Veterinary Sciences (Sep 2022)

Toothed Whales Have Black Neurons in the Blue Spot

  • Simona Sacchini,
  • Antonio Fernández,
  • Blanca Mompeó,
  • Raquel Ramírez,
  • Manuel Arbelo,
  • Unn Holgersen,
  • Oscar Quesada-Canales,
  • Ayoze Castro-Alonso,
  • Marisa Andrada

DOI
https://doi.org/10.3390/vetsci9100525
Journal volume & issue
Vol. 9, no. 10
p. 525

Abstract

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Neuromelanin (NM) is a dark polymer pigment that is located mostly in the human substantia nigra, and in the locus ceruleus, referred to as “the blue spot”. NM increases linearly with age, and has been described mainly in the human brain; however, it also occurs in the neurons of monkeys, horses, giraffes, cattle, sheep, goats, dogs, rats, and even in frogs. While in most of these mammals NM shows the histochemical and ultrastructural features typical of lipofuscins, human NM is confined within cytoplasmic organelles that are surrounded by a double membrane, suggesting an autophagic origin. In a study on the morphology of the locus ceruleus of the family Delphinidae, the presence of a variable quantity of NM in the interior of locus ceruleus neurons was observed for the first time; meanwhile, nothing is known about its ultrastructure and composition. Transmission electron microscopy demonstrated in two toothed whales—an Atlantic spotted dolphin (Stenella frontalis; family Delphinidae) and a Blainville’s beaked whale (Mesoplodon densirostris; family Ziphiidae)—the presence of melanin granules associated with lipid droplets and membranes that were very similar to that of human NM. The relationship between NM and neuronal vulnerability must be studied in depth, and cetaceans may offer a new natural-spontaneous comparative model for the study of NM and its implication in neurodegenerative diseases.

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