A Preliminary Study On The Degenerative Changes Of PV~+ Neurons In The Mouse Medial Prefrontal Cortex

The medial prefrontal cortex plays important roles in the cognition and memory by receiving long-term input from upstream brain region.Among the medial prefrontal cortical neurons,paralbumin-positive（PV⁺）interneurons are closely related to gamma oscillations,which signifies cognitive functioning.Research shows that,PV⁺neuron damage is a key factor that causes abnormal neural network and cognitive dysfunction in Alzheimer’s disease（AD）.In addition,the density of PV⁺neurons in the frontal cortex in AD mice decreased at 6-9 months of age.However,during the course of AD,the decreases of neuronal markers such as PV⁺neuron may cause the illusion of the number of neurons.Here,I selected the three-positive offspring of 5×FAD mice,Ai14 fluorescent reporter mice and PV-ires-Cre or Ch AT-ires-Cre mice as the experimental pathological model to study the the degenerative changes of PV⁺neuron in the medial prefrontal cortex in AD.The main findings are as follows:Firstly,This study investigated the pathological changes of 5×FAD triple-positive mice(5×FAD_{PV-ires-Cre:Ai14} and 5×FAD_{Ch AT-ires-Cre:Ai14})usingβ-amyloid（Aβ）plaque staining and behavioral studies.The results of Aβstaining showed that amyloid plaques were deposited in the brains of 4-month-old mice.The open-field,elevated plus maze,and new object recognition experiments showed that the pathological features of 5×FAD triple-positive mice and 5×FAD mice are consistent.There were no significant pathological changes in the exercise abilities of mice between the age of 4 and 12 months.the anxiety level of the mice decreased at the age of 4 months.The memory function of the mice at the age of 6 months declined.These pathological features become more obvious at the age of 6 to 12 months.Secondly,to explore whether the decline in memory function of 6-month-old mice is related to the changes in the PV⁺neuron circuits in the medial prefrontal cortex,I further studied the changes in the number of PV⁺neurons in AD.The results of the study showed that the number of PV⁺neurons did not decrease significantly in 6-month-old mice.The average number of PV⁺neurons in 9-month-old mice decreased by 16.67%in the prelimbic area and 23.70%in the infralimbic area.As the course of the disease progresses,the number of neurons decreases more.Subsequently,this study investigated the proportion of PV⁺neurons in GABA neurons and the distribution of PV⁺neurons in different sublayers.The results showed that the ratio of the number of PV⁺neurons to the number of GABAergic neurons did not change significantly.In 12-month-old5×FAD_{PV-ires-Cre:Ai14} mice,I found that the number of PV⁺neurons significantly decreased in the deep layer where there were more Aβplaques.Thirdly,This experiment studied the changes in the upstream input circuits of PV⁺neurons in the medial prefrontal cortex.Using rabies virus retrograde trans-synaptic labeling technology combined with fluorescent microscopy optical slice tomography system,I obtained the whole brain long-range input dataset of PV⁺neurons in the medial prefrontal prelimbic area.I found that their upstream input mainly came from the basal forebrain and neocortex,and the proportion of input neurons in these brain regions in6-month-old 5×FAD mice did not change significantly.Further study the changes in the number of neurons in the subcortical brain area in the upstream loop,and these experiments revealed that the number of cholinergic neurons and the number of PV⁺neurons in the basal forebrain of 5×FAD_{Ch AT-ires-Cre:Ai14} triple-positive mice at 6 months of age did not significantly decrease.In 9-month-old mice,the number of cholinergic neurons in the horizontal limbs of the diagonal band decreased by 24.50%,and in the substantial innominate,the number decreased by 20.75%.The number of cholinergic neurons decreased with the couse of AD.In 12-month-old mice,the number reduced by35.57%in the medial septum nucleus and the vertical limbs of the diagonal band.The number of PV⁺neurons in the basal forebrain did not change significantly at 12 months of age.In summary,I investigated the changes in the number of PV⁺nerves in the medial prefrontal cortex during the course of AD.The structure of the long-range input circuit in6-month-old mice has not changed.At 9 months of age,the number of PV⁺neurons in the prelimbic and infralimbic areas of the medial prefrontal cortex,the horizontal oblique nucleus of the basal forebrain and the innominate cholinergic neurons were significantly reduced.The number of cholinergic neurons in the medial septal nucleus and the vertical oblique band nucleus decreased significantly at the age of 12 months,while the number of PV⁺neurons did not change significantly.This topic can provide structural support for the study of neural circuit functional damage during the course of AD,promote the understanding of neuron and neural circuit damage mechanisms,and provide a reference for the treatment of neurodegenerative diseases.