Modulation And The Mechanism On AMPAkine And Ketamine In Prelimbic-Prefrontal Cortex Of Rats With Pain And Aversion

Objective: Firstly,the relevance of persistent pain and aversion to the activity of Prelimbic-Prefrontal Cortex(PL-PFC)neurons in rats was investigated.Next,the effect on AMPAkine and Ketamine in PL-PFC neurons of rats with persistent pain and aversion was observed.Finally,the mechanism of antinociceptive and anti-pain aversive emotion effects of AMPAkine and Ketamine was elucidated.Methods:1.Silicon probes or Optrodes were implanted in the PL-PFC for in vivo recording of neuronal spike activities in response to peripheral noxious(pin prick)or non-noxious(v F filaments)stimuli from freely moving Sprague-Dawley rats.The impact of persistent neuropathic pain induced by a spared nerve injury(SNI)model was evaluated by basal and peak firing rates extracted from each individual neuron’s perievent time histograms.2.GRIN lens was implanted in the PL-PFC for recording neural calcium activity in freely-behaving rats in response to either a noxious or non-noxious peripheral stimulus.The impact of pain aversive emotion was induced by inflammatory pain and was confirmed by Conditioned Place Aversion test.Also this is a verification of electrophysiology results.3.By systemic administration of a well-established AMPAkine(CX546)or control DMSO,we studied how the PL-PFC neuronal abnormality in the persistent pain state was rescued.4.By systemic administration of Ketamine or control saline,we studied how the PL-PFC neuronal calcium activity changes in the pain aversive state was rescued.5.We compared the persistent pain relief effects between systemic and intracranial administration of CX546 through mechanical allodynia and cold allodynia tests.Furthermore,optogenetic and pharmacological modulations of the PL-PFC neurons were used to verify whether CX546 could target AMPA receptors in the PL-PFC to relieve pain.6.Classic CPA test was used to observe the anti-aversive effects of Ketamine.Optogenetic and pharmacological modulations of the PL-PFC neurons were used to verify whether Ketamine could work in NMDA receptors of the PL-PFC to relieve pain-aversion.Finally,we calculated betweenness centrality and degree centrality as graph-network statistics to evaluate the importance of pain-responsive neurons in the flow of nociceptive information within pyramidal neurons of the PL-PFC.We compared the functional connectivity in PL-PFC neurons before and after injecting Ketamine in pain aversive rats.7.Results were given as mean ± SEM.For unpaired data,a Mann Whitney test was used.For paired data,a Wilcoxon matched-pairs signed rank test was used.To analyze the neuron population changes for pain response,a Fisher’s exact test was used.For all tests,a P value < 0.05 was considered statistically significant.Results:1.Neurons in the PL-PFC increase their firing rates in response to noxious stimulations,P < 0.05;persistent pain,however,suppresses this cortical pain response,P<0.05.2.Neurons in the PL-PFC increase their calcium fluorescence in response to noxious stimulations,P<0.05;persistent pain will induce pain aversive emotion and will suppresses this cortical pain response,P<0.05.3.CX546 restores the peak firing rats of PL-PFC neurons in persistent pain rats,P<0.05.4.Ketamine restores the calcium activity of PL-PFC neurons in pain-aversive rats,P<0.05.5.Both systemic administration and direct delivery of CX546 into the PL-PFC inhibited symptoms of persistent pain,P>0.05.after administered CX546,the 50%withdrawal threshold increased and the cold allodynia score decreased,P<0.05.Optogenetic inactivation of the PL-PFC neurons blocked the anti-nociceptive effects of CX546,P<0.05.6.Administration of AMPA receptor antagonists NBQX in PL-PFC blocked the anti-nociceptive effects of CX546,P<0.05.7.Ketamine restored the endogenous nociceptive response in the PL-PFC and produced anti-aversive effects,P<0.05.8.Blocking PL-PFC using optogenetics removed the anti-aversive effects of ketamine,P<0.05.NMDA receptors blocker AP5 in the PL-PFC removed painaversion in CFA-treated rats,P<0.05.Blocking PL-PFC using optogenetics or m TORC1 blocker Rapamycin infusion,however,removed the anti-aversive effects of ketamine,P<0.05.9.The stable resting-state functional connectivity between pain-responsive neurons and other neurons can be seen in na(?)ve rats.Persistent pain reduced interneuronal communication within the PL-PFC,P<0.05.Ketamine,however,can restore the functional connectivity,P<0.05.Conclusion:In this study,we have shown that the relevance of persistent pain and aversion to the activity of PL-PFC neurons is extremely strong in rats.Persistent pain suppresses the firing rates of PL-PFC neurons and the pain-aversive emotion suppresses the calcium fluorescence of PL-PFC neurons.AMPAkines can restore anti-nociceptive regulatory function of neurons in the PL-PFC to produce analgesic effects in persistent pain states.The molecular mechanism might be the activation of AMPA receptors in the PL-PFC to relieve persistent pain.Ketamine restores the calcium activity of PL-PFC neurons in pain-aversive rats and produced anti-aversive effects.The molecular mechanism might be that NMDA receptor blockade mediated by ketamine induces the activation of m TORC1,which increases local translation of synaptic proteins specifically in the PL-PFC to produce top-down control.Persistent pain reduced inter-neuronal communication within the PL-PFC,Ketamine restores the functional connectivity among PL-PFC neurons to produce anti-aversive effects.