Seungmoon Jung

Intracellular gold nanoparticles increase neuronal excitability and aggravate seizure activity in the mouse brain.

Due to their inert property, gold nanoparticles (AuNPs) have drawn considerable attention; their biological application has recently expanded to include nanomedicine and neuroscience. However, the effect of AuNPs on the bioelectrical properties of a single neuron remains unknown. Here we present the effect of AuNPs on a single neuron under physiological and pathological conditions in vitro. AuNPs were intracellularly applied to hippocampal CA1 neurons from the mouse brain. The electrophysiological property of CA1 neurons treated with 5- or 40-nm AuNPs was assessed using the whole-cell patch-clamp technique. Intracellular application of AuNPs increased both the number of action potentials (APs) and input resistance. The threshold and duration of APs and the after hyperpolarization (AHP) were decreased by the intracellular AuNPs. In addition, intracellular AuNPs elicited paroxysmal depolarizing shift-like firing patterns during sustained repetitive firings (SRF) induced by prolonged depolarization (10 sec). Furthermore, low Mg2+-induced epileptiform activity was aggravated by the intracellular AuNPs. In this study, we demonstrated that intracellular AuNPs alter the intrinsic properties of neurons toward increasing their excitability, and may have deleterious effects on neurons under pathological conditions, such as seizure. These results provide some considerable direction on application of AuNPs into central nervous system (CNS).

Subcellular Neural Probes from Single-Crystal Gold Nanowires

Size reduction of neural electrodes is essential for improving the functionality of neuroprosthetic devices, developing potent therapies for neurological and neurodegenerative diseases, and long-term brain–computer interfaces. Typical neural electrodes are micromanufactured devices with dimensions ranging from tens to hundreds of micrometers. Their further miniaturization is necessary to reduce local tissue damage and chronic immunological reactions of the brain. Here we report the neural electrode with subcellular dimensions based on single-crystalline gold nanowires (NWs) with a diameter of ∼100 nm. Unique mechanical and electrical properties of defect-free gold NWs enabled their implantation and recording of single neuron-activities in a live mouse brain despite a ∼50× reduction of the size compared to the closest analogues. Reduction of electrode dimensions enabled recording of neural activity with improved spatial resolution and differentiation of brain activity in response to different social situations for mice. The successful localization of the epileptic seizure center was also achieved using a multielectrode probe as a demonstration of the diagnostics potential of NW electrodes. This study demonstrated the realism of single-neuron recording using subcellular-sized electrodes that may be considered a pivotal point for use in diverse studies of chronic brain diseases.

Neuroprotective effect of a cell-free extract derived from human adipose stem cells in experimental stroke models.

A recent study suggested that a cell-free extract of human adipose stem cells (hASCs-E) has beneficial effects on neurological diseases by modulating the host environment. Here, we investigated the effects of hASCs-E in several experimental models of stroke in vitro (oxygen and glucose deprivation, OGD) and in vivo (transient or permanent focal cerebral ischemia and intracerebral hemorrhage, ICH). Ischemia was induced in vitro in Neuro2A cells, and the hASCs-E was applied 24h before the OGD or concurrently. Focal cerebral ischemia was induced by unilateral intraluminal thread occlusion of the middle cerebral artery (MCA) in rats for 90min or permanently, or by unilateral MCA microsurgical direct electrocoagulation in mice. The ICH model was induced with an intracerebral injection of collagenase in rats. The hASCs-E was intraperitoneally administered 1h after the stroke insults. Treatment of the hASCs-E led to a substantially high viability in the lactate dehydrogenase and WST-1 assays in the in vitro ischemic model. The cerebral ischemic and ICH model treated with hASCs-E showed decreased ischemic volume and reduced brain water content and hemorrhage volume. The ICH model treated with hASCs-E exhibited better performance on the modified limb placing test. The expression of many genes related to inflammation, immune response, and cell-death was changed substantially in the ischemic rats or neuronal cells treated with the hASCs-E. These results reveal a neuroprotective role of hASCs-E in animal models of stroke, and suggest the feasible application of stem cell-based, noninvasive therapy for treating stroke.

