Effects Of Low-intensity Focused Ultrasound On Learning And Memory In Mice

The proper functioning of learning and memory is important for human activity.With the popularization of relevant knowledge,the problem of related diseases has been increasingly prominent and attracted people's attention.At present,diseases related to learning and memory dysfunction,such as traumatic stress disorder and Alzheimer's Disease,not only have unclear pathogenesis,but also have no clear clinical treatment,causing serious family burden and social burden.Therefore,it is of great importance to find a technology that can regulate and treat related diseases.The existing neuromodulation techniques such as deep brain stimulation,transcranial magnetic stimulation,optogenetics and other method all have some inapplicability and limitations to solve the problems.Both electrical stimulation and optogenetic methods require invasive surgery,while magnetic stimulation has poor spatial resolution.As a new type of noninvasive neuromodulation,ultrasound stimulation can stimulate the deep brain nuclei noninvasively and in multiple places.In this paper,this technique was applied on the learning and memory-related cerebral nuclei to study the effect of ultrasonic neuromodulation to the learning and memory function.According to the advantage of ultrasonic neuromodulation,ultrasound transducer and collimator based on the basic knowledge and theory of ultrasonic wave were designed and manufactured to meet the demand of experiment.An ultrasound stimulation system was composed of a signal generator,a power amplifier and an ultrasound transducer,the ultrasound beam analyzer and 3D sound field scanner were used to measure the acoustic field distribution and parameter of ultrasound.Subsequently,ultrasound neuromodulation was studied in mice.Starts with the intervention of common C57 mice,the prefrontal cortex(PFC),a downstream nucleus associated with learning and memory circuits,was selected for ultrasound stimulation to seek the parameters that can modulate the function of learning and memory.Using pulsed ultrasound in mice(the control group,n = 36,the ultrasound group,n = 36)for acute single ultrasound stimulation,then doing behavior test associated with learning and memory functions,including Freezing cued fear conditioning test and Y-maze test.Fear conditioning test,the data of 20 times on the second day were analysed,and the Y-maze test statistics total times that the mice get into the arms,the times of enter the new open arm,the time of explore the new opened arm and alternation times.The experiment proves that the ultrasound can effectively modulation the learning and memory ability of mice.Using ultrasound parameters A to stimulate the prefrontal cortex of mice can promote the regression of the fear memory of mice;While using ultrasound parameters B,the fear memory of the mice in the ultrasound stimulation group was stronger than the sham group,ultrasound stimulation can inhibit the regression of the fear memory.The regulation effect of ultrasound on prefrontal cortex is bidirectional due to different parameters.In order to verify the role of ultrasound in modulation of learning and memory in Alzheimer's Disease(AD)model mice,a basic study was conducted in C57 mice.In this part,the dentate gyrus(DG),the upstream nucleus group of PFC and the brain nucleus associated with AD,was selected for ultrasound stimulation.Considering that the collimator installation requires surgery,the subsequent long-term ultrasound stimulation experiment are required for AD model mice,only the top of the mouse head is depilated and the ultrasound fundamental frequency is down-regulated in the basic experiment and AD model experiment.A single stimulation was performed on the mice by using ultrasound,and novel object recognition test was carried out.The experimental results showed that the mice stimulated by ultrasound showed stronger performance in exploring new things than those in the sham group,and they had better memory and discrimination ability for old object.Then this study uses the ultrasound neuromodulation technology to research on AD model mice.The ultrasonic parameters of the basic study of C57 mice were used in this part to ultrasonic stimulate every other day,and the EdU solution was injected every three days.The rotarod test was carried out on the 13 th day,the Y-maze test and open field test were carried out on the 14 th day.Finally,the brain was taken for the detection of EdU cell proliferation.Results: the hippocampal region of the mice was stimulated by ultrasound neuromodulation to improve the function of balance and coordination,forced movement,ability of discriminative learning and working memory of the mice.The intervention of ultrasound stimulation did not increase the anxiety,and did not affect the ability of explore and autonomous motor function in AD mice.There was obvious cell proliferation in the dentate gyrus of the hippocampus and cortex after ultrasound stimulation.It was speculated that the reason that ultrasound neuromodulation could improve the performance of learning and memory ability in AD mice might be that ultrasound stimulation promoted the proliferation of neurons in this area.In summary,this study designed the ultrasonic transducer and collimator in accordance with the experimental requirements,and established the ultrasound brain stimulation system.The system was firstly applied to the prefrontal cortex,hippocampal DG area of C57 mice and then hippocampal DG area of AD model mice,which proved that ultrasound neuromodulation can effectively affect the learning and memory ability of mice with bidirectional characteristics,and suggested that the reason for the improvement of learning and memory in mice may be that it causes the proliferation of neurons.This study not only provided new possibilities and experimental data for researching the mechanism of ultrasound neuromodulation,but also proposed new methods for the treatment of learning and memory-related diseases.