Biocytin

Biocytin is a conjugate of _D-biotin and _L-lysine, where the carboxylate of _D-biotin is coupled with the -amine of _L-lysine via a secondary amide bond. Biocytin is a classical neuroanatomical tracer commonly used to map brain connectivity. Biocytin is used as a versatile marker in anterograde, retrograde and intracellular neuroanatomical investigations and in biotinidase assays^[1][2]. In Vitro: Due to its high affinity for avidin, Biocytin can be visualized by using a host of avidin-conjugated markers at the light and electron microscopic level. Biocytin is used to visualize the morphology of dendritic and axonal arborizations^[1].
The Biocytin wide-field bipolar cell in rabbit retina is a sparsely populated ON cone bipolar cell with a broad dendritic arbor that does not contact all cones in its dendritic field. Identification of bipolar cells by selective uptake of Biocytin, labeled the cones with peanut agglutinin, and then identification of cone types using antibodies against blue cone opsin and red-green cone opsin. The Biocytin-labeled cells selectively contact cones whose outer segments stained for blue cone opsin and avoided cones that do not. Biocytin wide-field bipolar cell is an ON blue cone bipolar cell in the rabbit retina and is homologous to the blue cone bipolar cells that have been previously described in primate, mouse, and ground squirrel retinas^[3].