Early deficits in social behavior and cortical rhythms in pilocarpine-induced mouse model of temporal lobe epilepsy

Many patients with epilepsy are afflicted with psychiatric comorbidities including social dysfunction. However, although social deficits have been a major concern in epilepsy treatment, the relationship between social behavioral pathogenesis and the time course of epileptogenesis is not well defined. To address this, we investigated social behavioral alterations and cortical rhythms during two distinct periods in a mouse model of temporal lobe epilepsy (TLE): 1) a seizure-free, latent period after status epilepticus and 2) the subsequent, chronic period characterized by spontaneous recurrent seizures (SRSs). We found that severe social impairments, such as reduced sociability/social novelty preference, social interaction, social learning, and enhanced defensiveness, appeared during the latent period in mice with TLE. The social dysfunctions in the latent-period mice were nearly comparable to those in the chronic-period mice. We also found that both the latent- and chronic-period mice showed similar aberrant neural activities. They showed enhanced delta-band (1-4 Hz) activity and reduced alpha- (8.5-12 Hz) and gamma-band (30-55 Hz) activity during baseline behavior. Interestingly, concomitant increases in alpha- and gamma-band activities during social behavior, which were characteristic in control mice, were not observed in either latent- or chronic-period mice. Our results indicate that social deficits and abnormal neural activities appear at an earlier stage in epileptogenesis regardless of SRS occurrence. These findings may help to understand behavioral pathogenesis in patients with TLE and at-risk patients with initial insults that develop into TLE.

The immunosuppressant cyclosporin A inhibits recurrent seizures in an experimental model of temporal lobe epilepsy

The immunosuppressant, cyclosporin A (CsA), is neuroprotective following brain injury. Previous studies suggest that CsA treatment ameliorates seizure severity during status epilepticus (SE) or cell death following SE. The antiepileptic effects of CsA on recurrent seizures, however, have not been investigated. In the present study, the effects of CsA on spontaneous recurrent seizures (SRSs) in a kainate (KA)-induced mouse model of mesial temporal lobe epilepsy (TLE) were examined. Moreover, the effects of CsA on epileptiform activity in a 4-aminopyridine (4-AP)-induced in vitro seizure model were investigated. A mesial TLE mouse model was generated with a unilateral intrahippocampal injection of KA. SRSs were determined in the ipsilateral hippocampal CA1 region with a long-term video-EEG. CsA was systemically administrated to the epileptic mice exhibiting a stable occurrence of SRSs. A 1-mg/kg dose of CsA did not have any effect on SRSs in the epileptic mice. However, a 5-mg/kg dose of CsA significantly reduced the number of SRSs and decreased the severity of the seizures in the epileptic mice. Additionally, CsA treatment inhibited spontaneous burst discharges in 4-AP-treated hippocampal slices. The results of the present study demonstrate that CsA inhibits recurrent seizures in a mouse model of mesial TLE and suggest that CsA may afford both neuroprotection against SE and antiepileptic effects during the chronic period of epilepsy.

TRPM2, a Susceptibility Gene for Bipolar Disorder, Regulates Glycogen Synthase Kinase-3 Activity in the Brain

