Despite the intense research on the neurobiology of stress, the role of serotonin (5-HT)1A receptors still remains to be elucidated. In the hippocampus, post-synaptic 5-HT1A receptors activation induces anxiolytic effects in animals previously exposed to stressful situations. However, little is known about somatodendritic 5-HT1A receptors in the median raphe nucleus (MRN). Therefore, the aim of this study was to investigate the role of 5-HT1A receptors located in the MRN in rats exposed to forced swim stress. After recovering from surgery, rats were forced to swim for 15 min in a cylinder. Intra-MRN injections of saline, 8-OH-DPAT (3 nmol/0.2 µL) and/or WAY-100635 (0.3 nmol/0.2 µL) were performed immediately before or after pre-exposure or 24 h later (immediately before test). Non-stressed rats received the same treatment 24 h or 10 min before test. Our data showed that 8-OH-DPAT increased latency to display immobility while decreasing time spent immobile in almost all experimental conditions. These effects were not prevented by previous treatment with WAY-100635. No effects of different treatments were described in non-stressed animals. Taken together, our data suggest that in addition to activation of 5-HT1A, 5-HT7 receptors may also be involved in the behavioural consequences of exposure to swim stress.
Keywords: Serotonin 1A receptors; depression; forced swim stress; median raphe nucleus.