Department of Psychology, Cornell University Ithaca, NY, USA.
Front Hum Neurosci. 2014 Apr 8;8:190. doi: 10.3389/fnhum.2014.00190. eCollection 2014.
In adulthood, the isocortex of several species is characterized by a gradient in neurons per unit of cortical surface area with fewer neurons per unit of cortical surface area in the rostral pole relative to the caudal pole. A gradient in neurogenesis timing predicts differences in neurons across the isocortex: neurons per unit of cortical surface area are fewer rostrally, where neurogenesis duration is short, and higher caudally where neurogenesis duration is longer. How species differences in neurogenesis duration impact cortical progenitor cells across its axis is not known. I estimated progenitor cells per unit of ventricular area across the rostro-caudal axis of the isocortex in cats (Felis catus) and in dogs (Canis familiaris) mostly before layers VI-II neurons are generated. I also estimated the ventricular length across the rostro-caudal axis at various stages of development in both species. These two species were chosen because neurogenesis duration in dogs is extended compared with cats. Caudally, cortical progenitors expand more tangentially and in numbers in dogs compared with cats. Rostrally, the cortical proliferative zone expands more tangentially in dogs compared with cats. However, the tangential expansion in the rostral cortical proliferative zone occurs without a concomitant increase in progenitor cell numbers. The tangential expansion of the ventricular surface in the rostral cortex is mediated by a reduction in cell density. These different developmental growth patterns account for the disproportionate expansion of the rostral (i.e., frontal cortex) and caudal cortex (e.g., primary visual cortex) when neurogenesis duration lengthens in evolution.
在成年期，几种物种的大脑新皮质以神经元与皮质表面积之比的梯度为特征，相对于尾端，头部的神经元密度较低。神经发生时间的梯度预测了大脑新皮质中神经元的差异：头部神经元密度较低，因为神经发生持续时间较短，而尾部神经元密度较高，因为神经发生持续时间较长。物种之间神经发生持续时间的差异如何影响其轴上的皮质祖细胞尚不清楚。我在猫（Felis catus）和狗（Canis familiaris）的大脑新皮质的头侧-尾侧轴上，估计了单位脑室面积的祖细胞数量，这些祖细胞主要是在生成 6 层和 2 层神经元之前。我还估计了这两个物种在发育的各个阶段的脑室长度。选择这两个物种是因为狗的神经发生持续时间比猫长。在尾部，与猫相比，狗的皮质祖细胞更广泛地呈切线状增殖且数量更多。在头部，与猫相比，狗的大脑皮质增殖区更广泛地呈切线状扩张。然而，头部皮质增殖区的切线扩张并没有伴随着祖细胞数量的相应增加。头部皮质室表面的切线扩张是通过降低细胞密度来介导的。当神经发生持续时间在进化中延长时，这些不同的发育生长模式解释了大脑新皮质的头部（即额叶皮质）和尾部（例如初级视觉皮质）不成比例的扩张。
