Hair cell loss from acoustic trauma in chloroquine-treated red, black and albino guinea pigs.

In order to further elucidate the relationship between noise-induced hearing loss and pigmentation, a two-factor study was designed. Albino, red and black guinea pigs were divided into controls and chloroquine-treated groups and exposed to 1 kHz noise, 105 dB SPL, for 72 hours. One month later the animals were sacrificed and the loss of hair cells evaluated. The red guinea pigs developed a greater hair cell loss (OHC) in all three OHC rows than black or albino animals. Black and albino groups showed equal amounts of OHC loss. A high dosage of chloroquine seemed to reduce the OHC loss in albino, but not in black or red guinea pigs. The greater OHC loss in red compared with black animals is in accordance with the original hypothesis that melanin protects the inner ear against noise trauma. However, as red guinea pigs developed greater OHC loss than albinos, it is obvious that the original hypothesis needs to be modified to consider also the different melanin types, i.e., the black eumelanin and the red pheomelanin. The present results are interpreted as a toxic interaction in the strial melanocytes between pheomelanin and noise. It is suggested that the pathophysiology of noise-induced hearing loss involves cochlear mechanisms related to radical oxygen species (ROS) as melanin both generates and neutralizes ROS. A hypothesis about a linkage between dopamine, noise trauma and the cochlear melanocyte system is discussed.