【Acoustic signal characteristic detection by ventral nucleus neurons in the lateral lemniscus in mice】 [编辑]

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实验简介

Under free field conditions, we used single unit extracellular recording to study the detection of acoustic signals by neurons in the ventral nucleus of the lateral lemniscus (VNLL) in Kunming mouse (Mus musculus). The results indicate two types of firing patterns in VNLL neurons: onset and sustained. The first spike latency (FSL) of onset neurons was shorter than that of sustained neurons. With increasing sound intensity, the FSL of onset neurons remained stable and that of sustained neurons wa

参考文献


                        

实验原理

We assume that the firing pattern, intensity and frequency of VNLL neurons have some sort of connection. Despite being an animal model for acoustic studies, detection characteristics and frequency topologic organization of VNLL neurons to acoustic signals in Kunming mice (Mus musculus) remain unclear. Here, using single unit extracellular recording, we observed the firing patterns of VNLL neurons and compared FSL, frequency and intensity tuning characteristics under different firing patterns. Our results are helpful in more fully understanding correlations between VNLL neuron firing patterns and acoustic signal detection charac¬teristics, and exploring the physiological functions of VNLL neurons and the effects of ascending projections on the IC.

安全性


                                            

主要试剂/材料

homemade bipolar tungsten electrode 1-5 MΩ 2

【Acoustic signal characteristic detection by ventral nucleus neurons in the lateral lemniscus in mice】的实验步骤

第1步

 For the 98 VNLL neurons we recorded in this study, the dorsal ventral depth was 3 368±156.2 μm (2 844-4 090 μm); BF was 19.89±11.12 kHz (2.6-39 kHz); MT was 52.66±13.11 dB SPL (13.83-71.61 dB SPL); andFSL was 5.78±2.79 ms (2-18.5 ms). Linear regression analysis showed linear relationships between BF and dorsal ventral depth (R=-0.36, P<0.001) (Figure 1A). We found that neurons sensitive to high frequencies are located in the dorsal VNLL. From dorsal to ventral, the BF of VNLL neurons decreased, indicating frequency topological organization along the dorsal-ventral-axis of the VNLL. No linear relationships were found among FSL, MT and dorsal ventral depth (R=0.1, P>0.05; R=0.06, P>0.05). 

第2步

As one of the basic features of central auditory neurons, the temporal firing pattern reflects firing changes in neurons before and after stimulation. , With acoustic signals at BF and MT+20 dB, the firing patterns of 98 VNLL neurons were recorded. According to Zhang & Kelly (2006), our observed firing patterns were categorized into two types: onset and sustained. The onset type can be sub-categorized into: (1) phasic: only one or two spikes to the onset of the acoustic signals; (2) phasic burst: several spikes to the onset of the acoustic signals; and (3) double burst: fixed intervals can be found between the spikes to the onset of the acoustic signal. Likewise, the sustained type can also be sub-categorized into: (1) onset plus sustained: significant response can be found to the onset of the acoustic signals,then decreases and lasts through the entire duration; (2) tonic: a fixed firing rate lasts through the entire duration; and (3) primary-like: the firing rate to the onset of the acoustic signals quickly reaches maximum, then decreases to a certain level.

第3步

Under intensity at MT+20 dB, the FSL of onset VNLL neurons was 5.47±1.86 ms (2-11 ms), with 67.31% of the FSL within the range of 2.5-5 ms; the FSL of sustained VNLL neurons was 7.1±3.13 ms (2~19.5 ms) with a relatively wide distribution . The FSL of onset VNLL neurons was shorter than that of sustained neurons (P<0.001, unpaired t-test). When the intensity of the acoustic signal increased every 10 dB segment to MT+50 dB, no significant changes in the FSL of onset VNLL neurons were observed (one-way ANOVA, P>0.05), whereas, the FSL of sustained neurons decreased (one-way ANOVA, P<0.001)

实验结果

the FTC of the 71 VNLL neurons recorded here were divided into six types: (1) V-shape: with increasing intensity, the verges of high and low frequency are broadening; (2) U-shape:, the changes in FTC are independent of intensities [the V- and U-shape can be differentiated by bandwidth level intolerance (BLI, BLI=BWmax/BW10), if BLI<3, it is U-shape, if BLI≥3, it is V-shape]; (3) Lower-tail-upper-sharp (LTUS): the low frequency verge is characterized with a long tail and the high frequency verge is very sharp; (4) Upper-tail-lower-sharp (UTLS): the high frequency verge is characterized with a long tail and the low frequency verge is very sharp [in LTUS and UTLS, the SlopeMT+30-MT+10≥ 30%, otherwise, if   SlopeMT+30-MT+10<30%, the FTC is V- or U-shape]; (5) W-shape: two peaks can be found in FTC and the two frequency tuning segments are partitioned by an auditory completely insensitive area only under low intensity, but not under high intensity; and (6) Double V-shape: two peaks can be found in FTC and the two frequency tuning segments are partitioned by an auditory completely insensitive area under both low and high intensities

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