Impact of PReOperative Midazolam on OuTcome of Elderly patients (I-PROMOTE): study protocol for a multicentre randomised controlled trial.

INTRODUCTION: Premedication of surgical patients with benzodiazepines has become questionable regarding risk-benefit ratio and lack of evidence. Though preoperative benzodiazepines might alleviate preoperative anxiety, a higher risk for adverse events is described, particularly for elderly patients (≥ 65 years). Several German hospitals already withhold benzodiazepine premedication from elderly patients, though evidence for this approach is lacking. The patient-centred outcome known as global postoperative patient satisfaction is recognised as a substantial quality indicator of anaesthesia care incorporated by the American Society of Anesthesiologists. Therefore, we aim to assess whether the postoperative patient satisfaction after premedication with placebo compared to the preoperative administration of 3.75 mg midazolam in elderly patients differs. METHODS: This study is a multicentre, randomised, placebo-controlled, double-blinded, two-arm parallel, interventional trial, conducted in nine German hospitals. In total 614 patients (≥ 65-80 years of age) undergoing elective surgery with general anaesthesia will be randomised to receive either 3.75 mg midazolam or placebo. The primary outcome (global patient satisfaction) will be assessed with the validated EVAN-G questionnaire on the first postoperative day. Secondary outcomes will be assessed until the first postoperative day and then 30 days after surgery. They comprise among other things: functional and cognitive recovery, postoperative delirium, health-related quality of life assessment, and mortality or new onset of serious cardiac or pulmonary complications, acute stroke, or acute kidney injury. Analysis will adhere to the intention-to-treat principle. The primary outcome will be analysed with the use of mixed linear models including treatment effect and study centre as factors and random effects for blocks. Exploratory adjusted and subgroup analyses of the primary and secondary outcomes with regard to gender effects, frailty, pre-operative anxiety level, patient demographics, and surgery experience will also be performed. DISCUSSION: This is, to the best of our knowledge, the first study analysing patient satisfaction after premedication with midazolam in elderly patients. In conclusion, this study will provide high-quality data for the decision-making process regarding premedication in elderly surgical patients. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03052660 . Registered on 14 February 2017. EudraCT 2016-004555-79 .

Venom composition of adult Western Diamondback Rattlesnakes (Crotalus atrox) maintained under controlled diet and environmental conditions shows only minor changes.

Many species of snakes produce venom as a chemical means of procuring potentially fractious prey. Studies have increasingly focused on venom compositional variation between and within individual snakes of the same species/subspecies, with significant differences often being observed. This variation in composition has been attributed to differences in age, season, diet, and environment, suggesting that these factors could help explain the inter- and intra-specific variation found in some snake venoms, perhaps via some type of feedback mechanism(s). To address several of these possible sources of variation, this study utilized wild-caught Western Diamondback Rattlesnakes (Crotalus atrox) from Cochise Co., AZ. Sixteen adult C. atrox were maintained in the lab on a diet of NSA mice for eight months to determine whether venom composition changed in captivity under a static diet in a stable environment. Reducing 1-D SDS-PAGE, fibrinogen degradation assays, reversed-phase HPLC, and MALDI-TOF mass spectrometry revealed only minor differences over time within individuals. Venom L-amino acid oxidase (LAAO) and phosphodiesterase activities significantly increased over the course of captivity, with no changes occurring in azocasein metalloproteinase, kallikrein-like serine proteinase (KLSP), or thrombin-like serine proteinase (TLSP) activities. Snake total length was positively correlated with TLSP activity and negatively correlated with LAAO and KLSP activity. There was typically a much higher degree of variation between individuals than within individuals for all analyses performed and measurements collected. Because the overall "fingerprint" of each snake's venom remained more/less constant, it is concluded that biologically significant changes in venom composition did not occur within individual C. atrox as a function of captivity/diet. However, this study does indicate that differences in activity levels do occur in minor venom enzyme components, but the differences observed are likely to be of minimal significance to the production of antivenom or to subsequent treatment of human envenomations.

A Small Molecule Spinogenic Compound Enhances Functional Outcome and Dendritic Spine Plasticity in a Rat Model of Traumatic Brain Injury.

