Research Group Schmidt

We are interested in the mechanisms and the dynamics of information transfer between cortical neurons in the mammalian brain. In these processes the second messenger ion Ca²⁺​ is of fundamental importance. Ca²⁺​ triggers neurotransmitter release and regulates synaptic efficacy via ontogenetic and activity-dependent mechanisms of synaptic plasticity. We investigate synaptic transmission and plasticity on the cellular and molecular level, using techniques like paired patch-clamp recordings, two-photon (2P) microscopy and numerical computer simulations.

Synaptic transmission and plasticity

To lurk into neuronal communation we perform paired patch-clamp recordnigs in actue brain slices (Fig. 1). Qunatal synaptic release parameters are quantified by fluctuation analysis (Fig. 2) and synaptic Ca²⁺​​ signalling by dual-dye 2P- Ca²⁺​​​ imaging (Fig. 3). Numerical computer simulations constrained by the experimental data are used to derive estimates about active zone topography (Fig. 4).​Figure 1. Paired recordings from connected Purkinje neurons in the cerebellar cortex (left; from Bornschein et al., J. Physiol., 2013) and from pyramidal neurons in the neocortex (right; from Bornschein et al., 2019).

Figure 2. Fluctuations of EPSC amplitudes recorded from pairs of connected neurons at different extracellular Ca²⁺​ concentrations can be used to estimate quantal synaptic release parameters (quantal size, release probability, and number of release sites).Figure 3. Presynaptic 2P- Ca²⁺ imaging at a layer 5 pyramidal neuron in an acute brain slice (left). Dashed lines indicate the patch-pipette. Ca²⁺ signals were induced by single action potentials and recorded from individual presynaptic terminals located on an axon collateral (box and right; modified from Bornschein et al., 2019)​

Figure 4. Numerical computer simulations were used to predict changes in active active zone topography accounting for functional maturation of the parallel-fiber to Purkinje cell synapse in wild-type and in the absence of the active zone protein Munc13-3 (from Kusch et al., 2018).

​Ca²⁺ binding proteins: Mobility and Ca²⁺​ binding kinetics​

Ca​ binds to Ca​2+​ sensing proteins that can be mobile or immobile. The diffusional mobility of proteins and binding to other proteins can be analyzed in synaptic structures by point-mode 2P- fluorescence recovery after photobleaching (FRAP; Fig. 5). Furthermore, by combining Ca2+​ uncaging with presynaptic Ca2+​ imaging it is possible to quantify the Ca2+ binding kinetics of Ca2+ sensor proteins (Fig. 6).​Figure 5. FRAP recordings. Dendrite and spines of a Purkinje neuron filled with dye labelled Calbindin (CB, left). To the right a FRAP recording from the spine marked by the white crosshair is shown. The offset indicates binding of CB in the spine. The time course of the recovery (τ) allowed quantifying the diffusion coefficient of CB (modified from Schmidt at al., 2005).Figure 6. Ca²⁺ uncaging at neocortical boutons. A. Left: Two photon image of a pyramidal neuron equilibrated with a patch-pipette solution containing a Ca²⁺​ indicator dye, a caged Ca²⁺​ compound, and a red, Ca²⁺​ insensitive dye. Right: Two presumed presynaptic terminals indicated by the box in the left panel. B. Line-scan from the boutons in A during a flash photolysis experiment. Red and green fluorescence were recorded. Scale bar, 100 ms. C. ∆G/R quantification of the area indicated by the white box in B. The flash artifact has been blanked.​

Since 2023
SCHM1838/6-1: "Area-specific differences in cortical presynaptic coupling distances"

Since 2021
SCHM1838/4-1: “Use dependent regulation of the coupling distance between Ca2+ channels and release sensor as a mechanism of long-term plasticity”

2018
DFG SCHM1838/2-1: “Quantifying the synaptic Ca2+ -binding kinetics of Synaptotagmin-1, the Ca2+ sensor for transmitter release in the forebrain”

