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. Author manuscript; available in PMC: 2022 Apr 1.
Published in final edited form as: Curr Opin Physiol. 2021 Jan 13;20:8–15. doi: 10.1016/j.cophys.2020.12.006

Figure 3. Evidence for 5-HT as a neurotransmitter in Type III TRCs.

Figure 3.

(A) Confocal z-projection of a geniculate ganglion in a 5-HT3a-GFP mouse, showing co-expression of GFP (green) and P2X3 (magenta). White box outlines area that is magnified in the inset to the left. White arrows illustrate neurons that express both markers. (B) Type III TRC labeled with an antibody against 5-HT (magenta). 5-HT3a-GFP labels a single axon that wraps around and contacts the Type III TRC at multiple locations. (C) Representative calcium imaging recording of isolated geniculate ganglion neurons in response to ATP (10 µM), 5-HT (10 μM) and KCl (50 mM). The green trace (top) is from a GFP-labeled neuron, while the black trace (bottom) is from an unlabeled neuron. All neurons responded to both ATP and KCl, but only the GFP-labeled neurons responded to 5-HT. (D) Chorda tympani nerve recordings from 5-HT3a-KO and wildtype mice in response to acid stimuli. The knockout mice showed significant reductions in the response to both citric acid and HCl compared to their wildtype littermates. (Modified from [34).