Divergent opioid-mediated suppression of inhibition between hippocampus and neocortex across species and development

Opioid receptors within the CNS regulate pain sensation and mood and are key targets for drugs of abuse. Within the adult rodent hippocampus (HPC), μ-opioid receptor agonists suppress inhibitory parvalbumin-expressing interneurons (PV-INs), thus disinhibiting the circuit. However, it is uncertain if this disinhibitory motif is conserved in other cortical regions, species, or across development. We observed that PV-IN mediated inhibition is robustly suppressed by opioids in HPC but not neocortex in mice and nonhuman primates, with spontaneous inhibitory tone in resected human tissue also following a consistent dichotomy. This hippocampal disinhibitory motif was established in early development when immature PV-INs and opioids already influence primordial network rhythmogenesis. Acute opioid-mediated modulation was partially occluded with morphine pretreatment, with implications for the effects of opioids on hippocampal network activity during circuit maturation as well as learning and memory. Together, these findings demonstrate that PV-INs exhibit a divergence in opioid sensitivity across brain regions that is remarkably conserved across evolution and highlights the underappreciated role of opioids acting through immature PV-INs in shaping hippocampal development.

Evolutionary conservation of hippocampal mossy fiber synapse properties

Various specialized structural/functional properties are considered essential for contextual memory encoding by hippocampal mossy fiber (MF) synapses. Although investigated to exquisite detail in model organisms, synapses, including MFs, have undergone minimal functional interrogation in humans. To determine the translational relevance of rodent findings, we evaluated MF properties within human tissue resected to treat epilepsy. Human MFs exhibit remarkably similar hallmark features to rodents, including AMPA receptor-dominated synapses with small contributions from NMDA and kainate receptors, large dynamic range with strong frequency facilitation, NMDA receptor-independent presynaptic long-term potentiation, and strong cyclic AMP (cAMP) sensitivity of release. Array tomography confirmed the evolutionary conservation of MF ultrastructure. The astonishing congruence of rodent and human MF core features argues that the basic MF properties delineated in animal models remain critical to human MF function. Finally, a selective deficit in GABAergic inhibitory tone onto human MF postsynaptic targets suggests that unrestrained detonator excitatory drive contributes to epileptic circuit hyperexcitability.

A versatile viral toolkit for functional discovery in the nervous system

The ability to precisely control transgene expression is essential for basic research and clinical applications. Adeno-associated viruses (AAVs) are non-pathogenic and can be used to drive stable expression in virtually any tissue, cell type, or species, but their limited genomic payload results in a trade-off between the transgenes that can be incorporated and the complexity of the regulatory elements controlling their expression. Resolving these competing imperatives in complex experiments inevitably results in compromises. Here, we assemble an optimized viral toolkit (VTK) that addresses these limitations and allows for efficient combinatorial targeting of cell types. Moreover, their modular design explicitly enables further refinements. We achieve this in compact vectors by integrating structural improvements of AAV vectors with innovative molecular tools. We illustrate the potential of this approach through a systematic demonstration of their utility for targeting cell types and querying their biology using a wide array of genetically encoded tools.

NMDARs Drive the Expression of Neuropsychiatric Disorder Risk Genes Within GABAergic Interneuron Subtypes in the Juvenile Brain

Medial ganglionic eminence (MGE)-derived parvalbumin (PV)+, somatostatin (SST)+and Neurogliaform (NGFC)-type cortical and hippocampal interneurons, have distinct molecular, anatomical, and physiological properties. However, the molecular mechanisms regulating their maturation remain poorly understood. Here, via single-cell transcriptomics, we show that the obligate NMDA-type glutamate receptor (NMDAR) subunit gene Grin1 mediates transcriptional regulation of gene expression in specific subtypes of MGE-derived interneurons, leading to altered subtype abundances. Notably, MGE-specific early developmental Grin1 loss results in a broad downregulation of diverse transcriptional, synaptogenic and membrane excitability regulatory programs in the juvenile brain. These widespread gene expression abnormalities mirror aberrations that are typically associated with neurodevelopmental disorders. Our study hence provides a road map for the systematic examination of NMDAR signaling in interneuron subtypes, revealing potential MGE-specific genetic targets that could instruct future therapies of psychiatric disorders.

