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Expression of GABAergic receptors in mouse taste receptor cells.

Starostik MR, Rebello MR, Cotter KA, Kulik A, Medler KF - PLoS ONE (2010)

Bottom Line: Taste receptor cells (TRCs) in the circumvallate papillae express multiple subunits of the GABA(A) and GABA(B) receptors as well as multiple GATs.Both GABA(A)-and GABA(B)- immunoreactivity were detected in the peripheral taste receptor cells.Thus, we were able to identify that GABAergic receptors are expressed in some Type II and Type III taste cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America.

ABSTRACT

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).

Methodology/principal findings: 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/significance: 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.

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Mouse GAT4 immunoreactivity in circumvallate papillae from GAD67-GFP mice.A Z-stack of 5 LSCMs (0.5 µm each, collected 1 µm apart) of mouse circumvallate taste buds with GFP expression identifying the GAD67-expressing taste cells is shown in panel A. The corresponding image of the taste buds labeled with an anti-rat GAT3 (mouse GAT4) antibody is shown in B with the DIC image shown in C. D, The overlay of A, B, and C reveals that most GAT3 labeling is localized in the surrounding cells near the basolateral portion of the taste bud. A few GFP expressing taste cells have some overlap with the mouse GAT4 immunoreactivity (see arrowheads). The negative control is the same as Figure 9. Scale bars  = 20 µm.
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pone-0013639-g010: Mouse GAT4 immunoreactivity in circumvallate papillae from GAD67-GFP mice.A Z-stack of 5 LSCMs (0.5 µm each, collected 1 µm apart) of mouse circumvallate taste buds with GFP expression identifying the GAD67-expressing taste cells is shown in panel A. The corresponding image of the taste buds labeled with an anti-rat GAT3 (mouse GAT4) antibody is shown in B with the DIC image shown in C. D, The overlay of A, B, and C reveals that most GAT3 labeling is localized in the surrounding cells near the basolateral portion of the taste bud. A few GFP expressing taste cells have some overlap with the mouse GAT4 immunoreactivity (see arrowheads). The negative control is the same as Figure 9. Scale bars  = 20 µm.

Mentions: Immunocytochemical analysis of circumvallate taste buds with anti-rat GAT3 is shown in Figure 9 and corresponds to GAT4 immunoreactivity in the mouse. The most intense anti-mouse GAT4 immunoreactivity was localized to a few TRCs in the basolateral portion of the taste bud and in the cells surrounding the taste buds. Most anti-mouse GAT4 immunoreactivity was absent within the taste bud and we did not detect any overlap between anti-mouse GAT4 labeling and IP3R3-GFP expressing TRCs. Similar expression patterns for anti-mouse GAT4 were found in the GAD67-GFP expressing taste cells (Figure 10). There was some overlap between the GAD67-GFP fluorescence and the anti-mouse GAT4 labeling (see arrowheads), but this was very occasional as most anti-mouse GAT4 labeling was localized in the cells surrounding the taste buds. Due to these differences in terminology between rats and mice, our GAT4 findings parallel the report of GAT3 in rat taste cells [43], including the localization of the protein at the basolateral portion of the taste buds.


Expression of GABAergic receptors in mouse taste receptor cells.

Starostik MR, Rebello MR, Cotter KA, Kulik A, Medler KF - PLoS ONE (2010)

Mouse GAT4 immunoreactivity in circumvallate papillae from GAD67-GFP mice.A Z-stack of 5 LSCMs (0.5 µm each, collected 1 µm apart) of mouse circumvallate taste buds with GFP expression identifying the GAD67-expressing taste cells is shown in panel A. The corresponding image of the taste buds labeled with an anti-rat GAT3 (mouse GAT4) antibody is shown in B with the DIC image shown in C. D, The overlay of A, B, and C reveals that most GAT3 labeling is localized in the surrounding cells near the basolateral portion of the taste bud. A few GFP expressing taste cells have some overlap with the mouse GAT4 immunoreactivity (see arrowheads). The negative control is the same as Figure 9. Scale bars  = 20 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2964312&req=5

pone-0013639-g010: Mouse GAT4 immunoreactivity in circumvallate papillae from GAD67-GFP mice.A Z-stack of 5 LSCMs (0.5 µm each, collected 1 µm apart) of mouse circumvallate taste buds with GFP expression identifying the GAD67-expressing taste cells is shown in panel A. The corresponding image of the taste buds labeled with an anti-rat GAT3 (mouse GAT4) antibody is shown in B with the DIC image shown in C. D, The overlay of A, B, and C reveals that most GAT3 labeling is localized in the surrounding cells near the basolateral portion of the taste bud. A few GFP expressing taste cells have some overlap with the mouse GAT4 immunoreactivity (see arrowheads). The negative control is the same as Figure 9. Scale bars  = 20 µm.
Mentions: Immunocytochemical analysis of circumvallate taste buds with anti-rat GAT3 is shown in Figure 9 and corresponds to GAT4 immunoreactivity in the mouse. The most intense anti-mouse GAT4 immunoreactivity was localized to a few TRCs in the basolateral portion of the taste bud and in the cells surrounding the taste buds. Most anti-mouse GAT4 immunoreactivity was absent within the taste bud and we did not detect any overlap between anti-mouse GAT4 labeling and IP3R3-GFP expressing TRCs. Similar expression patterns for anti-mouse GAT4 were found in the GAD67-GFP expressing taste cells (Figure 10). There was some overlap between the GAD67-GFP fluorescence and the anti-mouse GAT4 labeling (see arrowheads), but this was very occasional as most anti-mouse GAT4 labeling was localized in the cells surrounding the taste buds. Due to these differences in terminology between rats and mice, our GAT4 findings parallel the report of GAT3 in rat taste cells [43], including the localization of the protein at the basolateral portion of the taste buds.

Bottom Line: Taste receptor cells (TRCs) in the circumvallate papillae express multiple subunits of the GABA(A) and GABA(B) receptors as well as multiple GATs.Both GABA(A)-and GABA(B)- immunoreactivity were detected in the peripheral taste receptor cells.Thus, we were able to identify that GABAergic receptors are expressed in some Type II and Type III taste cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University at Buffalo, The State University of New York, Buffalo, New York, United States of America.

ABSTRACT

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).

Methodology/principal findings: 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/significance: 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.

Show MeSH