Projektionsmuster GABAerger Neurone auf Dendriten von Martinotti-Zellen im somatosensorischen Kortex

Projection patterns of GABAergic neurons onto dendrites of Martinotti cells within the somatosensory cortex

by Janis Hülsemann
Doctoral thesis
Date of Examination:2021-11-04
Date of issue:2021-11-03
Advisor:Prof. Dr. Jochen F. Staiger
Referee:Prof. Dr. Jochen F. Staiger
Referee:Prof. Dr. Silvio O. Rizzoli
Persistent Address: http://dx.doi.org/10.53846/goediss-8907

 

 

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Abstract

English

Cortical processing of information is significantly influenced by inhibitory GABAergic Interneurons, although they only account for about 15-20% of all cortical neurons. Three main subpopulations can be distinguished based on molecular markers: VIP-, PV- and SOM-expressing cells, the latter of which are predominantly Martinotti cells. In addition to various interconnections with excitatory cells, GABAergic neurons can inhibit each other, thereby mediating disinhibition of downstream cells. This study analyzes the inhibitory projections from VIP- and PV-expressing cells onto Martinotti cells in the somatosensory cortex of the mouse. The presynaptic cells were se-lectively stimulated in vitro by means of optogenetics. Postsynaptic currents in Martinotti cells were electrophysiologically recorded and analyzed. The patterns of the axonal projec-tions of VIP- and PV-expressing cells onto Martinotti cells were studied by focused optical stimulation of the surroundings of a Martinotti cell in a grid-like pattern. This procedure was repeated after blocking action potentials via tetrodotoxin, thereby selectively stimu-lating the presynaptic terminals of VIP- or PV-expressing cells, to map the distribution of these synapses onto the dendritic tree of Martinotti cells in subcellular resolution. Martinotti cells in layer II/III and V of the somatosensory cortex of the mouse reliably receive inhibitory input from both VIP- and PV-expressing cells. While the axonal pattern of PV-expressing cells is rather horizontal and intralaminar, VIP axons are aligned in a vertical and translaminar pattern relative to the postsynaptic Martinotti cells, especially in layer V. The inhibitory postsynaptic currents differ in latency and rise time, which can be explained by different subcellular localizations of the synapses. PV-expressing cells prefer-entially project onto the somatic and peri-somatic regions, whereas synapses of VIP-expressing cells are distributed over the whole dendritic tree of Martinotti cells. The concept of inhibition of Martinotti cells and a thus mediated disinhibition is expanded by the knowledge of them receiving input from both VIP- and PV-expressing cells. Due to the distinct subcellular localization of their synapses, PV-expressing cells can effectively control the output of Martinotti cells, whereas VIP-expressing cells are positioned to in-fluence the integration of excitatory input onto proximal to distal dendrites of Martinotti cells.
Keywords: Martinotti cells; GABAergic neurons; GABAergic interneurons; projection patterns; sCRACM; PV-expressing cells; VIP-expressing cells; SOM-expressing cells; cortical circuitry; inhibitory interneurons; barrel cortex
Schlagwörter: Martinotti-Zellen; GABAerge Neurone; GABAerge Interneurone; Projektionsmuster; sCRACM; PV-exprimierende Zellen; VIP-exprimierende Zellen; SOM-exprimierende Zellen; kortikales Netzwerk; inhibitorische Interneurone; Barrel-Kortex
 
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