The tetra (ethylene glycol) derivative of benzothiazole aniline (SPG101) has been shown to improve dendritic spine density and cognitive memory in the triple transgenic mouse model of Alzheimer disease (AD) when administered intraperitoneally. The present study was designed to investigate the therapeutic effects of SPG101 on dendritic spine density and morphology and sensorimotor and cognitive functional recovery in a rat model of traumatic brain injury (TBI) induced by controlled cortical impact (CCI). Young adult male Wistar rats with CCI were randomly divided into the following two groups (n = 7/group): (1) Vehicle, and (2) SPG101. SPG101 (30 mg/kg) dissolved in vehicle (1% dimethyl sulfoxide in phosphate buffered saline) or Vehicle were intraperitoneally administered starting at 1 h post-injury and once daily for the next 34 days. Sensorimotor deficits were assessed using a modified neurological severity score and adhesive removal and foot fault tests. Cognitive function was measured by Morris water maze, novel object recognition (NOR), and three-chamber social recognition tests. The animals were sacrificed 35 days after injury, and their brains were processed for measurement of dendritic spine density and morphology using ballistic dye labeling. Compared with the vehicle treatment, SPG101 treatment initiated 1 h post-injury significantly improved sensorimotor functional recovery (days 7-35, p < 0.0001), spatial learning (days 32-35, p < 0.0001), NOR (days 14 and 35, p < 0.0001), social recognition (days 14 and 35, p < 0.0001). Further, treatment significantly increased dendritic spine density in the injured cortex (p < 0.05), decreased heterogeneous distribution of spine lengths in the injured cortex and hippocampus (p < 0.0001), modifications that are associated with the promotion of spine maturation in these brain regions. In summary, treatment with SPG101 initiated 1 h post-injury and continued for an additional 34 days improves both sensorimotor and cognitive functional recovery, indicating that SPG101 acts as a spinogenic agent and may have potential as a novel treatment of TBI.

Improve hip fracture outcome in the elderly patient (iHOPE): a study protocol for a pragmatic, multicentre randomised controlled trial to test the efficacy of spinal versus general anaesthesia.

INTRODUCTION: Hip fracture surgery is associated with high in-hospital and 30-day mortality rates and serious adverse patient outcomes. Evidence from randomised controlled trials regarding effectiveness of spinal versus general anaesthesia on patient-centred outcomes after hip fracture surgery is sparse. METHODS AND ANALYSIS: The iHOPE study is a pragmatic national, multicentre, randomised controlled, open-label clinical trial with a two-arm parallel group design. In total, 1032 patients with hip fracture (>65 years) will be randomised in an intended 1:1 allocation ratio to receive spinal anaesthesia (n=516) or general anaesthesia (n=516). Outcome assessment will occur in a blinded manner after hospital discharge and inhospital. The primary endpoint will be assessed by telephone interview and comprises the time to the first occurring event of the binary composite outcome of all-cause mortality or new-onset serious cardiac and pulmonary complications within 30 postoperative days. In-hospital secondary endpoints, assessed via in-person interviews and medical record review, include mortality, perioperative adverse events, delirium, satisfaction, walking independently, length of hospital stay and discharge destination. Telephone interviews will be performed for long-term endpoints (all-cause mortality, independence in walking, chronic pain, ability to return home cognitive function and overall health and disability) at postoperative day 30±3, 180±45 and 365±60. ETHICS AND DISSEMINATION: iHOPE has been approved by the leading Ethics Committee of the Medical Faculty of the RWTH Aachen University on 14 March 2018 (EK 022/18). Approval from all other involved local Ethical Committees was subsequently requested and obtained. Study started in April 2018 with a total recruitment period of 24 months. iHOPE will be disseminated via presentations at national and international scientific meetings or conferences and publication in peer-reviewed international scientific journals. TRIAL REGISTRATION NUMBER: DRKS00013644; Pre-results.

Emergence times and airway reactions during general anaesthesia with remifentanil and a laryngeal mask airway: A multicentre randomised controlled trial.

