Harmane is a beta-carboline, which binds to imidazoline receptors and it has been previously shown that it may have an antidepressant effect when administered acutely. This study is planned to investigate the effect of harmane on chronic unpredictable mild stress (CUMS) model and microglial (Iba-1) immunoreactivity in the same model as markers of neuroinflammation.

Male Wistar Albino rats (290–360 g) were divided into groups such as control (saline), CUMS, CUMS + Imipramine (20 mg/kg; i.p.), CUMS + Harmane5 (5 mg/kg; i.p.), CUMS + Harmane10 (10 mg/kg; i.p.) groups (n = 10–12 in each). In CUMS model, various stressors were applied for 40 days. On day 20, harmane administration was started for 20 days. At the end, sucrose preference and forced swimming tests were performed. Then, brains were removed with paraformaldehyde perfusion for Iba-1 immunohistochemical analysis in hippocampus. One-way analysis of variance and Tukey's test were used for statistical analysis.

The time of immobility in forced swim test was significantly reduced while sucrose preference was increased in Imipramine and CUMS + harmane10 groups. In immunohistochemical experiments, Iba-1 were overexpressed in CUMS group and Harmane significantly reduced the overexpression of Iba-1.

Our results suggest that chronic administration of harmane has an antidepressant-like activity in chronic stress model of depression. These results support the notion of imidazoline receptors involvement in depression by modulating neuroinflammation and at least a part of its antidepressant effect might be through modulating microglial activation as a reflection of neuroinflammation.

This research was supported by Marmara University, Scientific Research Projects – SAG-C-YLP-110915-0415 and SAG-E-120613-0233.

The authors have not supplied their declaration of competing interest.