Serotonergic Changes Produced by Repeated Exposure to Forced Swimming

Repeated forced swim resulted in a decrease in the concentrations of serotonin (5‐HT) and its metabolite 5‐hydroxyindoleacetic acid in the hypothalamus and amygdala 24 h after the second swim session. This stressor also increased the mRNA levels for tryptophan hydroxylase‐2, the rate‐limiting enzyme in neuronal 5‐HT synthesis, and 5‐HT transporter in the midbrain as well as 5‐HT1A receptor in the frontal cortex. Some of these serotonergic changes may be involved in the mechanisms of a depressive‐like behavior induced by a stress of repeated swim in these animals.