Mice Lacking TAAR1 Show No Early Behavioral Response to Acute Restraint Stress

The role of the TAAR1 receptor, one of the trace amine-associated receptors (TAARs) family, in the formation of the behavioral component of the stress response was studied. The behavior of female TAAR1 knockout mice and wild-type (WT) mice was investigated in tests of elevated plus maze and elevated zero maze (EPM and EZM) and forced swimming test (FST) under normal conditions and after uncontrolled restraint stress exposure for 30 min. In the EPM test, the initial level of locomotor and exploratory activity, as well as the anxiety, was identical in both groups of mice. In the EZM test, the initial indicators of anxiety in female TAAR1 KO mice compared to female WT mice were higher, and locomotor activity was lower. When testing mice in the EZM 30 minutes after the end of stress exposure, it was found that the anxiety in female WT mice sharply increased, and the indicators of locomotor activity and exploratory behavior significantly decreased. The behavioral indicators in the EZM test in TAAR1 KO mice before and after stress were identical. A pronounced behavioral component of the stress response was observed in both TAAR1 KO and WT mice during testing in EPM. There were no significant differences between TAAR1 KO and WT mice during testing in EPM four hours after stress exposure. In the FST test the latency to the first immobility was initially longer in TAAR1 KO mice compared to the WT mice, but 24 h after the stress this indicator has significantly decreased. As a result, TAAR1 KO and WT mice no longer differed in all behavioral indicators in the FST. Three weeks after acute restraint stress, both TAAR1 KO and WT groups showed a significant increase in immobility duration and a decrease in latency to the first immobility, however no difference between the both groups of animals were found. Thereby, we found the complete absence of behavioral change immediately after stressor exposure in TAAR1 KO compared to the WT mice.