Vitamin C Deficiency in Osteogenic Disorder Shionogi/Shi Jcl-od/od Rats: Effects on Sour Taste Preferences, Lick Rates, Chorda Tympani Nerve Responses, and Taste Transduction Elements.

Animals use sour taste to avoid spoiled food and to choose foods containing vitamins and minerals. To investigate the response to sour taste substances during vitamin C (ascorbic acid; AA) deficiency, we conducted behavioral, neural, anatomical, and molecular biological experiments with Osteogenic Disorder Shionogi/Shi Jcl-od/od rats, which lack the ability to synthesize AA. Rats had higher 3 mM citric acid and 10 mM AA preference scores when AA-deficient than when replete. Licking rates for sour taste solutions [AA, citric acid, acetic acid, tartaric acid, and HCl] were significantly increased during AA deficiency relative to pre- and post-deficiency. Chorda tympani nerve recordings were conducted to evaluate organic acid taste responses in the AA-deficient and replete rats. Nerve responses to citric acid, acetic acid and tartaric acid were significantly diminished in AA-deficient rats relative to replete controls. There was no significant difference in the number of fungiform papillae taste buds per unit area in the AA-deficient rats relative to the replete rats. However, mRNA expression levels of Gnat3 (NM_173139.1), Trpm5 (NM_001191896.1), Tas1r1 (NM_053305.1), Car4 (NM_019174.3), and Gad1 (NM_017007.1) in fungiform papillae taste bud cells from AA-deficient rats were significantly lower than those in replete rats. Our data suggest that AA deficiency decreases avoidance of acids and reduces chorda tympani nerve responses to acids. AA deficiency down-regulates some taste-related genes in fungiform papillae taste bud cells. However, the results also reveal that the mRNA expression of some putative sour taste receptors in fungiform papillae taste bud cells is not affected by AA deficiency.