Afferent synaptic transmission in the mammalian cochlea

描述（由申请人提供）：本提案的重点是研究哺乳动物耳蜗内毛细胞（IHC）传入突触的突触传递机制。听觉通路中最外周的化学突触充当翻译器，将毛细胞受体电位翻译成一系列兴奋性突触后电位，这些电位激活传入听觉神经纤维中的动作电位。IHC传入突触的具体特征决定了声音信号如何在内耳编码并通过听觉神经纤维活动传递到大脑。 我们的目的是表征在IHC传入纤维中形成突触后活动的突触前和突触后机制。我们将使用全细胞膜片钳方法记录突触后活动。记录部位为大鼠和小鼠耳蜗离体标本中直接位于内毛细胞突触的传入纤维末端和螺旋神经节中的传入纤维索马体。为了准确描述突触前刺激和突触后活动之间的关系，我们将从内毛细胞和传入纤维末梢进行双重记录。为了影响递质释放并定义量子大小，我们将记录兴奋性突触后电流并改变实验条件;即改变温度或离子环境并使用影响释放的毒素。为了了解突触传递的突触后决定因素，我们将提供兴奋性突触后电位波形的基本描述及其与动作电位激活的关系。使用药理学工具，我们将尝试识别塑造突触后电位波形的单个组件，重点关注不同类别的钾通道。我们也将研究传出输入对传入纤维活动的作用。大多数记录将使用出生后耳蜗在已经建立的准备中进行。同时，我们将扩大我们的录音成熟耳蜗，因为我们的最终目标是了解IHC传入突触的发育和成人功能。这些研究将进一步加深我们对周围听力的基本机制的认识，因此也将导致对异常听力和耳聋的更好理解。

DESCRIPTION (provided by applicant): This proposal focuses on investigating the mechanism of synaptic transmission at the inner hair cell (IHC) afferent synapse in the mammalian cochlea. This most peripheral chemical synapse in the auditory pathway serves as an interpreter translating the hair cell receptor potential into a train of excitatory postsynaptic potentials that activate action potentials in the afferent auditory nerve fibers. The specific features of the IHC afferent synapse critically determine how a sound signal is coded in the inner ear and transmitted to the brain via auditory nerve fiber activity. Our aim is to characterize pre- and postsynaptic mechanism that shape the postsynaptic activity in IHC afferent fibers. We will record postsynaptic activity using the whole cell patch clamp method. The recording sites will be the afferent fiber terminal directly at the inner hair cell synapse and the afferent fiber soma in the spiral ganglion in excised preparations of rat and mouse cochleae. To exactly describe the relationship between presynaptic stimulus and postsynaptic activity, we will make double recordings from IHCs and afferent fiber terminals. To affect transmitter release and define the quantal size, we will record excitatory postsynaptic currents and vary experimental conditions; i.e. changing the temperature or ionic environment and using release-affecting toxins. To understand postsynaptic determinants of synaptic transmission, we will provide a basic description of the waveform of the excitatory postsynaptic potential and its relation to the activation of action potentials. Using pharmacological tools, we will try to identify individual components that shape the postsynaptic potential waveform starting with a focus on different classes of potassium channels. We will also study the role of efferent inputs onto afferent fiber activity. Most recordings will be performed in the already established preparation using postnatal cochleae. In parallel we will extend our recordings to mature cochleae, as our ultimate aim is to understand both development and adult function of the IHC afferent synapse. These studies will further our knowledge of basic mechanisms of peripheral hearing and therefore also will lead to a better understanding of abnormal hearing and deafness.