Auditory Abnormalities And Cortical Mechanisms In MECP2 Autistic Mice

For advanced organisms,the most advanced center for processing auditory information is the auditory cortex.The normal function of the auditory cortex is essential for the communication and survival of the organism,such as enabling the animal to sense dangerous sound signals in time and make the right decisions.For humans,the normal function of the auditory cortex is important for auditory perception and language communication.Human bilateral auditory cortical dysfunction can seriously impair hearing function,leading to clinical manifestations such as central deafness and aphasia,leading to communication problems in patients.Loss of auditory cortex on both sides of the animal can cause the animal to lose auditory cognitive ability.The auditory cortex can be divided into several sub-regions according to its structural function,and one of the most important auditory cortex functional regions is the primary auditory cortex(A1).The primary auditory cortex directly receives the auditory information input from the thalamus,and the first station where the auditory information enters the cortex is the primary auditory cortex.Previous studies have shown that the primary auditory cortex plays a very important role in the processing of auditory information and participates in important auditory processes such as sound source localization and acoustic information extraction.Therefore,studying the basic information coding characteristics of primary auditory cortical neurons is the basis for our understanding of cortical auditory information processing.Autism spectrum disorder(ASD)is a general term for a large class of early-onset,complex neurodevelopmental disorders.Typical autistic patients have three core symptoms of social disorders,communication disorders,and narrowed interest,and a generalized differential type of developmental disorder(PDD-NOS),which has only one or two core symptoms,or has three core symptoms but is older than 3 years of age.At present,studies in genetics and neurobiology reveal that autism may have multiple pathogenic genes and are closely related to environmental factors.Genes with mutations in patients encode proteins that have important functions in nervous system development and synaptic transmission.Neurodevelopment and synaptic transmission abnormalities are likely to be important factors in autism.Methyl-CpG binding protein 2(MECP2)has important functions for regulating gene expression.When the MECP2 gene has a mutation in the deletion function,it causes Rett syndrome and increase in MECP2 gene copy number leads to MECP2 duplication syndrome.Both of these diseases are classified as a type of autism spectrum disorder.After H.Zoghbi team transferred the human MECP2 gene into mice in 2006,it was surprisingly found that transgenic mice carrying the human MECP2 gene showed autism phenotypes such as social interaction behavior defects.This mouse model has greatly promoted the study of autism.Most people with autism have auditory abnormalities.Most of the current research on autism and hearing is a study of autistic patients.The limitation is that the autistic patients have abnormal hearing due to the inability to use invasive recording methods,and the mechanism research is not deep enough.Studies in animal models of autism also lack the results of single-cell responses.We attempted to conduct auditory studies on animal models of autism from three different levels of auditory cortical local field potential(LFP),multi-unit response(MUA),and single unit response(SUA),and raised the following 4 questions: 1 Understand the neural mechanism of the primary auditory cortex on multi-peak frequency preferences;2 The basic electrophysiological properties of the primary auditory cortex of MECP2-TG mice differed from those of normal control mice;3 MECP2-TG mice primary auditory cortex response characteristics of noise stimulation and normal control mice;4 What is the difference between the sound perception of the primary auditory cortex of MECP2-TG mice in the noisy environment and the normal control mice.In order to answer the above questions,we applied the local field potential recording technique,extracellular multi-unit recording technique,in vivo loose patch clamp recording technique,in vivo whole-cell patch clamp recording technique,in vivo multi-channel recording technique and so on,to explore the above problems and the neurobiological mechanisms of auditory perception abnormalities in MECP2-TG mice.1.The synaptic mechanism of multi-peak frequency preference of primary auditory cortex in rats.For pure tone stimuli with different frequencies of specific sound intensity,the auditory neurons have a frequency response range,which is called the frequency tonal receptive field(TFR)or the frequency response zone.For most auditory neurons,there is one of the most reactive frequency points at a particular sound level,which we call the best frequency(BF).Studies have reported that in the auditory cortex of many organisms,in addition to the best frequency,there are other preferred frequency responses,showing a multi-peak frequency preference response phenomenon.However,most of these studies are based on data obtained by electrophysiological extracellular recording methods,and the current intracellular electrophysiological mechanisms of this multi-peak frequency preference phenomenon are still unclear.The frequency tuning of neurons in the auditory cortex depends on the integration of synaptic inputs,and it is unclear whether there is a similar electrophysiological mechanism for this multi-peak frequency preference phenomenon.Result: We observed a multi-modal frequency preference for pure tone stimulation in the primary auditory cortex of rats,and studied its single-cell response and synaptic input response,and found that(1)rat primary auditory cortex neurons(16/137,11.7%)had multi-peak frequency preference at the single cell response level with a preference point bandwidth of 0.3-0.4 audio layers.(2)There are also multi-peak frequency preferences in the excitatory synaptic input(EPSC)and inhibitory synaptic input(IPSC)levels of rat primary auditory cortical neurons,and their preference point bandwidth is also 0.3-0.4 audio layers.