| Psychological stress is a sense of urgency caused by too large pressure and high degree of tension in dangerous or sudden situation.Due to the intense social competition and the increasing pressure of life,people are often exposed to various stressors.Since the body itself can’t overcome the high intensity and long-term psychological stress,there are high incidences of psychological stress-related diseases.The study of psychological stress-related diseases is becoming one of the common concerns of scholars today.Previous studies results of our group showed that psychological stress can lead to changes in the structure and function of the rat’s jaw muscles,and proved that the sensory sensitivity of the oral and maxillofacial muscles increased after the psychological stress.However,the neurological mechanism of the increased oral nerve pain caused by psychological stress has rarely been studied.Trigeminal ganglion(TG)plays an important role in the transmission of the oral and maxillofacial sensory information.When oral and maxillofacial regions are nociceptically stimulated,the TG transmits the information to the brainstem,and then projects the data into the central neural system(CNS).The spinal trigeminal nucleus caudal subnucleus(Vc)located in the brainstem is particularly important for the transmission of maxillofacial pain information.It not only can integrate the information transmitted from the maxillofacial area,but also is the “gate” of the pain transmission to the CNS.According to the traditional view,the neurons in the nervous system are responsible for the transfer of information.And the glial cells are responsible for neuronal nutrition,support and cell metabolism.In recent years,more and more studies have confirmed that glial cells are also involved in the integration and regulation of neurological information,and participate in the occurrence and conduction of multiple types of pain.So,it is not yet fully clear that whether the activation of glial cells play a role in the masticatory muscle pain caused by psychological stress.Therefore,based on our previous study,the aim of this study is to explore the role of glial cells in the masticatory muscle pain caused by psychological stress,and to further explore the central mechanism and to lay the experimental basis of psychological stress related oral and maxillofacial pain.This study is divided into three parts: Part 1: The establishment of psychological stress model and the effect psychological stress on the masseter mechanical sensitivity40 SD rats were randomly divided into control group,restraint stress 3d group,7d group and 14 d group.Rats in the stress group were treated with restraint stress for 3d,7d,14 d,8h per day.When the last stress finished,the body weight,serological hormone test,behavior test and masseter mechanical sensitivity were measured.The pain threshold was measured by Von Frey fiber filament in the control group and each experimental group before stress(as baseline)and at the time points of 1 d,3d,7d and 14 d after restraint stress.The results showed that the body weight of stress rats was significantly lower than that of the control group.Serum corticosterone and adrenocorticotropic hormone levels were significantly increased;the behavioral changes were significantly changed.With the prolongation of stress time,the threshold of masseter muscle pain was decreased,that is,the pain sensitivity gradually increased.Therefore,the experimental results confirmed that restraint stress can cause a psychological stress state in rats,and lead to increased rat masseter muscle pain sensitivity.Part 2: The role of glial cells in the trigeminal ganglion in masseter hyperalgesia induced by psychological stress in ratsThe second part is divided into two experiments.In the first experiment,immunofluorescence staining was used to detect the expression of glial fibrillary acidic protein(GFAP)and the substance P(SP)in the satellite glial cells of the trigeminal ganglion after stress.The results showed that the number of GFAP-positive glial cells,fluorescence intensity and SP-positive neurons increased gradually with the prolongation of stress time,and the expression was significantly higher than that of the control group at 14 days.In order to further investigate the role of glial cells in this process,in the second experiment,we injected the rats with glial cell inhibitor L-α-aminoadipate(LAA)while giving stress.The results showed that the expression of interleukin-1β(IL-1β)and its receptor IL1-R1 was significantly increased in the trigeminal ganglion after stress,while the increased expression was significantly inhibited.The overexpression of SP in neurons after stress was also significantly inhibited.Moreover,the sensory sensitivity of the rats in the inhibitor group was also significantly lower than that in the stress group.The results suggest that psychological stress leads to the activation of satellite glial cells in the trigeminal ganglion and may be involved in psychological stress-induced masseter sensory sensation through IL-1β paracrine and IL1-RI up-regulation.Part 3: The role of glial cells in the spinal trigeminal nucleus caudal subnucleus in masseter hyperalgesia induced by psychological stress in ratsThe third part is divided into two experiments.In the first experiment,we observed the expression astrocytes and microglia activation markers GFAP and ionized calcium binding adaptor molecule-1(Iba-1)in the spinal trigeminal nucleus caudal subnucleus(Vc).The results showed that the expression of GFAP in Vc was significantly increased after stress,but the expression of Iba-1 did not change significantly.It indicated that astrocytes rather than microglia involved in the masseter hyperalgesia induced by psychological stress.In order to further explore the mechanism of involvement of astrocytes,in the second experiment,we gave astrocyte activation inhibitor LAA,and found that changed rat behavior,elevated masseter muscle sensory sensitivity induced by stress was effectively reversed.Furthermore,inhibition of astrocyte activation in Vc can block upregulation of IL-1β and NMDAR after chronic restraint stress.Therefore,we conclude that the activation of astrocytes in Vc caused by chronic restraint stress can release excess IL-1β,which in turn promotes NMDAR phosphorylation,leading to increased pain sensation of masseter muscle.Conclusion: 1.The psychological stress model in rats can be effectively established by restraint stress;psychological stress can lead to hyperalgesia of rat masseter muscle.2.Psychological stress leads to the activation of satellite glial cells in the trigeminal ganglion and may promote neuronal activation through IL-1β paracrine and IL1-RI up-regulation mechanisms,which are involved in process of masseter hyperalgesia induced by psychological stress.3.Psychological stress can cause the activation of astrocytes in Vc,which may lead to the release of excess IL-1β,promote NMDAR phosphorylation,and participate in the process of masseter hyperalgesia induced by psychological stress. |
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