Textlogo 'UFR', Abkürzung für 'Universität Freiburg'
Physiologisches Institut
Siegelement der Uni Freiburg in Form eines Kleeblatts

Electron Microscopy Group

Projects

A) Functional interaction of metabotropic receptors and ion channels in pre- and postsynaptic compartments of central neurons

Functionally diverse metabotropic GABAB and glutamate receptors (mGluRs) control neuronal excitability and synaptic transmission by activating or inhibiting various types of ion channels, such as high voltage-activated Ca2+ and K+ channels. The impact of receptor activation on synaptic integration and regulation of transmitter release depends on the spatial relationship and coupling of receptors and their effectors in subcellular compartments of the target neurons.

We have been investigating the structural and functional basis of metabotropic receptor-effector ion channel complex-mediated signaling in cortical principal cells and GABAergic interneurons, as well as studying the activity-dependent regulation of the surface dynamics of protein complexes using a combination of pharmacological and high-resolution quantitative immunoelectron microscopic approaches.

B) Regulation of intracellular Ca2+ concentration in central neurons

Calcium (Ca2+) plays a central role in many cellular processes in various cell types including neurons in the central nervous system (CNS). It regulates enzymatic activities and excitability, synaptic plasticity and excitation-transcription coupling, as well as controls release of neurotransmitters from presynaptic boutons (Clapham, 2007). Ca2+ influx into axon terminals, somata and dendrites of neurons can mainly be mediated by different high voltage-gated Ca2+ (Cav) channels (Cav1.2, Cav2.1, 2.2 and 2.3). These channels localize either to presynaptic membrane specialization of boutons of glutamatergic and GABAergic cells or distributed along the surface of somatic and dendritic membranes and are activated by action potentials and/or sub-threshold depolarizing signals. Calcium overload, however, has been associated with cell injury and cell death.

Therefore, it is essential for neurons to control cytoplasmic and stored Ca2+ very precisely, both temporally and spatially. The Ca2+ extrusion from the cytosol to the extracellular millieu via membrane-bound proteins, such as plasma membrane Ca2+-ATPases (PMCAs) and Na+/Ca2+ exchangers (NCXs), following neuronal activation, appears to be an important way to the maintenance and precise control of cytoplasmic Ca2+ balance in both presynaptic and postsynaptic compartments. We combine the high-resolution SDS-FRL immunoelectron microscopy with quantitative analysis of immunoreactivity for those proteins to determine the spatial distribution and surface density of Cav channels, PMCAs and NCXs on somato-dendritic and axonal membranes of central neurons.

C) Dendritic mechanisms underlying a sparse spatial code in the dentate gyrus

The hippocampus is essential for encoding the spatial features of the environment in which our daily experience is embedded. Formation of this neuronal code depends on activity-dependent changes in synaptic strength after synchronous activation of excitatory inputs that generate local dendritic activity. This process is under tight dendritic inhibitory control, which gates the generation of dendritic non-linearities and controls the assimilation of neurons into a neuronal engram. In the dentate gyrus, only a small subset of the granule cell population takes part in a cell assembly encoding a spatial context, a necessary condition for the pattern separation function of the dentate gyrus.

We hypothesize that during encoding of spatial information, granule cell dendrites undergo activity- and input-dependent changes in their morphological and physiological properties that affect the mechanism of synaptic integration and contribute to the emergence of dentate gyrus engrams. To investigate this hypothesis, we will combine the complementary expertise of Claudio Elgueta’s and my research groups to understand at the synaptic, cellular and network levels, the molecular and physiological mechanisms by which dendritic excitatory and inhibitory synaptic inputs control the emergence of dentate gyrus engrams.

Research Techniques

  • Conventional immunoelectron microscopic methods: pre-embedding immunoperoxidase and immunogold labeling
  • Sodium dodecyl sulfate (SDS)-digested freeze-fracture replica labeling (SDS-FRL) combined with sample analysis with transmission electron microscop (TEM)
  • Three-dimensional (3D) reconstruction of immunolabeled pre- and postsynaptic compartments of central neurons.
  • Focused Ion Beam Scanning Electron Microscopy (FIB/SEM)
  • Pharmacological manipulation of receptors and ion channels
  • Quantitative analysis of surface density and distribution pattern of signaling molecules using automatized computational cluster analysis, smoothed distance transform analysis and bivariate extension of Ripley’ H-analysis

