Changes of astrocytes following noxious oro-facial stimulation

Objectives: It has been reported that substance P (SP)- and calcitonin gene-related peptide (CGRP)-positive nerve endings increased in the lamiae I and II of the spinal trigeminal nucleus caudalis (Sp5C), which receive noxious stimulation from the oro-facial region. However, very few studies are available on the changes shown in astrocytes following noxious stimulation from the oro-facial region. In the present study, we examined those changes using immunohistochemical methods. In addition, double-labeling immunofluorescence was employed to investigate the morphological interrelationship between the astrocytes the nerve endings. Methods: 100 microliters of 10 % formalin was injected into the subcutaneous layer in the left oro-facial region (10 mm outside from the angle of mouth) of six Male Wistar rats. After the preparation of the serial cryostat sections (30 micrometers thickness), glial fibrillary acidic protein (GFAP) immunohistochemistry was employed for the identification of astrocytes, and SP, CGRP immunohistochemistry for that of nerve endings in the Sp5C. In every section of the Sp5C, the left sides were used as the experiment group (EG), and the right sides as the control group (CG). After the immunoreaction under the same conditions, we compared and examined the immunoreactivity in the EG and the CG. We also employed double-labeling immunofluorescence for the GFAP / SP and GFAP /CGRP . Results: Many GFAP-positive astrocytes and SP- and CGRP-positive nerve endings were observed in the lamiae I and II of the Sp5C. In the lamiae I and II of the EG, the GFAP-positive reaction demonstrated an increase, compared with that of the CG. Moreover, GFAP-positive reactions were observed in the regions where the SP- and CGRP-positive nerve endings existed. Conclusions: The results obtained in the present study indicated that astrocytes might play some roles in the signal transduction of noxious information from the oro-facial region.