Viral manipulation of functionally distinct interneurons in mice, non-human primates and humans

Recent success in identifying gene-regulatory elements in the context of recombinant adeno-associated virus vectors has enabled cell-type-restricted gene expression. However, within the cerebral cortex these tools are largely limited to broad classes of neurons. To overcome this limitation, we developed a strategy that led to the identification of multiple new enhancers to target functionally distinct neuronal subtypes. By investigating the regulatory landscape of the disease gene Scn1a, we discovered enhancers selective for parvalbumin (PV) and vasoactive intestinal peptide-expressing interneurons. Demonstrating the functional utility of these elements, we show that the PV-specific enhancer allowed for the selective targeting and manipulation of these neurons across vertebrate species, including humans. Finally, we demonstrate that our selection method is generalizable and characterizes additional PV-specific enhancers with exquisite specificity within distinct brain regions. Altogether, these viral tools can be used for cell-type-specific circuit manipulation and hold considerable promise for use in therapeutic interventions.

Activity-dependent tuning of intrinsic excitability in mouse and human neurogliaform cells

The ability to modulate the efficacy of synaptic communication between neurons constitutes an essential property critical for normal brain function. Animal models have proved invaluable in revealing a wealth of diverse cellular mechanisms underlying varied plasticity modes. However, to what extent these processes are mirrored in humans is largely uncharted thus questioning their relevance in human circuit function. In this study, we focus on neurogliaform cells, that possess specialized physiological features enabling them to impart a widespread inhibitory influence on neural activity. We demonstrate that this prominent neuronal subtype, embedded in both mouse and human neural circuits, undergo remarkably similar activity-dependent modulation manifesting as epochs of enhanced intrinsic excitability. In principle, these evolutionary conserved plasticity routes likely tune the extent of neurogliaform cell mediated inhibition thus constituting canonical circuit mechanisms underlying human cognitive processing and behavior.

Paradoxical network excitation by glutamate release from VGluT3+ GABAergic interneurons

In violation of Dale's principle several neuronal subtypes utilize more than one classical neurotransmitter. Molecular identification of vesicular glutamate transporter three and cholecystokinin expressing cortical interneurons (CCK+VGluT3+INTs) has prompted speculation of GABA/glutamate corelease from these cells for almost two decades despite a lack of direct evidence. We unequivocally demonstrate CCK+VGluT3+INT-mediated GABA/glutamate cotransmission onto principal cells in adult mice using paired recording and optogenetic approaches. Although under normal conditions, GABAergic inhibition dominates CCK+VGluT3+INT signaling, glutamatergic signaling becomes predominant when glutamate decarboxylase (GAD) function is compromised. CCK+VGluT3+INTs exhibit surprising anatomical diversity comprising subsets of all known dendrite targeting CCK+ interneurons in addition to the expected basket cells, and their extensive circuit innervation profoundly dampens circuit excitability under normal conditions. However, in contexts where the glutamatergic phenotype of CCK+VGluT3+INTs is amplified, they promote paradoxical network hyperexcitability which may be relevant to disorders involving GAD dysfunction such as schizophrenia or vitamin B6 deficiency.

Neto Auxiliary Subunits Regulate Interneuron Somatodendritic and Presynaptic Kainate Receptors to Control Network Inhibition

Although Netos are considered auxiliary subunits critical for kainate receptor (KAR) function, direct evidence for their regulation of native KARs is limited. Because Neto KAR regulation is GluK subunit/Neto isoform specific, such regulation must be determined in cell-type-specific contexts. We demonstrate Neto1/2 expression in somatostatin (SOM)-, cholecystokinin/cannabinoid receptor 1 (CCK/CB1)-, and parvalbumin (PV)-containing interneurons. KAR-mediated excitation of these interneurons is contingent upon Neto1 because kainate yields comparable effects in Neto2 knockouts and wild-types but fails to excite interneurons or recruit inhibition in Neto1 knockouts. In contrast, presynaptic KARs in CCK/CB1 interneurons are dually regulated by both Neto1 and Neto2. Neto association promotes tonic presynaptic KAR activation, dampening CCK/CB1 interneuron output, and loss of this brake in Neto mutants profoundly increases CCK/CB1 interneuron-mediated inhibition. Our results confirm that Neto1 regulates endogenous somatodendritic KARs in diverse interneurons and demonstrate Neto regulation of presynaptic KARs in mature inhibitory presynaptic terminals.

