Role of 5-HT 1A receptors in antidepressant-like effect of dichloromethane fraction of Kielmeyera coriacea in rats subjected to the forced swim test

Objective : We examined the involvement of 5-HT neurotransmission on the antidepressant-like effect of the dichloromethane (DcM) fraction of an extract from Kielmeyera coriacea stems.
Materials and Methods : Male Wistar rats treated chronically (45 days, gavage) with the DcM fraction received an intradorsal raphe nucleus (DRN) microinjection of saline or 5-HT_1A receptor ligands and were evaluated in the forced swimming test (FST) and in the open-field test (OFT).
Results : The DcM fraction (5.0 mg/kg) reduced immobility time in the FST without altering locomotion in the OFT. IntraDRN microinjection of the 5-HT_1A receptor agonist, (+)-8-OH-DPAT (0.10; 0.20 or 0.33 μg) increased immobility time and reduced locomotion at the higher dose whereas the 5-HT1A antagonists, (-)-pindolol (0.10; 0.20 or 0.40 μg) or WAY100635 (0.11; 0.22 or 0.43 μg) did not produce any effect in the behavioral tests. IntraDRN (+)-8-OH-DPAT (0.20 or 0.33 μg) in rats treated with the DcM fraction (5.0 mg/kg) blocked the changes in the immobility time or in locomotion produced by each drug. Intra-DRN (-)-pindolol (0.10 μg) or WAY100635 (0.43 μg) in rats treated with a subactive dose of the DcM fraction (4.0 mg/kg) synergistically reduced immobility time in the FST.
Conclusion : The DcM fraction of Kielmeyera coriacea produced an antidepressant-like effect in the FST and interacted with 5-HT_1A receptor ligands. Activation of 5-HT_1A receptors into DRN by (+) 8-OH-DPAT produced detectable changes in the FST or in the OFT.

Keywords
Depression, dorsal raphe nucleus, Kielmeyera coriacea, 5-HT_1A receptor