(3)Excitatory synaptic input and inhibitory synaptic input an excitatory/inhibition ratio imbalance occurs at the peak-to-valley frequency point of this multi-peak frequency preference.2.The auditory response of MECP2-TG miceAutism spectrum disorder(ASD)is a general term for a large class of early-onset,complex neurodevelopmental disorders.Methylated DNA binding protein 2(MECP2)has an important function of regulating gene expression.Deletion of the MECP2 gene or increased copy number can lead to autism-like manifestations in patients.An important reason why autistic patients communicate with others is that autistic patients have abnormal hearing perception compared with normal people.It has been reported in the literature that auditory brainstem evoked responses are normal in autistic patients,suggesting that auditory perception abnormalities in autistic patients may occur at a higher stage in the auditory system.However,many studies have focused on local field potential(LFP)or neuron population release levels,with few single-cell responses.Moreover,the sound stimulation information given is not comprehensive enough.Generally,only the click sound or a few simple pure sounds are used,and the frequency and intensity information are not complete enough.Exploring the auditory response characteristics of autistic model animals from a single-cell response level is particularly necessary for us to further understand the auditory perception abnormalities in autistic patients.Result: We used MECP2-TG mice as an animal model to study the auditory response characteristics of MECP2-TG mice from neuronal population response level and single cell response level.It was found that(1)the auditory brainstem evoked response of MECP2-TG mice was small compared with the normal control group.There were no significant differences in the rats.(2)The release threshold of MECP2-TG mice in the frequency bands of primary auditory cortex was higher than that of normal control mice.(3)The peak-to-valley ratio of the action potential of the fast-spiking(FS)neuron in MECP2-TG mice was lower than that in the normal control group.(4)Regardless of conventional spiking(RS)neurons or FS neurons,the peak latency of MECP2-TG mice was later than that of normal control mice.(5)Regardless of RS neurons or FS neurons,the response threshold of MECP2-TG mice was higher than that of normal control mice.3.The response of MECP2-TG mice to noise stimuliNoise stimuli are widespread in nature and in human life,and people are almost always exposed to a variety of noise stimuli in their daily life.There is a large body of literature reporting that people with autism often show unbearable reactions when exposed to noise levels that do not have much effect on normal people.However,the pure tone stimulation did not show a reaction similar to noise.In the current study of autistic model animals,the contrast between pure tone and noise response in the same study is still lacking.In addition,in the level of single-cell response of the auditory cortex,the response of pure tone stimulation to noise stimulation is different for autistic model animals,and it is still unclear.The study of MECP2 doubling syndrome patients and the animal model of MECP2 doubling syndrome is even rarer.Result: We used MECP2-TG mice as an animal model to reveal the response characteristics of MECP2-TG mice to noise stimuli from three levels: local field potential response level,neuron population response level and single cell reaction level.(1)MECP2-TG mice were found.Demonstrate behavioral performance that was more sensitive to noise stimuli.(2)The response of field potential of MECP2-TG mice to noise stimulation was significantly greater than that of pure tone stimulation,while the response of normal control mice to two stimulations was not significantly different.(3)The response of MECP2-TG mice to cell stimulation was significantly stronger than that of pure stimuli.Similarly,the normal control group did not respond significantly to the two stimuli.(4)The release of noise stimulation by MECP2-TG mouse RS neurons was higher than that of pure tone stimulation,while the normal control group mice FS neurons issued higher noise stimulation than pure tone stimulation.4.The auditory response of MECP2-TG mice in noisy environmentWhen autistic patients are in a quiet environment,it is easier to hear what others are saying,but when autistic people are in a moderately noisy environment,it is extremely difficult to hear what others are saying.It shows that a moderately loud noise environment can have a significant auditory perceptual impact on autistic patients.Studies in animal models of Reiter's syndrome have also shown that when the Reiter syndrome model rats are in a noisy environment,the sound resolution is reduced more than normal animals.Then,does the MECP2 multiplication syndrome model animal,like the Reiter syndrome model mouse,have a reduced ability to distinguish sound in a noisy environment? What are the characteristics of its single cell reaction? What is its neural mechanism? The above problems are not yet clear,and this is also the issue that we should focus on in this study.Results: We used MECP2-TG mice as an animal model to reveal the response of MECP2-TG mice to sound in a noisy environment,from the local field potential response level,neuron population response level and single cell response level.Chemical genetics regulated the activity of neurons in the auditory cortex and had corrected its behavioral abnormalities.We found that(1)the noise environment had a greater impact on the auditory perception of MECP2-TG mice than in the normal control group.(2)In the noisy environment,the field potential and population neuron responses to sound stimulation in the primary auditory cortex of MECP2-TG mice were higher than those in the quiet environment,while the normal control mice were stimuli in both environments.There were no significant differences in the response.(3)By activating the inhibitory neuronal del activity in the primary auditory cortex,the auditory perception behavior of MECP2-TG mice in a noisy environment can be improved.(4)In a noisy environment,RS neurons of MECP2-TG mice increased their response to sound stimuli,and FS neurons responded to sound stimuli.(5)By adjusting the activity of PV neurons in the primary auditory cortex,the auditory perception behavior of MECP2-TG mice in a noisy environment can be improved.