Spinal release of the amino acids with a time course in a rat model of postoperative pain

摘要

＜正＞ Background The mechanisms underlying postoperative pain remain unclear.Neurotransmitters of excitatory andinhibitory amino acids play an important role in the transmission and modulation of pain in the spinal dorsal horn.Thisstudy aimed to investigate the changes of release of excitatory and inhibitory amino acids in the spinal cord duringpostoperative pain and to provide a novel theoretical basis for postoperative pain management.Methods Loop microdialysis catheters were implanted subarachnoidally via the atlanto-occipital membrane in 16healthy Sprague-Dawley rats.All rats without neural deficits were divided into two groups,Group A and Group B,following 5 days of recovery.The tubes for microdialysis were connected and 25 μl microdialysate sample for baselinevalue was collected after one-hour washout in each rat.A plantar incision in the right hind paws of rats in Group A wereperformed under 1.2% isoflurane.All rats in Group B were only anesthetized by 1.2% isoflurane for the same duration.The microdialysate samples were collected at 3 hours,1 day,2 days and 3 days after the incision（or isofluraneanesthesia in Group B）in both groups.The cumulative pain scores were also assessed at the above time-points.Theamino acids in the microdialysate samples were tested using high performance liquid chromatography.Results Within Group A,the release of aspartate and glutamate at 3 hours after the incision was significantly higherthan the baseline values and the release of glycine at 1 day after the incision significantly increased compared with thebaseline values（P＜0.01）.Within Group B,the release of neurotransmitters at each time point had no significantdifference compared with the baseline values（P＞0.05）.The release of aspartate and glutamate at 3 hours after theincision in Group A was significantly higher than that in Group B（P＜0.01）.The release of glycine at 1 day after theincision in Group A significantly increased compared with Group B（P＜0.01）.The cumulative pain scores at 3 hours,1day and 2 days after the incision in Group A were significantly higher than those in Group B（P＜0.01）.Conclusions The release of the excitatory amino acids occurs in the early phase of postoperative pain and might notbe involved in the maintenance of pain in a rat model of incision pain.The release of inhibitory glycine lagged behind theexcitatory amino acids.The implication of inhibitory glycine release remained to be established further.