Albinism:

Most rats used in research are albinos, such as the Sprague Dawley stock. Albinism in rats is an inherited disorder of melanin metabolism caused by the lack of the enzyme tyrosinase, which has an impact both on melanocytes and neurons. Neuronal morphological abnormalities and functional impairments involve the following sites: medial vestibular nucleus, cochlear nuclei and retina. Studies comparing albino and pigmented animals have shown differences even in pharmacotoxic kinetics in these tissue areas.