Abstract:
Zinc deficiency is associated with both anxiety and depression in animal models. Zinc
supplementation reduces depression-like behaviors in the forced swim test and increases
grooming behavior and line crossing in the open field test. Zinc is a toxin, however, and
excess zinc has been associated with increased anxiety-like behaviors, including a
reduced ability to extinguish fear and greater thigmotaxicity in the Morris water maze.
The addition of copper was reported to remediate the negative effects of zinc
supplementation in this case. Many of the studies reporting the anti-depressant and anti-anxiety
effects of zinc supplementation employed a single, acute zinc dose, or treatment
over a short period of time. This study employed a chronic, pre- and post-natal zinc
supplementation paradigm to determine if there would be a difference between zinc, zinc
plus copper, or lab water fed rats, on behavioral measures of anxiety and depression in
rats. It was hypothesized that the zinc-supplemented rats would display a higher amount of anxiety- and depression-like behaviors than controls, and that the zinc + plus copper
animals would show fewer anxiety- and depression-like behaviors than the zinc-supplemented
rats, similar to controls. However, the results showed that there was no
difference in depression-like behaviors between the groups on the forced swim test.
There was also no difference in anxiety-like behaviors between the groups on the
elevated plus maze or on day one of the open field test. On day two of the open field test,
there was a significant interaction between water group and time. The zinc rats spent
more time in the center at the end of the trial than at the beginning, while the zinc +
copper animals and the lab animals spent less time in the center at the end of the trial than
at the beginning. The multiple, conflicting results in this field of research may be due to
the complex mechanisms behind the relationship between zinc homeostasis and affective
disorders, but are more likely due to differences in methodology and high variability.
Although zinc supplementation seems to be a promising treatment, it should seek to
restore zinc homeostasis without leading to a state of excess zinc.
