Response properties of fibers in the hamster superior laryngeal nerve

The purpose of the present investigation was to record electrophysiological responses from single fibers in the hamster superior laryngeal nerve (SLN) that were responsive to chemical stimulation of the larynx. Twenty chemical solutions, commonly used in studies of mammalian gustatory physiology, were applied to taste buds on and around the epiglottis. These stimuli were dissolved in physiological saline. Responses were the number of impulses elicited over a 15-s period following stimulus onset, above or below the background activity elicited by a previous rinse with saline. Unlike fibers in the hamster chorda tympani or glossopharyngeal nerves, SLN units were not easily classifiable into response types. Excitatory stimuli were primarily acids and bitter-tasting stimuli, with the order of their effectiveness being urea much greater than tartaric acid greater than HCl greater than KCl greater than citric acid greater than caffeine greater than quinine hydrochloride greater than acetic acid. The sweet-tasting stimuli and most salts other than KCl were primarily inhibitory, with the order of inhibitory effectiveness being CaCl2 greater than sucrose greater than fructose greater than LiCl greater than NaNO3 greater than Li2SO4 greater than NaCl. A hierarchical cluster analysis of fibers yielded no distinct clusters, yet differing sensitivities across the fibers were suggested. SLN fibers are highly responsive to sour and bitter stimuli, although they are not sensitive to fine differences in taste quality, as are fibers in other gustatory nerves.