Fig 1: Localization of neurokinin receptor 1 (NK1R), neurokinin receptor 2 (NK2R), neurokinin receptor 3 (NK3R) and contactin-associated protein 1 (CASPR) in relation to substance P (SP) in the rat trigeminal ganglion. (a) NK1R displayed robust immunoreactivity (ir) in the majority of observed neurons, neuron nuclei, Schwann cells and A-fibres (Asterix). The NK1R expression in SGCs and C-fibres was slightly weaker. NK1R was observed to co-localize with SP in C-fibres (arrow) and small to medium sized neurons (arrowhead). Insert: Three neurons displaying NK1R ir with one also expressing SP ir (arrowhead). Close-by a SP and NK1R immunoreactive C-fibre (arrow) can be observed. (b) NK2R was expressed in most observed neurons, neuron nuclei (arrow) and A-fibres. The expression in A-fibres was patchy and weaker than that of NK1R. NK2R ir co-localized with SP in neurons (arrowhead) but was not readily distinguished in associated C-fibres. Insert: An unevenly stained NK2R immunoreactive Aδ-fibre (arrowhead) near a SP immunoreactive C-fibre (arrow). (c) In general, NK3R ir resembled NK1R ir, though weaker and without a clearly visible nuclear envelope. NK3R ir was observed in most neurons (arrowhead), A-fibres, SGCs and Schwann cells. When co-stained with SP a weak co-localization could be observed in C-fibres (arrow). Insert: Co-localization of NK3R and SP in a medium sized neuron (arrowhead). A weakly stained C-fibre (arrow) can be seen projecting from its associated neuron. (d) The nodes of Ranvier were robustly revealed utilizing the specific CASPR antibody. Double immunohistochemistry with SP displayed several SP positive C-fibre boutons aligning with the node of Ranvier (arrow). Insert: A close-up on the CASPR positive paranodal regions of the Aδ-fibre axon flanking the node of Ranvier (arrowhead). A C-fibre bouton displaying SP ir (arrow) can be located nearby. The visible red ir in the C-fibre bouton is likely due to an unspecific binding of the polyclonal CASPR primary antibody.