Hippocampal GABAergic Inhibitory Interneurons

In the hippocampus GABAergic local circuit inhibitory interneurons represent only ~10-15% of the total neuronal population; however, their remarkable anatomical and physiological diversity allows them to regulate virtually all aspects of cellular and circuit function. Here we provide an overview of the current state of the field of interneuron research, focusing largely on the hippocampus. We discuss recent advances related to the various cell types, including their development and maturation, expression of subtype-specific voltage- and ligand-gated channels, and their roles in network oscillations. We also discuss recent technological advances and approaches that have permitted high-resolution, subtype-specific examination of their roles in numerous neural circuit disorders and the emerging therapeutic strategies to ameliorate such pathophysiological conditions. The ultimate goal of this review is not only to provide a touchstone for the current state of the field, but to help pave the way for future research by highlighting where gaps in our knowledge exist and how a complete appreciation of their roles will aid in future therapeutic strategies.

Pentraxins coordinate excitatory synapse maturation and circuit integration of parvalbumin interneurons

Circuit computation requires precision in the timing, extent, and synchrony of principal cell (PC) firing that is largely enforced by parvalbumin-expressing, fast-spiking interneurons (PVFSIs). To reliably coordinate network activity, PVFSIs exhibit specialized synaptic and membrane properties that promote efficient afferent recruitment such as expression of high-conductance, rapidly gating, GluA4-containing AMPA receptors (AMPARs). We found that PVFSIs upregulate GluA4 during the second postnatal week coincident with increases in the AMPAR clustering proteins NPTX2 and NPTXR. Moreover, GluA4 is dramatically reduced in NPTX2(-/-)/NPTXR(-/-) mice with consequent reductions in PVFSI AMPAR function. Early postnatal NPTX2(-/-)/NPTXR(-/-) mice exhibit delayed circuit maturation with a prolonged critical period permissive for giant depolarizing potentials. Juvenile NPTX2(-/-)/NPTXR(-/-) mice display reduced feedforward inhibition yielding a circuit deficient in rhythmogenesis and prone to epileptiform discharges. Our findings demonstrate an essential role for NPTXs in controlling network dynamics highlighting potential therapeutic targets for disorders with inhibition/excitation imbalances such as schizophrenia.

Developmental origin dictates interneuron AMPA and NMDA receptor subunit composition and plasticity

Disrupted excitatory synapse maturation in GABAergic interneurons may promote neuropsychiatric disorders such as schizophrenia. However, establishing developmental programs for nascent synapses in GABAergic cells is confounded by their sparsity, heterogeneity and late acquisition of subtype-defining characteristics. We investigated synaptic development in mouse interneurons targeting cells by lineage from medial ganglionic eminence (MGE) or caudal ganglionic eminence (CGE) progenitors. MGE-derived interneuron synapses were dominated by GluA2-lacking AMPA-type glutamate receptors (AMPARs), with little contribution from NMDA-type receptors (NMDARs) throughout development. In contrast, CGE-derived cell synapses had large NMDAR components and used GluA2-containing AMPARs. In neonates, both MGE- and CGE-derived interneurons expressed primarily GluN2B subunit-containing NMDARs, which most CGE-derived interneurons retained into adulthood. However, MGE-derived interneuron NMDARs underwent a GluN2B-to-GluN2A switch that could be triggered acutely with repetitive synaptic activity. Our findings establish ganglionic eminence-dependent rules for early synaptic integration programs of distinct interneuron cohorts, including parvalbumin- and cholecystokinin-expressing basket cells.