BACKGROUND: Avoidance of airway complications and rapid emergence from anaesthesia are indispensable for the use of a laryngeal mask airway (LMA). Evidence from adequately powered randomised studies with a low risk of bias for the optimal anaesthetic in this context is limited. OBJECTIVE: We tested the hypothesis that when using remifentanil-based intra-operative analgesia, desflurane would be the most suitable anaesthetic: with noninferiority in the occurrence of upper airway complications and superiority in emergence times compared with sevoflurane or propofol. DESIGN: A randomised, multicentre, partially double-blinded, three-arm, parallel-group study. SETTING: Two university and two regional German hospitals, from February to October 2015. PATIENTS: A total of 352 patients (age 18 to 75 years, ASA physical status I to III, BMI less than 35 kg m and fluent in German) were enrolled in this study. All surgery was elective with a duration of 0.5 to 2 h, and general anaesthesia with a LMA was feasible. INTERVENTION: The patients were randomised to receive desflurane, sevoflurane or propofol anaesthesia. MAIN OUTCOME MEASURES: This study was powered for the primary outcome 'time to state date of birth' and the secondary outcome 'intra-operative cough'. Time to emergence from anaesthesia and the incidence of upper airway complications were assessed on the day of surgery. RESULTS: The primary outcome was analysed for 343 patients: desflurane (n=114), sevoflurane (n=111) and propofol (n=118). The desflurane group had the fastest emergence. The mean (± SD) times to state the date of birth following desflurane, sevoflurane and propofol were 8.1 ±â€Š3.6, 10.1 ±â€Š4.0 and 9.8 ±â€Š5.1 min, respectively (P < 0.01). There was no difference in upper airway complications (cough and laryngospasm) across the groups, but these complications were less frequent than in previous studies. CONCLUSION: When using a remifentanil infusion for intra-operative analgesia in association with a LMA, desflurane was associated with a significantly faster emergence and noninferiority in the incidence of intra-operative cough than either sevoflurane or Propofol. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02322502; EudraCT identifier: 2014-003810-96.

PDE4D regulates Spine Plasticity and Memory in the Retrosplenial Cortex.

The retrosplenial cortex (RSC) plays a critical role in episodic memory, but the molecular mechanisms governing plasticity in this structure are poorly understood. Diverse studies have demonstrated a role for RSC in acquisition, early consolidation and retrieval similar to the hippocampus (HC), as well as in systems consolidation similar to the anterior cingulate cortex. Here, we asked whether established molecular and structural substrates of memory consolidation in the HC also engage in RSC shortly after learning. We show striking parallels in training induced gene-activation in HC and RSC following contextual conditioning, which is blocked by systemic administration of an NMDA receptor antagonist. Long-term memory is enhanced by retrosplenial and hippocampal knockdown (KD) of the cAMP specific phosphodiesterase Pde4d. However, while training per se induces lasting spine changes in HC, this does not occur in RSC. Instead, increases in the number of mature dendritic spines are found in the RSC only if cAMP signaling is augmented by Pde4d KD, and spine changes are at least partially independent of training. This research highlights parallels and differences in spine plasticity mechanisms between HC and RSC, and provides evidence for a functional dissociation of the two.

Modeling consequences of prolonged strong unpredictable stress in zebrafish: Complex effects on behavior and physiology.

Chronic stress is the major pathogenetic factor of human anxiety and depression. Zebrafish (Danio rerio) have become a novel popular model species for neuroscience research and CNS drug discovery. The utility of zebrafish for mimicking human affective disorders is also rapidly growing. Here, we present a new zebrafish model of clinically relevant, prolonged unpredictable strong chronic stress (PUCS). The 5-week PUCS induced overt anxiety-like and motor retardation-like behaviors in adult zebrafish, also elevating whole-body cortisol and proinflammatory cytokines - interleukins IL-1ß and IL-6. PUCS also elevated whole-body levels of the anti-inflammatory cytokine IL-10 and increased the density of dendritic spines in zebrafish telencephalic neurons. Chronic treatment of fish with an antidepressant fluoxetine (0.1mg/L for 8days) normalized their behavioral and endocrine phenotypes, as well as corrected stress-elevated IL-1ß and IL-6 levels, similar to clinical and rodent data. The CNS expression of the bdnf gene, the two genes of its receptors (trkB, p75), and the gfap gene of glia biomarker, the glial fibrillary acidic protein, was unaltered in all three groups. However, PUCS elevated whole-body BDNF levels and the telencephalic dendritic spine density (which were corrected by fluoxetine), thereby somewhat differing from the effects of chronic stress in rodents. Together, these findings support zebrafish as a useful in-vivo model of chronic stress, also calling for further cross-species studies of both shared/overlapping and distinct neurobiological responses to chronic stress.

Multiple Behavior Phenotypes of the Fragile-X Syndrome Mouse Model Respond to Chronic Inhibition of Phosphodiesterase-4D (PDE4D).

