Direct phosphorylation of GluA1 by PKC controls α‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid (AMPA) receptor (AMPAR) incorporation into active synapses during long‐term potentiation (LTP). Numerous signalling molecules that involved in AMPAR incorporation have been identified, but the specific PKC isoform(s) participating in GluA1 phosphorylation and the molecule triggering PKC activation remain largely unknown. Here, we report that the atypical isoform of PKC, PKCλ, is a critical molecule that acts downstream of phosphatidylinositol 3‐kinase (PI3K) and is essential for LTP expression. PKCλ activation is required for both GluA1 phosphorylation and increased surface expression of AMPARs during LTP. Moreover, p62 interacts with both PKCλ and GluA1 during LTP and may serve as a scaffolding protein to place PKCλ in close proximity to facilitate GluA1 phosphorylation by PKCλ. Thus, we conclude that PKCλ is the critical signalling molecule responsible for GluA1‐containing AMPAR phosphorylation and synaptic incorporation at activated synapses during LTP expression.

SUMMARY The neocortex contains glutamatergic excitatory neurons and GABAergic inhibitory interneurons. Extensive studies have revealed substantial insights into excitatory neuron production. However, our knowledge of the generation of GABAergic interneurons remains limited. Here we show that periventricular blood vessels selectively influence neocortical interneuron progenitor behavior and neurogenesis. Distinct from those in the dorsal telencephalon, radial glial progenitors (RGPs) in the ventral telencephalon responsible for producing neocortical interneurons progressively grow radial glial fibers anchored to periventricular vessels. This progenitor-vessel association is robust and actively maintained as RGPs undergo interkinetic nuclear migration and divide at the ventricular zone surface. Disruption of this association by selective removal of INTEGRIN β1 in RGPs leads to a decrease in progenitor division, a loss of PARVALBUMIN and SOMATOSTATIN-expressing interneurons, and defective synaptic inhibition in the neocortex. These results highlight a prominent interaction between RGPs and periventricular vessels important for proper production and function of neocortical interneurons.

Background and Purpose-We characterized the differential effects of glycine at different levels in the induction of postischemic long-term potentiation, as well as in the neuronal damage induced by focal ischemia. Methods-Whole-cell patch clamp recordings were obtained from rat hippocampal slice preparations. In vitro ischemia and postischemic long-term potentiation were induced by oxygen and glucose deprivation. In vivo ischemia was induced by transient middle cerebral artery occlusion. Results-In both in vitro and in vivo ischemia models, glycine at low level exerts deleterious effects in postischemic long-term potentiation and ischemic neuronal injury by modulation of the N-methyl-D-aspartate receptor coagonist site; whereas glycine at high level exerts neuroprotective effects by activation of glycine receptor and subsequent differential regulation of N-methyl-D-aspartate receptor subunit components. Conclusions-Our results provide a molecular basis for the dual roles of glycine in ischemic injury through distinct mechanisms, and they suggest that glycine receptors could be a potential target for clinical treatment of stroke. (Stroke. 2012;43:2212-2220.)Key Words: glycine Ⅲ ischemia Ⅲ electrophysiology Ⅲ middle cerebral artery occlusion Ⅲ N-methyl-D Ⅲ aspartate receptor A pathological form of plasticity, named postischemic long-term potentiation (i-LTP), was observed in glutamatereceptor-mediated neurotransmission after stroke. [1][2][3] There is evidence that i-LTP in the hippocampus may exert a detrimental effect via facilitation of excitotoxic damage. 3 This long-term enhancement in AMPA-and NMDA-receptor-mediated excitatory responses was mainly attributable to overstimulation of glutamatergic neurotransmission by excessively released extracellular glutamate in the postischemic brain. Given that overexcitation of neurons caused by stroke disturbs the balance between excitation and inhibition, restoring this balance via intervention with additional inhibition seems to be a potential and practical strategy.Ischemia elicits the rapid release of various amino acid neurotransmitters, including glycine. 4,5 Glycine is a 2-faceted bioactive molecule in the central nervous system. 6 Glycine is a strychnine-insensitive coagonist for N-methyl-D-aspartate receptors (NMDAR) and is essential for activation of NMDARs. [7][8][9] And yet, glycine is one of the main inhibitory neurotransmitters in the central nervous system. 10 Over the past decade, accumulating evidence has suggested that functional glycine receptors are present throughout all regions in the hippocampus, and they play an important role in regulating excitability and plasticity. These strychnine-sensitive glycine receptors (GlyR), if located postsynaptically, are mostly in extrasynaptic sites. 11 Because GlyRs activation induces Cl Ϫ flux and neuronal hyperpolarization, and thus suppresses neuronal excitability, we sought to determine whether and how activation of extrasynaptic GlyRs could help restore excitation-inhibition balance and activity-dependent p...