Competition from newborn granule cells does not drive axonal retraction of silenced old granule cells in the adult hippocampus

In the developing nervous system synaptic refinement, typified by the neuromuscular junction where supernumerary connections are eliminated by axon retraction leaving the postsynaptic target innervated by a single dominant input, critically regulates neuronal circuit formation. Whether such competition-based pruning continues in established circuits of mature animals remains unknown. This question is particularly relevant in the context of adult neurogenesis where newborn cells must integrate into preexisting circuits, and thus, potentially compete with functionally mature synapses to gain access to their postsynaptic targets. The hippocampus plays an important role in memory formation/retrieval and the dentate gyrus (DG) subfield exhibits continued neurogenesis into adulthood. Therefore, this region contains both mature granule cells (old GCs) and immature recently born GCs that are generated throughout adult life (young GCs), providing a neurogenic niche model to examine the role of competition in synaptic refinement. Recent work from an independent group in developing animals indicated that embryonically/early postnatal generated GCs placed at a competitive disadvantage by selective expression of tetanus toxin (TeTX) to prevent synaptic release rapidly retracted their axons, and that this retraction was driven by competition from newborn GCs lacking TeTX. In contrast, following 3-6 months of selective TeTX expression in old GCs of adult mice we did not observe any evidence of axon retraction. Indeed ultrastructural analyses indicated that the terminals of silenced GCs even maintained synaptic contact with their postsynaptic targets. Furthermore, we did not detect any significant differences in the electrophysiological properties between old GCs in control and TeTX conditions. Thus, our data demonstrate a remarkable stability in the face of a relatively prolonged period of altered synaptic competition between two populations of neurons within the adult brain.

Young dentate granule cells mediate pattern separation, whereas old granule cells facilitate pattern completion

Adult-born granule cells (GCs), a minor population of cells in the hippocampal dentate gyrus, are highly active during the first few weeks after functional integration into the neuronal network, distinguishing them from less active, older adult-born GCs and the major population of dentate GCs generated developmentally. To ascertain whether young and old GCs perform distinct memory functions, we created a transgenic mouse in which output of old GCs was specifically inhibited while leaving a substantial portion of young GCs intact. These mice exhibited enhanced or normal pattern separation between similar contexts, which was reduced following ablation of young GCs. Furthermore, these mutant mice exhibited deficits in rapid pattern completion. Therefore, pattern separation requires adult-born young GCs but not old GCs, and older GCs contribute to the rapid recall by pattern completion. Our data suggest that as adult-born GCs age, their function switches from pattern separation to rapid pattern completion.

NG2 cell response in the CNP-EGFP mouse after contusive spinal cord injury

NG2(+) cells in the adult CNS are a heterogeneous population. The extent to which the subpopulation of NG2(+) cells that function as oligodendrocyte progenitor cells (OPCs) respond to spinal cord injury (SCI) and recapitulate their normal developmental progression remains unclear. We used the CNP-EGFP mouse, in which oligodendrocyte lineage cells express EGFP, to study NG2(+) cells in the normal and injured spinal cord. In white matter of uninjured mice, bipolar EGFP(+)NG2(+) cells and multipolar EGFP(neg)NG2(+) cells were identified. After SCI, EGFP(+)NG2(+) cell proliferation in residual white matter peaked at 3 days post injury (DPI) rostral to the epicenter, while EGFP(neg)NG2(+) cell proliferation peaked at 7 DPI at the epicenter. The expression of transcription factors, Olig2, Sox10, and Sox17, and the basic electrophysiological membrane parameters and potassium current phenotype of the EGFP(+)NG2(+) population after injury were consistent with those of proliferative OPCs during development. EGFP(neg)NG2(+) cells did not express transcription factors involved in oligodendrogenesis. EGFP(+)CC1(+) oligodendrocytes at 6 weeks included cells that incorporated BrdU during the peak of EGFP(+)NG2(+) cell proliferation. EGFP(neg)CC1(+) oligodendrocytes were never observed. Treatment with glial growth factor 2 and fibroblast growth factor 2 enhanced oligodendrogenesis and increased the number of EGFP(neg)NG2(+) cells. Therefore, based on EGFP and transcription factor expression, spatiotemporal proliferation patterns, and response to growth factors, two populations of NG2(+) cells can be identified that react to SCI. The EGFP(+)NG2(+) cells undergo cellular and physiological changes in response to SCI that are similar to those that occur in early postnatal NG2(+) cells during developmental oligodendrogenesis.

