Harlow Danielle E, Barlow Linda A
Department of Cell and Developmental Biology, Rocky Mountain Taste and Smell Center, University of Colorado Denver Health Sciences Center, Anschutz Medical Campus, Aurora, CO 80045, USA.
Dev Biol. 2007 Oct 15;310(2):317-28. doi: 10.1016/j.ydbio.2007.07.042. Epub 2007 Aug 15.
Cranial nerves VII, IX and X provide both gustatory (taste) and non-gustatory (touch, pain, temperature) innervation to the oral cavity of vertebrates. Gustatory neurons innervate taste buds and project centrally to the rostral nucleus of the solitary tract (NTS), whereas neurons providing general epithelial innervation to the oropharynx project to non-gustatory hindbrain regions, i.e., spinal trigeminal nucleus. In addition to this dichotomy in function, cranial ganglia VII, IX and X have dual embryonic origins, comprising sensory neurons derived from both cranial neural crest and epibranchial placodes. We used a fate mapping approach to test the hypothesis that epibranchial placodes give rise to gustatory neurons, whereas the neural crest generates non-gustatory cells. Placodal ectoderm or neural crest was grafted from Green Fluorescent Protein (GFP) expressing salamander embryos into unlabeled hosts, allowing us to discern the postembryonic central and peripheral projections of each embryonic neuronal population. Neurites that innervate taste buds are exclusively placodal in origin, and their central processes project to the NTS, consistent with a gustatory fate. In contrast, neural crest-derived neurons do not innervate taste buds; instead, neurites of these sensory neurons terminate as free nerve endings within the oral epithelium. Further, the majority of centrally directed fibers of neural crest neurons terminate outside the NTS, in regions that receive general epithelial afferents. Our data provide empirical evidence that embryonic origin dictates mature neuron function within cranial sensory ganglia: specifically, gustatory neurons derive from epibranchial placodes, whereas neural crest-derived neurons provide general epithelial innervation to the oral cavity.
脑神经VII、IX和X为脊椎动物的口腔提供味觉（味觉）和非味觉（触觉、疼痛、温度）神经支配。味觉神经元支配味蕾并向孤束核（NTS）的吻侧核中央投射，而向口咽提供一般上皮神经支配的神经元则投射到非味觉后脑区域，即脊髓三叉神经核。除了这种功能上的二分法，脑神经节VII、IX和X有双重胚胎起源，包括来自颅神经嵴和鳃上板的感觉神经元。我们使用命运图谱方法来检验以下假设：鳃上板产生味觉神经元，而神经嵴产生非味觉细胞。将表达绿色荧光蛋白（GFP）的蝾螈胚胎的板层外胚层或神经嵴移植到未标记的宿主中，使我们能够辨别每个胚胎神经元群体的胚胎后中央和外周投射。支配味蕾的神经突完全起源于板层，它们的中央突起投射到NTS，这与味觉命运一致。相比之下，神经嵴衍生的神经元不支配味蕾；相反，这些感觉神经元的神经突在口腔上皮内终止为游离神经末梢。此外，神经嵴神经元的大多数向中央的纤维在NTS之外的区域终止，这些区域接受一般上皮传入纤维。我们的数据提供了经验证据，表明胚胎起源决定了颅感觉神经节内成熟神经元的功能：具体而言，味觉神经元来源于鳃上板，而神经嵴衍生的神经元为口腔提供一般上皮神经支配。
