DCA3?LS?PFN Circuit Mediates And Regulates Social Avoidance Behavior Of Mice

Part ? Effect and mechanism of dCA3 CaMKII?neurons on regulating social avoidance behavior of miceObjective:Dorsal hippocampal CA3(dCA3)plays an important role in the regulation of fear memory and social behavior,and the CaMKII?neurons in dCA3 are considered to be involved in the regulation of multiple behaviors.At the same time,these neurons have been shown to be sensitive and adaptive to chronic stress.Whether these neurons are involved in social avoidance induced by chronic stress remains unclear.In this part,the regulation of CaMKII?neurons on social avoidance behavior in dCA3 was studied by using the chronic social defeat stress(CSDS),subthreshold social defeat stress(SSDS).Methods:CSDS paradigm was utilized to induce social avoidance behavior in mice;the social avoidance behaviors,such as avoidance motivation(the speed of avoidance),numbers and ratio,were assessed with social interaction test(SIT).Three-chamber test was used to measure the social preferences of mice.The open-field test(OFT)and tail suspension test(TST)were employed to test the locomotion activity and anxiety-like behavior in mice.The c-Fos immunofluorescence technique was employed to detect the correlation between dCA3 and social behavior.The fiber photometry recording was used to detect real-time changes in dCA3 CaMKII?neurons in social behavior.We used patch-clamp technique to record the action potential of CaMKII?neurons in dCA3 of control and CSDS mice,respectively;To further demonstrate the regulatory role of CaMKII?neurons in social avoidance behavior in dCA3,we used chemical genetics to specifically regulate the excitation level of CaMKII?neurons in dCA3,and recorded the behavioral changes.RNA-seq technique was used to analyze the transcriptional histology of the dCA3 brain tissues of control and CSDS mice,and the results of histological analysis were verified by PCR technique.Results:(1)After CSDS treatment,susceptible mice showed significant avoidance behavior,enhanced social avoidance motivation level(avoidance speed),and significantly increased social avoidance number and ratio,indicating that chronic stress effectively causes social avoidance behavior in mice.However,SSDS did not directly affect the social function of mice.(2)With c-fos fluorescence,we found that the c-fos positive neurons of pyramidal cell layer in dCA3 was significantly increased in control group mice after exposure to unfamiliar mice,while dCA3 in CSDS group mice was not changed.(3)Using fiber photometry recording in dCA3,we observed persistent Ca²⁺transients that started immediately at the onset of targeting CD1 mouse and were sustained throughout the interaction process in control mice,while we observed no Ca²⁺transients that started immediately when the CSDS mice interacted with CD1 mouse.(4)In patch-clamp recording,we found that CSDS decreased the number of evoked action potentials in response to current(500 ms duration,0 to 350p A,50 p A steps)injections compared with control group.Consistent with this decreased neuronal excitability,we also observed an increased threshold to induce the first spike(rheobase)in response to current injections in CSDS group.(5)Using chemical genetics technology,the excitability of dCA3 CaMKII?neurons in control and CSDS mice were increased in social behavior tests.Meanwhile,we observed the increased social interaction time of mice,and the reversed social avoidance behavior induced by CSDS,indicating that the CaMKII?neurons in dCA3 could directly regulate social avoidance behavior.(6)RNA-seq histology showed that CSDS induced decreased expression of Kcna4 and the increased expression of Kcnj14 in dCA3 of mice,which led to a significant decrease in neuronal excitability.Conclusion:CSDS reduces the excitability of CaMKII?neurons in dCA3 to enhance the social avoidance behavior,which involved in the regulation of potassium channel.Increased the excitability of CaMKII?neurons in dCA3 improves social avoidance behavior of mice.Part ? Neural circuit mechanism of CaMKII? neurons of dCA3 in regulating social avoidance behavior of miceObjective: As the main functional neurons in dCA3,CaMKII? neurons play an important regulatory role in memory,fear and social functions by projecting to different brain regions.Previous studies have shown that lateral septum nucleus(LS)is the main projection site of CaMKII? neurons in dCA3,and LS has also been shown to be involved in the regulation of social behavior.LS projects downstream to Parvafox nucleus(PFN),which is considered to be involved in defensive behavior.Whether dCA3 regulates social avoidance depends on this circuit and the role of LS in social avoidance behavior are still unclear.In order to solve these problems,the dCA3?LS?PFN circuit was analyzed by using neuronal circuit tracing and optogenetics.This part investigates whether CaMKII? neurons in dCA3 regulates social avoidance behavior through this neural circuit.Methods: CSDS paradigm was utilized to induce social avoidance behavior in mice,and SSDS paradigm was utilized to study the sensitivity of social avoidance in mice.Using the technique of neuronal circuit tracing,we labeled dCA3 ? LS ? PFN neuronal circuit with adeno-associated virus.By using patch-clamp recording combined with optogenetics,the connectivity of the circuit was validated by recording the optical evoked excitatory postsynaptic current(e EPSC)and inhibitory postsynaptic current(e IPSC)downstream of the projection.By using optogenetics techniques,the excitability of neuronal circuits was regulated to investigate the effects on social avoidance behavior.Results:(1)dCA3 CaMKII? neurons had direct projections to LS,and they mainly projected to the GABAergic neurons in LS.(2)Optogenetic stimulation of dCA3 CaMKII??LS projection reversed the social avoidance induced by chronic stress and increased the social time,while inhibition of this projection induced social avoidance in SSDS mice.(3)GABAergic neurons in LS projected to PFN.(4)Optogenetic stimulation of LSGABA?PFN projection reversed social avoidance induced by chronic stress,while inhibition of LSGABA?PFN projection induced social avoidance in SSDS mice.(5)In PFN,Foxb1 positive neurons received the projections from the LSGABA neurons,and played an important role in the regulation of social avoidance.(6)Optogenetic stimulation of PFNFoxb1?l PAG projection promoted social avoidance and decreased social interaction?Conclusion: The dCA3 CaMKII? neurons regulate social avoidance behavior through the dCA3 CaMKII??LSGABA?PFN Foxb1?l PAG circuit.