The active electrical properties of dendrites shape neuronal input and output and are fundamental to brain function. However, our knowledge of active dendrites has been almost entirely acquired from studies of rodents. In this work, we investigated the dendrites of layer 2 and 3 (L2/3) pyramidal neurons of the human cerebral cortex ex vivo. In these neurons, we discovered a class of calcium-mediated dendritic action potentials (dCaAPs) whose waveform and effects on neuronal output have not been previously described. In contrast to typical all-or-none action potentials, dCaAPs were graded; their amplitudes were maximal for threshold-level stimuli but dampened for stronger stimuli. These dCaAPs enabled the dendrites of individual human neocortical pyramidal neurons to classify linearly nonseparable inputs—a computation conventionally thought to require multilayered networks.

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Graduate student at the Freie Universität Berlin Olfaction in mammals involves the binding of odorants to a subset of the large number of different G protein-coupled receptors that are present in the cilia of olfactory sensory neurons (OSNs) 1 . These neurons are predominantly found in the MOE, which senses and discriminates myriad volatile compounds. In the mouse, the nose contains additional, apparently more specialized olfactory organs, such the septal organ of Masera and the VNO 2 . Sensory neurons in the VNO are morphologically distinct and use odorant receptors and signal transduction cascades that differ from those found in the MOE.In the canonical OSN signal transduction pathway, odorant binding to the receptor locally increases cytosolic cAMP through activation of the olfactory G protein G olf and adenylate cyclase type III 1,2 . cAMP then opens heteromeric cyclic nucleotide-gated (CNG) cation channels 3 . The resulting influx of Na + and Ca 2+ depolarizes the plasma membrane and raises the cytosolic Ca 2+ concentration ([Ca 2+ ] i ), thereby activating Ca 2+ -activated Cl -channels 1,4-10 . All these components of the signal transduction cascade are localized to sensory cilia, which are embedded in the mucus covering the MOE. These cilia provide a large interaction surface for odorants, and the cilia's small diameters facilitate large local increases in cytosolic cAMP and [Ca 2+ ].There has been broad consensus that Ca 2+ -activated Cl -channels powerfully amplify olfactory signal transduction 1,4-10 . These channels are thought to mediate an outward flow of Cl -, which generates a depolarizing current that, in rodents, is five-to tenfold larger than currents through CNG channels 8,11,12 . A prerequisite for Cl -efflux 3 is an inside-out electrochemical Cl --gradient. It is believed that cytosolic chloride concentration of OSNs is raised by the Na + K + 2Cl -co-transporter Nkcc1 9,10,13 and that [Cl -] is low in the mucus surrounding the cilia 14,15 . However, mucosal ion concentrations are difficult to measure in vivo, and Nkcc1 knockout mice display attenuated electro-olfactograms (EOGs) 11,16 , but normal olfactory sensitivity 17 .To investigate the role of Ca 2+ -activated Cl -channels in olfaction, we disrupted Ano2 in mice. Ano2 is a member of the Anoctamin (Tmem16) gene family, which encodes several Ca 2+ -activated Cl -channels [18][19][20] . Agreeing with recent results 13,21-23 , our knockout-controlled immunolabeling showed Ano2 expression in cilia of OSNs in the MOE, in microvilli of VNO sensory neurons and in synapses of photoreceptors. Additionally, we found Ano2 in the olfactory bulb. Ano1 expression overlapped with Ano2 in the VNO and the retina, but not in the MOE. Patch-clamp analysis showed that Ca 2+ -activated Cl -currents were undetectable in Ano2 -/-OSNs.Unexpectedly, however, EOGs of Ano2 -/-mice were reduced by only up to ~40%, and Ano2 -/-mice were able to smell normally. Our work calls for a revision of the current view that Ca 2+ -activated Cl -channels have a crucial role...

Members of the CLC protein family of ClMutating the gating glutamate of ClC-6 yielded an ohmic anion conductance that was increased by additionally mutating the "anion-coordinating" tyrosine. Additionally changing the chloride-coordinating serine 157 to proline increased the NO 3 ؊ conductance of this mutant. Taken together, these data demonstrate for the first time that ClC-6 is a Cl ؊ /H ؉ antiporter.The CLC gene family, originally thought to encode exclusively chloride channels, is now recognized to comprise both channels and anion-proton antiporters (1). Following the discovery that the bacterial EcClC-1 (one of the two CLC isoforms in Escherichia coli) functions as a 2ClϪ /H ϩ exchanger (2), mammalian endosomal ClC-4 and -5 were shown to mediate anion/proton exchange as well (3, 4). These endosomal electrogenic exchangers may facilitate endosomal acidification by shunting currents of the V-type ATPase and have a role in luminal Cl Ϫ accumulation (5, 6). The plant AtClC-a functions physiologically as an NO 3 Ϫ /H ϩ exchanger that uses the pH gradient over the vacuole membrane to accumulate the nutrient NO 3 Ϫ into that organelle (7). With the notable exception of renal ClC-K channels (8), both channel-and exchanger-type CLC proteins share a glutamate in the permeation pathway that is involved in gating (in CLC channels) and in coupling chloride to proton countertransport (in CLC exchangers), respectively. Mutations in this gating glutamate profoundly affect CLC channel gating and uncouple anion from proton countertransport in CLC exchangers. All confirmed CLC antiporters display another glutamate (the proton glutamate) at their cytoplasmic surface that probably transfers protons to the central exchange site given by the gating glutamate (9 -11). Because this proton glutamate is not found in confirmed CLC channels, its presence might indicate that the respective CLC is an exchanger.Based on this hypothesis, ClC-3-7 should function as Cl Ϫ /H ϩ exchangers, but this remains to be shown for ClC-3, -6, and -7 by heterologous expression. Contrasting with ClC-4 and -5, which reach the plasma membrane to a degree that allows for detailed biophysical studies, currents mediated by ClC-3 were too low to determine whether it transports protons (3, 12). On the other hand, ClC-3 is ϳ80% identical in sequence to the established exchangers ClC-4 and ClC-5, with which it shares current properties that are similarly affected by mutations in the gating glutamate (12, 13). Hence, it is very likely that ClC-3 also functions as an exchanger. So far, it has been impossible to functionally express ClC-6 and ClC-7, which form a distinct branch of the CLC family (14), in the plasma membrane. This may be a consequence of their efficient targeting to late endosomes and lysosomes, respectively. ClC-7 is the only member of the CLC family significantly expressed on lysosomes (15-17). Lysosomes display 2Cl Ϫ /H ϩ exchange activity (18,19), which was strongly reduced by small interfering RNA in culture (18) and in ClC-7 knock-out (KO) 2 mic...

