Comparative quantitative analysis of the cellular composition of the prefrontal cortex in the superorder Cetartiodactyla, using DTI and isotropic fractionator technique.

哺乳动物的大脑大小相差大约10万倍，绝对的大脑大小从不到0.1克（食虫动物）到9000克（抹香鲸）不等。大脑的大小是由多种因素决定的，如：神经元的数量、神经胶质细胞的数量、细胞体的大小、树突和轴突的树突以及血管和心室系统的大小。通常认为神经元数量是神经元功能和行为的决定因素。直到最近，人们对哺乳动物大脑的定量细胞组成知之甚少；然而，随着各向同性分分器技术的发展，迄今为止已经在4种不同的哺乳动物目中检测了神经元和胶质细胞的总数。与传统观点相反，神经元密度似乎并不随着大脑大小的增加而减少，相反，大脑的规模是神经元数量的顺序特定功能。此外，神经胶质细胞密度在不同目的物种之间似乎是相对恒定的，并不像之前假设的那样随着大脑大小的增加而增加。哺乳动物的超级目鲸足目是由偶趾有蹄类动物和鲸目动物组成的，因为它们有一个共同的单系祖先。鲸目动物有近300个现存物种，是中型到大型哺乳动物中种类最多的一目，它们的大脑和身体大小变化很大，这一超级目的物种是研究大脑缩放规律的理想标本。本研究计划的总体目标是使用各向同性分划技术，与先前研究的哺乳动物目相比，研究哺乳动物超目鲸趾动物的大脑大小是如何作为神经元和胶质细胞数量的函数的。此外，我们对这些细胞如何在不同的结构中组织感兴趣，特别是前额皮质，这将通过MRI/DTI来描绘。这种比较分析将使我们深入了解不同哺乳动物目之间共享的细胞大脑缩放规则，从而可能从一个共同的祖先那里继承和保留，以及哪些规则不同，从而可能反映这些目之间的系统发育差异。

Brain size between mammals varies by a factor of approximately 100,000X, with an absolute brain size ranging from less than 0.1g (insectivore) up to 9,000g (sperm whale). The size of the brain is determined by a large variety of factors such as: number of neurons, number of glial cells, cell-body size, dendritic and axonal arborisation as well as by the size of the vascular and ventricular systems. It is often assumed that the neuronal number is determinant for neuronal function and hence for behaviour. Until recently, very little was known about the quantitative cellular composition of mammalian brains; however with the development of the isotropic fractionator techniques the total neuronal and glial number has been examined in 4 different mammalian orders to date. Contrary to the traditional view it seems that the neuronal density does not decrease with increasing brain size, rather the brains scale as order-specific functions of their numbers of neurons. Moreover the glia cell density seems to be relatively constant across species of different orders and does not increase with increasing brain size as was previously assumed.The mammalian superorder Cetartiodactyla is comprised of the even-toed ungulates and the cetaceans, as they share a monophyletic ancestry. Cetartiodactyla contains nearly 300 extant species and is the most diverse order of medium to large bodied mammals, with a large variety in brain and body size, making the species of this superorder the ideal specimens in which to study brain scaling rules. The global aim of the present research proposal is to examine how brain size scales across the mammalian superorder Cetartiodactyl as a function of the numbers of neuronal and glial cells in comparison to the previously examined mammalian orders, using the isotropic fractionator technique. Furthermore we are interested in how these cells are organized in different structures, especially the prefrontal cortex, which will be delineated using MRI/DTI. Such a comparative analysis will give insight into cellular brain scaling rules that are shared between different mammalian orders and therefore might be inherited and retained from a common ancestor and what rules are different and thus might reflect phylogenetic variance across these orders.