Effect of Restraint Stress on Pain Sensitivity, Spinal Trigeminal Nucleus Neurons, and Astrocytes in the Masseter Area of Rats

Abstract

To explore the changes of pain sensitivity (PS) in the masseter area (MA) in the rat model of psychological stress and the mechanism of action between spinal nucleus neurons and astrocytes in the trigeminal ganglion. The 40 Sprague-Dawley rats were randomly divided into control group (no treatment), group A (restraint stress (RS) 1 d), group B (RS 7 d), and group C (RS 14 d). The body weight growth rates (WGR) of rats in each group were compared and the difference of CORT and ACTH in serum was analyzed by ELISA. The open field test and the elevated “cross” maze test were adopted to detect the behavioral changes of rats. Finally, pain threshold of the MA in rats, the activation amount of brain tissue medulla oblongata parts astrocytes markers Glial fibrillary acidic protein (GFAP), and the protein expression of IL-1β and IL-1RI were detected. The results showed the WGR at 7 d and 14 d was greatly lower than control group ( $P<0.01$ ). In addition, the activity level and serum CORT and ACTH levels AND mean pain threshold in the MA of groups B and C were greatly lower than control group ( $P<0.05$ ). The activation rate of GFRP in group C ( $P<0.01$ ) and the protein expression of IL-1β and IL-1RI ( $P<0.05$ ) in rat trigeminal ganglion astrocytes of groups B and C was greatly higher than control group, indicating the increase of RS time, the release of IL-1β and IL-1RI can activate neurons and astrocytes in spinal trigeminal nucleus (STN) nerve and increase the PS of the MA.