The Effect And Mechanism Of Short-Chain Fatty Acids On Ameliorating Cognitive Impairment Induced By Chronic Postoperative Pain In Rats

Objective: To investigate the differences of gut microbiota and synaptic transmission in Chronic postsurgical pain(CPSP)rats with and without cognitive dysfunction and to further explore the impact of SCFAs on chronic pain-induced cognitive impairment and underlying mechanisms in CPSP rats.Methods: Male SD rats(age: 6 weeks)were used to induce a rat model of CPSP by a skin/muscle incision and retraction(SMIR).According to our hierarchical clustering analysis of the cognitive behavior,the CPSP rats were divided into cognitively compromised pain rats and cognitively normal pain rats.16 S rRNA analysis and feces microbiota transplantation(FMT)were used to explore the differences in the alteration of gut microbiota and to investigate the causal relationship between cognitive-behavioral and bacteria composition.Then,PET-CT,clamp-patch,molecular biological techniques,and transmission electron microscopy were used to explore the differences of synaptic transmission from the mPFC,hippocampal CA1,and CeA neurons in CPSP rats with and without cognitive dysfunction.Next,CPSP rats were given acetate and butyrate supplements to test whether SCFAs administration decreased the occurrence of cognitive impairment in the CPSP rats.Histone acetylation assessed by western blot and miniature postsynaptic currents recorded by patch-clamp were tested to verify the modulation of SCFAs supplementation on cognitively compromised pain rats.Results:(1)According to the clustering analysis of the cognitive behavior evaluation data,nearly two-thirds of the CPSP rats suffered cognitive impairment.The microbiome structure was considerably different between the cognitively impaired CPSP rats and cognitively normal CPSP rats after SMIR.The cognitively impaired CPSP rats had a reduced composition of gut SCFA-producing bacteria.What’s more,FMT from the cognitively impaired CPSP rats induced cognitive impairment behaviors and reshaped the gut microbiome.Similarly,the number of genera that generated SCFAs was decreased in the fecal samples from recipients of cognitive impairment microbiota.(2)Brain metabolic activity,spontaneous synaptic transmissions,synaptic transmission-related proteins,and the synapse ultrastructure differed significantly between the cognitively compromised pain rats and the cognitively normal pain rats.(3)Treatment with the SCFAs alleviated the cognitivebehavioral deficits in the CPSP rats,and SCFAs supplementation improved histone acetylation and synaptic deficits in the mPFC,CeA,and hippocampal CA1 area via the ACSS2-HDAC2 axis in the CPSP rats.Conclusions: 1.There are significant differences in gut microbiota composition between CPSP rats with and without cognitive impairment,and the gut SCFAs-producing microbiome may mediate pain-induced cognitive impairments;2.The synaptic transmission changes from the mPFC,CeA,and hippocampal CA1 neurons were strikingly different between the CPSP rats with and without cognitive impairment;3.SCFAs consumption may alleviate chronic postsurgical pain–induced cognitive deficits by improving histone acetylation and synaptic transmission in the mPFC,CeA,and hippocampal CA1 neurons via the ACSS2-HDAC2 axis.Part Ⅰ: Alterations of gut microbiota in CPSP rats with and without Cognitive ImpairmentObjective: To investigate the differences of gut microbiota in CPSP rats with and without cognitive impairment and to explore the role of SCFAs in chronic pain-induced cognitive impairment.Methods: Male SD rats(age: 6 weeks)were used to induce a rat model of CPSP by a SMIR。 According to the hierarchical clustering analysis of the cognitive behavior,the CPSP rats were divided into the su group(cognitively compromised pain rats)and the Uns group(cognitively normal pain rats).16 S rRNA analysis and feces microbiota transplantation(FMT)were used to explore the differences of gut microbiota in the su group and the Uns group and to investigate the causal relationship between cognitive-behavioral and bacteria composition.The concentrations of SCFAs were detected by gas chromatography.Results: Nearly two-thirds of the CPSP rats suffered cognitive impairment.The microbiome structure was considerably different between the su group and the Uns group after SMIR,and the su group had a reduced composition of gut SCFA-producing bacteria(P = 0.0032).Surprisingly,the su group had greater butyrate concentrations than the Sham rats.Then,FMT from the su group reshaped the gut microbiome and induced cognitive impairment behaviors(P = 0.0003).Similarly,the number of bacteria that generated SCFAs was decreased in the fecal samples from the recipients of su group microbiota.Conclusions: There are significant differences in gut microbiota composition between CPSP rats with and without cognitive impairment,and the gut SCFAs-producing microbiome may mediate pain-induced cognitive impairments.Part Ⅱ: Differential Synaptic Mechanism Underlying the Neuronal Modulation in Response to Chronic Postsurgical Pain with or without Cognitive Impairment in RatsObjective: To comprehensively investigate the differences of synaptic transmission in CPSP rats with and without cognitive impairment.Methods: According to the hierarchical clustering analysis of the cognitive behavior,the CPSP rats were divided into the Su group(cognitively compromised pain rats)and the Uns group(cognitively normal pain rats).PET-CT,clamp-patch,molecular biological techniques,and transmission electron microscopy were used to explore the differences of synaptic transmission in the Su group and the Uns group from the mPFC,CeA,and hippocampal CA1 neurons.Results: Brain metabolic activity differed significantly between the Su group and the Uns group;The whole-cell voltage-clamp recordings revealed that the neuronal excitability and synaptic transmission in the mPFC and CeA were enhanced in the Uns group,while these parameters remained the same in the Su group.Moreover,the neuronal excitability and synaptic transmission in CA1 neurons demonstrated the opposite trend.Correspondingly,the levels of synaptic transmission-related proteins demonstrated a tendency similar to that of the excitatory and inhibitory synaptic transmission;The length of postsynaptic density differed significantly between the Su group and the Uns group(mPFC: P = 0.02;CeA: P = 0.01;CA1: P = 0.0005).Conclusions: The synaptic transmission changes from the mPFC,CeA,and hippocampal CA1 neurons were strikingly different between the CPSP rats with and without cognitive impairment.Part Ⅲ: SCFAs Ameliorate Chronic Postsurgical Pain–induced Cognition Impairment via the ACSS2?HDAC2 Axis in RatsObjective: To explore the impact of SCFAs on chronic pain-induced cognitive impairment and underlying mechanisms in rats.Methods: CPSP rats were given acetate and butyrate supplements to test whether SCFAs administration decreased the occurrence of cognitive impairment in the CPSP rats.Histone acetylation assessed by Western blot and miniature postsynaptic currents recorded by patchclamp were tested to verify the modulation of SCFAs supplementation on the cognitively compromised pain rats.Results: Treatment with the SCFAs alleviated the cognitive-behavioral deficits in the cognitively compromised pain rats(P = 0.0341),and considerably decreased the occurrence of cognitive impairment in the CPSP rats(SMIR rats: 72.22%,SMIR rats with acetate: 54.55%,SMIR rats with butyrate: 45.46%,SMIR rats with acetate and butyrate: 20%).In addition,SCFAs supplementation improved histone acetylation in the mPFC,CeA,and hippocampal CA1 area via the ACSS2-HDAC2 axis in the CPSP rats;Similarly,SCFAs supplementation improved synaptic deficits in the mPFC,CeA,and hippocampal CA1 area in the CPSP rats.Conclusions: SCFAs consumption alleviates chronic postsurgical pain–induced cognitive impairment by improving histone acetylation and synaptic transmission via the ACSS2-HDAC2 axis in the mPFC,CeA,and hippocampal CA1.