Woosuk Chung

Enhanced NMDA Receptor-Mediated Synaptic Transmission, Enhanced Long-Term Potentiation, and Impaired Learning and Memory in Mice Lacking IRSp53

IRSp53 is an adaptor protein that acts downstream of Rac and Cdc42 small GTPases and is implicated in the regulation of membrane deformation and actin filament assembly. In neurons, IRSp53 is an abundant postsynaptic protein and regulates actin-rich dendritic spines; however, its in vivo functions have not been explored. We characterized transgenic mice deficient of IRSp53 expression. Unexpectedly, IRSp53−/− neurons do not show significant changes in the density and ultrastructural morphologies of dendritic spines. Instead, IRSp53−/− neurons exhibit reduced AMPA/NMDA ratio of excitatory synaptic transmission and a selective increase in NMDA but not AMPA receptor-mediated transmission. IRSp53−/− hippocampal slices show a markedly enhanced long-term potentiation (LTP) with no changes in long-term depression. LTP-inducing theta burst stimulation enhances NMDA receptor-mediated transmission. Spatial learning and novel object recognition are impaired in IRSp53−/− mice. These results suggest that IRSp53 is involved in the regulation of NMDA receptor-mediated excitatory synaptic transmission, LTP, and learning and memory behaviors.

Social deficits in IRSp53 mutant mice improved by NMDAR and mGluR5 suppression

Social deficits are observed in diverse psychiatric disorders, including autism spectrum disorders and schizophrenia. We found that mice lacking the excitatory synaptic signaling scaffold IRSp53 (also known as BAIAP2) showed impaired social interaction and communication. Treatment of IRSp53−/− mice, which display enhanced NMDA receptor (NMDAR) function in the hippocampus, with memantine, an NMDAR antagonist, or MPEP, a metabotropic glutamate receptor 5 antagonist that indirectly inhibits NMDAR function, normalized social interaction. This social rescue was accompanied by normalization of NMDAR function and plasticity in the hippocampus and neuronal firing in the medial prefrontal cortex. These results, together with the reduced NMDAR function implicated in social impairments, suggest that deviation of NMDAR function in either direction leads to social deficits and that correcting the deviation has beneficial effects.

Selected SALM (Synaptic Adhesion-Like Molecule) Family Proteins Regulate Synapse Formation

Synaptic cell adhesion molecules regulate various steps of synapse formation. Despite the great diversity of neuronal synapses, relatively few adhesion molecules with synaptogenic activity have been identified. Synaptic adhesion-like molecules (SALMs) are members of a family of cell adhesion molecules known to regulate neurite outgrowth and synapse maturation; however, the role of SALMs in synapse formation remains unknown. We found that expression of the SALM family proteins SALM3 and SALM5 in nonneural and neural cells induces both excitatory and inhibitory presynaptic differentiation in contacting axons. SALM3 and SALM5 proteins are enriched in synaptic fractions, and form strong (SALM3) or weak (SALM5) complexes with postsynaptic density-95 (PSD-95), an abundant postsynaptic scaffolding protein at excitatory synapses. Aggregation of SALM3, but not SALM5, on dendritic surfaces induces clustering of PSD-95. Knockdown of SALM5 reduces the number and function of excitatory and inhibitory synapses. These results suggest that selected SALM family proteins regulate synapse formation, and that SALM3 and SALM5 may promote synapse formation through distinct mechanisms.

The Effects of Lifestyle Modification on Symptoms and Quality of Life in Patients with Irritable Bowel Syndrome: A Prospective Observational Study

Background/Aims Although notably common, irritable bowel syndrome (IBS) has no specific cure. Lifestyle modification may be as important as medication; however, few studies support the effectiveness of such modifications. We performed this observational study of IBS patients to explore further the role of lifestyle changes in treatment. Methods This study included 831 men who enlisted in 2010 as armed surgeon cadets and 85 women who concurrently entered the Armed Forces Nursing Academy. Of these 916 participants, 89 were diagnosed with IBS using the Rome III criteria. Subjective changes in bowel habits, quality of life, pain, stress, stool frequency and stool consistency were surveyed before and after 9 weeks of army training. We evaluated the lifestyle risk factors that impacted improvement in IBS symptoms by comparing those who responded to lifestyle modification (the responding group) to those who did not respond (the nonresponding group). Results More than half of the participants (63%) reported that their symptoms improved after training. The quality of life and levels of pain and stress significantly improved after military training. Initial stress levels before military training and smoking history affected IBS symptom improvement. Conclusions Lifestyle modification may be effective in managing IBS patients.

Sevoflurane exposure during the neonatal period induces long‐term memory impairment but not autism‐like behaviors

To examine whether neonatal exposure to sevoflurane induces autism‐like behaviors in mice.