Fragile-X syndrome (FXS) patients display intellectual disability and autism spectrum disorder due to silencing of the X-linked, fragile-X mental retardation-1 (FMR1) gene. Dysregulation of cAMP metabolism is a consistent finding in patients and in the mouse and fly FXS models. We therefore explored if BPN14770, a prototypic phosphodiesterase-4D negative allosteric modulator (PDE4D-NAM) in early human clinical trials, might provide therapeutic benefit in the mouse FXS model. Daily treatment of adult male fmr1 C57Bl6 knock-out mice with BPN14770 for 14 days reduced hyperarousal, improved social interaction, and improved natural behaviors such as nesting and marble burying as well as dendritic spine morphology. There was no decrement in behavioral scores in control C57Bl6 treated with BPN14770. The behavioral benefit of BPN14770 persisted two weeks after washout of the drug. Thus, BPN14770 may be useful for the treatment of fragile-X syndrome and other disorders with decreased cAMP signaling.

IGFBP2 Produces Rapid-Acting and Long-Lasting Effects in Rat Models of Posttraumatic Stress Disorder via a Novel Mechanism Associated with Structural Plasticity.

Background: Posttraumatic stress disorder is an anxiety disorder characterized by deficits in the extinction of aversive memories. Insulin-like growth factor 1 (IGF1) is the only growth factor that has shown anxiolytic and antidepressant properties in human clinical trials. In animal studies, insulin-like growth factor binding protein 2 (IGFBP2) shows both IGF1-dependent and IGF1-independent pharmacological effects, and IGFBP2 expression is upregulated by rough-and-tumble play that induces resilience to stress. Methods: IGFBP2 was evaluated in Porsolt, contextual fear conditioning, and chronic unpredictable stress models of posttraumatic stress disorder. The dependence of IGFBP2 effects on IGF1- and AMPA-receptor activation was tested using selective receptor antagonists. Dendritic spine morphology was measured in the dentate gyrus and the medial prefrontal cortex 24 hours after in vivo dosing. Results: IGFBP2 was 100 times more potent than IGF1 in the Porsolt test. Unlike IGF1, effects of IGFBP2 were not blocked by the IGF1-receptor antagonist JB1, or by the AMPA-receptor antagonist 2,3-Dioxo-6-nitro-1,2,3,4 tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX) in the Porsolt test. IGFBP2 (1 µg/kg) and IGF1 (100 µg/kg i.v.) each facilitated contextual fear extinction and consolidation. Using a chronic unpredictable stress paradigm, IGFBP2 reversed stress-induced effects in the Porsolt, novelty-induced hypophagia, sucrose preference, and ultrasonic vocalization assays. IGFBP2 also increased mature dendritic spine densities in the medial prefrontal cortex and hippocampus 24 hours postdosing. Conclusions: These data suggest that IGFBP2 has therapeutic-like effects in multiple rat models of posttraumatic stress disorder via a novel IGF1 receptor-independent mechanism. These data also suggest that the long-lasting effects of IGFBP2 may be due to facilitation of structural plasticity at the dendritic spine level. IGFBP2 and mimetics may have therapeutic potential for the treatment of posttraumatic stress disorder.

Early life diet containing prebiotics and bioactive whey protein fractions increased dendritic spine density of rat hippocampal neurons.

Early life nutrition plays an important role in brain development. Emerging research in rodents, piglets and humans suggest that prebiotics, milk fat globule membrane and lactoferrin may each play unique roles in brain development and cognitive functions. However, knowledge of their combined impact is lacking. We show here that providing weanling rats with a diet containing milk fat globule membrane, lactoferrin and a polydextrose/galactooligosaccharide prebiotic blend led to a significant increase in total dendritic spine density in hippocampal dentate gyrus neurons. Region-specific alterations in dendritic spine density and morphology could provide a mechanistic basis underlying broader cognitive benefits, but further research is required to demonstrate functional consequences of these observations.

REDD1 is essential for stress-induced synaptic loss and depressive behavior.

