The relative effects of transection of the gustatory branches of the seventh and ninth cranial nerves on NaCl taste detection in rats.

Abstract

Chorda tympani nerve (CT) transection in rats severely impairs NaCl taste detection. These rats can detect higher concentrations of NaCl, however, suggesting that remaining oral nerves maintain some salt sensibility. Rats were tested in a gustometer with a 2-response operant taste-detection task before and after sham surgery (n = 5), combined transection of the CT and the greater superficial petrosal nerves (GSP; 7x, n = 6), or transection of the glossopharyngeal nerve (GL; 9x, n = 4). Thresholds did not significantly change after sham surgery. Although the GL responds to NaCl and innervates nearly 60% of total taste buds, 9x surgery had no effect. However, 7x surgery increased NaCl detection threshold by approximately 2.5 log(10) units, greater than that reported for CT transection alone. These results suggest that the GSP contributes to NaCl sensitivity in rats and also demonstrate that the GL and perhaps the superior laryngeal and lingual nerve proper can maintain some NaCl detectability at high concentrations. These findings confirm the primacy of the 7th nerve relative to the 9th nerve in sensibility of NaCl in the rat model.

Salt craving: The psychobiology of pathogenic sodium intake

“…Inhibiting the depolarization of sodium taste receptors by blocking sodium channels with amiloride produces a significant impairment of sodium ingestion in depleted rats [91][92][93] and also reduces responsivity to NaCl in sodium replete rats in the CT and GSP nerves [94]. This effect is compounded when combined with a CT transection or a CT plus GSP transection [92,95].…”

Orosensory detection of sucrose, maltose, and glucose is severely impaired in mice lacking T1R2 or T1R3, but Polycose sensitivity remains relatively normal

“…During each NaCl session, one concentration of NaCl was tested against water. Testing was conducted with a modified descending method of limits procedure across sessions, as previously used (5). The NaCl concentration was systematically decreased with a single concentration presented on Tuesday and Thursday sessions.…”

Learning-based recovery from perceptual impairment in salt discrimination after permanently altered peripheral gustatory input

“…Training and testing for experiments 1 and 2 took place in a gustometer as described in detail by Spector et al (53) and modified as described by Blonde et al (1). Briefly, water-restricted rats were placed in an operant chamber within a sound attenuation enclosure.…”

“…This suggests that the remaining peripheral gustatory input provides some degree of salt discriminability. Indeed, removal of all gustatory input from the seventh cranial nerve by CTx and transection of the greater superficial petrosal (GSP) nerve (GSPx), a branch of the seventh cranial nerve innervating the palate, including the nasoincisor ducts (NIDs) in the rat, has been shown to affect sodium detection and salt discrimination more than CTx alone (1,17), suggesting that the signal from the GSP does support some degree of salt discriminability. Although not as robustly as the CT, the GSP responds relatively well to NaCl (22,36) and innervates taste buds that appear to contain ENaCs, as amiloride reduces overall GSP responsiveness to sodium salts (19,49).…”