Role of spontaneous activity for the development of the giant synapse formed by the calyx of Held and principal neurons of the MNTB

赫尔德花萼是听觉脑干中一个巨大的突触前终末。其特殊的结构保证了耳蜗核（CN）的球状丛状细胞（GBCs）与梯形体（MNTB）内侧核的主要神经元之间快速、可靠和安全的神经传递。导致耳蜗花萼形成和MNTB神经元单神经支配的确切机制在很大程度上是未知的。在这里，我们将研究自发活动在该突触发育中的作用。为此，破伤风神经毒素将通过ccr - loxp和四环素依赖的转基因小鼠系表达系统在GBCs中表达以阻断神经传递。为了研究竞争性神经元活动的作用，这种遗传系统也将被用来沉默GBCs的一个亚群。为了分析神经元沉默对Held花萼形成和突触后结构的影响，将对选定的标记蛋白进行免疫组织化学。此外，将通过轴突示踪研究投射的单神经支配和张力组织。综上所述，我们的结果将确定（竞争性）自发活动在听觉脑干中形成这个巨大突触的作用。这将加深我们对神经元系统中靶向神经支配机制的认识。此外，将生成一个多功能遗传系统，允许对GBCs中的单个基因进行功能分析，以及对听觉脑干中自发和声驱动活动的作用进行调查。

The calyx of Held is a giant presynaptic terminal in the auditory brainstem. Its specialized structure ensures fast, reliable and secure neurotransmission between globular bushy cells (GBCs) of the cochlear nucleus (CN) and principal neurons of the medial nucleus of the trapezoid body (MNTB). The precise mechanisms which lead to the formation of the calyx and the monoinnervation of MNTB neurons prior hearing-onset are largely unknown. Here, we will investigate the role of spontaneous activity for the development of this synapse. To this end, the tetanus neurotoxin will be expressed in GBCs to block neurotransmission by using the Cre-LoxP and a tetracycline-dependent expression system in a transgenic mouse line. This genetic system will also be used to silence only a subpopulation of GBCs in order to study the role of competitive neuronal activity. To analyse the consequences of neuronal silencing on the formation of the calyx of Held and the postsynaptic structure, immunohistochemistry will be performed with selected marker proteins. In addition, monoinnervation and tonopotic organisation of the projection will be studied by axonal tracing. Taken together, our results will identify the role of (competitive) spontaneous activity for the formation of this giant synapse in the auditory brainstem. This will deepen our knowledge concerning mechanisms of targeted innervation in neuronal systems. In addition, a versatile genetic system will be generated which allows functional analysis of individual genes in GBCs as well as investigations into the role of spontaneous and acoustically driven activity in the auditory brainstem.