Selected Publications

  1. Martin-Belmonte M, Aguado C, Alfaro-Ruiz R, Kulik A, de la Ossa L, Moreno-Martinez AE, Alberquilla S, Garcia-Carracedo L, Fernandez M, Fajardo-Serrano A, Aso E, Shigemoto R, Martin ED, Fukazawa Y, Ciruela F, Lujan R (2024) Nanoarchitecture of Cav2.1 channels and GABAB receptors in the mouse hippocampus: Impact of APP/PS1 pathology. Brain Pathology 17:e13279.
  2. Kaufhold, D, Maristany de Las Casas E, Ocana -Fernandez MDA, Cazala A, Yuan M, Kulik A, Cholvin T, Steup S, Sauer JF, Eyre MD, Elgueta C, Strüber M, Bartos M (2024) Spine plasticity of dentate gyrus parvalbumin-positive interneurons is regulated by experience. Cell rep 43:113806.
  3. Grigoryan G, Harada H, Knobloch-Bollmann HS, Kilias A, Kaufhold D, Kulik A, Eyre MD, Bartos M (2023) Synaptic plasticity at the dentate gyrus granule cell to somatostatin-expressing interneuron synapses supports object location memory. Proc Natl Acad Sci USA 120, e2312752120.
  4. Bhandari P, Vandael D, Fernandez-Fernandez D, Fritzius T, Kleindienst D, Önal C, Montanaro J, Gassmann M, Jonas P, Kulik A, Bettler B, Shigemoto R, Koppensteiner P (2021) GABAB receptor auxiliary subunits modulate Cav2.3-mediated release from medial habenula terminals. eLife 9:e68274.
  5. Booker SA, Harada H, Elgueta C, Bank J, Bartos M, Kulik A*, Vida I* (2020) Presynaptic GABAB receptors functionally uncouple somatostatin interneurons from the active hippocampal network. eLife 9: e51156.
  6. Schwenk J, Boudkkazi S, Kocylowski M, Brechet A, Zolles G, Bus T, Costa K, Bildl W, Sprengel R, Kulik A, Roeper J, Schulte U, Fakler B (2019) ER assembly line of AMPA-receptors controls excitatory neurotransmission and its plasticity. Neuron 104:680-692.
  7. Booker SA, Loreth D, Gee AL, Watanbe M, Kind PC, Wyllie DJA, Kulik A*, Vida I* (2018) Postsynaptic GABABRs inhibit L-type calcium channels and abolish long-term potentiation in hippocampal somatostatin interneurons. Cell Rep 22:36-43.
  8. Kulik A, Booker SA, Vida I (2018) Differential distribution and function of GABABRs in somato-dendritic and axonal compartments of principal cells and interneurons in cortical circuits. Neuropharmacology 136:80-91.
  9. Nieto-Rostro M, Ramgoolam K, Pratt WS, Kulik A, Dolphin AC (2018) Visualizing endogenous N-type calcium channels in the pain pathway in vivo: a2d1 ablation abolishes their cell surface trafficking. Proc Natl Acad Sci USA 115:12043-12052.
  10. Booker SA, Althof D, Gross A, Loreth D, Müller J, Unger A, Fakler B, Varro A, Watanabe M, Gassmann M, Bettler B, Shigemoto R, Vida I*, Kulik A* (2017) KCTD12 auxiliary proteins modulate kinetics of GABAB receptor-mediated inhibition in cholecystokinin-containing interneurons. Cereb Cortex 27:2318-2334.
  11. Sibbe M, Kulik A (2017) GABAergic regulation of adult hippocampal neurogenesis. Mol Neurobiol 54:5497-5510.
  12. Althof D, Baehrens D, Watanabe M, Suzuki N, Fakler B, Kulik A (2015) Inhibitory and excitatory axon terminals share a common nano-architecture of their Cav2.1 (P/Q-type) Ca2+ channels. Front Cell Neurosci 9:315.
  13. Hainmüller T, Krieglstein K, Kulik A, Bartos M (2014) Joint CP-AMPA and group I mGlu receptor activation is required for synaptic plasticity in dentate gyrus fast spiking interneurons. Proc Natl Acad Sci USA 111:13211-13216.
  14. Booker SA, Gross A, Althof D, Shigemoto R, Bettler B, Frotscher M, Hearing M, Wickman K, Watanabe M, Kulik A*, Vida I* (2013) Differential GABAB receptor-mediated effects in perisomatic- and dendrite-targeting parvalbumin interneurons. J Neurosci 33:7961-7974.
  15. Parajuli LK, Nakajima C, Kulik A*, Matsui K, Schneider T, Shigemoto R, Fukazawa Y* (2012) Quantitative regional and ultrastructural localization of the Cav2.3 subunit of R-type calcium channel in mouse brain. J Neurosci 32:13555-13567.
  16. Holderith N, Lorincz A, Katona G, Rozsa B, Kulik A, Watanabe M, Nusser Z (2012) Release probability of hippocampal glutamatergic terminals scales with the size of the active zone. Nat Neurosci 15:988-997.
  17. Guetg N, Seddik R, Vigot R, Turecek R, Gassmann M, Vogt KE, Bräuner-Osborne H, Shigemoto R, Kretz O, Frotscher M, Kulik A*, Bettler B* (2009) The GABAB1a isoform mediates heterosynaptic depression at hippocampal mossy fiber synapses. J Neurosci 29:1414-1423.
  18. Bucurenciu I, Kulik A, Schwaller B, Frotscher M, Jonas P (2008) Nanodomain coupling between Ca2+ channels and Ca2+ sensors promotes fast and efficient transmitter release at a cortical GABAergic synapse. Neuron 57:536-545.
  19. Kulik A, Vida I, Fukazawa Y, Guetg N, Kasugai Y, Marker C, Rigato F, Bettler B, Wickman K, Frotscher M, Shigemoto R (2006) Compartment-dependent colocalization of Kir3.2-containing K+ channels and GABAB receptors in hippocampal pyramidal cells. J Neurosci 26:4289-4297.
  20. Kulik A, Nakadate K, Hagiwara A, Fukazawa Y, Lujan R, Saito H, Suzuki N, Futatsugi A, Mikoshiba K, Frotscher M, Shigemoto R (2004) Immunocytochemical localization of the a1A subunit of the P/Q-type calcium channel in the rat cerebellum. Eur J Neurosci 19:2169-2178.
  21. Kulik A, Vida I, Lujan R, Haas CA, Lopez-Bendito G, Shigemoto R, Frotscher M (2003) Subcellular localization of metabotropic GABAB receptor subunits GABAB1a/b and GABAB2 in the rat hippocampus. J Neurosci 23:11026-11035.