Differential synaptic integration of interneurons in the outer and inner molecular layers of the developing dentate gyrus

The dentate gyrus (DG) undergoes continued reorganization and lamination during early postnatal development. Interneurons with anatomically identified synaptic contacts migrate from the outer to the inner regions of the molecular layer (ML) of the DG. By using the 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-enhanced green fluorescent protein transgenic mouse, we were able to target and physiologically characterize Dlx2(+) developing ML interneurons. We investigated whether synapses on migrating ML interneurons were functional and defined properties of synaptic inputs onto interneurons that were located in the outer ML (OML) or inner ML (IML). Consistent with ongoing maturation, IML interneurons displayed lower input resistances and more hyperpolarized resting membrane potentials than OML interneurons. Both OML and IML interneurons received a direct excitatory monosynaptic input from the entorhinal cortex via the perforant paths, but this input was differentially sensitive to activation of presynaptic group II and III metabotropic glutamate receptors. Furthermore, only IML interneurons also received significant synaptic input from the CA3/hilar region, especially under conditions of experimentally induced disinhibition. These changes are attributed to a significant reorganization of dendritic fields. GABA(A) receptor-mediated innervation of OML and IML interneurons also displayed significant differences in miniature IPSC amplitude, frequency, and decay kinetics. Finally, cell-attached recordings indicated that GABA(A) receptor activation was depolarizing in OML interneurons but predominantly shunting in IML interneurons. Our data provide evidence that developing ML interneurons receive functional glutamatergic and GABAergic inputs and undergo significant changes in synaptic integration during migration from the OML to the IML.

Downregulation of platelet-derived growth factor-alpha receptor-mediated tyrosine kinase activity as a cellular mechanism for K+-channel regulation during oligodendrocyte development in situ

Oligodendrocyte maturation has been defined based on expression of developmentally regulated antigens. However, transitions at early stages of the lineage have not been functionally characterized fully in situ. Combining 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-promoter driven enhanced green fluorescent protein expression and whole-cell capacitance measurements permitted a reliable distinction between subcortical white matter NG2+ oligodendrocyte progenitors (OPs) and O4+ preoligodendrocytes (pre-OLs) in situ. We focused on K+ channels because their expression has been associated previously with the proliferation and differentiation potential of OPs. Using whole-cell patch clamp, we observed a downregulation of the delayed outward-rectifying current (IKDR) between the NG2+ and O4+ stages but no significant changes in transient K+-channel current (IKA) amplitude. Tyrosine kinase inhibition in NG2+ cells reduced IKDR amplitude with no effect on IKA, which mimicked the endogenous changes observed between OPs and pre-OLs. Tyrosine kinase inhibition also reduced the proliferative capacity of NG2+ OPs in slice cultures. Conversely, acute platelet-derived growth factor receptor-alpha (PDGFR-alpha) activation caused an increase of IKDR in NG2+ but not in O4+ cells. Consistent with this finding, PDGFR-alpha immunoreactivity was confined to NG2+ cells with undetectable levels in O4+ cells, suggesting that PDGFR-alpha signaling is absent in pre-OLs in situ. Importantly, the PDGF-induced increase of IKDR in NG2+ cells was prevented by tyrosine kinase inhibition. Together, these data indicate that PDGFR-alpha and tyrosine kinase activity act via a common pathway that influences functional expression of K+ channels and proliferative capacity of OPs in situ.

Shaker-type potassium channel subunits differentially control oligodendrocyte progenitor proliferation

Oligodendrocyte precursor (OP) cells are exposed to multiple extrinsic signals that control their proliferation and differentiation. Previous cell proliferation studies and electrophysiological analysis in cultured cells and in brain slices have suggested that outward potassium channels, particularly Kv1 subunits, may have a prominent role in OP cell proliferation. In the present study, we assessed to what extent overexpression of Kv1.3, Kv1.4, Kv1.5, and Kv1.6 can affect OP cell proliferation and differentiation in culture. We observed that overexpression of Kv1.3 or Kv1.4 increased OP cell proliferation in the absence of mitogens, whereas Kv1.6 overexpression inhibited mitogen-induced OP cell cycle progression. Interestingly, Kv1.3, Kv1.4, Kv1.5, and Kv1.6 overexpression did not interfere with the kinetics of oligodendrocyte differentiation. This study represents the first demonstration that the activity of potassium channels containing distinct Kv1 subunit proteins directly controls oligodendroglial proliferation in the presence of mitogens, as well as in growth factor-free conditions.