Clinical and experimental evidence suggest that the subiculum plays an important role in the maintenance of temporal lobe seizures. Using the pilocarpine-model of temporal lobe epilepsy (TLE), the present study examines the vulnerability of GABAergic subicular interneurons to recurrent seizures and determines its functional implications. In the subiculum of pilocarpine-treated animals, the density of glutamic acid decarboxylase (GAD) mRNA-positive cells was reduced in all layers. Our data indicate a substantial loss of parvalbumin-immunoreactive neurons in the pyramidal cell and molecular layer whereas calretinin-immunoreactive cells were predominantly reduced in the molecular layer. Though the subiculum of pilocarpine-treated rats showed an increased intensity of GAD65 immunoreactivity, the density of GAD65 containing synaptic terminals in the pyramidal cell layer was decreased indicating an increase in the GAD65 intensity of surviving synaptic terminals. We observed a decrease in evoked inhibitory post-synaptic currents that mediate dendritic inhibition as well as a decline in the frequency of miniature inhibitory post-synaptic currents (mIPSCs) that are restricted to the perisomatic region. The decrease in mIPSC frequency (-30%) matched with the reduced number of perisomatic GAD-positive terminals (-28%) suggesting a decrease of pre-synaptic GABAergic input onto pyramidal cells in epileptic animals. Though cell loss in the subiculum has not been considered as a pathogenic factor in human and experimental TLE, our data suggest that the vulnerability of subicular GABAergic interneurons causes an input-specific disturbance of the subicular inhibitory system.

Objective: Maternal autoantibodies are a risk factor for impaired brain development in offspring. Antibodies (ABs) against the NR1 (GluN1) subunit of the N-methyl-D-aspartate receptor (NMDAR) are among the most frequently diagnosed anti-neuronal surface ABs, yet little is known about effects on fetal development during pregnancy. Methods: We established a murine model of in utero exposure to human recombinant NR1 and isotype-matched nonreactive control ABs. Pregnant C57BL/6J mice were intraperitoneally injected on embryonic days 13 and 17 each with 240μg of human monoclonal ABs. Offspring were investigated for acute and chronic effects on NMDAR function, brain development, and behavior. Results: Transferred NR1 ABs enriched in the fetus and bound to synaptic structures in the fetal brain. Density of NMDAR was considerably reduced (up to −49.2%) and electrophysiological properties were altered, reflected by decreased amplitudes of spontaneous excitatory postsynaptic currents in young neonates (−34.4%). NR1 AB-treated animals displayed increased early postnatal mortality (+27.2%), impaired neurodevelopmental reflexes, altered blood pH, and reduced bodyweight. During adolescence and adulthood, animals showed hyperactivity (+27.8% median activity over 14 days), lower anxiety, and impaired sensorimotor gating. NR1 ABs caused long-lasting neuropathological effects also in aged mice (10 months), such as reduced volumes of cerebellum, midbrain, and brainstem. Interpretation: The data collectively support a model in which asymptomatic mothers can harbor low-level pathogenic human NR1 ABs that are diaplacentally transferred, causing neurotoxic effects on neonatal development. Thus, ABmediated network changes may represent a potentially treatable neurodevelopmental congenital brain disorder contributing to lifelong neuropsychiatric morbidity in affected children.

KCNQ2 (Kv7.2) and KCNQ3 (Kv7.3) K þ channels dampen neuronal excitability and their functional impairment may lead to epilepsy. Less is known about KCNQ5 (Kv7.5), which also displays wide expression in the brain. Here we show an unexpected role of KCNQ5 in dampening synaptic inhibition and shaping network synchronization in the hippocampus. KCNQ5 localizes to the postsynaptic site of inhibitory synapses on pyramidal cells and in interneurons. Kcnq5 dn/dn mice lacking functional KCNQ5 channels display increased excitability of different classes of interneurons, enhanced phasic and tonic inhibition, and decreased electrical shunting of inhibitory postsynaptic currents. In vivo, loss of KCNQ5 function leads to reduced fast (gamma and ripple) hippocampal oscillations, altered gamma-rhythmic discharge of pyramidal cells and impaired spatial representations. Our work demonstrates that KCNQ5 controls excitability and function of hippocampal networks through modulation of synaptic inhibition.

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