Fig 1.
Photomicrographs of immunohistochemical labeling for tyrosine hydroxylase (TH) and histological analysis.
(A) Photomicrographs of immunohistochemical labeling for TH of the striatum and substantia nigra (SN). TH immunoreactivity was visualized in sections using diaminobenzidine tetrahydrochloride (DAB). Immunoreactivity for TH was high in the bilateral striatum and SN in sham rats with bilateral saline administration into the medial forebrain bundle (MFB). Rats with bilateral 6-OHDA administration into the MFB indicated a striking reduction in TH immunoreactivity in the striatum and SN on both sides. Scale bar stands for 1mm. (B) Photomicrographs of the SN pars compacta (pc) cells. TH–immunoreactive (TH-IR) cells visualized with diaminobenzidine tetrahydrochloride (DAB) and cells stained with cresyl violet (TH-negative cells) in the SNpc were found in sham rats and 6-OHDA rats. Scale bar stands for 100 μm. (C) The total number of TH-IR cells in the SNpc (mean ± SEM, ***p < 0.001). The number of TH-IR cells in 6-OHDA rats without formalin administration was significantly lower than that of sham rats. The number of TH-IR cells in 6-OHDA rats with formalin administration was significantly lower than that of sham rats. (D) The total number of TH-negative cells in the SNpc (mean ± SEM). No significant difference was found between the number of TH-negative cells of 6-OHDA rats and that of sham rats with and without formalin administration.
Fig 2.
Number of face rubbing behaviors induced by subcutaneous formalin injection into the vibrissa pad.
(A) The number of face rubbing behaviors per 5 min (mean ± SEM) of both groups. Subcutaneous formalin administration induced a two-phase increase in face rubbing behavior. (B) The number of face rubbing behaviors in the first phase (0–5 min) and second phase (10–60 min) (mean ± SEM). The number of face rubbing behaviors of rats with bilateral 6-OHDA administration did not change significantly compared with that of rats with bilateral saline administration in both phases (Fig. 2B).
Fig 3.
Immunohistochemical labeling for c-Fos in the trigeminal spinal subnucleus caudalis (Vc) induced by subcutaneous formalin administration into the vibrissa pad.
(A) Photomicrographs of c-Fos–immunoreactive (c-Fos-IR) cells in the Vc. Immunoreactivity of c-Fos was visualized in sections using DAB. In rats with bilateral 6-OHDA or saline administration that received subcutaneous formalin administration, c-Fos-IR cells were found mostly in the superficial layers of the Vc. Scale bar stands for 200 μm. (B) Significantly increased number of c-Fos-IR cells were found in 6-OHDA rats with subcutaneous formalin administration compared with sham rats with formalin administration (mean ± SEM, **p < 0.01). In the groups without formalin administration, 6-OHDA rats showed no significant change in the number of c-Fos-IR cells compared with sham rats.
Fig 4.
Immunohistochemical labeling for c-Fos in the PVN.
(A) Photomicrographs of c-Fos–immunoreactive (c-Fos-IR) cells in the PVN. DAB was used for visualizing c-Fos immunoreactivity. 3V: third ventricle, dp: dorsal parvicellular, mp: medial parvicellular, vp: ventral parvicellular, pm: posterior magnocellular. Scale bar stands for 100 μm. (B) The total number of c-Fos-IR cells in the PVN (mean ± SEM, ***p < 0.001). No significant difference was found in the total number of c-Fos-IR cells in the PVN between 6-OHDA rats without formalin administration and sham rats without formalin administration. The total number of c-Fos-IR cells in the PVN of 6-OHDA rats with formalin administration was significantly lower than that of sham rats with formalin administration.