2014-2017
DFG SCHM1838/1-1: “Developmental changes in Ca2+-influx – release coupling at the active zone of excitatory cortical synapses”

2009-2013
DFG EI342/4-1: "Immobilisierung endogener Ca2+-Puffer als Determinande der Paarpulsplastizität an einer kortikalen Synapse"
Gemeinschaftsantrag mit J. Eilers

2005-2014
DFG-Graduiertenkolleg 1097 InterNeuro, Universität Leipzig.
Teilprojekt P11:"Regulation der IP3 - Signalkaskade durch Calbindin D28k", gemeinsam mit J. Eilers.​

• Doctoral theses for medical students
• Bachelor or Master theses for students of natural sciences​

Research Paper

Weichard I, Taschenberger H, Gsell F, Bornschein G, Ritzau-Jost A, Schmidt H, Kittel RJ, Eilers J, Neher E, Hallermann A, Nerlich J (2023)
Fully-primed slowly-recovering vesicles mediate presynaptic LTP at neocortical neurons.
PNAS, 120(43): e2305460120

Wender M*, Bornschein G*, Brachtendorf S, Hallermann S, Eilers J, Schmidt H (2023)
Cav2.2 channels sustain vesicle recruitment at a mature glutamatergic synapse.
*Equal contribution
J Neurosci, 43(22): 4005-4018
Model code is available at https://github.com/Hartmut-Schmidt/JNeurosci_2023

Paul MM, Dannhäuser S, Morris L, Mrestani A, Hübsch M, Gehring J, Hatzopoulos GN, Pauli M, Auger GM, Bornschein G, Scholz N, Ljaschenko D, Müller M, Sauer M, Schmidt H, Kittel RJ, DiAntonio A, Vakonakis I, Heckmann M, Langenhan T (2022)
The human cognition-enhancing CORD7 mutation increases active zone number and synaptic release.
Brain, 145(11): 3787-3802

Eshra A, Schmidt H, Eilers J, Hallermann S (2021)
Calcium dependence of neurotransmitter release at a high fidelity synapse.
eLife, 10: e70408

Köhler S, Schmidt H, Fülle P, Hirrlinger J, Winkler U (2020)
A dual sensor approach to determine the cytosolic concentration of ATP in astrocytes.
Front Cell Neurosci, 14: 565921

Bornschein G, Brachtendorf S, Schmidt H (2020)
Developmental increase of neocortical presynaptic efficacy via maturation of vesicle replenishment.
Front Synaptic Neurosci, 15: 11-36

Bornschein G, Eilers J, Schmidt H (2019)
Neocortical high probability release sites are formed by distinct Ca2+ channel to release sensor topographies during development.
Cell Rep, 28(6): 1410-1418.e4

Kusch V*, Bornschein G*, Loreth D, Bank J, Jordan J, Baur D, Watanabe M, Kulik A, Heckmann M, Eilers J, Schmidt H (2018)
Munc13-3 is required for the developmental localization of Ca2+ channels to active zones and the nanopositioning of Cav2.1 near release sensors.
Cell Reports, 22: 1965-1973

Doussau F, Schmidt H, Dorgans K, Valera AM, Poulain B, Isope P (2017)
Frequency-dependent mobilization of heterogeneous pools of synaptic vesicles shapes presynaptic plasticity.
eLife 6:e28935 doi: 10.7554/eLife.28935

Mondragão MA, Schmidt H, Kleinhans C, Langer J, Kafitz KW, Rose CR (2016)
Extrusion versus diffusion: mechanisms for recovery from sodium loads in mouse CA1 ​pyramidal neurons.
J Physiol, 594(19): 5507-27

Baur D, Bornschein G, Althof D, Watanabe M, Kulik A, Eilers J, Schmidt H (2015)
Developmental tightening of cerebellar cortical synaptic influx-release coupling.
J Neurosci, 35(5): 1858-1871

