Mirko Witte

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Dr. rer. nat. Mirko Witte
Location Göttingen
Position Postdoc
Tel. +49-(0)551/39-66876
Tel. +49-(0)551/39-7992
mirko.witte@med.uni-goettingen.de

CV

      •  Since August 2010
      Postdoctoral Fellow at the University Medical Center Göttingen of the Georg-August-University, Centre of Anatomy, Institute of Neuroanatomy in the Barrel group of Prof. Dr. J. Staiger
      • 2010 PhD Thesis
      in the Laboratory for Neurobiology at the University of Leipzig under the supervision of Prof. Dr. R. Ruebsamen, Title: "Differentiation and maturation of GABAergic and glycinergic neurotransmission in the anteroventral cochlear nucleus of gerbil"
      • 2008 - 2009
      Research assistant at the University of Leipzig, Institute of Biology II, Laboratory for Neurobiology of Prof. Dr. R. Ruebsamen
      • April 2005 - April 2010
      Member and sponsored candidate at the post graduate program "Interneuro" and at the doctorate program "Von der Signalverarbeitung zum Verhalten"
      http://www.uni-leipzig.de/~ineuro/
      http://www.uni-leipzig.de/zhs/ipp/
      • 2005 Diploma Thesis
      in the Laboratory for Neurobiology at the University of Leipzig under the supervision of Prof. Dr. R. Ruebsamen, Title: "Entwicklung inhibitorischer Einflüsse im Cochleariskern: eine Patch-clamp Studie"
      • 2003 Project thesis
      in the "Behavioral Physiology Group" at the University of Leipzig under the supervision of Prof. Dr. P. A. Stevenson and Prof. Dr. K. Schildberger, Title: "The aminergic modulation of the mandible closer-muscle in crickets (Gryllus bimaculatus)"
      • 2001 - 2005
      Advanced study of biology at the University of Leipzig (main subjects: Neurobiology, Genetic, Behavioral Physiology, Zoology, Biochemistry)
      • 1999 - 2001
       Basic study of biology at the University of Leipzig














Research Overview

    • Functional Analysis of Networks build by GABAergic Interneurons in the primary somatosensory (Barrel) Cortex

      Besides pyramidal cells, GABA-releasing interneurons are essentially involved in the information processing of the cortex and integrated in the somatosensory circuitry. Martinotti cells, a clearly identifiable type of GABAergic interneurons, play a decisive role in modulation of dendritic excitation of pyramidal cells. Therefore they exhibit an immediate effect on the neocortical outcome of the barrel cortex. Martinotti cells receive excitatory inputs from neighboring pyramidal cells and additionally pronounced behavior-dependent inhibitory inputs from an unknown source.
      In this study I want to investigate the origin of the inhibitory projections to the Martinotti cells of layer 2/3 and 5 of the barrel cortex using combined whole-cell patch-clamp recordings and local photolysis of caged-glutamate in acute brain slices. Afterwards I will use the paired patch-clamp method to record Martinotti cells and their upstream connected inhibitory interneuron to identify and characterize those interneurons. The results will contribute to a model of processing sensory information in the barrel cortex and will also improve the understanding of the GABAergic interneuron network.

      Research aims:

      (I) Patch-clamp-recordings from Martinotti cells and identification of neocortical layers, in which inhibitory neurons project to the Martinotti cells, by using caged-glutamate photolysis

      (II) Establishment of a method for the identification of connected GABAergic interneurons in the selected layers (I) in acute brain slices

      (III) Paired patch-clamp-recordings of Martinotti cells and their upstream connected inhibitory interneurons and their characterization according to the "petilla terminology"

Publications

    • 2017
    • Nicotine reverses hypofrontality in animal models of addiction and schizophrenia.
      Koukouli,F.; Rooy,M.; Tziotis,D.; Sailor,K.A.; O'Neill,H.C.; Levenga,J.; Witte,M.; Nilges,M.; Changeux,J.P.; Hoeffer,C.A.; Stitzel,J.A.; Gutkin,B.S.; DiGregorio,D.A.; Maskos,U..
      Nature Medicine, 2017.
      abstract link

