Sequences of pseudocoloured images of a mucosa slice (stage 53) showing that stimulation with forskolin (50 μM, A-C), pCPT-cAMP (2.5 mM, D -F) and the mixture of amino acids (200 μM, each, G-I) transiently elevates calcium-dependent fluorescence in two different ensembles of ORNs (encircled in B, E and H). The upper images show the fluorescence images before application (t 0 s), the images in the middle at the peak of the response (t 30 s in B and E, t 16 s in H) and the bottom images after return to the basal fluorescence levels (t 230 s in C and F, t 60 s in I). J, schematic diagram showing superimposition of the forskolin and pCPT-cAMP-sensitive ORNs and the amino acid-sensitive ORNs (encircled in B, E and H). ORNs sensitive to forskolin and pCPT-cAMP (green), to amino acids (red) and both (yellow). Only one ORN showed a response to both stimuli. The responses of the ORNs indicated with arrows are shown in Fig. 5. K, occurences of correlated and uncorrelated responses to forskolin and amino acids plotted as a histogram (n = 44 slices). Scale bar 20 μM.