Basic Studies Of HPA Axis Dysfunction And Glucocorticoids Therapy In Traumatic Brain Injury

Backgrounds:The application of Glucocorticoids (GCs) in Traumatic Brain Injury (TBI) has been undergoing a long and tortuous process of over40years. High-dose GCs regimen went from being highly recommended to being totally denied, while current opinion goes to stress-dose GCs treatment. The application of GCs in TBI is embracing controversy and hope. Whether we should and how to use GCs to treat CNS injury, there is not yet a clear answer. Recently, many clinicians and researchers put extensive attention on the dysfunction of Hypothalamic-Pituitary-Adrenal axis (HPA axis). In-depth study of the pathogenesis of the HPA axis dysfunction after TBI, and of the impact of GCs on its dysfunction, will lay the foundation for the development of a reasonable GCs regimen.Objectives:(1) To study the impact of different types and doses of GCs on spatial learning and long-term retrograde memory after TBI. And to clarify the pathogenesis of GCs affecting cognitive function after TBI.(2) To study the functional change of HPA axis after TBI, and its relation with complication and prognosis.(3) To observe of the pathological changes of HPA axis, and to comprehensively study the pathogenesis of HPA axis dysfunction.(4) To study the impact of different doses of GCs on the HPA axis dysfunction and its pathological changes, to clarify the reason for high-dose GCs raising TBI mortality, and to explore the different role of GCs in the treatment of acute TBI with acute spinal cord injury.(5) To investigate the impact of stress-dose GCs on the angiogenesis in the peri-injury zone and the functional regeneration of Blood Brain Barrier, and to study the potential neural protection of stress-dose GCs in the treatment of acute TBI.Methods:(1) Experiment1:Rats were randomly allocated to Naive, Dexamethasone (DXM) Normal Treatment, Methylprednisolone (MP) Treatment, Injury Control, Low-dose DXM Treatment, Moderate-dose DXM Treatment, High-dose DXM Treatment, Low- dose MP Treatment, Moderate-dose MP Treatment, and High-dose MP Treatment group. Reference memory probe trials of Morris Water Maze test were performed on post-injury day7and day14, while TUNEL staining on post-injury24hr,48hr,1week, and2weeks.(2) Experiment2:Rats were randomly allocated to Naive, Sham, Injury Control, Saline Treatment, Moderate-dose DXM Treatment, and High-dose DXM Treatment. Spatial acquisition training of Morris Water Maze test was performed since post-injury day7, while Golgi staining and Sholl analysis on post-injury day7.(3) Experiment3:Rats were randomly allocated to TBI and sham group. The level of corticosterone (CORT) in the peripheral blood was assayed by ELISA before injury, on post-injury3hr.6hr,12hr,1day,2days,3days,7days and14days.(4) Experiment4:Rats were randomly allocated to Naive, Sham, and TBI group. Electrical Stimulation was performed on post-injury day7and14. The dynamic change of peripheral blood CORT was assayed by ELISA.(5) Experiment5:Rats were randomly allocated to Naive, MP Normal Treatment. Injury Control, Low-dose MP Treatment, and High-dose MP Treatment. Electrical Stimulation was performed7days before injury,7days after injury, and14days after injury. The dynamic change of CORT was assayed by ELISA. TUNEL staining and TEM were used to observe the pathological change of HPA axis.(6) Experiment6:Rats were randomly allocated to Naive, Injury Control. Non-injury MP Treatment, Pre-TBI MP Treatment, and Post-TBI MP Treatment. Endothelial progenitor cells (EPCs) in the peripheral blood were assayed by using Flow Cytometry to capture their membrane markers of CD34/CD133. Microvascular density was analyzed by CD34immunohistochemical staining, and the extent of brain edema and functional changes of blood-brain-barrier by examing Evans Blue tracer extravastation.Results:(1) The early application of high-dose GCs could aggravate neural apoptosis, apical and basal dendritic atrophy, causing the damage of neural connection network. This exacerbates spatial learning and long-term retrograde memory deficits. However, low-and moderate-dose of GCs do not have the same effect.(2) TBI could yield apoptosis of Hypothalamic CRF cells and pituitary ACTH cells, cause primary/secondary injury to HPA axis, lead to the dysfunction of HPA axis, and finally result in stress insufficiency and Critical Illness-Related Corticosteroid Insufficiency (CIRCI). If additional stresses (e.g. pneumonia, peptic ulcer) occur, HPA axis function fails and results in death.(3) The early application of high-dose GCs could aggravate the apoptosis of Hypothalamic CRF cells and pituitary ACTH cells, exacerbate HPA axis injury and dysfunction, and make stress insufficiency and CIRCI even worse. To some extent, it results in HPA axis failure and raise mortality after TBI. However, low-and moderate-dose GCs do not aggrieve HPA axis injury and dysfunction.(4) Stress-dose GCs could not only increase EPCs expression in the peripheral blood in the naive rats, but also further raise the expression level of EPCs in the injured rats. It could also increase microvascular density in the peri-injury zone, lessen the damage severity of blood-brain-barrier, and to mitigate cerebral edema.Conclusions:(1) TBI could cause neural apoptosis in hypothalamus and pituitary, lead to primary and secondary HPA axis injury, and result in HPA axis dysfunction.(2) HPA axis dysfunction is closely correlated with bad prognosis after TBI. If additional stresses occur at the critical moment, HPA axis fails and leads to stress insufficiency and CIRCI, which finally result in death.(3) The early application of high-dose glucocorticoids could aggravate HPA axis injury and dysfunction, consequently render the body impossible to survive additional stresses, and thus raise mortality. It also excacerbates the neural synapse network of hippocampus, and worsens spatial learning and long-term retrograde memory deficits. However, low-and moderate dose of glucocorticoids do not have the aforementioned adverse effects.(4) The early application of stress-dose glucocorticoids could increase EPCs expression in the peripheral blood, facilitate EPCs homing to the injured zone, increase the microvascular density in the peri-injury zone, repair injuryed blood-brain-barrier, lessen the severity of cerebral edema, and result in neural repair and protection effects.