| The first response of body to severe trauma is stress response, and the aim of it is to strengthen the resistance to the attack and resume the turbulence in the body. But the attack of severe trauma is so strong that the stress is usually in disorder. The main character of stress disorder is over excitation of hypothalamo-pituitary-adrenal axis (HPA axis) which could play an important role in the ignition and development of systemic inflammatory response syndrom (SIRS) and multiple organ dysfunction syndrom (MODS) partially resulted from immune inhibition, so it is important to explore the mechanisms of over excitation of HPA axis following severe trauma and control the over excitation of HPA axisBecause hippocamus are considered to be the prominent brain regions that are involved in the control of HPA axis activity under stress condition, over excitation of HPA axis may arise from changes of hippocampal function. In present, hippocampal N-methyl-D-aspartate (NMDA) receptors are thought to be involved in stress-induced alterations of brain function especially hippocampal function. We have hypothesized that changes of hippocampal NMDA receptors maybe responsible for the overexcitation of HPA axis. Acceding to this hypothesis, we applied 30% TBSA full thickness scalding (burn) as severe trauma stress disorder model. Using this model, we analyzed hippocampal NMDA receptor affinity, maximal binding capacity and channel property after burn with radio-ligand binding assay and cell-attached patch clamp technique, explored the roles of hippocampal NMDA receptors in thechanges of HPA axis activity after burn with in situ hybridization andliRIA(radio-immune assay), investigated the mechanisms for hippocampal NMDA receptors taking part in HPA axis over excitation with RT-PCR, western-blot and hippocampal microinjection. Moreover, we studied the mechanisms for hippocampal NMDA receptor activation after burn with immunoprecipitation+western-blot and RT-PCR. Our main results and conclusions are as follows:1. Changes of hippocampal NMDA receptor activity in burn ratsKd value of hippocampal NMDA receptor was decreased significantly in rats at 0.5h, Ih, 2h, 4h, 8h, 24h, and 48h after burn. The changes was most significant at 2h. Receptor maximal binding capacity (Bmax) was markedly elevated from Ih to 48h, especially at 2h. These results indicate that burn enhances NMDA receptor activity.Open-state probability of 35pS and lOOpS NMDA-receptor channels was increased markedly in all time-point burn group, with most significant change in 2h burn group. Open time of these channels was also increased in some burn groups. There was no significant change of NMDA receptor current amplitude and close time in each burn group, these results suggest that burn induces hyperactivation of hippocampal NMDA receptor.2. Effects of hippocampal NMDA receptor activation on HPA axis activity following burnSerum cortisol concentration and hypothalamus CRHmRNA levels were markedly elevated at 0.5h, Ih, 2h. 4h, 8h, 24h, and 48h after burn, especially at 2h. these results demonstrate that burn resulted in over excitation of HPA axis.The changing tendency of HPA axis activity was correlated with that of hippocampal NMDA receptor activity. This indicate that hippocampal NMDA receptor maybe related to hyperactivation of HPA axis following burn.Intrahippocampal microinjection of MK-801(an non-competitive NMDAreceptor antagonist) 6ug resulted in an significant decrease of Serum cortisolinconcentration and hypothalamus CRHmRNA level at 2h after burn, and microinjection of MK-801 12u?resulted in a more significant decrease of these values. This indicate that HPA axis activity is in some extent depend on hippocampal NMDA receptor activity after burn and demonstrate that activation of hippocampal NMDA receptor play a important role in over excitation of HPA axis following burn.In accordance with the results of microinjection of MK-801, Intrahippocampal microinjection of NMDA receptor antisense ol...
|
PDF Full Text Request