Brain size-dependent scaling of dendritic and somatic functions in an evolutionary conserved neuronal circuit in mammals.

在哺乳动物中，大脑和神经元的大小随着头部大小的增加而增加。不可避免地，神经元尺寸的增加导致膜电容的增加。为了实现大小无关的突触整合，因此，功能，神经元特性，如输入电阻，树突形态，突触电导以及离子通道和突触的数量和位置必须按比例缩放。研究这种缩放的细胞机制的先决条件是进化保守的神经元群体，其独立于头部和大脑大小实现相同的电路功能。斜方体内侧核（MNTB）的神经元满足这些标准，并参与双耳处理和上行听觉通路中的频谱-时间整合。MNTB神经元的生物物理和形态细胞参数和它们的突触输入大小以及在不同大小的哺乳动物物种，即伊特鲁里亚鼩，沙鼠和大鼠中的通道和突触位置的定量，使我们能够掌握脑大小依赖性神经元缩放的后果。我们的电生理和免疫荧光研究结果将最终在一个计算模型，以了解个别神经元元素的功能意义。此外，我们可以利用这种比较的方法来研究MNTB树突的功能作用，这在很大程度上仍然未知。具体而言，通过定量确定树突突触输入对突触潜伏期和动作电位产生的成功的影响，我们可以捕捉它们在高频输出产生中的潜在作用。

In mammals, brain and neuron size enlarges with increasing head size. Inevitably, an increase in neuron size results in an increased membrane capacitance. To achieve size-independent synaptic integration and, thus, the function, neuronal properties like input resistance, dendritic morphology, synaptic conductance as well as the number and location of ion channels and synapses must scale proportionally. A prerequisite to investigate the cellular mechanisms of such a scaling is an evolutionary conserved neuronal population that fulfills the same circuit function independent of head and brain size. The neurons of the medial nucleus of the trapezoid body (MNTB) fulfill these criteria and are involved in binaural processing and spectro-temporal integration in the ascending auditory pathway. Quantification of the biophysical and morphological cellular parameters of MNTB neurons and their synaptic input size as well as channel and synapse location in differently sized mammalian species, i.e. Etruscan shrew, gerbil and rat, allows us to grasp the consequences of brain size-dependent neuron scaling. Our electrophysiological and immunofluorescence findings will culminate in a computational model to understand the functional significances of individual neuronal elements. Moreover, we can utilize this comparative approach to investigate the functional role of MNTB dendrites, which remains largely unknown. Specifically, by quantitatively determining the influence of dendritic synaptic inputs on synaptic latency and the success of action potential generation, we can capture their potential role in the generation of high frequency outputs.