NG2-expressing cells in the subventricular zone are type C-like cells and contribute to interneuron generation in the postnatal hippocampus

The subventricular zone (SVZ) is a source of neural progenitors throughout brain development. The identification and purification of these progenitors and the analysis of their lineage potential are fundamental issues for future brain repair therapies. We demonstrate that early postnatal NG2-expressing (NG2+) progenitor cells located in the SVZ self-renew in vitro and display phenotypic features of transit-amplifier type C-like multipotent cells. NG2+ cells in the SVZ are highly proliferative and express the epidermal growth factor receptor, the transcription factors Dlx, Mash1, and Olig2, and the Lewis X (LeX) antigen. We show that grafted early postnatal NG2+ cells generate hippocampal GABAergic interneurons that propagate action potentials and receive functional glutamatergic synaptic inputs. Our work identifies Dlx+/Mash1+/LeX+/NG2+/GFAP-negative cells of the SVZ as a new class of postnatal multipotent progenitor cells that may represent a specific cellular reservoir for renewal of postnatal and adult inhibitory interneurons in the hippocampus.

NG2-positive cells in the mouse white and grey matter display distinct physiological properties

Cells that express the NG2 proteoglycan are the largest proliferative progenitor population in the postnatal central nervous system (CNS). Although this entire population has long been considered to be oligodendrocyte progenitors, numerous NG2(+) cells are present in the cerebral cortex, where relatively little myelination occurs, and also persist long after myelination is complete in the CNS. Several studies have alluded to the presence of distinct NG2(+) cell subtypes based on marker expression, but no experimentally derived hypotheses about the physiological role of these subtypes has been proposed. In the current study, whole-cell patch-clamp data from acutely isolated slices demonstrate that subcortical white matter and cortical NG2(+) cells display distinct membrane properties in addition to possessing differing K(+)- and Na(+)-channel expression profiles. A striking observation is that a subpopulation of cortical, but not white matter NG2(+) cells, elicit depolarization-induced spikes that are akin to immature action potentials. Our data demonstrate that a population of cortical NG2(+) cells display physiological properties that differ from their white matter counterparts.

Postnatal NG2 proteoglycan-expressing progenitor cells are intrinsically multipotent and generate functional neurons

Neurogenesis is known to persist in the adult mammalian central nervous system (CNS). The identity of the cells that generate new neurons in the postnatal CNS has become a crucial but elusive issue. Using a transgenic mouse, we show that NG2 proteoglycan-positive progenitor cells that express the 2',3'-cyclic nucleotide 3'-phosphodiesterase gene display a multipotent phenotype in vitro and generate electrically excitable neurons, as well as astrocytes and oligodendrocytes. The fast kinetics and the high rate of multipotent fate of these NG2+ progenitors in vitro reflect an intrinsic property, rather than reprogramming. We demonstrate in the hippocampus in vivo that a sizeable fraction of postnatal NG2+ progenitor cells are proliferative precursors whose progeny appears to differentiate into GABAergic neurons capable of propagating action potentials and displaying functional synaptic inputs. These data show that at least a subpopulation of postnatal NG2-expressing cells are CNS multipotent precursors that may underlie adult hippocampal neurogenesis.

