Leeyup Chung

Altered mGluR5-Homer scaffolds and corticostriatal connectivity in a Shank3 complete knockout model of autism.

Human neuroimaging studies suggest that aberrant neural connectivity underlies behavioural deficits in autism spectrum disorders (ASDs), but the molecular and neural circuit mechanisms underlying ASDs remain elusive. Here, we describe a complete knockout mouse model of the autism-associated Shank3 gene, with a deletion of exons 4–22 (Δe4–22). Both mGluR5-Homer scaffolds and mGluR5-mediated signalling are selectively altered in striatal neurons. These changes are associated with perturbed function at striatal synapses, abnormal brain morphology, aberrant structural connectivity and ASD-like behaviour. In vivo recording reveals that the cortico-striatal-thalamic circuit is tonically hyperactive in mutants, but becomes hypoactive during social behaviour. Manipulation of mGluR5 activity attenuates excessive grooming and instrumental learning differentially, and rescues impaired striatal synaptic plasticity in Δe4–22−/− mice. These findings show that deficiency of Shank3 can impair mGluR5-Homer scaffolding, resulting in cortico-striatal circuit abnormalities that underlie deficits in learning and ASD-like behaviours. These data suggest causal links between genetic, molecular, and circuit mechanisms underlying the pathophysiology of ASDs.

Cholecystokinin enhances GABAergic inhibitory transmission in basolateral amygdala

The neuropeptide cholecystokinin (CCK) is anxiogenic in studies of human and animal behavior. As the amygdala formation has been implicated in generation of emotional states such as anxiety, we tested the effect of CCK on spontaneous synaptic events in the basolateral amygdala (BLA) using whole cell patch recordings in rat brain slice preparation. We found that CCK increased the frequency of spontaneous inhibitory postsynaptic potentials (sIPSPs) and currents (sIPSCs). This effect was blocked by the fast sodium channel blocker tetrodotoxin (TTX), indicating that the CCK effect is likely mediated by direct excitation of GABAergic interneurons. The CCK(B) receptor subtype antagonist, CR2945, blocked the CCK effect, while CCK4, a specific CCK(B) agonist, increased sIPSC frequency. We hypothesize that these actions may underlie the anxiogenic effects of CCK observed in behavioral studies.

Cholecystokinin Excites Interneurons in Rat Basolateral Amygdala

The amygdala formation is implicated in generation of emotional states such as anxiety and fear. Many substances that modulate neuronal activity in the amygdala alter anxiety. Cholecystokinin (CCK) is an endogenous neuropeptide that induces anxiety states in behavioral studies in both animals and humans. Using a brain slice preparation, we found that application of CCK increases inhibitory synaptic transmission measured in projection neurons of the basolateral amygdala. To determine the source of the increased inhibition we examined the direct effect of CCK on local interneurons in this region. CCK most strongly depolarized fast-spiking interneurons. Burst-firing and regular-firing interneurons were also depolarized, although to a lesser degree. However, another distinct group of interneurons was unaffected by CCK. These effects were mediated by the CCKB receptor subtype. The excitatory effect of CCK appeared to be mediated by both a nonselective cation and a K+ current.

Neuropeptides modulate compound postsynaptic potentials in basolateral amygdala.

Previous behavioral studies have shown that neuropeptides intrinsic to the amygdala formation can alter fear and anxiety states. We have previously shown that the anxiogenic neuropeptide cholecystokinin (CCK) increases inhibitory neurotransmission in basolateral amygdala. We have since observed that CCK induces synchronized rhythmic activity composed of compound postsynaptic potentials (cPSPs). We have now further characterized these cPSPs by inducing cPSPs routinely in 5 mM extracellular K(+). CCK facilitated cPSP occurrence in a dose dependent manner in brain slices from both young and mature rats. The cPSPs were attenuated by glutamate receptor antagonists (NBQX or DL-AP5) or low concentrations of GABA(A) receptor antagonists (bicuculline methiodide (BMI), SR95531, or picrotoxin), but not by the GABA(B) receptor antagonist, CGP52432. Low concentrations of tetrodotoxin (TTX, 10 nM) also attenuated the cPSPs. The Na-K-2Cl cotransporter blocker, bumetanide (1 or 10 microM) also blocked the cPSPs. The anxiogenic neuropeptide corticotropin-releasing factor (CRF) facilitated cPSPs while anxiolytic neuropeptides (neuropeptide Y (NPY) and somatostatin) attenuated cPSPs. The benzodiazepine agonist diazepam dose-dependently modulated cPSPs. Mefloquine facilitated cPSPs within 10 min of application. We hypothesize that cPSPs are generated by positive feedback between a subset of interneurons and a subset of glutamatergic projection neurons.