Glycine in the hippocampus can exert its effect on both synaptic NMDA receptors (NMDARs) and extrasynaptic functional glycine receptors (GlyRs) via distinct binding sites. Previous studies have reported that glycine induces long-term potentiation (LTP) through the activation of synaptic NMDARs. However, little is known about the potential role of the activated GlyRs that are largely located in extrasynaptic regions. We report here that relatively high levels of glycine achieved either by exogenous glycine application or by the elevation of endogenous glycine accumulation with an antagonist of the glycine transporter induced long-term depression (LTD) of excitatory postsynaptic currents (EPSCs) in hippocampal CA1 pyramidal neurons. The co-application of glycine with the selective GlyR antagonist strychnine changed glycine-induced LTD (Gly-LTD) to LTP. Blocking the postsynaptic GlyR-gated net chloride flux by manipulating intracellular chloride concentrations failed to elicit any changes in EPSCs. These results suggest that GlyRs are involved in Gly-LTD. Furthermore, this new form of chemical LTD was accompanied by the internalization of postsynaptic AMPA receptors and required the activation of NMDARs. Therefore, our present findings reveal an important function of GlyR activation and modulation in gating the direction of synaptic plasticity.

Cerebral cortex expansion is a hallmark of mammalian brain evolution; yet, how increased neurogenesis is coordinated with structural and functional development remains largely unclear. The T-box protein TBR2/EOMES is preferentially enriched in intermediate progenitors and supports cortical neurogenesis expansion. Here we show that TBR2 regulates fine-scale spatial and circuit organization of excitatory neurons in addition to enhancing neurogenesis in the mouse cortex. TBR2 removal leads to a significant reduction in neuronal, but not glial, output of individual radial glial progenitors as revealed by mosaic analysis with double markers. Moreover, in the absence of TBR2, clonally related excitatory neurons become more laterally dispersed and their preferential synapse development is impaired. Interestingly, TBR2 directly regulates the expression of Protocadherin 19 (PCDH19), and simultaneous PCDH19 expression rescues neurogenesis and neuronal organization defects caused by TBR2 removal. Together, these results suggest that TBR2 coordinates neurogenesis expansion and precise microcircuit assembly via PCDH19 in the mammalian cortex.

PKMζ has been proposed to be essential for maintenance of long-term potentiation (LTP) and long-term memory (LTM). However, recent data from PKMζ-knockout mice has called this role into question. Instead, the other atypical isoform, protein kinase C iota/lambda (PKCι/λ), has emerged as a potential alternative player. Therefore, the nature of the "memory molecule" maintaining learned information remains uncertain. Here, we report knockdown (KD) of PKCι/λ and PKMζ in the dorsal hippocampus and find deficits in early expression and late maintenance, respectively, during both LTP and hippocampus-dependent LTM. Sequential increases in the active form of PKCι/λ and PKMζ are detected during LTP or fear conditioning. Importantly, PKMζ, but not PKCι/λ, KD disrupts previously established LTM. Thus, PKCι/λ and PKMζ have distinct functions in LTP and memory, with PKMζ playing a specific role in memory maintenance. This relaying pattern may represent a precise molecular mechanism by which atypical PKCs regulate the different stages of memory.

