Fujimoto S, Yamamoto K, Yoshizuka M, Yokoyama M
Department of Anatomy, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan.
Microsc Res Tech. 1993 Oct 1;26(2):120-32. doi: 10.1002/jemt.1070260205.
The epithelial downgrowth arises in the presumptive foliate papilla region of the tongue approximately at prenatal day 22, and the distal portion of the primary epithelial cell cords transforms to the bifurcated serous gland and excretory duct between prenatal day 30 and postnatal day 2. The excretory ducts extend upward through the primary epithelial cell cords at rather random intervals and are open to the tongue surface between postnatal days 1 and 2. In this process, successive connections between the adjacent ascending excretory ducts occur mainly due to desquamation of the keratinized lining cells of the ducts, resulting in the formation of the foliate gutter. Taste bud primordia appear in the primary epithelial cell cords by nerve penetration through the basal lamina from prenatal day 30 and nearly fully formed taste buds facing the ascending excretory ducts have been already observed before the foliate gutter formation is completed. In the differentiation process of chemoreceptor (type III) cells from less-differentiated basal (type IV) cells, subsurface cisterns of endoplasmic reticulum are occasionally present where nerve endings make contact. Since subsurface cisterns have been considered to be involved in reciprocal or efferent synaptic transmission, it is reasonable to consider that these morphological specializations may take a role in neurotrophic signals for differentiation of the chemoreceptor cells.
上皮向下生长大约在胚胎第22天出现在舌的叶状乳头原基区域，在胚胎第30天至出生后第2天之间，初级上皮细胞索的远端部分转变为分叉的浆液腺和排泄管。排泄管以相当随机的间隔向上穿过初级上皮细胞索，并在出生后第1天至第2天之间通向舌表面。在此过程中，相邻上升排泄管之间的连续连接主要是由于排泄管角质化内衬细胞的脱落，从而形成叶状沟。味蕾原基在胚胎第30天通过神经穿透基底层出现在初级上皮细胞索中，并且在叶状沟形成完成之前已经观察到面向上升排泄管的几乎完全形成的味蕾。在化学感受器（III型）细胞从分化程度较低的基底（IV型）细胞的分化过程中，在内质网的表面下池偶尔会出现在神经末梢接触的地方。由于表面下池被认为参与了相互或传出突触传递，因此有理由认为这些形态学特化可能在化学感受器细胞分化的神经营养信号中起作用。