Expression of the green fluorescent protein in the oligodendrocyte lineage: a transgenic mouse for developmental and physiological studies

We generated a transgenic mouse expressing the enhanced green fluorescent protein (EGFP) under the control of the 2'-3'-cyclic nucleotide 3'-phosphodiesterase (CNP) promoter. EGFP(+) cells were visualized in live tissue throughout embryonic and postnatal development. Immunohistochemical analysis in brain tissue and in sciatic nerve demonstrated that EGFP expression was restricted to cells of the oligodendrocyte and Schwann cell lineages. EGFP was also strongly expressed in "adult" oligodendrocyte progenitors (OPs) and in gray matter oligodendrocytes. Fluorescence-activated cell sorting allowed high-yield purification of EGFP(+) oligodendrocyte-lineage cells from transgenic brains. Electrophysiological patch clamp recordings of EGFP(+) cells in situ demonstrated that OP cells displayed large outward tetraethylammonium (TEA)-sensitive K(+) currents and very small inward currents, whereas mature oligodendrocytes were characterized by expression of large inward currents and small outward K(+) currents. The proliferation rate of EGFP(+) cells in developing white matter decreased with the age of the animals and was strongly inhibited by TEA. Oligodendrocyte development and physiology can be studied in live tissue of CNP-EGFP transgenic mice, which represent a source of pure EGFP(+) oligodendrocyte-lineage cells throughout development.

Regulation of Kv1 subunit expression in oligodendrocyte progenitor cells and their role in G1/S phase progression of the cell cycle

Proliferative oligodendrocyte progenitor cells (OPs) express large, delayed outward-rectifying K(+) currents (I(K)), whereas nondividing immature and mature oligodendrocytes display much smaller I(K). Here, we show that up-regulation of I(K) occurs in G(1) phase of the cell cycle in purified cultured OPs and is the result of an RNA synthesis-dependent, selective increase of the K(+) channel subunit proteins Kv1.3 and Kv1.5. In oligodendrocyte cells acutely isolated from developing rat brain, a decrease of cyclin D expression is observed as these cells mature along their lineage. This is accompanied by a decrease in Kv1.3 and Kv1.5 subunit expression, suggesting a role for these subunits in the proliferative potential of OPs in situ. I(K) expressed in OPs in subventricular zone and developing white matter in acutely isolated slice preparations were selectively blocked by antagonists of Kv1.3, illustrating the functional presence of this subunit in situ. Interestingly, Kv1.3 block inhibited S-phase entry of both purified OPs in culture and in tissue slice cultures. Thus, we employ both in vitro and in situ experimental approaches to show that (i) RNA-dependent synthesis of Kv1.3 and Kv1.5 subunit proteins occurs in G(1) phase of the OP cell cycle and is responsible for the observed increase in I(K), and (ii) currents through Kv1.3-containing channels play a crucial role in G(1)/S transition of proliferating OPs.

PDZ proteins interacting with C-terminal GluR2/3 are involved in a PKC-dependent regulation of AMPA receptors at hippocampal synapses

We investigated the role of PDZ proteins (GRIP, ABP, and PICK1) interacting with the C-terminal GluR2 by infusing a ct-GluR2 peptide ("pep2-SVKI") into CA1 pyramidal neurons in hippocampal slices using whole-cell recordings. Pep2-SVKI, but not a control or PICK1 selective peptide, caused AMPAR-mediated EPSC amplitude to increase in approximately one-third of control neurons and in most neurons following the prior induction of LTD. Pep2-SVKI also blocked LTD; however, this occurred in all neurons. A PKC inhibitor prevented these effects of pep2-SVKI on synaptic transmission and LTD. We propose a model in which the maintenance of LTD involves the binding of AMPARs to PDZ proteins to prevent their reinsertion. We also present evidence that PKC regulates AMPAR reinsertion during dedepression.

Hippocampal LTD expression involves a pool of AMPARs regulated by the NSF-GluR2 interaction

We investigated whether the interaction between the N-ethyl-maleimide-sensitive fusion protein (NSF) and the AMPA receptor (AMPAR) subunit GluR2 is involved in synaptic plasticity in the CA1 region of the hippocampus. Blockade of the NSF-GluR2 interaction by a specific peptide (pep2m) introduced into neurons prevented homosynaptic, de novo long-term depression (LTD). Moreover, saturation of LTD prevented the pep2m-induced reduction in AMPAR-mediated excitatory postsynaptic currents (EPSCs). Minimal stimulation experiments indicated that both pep2m action and LTD were due to changes in quantal size and quantal content but were not associated with changes in AMPAR single-channel conductance or EPSC kinetics. These results suggest that there is a pool of AMPARs dependent on the NSF-GluR2 interaction and that LTD expression involves the removal of these receptors from synapses.

