Development and maturation of taste buds of the palatal epithelium of the rat: Histological and immunohistochemical study

Palatal. taste buds are intriguing partners in the mediation of taste behav ior and their spatial distribution is functionally important for suckling b ehavior, especially in the neonatal life. Their prenatal development has no t been previously elucidated in the rat, and the onset of their maturation remains rather controversial. We delineated the development and frequency d istribution of the taste buds as well as the immunohistochemical expression of alpha -gustducin, a G protein closely related to the transduction of ta ste stimuli, in the nasoincisor papilla (NIP) and soft palate (SP) from the embryonic day 17 (E17) till the postnatal day 70 (PN70). The main findings in the present study were the development of a substantial number of taste pores in the SP of fetal rats (60.3 +/- 1.7 out of 122.8 +/- 5.5; mean +/- SD/animal at E19) and NIP of neonatal rats (9.8 +/- 1.0 out of 44.8 +/- 2. 2 at PN4). alpha -gustducin-like immunoreactivity (-LI) was not expressed i n the pored taste buds of either prenatal or newborn rats. The earliest exp ression of alpha -gustducin-LI was demonstrated at PN1 in the SP (1.5 +/- 0 .5 cells/taste bud; mean +/- SD) and at PN4 in the NIP (1.4 +/- 0.5). By ag e the total counts of pored taste buds continuously increased and their mor phological features became quite discernible. They became pear in shape, ch aracterized by distinct pores, long subporal space, and longitudinally orie nted cells. Around the second week, a remarkable transient decrease in the total number of taste buds was recorded in the oral epithelium of NIP and S P, which might be correlated with the changes of ingestive behaviors. The t otal counts of cells showing alpha -gustducin-LI per taste bud gradually in creased till the end of our investigation (14.1 +/- 2.7 in NIP and 12.4 +/- 2.5 in SP at PN70). We conclude that substantial development of taste buds began prenatally in the SP, whereas most developed entirely postnatal in t he NIP. The present study provides evidence that the existence of a taste p ore which is considered an important criterion for the morphological matura tion of taste buds is not enough for the onset of the taste transduction, w hich necessitates also mature taste cells. Moreover, the earlier maturation of palatal taste buds compared with the contiguous populations in the oral cavity evokes an evidence of their significant role in the transmission of gustatory information, especially in the early life of rat. Anat Rec 263:2 60-268, 2001. (C) 2001 Wiley-Liss, Inc.