Gáti Georgina, Lendvai Dávid, Hökfelt Tomas, Harkany Tibor, Alpár Alán
Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary.
Brain Behav Evol. 2014;83(2):82-92. doi: 10.1159/000357834. Epub 2014 Apr 24.
In the vertebrate nervous system, the Ca(2+)-binding proteins parvalbumin, calbindin and calretinin have been extensively used to elaborate the molecular diversity of neuronal subtypes. Secretagogin is a phylogenetically conserved Ca(2+)-binding protein, which marks neuronal populations largely distinct from other Ca(2+)-binding proteins in mammals. Whether secretagogin is expressed in nonmammalian vertebrates, particularly in birds, and, if so, with a brain cytoarchitectonic design different from that of mammals is unknown. Here, we show that secretagogin is already present in the hatchlings' brain with continued presence into adulthood. Secretagogin-immunoreactive neurons primarily accumulate in the olfactory bulb, septum, subpallial amygdala, hippocampus, hypothalamus, habenular nuclei and deep layers of the optic tectum of adult domestic chicks (Gallus domesticus). In the olfactory bulb, secretagogin labels periglomerular neurons as well as a cell continuum ascending dorsomedially, reaching the ventricular wall. Between the hippocampus and septal nuclei, the interconnecting thin septal tissue harbors secretagogin-immunoreactive neurons that contact the ventricular wall with their ramifying dendritic processes. Secretagogin is also present in the neuroendocrine hypothalamus, with particularly rich neuronal clusters seen in its suprachiasmatic and infundibular nuclei. Secretagogin expression identified a hitherto undescribed cell contingent along intratelencephalic cell-free laminae separating brain regions or marking the palliosubpallial boundary, as well as a dense neuronal population in the area corticoidea lateralis. In both the telencephalon and midbrain, secretagogin complemented the distribution of the canonical 'neuronal' Ca(2+)-binding proteins. Our findings identify novel neuronal subtypes, connectivity patterns in brain areas functionally relevant to olfaction, orientation, behavior as well as endocrine functions, which will help refine existing concepts on the neuronal diversity and organizational principles of the avian brain.
在脊椎动物神经系统中，钙结合蛋白小白蛋白、钙结合蛋白和钙视网膜蛋白已被广泛用于阐述神经元亚型的分子多样性。分泌促胃液素是一种在系统发育上保守的钙结合蛋白，它标记的神经元群体在很大程度上不同于哺乳动物中的其他钙结合蛋白。分泌促胃液素是否在非哺乳动物脊椎动物中表达，特别是在鸟类中表达，以及如果表达，其脑组织结构设计是否与哺乳动物不同，目前尚不清楚。在这里，我们表明分泌促胃液素在雏鸟大脑中已经存在，并持续存在至成年期。分泌促胃液素免疫反应性神经元主要聚集在成年家鸡（原鸡）的嗅球、隔区、皮质下杏仁核、海马体、下丘脑、缰核和视顶盖深层。在嗅球中，分泌促胃液素标记球周神经元以及向背内侧上升并到达室壁的细胞连续体。在海马体和隔核之间，相互连接的薄隔组织中含有分泌促胃液素免疫反应性神经元，这些神经元通过其分支的树突过程与室壁接触。分泌促胃液素也存在于神经内分泌下丘脑，在其视交叉上核和漏斗核中可见特别丰富的神经元簇。分泌促胃液素的表达确定了沿着分隔脑区或标记皮质下皮质边界的脑室内无细胞层的一个迄今未描述的细胞群体，以及外侧皮质样区域中的密集神经元群体。在端脑和中脑中，分泌促胃液素补充了典型“神经元”钙结合蛋白的分布。我们的发现确定了与嗅觉、定向、行为以及内分泌功能相关的脑区中的新型神经元亚型、连接模式，这将有助于完善关于鸟类大脑神经元多样性和组织原则的现有概念。
