GABA and glycine co-transmission in the developing mouse respiratory network

by Md Jamilur Rahman
Doctoral thesis
Date of Examination:2014-04-02
Date of issue:2014-11-18
Advisor:Prof. Dr. Swen Hülsmann
Referee:Prof. Dr. Swen Hülsmann
Referee:Prof. Dr. Ralf Heinrich
Persistent Address: http://dx.doi.org/10.53846/goediss-4784

 

 

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Abstract

English

Inhibitory neurons in the pre-Bötzinger complex - a kernel for respiratory rhythm generation, are involved in the respiratory rhythm modulation. The co-transmission of GABA and glycine has been reported in different brain regions but not in the preBötC. The current study showed that GABA and glycine co-transmission is present in the neonatal mouse pre-Bötzinger complex. The co-transmission mediated inhibition was estimated up to 46.8% in the preBötC glycinergic neurons by the optimized “EPF” method based on decay kinetics of inhibitory postsynaptic currents. The co-transmission in the preBötC was further corroborated by single cell RT-PCR that showed 64% glycinergic neurons co-express GABAergic neuronal markers. The drastically reduced VIAAT expression in the preBötC and hypoglossal nucleus of the conditional VIAAT KO embryos strongly suggest that glycinergic neuronal marker (GlyT2) is co-expressed in most of GABAergic neurons in embryonic brainstem. The complete absence of sIPSCs in embryonic hypoglossal motoneurons further confirms wide expression of cre-recombinase among inhibitory neurons in a brainstem region which innervates hypoglossal nucleus. These results strongly suggest that GABA and glycine co-transmission could be ubiquitously present in the embryonic respiratory network and its distribution and relevance decreases during development.  The cVIAAT KO embryos died due to respiratory failure resulting from complete loss of inhibitory transmission which is required for coupling between the preBötC and the pFRG to produce a normal respiratory rhythm. A disturbance in either glycine transmission or GABAergic transmission alone does not deteriorate the respiratory network immediately because the co-transmission of GABA and glycine provides a mechanism of compensation for loss of single inhibitory transmitter as gephyrin KO, GlyT2 KO and GAD67 mouse models survive longer than cVIAAT and VIAAT KO embryos. The cVIAAT KO embryos without any exception showed very common striking features like omphalocele, cleft palate and kyphotic posture which must be due to the loss of all inhibition but not with either GABAergic or glycinergic inhibition alone.
Keywords: Respiratory network; pre-Bötzinger complex; co-transmission; co-release; GABA and glycine; VIAAT; GLYT2; mIPSC; mixed-mIPSC; brainstem; medulla; Respiration; Breathing; Diaphragm; Embryonic development; Single cell PCR; Immunostaining; Reverse transcription PCR
 
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