Brachtendorf S, Eilers J, Schmidt H (2015)
​A use-dependent increase in release sites drives facilitation at calretinin-deficient cerebellar parallel-fiber synapses.
Front Cell Neurosci, 9: 27

Ishiyama S, Schmidt H, Cooper BH, Brose N, Eilers J (2014)
Munc13-3 superprimes synaptic vesicles at granule cell-to-basket cell synapses in the mouse cerebellum.
J Neurosci, 34(44): 14687-14696

Mortensen LS, Schmidt H, Farsi Z, Barrantes-Freer A, Rubio ME, Ufartes R, Eilers J, Sakaba T, Stühmer W, Pardo LA (2014)
KV10.1 potassium channels modulate presynaptic short-term plasticity at the parallel fiber - Purkinje cell synapse.
J Physiol, 593(1): 181-96

Arendt O, Schwaller B, Brown EB, Eilers J, Schmidt H (2013)
Restricted diffusion of calretinin in cerebellar granule cell dendrites implies Ca2+-dependent interactions via its EF-hand 5 domain.
J Physiol, 591(16): 3887-99

Bornschein G, Arendt O, Hallermann S, Brachtendorf S, Eilers J, Schmidt H (2013)
Paired-pulse facilitation at recurrent Purkinje neuron synapses is independent of calbindin and parvalbumin during high-frequency activation.
J Physiol, 591(13): 3355-3370

Schmidt H*, Brachtendorf S*, Arendt O, Hallermann S, Ishiyama S, Bornschein G, Gall D, Schiffmann SN, Heckmann M, Eilers J (2013)
Nanodomain Coupling at an Excitatory Cortical Synapse.
Curr Biol, 3: 244-249.

Schmidt H, Arendt O, Eilers J (2011)
Diffusion and extrusion shape standing calcium gradients during ongoing parallel fiber activity in dendrites of Purkinje neurons.
Cerebellum, 11(3): 694-705

Hallermann S, Fetjova A, Schmidt H, Weyhersmüller A, Silver RA, Gundelfinger ED, Eilers J (2010)
Bassoon speeds vesicle reloading at a central excitatory synapse.
Neuron, 68(4): 710-23

Guzman SJ, Schmidt H, Franke H, Krügel U, Eilers J, Gerevich Z (2010)
P2Y1 receptors inhibit long-term depression in the prefrontal cortex.
Neuropharmacology, 59(6): 406-15

Schaarschmidt G, Wegener F, Schwarz, SC, Schmidt H, Schwarz J (2009b)
Characterization of voltage gated potassium channels in human neural progenitor
cells.
PLOS One, 4(7): e6168

Schaarschmidt G, Schewtschik S, Eilers J, Schwarz J, Schmidt H (2009a)
​A new culturing strategy optimizes functional neuronal development of midbrain ​derived precursors.
J Neurochem, 109: 238-247.

Schmidt H, Eilers J (2009)
Regulation of Ca2+ buffer mediated spino-dendritic cross-talk by the spine neck geometry.
J Comput Neurosci, 27(2): 229-43

Schmidt H, Kuhnert S, Wilms C, Strotmann R, Eilers J (2007b)
Spino-dendritic cross-talk mediated by mobile endogenous Ca2+ binding proteins.
J Physiol, 581(Pt 2): 619-29

Schmidt H, Arendt O, Brown EB, Schwaller B, Eilers J (2007a)
Parvalbumin is freely mobile in axons, somata and nuclei of cerebellar Purkinje neurons.
J Neurochem, 100: 727-735

Wilms C, Schmidt H, Eilers J (2006)
Quantitative two-photon Ca2+ imaging via fluorescence lifetime analysis.
Cell Calcium, 40: 73-79

Schmidt H, Schwaller B, Eilers J (2005)
Calbindin D28k targets myo-inositol monophosphatase in spines and dendrites of cerebellar Purkinje neurons.
PNAS, 102: 5850-5855

Küppers-Munther B, Letzkus JJ, Lüer K, Technau GM, Schmidt H, Prokop A (2004)
A new culturing strategy optimises Drosophila primary cell cultures for structural and functional analyses of synapses.
Dev Biol, 269(2): 459-78 This work forms the basis for the grant of the patent on cell culture media.

