Thalamocortical Innervation of GABAergic Interneurons in Mouse Primary Vibrissal Somatosensory Cortex

by Michael Feyerabend
Doctoral thesis
Date of Examination:2019-12-03
Date of issue:2020-11-26
Advisor:Prof. Dr. Jochen Staiger
Referee:Camin Phd Dean
Referee:Prof. Dr. Tobias Moser
Persistent Address: http://dx.doi.org/10.53846/goediss-8331

 

 

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Abstract

English

Interneurons utilizing gamma-aminobutyric acid (GABA) as primary neurotransmitter are thought to play a key role in neocortical processing. Their striking diversity has been in focus of numerous studies for decades. However, with the exception of fast spiking cells, their possible innervation by thalamocortical afferents (TCAs) has rarely been looked at systematically. This project investigates the innervation of somatostatin (SST) and vasoactive intestinal polypeptide (VIP) expressing cells throughout all layers of the mouse barrel cortex by its two dominant thalamic input sources: the ventral posteromedial nucleus of the thalamus (VPM) and the medial part of the posterior thalamic nuclear group (POm). Understanding how GABAergic interneurons are recruited by thalamocortical circuits is crucial to understand their overall role in neocortical processing. Our aim is thus to characterize the extension of inputs in a cell type and layer specific manner assessing efficacy and other synaptic properties. We use optogenetics combined with in-vitro whole cell recordings of animals aged P42 –P58. Channelrhodopsin-2 (ChR2) expression is achieved by stereotactic injections of an adeno-associated virus. Our data show a strong and almost ubiquitous thalamic innervation of VIP cells by both POm and VPM across all layers. Input of SST cells is comparatively weak, but also occurs frequently throughout the cortical depth. Cell type identity has at best a minor influence on the likelihood of receiving direct input from either nucleus. Two findings stand out: 1) VIP cell recruitment, which was thought to be predominantly driven by corticocortical or neuromodulatory inputs is also possible by bottom-up circuits. 2) SST cells are also innervated by POm afferents.
Keywords: GABAergic Interneurons; thalamocortical circuits; ChR2-assisted circuit mapping; primary somatosensory cortex
 
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