Expression of GABAergic receptors in mouse taste receptor cells.
BACKGROUND
Multiple excitatory neurotransmitters have been identified in the mammalian taste transduction, with few studies focused on inhibitory neurotransmitters. Since the synthetic enzyme glutamate decarboxylase (GAD) for gamma-aminobutyric acid (GABA) is expressed in a subset of mouse taste cells, we hypothesized that other components of the GABA signaling pathway are likely expressed in this system. GABA signaling is initiated by the activation of either ionotropic receptors (GABA(A) and GABA(C)) or metabotropic receptors (GABA(B)) while it is terminated by the re-uptake of GABA through transporters (GATs).


RESULTS
Using reverse transcriptase-PCR (RT-PCR) analysis, we investigated the expression of different GABA signaling molecules in the mouse taste system. Taste receptor cells (TRCs) in the circumvallate papillae express multiple subunits of the GABA(A) and GABA(B) receptors as well as multiple GATs. Immunocytochemical analyses examined the distribution of the GABA machinery in the circumvallate papillae. Both GABA(A)-and GABA(B)- immunoreactivity were detected in the peripheral taste receptor cells. We also used transgenic mice that express green fluorescent protein (GFP) in either the Type II taste cells, which can respond to bitter, sweet or umami taste stimuli, or in the Type III GAD67 expressing taste cells. Thus, we were able to identify that GABAergic receptors are expressed in some Type II and Type III taste cells. Mouse GAT4 labeling was concentrated in the cells surrounding the taste buds with a few positively labeled TRCs at the margins of the taste buds.


CONCLUSIONS
The presence of GABAergic receptors localized on Type II and Type III taste cells suggests that GABA is likely modulating evoked taste responses in the mouse taste bud.
Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America.
Margaret R
MR
Starostik
Michelle R
MR
Rebello
Kellie A
KA
Cotter
Akos
A
Kulik
Kathryn F
KF
Medler
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D049452:Green Fluorescent Proteins / Q000235:genetics; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D018079:Receptors, GABA / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013650:Taste Buds / Q000378:metabolism*
D017931:DNA Primers; D018079:Receptors, GABA; D049452:Green Fluorescent Proteins