Long-term zinc deficiency decreases taste sensitivity in rats

The effects of zinc deficiency on taste sensitivity were examined in rats b y recording the electrophysiological responses of the chorda tympani (CT) n erve and by use of a preference test. Male 4-wk-old Sprague-Dawley rats wer e given free access to a diet containing 2.2 (zinc-deficient), 4.1 (low zin c) or 33.7 (zinc-sufficient) mg zinc/kg diet. A fourth group was pair-fed t he zinc-sufficient diet (with respect to the zinc-deficient rats). A two-bo ttle preference test using 0.15 mol/L NaCl and water revealed that NaCl pre ference was greater in the zinc-deficient and low zinc groups than in the c ontrol groups (zinc-sufficient and pair-fed) after 4 d of feeding. In the c ase of quinine hydrochloride solution (0.01 mmol/L), the preference was gre ater in zinc-deficient rats than in the other groups after 9 d, and the low zinc rats never showed a preference. Electrophysiological recording indica ted that in the zinc-deficient rats, the CT nerve response to 0.20 mol/L Na Cl was significantly less than that in the control rats after 21 d of feedi ng. In the low zinc rats, this response was significantly less than in the control rats after 35 d. The responses to quinine hydrochloride (0.02 mol/L ), L-glutamic acid, HCl (0.01 mol/L) and NH4Cl (0.25 mol/L) in the zinc-def icient rats were not significantly reduced until d 42. These findings sugge st that long-term zinc deficiency decreases taste sensitivity at the level of the CT nerve and that the change in NaCl preference due to zinc deficien cy occurs before any change in NaCl taste sensitivity.