Schichtenspezifische Charakterisierung von Parvalbumin-exprimierenden Neuronen im primären somatosensorischen Kortex der Maus

Layer-specific characterization of parvalbumin-expressing Neurons in the primary somatosensory cortex

by Bettina Anna Pater
Doctoral thesis
Date of Examination:2020-07-20
Date of issue:2020-07-06
Advisor:Prof. Dr. Jochen Staiger
Referee:Prof. Dr. Tim Gollisch
Referee:Prof. Dr. Rainer Mausberg
Persistent Address: http://dx.doi.org/10.53846/goediss-8059

 

 

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Abstract

English

The neurons of the primary somatosensory cortex of the mouse can be divided into inhibitory and excitatory populations. The group of inhibitory interneurons, which comprise about 15-20% of the neurons, release the neurotransmitter GABA and are called GABAergic neurons. They can be further divided into subpopulations based on their electrophysiological, morphological and molecular properties. With regard to the expression of parvalbumin (PV), somatostation (SOM) and the ionotropic serotonin receptor 5HT3a, three molecularly distinct subpopulations of GABAergic neurons can be distinguished. The 5HT3aR population is further divided into the subgroup of vasoactive intestinal peptide VIP (vasoactive intestinal polypeptide) (40%) and non-VIP expressing cells (60%). In the present study the transgenic PVcre/tdTomato mouse generated by the Cre/loxP technique was used, in which PV-expressing GABAergic neurons carry the red fluorescent tdTomato protein. In this work, the PVcre mouse line should be characterized by immunohistochemistry and fluorescence in situ hybridization in the somatosensory cortex (barrel cortex). The tdTomato-positive cells were examined for the expression of specific interneuron markers such as parvalbumin (PV), somatostatin (SOM) and vasoactive intestinal polypeptide (VIP). In addition, the red fluorescing cells were tested for their inhibitory property (marker Gad1) and the crossmatch was performed with the excitatory marker Vglut1. Furthermore, it should be investigated to what extent perineural networks (marker WFA) occur at the PV-expressing neurons. The aim of this study is to obtain information on the layer-specific cell distribution of tdTomato-positive cells and the specificity of the tdTomato signal for PV-expressing GABAergic neurons in the barrel cortex. The layer-specific analysis of the PVcre/tdTomato mouse line in the barrel cortex showed a strong preference of tdTomato cells for layers IV (28.7%) and Vb (24.7%). Colocalization with the inhibitory marker Gad1 was found in only 92.1 % of the cells. Especially in the cortical layers Va and Vb, about 7 % (Va) and 18 % (Vb) of the tdTomato cells showed co-expression with Vglut1 and therefore have excitatory properties. In the evaluation of markers for GABAergic neurons, 87.6 % of the tdTomato cells express parvalbumin and can therefore be considered as PV-expressing GABAergic neurons. A small number of tdTomato cells express the neuropeptide somatostatin (5.3 %), especially in layers Vb and VI. In contrast, colocalisation with the Vip probe could be almost excluded (0.2 %). In the PVcre/tdTomato mouse 70.9 % of the tdTomato cells in the barrel cortex carried perineural networks, with the highest overlap of 92.1 % in layer IV. Interestingly, 99.2 % of all PNN carrying cells are marked by the tdTomato signal. In summary, this study demonstrated that the PVcre mouse is not a specific mouse model for PV-expressing GABAergic neurons. Especially the high number of labeled excitatory neurons in layer V should be noted by the users of the line. It is recommended to apply further characterization methods to obtain reliable and reproducible results for this mouse line.
Keywords: parvalbumin; somatosensory cortex; barrel cortex; WFA
Schlagwörter: Barrel Kortex; Parvalbumin; Perineuronale Netze
 
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