Fig. 4
From: TrkB expression and dependence divides gustatory neurons into three subpopulations
A small subpopulation of taste neurons (Phox2b-positive) do not depend on TrkB expression during development. a) A Z-stack composite image of a whole mount geniculate ganglion at P20 from Phox2b-Cre::tdTomato::TrkBGFP/+ (control). A higher magnification image of a single optical section from this ganglion illustrates that some tdTomato positive neurons also express GFP (arrows), while others do not (asterisks). b) Far fewer tdTomato-positive neurons can be observed in the whole mount of a geniculate ganglion at P20 from a Phox2b-Cre::tdTomato::TrkBGFP/loxP (conditional knockout) mouse. A higher magnification image of a single optical section illustrates that tdTomato-positive neurons do not express GFP (asterisks). c) Mean ± SEM of Phox2b + neurons remaining after TrkB removal from oral cavity-projecting neurons (control, n = 5; conditional knockout, n = 8 conditional knockout). d) In control mice (Phox2b-Cre::tdTomato::TrkBGFP/+), a small number of brightly labeled calbindin positive neurons that also express tdTomato are present in the ganglion. Triple labeling with GFP (green), tdTomato (red) and calbindin (white) reveals that neurons double-labeled for both tdTomato and calbindin are not GFP positive (D, top arrows). Removal of TrkB from Phox2b positive neurons (Phox2b-Cre::tdTomato::TrkBGFP/loxP) results in a complete loss of this neuron population. Remaining tdTomato positive neurons do not express either calbindin or GFP (D, bottom, arrows). Scale bars in A and B = 100 μm, the scale bar in D = 50 μm and applies to all high magnification images. ***p < 0.001