Bipolar disorder (BD) is a psychiatric disease that causes mood swings between manic and depressed states. Although genetic linkage studies have shown an association between BD and TRPM2, a Ca2+-permeable cation channel, the nature of this association is unknown. Here, we show that D543E, a mutation of Trpm2 that is frequently found in BD patients, induces loss of function. Trpm2-deficient mice exhibited BD-related behavior such as increased anxiety and decreased social responses, along with disrupted EEG functional connectivity. Moreover, the administration of amphetamine in wild-type mice evoked a notable increase in open-field activity that was reversed by the administration of lithium. However, the anti-manic action of lithium was not observed in the Trpm2−/− mice. The brains of Trpm2−/− mice showed a marked increase in phosphorylated glycogen synthase kinase-3 (GSK-3), a key element in BD-like behavior and a target of lithium. In contrast, activation of TRPM2 induced the dephosphorylation of GSK-3 via calcineurin, a Ca2+-dependent phosphatase. Importantly, the overexpression of the D543E mutant failed to induce the dephosphorylation of GSK-3. Therefore, we conclude that the genetic dysfunction of Trpm2 causes uncontrolled phosphorylation of GSK-3, which may lead to the pathology of BD. Our findings explain the long-sought etiologic mechanism underlying the genetic link between Trpm2 mutation and BD. SIGNIFICANCE STATEMENT Bipolar disorder (BD) is a mental disorder that causes changes in mood and the etiology is still unknown. TRPM2 is highly associated with BD; however, its involvement in the etiology of BD is still unknown. We show here that TRPM2 plays a central role in causing the pathology of BD. We found that D543E, a mutation of Trpm2 frequently found in BD patients, induces the loss of function. Trpm2-deficient mice exhibited mood disturbances and impairments in social cognition. TRPM2 actively regulates the phosphorylation of GSK-3, which is a main target of lithium, a primary medicine for treating BD. Therefore, abnormal regulation of GSK-3 by hypoactive TRPM2 mutants accounts for the pathology of BD, providing the possible link between BD and TRPM2.

Social deficits in the AY-9944 mouse model of atypical absence epilepsy

Atypical absence epilepsy (AAE) showing slow spike-and-wave discharges (SWD) is characterized by severely abnormal cognition and neurodevelopmental or neurological outcomes in humans. However, despite the severe behavioral outcomes in AAE, the relationship between AAE and social-behavioral dysfunctions has not defined well, either experimentally or in patients with AAE. Experimentally, AAE can be produced by administering AY-9944 (AY), a cholesterol biosynthesis inhibitor. In this study, we characterized social behavior in the AY mouse model of AAE. AAE in the mouse was induced by repeated postnatal administration of AY every 6 days from postnatal day (P) 2 to P20. AY-treated mice exhibited spontaneous, recurrent, and synchronous SWD (4-5 Hz) in electroencephalographic recordings. AY-treated mice performed tasks involving sociability/social novelty preference, social interaction with a juvenile conspecific, observational fear, and resident-intruder aggression. They showed behavioral dysfunction in social interactions with a juvenile conspecific and sociability/social novelty preference tasks. They also exhibited reduced social fear learning in observational fear conditioning. Interestingly, they showed increased levels of offensive behaviors in a resident-intruder task. However, AY-treated mice displayed normal levels of anxiety in light/dark transition and the elevated plus maze tasks, and showed slightly increased locomotor activity in an open-field task. These results demonstrate social dysfunction in the AY-induced AAE model. Our study of social behavior can also provide valuable information about Lennox-Gastaut syndrome, in which AAE is a component. Thus, our findings may help to understand behavioral pathogenesis or characteristics of patients with AAE.

Protein arginine methylation facilitates KCNQ channel-PIP2 interaction leading to seizure suppression

KCNQ channels are critical determinants of neuronal excitability, thus emerging as a novel target of anti-epileptic drugs. To date, the mechanisms of KCNQ channel modulation have been mostly characterized to be inhibitory via Gq-coupled receptors, Ca2+/CaM, and protein kinase C. Here we demonstrate that methylation of KCNQ by protein arginine methyltransferase 1 (Prmt1) positively regulates KCNQ channel activity, thereby preventing neuronal hyperexcitability. Prmt1+/- mice exhibit epileptic seizures. Methylation of KCNQ2 channels at 4 arginine residues by Prmt1 enhances PIP2 binding, and Prmt1 depletion lowers PIP2 affinity of KCNQ2 channels and thereby the channel activities. Consistently, exogenous PIP2 addition to Prmt1+/- neurons restores KCNQ currents and neuronal excitability to the WT level. Collectively, we propose that Prmt1-dependent facilitation of KCNQ-PIP2 interaction underlies the positive regulation of KCNQ activity by arginine methylation, which may serve as a key target for prevention of neuronal hyperexcitability and seizures. DOI: http://dx.doi.org/10.7554/eLife.17159.001

