Figure 5.

Representative confocal images of NK₁ receptor (NK1r) internalization induced by a unilateral injection of formalin (5%) into the hindpaw. Images in (a–c) are from the ipsilateral spinal cord. (a) An image of formalin-evoked NK1r internalization from a rat administered i.t. saline. Notice the lack of a homogeneous cell membrane and the presence of NK₁-containing endosomes internalizing into the cytoplasm. (b) Intrathecal dexmedetomidine (1 μg) did not reduce the formalin-evoked NK1r internalization. (c) Intrathecal morphine (20 μg) blocked the formalin-evoked NK1r internalization. Notice the presence of a homogeneous cell membrane and the lack of NK₁-containing endosomes internalizing into the cytoplasm. (d) Sample image of a cell from the contralateral superficial dorsal horn of a saline-treated rat demonstrating the lack of NK1r internalization. Confocal images were taken using a × 63 objective with 5–10 optical sections along the z-axis separated by approximately 0.5 μm. Scale bar is 10 μm.