Major depressive disorder (MDD) affects up to 17% of the population, causing profound personal suffering and economic loss. Clinical and preclinical studies have revealed that prolonged stress and MDD are associated with neuronal atrophy of cortical and limbic brain regions, but the molecular mechanisms underlying these morphological alterations have not yet been identified. Here, we show that stress increases levels of REDD1 (regulated in development and DNA damage responses-1), an inhibitor of mTORC1 (mammalian target of rapamycin complex-1; ref. 10), in rat prefrontal cortex (PFC). This is concurrent with a decrease in phosphorylation of signaling targets of mTORC1, which is implicated in protein synthesis-dependent synaptic plasticity. We also found that REDD1 levels are increased in the postmortem PFC of human subjects with MDD relative to matched controls. Mutant mice with a deletion of the gene encoding REDD1 are resilient to the behavioral, synaptic and mTORC1 signaling deficits caused by chronic unpredictable stress, whereas viral-mediated overexpression of REDD1 in rat PFC is sufficient to cause anxiety- and depressive-like behaviors and neuronal atrophy. Taken together, these postmortem and preclinical findings identify REDD1 as a critical mediator of the atrophy of neurons and depressive behavior caused by chronic stress exposure.

A map of LTP-related synaptic changes in dorsal hippocampus following unsupervised learning.

Recent work showed that unsupervised learning of a complex environment activates synaptic proteins essential for the stabilization of long-term potentiation (LTP). The present study used automated methods to construct maps of excitatory synapses associated with high concentrations of one of these LTP-related proteins [CaMKII phosphorylated at T286/287, (pCaMKII)]. Labeling patterns across 42 sampling zones covering entire cross sections through rostral hippocampus were assessed for two groups of rats that explored a novel two-room arena for 30 min, with or without a response contingency involving mildly aversive cues. The number of pCaMKII-immunopositive (+) synapses was highly correlated between the two groups for the 21 sampling zones covering the dentate gyrus, CA3c/hilus, and apical dendrites of field CA1, but not for the remainder of the cross section. The distribution of pCaMKII+ synapses in the large uncorrelated segment differed markedly between the groups. Subtracting home-cage values removed high scores (i.e., sampling zones with a high percentage of pCaMKII+ contacts) in the negative contingency group, but not in the free-exploration animals. Three sites in the latter had values that were markedly elevated above other fields. These mapping results suggest that encoding of a form of memory that is dependent upon rostral hippocampus reliably occurs at high levels in discrete anatomical zones, and that this regionally differentiated response is blocked when animals are inhibited from freely exploring the environment by the introduction of a mildly aversive stimulus.

Integrin dynamics produce a delayed stage of long-term potentiation and memory consolidation.

Memory consolidation theory posits that newly acquired information passes through a series of stabilization steps before being firmly encoded. We report here that in rat and mouse, hippocampus cell adhesion receptors belonging to the ß1-integrin family exhibit dynamic properties in adult synapses and that these contribute importantly to a previously unidentified stage of consolidation. Quantitative dual immunofluorescence microscopy showed that induction of long-term potentiation (LTP) by theta burst stimulation (TBS) activates ß1 integrins, and integrin-signaling kinases, at spine synapses in adult hippocampal slices. Neutralizing antisera selective for ß1 integrins blocked these effects. TBS-induced integrin activation was brief (<7 min) and followed by an ∼45 min period during which the adhesion receptors did not respond to a second application of TBS. Brefeldin A, which blocks integrin trafficking to the plasma membrane, prevented the delayed recovery of integrin responses to TBS. ß1 integrin-neutralizing antisera erased LTP when applied during, but not after, the return of integrin responsivity. Similarly, infusions of anti-ß1 into rostral mouse hippocampus blocked formation of long-term, object location memory when started 20 min after learning but not 40 min later. The finding that ß1 integrin neutralization was effective in the same time window for slice and behavioral experiments strongly suggests that integrin recovery triggers a temporally discrete, previously undetected second stage of consolidation for both LTP and memory.

Identifying resource needs for sepsis care and guideline implementation in the Democratic Republic of the Congo: a cluster survey of 66 hospitals in four eastern provinces.

The ongoing conflict in the Eastern Republic of the Congo (DRC) has claimed up to 5.4 million lives by 2008. Whereas few deaths were directly due to violence, most victims died from medical conditions such as infectious diseases. This survey investigates the availability of resources required to provide adequate sepsis care in Eastern DRC. The study was conducted as a self-reported, questionnaire-based survey in four Eastern provinces of the DRC. Questionnaires were sent to a cluster of 80 urban-based hospitals in the North Kivu, South Kivu, Maniema and Orientale provinces. The questionnaire contained 74 questions on the availability of resources required to adequately treat sepsis patients as suggested by the latest Surviving Sepsis Campaign (SSC) guidelines. Sixty-six questionnaires were returned (82.5%) and analyzed. Crystalloid solutions and intravenous fluid giving sets were the only resources constantly available in all hospitals. None of the respondents reported to have constant access to piperacillin, carbapenems, fresh frozen plasma, platelets, dobutamine, activated protein C, echocardiography or equipment to measure lactate levels, invasive blood pressure, central venous pressure, cardiac output, pulmonary artery pressure or endtidal carbon dioxide. No respondent stated that a mechanical ventilator, syringe pump, fluid infuser, peritoneal dialysis or haemodialysis/hemofiltration machine was constantly available at his/her hospital. Resources required for consistent implementation of the SSC guidelines were not available in any hospital. care and implement the SSC guidelines in a cluster of hospitals in the Eastern DRC.

