2.8. Measurement of brain monoamine neurotransmitter levels

After the behavioral test on Day 30, the rats were sacrificed, and the whole brains were quickly collected and stored at -80 °C for biochemical analysis. The cerebral cortex and the hippocampus were taken from the whole brain. These tissues were weighed and then homogenized in PBS (tissue weight (g): PBS volume (mL) = 1:9) with a glass homogenizer on ice. The homogenates were then centrifuged at 5000 × g for 5 min at 4 °C to get the supernatant. The levels of DA and 5-HT were measured by ELISA (Elabscience Biotechnology Co. Ltd, Catalog No. E-EL-0046, Houston, USA). The intra-assay coefficient of variation of DA and 5-HT were less than 10%. The sensitivities of assays for DA and 5-HT were 18.75 pg/mL and 9.38 ng/mL, respectively.