Upper panel: Photomicrograph of a rat brain slice at the level of the dorsal raphe nucleus taken through the electrophysiology microscope. A recording electrode can be seen patched onto a neuron.

Middle panel: Single evoked action potential recorded from a 5-HT dorsal raphe neuron.

Lower panel: Fluorescent photomicrograph of the 5-HT dorsal raphe neuron whose recording is shown in the middle panel. The recorded cell is filled with biocytin and the slice subsequently immunohistochemically processed. The recorded cell is double-labeled for biocytin (red) and 5-HT (green), and therefore appears yellow.