary. MAIN RESULTS: Three trials containing a total of 79 patients met the inclusion criteria. No mortality or adverse effects associated with surfactant administration were reported in any of these trials. In the three trials, use of surfactant was associated with a decrease in duration of mechanical ventilation by 2.6 days (95% confidence interval (CI) -5.34 to 0.18 days; P value 0.07) and a decrease in ICU length of stay by 3.3 days (95% CI -6.38 to -0.23 days; P value 0.04). In two studies with 59 patients, in which duration of mechanical ventilation in the control groups was more comparable, surfactant was associated with a decrease in ventilator days by 1.21 days (95% CI 0.75 to 1.67 days) and a decrease in ICU stay by 1.81 days (95% CI 1.19 days to 2.42 days). Individually the studies reported some short term benefit of surfactant on pulmonary mechanics and gas exchange. AUTHORS' CONCLUSIONS: Available data on surfactant were not sufficient to provide reliable estimates of its effects in mechanically ventilated infants and children with bronchiolitis. Future studies should be adequately powered and will need to address unresolved questions regarding which surfactant preparation may be best suited for the treatment of bronchiolitis, the appropriate dose and administration interval, and how the choice of ventilator strategy may modify its effects.

Efficacy of interventions for bronchiolitis in critically ill infants: a systematic review and meta-analysis.

BACKGROUND: Viral bronchiolitis is the leading cause of respiratory failure among infants in the United States. Currently, the mainstay of treatment is supportive care. The effectiveness of treatments used for mechanically ventilated infants with bronchiolitis is unclear. OBJECTIVE: To evaluate the strength of the evidence supporting the use of currently available treatments for critically ill infants with bronchiolitis. DATA SOURCE: We searched PubMed, citations of relevant articles, personal files, and conference proceedings, and we contacted experts in the field. STUDY SELECTION: Randomized, controlled trials evaluating any therapy for bronchiolitis that included children in an intensive care unit. DATA EXTRACTION: Two reviewers independently extracted data and assessed methodologic quality. DATA SYNTHESIS: A total of 2,319 citations were screened, and 16 randomized, controlled trials were included. There were three trials of surfactant, three of ribavirin, three of immune globulin, three of systemic corticosteroids, and one each of vitamin A, interferon, erythropoietin, and heliox. A meta-analysis of the three surfactant studies showed a strong trend toward a decrease in duration of mechanical ventilation of 2.58 days (95% confidence interval, -5.34 to 0.18 days; p =.07) and a significant decrease of 3.3 intensive care unit days (95% confidence interval, -6.38 to -0.23 days; p =.04). A meta-analysis of the three systemic corticosteroid studies showed no overall effect on duration of mechanical ventilation when all three trials were combined (-0.62 day; 95% confidence interval, -2.78 to 1.53 days; p =.57). We identified one published meta-analysis of three ribavirin studies showing a significant decrease in ventilator days with ribavirin (-1.2 days; 95% confidence interval, -0.2 to -3.4 days; p =.2). CONCLUSIONS: Currently, there are no clearly effective interventions available to improve the outcome of critically ill infants with bronchiolitis. Surfactant seems to be a promising intervention, and corticosteroids or ribavirin may also be beneficial.

Arginine and nitric oxide metabolism in critically ill septic pediatric patients.

OBJECTIVE: To investigate whole body, arginine metabolism and nitric oxide synthesis rates in septic, critically ill pediatric patients. DESIGN: Prospective study. SETTING: Pediatric intensive care unit at a general hospital. PATIENTS: Ten consecutive septic patients age 6-16 yrs. INTERVENTIONS: Septic patients received an 8-hr primed, constant intravenous tracer infusion of L-[guanidino-15N2]arginine, L-[1-13C]leucine, and [13C]urea. A 24-hr urine collection was obtained for determination of [15N]nitrate enrichment (15NO3(-)) and urinary nitrogen. The next day they received an infusion of L-[5-13C]arginine and L-[5-13C-ureido, 5,5, 2H2]citrulline. Blood samples were obtained for determination of plasma isotopic enrichment of the tracers given and of derived [15N]citrulline (nitric oxide synthesis), L-[13C-guanidino 5,5, 2H2]arginine (M+3 arg) (arginine synthesis), and [15N]urea (urea formation). Data are compared with historic controls from studies in healthy young adults. MEASUREMENTS AND MAIN RESULTS: Plasma arginine fluxes were 67 +/- 21 and 72 +/- 17 micromol x kg(-1) x hr(-1), respectively, for the [15N2 guanidino] and the [13C] arginine labels, which were not different from reported adult values. The rates of arginine oxidation were 22.9 +/- 10.8 micromol x kg(-1) x hr(-1) and were higher than arginine synthesis rates of 9.6 +/- 4.2 micromol x kg(-1) x hr(-1) (p <.01); therefore, these patients were in a negative arginine balance. The rates of nitric oxide synthesis as estimated by the [15N]citrulline method were 1.58 +/- 0.69 micromol x kg(-1) x hr(-1) for septic patients and higher (p <.05) than values of 0.96 +/- 0.1 micromol x kg(-1) x hr(-1) in healthy adults. Septic patients were in a negative protein (leucine) balance of about -1.00 +/- 0.40 g x kg(-1) x day(-1). CONCLUSIONS: Homeostasis of plasma arginine in septic patients was impaired compared with reported adult values. The rates of arginine oxidation were increased whereas net arginine synthesis was unchanged, leading to a negative arginine balance. The rates of nitric oxide synthesis and the fraction of plasma arginine used for nitric oxide and urea formation were increased. These findings suggest that under condition of sepsis, arginine becomes essential in critically ill children.