The image shows co-injection of two tracers into the Giant Fiber Interneuron (GFI) of the Drosophila thoracic ganglia. TRITC (red) labels the injected neuron while the smaller neurobiotin (yellow) passes through gap junctions to reveal the extensive connectivity of the neural circuit. This brain lacks Fragile X Mental Retardation Protein (FMRP) which results in a selective increase in neurobiotin uptake via a mechanism unrelated to gap junctions. For more information, see the article by Kennedy and Broadie (pages 9844–9858).