Mulders W H, Robertson D
The Auditory Laboratory, Department of Physiology, The University of Western Australia, 6907, Nedlands, WA, Australia.
Hear Res. 2000 Nov;149(1-2):11-23. doi: 10.1016/s0378-5955(00)00157-x.
The inferior colliculus (IC) has been shown anatomically to make direct descending connections with medial olivocochlear (MOC) neurones in the auditory brainstem. The MOC neurones project to the outer hair cells in the cochlea and inhibit cochlear neural output. This study investigated the effect of IC stimulation on cochlear output in both guinea pigs and rats in order to determine the functional significance of the IC-to-olivocochlear system projection. Stimulation of the central nucleus and the external cortex of the IC in paralysed guinea pigs, both contra- and ipsilaterally to the test cochlea, resulted in a small increase of the cochlear microphonic amplitude and a small decrease of the compound action potential (CAP) amplitude, the latter equivalent to a 3-6 dB change in acoustic input. Effects on the CAP were maximal in the frequency range 6-10 kHz. These effects were consistent with partial activation of the MOC system. In unparalysed rats, stimulation of the inferior colliculus evoked a large, prolonged suppression ranging from 5-12 dB in the amplitude of distortion product otoacoustic emissions (2f(1)-f(2); DPOAE), as reported previously by Scates et al. (1999). However, this suppression was decreased to only 0-3 dB when the animals were paralysed, suggesting that the larger suppression in the unparalysed state was the consequence of either a general masking effect caused by animal movement, or activation of middle ear muscles by the inferior colliculus stimulation. The results indicate a small but significant excitatory effect of the inferior colliculus on the medial olivocochlear system under conditions of anaesthesia and paralysis.
在解剖学上，下丘（IC）已被证明可与听觉脑干中的内侧橄榄耳蜗（MOC）神经元建立直接的下行连接。MOC神经元投射到耳蜗中的外毛细胞，并抑制耳蜗神经输出。本研究调查了IC刺激对豚鼠和大鼠耳蜗输出的影响，以确定IC到橄榄耳蜗系统投射的功能意义。在瘫痪的豚鼠中，对IC的中央核和外侧皮质进行刺激，无论是在测试耳蜗的对侧还是同侧，均导致耳蜗微音器电位幅度略有增加，复合动作电位（CAP）幅度略有降低，后者相当于声学输入有3-6 dB的变化。对CAP的影响在6-10 kHz频率范围内最大。这些影响与MOC系统的部分激活一致。在未瘫痪的大鼠中，如下丘刺激可诱发畸变产物耳声发射（2f(1)-f(2); DPOAE）幅度出现5-12 dB的大幅度、长时间抑制，这与Scates等人（1999年）之前的报道一致。然而，当动物瘫痪时，这种抑制仅降至0-3 dB，这表明在未瘫痪状态下更大的抑制是动物运动引起的一般掩蔽效应或下丘刺激激活中耳肌肉的结果。结果表明，在麻醉和瘫痪条件下，下丘对内侧橄榄耳蜗系统有微小但显著的兴奋作用。
