Aging Decreases Chorda-Tympani Nerve Responses to NaCl and Alters Morphology of Fungiform Taste Pores in Rats

Abstract

Sensory processing is susceptible to decline with age. The sense of taste is, however, generally thought to be resistant to aging. We investigated how chorda-tympani nerve responses and fungiform-taste pores are affected by aging in the Sprague-Dawley rat, a model system for salt taste. First, we measured chorda-tympani nerve responses to NH4Cl and NaCl solutions in young (3-5 months old) and aged (14-15 months old) rats. Aged rats had significantly attenuated chorda-tympani responses to 0.01, 0.03, 0.1, and 0.3 M NaCl, whereas responses to NH4Cl were statistically similar between age groups. Second, we investigated if fungiform papillae, which harbor taste buds innervated by the chorda-tympani nerve, were affected by aging in "young" (4-7 months old) and "aged" ("aged1" 18 months old and "aged2" 24-28 months old) rats. Using scanning electron microscopy, we found that aging significantly reduced morphological characteristics associated with intact fungiform-taste pores (hillock, rim, pore presence, and open pore). We conclude that the structure and function of the peripheral-taste system may not be as resistant to aging as previously reported.

Keywords: aging; fungiform; microscopy; nerve; neurophysiology; taste.