Cholecystokinin action on layer 6b neurons in somatosensory cortex

Layer 6b in neocortex is a distinct sublamina at the ventral portion of layer 6. Corticothalamic projections arise from 6b neurons, but few studies have examined the functional properties of these cells. In the present study we examined the actions of cholecystokinin (CCK) on layer 6b neocortical neurons using whole-cell patch clamp recording techniques. We found that the general CCK receptor agonist CCK8S (sulfated CCK octapeptide) strongly depolarized the neurons, and this action persisted in the presence of tetrodotoxin, suggesting a postsynaptic site of action. The excitatory actions of CCK8S were mimicked by the selective CCK(B) receptor agonist CCK4, and attenuated by the selective CCK(B) receptor antagonist L365260, indicating a role for CCK(B) receptors. Voltage-clamp recordings revealed that CCK8S produced a slow inward current associated with a decreased conductance with a reversal potential near the K(+) equilibrium potential. In addition, intracellular cesium also blocked the inward current, suggesting the involvement of a K(+) conductance, likely K(leak). Our data indicate that CCK, acting via CCK(B) receptors, produces a long-lasting excitation of layer 6b neocortical neurons, and this action may play a critical role in modulation of corticothalamic circuit activity.

Cellular reprogramming: a novel tool for investigating autism spectrum disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairment in reciprocal social interaction and communication, as well as the manifestation of stereotyped behaviors. Despite much effort, ASDs are not yet fully understood. Advanced genetics and genomics technologies have recently identified novel ASD genes, and approaches using genetically engineered murine models or postmortem human brain have facilitated understanding ASD. Reprogramming somatic cells into induced pluripotent stem cells (iPSCs) provides unprecedented opportunities in generating human disease models. Here, we present an overview of applying iPSCs in developing cellular models for understanding ASD. We also discuss future perspectives in the use of iPSCs as a source of cell therapy and as a screening platform for identifying small molecules with efficacy for alleviating ASD.

Therapeutic approaches for shankopathies.

Despite recent advances in understanding the molecular mechanisms of autism spectrum disorders (ASD), the current treatments for these disorders are mostly focused on behavioral and educational approaches. The considerable clinical and molecular heterogeneity of ASD present a significant challenge to the development of an effective treatment targeting underlying molecular defects. Deficiency of SHANK family genes causing ASD represent an exciting opportunity for developing molecular therapies because of strong genetic evidence for SHANK as causative genes in ASD and the availability of a panel of Shank mutant mouse models. In this article, we review the literature suggesting the potential for developing therapies based on molecular characteristics and discuss several exciting themes that are emerging from studying Shank mutant mice at the molecular level and in terms of synaptic function.

Synaptic plasticity in mouse models of autism spectrum disorders.

Analysis of synaptic plasticity together with behavioral and molecular studies have become a popular approach to model autism spectrum disorders in order to gain insight into the pathosphysiological mechanisms and to find therapeutic targets. Abnormalities of specific types of synaptic plasticity have been revealed in numerous genetically modified mice that have molecular construct validity to human autism spectrum disorders. Constrained by the feasibility of technique, the common regions analyzed in most studies are hippocampus and visual cortex. The relevance of the synaptic defects in these regions to the behavioral abnormalities of autistic like behaviors is still a subject of debate. Because the exact regions or circuits responsible for the core features of autistic behaviors in humans are still poorly understood, investigation using region-specific conditional mutant mice may help to provide the insight into the neuroanatomical basis of autism in the future.

Ginsenoside Rg3 regulates GABAA receptor channel activity: Involvement of interaction with the γ2 subunit

Ginseng exhibits beneficial effects on GABAA receptor-related anxiety and sleep disorders. However, little is known regarding the cellular and molecular bases of the ginseng action on GABAA receptor. The present study was performed to elucidate the molecular mechanism of the ginseng effect on GABAA receptor. The effect of ginsenoside Rg₃ (Rg₃), one of the active ingredients of ginseng, on γ-aminobutyric acid (GABA)A receptor channel activity was examined in Xenopus oocytes using two-electrode voltage-clamp technique. Rg₃ itself evoked an inward current in Xenopus oocytes expressing GABAA receptor subunits (α₁β₁γ₂) and the Rg₃ itself-elicited inward current was only selective to γ₂ subunit expression ratio, since Rg₃ alone had no effects in oocytes expressing other subunits such as γ₁, γ₃, δ, or ε. Co-treatment of Rg₃ with GABA enhanced GABA receptor (α₁β₁γ₂)-mediated inward currents (IGABA) but Rg₃-mediated IGABA enhancement was independent on γ₂. Rg₃ itself-elicited inward current was blocked by GABAA receptor antagonist. The present results indicate that Rg₃-induced GABAA receptor activation via the γ₂ subunit and IGABA enhancement by Rg₃ might be one of the molecular bases of ginseng effects on GABAA receptor.

Recent Progress in GABAergic Excitation from Mature Brain

The excitatory effect of γ-Aminobutyric acid (GABA) has been recognized in very young animals and in seizure generation, but not so much in animals after weaning age or in adults. The existence of this phenomenon in mature brain is still controversial. In the course of debate, creative studies have identified and characterized the phenomenon in suprachiasmatic nucleus, cortex, hippocampus and basolateral amygdala, albeit mostly in single neurons. In neural circuit activity, presumed GABAergic excitation was observed in basolateral amygdala during the study of a neuropeptide, cholecystokinin. Though the functional meaning of this phenomenon in vivo remains to be uncovered, it may be implicated in epilepsy or anxiety in the adult brain.