Intra-RMTg DS injection reduces glutamic acid decarboxylase (GAD-67) and μ opioid receptor (MOR) immunoreactivity (IR) in the RMTg. Figure (A–C) and (D–F) shows representative photomicrographs of MOR- and GAD67-IR in coronal sections of the RMTg at the level of −6.72 mm from bregma on 34th day after intra-RMTg injection with vehicle, BS or DS. The statistical result of MOR and GAD67 IR cell quantification on 14th and 34th day of injection has been summarized in (G) and (H). *** p < 0.001, vs. either vehicle- or BS-treated rats (n = 5 rats in each group). cp, cerebral peduncle; IPN, interpeduncular nucleus; ml, medial lemniscus. Scale bar = 100 mm in F and 100 μm in f.