Altered behavior and neural activity in conspecific cagemates co-housed with mouse models of brain disorders

The psychosocial environment is one of the major contributors of social stress. Family members or caregivers who consistently communicate with individuals with brain disorders are considered at risk for physical and mental health deterioration, possibly leading to mental disorders. However, the underlying neural mechanisms of this phenomenon remain poorly understood. To address this, we developed a social stress paradigm in which a mouse model of epilepsy or depression was housed long-term (>4weeks) with normal conspecifics. We characterized the behavioral phenotypes and electrophysiologically investigated the neural activity of conspecific cagemate mice. The cagemates exhibited deficits in behavioral tasks assessing anxiety, locomotion, learning/memory, and depression-like behavior. Furthermore, they showed severe social impairment in social behavioral tasks involving social interaction or aggression. Strikingly, behavioral dysfunction remained in the cagemates 4weeks following co-housing cessation with the mouse models. In an electrophysiological study, the cagemates showed an increased number of spikes in medial prefrontal cortex (mPFC) neurons. Our results demonstrate that conspecifics co-housed with mouse models of brain disorders develop chronic behavioral dysfunctions, and suggest a possible association between abnormal mPFC neural activity and their behavioral pathogenesis. These findings contribute to the understanding of the psychosocial and psychiatric symptoms frequently present in families or caregivers of patients with brain disorders.

Altered intrinsic functional connectivity in the latent period of epileptogenesis in a temporal lobe epilepsy model

&NA; The latent period, a seizure‐free phase, is the duration between brain injury and the onset of spontaneous recurrent seizures (SRSs) during epileptogenesis. The latent period is thought to involve several progressive pathophysiological events that lead to the evolution of the chronic epilepsy phase. Hence, it is vital to investigate the changes in the latent period during epileptogenesis in order to better understand temporal lobe epilepsy (TLE), and to achieve early diagnosis and appropriate management of the condition. Accordingly, recent studies with patients with TLE using resting‐state functional magnetic resonance imaging (rs‐fMRI) have reported that alterations of resting‐state functional connectivity (rsFC) during the chronic period are associated with some clinical manifestations, including learning and memory impairments, emotional instability, and social behavior deficits, in addition to repetitive seizure episodes. In contrast, the changes in the intrinsic rsFC during epileptogenesis, particularly during the latent period, remain unclear. In this study, we investigated the alterations in intrinsic rsFC during the latent and chronic periods in a pilocarpine‐induced TLE mouse model using intrinsic optical signal imaging (IOSI). This technique can monitor the changes in the local hemoglobin concentration according to neuronal activity and can help investigate large‐scale brain intrinsic networks. After seeding on the anatomical regions of interest (ROIs) and calculating the correlation coefficients between each ROI, we established and compared functional correlation matrices and functional connectivity maps during the latent and chronic periods of epilepsy. We found a decrease in the interhemispheric rsFC at the frontal and temporal regions during both the latent and chronic periods. Furthermore, a significant decrease in the interhemispheric rsFC was observed in the somatosensory area during the chronic period. Changes in network configurations during epileptogenesis were examined by graph theoretical network analysis. Interestingly, increase in the power of low frequency oscillations was observed during the latent period. These results suggest that, even if there are no apparent ictal seizure events during the latent period, there are ongoing changes in the rsFC in the epileptic brain. Furthermore, these results suggest that the pathophysiology of epilepsy may be related to widespread altered intrinsic functional connectivity. These findings can help enhance our understanding of epileptogenesis, and accordingly, changes in intrinsic functional connectivity can serve as an early diagnosis.