Hemokinin-1 mediates anxiolytic and anti-depressant-like actions in mice

- Hemokinin-1 exerts anxiolytic and anti-depressant-like actions in mouse models.
- Stress-induced neuronal activation is decreased in hemokinin-1-deficient mice.
- Deleting and blocking the NK-1 receptors decrease depression-like behavior.
- Hemokinin-1 regulates stress/depression via unknown target-mediated mechanisms.

The tachykinin NK1 receptor was suggested to be involved in psychiatric disorders, but its antagonists have failed to be effective as antidepressants in clinical trials. Hemokinin-1 (HK-1), the newest tachykinin, is present in several brain regions and activates the NK1 receptor similarly to substance P (SP), but acts also through other mechanisms. Therefore, we investigated the roles of the Tac4 gene-derived HK-1 in comparison with SP and neurokinin A (NKA) encoded by the Tac1 gene, as well as the NK1 receptor in anxiety and depression-like behaviors in mice.Mice lacking SP/NKA, HK-1 or the NK1 receptor (Tac1−/−, Tac4−/−, Tacr1−/−, respectively) compared to C57Bl/6 wildtypes (WT), and treatment with the NK1 antagonist CP99994 were used in the experiments. Anxiety was evaluated in the light-dark box (LDB) and the elevated plus maze (EPM), locomotor activity in the open field (OFT) tests. Hedonic behavior was assessed in the sucrose preference test (SPT), depression-like behavior in the tail suspension (TST) and forced swim (FST) tests. FST-induced neuronal responsiveness was evaluated with Fos immunohistochemistry in several stress-related brain regions.In the LDB, Tac4−/− mice spent significantly less, while Tacr1−/− and CP99994-treated mice spent significantly more time in the lit compartment. In the EPM only Tac4−/− showed reduced time in the open arms, but no difference was observed in any other groups. In the OFT Tac4−/− mice showed significantly reduced, while Tac1−/− and Tacr1−/− animals increased motility than the WTs, but CP99994 had no effect. NK1−/− consumed markedly more, while Tac4−/− less sucrose solution compared to WTs. In the TST and FST, Tac4−/− mice showed significantly increased immobility. However, depression-like behavior was decreased both in cases of genetic deletion and pharmacological blockade of the NK1 receptor. FST-induced neuronal activation in different nuclei involved in behavioral and neuroendocrine stress responses was significantly reduced in the brain of Tac4 −/− mice.Our results provide the first evidence for an anxiolytic and anti-depressant-like actions of HK-1 through a presently unknown target-mediated mechanism. Identification of its receptor and/or signaling pathways might open new perspectives for anxiolytic and anti-depressant therapies.