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The effects of forced swimming for 30 min on extracellular 5-hydroxytryptamine (5-HT) levels were examined in five brain regions in rats using in vivo microdialysis. A single dialysis probe was implanted under surgical anesthesia into either the striatum, ventral hippocampus, frontal cortex, amygdala, or lateral septum on the day before the study. Dialysate content of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) was measured by HPLC. Forced swimming elevated extracellular levels of 5-HT in the striatum to a maximum of 90% above baseline. In contrast, forced swimming reduced 5-HT levels in the amygdala and lateral septum to 50 and 40% of baseline, respectively. In the hippocampus and frontal cortex, 5-HT levels were not altered significantly by forced swimming. In all five brain regions, forced swimming reduced 5-HIAA levels to 45-60% of baseline. These results suggest that forced swimming modulates 5-HT neurotransmission in a regionally specific manner. Aside from being a significant biological stressor, the forced swimming test is used as an animal behavioral model to detect antidepressant drugs, including drugs that alter 5-HT neurotransmission. It is possible that the alterations of extracellular levels of 5-HT produced by forced swimming in certain brain regions may be associated with the ability of antidepressant drugs to selectively alter behavioral performance during the forced swimming test.
Kirby et al. (Thu,) studied this question.