Mice lacking the synaptic adhesion molecule Neph2/Kirrel3 display moderate hyperactivity and defective novel object preference

Synaptic adhesion molecules regulate diverse aspects of neuronal synapse development, including synapse specificity, formation, and maturation. Neph2, also known as Kirrel3, is an immunoglobulin superfamily adhesion molecule implicated in intellectual disability, neurocognitive delay associated with Jacobsen syndrome, and autism spectrum disorders. We here report mice lacking Neph2 (Neph2-/- mice) display moderate hyperactivity in a familiar, but not novel, environment and defective novel object recognition with normal performances in Morris water maze spatial learning and memory, contextual fear conditioning and extinction, and pattern separation tests. These mice also show normal levels of anxiety-like behaviors, social interaction, and repetitive behaviors. At the synapse level, Neph2-/- dentate gyrus granule cells exhibit unaltered dendritic spine density and spontaneous excitatory synaptic transmission. These results suggest that Neph2 is important for normal locomotor activity and object recognition memory.

Activation of the HMGB1-RAGE axis upregulates TH expression in dopaminergic neurons via JNK phosphorylation

The derangement of tyrosine hydroxylase (TH) activity reduces dopamine synthesis and is implicated in the pathogenesis of Parkinsons disease. However, the extracellular modulator and intracellular regulatory mechanisms of TH have yet to be identified. Recently, high-mobility group box 1 (HMGB1) was reported to be actively secreted from glial cells and is regarded as a mediator of dopaminergic neuronal loss. However, the mechanism for how HMGB1 affects TH expression, particularly through the receptor for advanced glycation endproducts (RAGE), has not yet been investigated. We found that recombinant HMGB1 (rHMGB1) upregulates TH mRNA expression via simultaneous activation of JNK phosphorylation, and this induction of TH expression is blocked by inhibitors of RAGE and JNK. To investigate how TH expression levels change through the HMGB1-RAGE axis as a result of MPP+ toxicity, we co-treated SN4741 dopaminergic cells with MPP+ and rHMGB1. rHMGB1 blocked the reduction of TH mRNA following MPP+ treatment without altering cell survival rates. Our results suggest that HMGB1 upregulates TH expression to maintain dopaminergic neuronal function via activating RAGE, which is dependent on JNK phosphorylation.

Single and multiple sevoflurane exposures during pregnancy and offspring behavior in mice

The second trimester is a period of neurogenesis and neuronal migration, which can be affected by exposure to anesthetics. Studies also suggest that multiple exposures may have a greater impact on neurodevelopment.

Sevoflurane Exposure during the Critical Period Affects Synaptic Transmission and Mitochondrial Respiration but Not Long-term Behavior in Mice

Background: Anesthesia during the synaptogenic period induces dendritic spine formation, which may affect neurodevelopment. The authors, therefore, evaluated whether changes in synaptic transmission after dendritic spine formation induced by sevoflurane were associated with long-term behavioral changes. The effects of sevoflurane on mitochondrial function were also assessed to further understand the mechanism behind spinogenesis. Methods: Postnatal day 16 to 17 mice were exposed to sevoflurane (2.5% for 2 h), and synaptic transmission was measured in the medial prefrontal cortex 6 h or 5 days later. The expression of postsynaptic proteins and mitochondrial function were measured after anesthesia. Long-term behavioral changes were assessed in adult mice. Results: Sevoflurane increased the expression of excitatory postsynaptic proteins in male and female mice (n = 3 to 5 per group). Sevoflurane exposure in male mice transiently increased miniature excitatory postsynaptic current frequency (control: 8.53 ± 2.87; sevoflurane: 11.09 ± 2.58) but decreased miniature inhibitory postsynaptic current frequency (control: 10.18 ± 4.66; sevoflurane: 6.88 ± 2.15). Unexpectedly, sevoflurane increased miniature inhibitory postsynaptic current frequency (control: 1.81 ± 1.11; sevoflurane: 3.56 ± 1.74) in female mice (neurons, n = 10 to 21 per group). Sevoflurane also increased mitochondrial respiration in male mice (n = 5 to 8 per group). However, such changes from anesthesia during the critical period did not induce long-term behavioral consequences. Values are presented as mean ± SD. Conclusions: Sevoflurane exposure during the critical period induces mitochondrial hyperactivity and transient imbalance of excitatory/inhibitory synaptic transmission, without long-lasting behavioral consequences. Further studies are needed to confirm sexual differences and to define the role of mitochondrial activity during anesthesia-induced spine formation.

Down-regulation of RalBP1 expression reduces seizure threshold and synaptic inhibition in mice

Idiopathic epilepsy is characterized by seizures without a clear etiology and is believed to have a strong genetic component but exhibits a complex inheritance pattern. Genetic factors seem to confer a low seizure threshold to susceptible individuals and thereby enhance epileptogenesis. However, the identity of susceptibility genes and the mechanisms regulating seizure threshold are still poorly understood. Here, we describe that reduced expression of RalBP1, a downstream effector of the small GTPases RalA and RalB, lowers the seizure threshold in mice. The intraperitoneal injection of the chemoconvulsant pentylenetetrazol induced more severe seizures in RalBP1 hypomorphic mice than in their wild-type littermates. The reduction of RalBP1 in the brain has no effect on neuronal excitability, but does decrease the inhibitory synaptic transmission onto CA1 pyramidal neurons. This impaired synaptic inhibition was associated with the loss of GABAergic interneurons in the CA1 subfield of the hippocampus. The present study identifies RalBP1 as a gene regulating the seizure threshold in mice and provides direct evidence for the role of RalBP1 in synaptic inhibition in vivo.