Fig. 1

Morphology and function of taste sensilla of the PO. A Schemes of the head, the PO, and the single uniporous sensilla at different scales of R. prolixus. A longitudinal and ventral view of the head and pharynx, unveiling the eight taste sensilla of the PO. The PO is located antero-dorsally to the head and pharynx. B–C Photographs of histological cross sections of the PO. B Dorsally to the pharynx (p), indicated with arrows, a taste sensillum and two cell bodies can be identified. Horizontal bar denotes 2 µm. C A dendrite of a putative PO-GRN is shown with an arrow. Horizontal bar indicates 10 µm. D–E Electrophysiological responses of PO-GRNs. D Example of spike discharges of the GRNs of the PO. Typical responses to NaCl, ATP, and caffeine are shown. Circles and bars below traces represent the spike events following spike sorting. E1–2 Scatter plots are shown, and the horizontal lines represent the mean responses (mean ± s.e.) of the summed spike events of the PO-GRNs upon stimulation. E1 ATP and caffeine produced significantly more spike events than NaCl. The solutions of ATP and caffeine also contained NaCl (0.15 M), used as control stimulation. Asterisks indicate statistical differences between insects stimulated with ATP or caffeine versus those stimulated with NaCl alone (p < 0.0005) (NaCl, n = 14; ATP, n = 13; caffeine, n = 9). E2 Increasing doses of NaCl elicited a corresponding increase in the firing responses. Asterisks indicate statistical differences between insects stimulated with 0.05 M NaCl versus those stimulated with 0.15 M and 1 M NaCl (p < 0.05) (NaCl 0.05 M, n = 11; NaCl 0.15 M, n = 10; NaCl 1 M, n = 12). F–L Anterograde staining of the PO-GRNs. F–K Photographs at different levels of the brain of insects, showing two subtypes of PO-GRNs reaching the subesophageal zone (SEZ). One subtype constituted by thick axons showed to project contralaterally in the SEZ exclusively (denoted in pink). Another subtype of PO-GRNs (denoted in gray) arborise ipsilaterally at the medial and dorsal region of the SEZ and continue to the posterior ganglions (data not shown). L Reconstruction of the arborizations of PO-GRNs that reach the brain. fn frontal nerve, ln labral nerve, an antennal nerve, FG frontal ganglion, T tritocerebrum, AL antennal lobe, AMMC antennal motor mechanosensory center, SEZ subesophageal zone, a anterior, p posterior, d dorsal, v ventral