Acetylcholine And Nicotinic Acetylcholine Receptor Subtype Alpha 5 In MHB-IPN Circuit

Medial habenula(MHb),dominantly projecting to Interpeduncular(IPN),with stria medullaris(SM)and fasciculus retroflexus(FR),constitutes the dorsal diencephalic conduction(DDC)that relay the information from forebrain to metencephalon.Studies established the relationship between MHb-IPN pathway and psychiatric disorders,such as autism,schizophrenia,post-trauma stress disorder,though there's little evidence to distinguish the functions of subnucleus cell-type specificly.In this study,we combined molecular biology,transgenics,cytogenetics,pharmacogenetics and chemogentics to labeling,lesion,activation and inhibition of specific neurons in MHb-IPN and determined the behavioral functions.To determine the role of MHb subnucleus,we firstly constructed 6 knock out mouse lines of the genes highly expressing in MHb and conducted behavior tests to assess the effects on fear memory generation and extinction by Fear Conditioning Test.The results showed that the mice with genes CNNM2 and TSPAN18 in ventral MHb and gene CADPS2 in whole MHb knockout led to impaired fear memory extinction,whereas gene SYT6 in superior MHb knockout did not affect fear memory extinction,and the fear response of mice with genes TMEM176A/B and HCN3 in whole MHb knockout fell in between the two former groups,that is,higher fear response and same extinction rate.Specific Cholinergic neurons in ventral MHb lesion caused a prolonged fear memory extinction timecourse,and minor effect on fear memory extinction rate but enhanced fear response on training of dorsal MHb lesioned.Direct activation of IPN neurons by acetylcholine,glutmate and senktide accelerated fear memory extinction.Anatomy analysis also showed a afferent difference in BAC and LPO between CHAT-CRE and TAC2-CRE mice.Ventral MHb lesion showed a anxiolytic effect,decreased social interaction motivation,lowered adaptive capacity to environment,loss of odorant recognition,and impaired cognitive and spatial memory,but little impact on mice locomotion and reward-related behavior.RT-qPCR with dissected rats IPN and demonstrated a positive correlation between them,the higher the CHRNA5 mRNA level was,the more Nicotine rats consumed,and the CHRNA5 mRNA level per se did not up-regelated by the amount of nicotine consumed.To label and manipulate the CHRNA5 neurons in IPN,a transgenic Cre recombinase knockin rat line was constructed with CRISPR/Cas9 technology.IPN neurons could be activated by Nicotine both at low(0.5 mg/kg)and high(2.0 mg/kg)dose,but MHb neurons could be activated only by the higher dose.Chemogentics activation of IPN CHRNA5 neurons increase rats nicotine intake and inhibition of IPN CHRNA5 neurons caused a reduction of rats nicotine intake.In conclusion,MHb got involved in fear memory generation and extinction and affective behavior expression with specific subnucleus,and IPN CHRNA5 neurons regulated nicotine intake,which suggests new insights for related psychiatric disorders treatment and nicotine addiction control.