Fig. (4) Metabotropic Glutamate Receptor 4 (mGluR4) Immunostaining: PAG: (left) Representative images of mGluR4 immunohistochemical images for Sham (A) and NP-treated (B) 4 weeks after surgery (dark spots represent positive staining; scale bar = 100 µm). Expression level of mGluR4 in the PAG did not vary in sham or NP-treated animals. RN: Expression level of mGluR4 in the RN did not vary in sham or NP-treated animals. Data are presented as mean ± standard deviation.