* corresponding authors

Research Grants

2008-2012
German Research Foundation (DFG, SFB-780): ‘Role of metabotropic receptors and their effector Kir3 channels in synaptic transmission’. A. Kulik.

2012-2014
BIOSS Centre for Biological Signalling Studies Project Package (BIOSS-2): ‘Quantitative analysis of axonal Ca2+ channels in cortical GABAergic neurons’. A. Kulik.

2015-2017
German Research Foundation (DFG, Research Unit (FOR 2143): ‘Subcellular distribution and dynamics of glutamate receptors and Cav channels in interneuron plasticity’. A. Kulik.

2015-2018
BIOSS Centre for Biological Signalling Studies Project Package (BIOSS-2): ‘Nano-scale organization and dynamics of presynaptic Ca2+ channels’. A. Kulik.

2018-2021
German Research Foundation (DFG, Research Unit (FOR 2143): ‘Subcellular distribution and dynamics of neurotransmitter receptors and Cav channels in interneuron plasticity’. A. Kulik.

2024-2027
German Research Foundation (DFG, CRC/TRR 384): ‘Dendritic mechanisms underlying a sparse spatial code in the dentate gyrus’. C. Elgueta, A. Kulik.

2024-2027
German Research Foundation (DFG, CRC/TRR 384): ‘Light and electron microscopic imaging and morphometric analysis of inhibitory neuronal circuits and signaling proteins’. A. Kulik, I. Vida.

Team

Portrait of Prof. Dr. Akos Kulik

Prof. Dr. Ákos Kulik

Head of EM Group

Portrait of Dr. Laxmi Kumar

Dr. Laxmi Kumar

Research Associate

Portrait of Dr. Nithya Sethumadhavan

Dr. Nithya Sethumadhavan

Research Associate

Portrait placeholder

Marco Ross

Technical Assistant

Portrait placeholder

Nathalie Wernet

Technical Assistant