      The prefrontal cortex (PFC) underlies higher cognitive processes that are modulated by nicotinic acetylcholine receptor (nAChR) activation by cholinergic inputs. PFC spontaneous default activity is altered in neuropsychiatric disorders, including schizophrenia-a disorder that can be accompanied by heavy smoking. Recently, genome-wide association studies (GWAS) identified single-nucleotide polymorphisms (SNPs) in the human CHRNA5 gene, encoding the α5 nAChR subunit, that increase the risks for both smoking and schizophrenia. Mice with altered nAChR gene function exhibit PFC-dependent behavioral deficits, but it is unknown how the corresponding human polymorphisms alter the cellular and circuit mechanisms underlying behavior. Here we show that mice expressing a human α5 SNP exhibit neurocognitive behavioral deficits in social interaction and sensorimotor gating tasks. Two-photon calcium imaging in awake mouse models showed that nicotine can differentially influence PFC pyramidal cell activity by nAChR modulation of layer II/III hierarchical inhibitory circuits. In α5-SNP-expressing and α5-knockout mice, lower activity of vasoactive intestinal polypeptide (VIP) interneurons resulted in an increased somatostatin (SOM) interneuron inhibitory drive over layer II/III pyramidal neurons. The decreased activity observed in α5-SNP-expressing mice resembles the hypofrontality observed in patients with psychiatric disorders, including schizophrenia and addiction. Chronic nicotine administration reversed this hypofrontality, suggesting that administration of nicotine may represent a therapeutic strategy for the treatment of schizophrenia, and a physiological basis for the tendency of patients with schizophrenia to self-medicate by smoking.

    • 2016
    • Intracortical Network Effects Preserve Thalamocortical Input Efficacy in a Cortex Without Layers.
      Guy,J.; Sachkova,A.; Möck,M.; Witte,M.; Wagener,R.J.; Staiger,J.F..
      Cerebral Cortex DOI 10.1093/cercor/bhw281, 2016.
      abstract

      Layer IV (LIV) of the rodent somatosensory cortex contains the somatotopic barrel field. Barrels receive much of the sensory input to the cortex through innervation by thalamocortical axons from the ventral posteromedial nucleus. In the reeler mouse, the absence of cortical layers results in the formation of mispositioned barrel-equivalent clusters of LIV fated neurons. Although functional imaging suggests that sensory input activates the cortex, little is known about the cellular and synaptic properties of identified excitatory neurons of the reeler cortex. We examined the properties of thalamic input to spiny stellate (SpS) neurons in the reeler cortex with in vitro electrophysiology, optogenetics, and subcellular channelrhodopsin-2-assisted circuit mapping (sCRACM). Our results indicate that reeler SpS neurons receive direct but weakened input from the thalamus, with a dispersed spatial distribution along the somatodendritic arbor. These results further document subtle alterations in functional connectivity concomitant of absent layering in the reeler mutant. We suggest that intracortical amplification mechanisms compensate for this weakening in order to allow reliable sensory transmission to the mutant neocortex

    • Parvalbumin- and vasoactive intestinal polypeptide-expressing neocortical interneurons impose differential inhibition on Martinotti cells.
      Walker F, Möck M, Feyerabend M, Guy J, Wagener RJ, Schubert D, Staiger JF, Witte M.
      Nature Comunications 7:13664 (DOI: 10.1038/ncomms13664, 2016.
      abstract link

      Disinhibition of cortical excitatory cell gate information flow through and between corticalcolumns. The major contribution of Martinotti cells (MC) is providing dendritic inhibition toexcitatory neurons and therefore they are a main component of disinhibitory connections.Here we show by means of optogenetics that MC in layers II/III of the mouse primarysomatosensory cortex are inhibited by both parvalbumin (PV)- and vasoactive intestinalpolypeptide (VIP)-expressing cells. Paired recordings revealed stronger synaptic inputonto MC from PV cells than from VIP cells. Moreover, PV cell input showed frequencyindependentdepression, whereas VIP cell input facilitated at high frequencies. Thesedifferences in the properties of the two unitary connections enable disinhibition with distincttemporal features.

