The neural induction of taste buds in the salivary ducts of the lingual gland of von Ebner

Abstract

Taste buds appear in the vallate papilla when tongue grafts are combined with sensory ganglia grafts in the anterior chamber of rats' eyes. After 50 days, many of the tongue grafts (but not the ganglion grafts) developed cysts, the papilla atrophied, and fewer taste buds were found in them than at earlier postoperative times. A study was therefore undertaken to determine whether exteriorizing the tongue graft (i.e., placing it in the confines of a corneal biopsy opening with the epithelial surface of the papilla facing outward) would better preserve the morphology of long-term grafts. In isogenic adult Lewis rats, tongue grafts were exteriorized alone or with nodose ganglia and examined after 90 to 100 days. The tongue grafts were better preserved irrespective of whether they were transplanted with or without a nodose ganglion. In addition, taste buds were now found in the epithelium of the ducts of von Ebner's lingual salivary gland. These glands lie just below the vallate papilla and because their ducts empty into the base of the papilla, portions of the ducts are unavoidably contained in tongue grafts. It appeared that intrinsic nerve fibers of the eye, just like nerve fibers from ganglia, induced the formation of ductal buds since ductal buds appeared in ten of 12 tongue grafts transplanted without added ganglia. Of significance was the observation that intense cholinesterase activity was seen in intragemmal nerve fibers of ganglionic neurons whereas no such activity was seen in intragemmal fibers when they were derived from intrinsic nerve fibers of the eye. These results indicate that exteriorization of tongue grafts better preserves their structure, that epithelium in the ducts of von Ebner's gland can be transformed into taste bud cells, that intrinsic nerve fibers of the eye can induce taste bud formation, and that there are two types of sensory neurons (based on intragemmal cholinesterase activity of their nerve fibers) which can cause taste bud development.