Concomitant arginine-vasopressin and hydrocortisone therapy in severe septic shock: association with mortality.

PURPOSE: To evaluate the association between concomitant arginine-vasopressin (AVP)/hydrocortisone therapy and mortality in severe septic shock patients. METHODS: This retrospective study included severe septic shock patients treated with supplementary AVP. To test the association between concomitant AVP/hydrocortisone use and mortality, a multivariate regression and Cox model (adjusted for admission year, initial AVP dosage and the Sepsis-related Organ Failure Assessment score before AVP) as well as a propensity score-based analysis were used. In both models, intensive care unit (ICU) and 28-day mortality served as outcome variables. RESULTS: One hundred fifty-nine patients were included. Hydrocortisone was administered to 76 (47.8%) at a median daily dosage of 300 (200-300) mg. In the multivariate logistic regression model, concomitant use of AVP and hydrocortisone was associated with a trend towards lower ICU (OR, 0.51; CI 95%, 0.24-1.08; p = 0.08) and 28-day (HR, 0.69; CI 95%, 0.43-1.08; p = 0.11) mortality. The probability of survival at day 28, as predicted by the regression model, was significantly higher in patients treated with concomitant AVP and hydrocortisone compared to those receiving AVP without hydrocortisone (p = 0.001). In a propensity score-based analysis, ICU (45 vs. 65%; OR, 0.69; CI 95% 0.38-1.26; p = 0.23) and 28-day mortality (35.5 vs. 55%; OR, 0.59; CI 95%, 0.27-1.29; p = 0.18) was not different between patients treated with (n = 40) or without concomitant hydrocortisone (n = 40). CONCLUSION: Concomitant AVP and hydrocortisone therapy may be associated with a survival benefit in septic shock. An adequately powered, randomised controlled trial appears warranted to confirm these preliminary, hypothesis-generating results.

BDNF signaling during learning is regionally differentiated within hippocampus.

Learning-induced neurotrophic signaling at synapses is widely held to be critical for neuronal viability in adult brain. A previous study provided evidence that unsupervised learning of a novel environment is accompanied by activation of the TrkB receptor for brain-derived neurotrophic factor (BDNF) in hippocampal field CA1b of adult rats. Here we report that this effect is regionally differentiated, in accord with "engram" type memory encoding. A 30 min exposure to a novel, complex environment caused a marked, NMDA receptor-dependent increase in postsynaptic densities associated with activated (phosphorylated) Trk receptors in rostral hippocampus. Increases were pronounced in field CA3a, moderate in the dentate gyrus, and absent in field CA1a. Synapses with Trk activation were significantly larger than their neighbors. Surprisingly, unsupervised learning had no effect on Trk phosphorylation in more temporal sections of hippocampus. It thus appears that commonplace forms of learning interact with regional predispositions to produce spatially differentiated effects on BDNF signaling.

Hippocampal dysfunction and cognitive impairments provoked by chronic early-life stress involve excessive activation of CRH receptors.

Chronic stress impairs learning and memory in humans and rodents and disrupts long-term potentiation (LTP) in animal models. These effects are associated with structural changes in hippocampal neurons, including reduced dendritic arborization. Unlike the generally reversible effects of chronic stress on adult rat hippocampus, we have previously found that the effects of early-life stress endure and worsen during adulthood, yet the mechanisms for these clinically important sequelae are poorly understood. Stress promotes secretion of the neuropeptide corticotropin-releasing hormone (CRH) from hippocampal interneurons, activating receptors (CRF(1)) located on pyramidal cell dendrites. Additionally, chronic CRF(1) occupancy negatively affects dendritic arborization in mouse organotypic slice cultures, similar to the pattern observed in middle-aged, early-stressed (CES) rats. Here we found that CRH expression is augmented in hippocampus of middle-aged CES rats, and then tested whether the morphological defects and poor memory performance in these animals involve excessive activation of CRF(1) receptors. Central or peripheral administration of a CRF(1) blocker following the stress period improved memory performance of CES rats in novel-object recognition tests and in the Morris water maze. Consonant with these effects, the antagonist also prevented dendritic atrophy and LTP attenuation in CA1 Schaffer collateral synapses. Together, these data suggest that persistently elevated hippocampal CRH-CRF(1) interaction contributes importantly to the structural and cognitive impairments associated with early-life stress. Reducing CRF(1) occupancy post hoc normalized hippocampal function during middle age, thus offering potential mechanism-based therapeutic interventions for children affected by chronic stress.

