1 The acute inhibitory effect of selective 5-hydroxytryptamine (serotonin) reuptake inhibitors (SSRIs) on 5-HT neuronal activity may offset their ability to increase synaptic 5-HT in the forebrain.2 Here, we determined the effects of the SSRI, paroxetine, and a novel selective 5-HTIA receptor antagonist, WAY 100635, on 5-HT cell firing in the dorsal raphe nucleus (DRN), and on extracellular 5-HT in both the DRN and the frontal cortex (FCx). Extracellular electrophysiological recording and brain microdialysis were used in parallel experiments, in anaesthetized rats.