3.2 Antidepressant-like effects of D-serine in the FST and TST of mice
FST and TST in mice are widely used for detecting potential antidepressant-like activity(Wang et al., 2020). D-serine was injected into the bilateral NAc, with fluoxetine used as the positive control. Analysis indicated that compared with the vehicle group, D-serine (2, 5 ug/perside) or fluoxetine treatment significantly decreased the immobility time in the FST (Figure 2A). Similar to the consequences of FST, D-serine administration robustly reduced the duration of immobility of mice in the TST, compared with the vehicle group (Figure 2B). The magnitude of the D-serine (5 ug/perside) induced anti-immobility effect was comparable with that of fluoxetine (5 ug/perside).
To exclude the probability that the reduced immobility in these tests might be as a result of an increase in spontaneous locomotor activity(Eissa et al., 2020), mice were exposed to the open-field test. We found no important differences in the number of squares an animal crossed between the center region or the periphery region in all the groups (Figure 2C), and no effects for drug administration. These data indicated that the decrease of immobility observed in the two tests after D-serine disposal was not because of locomotor hyperactivity. Together, the data from the three tests revealed that D-serine may have antidepressant-like effects in control mice.