Chorda tympani proper nerve responses to intra-arterial and surface stimulation of the tongue in rhesus monkey and rat

The effect of intra-arterial injection of the proteins monellin, thaumatin and miraculin on the activity of the chorda tympani proper nerve were recorded in the rhesus monkey (Macaca mulatto) and the rat (Sprague-Dawley). The substances were injected into the blood stream to the lingual artery. It was found that monellin and thaumatin elicited a response only in the monkey and not in the rat. Acetylated thaumatin, a tasteless substance, gave no increase of the nerve activity. Miraculin had no effect in either species. NaCl, sucrose and citric acid injected intra-arterially gave a response in both species. It is concluded that the responses to intra-arterial injections were caused by stimulation of the taste buds and not nerve fibers. The results suggest there are taste receptors also on the parts of the taste cells not facing the oral cavity. The finding that there was no cross-adaptation between intra-arterial and oral application supports this conclusion.