Effects of Spadin on neurogenesis, CREB activation and Serotoninergic neurotransmission. A) Spadin increases neurogenesis: (left), Representative photomicrographs of BrdU-labeled neurons in the dentate gyrus of the mouse hippocampus treated either with saline or with spadin (i.v., 10⁻⁶ M) for 4 days. (Right) Quantitation of BrdU positive cells of hippocampus treated with saline, fluoxetine or spadin (10⁻⁵ M) for 4 days. 85% of BrdU-labeled cells are positive to DCX. B) Enhanced spadin treatment-induced CREB activation in the hippocampus, as assessed by measuring phosphoCREB (pCREB) immunoreactivity. (left), Immunological distribution of pCREB in the mouse hippocampus after a 4-day i.v treatment. pCREB is phosphorylated in the cells near the subgranular zone (SGZ). Right: Quantification of pCREB positive cells/mm² in hippocampal SGZ. C) Effect of spadin on the firing rate of DRN 5-HT neurons. Spadin (10⁻⁵ M in a 100 μL bolus) or its vehicle is i.p. administered. Recordings start 30 min after the injection, and are performed for a maximal duration of 210 min thereafter. Left: Samples of “descents” performed along the DRN, showing typical integrated firing rate histograms in a vehicle-, TREK-1 KO- or spadin-treated animal. Right: 5-HT neuron firing activity, calculated on the basis of all the cells recorded within the successive tracks performed along the DRN.