Study of Maturation of Synapses in the Human Tongue Epithelium Using Synaptophysin as Marker: An Immunohistochemical Approach

BACKGROUND: Development of taste in higher organisms is fascinating yet poorly understood among the five senses. Many events including the development of taste receptors, neuronal connections and the gustatory cortex determine the overall advent of taste in a human fetus. This study was designed to assess the changes in the tongue epithelium of human fetuses over the age group of 14 to 20 weeks. METHODS: Sagittal sections of tongue from 5 human fetuses of ages ranging from 14 to 20 weeks were used to study the appearance of taste buds under light microscope using hematoxylin and eosin staining, and also to observe the expression of synaptophysin, a 38 kDa integral membrane protein using immunohistochemistry with anti-synaptophysin monoclonal antibody. RESULTS: With increasing age, an increase in the number of papillae on the dorsum of tongue was noted with maturation from primary to secondary papilla. In the 22 week fetus, probable taste buds were identified, which showed higher level of cellular organization. Faint expression of synaptophysin was seen in the epithelium and within the muscle layer in age groups of 20th and 22nd weeks, suggesting the beginning of synaptogenesis and vesicle formation in the 20 and 22 week old fetuses. From 16th week onwards, lingual glands were observed in the posterior part of the tongue, another important observation regarding taste development. CONCLUSION: The work indicated that the maturation of taste buds and synaptic vesicles in human fetal tongue epithelium had started at around 20-22 weeks of age. This observation will pave the way for future understanding of the development of taste reception in utero.