TASTE DYSFUNCTION IN ZINC-DEPLETED RATS

An operant conditioning procedure for assessing gustatory sensory capacity in the rat was used to examine the effects of zinc depletion on the detection and discrimination of tastants. Initially, animals were separated into three groups with comparable serum zinc concentrations. Each animal was then tested for NaCl threshold and on a two-tastant discrimination task prior to, during, and after zinc depletion or paired feeding with supplemental zinc control procedures. The groups were maintained on a zinc-free food diet and drinking water was supplemented with 100 ppm zinc ion per day in the pre- and posttreatment phases. During the zinc manipulation phase, zinc supplement was withdrawn or reduced to 5 ppm zinc ion per day for the zinc-deprived groups or maintained for the control zinc groups. NaCl thresholds increased more than 8- and 22-fold from pre- to posttreatment in the moderately and severely zinc-depleted groups, respectively, but remained unchanged in controls. In comparison to controls, the moderately and severely zinc-depleted groups made more total errors on the two-tastant discrimination task. After 26 days of zinc repletion, detection thresholds and discrimination accuracy did not improve in the experimental groups. Analysis of plasma zinc samples after 24 days of zinc depletion indicated significantly decreased mean serum zinc content ((mu)g/dl) in the moderately (60) and severely (38) zinc-depleted groups, as compared to controls (101). Twenty-seven days of zinc repletion did not significantly increase serum zinc ((mu)g/dl) content in the former moderately (69) and severely (42) zinc-depleted groups. These results demonstrate that zinc depletion leads to altered taste function.