Schmidt H, Stiefel KM, Racay P, Schwaller B, Eilers J (2003b)
Mutational analysis of dendritic Ca2+ kinetics in cerebellar Purkinje cells: Role of parvalbumin and calbindin D28k.
J Physiol, 551(Pt 1): 13-32

Schmidt H, Brown EB, Schwaller B, Eilers J (2003a)
Diffusional mobility of parvalbumin in spiny dendrites of cerebellar Purkinje neurons quantified by fluorescence recovery after photobleaching.
Biophys J, 84: 2599-2608

Schmidt H, Lüer K, Hevers W, Technau GM (2000)
Ionic currents of Drosophila embryonic neurons derived from selectively cultured CNS midline precursors.
J Neurobiol, 44: 392-413

Schmidt H, Rickert C, Bossing T, Vef O, Urban J, Technau GM (1997)
The embryonic central nervous system lineages of Drosophila melanogaster. II. Neuroblast lineages derived from the dorsal part of the neruoectoderm.
Dev Biol, 189: 186-204

Review Articles (Peer Review)

Schmidt H (2019)
Control of Presynaptic Parallel Fiber Efficacy by Activity Dependent Regulation of the Number of Occupied Release Sites.
Front Syst Neurosci, 13: 30

Bornschein G, Schmidt H (2018)
Synaptotagmin Ca2+ sensors and their spatial coupling to presynaptic Cav channels in central cortical synapses.
Front Mol Neurosci, 11: 494-510
Front. Mol. Neurosci. 11, 494. doi: 10.3389/fnmol.2018.00494.

Schmidt H (2019)
Control of presynaptic parallel fiber efficacy by activity dependent regulation of the number of occupied release sites.
Front Syst Neurosci, 13: 30

Isope P, Wilms CD, Schmidt H (2016)
Determinants of synaptic information transfer: From Ca2+ binding proteins to Ca2+ signaling domains.
Front Cell Neurosci, 10: 69

Schmidt H (2012)
Three functional facets of calbidin-28k.
Front Mol Neurosci, 5: 25

Book Chapter

Schmidt H (2013)
27. Calcium buffering: Models of Ca2+-dynamics and steady-state approximations.
In: Encyclopedia of Computational Neuroscience. Eds: Jaeger D, Jung R; Springer Science Business New York

Schmidt H, Eilers J (2010)
A practical guide: dye loading with patch pipettes.
In: Imaging in neuroscience and development: a laboratory manual, Eds: Yuste R, Konnerth A; Cold Spring Harbor Laboratory Press, New York.

Schmidt H, Eilers J (2007c)
Combined fluorometric and electrophysiological recordings.
In: Patch-Clamp Analysis: Advanced techniques. Eds: Boulton AA, Baker GB, Waltz W; Humana Press Inc, Totowa, New Jersey.

Schmidt H, Eilers J (2002)
Combined fluorometric and electrophysiological recordings.
In: Advanced techniques for patch-clamp analysis. Eds: Boulton AA, Baker GB, Waltz W; Humana Press Inc, Totowa, New Jersey.

Other Publications

Schmidt H (2012)
Forschen, glauben, chillen.
Interview in: KANT Magazin, Hamburg, 06: 60-63​

Prof. Dr. rer. nat. habil. Hartmut Schmidt
CLI für Physilogie
Liebigstr. 27a
04103 Leipzig, Germany

email: hartmut.schmidt@medizin.uni-leipzig.de
phone: +49 (0) 341 9715504
fax: +49 (0) 341 9715529