Kainate receptors: subunits, synaptic localization and function

Although it is well established that kainate receptors constitute an entirely separate group of proteins from AMPA receptors, their physiological functions remain unclear. The molecular cloning of subunits that form kainate receptors and the ability to study recombinant receptors is leading to an increased understanding of their functional properties. Furthermore, the development of kainate receptor-selective agonists and antagonists over the past few years is now allowing the physiological roles of these receptors and, in some cases, specific subunits to be investigated. As a consequence, the synaptic activation of postsynaptic kainate receptors and the presence of presynaptic kainate receptors that serve to regulate excitatory and inhibitory synaptic transmission have been described, and will be discussed in this article by Ramesh Chittajallu, Steven Braithwaite, Vernon Clarke and Jeremy Henley.

Ca2+ and synaptic plasticity

A major effort in neuroscience is directed towards understanding the roles of Ca2+ signalling in the induction of synaptic plasticity. Here, we summarize the evidence concerning Ca2+ signalling, paying particular attention to CA1 excitatory synapses, and its relationship to the induction of long-term potentiation and long-term depression. We discuss the ways in which synaptic activation can elevate Ca2+ postsynaptically and how dendritic spines may act as a Ca2+ compartment which can both isolate and integrate Ca2+ signals.

Surveillance of patients with Barrett's esophagus for dysplasia and cancer with balloon cytology

BACKGROUND & AIMS

A less costly cancer surveillance method for Barrett's esophagus is desirable. The aim of this study was to compare nonendoscopic balloon cytology with biopsy and brush cytology for detecting dysplasia and carcinoma in patients with Barrett's esophagus.

METHODS

Patients in a surveillance program underwent balloon cytology before endoscopy with biopsy and brush cytology. Results of cytology were compared with those of histology.

RESULTS

Adequate columnar epithelium was obtained in 52 of 63 (83%) patients with balloon cytology and 59 of 61 (97%) with brush cytology. Balloon cytology obtained abnormal cells in 6 of 8 patients with adenocarcinoma, 2 of 2 patients with high-grade dysplasia, and 2 of 8 patients with low-grade dysplasia. Sensitivity of balloon cytology for high-grade dysplasia or carcinoma was 80% but only 25% for low-grade dysplasia. No patients without dysplasia or carcinoma had abnormal cells. Brush cytology was abnormal in all 11 patients with high-grade dysplasia or carcinoma but only 2 of 9 patients with low-grade dysplasia (sensitivity, 22%). Two of 39 patients without dysplasia had abnormal cells (specificity, 95%). Balloon cytology cost was sixfold less than endoscopy with biopsy.

CONCLUSIONS

Balloon cytology detected 80% of patients with high-grade dysplasia or carcinoma when sampling was adequate. Brush cytology data suggest that a more abrasive balloon may improve balloon cytology sensitivity. The potential cost savings of balloon cytology compared with endoscopic cancer surveillance in Barrett's esophagus support further studies of this technique.

Regulation of glutamate release by presynaptic kainate receptors in the hippocampus

Most reported actions of kainate are mediated by AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors. Here we report that, unlike AMPA which stimulates, kainate elicits a dose-dependent decrease in L-glutamate release from rat hippocampal synaptosomes and also depresses glutamatergic synaptic transmission. Brief exposure to kainate inhibited Ca(2+)-dependent [3H]L-glutamate release by up to 80%. Inhibition was reversed by kainate antagonists but not by the AMPA-selective non-competitive antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466). A corresponding reversible kainate-evoked depression of NMDA (N-methyl-D-aspartate) receptor-mediated excitatory postsynaptic currents (e.p.s.cs) was observed when AMPA receptors were blocked by GYKI 52466. The synaptic depression was preceded by a brief period of enhanced release and a small inward current was also observed. The effects of kainate were unaffected by metabotropic glutamate (mGlu), GABAA, GABAB, glycine and adenosine receptor antagonists. These results indicate that glutamate release can be modulated directly by kainate autoreceptors.