Serotonergic transmission is required for the anxiolytic-like behavioral effects of YL-IPA08, a selective ligand targeting TSPO.

Anxiety disorders are the most prevalent group of mental disorders globally, leading to considerable losses in health, functioning and increase of medical costs. Till now, the search for novel pharmacological treatments is driven by the growing medical need to improve on the effectiveness and the side effect profile of existing drugs. In central nervous system, the mitochondrially located translocator protein (18 kDa, TSPO) serves as the rate-limiting step for neurosteroidogenesis and influences GABAergic transmission. Since 5-HT is one of the most comprehensively studied neurotransmitter systems in the anxiety field, in the present study, we want to investigate whether 5-HT system is involved in the anxiolytic-like effects of YL-IPA08, a novel TSPO ligand designed and synthesized at our institute. Our data showed that YL-IPA08 could potentiate the 5-HTP-induced head-twitch response, and the anxiolytic-like effect of YL-IPA08 was abolished by pCPA or 5,7-DHT pretreatment in mice. Furthermore, we found that YL-IPA08 increased the extracellular levels of 5-HT in the rat ventral hippocampus in freely moving rat using the rapid and validated HPLC coupled with microdialysis. In addition, 5-HT level was positively correlated with the level of allopregnanolone. The above results suggest that 5-HT neurotransmission may play a critical role in the anxiolytic-like effects of YL-IPA08.