Brainbow

[1] The original technique has been adapted for use with other model research organisms including the fruit fly (Drosophila melanogaster), zebrafish (Danio rerio[2]), and Arabidopsis thaliana.

[4] Brainbow was originally created as an improvement over more traditional neuroimaging techniques, such as Golgi staining and dye injection, both of which presented severe limitations to researchers in their ability to visualize the intricate architecture of neural circuitry in the brain.

[1] While older techniques were only able to stain cells with a constricted range of colors, often utilizing bi- and tri-color transgenic mice to unveil limited information in regards to neuronal structures, Brainbow is much more flexible in that it has the capacity to fluorescently label individual neurons with up to approximately 100 different hues so that scientists can identify and even differentiate between dendritic and axonal processes.

[4] Brainbow techniques rely on the Cre-Lox recombination, in which the protein Cre recombinase drives inversion or excision of DNA between loxP sites.

[5] Brainbow is implemented in vivo by crossing two transgenic organism strains: one that expresses the Cre protein and another that has been transfected with several versions of a loxP/XFP construct.

In order to elucidate differential XFP expression patterns into a visible form, brain slices are imaged with confocal microscopy.

When exposed to a photon with its particular excitation wavelength, each fluorophore emits a signal that is collected into a red, green, or blue channel, and the resultant light combination is analyzed with data analysis software.

Brainbow has predominantly been tested in mice to date; however, the basic technique described above has also been modified for use in more recent studies since the advent of the original method introduced in 2007.

More examples of neurons examined using the Brainbow technique in transgenic mice are located in the motor nerve innervating ear muscles, axon tracts in the brainstem, and the hippocampal dentate gyrus.

[4] The complexity of the Drosophila brain, consisting of about 100,000 neurons, makes it an excellent candidate for implementing neurophysiology and neuroscience techniques like Brainbow.

Ultimately, this technique provides the ability to efficaciously map the neuronal circuitry in Drosophila so that researchers are able to uncover more information about the brain structure of this invertebrate and how it relates to its ensuing behavior.

[4] In addition, due to the random nature in the expression of the fluorescent proteins, scientists are unable to precisely control the labeling of neural circuitry, which may result in the poor identification of specific neurons.

The sheer density of neurons coupled with the presence of long tracts of axons make viewing larger regions of the CNS with high resolution difficult.