Figure 6. Heat- and mechanically-induced NK₁ receptor internalization in mice.

In mice, internalization of NK₁ receptors was induced by immersion of the right hindpaw for 38 seconds in a 49°C water bath or by applying (with calibrated forceps) a 200 g mechanical pressure on the right hindpaw, also for 38 seconds. Animals were perfused either without receiving any noxious stimulation (A), 10 minutes after receiving the noxious thermal (B) or the noxious mechanical (C) stimulation. Lamina I NK₁ receptor-immunoreactive neurons were observed by immunofluorescence. Confocal images showed that non stimulated animals present a cell-surface localization of NK₁ receptor labeling (A). Application of the thermal stimulus (B) or the mechanical pressure (C) both induces strong internalization of NK₁ receptors in the ipsilateral side of the lumbar segment of the spinal cord (D). **p < 0.01 and ***p < 0.001, one-way ANOVA with Bonferroni’s post hoc test. The numbers in parentheses represent the number of animals per group. Error bars indicate the Standard Error of the Mean (SEM). Scale bar: A, 30μm