Effect Of Click On The Tone Response Of Central Nucleus Of Inferior Colliculus Neurons Of Mouse And Its Mechanism

Sound,is an important media to know about the outside world and communicate with the same kind of other animals and it is important to animals and humans.Hearing,as the perception of sound stimulation,is a kind of special feeling,which we obtain,extract and identify useful information from the outside world for our complex acoustic environment is indispensable to us.In the natural environment full of different kinds of voice in the world,click,as a kind of common voice,affect our perception of external voice signal imperceptibly.For example,the sound that suddenly hit the table with a hard object contain a click sound.At the beginning of the sound we give out suddenly,it always has an element of the click sound.So it's about to contain a click when we talk at the beginning of time.In this case,we have the feeling and identification of sound,at most times,was affected by click and extract the information of different sounds behind under the influence of the click at the beginning.So how does our auditory system deal with the situation that we perceive the information of the voice behind under the influence of the click?Amount different auditory nucleus,inferior colliculus,as a critical nucleus,plays an important role as the transfer station in the auditory pathway.It not only accepts the upward projection from lower brain stem nuclei,but also at the same time,accept the downward projection from higher nuclear of thalamus and auditory cortex.Inferior colliculus is very important in the entitle auditory pathway.Therefore,in this experiment,we selected the inferior colliculus as the auditory nuclei to research how the perception of other sound is under the influence of the click.The influence of two sounds we research the most detailed is two-tone interaction,therefore,we study the effect of click on tone reaction of mouse inferior colliculus neurons from simple sound.Studies before mainly concentrated on two pure tone(two-tone)stimulation,reveal regions of inhibition in auditory spectral receptive fields.Through a fixed masker-probe time interval,researches find out how different frequency excite or inhibit the neuron to an excitatory frequency response.In addition,the influence between noise and tone has been extensively studied in animal models.Those studies reveal the effect of noise on tone through using the noise as a sound masker before tone,or setting a noise as a background sound to tone.Yinting Peng research suggested that the frequency-level tuning curve of tone of a cortical neuron were modulated dynamically by a varying preceding noise.The greater the intensity of noise or the shorter interval between noise and tone,the greater influence of noise on tone of frequency-level receptive fields we could find in the study.Different models were previously proposed to describe the effect of background noise.There are only few of researches about the influence of click on tone.Palmer recorded in round window of the guinea pigs,and reveal that the compound action potential of broadband click stimulus was impacted by the suppression of pure tone.The results showed that the degree of inhibition depends on the relative intensity of masking pure tone and click,and the frequency of pure tone,which had the most obvious inhibition frequency range in 8 to 12 kHz.There were some studies only focus on click.Pedemonte recorded synaptic activity of click evoked in guinea pigs under anesthetic with the way of intracellular recording.In general,we has known little about the impact and the features of click on tone for now.In this experiment,with in vivo cell-attached recordings and whole-cell recording in neurons of inferior collicus of anaesthetic mice,we systematically examined the effect of click on tone reaction of IC neurons.In this study,we first gave the click and tone stimulus respectively,and found out the characteristics of neurons in the inferior colliculus response to click and tone.Then we examined the effect of click to tone reaction of the neuron with different time intervals between click and tone using the click + tone stimulus.We fixed the time interval of click and tone and the intensity of click and changed the intensity and frequency of tone,in order to examined the influence of click on tone receptive field of neurons under the same influence level of click on tone response(tone SC descended 20%).In the study,we recorded 108 neurons which had a response of sound stimulus.All these neurons had divide into two types according to the presence of the response to the click.One type was the neurons that had a response to click(click+),another was the neurons that had no response to click(click-).All neurons had response to the tone.1 The results suggested that there were no different in the CF,MT and BW10 of neuron's response to tone between(click+)neurons and(click-)neurons.