Regulation of neuronal NMDA receptor (NMDAR) is critical in synaptic transmission and plasticity. Protein kinase C (PKC) promotes NMDAR trafficking to the cell surface via interaction with NMDAR-associated proteins (NAPs). Little is known, however, about the NAPs that are critical to PKC-induced NMDAR trafficking. Here, we showed that calcium/calmodulin-dependent protein kinase II (CaMKII) could be a NAP that mediates the potentiation of NMDAR trafficking by PKC. PKC activation promoted the level of autophosphorylated CaMKII and increased association with NMDARs, accompanied by functional NMDAR insertion, at postsynaptic sites. This potentiation, along with PKC-induced long term potentiation of the AMPA receptor-mediated response, was abolished by CaMKII antagonist or by disturbing the interaction between CaMKII and NR2A or NR2B. Further mutual occlusion experiments demonstrated that PKC and CaMKII share a common signaling pathway in the potentiation of NMDAR trafficking and longterm potentiation (LTP) induction. Our results revealed that PKC promotes NMDA receptor trafficking and induces synaptic plasticity through indirectly triggering CaMKII autophosphorylation and subsequent increased association with NMDARs.The NMDA receptor (NMDAR) 3 plays a critical role in neural development, learning and memory, sensory perception, and synaptic plasticity (1, 2). Therefore, regulation of neuronal NMDARs is of great importance to synaptic transmission. PKC increases the NMDA channel opening rate and delivers new NMDARs to the plasma membrane through regulated exocytosis (3, 4). This potentiation of NMDAR trafficking is not due to phosphorylation of the NMDAR by PKC (5), suggesting that PKC indirectly exerts its effect through interaction with NMDAR-associated signaling and/or trafficking protein(s) (3, 4). Very recently, two elegant studies revealed that a SNARE protein, either SNAP-23 or SNAP-25, is such an NMDAR-associated trafficking protein that is critical to the promotion of NMDAR trafficking by PKC (6, 7). The PKC-dependent activation of the Src family of non-receptor protein kinases enhances NMDAR function mainly through increasing NMDAR channel gating (3, 8 -11). It is still uncertain, however, whether an NMDAR-associated signaling protein that interacts with PKC displays a similar enhancing effect in NMDAR trafficking.Numerous studies performed as early as the late 1980s support the idea of functional and positive cross-talk between CaMKII and PKC (12-15). One speculation based on these findings is that PKC and CaMKII act in series and share, at least partially, a common pathway by convergence in regulating certain common substrates. Interestingly, NMDAR could be such a common molecular target. Both PKC and CaMKII have phosphorylation sites on NMDAR. CaMKII is associated with both NR2A and NR2B NMDAR subunits (16 -18). PKC potentiates NMDAR gating and in turn enhances Ca 2ϩ influx and intracellular Ca 2ϩ /camodulin, which could trigger CaMKII autophosphorylation and increase association with NR2A and NR2B sub...

Alzheimer’s disease (AD) is the most common cause of dementia in the elderly. At the early stages of AD development, the soluble β-amyloid (Aβ) induces synaptic dysfunction, perturbs the excitation/inhibition balance of neural circuitries, and in turn alters the normal neural network activity leading to cognitive decline, but the underlying mechanisms are not well established. Here by using whole-cell recordings in acute mouse brain slices, we found that 50 nM Aβ induces hyperexcitability of excitatory pyramidal cells in the cingulate cortex, one of the most vulnerable areas in AD, via depressing inhibitory synaptic transmission. Furthermore, by simultaneously recording multiple cells, we discovered that the inhibitory innervation of pyramidal cells from fast-spiking (FS) interneurons instead of non-FS interneurons is dramatically disrupted by Aβ, and perturbation of the presynaptic inhibitory neurotransmitter gamma-aminobutyric acid (GABA) release underlies this inhibitory input disruption. Finally, we identified the increased dopamine action on dopamine D1 receptor of FS interneurons as a key pathological factor that contributes to GABAergic input perturbation and excitation/inhibition imbalance caused by Aβ. Thus, we conclude that the dopamine receptor 1-dependent disruption of FS GABAergic inhibitory input plays a critical role in Aβ-induced excitation/inhibition imbalance in anterior cingulate cortex.