Chronic Oral Capsaicin Highlights the Relationship Between the Lingual and Chorda Tympani Nerves

Capsaicin, the chemical that gives chili peppers their spicy heat, is a neurotoxin which causes damage to the lingual nerve of the tongue. The lingual nerve is responsible for conveying somatosensory information (e.g. temperature, pressure, spiciness) to the brain and is found primarily in structures called fungiform papillae, which are located on the front 2/3 of the tongue. Housed within these papillae are the taste buds, which convey information about taste to the brain by way of the chorda tympani (CT) nerve. Surgically destroying the lingual nerve has been shown to cause age-dependent differences in taste bud volume. This suggests that while the CT and lingual nerves are distinctly different in location and function, some integrated relationship exists between them in supporting taste structures. In an attempt to understand this phenomenon, moderate doses of a capsaicin-containing solution were fed to SpragueDawley rats daily, for 40 days. Animals began treatment at young (5 days) or adult (40 days) ages and were sacrificed either two or 50 days after treatments concluded, to allow examination of system plasticity across different developmental stages. Capsaicin-related reductions in taste bud volume were limited to young animals examined 50 days after treatment. Chronic capsaicin exposure thus provides a naturalistic vehicle to study the CT-lingual relationship; since capsaicin is solely a lingual irritant its effect on taste bud volume provides additional evidence of lingual-CT nerve integration. Further exploration will be needed to elucidate both the exact nature of the nerves’ relationship and how capsaicin exerts its effects