Deciphering Contribution Of Hyper-excitabilities Of Corticothalamic Pyramidal Tract Neurons In MPFC To Increased Aggressivity Of 3xTg Model Of Alzheimer’s Disease

OBJECTIVE:Alzheimer’s Disease（AD）is clinically characterized by the presence of neurological and neuropsychiatric symptoms.Neuropsychiatric symptoms occur in up to 80%of patients with Alzheimer’s disease（AD）.Even during mild cognitive impairment（MCI）,about half of patients develop at least one neuropsychiatric symptom,of which rhythm disorders,irritability,social apathy,auditory hallucinations,and depression and anxiety are most common.AD patients with neuropsychiatric symptoms tend to have a more rapid decline in cognition compared to that of without neuropsychiatric problems.Hence,understanding the mechanism of neuropsychiatric symptoms of AD and finding effective mitigation and treatment measures not only provides a basis for the treatment of AD,but also greatly reduces the personnel and social pressure caused by AD.The medial prefrontal cortex（PFC）plays a key role in a variety of important neural processes,including cognition,mood regulation,and sensory gating.Pyramidal neurons in the fifth layer of PFC are divided into pyramidal tract（PT）and intratelencephalic（IT）neurons according to the projection brain region,both of which project to the telencephalon.In addition,PT neurons also project to outside the telencephalon,such as thalamus,superior thalamus,medulla oblongata,pons.Pathological changes in PT neurons but not IT neurons with a significant decrease in excitability and a weakening of excitability transmission have been found in mouse models of AD.Disturbance toγ-oscillations is one of the important manifestations of neurological diseases such as AD.PT neurons play a more important role inγ-oscillations than IT neurons.Notably,compared with IT neurons,the types of PT neurons are more diverse,and the single-cell RNA sequencing results show that PT neurons can be divided into two populations according to molecular markers,which not only have large differences in gene expression,but also have different electrophysiological characteristics and projection ranges.Nevertheless,whether these two types of neurons play different roles in AD neuropsychiatric symptoms remains elusive.In this study,Using retrograde AAV,whole-cell recording,chemical genetics,single-cell quantitative PCR,immunofluorescence,and gene overexpression,we investigated the electrophysiological abnormalities of two types of PT neurons,and dicephered the molecular basis of abnormal PT_A-type neurons.METHODS:In this study,wild type and 3x Tg model were used for animal objectives.（1）The social behavior test and the resident-intruder test were used to observe the aggressive behaviors of mice;（2）Using electrophysiological characteristics or retrograde AAV,PT neurons and subtypes of PT neurons were well defined,and the intrinsic excitability of each neuronal type was recorded;（3）Regualtion of PT_A-type neuron activities by h M3Dq or h M4Di led to change the aggressive behaviors of mice;（4）single-cell q PCR and immunofluorescence were used to quantitative analysis of Kv6.3 m RNA and protein levels in PT_A-type neurons;（5）Restoring Kv6.3 in PTA-type neurons of 3x Tg mice was employed to observe whether the electrophysiological abnormalities of these neurons and the abnormal aggressive behavior of mice were reversed.RESULTS:（1）3x Tg mice showed increased aggressive behaviorscompared to that of wild type,and a certain degree of reduction in avoidance behaviors;（2）Intrinsic excitatory changes and action potential changes in PT neurons in 3x Tg mice were notdirectly related to each other.Increased half-width and decreased number of action potentials but not increased intrinsic excitability are presented in 3x Tg mice compared to that of wild type;（3）PT_A-type and PT_B-typeneurons showed different abnormalities in 3x Tg mice.Both the intrinsic excitability and the number of action potentials increased in PT_A-type neurons,on the contray,PT_B-type neurons exhibited longer potential half-width and decreased number of action potentials;（4）Exciting or silencing PT_A-type neurons significantly change the aggressive behaviors of mice;（5）The decreased level of Kv6.3 was found in PT_A-type neurons in 3x Tg mice.Increasing Kv6.3 in such neurons robustly reversed electrophysiological and aggressive behavioral abnormalities in 3x Tg mice.CONCLUSIONS:In this study,we explored how PT_A-type neurons in the m PFC mediate increased aggressive behavior in 3x Tg mice.The results demonstrated that PT neurons in the m PFC show age-related diverse changes in 3x Tg mice.Increased excitability of PT_A-typeneurons projecting to the thalamus and midbrain mediated the over-aggressivity in 3x Tg mice.The decreased Kv6.3 leads to the increased excitability of PT_A-type neurons.Overexpression of Kv6.3 can reduce the excitability of PT_A-type neurons and alleviate the abnormal aggressive behaviors of 3x Tg mice.In summary,these results provide a new sight of understanding how the neuronal cell type-specific changes in their neural activities contributes to increased aggressive behaviors in the model of Alzheimer’s disease,which suggests a novelly molecular basis for the distinct characteristics of m PFC neuron types.