Bong-Kiun Kaang

NMDA receptor-dependent long-term potentiation comprises a family of temporally overlapping forms of synaptic plasticity that are induced by different patterns of stimulation.

N-methyl-d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) is extensively studied since it is believed to use the same molecular mechanisms that are required for many forms of learning and memory. Unfortunately, many controversies exist, not least the seemingly simple issue concerning the locus of expression of LTP. Here, we review our recent work and some of the extensive literature on this topic and present new data that collectively suggest that LTP can be explained, during its first few hours, by the coexistence of at least three mechanistically distinct processes that are all triggered by the synaptic activation of NMDARs.

Optimization of AAV expression cassettes to improve packaging capacity and transgene expression in neurons

Adeno-associated virus (AAV) vectors can deliver transgenes to diverse cell types and are therefore useful for basic research and gene therapy. Although AAV has many advantages over other viral vectors, its relatively small packaging capacity limits its use for delivering large genes. The available transgene size is further limited by the existence of additional elements in the expression cassette without which the gene expression level becomes much lower. By using alternative combinations of shorter elements, we generated a series of AAV expression cassettes and systematically evaluated their expression efficiency in neurons to maximize the transgene size available within the AAV packaging capacity while not compromising the transgene expression. We found that the newly developed smaller expression cassette shows comparable expression efficiency with an efficient vector generally used for strong gene expression. This new expression cassette will allow us to package larger transgenes without compromising expression efficiency.

Shank mutant mice as an animal model of autism

In this review, we focus on the role of the Shank family of proteins in autism. In recent years, autism research has been flourishing. With genetic, molecular, imaging and electrophysiological studies being supported by behavioural studies using animal models, there is real hope that we may soon understand the fundamental pathology of autism. There is also genuine potential to develop a molecular-level pharmacological treatment that may be able to deal with the most severe symptoms of autism, and clinical trials are already underway. The Shank family of proteins has been strongly implicated as a contributing factor in autism in certain individuals and sits at the core of the alleged autistic pathway. Here, we analyse studies that relate Shank to autism and discuss what light this sheds on the possible causes of autism.

Synaptic Protein Degradation in Memory Reorganization

The ubiquitin-proteasome system (UPS) is a ubiquitous, major pathway of protein degradation that is involved in most cellular processes by regulating the abundance of certain proteins. Accumulating evidence indicates a role for the UPS in specific functions of neurons. In this chapter, we first introduce the role of the UPS in neuronal function and the mechanism of UPS regulation following synaptic activity. Then, we focus on the recently revealed, distinct role of the UPS in the destabilization of a reactivated memory. Finally, we discuss the physiological role of this destabilization process. The reactivated memory may undergo modification from the initial memory depending on the context in which the memory is reactivated, which we will term memory reorganization. We will introduce the role of the protein degradation-dependent destabilization process for memory reorganization and suggest a hypothetical model combining the recent findings.

Neuronal activity-dependent regulation of MicroRNAs.

MicroRNAs are non-coding short (~23 nucleotides) RNAs that mediate post-transcriptional regulation through sequence-specific gene silencing. The role of miRNAs in neuronal development, synapse formation and synaptic plasticity has been highlighted. However, the role of neuronal activity on miRNA regulation has been less focused. Neuronal activity-dependent regulation of miRNA may fine-tune gene expression in response to synaptic plasticity and memory formation. Here, we provide an overview of miRNA regulation by neuronal activity including high-throughput screening studies. We also discuss the possible molecular mechanisms of activity-dependent induction and turnover of miRNAs.

Differential distribution of PI3K isoforms in spinal cord and dorsal root ganglia: Potential roles in acute inflammatory pain

Summary Only spinal PI3K&bgr; antagonism reduced allodynia and spinal AMPA trafficking, while intraplantar PI3K&ggr; antagonism was the most effective anti‐allodynic. This reflected each isoforms unique distribution. ABSTRACT PI3‐kinases (PI3Ks) participate in nociception within spinal cord, dorsal root ganglion (DRG), and peripheral nerves. To extend our knowledge, we immunohistochemically stained for each of the 4 class I PI3K isoforms along with several cell‐specific markers within the lumbar spinal cord, DRG, and sciatic nerve of naive rats. Intrathecal and intraplantar isoform specific antagonists were given as pretreatments before intraplantar carrageenan; pain behavior was then assessed over time. The &agr;‐isoform was localized to central terminals of primary afferent fibers in spinal cord laminae IIi to IV as well as to neurons in ventral horn and DRG. The PI3K&bgr; isoform was the only class I isoform seen in dorsal horn neurons; it was also observed in DRG, Schwann cells, and axonal paranodes. The &dgr;‐isoform was found in spinal cord white matter oligodendrocytes and radial astrocytes, and the &ggr;‐isoform was seen in a subpopulation of IB4‐positive DRG neurons. No isoform co‐localized with microglial markers or satellite cells in naive tissue. Only the PI3K&bgr; antagonist, but none of the other antagonists, had anti‐allodynic effects when administered intrathecally; coincident with reduced pain behavior, this agent completely blocked paw carrageenan‐induced dorsal horn 2‐amino‐3‐(3‐hydroxy‐5‐methyl‐isoxazol‐4‐yl) propanoic acid (AMPA) receptor trafficking to plasma membranes. Intraplantar administration of the &ggr;‐antagonist prominently reduced pain behavior. These data suggest that each isoform displays specificity with regard to neuronal type as well as to specific tissues. Furthermore, each PI3K isoform has a unique role in development of nociception and tissue inflammation.

