Fig. 2
Expression of 5-HT in relation to 5-HT1B/1D/1F receptors. A majority of observed TG neurons expressed 5-HT-ir in a heterogeneous granular pattern. This pattern was reminiscent of cytoplasmic vesicles and which was often visualized close to the cell membrane. 5-HT was generally weakly expressed in Aδ-fibres, Schwann cells and satellite glial cells. A 5-HT1B receptor ir was found in all observed neuronal cell bodies and more faintly in Aδ-fibres. 5-HT1B-ir was observed in an evenly distributed granular pattern across the neuron cytoplasm. 5-HT1B co-localized with 5-HT in the neuronal cytoplasm. Insert: Arrowheads mark a neuron where 5-HT is intensely expressed close to the cell membrane and 5-HT1B is more evenly distributed across the whole cell body. B A majority of observed neurons displayed 5-HT1D receptor ir in a vesicular pattern. Unlike the intense and evenly distributed ir of 5-HT1B receptor, the 5-HT1D receptor displayed both strong and weak ir in different subsets of neurons. Arrowheads mark a neuron with a fainter 5-HT1D expression than a neighbouring neuron. Furthermore, 5-HT1D displayed a distinct Aδ-fibre ir. Arrows mark a visible Aδ-fibre. Double IHC showed that 5-HT1D co-localized with 5-HT in the neuron cell bodies. 5-HT expression could be observed in 5-HT1D-positive Aδ-fibres, albeit inconsistent and faint. Insert: Arrows mark Aδ-fibre expressing both 5-HT1D and 5-HT ir. C 5-HT co-localized with the faintly positive 5-HT1F receptor in neuron cell bodies. No nerve fibre ir was observed for the 5-HT1F receptor. Insert: Arrowhead marks a 5-HT positive neuron with a faint 5-HT1F expression