Fig. 3. Focal brain application of 5-HT indirectly inhibits the swim-gating neuron 204 (recorded in M11). Cell 204 becomes hyperpolarized and its tonic firing rate is suppressed in response to the brain application of 5-HT (5 µmol l^–1) (middle), but not by octopamine (50 µmol l^–1) (OA; bottom). During perfusion of amine-free saline (top), cell 204 fired action potentials at a constant rate of about 10 Hz. A schematic of the experimental preparation, cell 204 recording site, and placement of amine is shown to the left.