Faculty of Health Sciences, School of Anatomical Sciences, University of the Witwatersrand, Parktown, Johannesburg, Republic of South Africa.
Faculty of Basic Medical Sciences, Department of Anatomy, College of Health Sciences, University of Ilorin, Ilorin, Nigeria.
J Comp Neurol. 2018 Nov 1;526(16):2570-2684. doi: 10.1002/cne.24519. Epub 2018 Oct 16.
Here, we used a range of immunohistochemical stains, focussing on tyrosine hydroxylase and dopamine-β-hydroxylase, to show that within the pons of tree pangolins clusters of noradrenergic neurons are present. No noradrenergic neurons were observed in the pontine periventricular gray matter (A6 and A4 groups missing), with all noradrenergic neurons being found within the pontine tegmentum (A7 and A5 groups). The tree pangolin is unique in lacking the locus coeruleus (A6) cell group observed in all vertebrates previously studied; however, noradrenergic axons and terminal networks were found throughout the cerebral cortex. We propose this is achieved through a unique structural reorganization of this system. First, the number of noradrenergic neurons in the compact portion of the subcoeruleus (A7sc) of the tree pangolin is increased, providing a total number of noradrenergic neurons in the pontine tegmentum (A7diffuse, A7sc, A5) that is equivalent to the entire locus coeruleus complex in related species of similar brain mass. Second, the most medially located noradrenergic neurons of the A7sc have dendrites that extend into the ventrolateral periventricular gray matter, in the location where the A6 neurons should have been located, forming a "pseudo A6" region. Third, the topological relationships of this "pseudo A6" region to other neurochemical systems that interact with the A6 neurons, such as the orexinergic, cholinergic, and serotonergic systems, appear to be maintained. Thus, a unique structural plasticity of this region appears to maintain the standard functions of the locus coeruleus complex in this unusual mammalian species.
在这里，我们使用了一系列免疫组织化学染色方法，重点关注酪氨酸羟化酶和多巴胺-β-羟化酶，以证明在树穿山甲的脑桥中存在去甲肾上腺素能神经元簇。在脑桥室周灰质（A6 和 A4 组缺失）中未观察到去甲肾上腺素能神经元，所有去甲肾上腺素能神经元均位于脑桥被盖（A7 和 A5 组）内。树穿山甲的独特之处在于缺乏先前研究的所有脊椎动物中观察到的蓝斑核（A6）细胞群；然而，去甲肾上腺素能轴突和末梢网络遍布大脑皮层。我们提出，这是通过该系统的独特结构重组来实现的。首先，树穿山甲的蓝斑核紧凑部分（A7sc）中的去甲肾上腺素能神经元数量增加，提供了脑桥被盖（A7diffuse、A7sc、A5）中去甲肾上腺素能神经元的总数，相当于相关物种中整个蓝斑核复合体的数量相似的脑质量。其次，A7sc 中最靠近中线的去甲肾上腺素能神经元的树突延伸到腹外侧室周灰质，在 A6 神经元应该存在的位置，形成一个“假 A6”区域。第三，该“假 A6”区域与其他与 A6 神经元相互作用的神经化学系统（如食欲素能、胆碱能和血清素能系统）的拓扑关系似乎得以维持。因此，该区域的独特结构可塑性似乎维持了这个异常哺乳动物物种中蓝斑核复合体的标准功能。
