TAAR4a, 4b expression and amine responses occur in sparsely distributed olfactory neurons.
In situ hybridization was performed for TAAR4a and TAAR4b using horizontal sections of larval Xenopus laevis head tissue. Enlargements containing labeled cell(s) are shown to the right of each complete section. A ring of dark brown melanophores delineates the basal border of the epithelium; apical is toward the lumen. TAAR4a-expressing cells are found apically and laterally, whereas TAAR4b-expressing cells lie more basal and show no obvious enrichment in the medial-to-lateral dimension. Amine- and amino acid-responsive cells were identified by calcium imaging (green and red ovals, respectively). Traces for all cells depicted by colored ovals are shown to the right of the respective micrographs, with odor stimulus period indicated by the black bar (fluorescence intensity values are given as ΔF/F, see Materials and Methods). To be able to show several traces for amines, a slice with above average frequency of amine-responsive cells was chosen.