The Role Of TLR4Signaling In Postoperative Cognitive Deficits In Old Rats

Object:(1) discuss which has predominant effect on postoperative cognitive deficits between surgery and anesthesia by observing the change of behavior in aged rats after surgery;(2) explain the effects of TLR4signaling on postoperative cognitive deficits in aged rats by detecting and comparing the expression of TLR4and the key factors downstream before and after surgery and/or anesthesia.Method:(1) Part1:70female Sprague Dawley rats (22-23-month-old) were divided into7groups (n=10) randomly after6-day-training in Morris Water Maze. Rats in Group S1, S3and S7received splenectomy under2%isoflurane inhalation anesthesia for2hs; Group A1, A3and A7underwent2%isoflurane inhalation anesthesia for2hs only; Group Control inhaled mixed oxygen for2hs. Vital signs were monitored during surgery and/or anesthesia. Group S1and A1, Group S3and A3and Group S7and A7were killed on Day1,3and7after surgery/anesthesia respectively after reversal test. The platform was located in opposite zone in reversal test. Latency, distance and speed were recorded and analyzed.5of the rat’s brains in each group were acquired without any additional treatment and stored in liquid nitrogen, and the rest were stored in1%sodium azide solution after perfusion with4%paraformaldehyde solution.(2) Part2:locate TLR4and detect the expressions of TLR4, the downstream factors MyD88, TRIF, NF-κB and pro-inflammatory cytokines TNF-α, IL-1β and IL-6in hippocampal CA3area, by the way of immunohistochemistry, immunofluorescence, western blot and RT-PCR. Observe the neurons change in number and morphology in hippocampal CA3area by Nissl’s staining.Results:(1) The rats underwent splenectomy showed noticed prolonged latency and increased distance. This increasing in S1and S3was statistically significant. Although the rats received inhalation anesthesia showed prolonged latency and increased distance too, the degree and duration were apparently less than those in Group S.(2) In hippocampal CA3area, microglia was activated both after splenectomy and inhalation anesthesia, but the surgery-induced activation was more serious. Immunofluorescence technique was utilized to locate TLR4and found TLR4mainly expressed on microglia and neuron. Splenectomy lead to prominent high expression of TLR4both on microglia and neuron, and the peak appeared in Group S1. The increased expression was also significant in Group S3. Anesthesia-induce increased expression of TLR4was not so remarkable as that in Group S. The results of western blot and RT-PCR showed the same change as immunofluorescence. As downstream key factors in TLR4signaling, MyD88、TRIF and NF-κB showed parallel changes as TLR4, as well as pro-inflammatory factors TNF-α, IL-1β and IL-6. The number of neuron in hippocampal CA3area showed no significant change.Conclusion:(1) Both surgery and anesthesia result in cognitive deficits in aged rats, and surgery seems to play a more important role in this procedure.(2) TLR4signaling activates microglia to produce multiple pro-inflammatory cytokines, which lead to CNS inflammation and ultimately damage neurons. This is a possible mechanism of surgery-induced cognitive deficits in aged rats. Figures11, tables5, references106.