(14.25-7.22 kHz and 7.22 +/-8.09 kHz,22.34 +/-12.45 dB SPL and 21.29 +/-11.47 dB SPL,5.46-4.25 kHz and 4.25 +/-6.20 kHz,P = 0.47,0.69 and 0.93)These results showed that it didn't represent the frequency characteristics of click in the neurons of inferior colliculus.2 When we applied the click+tone stimulus paradigm,we found that with the time interval between click and tone decreases,the inhibitory effect of click on tone response of IC neurons such as the decrease of spike counts and the increase of FSL became greater.3 In order to study the effect of click on tone receptive field,we examined the influence of click on different intensities of tone and the change of tone receptive field in the same inhibitory level of click on tone when SC of tone decrease 20%affected by click.The result came out that although at the MT of tone,the degree of the influence of SC and FSL of tone under click stimulus was the greatest,there were no significant differences of SC or FSL of different intensities of tone between click+tone stimulus paradigm and tone paradigm.This result suggested thatunder click + tone stimulation,among the different intensities above tone MT,tone was equally affected by click.In the research of the effect of click on tone frequency-level receptive field,we found out that the effect of click stimulation only increases the minimal threshold(MT)of tone.However,there were no differences for the CF of tone and bandwidth at 10 dB above the threshold.These phenomena illustrated the click stimulation did not change the characteristics of frequency response of neurons.It just had an effect on the intensity of response of tone.4 In order to study the impact of click on the response of tone under synaptic mechanism,we adopted the way of whole-cell voltage clamp recording to research the excitatory and inhibitory synaptic input of click and tone stimulation in the neurons of inferior collicus.In the experiment,we recorded 5 neurons under the way of whole-cell voltage clamp recording which the voltage held on-70mV and OmV respectively.With the help of whole-cell voltage clamp recording,we could observe the excitatory and inhibitory synaptic input of click and tone simultaneously.The result turned out that,when under the click + tone stimulation,the excitatory and inhibitory postsynaptic currents(EPSC and IPSC)of tone decreased when compared with the tone stimulation.When the time interval between click and tone became smaller,the EPSC and IPSC of tone increased gradually and the amplitude of the IPSC was bigger.In order to observe the change of synaptic input of different intensities of tone under the influence of click,we fixed the interval between click and tone and the intensity of the click.We found out that with the decrease of the intensity of tone,EPSC and IPSC of tone increased gradually.The results of electrophysiology suggested that the click stimulation have broad influence of neurons in inferior colliculus.In the inferior colliculus,we recorded the neurons whose CF gathered in the high frequency area when responded to a pure tone also responded to click stimulation.In that way,how did the neurons respond to click distribute in the inferior colliculus?We couldn't get overall understanding of the distribution of activating neurons affected by click in inferior colliculus because of the restrictions of in vivo electrophysiological recording that the number of neurons we could record was very limited and therefore we adopted c-fos immunohistochemistry to mark the active neurons affected by click stimulus.C-fos immunohistochemical markers can be a symbol of accepting some stimulations that activated the neurons.As a way to mark the activated neurons,c-fos immunohistochemistry had been used in researches of different animals and sound stimulations of the auditory system,but most of them are concentrated on pure tone,and the studies of the click stimulation were very little.Therefore,in this experiment,we use the click as an acoustic stimulation to observe the distribution of the active neurons in inferior colliculus,and from cochlear nucleus to the nuclei of lateral lemniscus below inferior colliculus,and from thalamus to auditory cortex above inferior colliculus.Results showed that the c-fos expression of neurons of click stimulus mainly concentrated in DCIC,and most part of the ICC,while the ECIC and the deep(high frequency)area of the ICC only had a small amount of positive cells.The result is different from the distribution of the active neurons to tone in the central nuclei of inferior colliculus which has the characteristics of tonotopic axis from low to high frequency runs from dorsolateral to ventromedial in the central nuclei of inferior colliculus.The distribution of positive cells activated by click ran from dorsal to ventral in DCN,and according to previous studies,the distribution of active neurons of tone has tonotopic axis from high to low frequency runs from dorsal to ventral in DCN.In AC,click c-fos expression mainly gathered in layer 2/3 and layer 5/6.To sum up,this study comes to some conclusions.1.Neurons respond to click does not reflect the frequency characteristics of the click in the inferior colliculus of anesthesia mice.2.Inhibition is the mainly effect of the influence of neuron response to tone affected by click showing that the decrease of spike counts and increase of the first spike latency in the inferior colliculus of anesthesia mice.3 the influence of the neuron reaction of different intensities of tone affected by click is at the same degree.4 At the synaptic level,the synaptic input of click reduce the excitatory and inhibitory synaptic input of neurons response to tone.5 The distribution of c-fos expression activated by click in inferior colliculus of awaken mice is focus in the contralateral of DCIC and the majority of the ICC,and there is a small amount of positive neurons in the ECIC and the deep area of the ICC.