    • 2015
    • Thalamocortical Connections Drive Intracortical Activation of Functional Columns in the Mislaminated Reeler Somatosensory Cortex .
      Robin J. Wagener, Mirko Witte, Julien Guy, Nieves Mingo-Moreno, Sebastian Kügler, Jochen F. Staiger.
      Cerebral Cortex, 2015.
      abstract link

      Neuronal wiring is key to proper neural information processing. Tactile information from the rodent's whiskers reaches the cortex via distinct anatomical pathways. The lemniscal pathway relays whisking and touch information from the ventral posteromedial thalamic nucleus to layer IV of the primary somatosensory "barrel" cortex. The disorganized neocortex of the reeler mouse is a model system that should severely compromise the ingrowth of thalamocortical axons (TCAs) into the cortex. Moreover, it could disrupt intracortical wiring. We found that neuronal intermingling within the reeler barrel cortex substantially exceeded previous descriptions, leading to the loss of layers. However, viral tracing revealed that TCAs still specifically targeted transgenically labeled spiny layer IV neurons. Slice electrophysiology and optogenetics proved that these connections represent functional synapses. In addition, we assessed intracortical activation via immediate-early-gene expression resulting from a behavioral exploration task. The cellular composition of activated neuronal ensembles suggests extensive similarities in intracolumnar information processing in the wild-type and reeler brains. We conclude that extensive ectopic positioning of neuronal partners can be compensated for by cell-autonomous mechanisms that allow for the establishment of proper connectivity. Thus, genetic neuronal fate seems to be of greater importance for correct cortical wiring than radial neuronal position.

    • Characterizing VIP Neurons in the Barrel Cortex of VIPcre/tdTomato Mice Reveals Layer-Specific Differences.
      Prönneke A, Scheuer B, Wagener RJ, Möck M, Witte M, and Staiger JF.
      Cereb. Cortex (2015) 25 (12): 4854-4868. doi: 10.1093/cercor/bhv202 , 2015.
      abstract pdf link

      Neocortical GABAergic interneurons have a profound impact on cortical circuitry and its information processing capacity. Distinct subgroups of inhibitory interneurons can be distinguished by molecular markers, such as parvalbumin, somatostatin, and vasoactive intestinal polypeptide (VIP). Among these, VIP-expressing interneurons sparked a substantial interest since these neurons seem to operate disinhibitory circuit motifs found in all major neocortical areas. Several of these recent studies used transgenic Vip-ires-cre mice to specifically target the population of VIP-expressing interneurons. This makes it necessary to elucidate in detail the sensitivity and specificity of Cre expression for VIP neurons in these animals. Thus, we quantitatively compared endogenous tdTomato with Vip fluorescence in situ hybridization and αVIP immunohistochemistry in the barrel cortex of VIPcre/tdTomato mice in a layer-specific manner. We show that VIPcre/tdTomato mice are highly sensitive and specific for the entire population of VIP-expressing neurons. In the barrel cortex, approximately 13% of all GABAergic neurons are VIP expressing. Most VIP neurons are found in layer II/III (∼60%), whereas approximately 40% are found in the other layers of the barrel cortex. Layer II/III VIP neurons are significantly different from VIP neurons in layers IV-VI in several morphological and membrane properties, which suggest layer-dependent differences in functionality.

    • What types of neocortical GABAergic neurons do really exist?.
      Jochen F. Staiger, Martin Möck, Alvar Prönneke, Mirko Witte .
      e-Neuroforum (Springer), 2015.
      abstract link

