Study on time-dependent variability in response properties found in mammalian taste neurons using sieve electrodes.

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The receptor cells of taste buds have a life span of about 10 days but it is not known if the response characteristics of these receptors alters during this turnover. To examine taste cell responses over time, a micromachined polyimide sieve electrode array was implanted between the cut ends of the rat chorda tympani nerve. We made the new version of sieve electrodes that have Iridium metal surface on each recording site. With this change, stability of recordings and expansion of recording period were achieved. Long-term stable recordings from regenerated single afferent fibers innervating taste buds were possible using this technique for up to a few weeks. Taste stimuli recorded from the same single fiber changed with time. The changes occurred in both the magnitude of response and the relative response profiles to four chemical stimuli, NaCl, sucrose, HCl and quinine HCl. These changes in response characteristics were hypothesized to result from changes in the taste receptor cells innervated by the afferent fiber as the receptor cells turn over in the taste buds.Our results might pose a significant question regarding the theories of coding of taste quality since the electrophysiological data on which these theories have been based has been obtained in acute single fiber recordings nearly all of which are from cut decentralized nerves. Since the response characteristics change from day to day how is the information of taste quality is maintained? For example, based on the results of the chronic recordings tomorrow's "sweet pattern" will be different from today's "sweet pattern". Further experiments will hopefully confirm these findings and provide new information on the cell biology of the taste receptors.