Novel And Specific Target For Schizophrenia-like Negative Symptoms

Schizophrenia is a kind of common psychosis with complex pathological mechanism,and negative symptoms in schizophrenia strongly contribute to poor functional outcomes.The mechanism of negative symptoms in schizophrenia is not clear and the current antipsychotic drugs are not highly-efficient or exclusive for the treatment of negative symptoms.Therefore,it is urgent to clarify the pathogenesis of negative symptoms in schizophrenia and search for effective and precise drug targets.Previous studies have found that histamine H₁ receptor?H₁R?is related to the occurrence of schizophrenia and there is a cell-specific regulatory role of H₁R in the brain.Thence,we deleted H₁R in different neurons by using Cre/Loxp technology and evaluated a variety of schizophrenia related behaviors,such as motor function,social behavior,learning and memory.Then schizophrenia patient brain samples were used to determine the role of histamine H₁R in cholinergic neurons in the occurrence of schizophrenia negative symptoms.Further,the role of H₁R in different neurons in the process of schizophrenia and its neural loop mechanism were studied by viral H₁R-overexpression or chemical genetics combined with electrophysiology,microdialysis,western blotting and other technologies.Here,we found that deletion of the Hrh1 in cholinergic neurons(ChAT-Cre;Hrh1^fl/fl)resulted in behavioral deficits related to negative symptoms in schizophrenia,including abnormal social behaviors and anhedonia,as well as impaired prepulse inhibition?PPI?,cognitive impairment and anxiety-like behavior,without hyperlocomotion linked to the positive symptoms.The deficits in sensorimotor gating can be rescued by both the typical and atypical antipsychotics,while the deficits in social interaction was only rescued by the atypical antipsychotics.However,deletion of the Hrh1 in neither glutamatergic(CaMKIIa-Cre;Hrh1^fl/fl)nor dopaminergic neurons(DAT-Cre;Hrh1^fl/fl)evoked such behavioral deficits.In addition,the expression of H₁R in BF cholinergic neurons was decreased in schizophrenia patients with negative symptoms,but not that with positive symptoms only.These results implicate that H₁R in cholinergic neurons,rather than dopaminergic or glutamatergic neurons,may be involved in pathogenesis of schizophrenia including negative symptoms.Further,we found that deletion of H₁R in cholinergic neurons selectively induces dysfunction of cholinergic neurons in the BF and excitation/inhibition imbalance in the PFC,including decreased ChAT expression,acetylcholine content and excitability of cholinergic neurons in BF,reduced ChAT expression and extracellular Ach content in PFC,which could be the underlying mechanism for the behavioral deficits observed here.Moreover,the reduced expression of ChAT and excitability of cholinergic neurons in the BF can be rescued by a chronic treatment of risperidone.The sEPSC charge transfer of mPFC layer 2/3 pyramidal cells was unchanged while the sIPSC charge transfer was robustly decreased in ChAT-Cre;Hrh1^fl/fl mice,leading to an increased sEPSC/sIPSC charge ransfer ratio,which can also be reversed by a treatment of risperidone.The decrease of sIPSC and increase of sEPSC/sIPSC charge transfer ratio were also observed in pyramidal cells in layer 5,although the alteration was less prominent compared with that in layer 2/3.These results indicate that deletion of H₁R in cholinergic neurons selectively induces dysfunction of cholinergic neurons in the BF,a subsequent decrease in Ach release,and excitation/inhibition imbalance in the mPFC,which could be the underlying mechanism for the behavioral deficits observed here.To further prove the mechanism,we found that the behavioral deficits of ChAT-Cre;Hrh1^fl/fll/fl mice can be rescued by re-expressing H₁R in cholinergic neurons in the BF rather than caudate putamen,indicating that loss of function of histamine H₁R in BF rather than CPu cholinergic neurons is pivotal in the formation of the behavioral deficits seen in ChAT-Cre;Hrh1^fl/fll/fl mice.Moreover,the behavioral deficits of ChAT-Cre;Hrh1^fl/fll/fl mice can be rescued by chemogenetic activation of BF cholinergic neurons or mPFC projection.These results indicate that the dysfunction of BF cholinergic neurons,in particular with their projections to the mPFC,contributes to sensorimotor gating ability deficit,social impairments and anhedonia induced by the deletion of H₁R in cholinergic neurons.However,direct chemogenetic inhibition of BF cholinergic neurons not only produced such behavioral deficits related to negative symptoms,but also increased the susceptibility of experimental mice to hyperlocomotion induced by MK-801.Although the sEPSC/sIPSC charge transfer ratio in mPFC layer 2/3 pyramidal cells was also increased after chemogenetic inhibition of cholinergic neurons,the charge transfer in sEPSC and sIPSC displayed different pattern of alterations compared with that in ChAT-Cre;Hrh1^fl/fl mice,as sEPSC charge transfer was increased while the sIPSC charge transfer was unchanged.These findings further support the proposal that histamine H₁R-dependent inhibition of BF cholinergic neurons,but not direct inhibition of cholinergic neurons,may be specifically involved in the behavioral deficits related to negative symptoms in schizophrenia.Furthermore,over-expression of H₁R in cholinergic neurons in the BF selectively rescued the behavioral deficits related to negative symptoms,except hyperlocomotion,in MK-801-induced schizophrenia models.These findings provide a foundation for development of therapeutic treatments for negative symptoms in schizophrenia using the H₁R in cholinergic neurons as a target.Taken together,our study shows that deletion of Hrh1 in cholinergic rather than dopaminergic or glutamatergic neurons resulted in functional deficiency of cholinergic projections from the BF to mPFC and in the formation of behavioral deficits.Our results suggest that histamine H₁R in cholinergic neurons could serve as a novel and selective therapeutic target and ChAT-Cre;Hrh1^fl/fl mice could be a new animal model with specific negative symptoms of schizophrenia given that functional deficiency of this receptor in BF cholinergic neurons is crucial for the pathogenesis of negative symptoms in schizophrenia.