      The neocortex is regarded as the brain structure responsible for mediating higher brain functions, like conscious perception of sensory signals, learning and memory or programming of goal-directed behavior. Cortical circuits that enable these functions are formed by, first, a larger population of excitatory so-called principal cells (i.e., glutamatergic pyramidal cells; ca. 80–85 %), which issue long-distance projections, in addition to local recurrent collaterals, which form the major part of local cortical excitatory circuits. A second, smaller population of inhibitory also called local or short-axoned interneurons (i.e., GABAergic neurons; ca. 15–20 %), however, contribute heavily to intracortical microcircuits too. They can be subdivided by their location in specific areas, layers, or columns, which possess specific input–output relationships, but also in terms of morphology, electrophysiology, molecular expression profiles, and subcellular target specificity. Here it is proposed that, at present, in the rodent neocortex this population of GABAergic neurons can be reasonably divided into six different types, mainly due to their unique axonal patterns and subcellular target specificity: (i) axo-axonic cells, (ii) basket cells, (iii) Martinotti cells, (iv) bipolar/bitufted cells, (v) neurogliaform cells, and (vi) projection neurons. These different types of GABAergic neurons strongly govern the working of cortical circuits for meaningful behavior by feed-forward and feedback inhibition as well as disinhibition. Thus, they keep excitation in check, perform gain modulation, and open temporal or spatial windows for input control or output generation.

    • 2014
    • Depolarizing chloride gradient in developing cochlear nucleus neurons: Underlying mechanism and implication for calcium signaling.
      Witte M, Reinert T., Dietz B., Nerlich J., Rübsamen R., Milenkovic I..
      Neuroscience 261: 207-222 , 2014.
      abstract link

      Precise regulation of the chloride homeostasis crucially determines the action of inhibitory transmitters GABA and glycine and thereby endows neurons or even discrete neuronal compartments with distinct physiological responses to the same transmitters. In mammals, the signaling mediated by GABAA/glycine receptors shifts during early postnatal life from depolarization to hyperpolarization, due to delayed maturation of the chloride homeostasis system. While the activity of the secondary active, K+-Cl--extruding cotransporter KCC2, renders GABA/glycine hyperpolarizing in auditory brainstem nuclei of altricial rodents, the mechanisms contributing to the initially depolarizing transmembrane gradient for Cl- in respective neurons remained unknown. Here we used gramicidin-perforated patch recordings, non-invasive Cl- and Ca2+ imaging, and immunohistochemistry to identify the Cl--loading transporter that renders depolarizing effects of GABA/glycine in early postnatal life of spherical bushy cells in the cochlear nucleus of gerbil. Our data identify the 1Na+:1K+:2Cl- cotransporter 1 (NKCC1) as the major Cl--loader responsible for depolarizing action of GABA/glycine at postnatal days 3-5 (P3-5). Extracellular GABA/muscimol elicited calcium signaling through R-, L-, and T-type channels, which was dependent on bumetanide- and [Na+]e-sensitive Cl- accumulation. The "adult like", low intracellular Cl- concentration is established during the second postnatal week, through a mechanism engaging the NKCC1-down regulation between P5 and P15 and ongoing KCC2-mediated Cl--extrusion.

    • 2010
    • Presynaptic and postsynaptic origin of multicomponent extracellular spike waveforms at the endbulb of held/spherical bushy cell synapse..
      Typlt M., Haustein M., Dietz B., Steinert J., Witte M., Englitz B., Milenkovic I., Kopp-Scheinpflug C., Forsythe I., Rübsamen R..
      Eur J Neuroscience 31(9):1574-81 , 2010.
      abstract link

      Extracellular signals from the endbulb of Held-spherical bushy cell (SBC) synapse exhibit up to three component waves ('P', 'A' and 'B'). Signals lacking the third component (B) are frequently observed but as the origin of each of the components is uncertain, interpretation of this lack of B has been controversial: is it a failure to release transmitter or a failure to generate or propagate an action potential? Our aim was to determine the origin of each component. We combined single- and multiunit in vitro methods in Mongolian gerbils and Wistar rats and used pharmacological tools to modulate glutamate receptors or voltage-gated sodium channels. Simultaneous extra- and intracellular recordings from single SBCs demonstrated a presynaptic origin of the P-component, consistent with data obtained with multielectrode array recordings of local field potentials. The later components (A and B) correspond to the excitatory postsynaptic potential (EPSP) and action potential of the SBC, respectively. These results allow a clear interpretation of in vivo extracellular signals. We conclude that action potential failures occurring at the endbulb-SBC synaptic junction largely reflect failures of the EPSP to trigger an action potential and not failures of synaptic transmission. The data provide the basis for future investigation of convergence of excitatory and inhibitory inputs in modulating transmission at a fully functional neuronal system using physiological stimulation.

