蹄蝠听性脑干诱发电位特点分析

目的对野生蹄蝠进行短纯音（ToneBurst）和短声（Click）诱导听性脑干反应（ABR）分析，对其ABR特点与已有的研究进行比较，分析其中差异，加深我们对回声定位蝙蝠听觉功能的认识。方法捕捉并饲养野生蹄蝠，运用美国TDT公司（Tucker-Davis Technologies）TDT System Ⅲ诱发电位仪对蝙蝠进行短声和短纯音的听阈测定，分析其波形变化规律，确定其短纯音听阈阈值，分析听力图的特点。结果（1）蹄蝠听阈呈“W”形分布，经统计学分析各听阈区段有统计学意义（P〈0．05）。存在2个听敏区：28kHz处为最敏感的第一听敏区，阈值最低可达15dBSPL，平均29.1dBSPL；40kHz附近出现第二个听敏区，阈值最低25dBSPL，平均35．9dBSPL；在12kHz～64kHz听阈不超过55．9dBSPL。（2）短声引出的蹄蝠ABR可见4个相对稳定的波峰：波I的潜伏期为1．26ms：波Ⅱ较高且尖，潜伏期为1．94ms；波Ⅲ相对稳定，潜伏期为2．47ms；波Ⅴ潜伏期为3．40ms。随着短声强度的上升，在20～80dBSPL声强范围，各个波振幅逐渐增大、潜伏期缓慢缩短。（3）短纯音引出的蹄蝠ABR各波随刺激频率的提高而潜伏期缓慢地缩短，在64kHz以上潜伏期又逐渐延长；在28kHz、80dBSPL条件下，各波潜伏期分别为I波1．74ms，Ⅱ波2．72ms，Ⅲ波3．60ms，Ⅳ波4．58ms，Ⅴ波5．76ms。频率28kHz、声强在45～100dBSPL范围内上升时，主波振幅逐渐增大；但在部分蝙蝠出现主波振幅在达到最大后，随着声强的上升．振幅逐渐减小。（4）在高声强诱发下，短纯音和短声诱发的ABR均可见Ⅰ波分化为2个波峰，Ⅰa和Ⅰb波。（5）越接近敏感频率，ABR波形就越典型，振幅越大。结论（1）蹄蝠听闯呈“W”形分布，类似我们已知的其他回声定位蝙蝠，存在2个听敏区：28kHz处达到最敏感的第一听敏区，40kHz附近出现第二个昕敏区，在12kHz。64kHz听阈不超过55．9dBSPL。（2）从蹄蝠主波与声强、频率的关系可以看出，蝙蝠主波振幅与声强存在一定的正相关。随着接近其敏感听觉频率，波形逐渐变得更为典型，波幅也愈来愈高，反应阈值愈来愈低。但部分蹄蝠在声强高于80dBSPL时，出现振幅随声强增加而下降的趋势，提示可能与中枢某种调节性抑制有关。（3）在高声强诱发下，蹄蝠ABR可以看到Ⅰ波分化为2个波峰，Ⅰa和Ⅰb波，这可能与蝙蝠耳蜗的某些特化结构的“听黄斑”相关。

Characteristics of auditory brainstem responses in hipposideros bat

Objective To increase our understanding of auditory functions in the bat via studying bat auditory brainstem response (ABR) characteristics. Methods Auditory thresholds were assessed in wild Hipposideros under anesthesia by testing click- and tone burst-evoked ABRs using a Tucker-Davis Technologies System. Results (1) ABR thresholds in Hipposideros were "W" shaped on an "audiogram", with statistically significant differences among different threshold segments(P< 0.05). The lowest thresholds were at 28 kHz(mean = 29.1 dB SPL) and 40 kHz (mean = 35.9 dB SPL). Thresholds were at 55.9 dB SPL or lower between 12 and 64 kHz. (2) Four amplitude peaks were regularly recog-nized in click-evoked ABRs. Peaks latencies were 1.26 ms for Wave Ⅰ , 1.94 ms for Wave Ⅱ, 2.47 ms for Wave Ⅲ, and 3.40 ms for Wave Ⅴ, respectively, which were quite variable. ABR peak amplitudes increased and latencies decreased as the click level was increased from 20 to 80 dB SPL. (3) ABR latency decreased as tone burst frequency was increased, but increased again when tone burst frequency was beyond 64 kHz. At 28 kHz, peak latencies in response to 80 dB SPL tone bursts were 1.74 ms for Wave Ⅰ , 2.72 ms for Wave Ⅱ, 3.6 ms for Wave Ⅲ, 4.58 ms for Wave Ⅳ and 5.76 ms for Wave Ⅴ. At the same frequency, changes of the tone burst level from 45 to 100 dB SPL corresponded to a gradual increase in peak amplitudes, although in some animals the increase seemed to max at 75 dB SPL followed by a decrease. (4) Double tip in Wave Ⅰ was seen in some animals at high stimulus levels (Ⅰa and Ⅰb). (5) ABR waveforms were increasingly consistent with increasing amplitudes as tone burst frequencies approached 28 kHz and 40 kHz. Conclusion (1) The auditory sensitivity in Hipposideros appears to be in a "W" shaped configuration, similar to other echolocation bats, with two sensitive areas at 28 and 40 kHz. From 12 to 64kHz, the threshold was at 55.9 dB SPL or lower. (2) While response amplitude increases with the stimulus level, it may peak and then decrease as the stimulus intensity reaches 75 dB SPL or higher, suggesting an adjustment perhaps by central inhibition. (3) The peak split in Wave I at high stimulus levels may indicate influence by unique structures in the bat cochlea, such as "acoustic fovea".