Myosin IIb regulates actin dynamics during synaptic plasticity and memory formation.

Reorganization of the actin cytoskeleton is essential for synaptic plasticity and memory formation. Presently, the mechanisms that trigger actin dynamics during these brain processes are poorly understood. In this study, we show that myosin II motor activity is downstream of LTP induction and is necessary for the emergence of specialized actin structures that stabilize an early phase of LTP. We also demonstrate that myosin II activity contributes importantly to an actin-dependent process that underlies memory consolidation. Pharmacological treatments that promote actin polymerization reversed the effects of a myosin II inhibitor on LTP and memory. We conclude that myosin II motors regulate plasticity by imparting mechanical forces onto the spine actin cytoskeleton in response to synaptic stimulation. These cytoskeletal forces trigger the emergence of actin structures that stabilize synaptic plasticity. Our studies provide a mechanical framework for understanding cytoskeletal dynamics associated with synaptic plasticity and memory formation.

Physiological activation of synaptic Rac>PAK (p-21 activated kinase) signaling is defective in a mouse model of fragile X syndrome.

The abnormal spine morphology found in fragile X syndrome (FXS) is suggestive of an error in the signaling cascades that organize the actin cytoskeleton. We report here that physiological activation of the small GTPase Rac1 and its effector p-21 activated kinase (PAK), two enzymes critically involved in actin management and functional synaptic plasticity, is impaired at hippocampal synapses in the Fmr1-knock-out (KO) mouse model of FXS. Theta burst afferent stimulation (TBS) caused a marked increase in the number of synapses associated with phosphorylated PAK in adult hippocampal slices from wild-type, but not Fmr1-KO, mice. Stimulation-induced activation of synaptic Rac1 was also absent in the mutants. The polymerization of spine actin that occurs immediately after theta stimulation appeared normal in mutant slices but the newly formed polymers did not properly stabilize, as evidenced by a prolonged vulnerability to a toxin (latrunculin) that disrupts dynamic actin filaments. Latrunculin also reversed long-term potentiation when applied at 10 min post-TBS, a time point at which the potentiation effect is resistant to interference in wild-type slices. We propose that a Rac>PAK signaling pathway needed for rapid stabilization of activity-induced actin filaments, and thus for normal spine morphology and lasting synaptic changes, is defective in FXS.

Correlated memory defects and hippocampal dendritic spine loss after acute stress involve corticotropin-releasing hormone signaling.

Stress affects the hippocampus, a brain region crucial for memory. In rodents, acute stress may reduce density of dendritic spines, the location of postsynaptic elements of excitatory synapses, and impair long-term potentiation and memory. Steroid stress hormones and neurotransmitters have been implicated in the underlying mechanisms, but the role of corticotropin-releasing hormone (CRH), a hypothalamic hormone also released during stress within hippocampus, has not been elucidated. In addition, the causal relationship of spine loss and memory defects after acute stress is unclear. We used transgenic mice that expressed YFP in hippocampal neurons and found that a 5-h stress resulted in profound loss of learning and memory. This deficit was associated with selective disruption of long-term potentiation and of dendritic spine integrity in commissural/associational pathways of hippocampal area CA3. The degree of memory deficit in individual mice correlated significantly with the reduced density of area CA3 apical dendritic spines in the same mice. Moreover, administration of the CRH receptor type 1 (CRFR(1)) blocker NBI 30775 directly into the brain prevented the stress-induced spine loss and restored the stress-impaired cognitive functions. We conclude that acute, hours-long stress impairs learning and memory via mechanisms that disrupt the integrity of hippocampal dendritic spines. In addition, establishing the contribution of hippocampal CRH-CRFR(1) signaling to these processes highlights the complexity of the orchestrated mechanisms by which stress impacts hippocampal structure and function.