    • 2009
    • P2 receptor-mediated signaling in spherical bushy cells of the mammalian cochlear nucleus..
      Milenkovic, I., Rinke I, Witte M, Dietz, B., Rübsamen R..
      J Neurophysiol. 102(3):1821-1833, 2009.
      abstract link

      Purinoreceptors of the P2 family contribute strongly to signaling in the cochlea, but little is known about the effects of purinergic neurotransmission in the central auditory system. Here we examine P2 receptor-mediated signaling in the large spherical bushy cells (SBCs) of Mongolian gerbils around the onset of acoustically evoked signal processing (P9-P14). Brief adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) application evoked inward current, membrane depolarization, and somatic Ca2+ signals. Moreover, ATPgammaS changed the SBCs firing pattern from phasic to tonic, when the application was synchronized with depolarizing current injection. This bursting discharge activity was dependent on [Ca2+]i and Ca2+-dependent protein kinase (PKC) activity and is presumably caused by modulation of low-threshold K+ conductance. Activation of P2Y1 receptors could not evoke these changes per se, thus it was concluded that the involvement of P2X receptors seems to be necessary. Ca2+ imaging data showed that both P2X and P2Y1 receptors mediate Ca2+ signals in SBCs where P2Y1 receptors most likely activate the PLC-IP3 (inositol trisphosphate) pathway and release Ca2+ from internal stores. Immunohistochemical staining confirmed the expression of P2X2 and P2Y1 receptor proteins in SBCs, providing additional evidence for the involvement of both receptors in signal transduction in these neurons. Purinergic signaling might modulate excitability of SBCs and thereby contribute to regulation of synaptic strength. Functionally, the increase in firing rate mediated by P2 receptors could reduce temporal precision of the postsynaptic firing, e.g., phase locking, which has an immediate effect on signal processing related to sound localization. This might provide a mechanism for adaptation to the ambient acoustic environment.

    • 2007
    • Development of chloride-mediated inhibition in neurons of the anteroventral cochlear nucleus of gerbil (Meriones unguiculatus).
      Milenkovic I., Witte M., Turecek R., Heinrich M., Reinert T., Rübsamen R..
      J Neurophysiol 98: 1634-1644, 2007.
      abstract link

      At the initial stages in neuronal development, GABAergic and glycinergic neurotransmission exert depolarizing responses, assumed to be of importance for maturation, which in turn shift to hyperpolarizing in early postnatal life due to development of the chloride homeostasis system. Spherical bushy cells (SBC) of the mammalian cochlear nucleus integrate excitatory glutamatergic inputs with inhibitory (GABAergic and glycinergic) inputs to compute signals that contribute to sound localization based on interaural time differences. To provide a fundamental understanding of the properties of GABAergic neurotransmission in mammalian cochlear nucleus, we investigated the reversal potential of the GABA-evoked currents (E GABA) by means of gramicidin-perforated-patch recordings in developing SBC. The action of GABA switches from depolarizing to hyperpolarizing by the postnatal day 7 due to the negative shift in E GABA. Furthermore, we studied the expression pattern of the K+-Cl(-)-extruding cotransporter KCC2, previously shown to induce a switch from neonatal Cl(-) efflux to the mature Cl(-) influx in various neuron types, thereby causing a shift from depolarizing to hyperpolarizing GABA action. The KCC2 protein is expressed in SBC already at birth, yet its activity is attained toward the end of the first postnatal week as indicated by pharmacological inhibition. Interruption of the Cl(-) extrusion by [(dihydroindenyl)oxy] alkanoic acid or furosemide gradually shifted E(GABA) in positive direction with increasing maturity, suggesting that KCC2 could be involved in maintaining low [Cl(-)]i after the postnatal day 7 thereby providing the hyperpolarizing Cl(-)-mediated inhibition in SBC.

Teachings