Electrophysiology Analysis Of Formalin Pain Rats And Preliminary Study Of DBS Analgesic Mechanism

Background:The two major unresolved issues in treating pain are the absence of objective monitoring methods and insufficient treatment for intractable pain. Early researches reported that noxious stimulus intensity and the intensity of neuropathic pain were associated with the spontaneous and induced firing activity of VPL neurons. However, the relationship between the intensity of nociceptive pain and spontaneous firing activity of neurons is unclear. One of the objectives of this study was to looking into the relationship between the intensity of nociceptive pain and spontaneous firing activity of neurons, decoding nociceptive pain intensity, to lay a foundation for discovering objective monitoring methods of pain. Another objective of this study was to explore the efficiency and mechanism of the new treatment for pain--DBS, by study the electrophysiology characteristics of neurons.Methods:Randomly assigned healthy SD rats into saline control group, formalin acute pain group and DBS group(including PAG combined with VPL stimulation group, PAG stimulation group and VPL stimulation group).Monitoring and stimulation electrodes were implanted into brain with stereotaxic apparatus-assisted. After7days of recovery from implantation surgery, we monitored the electrophysiology characteristics of VPL neurons and the licking pain behavior. Results:1. Acute inflammatory pain was induced by formalin, and electrophysiology activity of VPL neurons was changed at the same time. Spontaneous firing rates of VPL neurons showed two phase change, which was consistent with pain intensity. What’s more, they had a positive correlation. We surveyed the first5minutes after injection of formalin, compared with saline control group, the number of burst events and the percentage of spikes in burst of VPL neurons in formalin pain group rats were increased significantly, whereas changes in the opposite direction were noted for mean interburst time values.2. The time of licking behavior was decreased significantly in rats with DBS compared to those in formalin rats. Meanwhile, DBS reversed the abnormal electrophysiological changes induced by formalin.Conclusion:VPL neurons participate in the encoding of acute pain intensity, the spontaneous firing rates and the patterns of burst firing of neurons have relationship with acute pain intensity.