Fig. 7. Swim-gating neuron 204 (in M11) is indirectly hyperpolarized in response to a 30-min focal brain application of the 5-HT/OA mixture (50 µmol l^–1). (A) A schematic of the experimental preparation, emphasizing that cell 204 was not directly exposed to the amine mixture. (B) During brain perfusion of the saline baseline (top), cell 204 fired action potentials at a constant rate. After a 30-min application of the mixture (middle), 204 became hyperpolarized (6 mV) and all action potentials ceased. This depression translated into a decrease in the excitatory drive to the swim CPG and no swimming was observed. During washout of the mixture (bottom), 204 partially repolarized and showed rhythmic depolarizations phase-locked with individual swim motor bursts in the DP nerve.