Effect of xanthone from Kielmeyera coriacea stems on serotonergic neurons of the median raphe nucleus.

Kielmeyera coriacea Mart. (Clusiaceae), known as "Pau Santo", is used to treat several tropical diseases. The hydroethanolic extract (HE) of Kielmeyera coriacea stems and its semi-pure dichloromethane constituent (DCM) produced an anti-immobility effect in rats submitted to the forced swimming test (FST), suggesting a antidepressant-like profile. This study evaluated the effect of intra-median raphe nucleus (MRN) microinjection of 1,3,7-trihydroxy-2-(3-methylbut-2-enyl)-xanthone, present in large quantity in the HE from Kielmeyera coriacea stems, on immobility behaviour in the FST in rats. The effects of xanthone were compared with intra-MRN microinjections of Way100635 (5-HT1A antagonist) or (+) 8-OH-DPAT (5-HT1A agonist). Locomotor activity in the open-field test (OFT) was evaluated as a complementary measure. Xanthone (0.3ng) or Way100635 (2.5microg) reduced, whereas (+) 8-OH-DPAT (5.0microg) increased immobility time in the FST. Way100635 (2.5 or 5.0microg) completely reversed the effects of (+) 8-OHDPAT (5.0microg), and potentiated the anti-immobility effect of the ineffective dose of xanthone (0.2ng) in the FST. The association of effective doses of (+) 8-OH-DPAT (5.0microg) and xanthone (0.3ng) annulled the effect of each compound on immobility time. These results suggest that xanthone acts as an antagonist at 5-HT1A autoreceptors in MRN and increases serotonin (5-HT) availability in projection regions, proving to be a prototype drug that may be useful in mood isorders such as depression, or indeed be a beneficial adjunctive treatment improving the efficacy and/or accelerating the effects of antidepressant drugs in patients with major depression.