Involvement of glutathione, ERK1/2 phosphorylation and BDNF expression in the antidepressant-like effect of zinc in rats

We investigated the antidepressant-like effect of zinc chloride (zinc) administered acutely during 7 days (i.p. route), or chronically during 30 days (oral route) in the forced swimming test (FST) in rats. It was also investigated whether the antidepressant-like effect of zinc is associated with changes in the glutathione antioxidant system in the Wistar rat brain. Animals receiving a single zinc dose (5, 15 and 30 mg/kg, i.p.) 24 h prior to analysis showed no changes in the FST, but glutathione reductase and glutathione S-transferase activity were reduced in the hippocampus and cerebral cortex. This treatment did not, however, affect the glutathione status (GSH and GSSG) in both brain structures. The 7-day zinc treatment (1, 5 and 15 mg/kg, i.p.) caused a mild though significant antidepressant-like effect in the FST at the highest dosing, without affecting the glutathione antioxidant system. Finally, a consistent antidepressant-like effect was achieved in the FST after chronic (30 days) zinc treatment (300 mg/L, p.o.). This was accompanied by a significant increase in total glutathione levels in the hippocampus and cerebral cortex. The good response to oral treatment in the FST led us to investigate other variables, such as ERK phosphorylation and BDNF expression. Similar to therapeutic antidepressants, zinc in chronic oral treatment produced an increase in ERK phosphorylation and BDNF expression in the cerebral cortex. It is our hypothesis that up-regulation of neuroprotective effectors (GSH, ERK and BDNF) may be related to the antidepressant properties of zinc, but this will require additional work to be confirmed.