Effect of Chronic Stress on TAAR1 Knockout Mice Tested for Depressive-like Behavior

The aim of the study was to investigate the functional role of the TAAR1 receptor in the formation of the stress response behavioral component. The behavior of TAAR1 knockout (TAAR1-KO) and wild-type (WT) mice was studied in tests reflecting a depressive-like state before and after chronic stress exposure (predator stress model), as well as delayed behavioral changes six weeks later. In the tail suspension test and the Porsolt forced swim test, no differences in depressive-like behavior were observed between TAAR1-KO and WT mice, either under normal conditions or after chronic stress exposure. However, TAAR1-KO mice exhibited motor hyperactivity at the onset of testing when placed in a stressful situation, leading to a sharp increase in the latency to first immobility in both tests. TAAR1 knockout did not affect signs of depressive-like behavior but led to a characteristic increase in motor activity levels. TAAR1-KO mice demonstrated a more pronounced response to chronic stress, with slower body weight recovery after stress cessation, such that their body weight remained significantly lower than that of WT mice for the last five weeks. It was found that six weeks after stress exposure, the indices of a depressive-like state continued to increase in both TAAR1-KO and WT mice.