Amiloride-sensitive sodium signals and salt appetite: multiple gustatory pathways

In the rat, the ionic specificity of Na+ appetite is thought to rely on amiloride-sensitive Na+ signals conveyed by the chorda tympani (CT) nerve. We evaluated whether robust Na+ appetite relies exclusively on CT-mediated amiloride-sensitive Na+ signals. Amiloride dramatically reduced sham drinking of NaCl (41.9 +/- 9.0 vs. 6.9 +/- 3.7 ml, 0.1 M NaCl without vs. with 100 mu M amiloride), which resulted in intake that was not different from intake of a non-Na+ salt solution (8.8 +/- 2.3 ml, 0.15 M KCl). In addition, intake of 0.1 M NaCl in CT-transected (CTX) rats was reduced (35.8 +/- 13.3 vs. 8.67 +/- 3.4 ml, sham-operated vs. CTX rats), but the addition of amiloride (100 mu M) further reduced intake in CTX rats (0.5 +/- 0.29 ml). These data support the idea that amiloride-sensitive Na+ channels are the critical gustatory substrate for Na+ identification during Na+ appetite in the rat. However, the data indicate that these amiloride-sensitive signals are not conveyed exclusively by the CT nerve but by an additional afferent pathway.