Effects of PI3Kγ overexpression in the hippocampus on synaptic plasticity and spatial learning

Previous studies have shown that a family of phosphoinositide 3-kinases (PI3Ks) plays pivotal roles in the brain; in particular, we previously reported that knockout of the β isoform of PI3K (PI3Kβ) in mice impaired synaptic plasticity and reduced behavioral flexibility. To further examine the role of PI3Kβ in synaptic plasticity and hippocampus-dependent behavioral tasks we overexpressed p110β, the catalytic subunit of PI3Kβ, in the hippocampal CA1 region. We found that the overexpression of p110β impairs NMDA receptor-dependent long-term depression (LTD) and hippocampus-dependent spatial learning in the Morris water maze (MWM) task. In contrast, long-term potentiation (LTP) and contextual fear memory were not affected by p110β overexpression. These results, together with the previous knockout study, suggest that a critical level of PI3Kβ in the hippocampus is required for successful induction of LTD and normal learning.

N-Type Voltage Gated Calcium Channels Mediate Excitatory Synaptic Transmission in the Anterior Cingulate Cortex of Adult Mice

Voltage gated calcium channels (VGCCs) are well known for its importance in synaptic transmission in the peripheral and central nervous system. However, the role of different VGCCs in the anterior cingulate cortex (ACC) has not been studied. Here, we use a multi-electrode array recording system (MED64) to study the contribution of different types of calcium channels in glutamatergic excitatory synaptic transmission in the ACC. We found that only the N-type calcium channel blocker ω-conotoxin-GVIA (ω-Ctx-GVIA) produced a great inhibition of basal synaptic transmission, especially in the superficial layer. Other calcium channel blockers that act on L-, P/Q-, R-, and T-type had no effect. We also tested the effects of several neuromodulators with or without ω-Ctx-GVIA. We found that N-type VGCC contributed partially to (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid- and (R)-Baclofen-induced synaptic inhibition. By contrast, the inhibitory effects of 2-Chloroadenosine and carbamoylcholine chloride did not differ with or without ω-Ctx-GVIA, indicating that they may act through other mechanisms. Our results provide strong evidence that N-type VGCCs mediate fast synaptic transmission in the ACC.

Analysis of phosphoinositide-binding properties and subcellular localization of GFP-fusion proteins.

Specific protein-phosphoinositide (PI) interactions are known to play a key role in the targeting of proteins to specific cellular membranes. Investigation of these interactions would be greatly facilitated if GFP-fusion proteins expressed in mammalian cells and used for their subcellular localization could also be employed for in vitro lipid binding. In this study, we found that lysates of cells overexpressing GFP-fusion proteins could be used for in vitro protein-PI binding assays. We applied this approach to examine the PI-binding properties of Aplysia Sec7 protein (ApSec7) and its isoform ApSec7(VPKIS), in which a VPKIS sequence is inserted into the PH domain of ApSec7. EGFP-ApSec7 but not EGFP-ApSec7(VPKIS) did specifically bind to PI(3,4,5)P3 in an in vitro lipid-coated bead assay. Overexpression of EGFP-ApSec7 but not EGFP-ApSec7(VPKIS) did induce neurite outgrowth in Aplysia sensory neurons. Structure modeling analysis revealed that the inserted VPKIS caused misfolding around the PI(3,4,5)P3-binding pocket of ApSec7 and disturbed the binding of PI(3,4,5)P3 to the pleckstrin homology (PH) domain. Our data indicate that plasma membrane localization of EGFP-ApSec7 via the interaction between its PH domain and PI(3,4,5)P3 might play a key role in neurite outgrowth in Aplysia.

Development of a Touch-Screen-Based Paradigm for Assessing Working Memory in the Mouse

Assessing the working memory of the rodent by using a touch-screen system has several advantages (e.g., allowing highly accurate data collection and flexibility in memory task design). However, there is currently no available testing paradigm utilizing touch-screen systems that can assess working memory in the mouse. In this study, we developed a touch-screen testing paradigm in which mice were trained to choose a location that is matched to a sample location after a time delay. Consistent with previous studies, this study showed that mice could not only learn the rule in the delayed matched to position (DMTP), but also could retain a transitory memory of the sample position during delay. This indicates that a touch-screen system can provide a DMTP testing platform to assess working memory in the mouse.