Abstract
Cetacean brain sampling may be an arduous task due to the difficulty of collecting and histologically preparing such rare and large specimens. Thus, one of the main challenges of working with cetaceans’ brains is to establish a valid methodology for an optimal manipulation and fixation of the brain tissue, which allows the samples to be viable for neuroanatomical and neuropathological studies. With this in view, we validated a methodology in order to preserve the quality of such large brains (neuroanatomy/neuropathology) and at the same time to obtain fresh brain samples for toxicological, virological, and microbiological analysis (neuropathology). A fixation protocol adapted to brains, of equal or even three times the size of human brains, was studied and tested. Finally, we investigated the usefulness of a panel of 20 antibodies (neuromarkers) associated with the normal structure and function of the brain, pathogens, age-related, and/or functional variations. The sampling protocol and some of the 20 neuromarkers have been thought to explore neurodegenerative diseases in these long-lived animals. To conclude, many of the typical measures used to evaluate neuropathological changes do not tell us if meaningful cellular changes have occurred. Having a wide panel of antibodies and histochemical techniques available allows for delving into the specific behavior of the neuronal population of the brain nuclei and to get a “fingerprint” of their real status.
Highlights
Accepted: 19 January 2022In the course of evolution, cetaceans have undergone modifications with respect to their ancestral terrestrial status
Brains were obtained from 51 specimens of six different species of the suborder Odontoceti: striped dolphin (Stenella coeruleoalba) (n = 10), Atlantic spotted dolphin (Stenella frontalis) (n = 7), common dolphin (Delphinus delphis) (n = 3), bottlenose dolphin (Tursiops truncatus) (n = 3); short-finned pilot whale (Globicephala macrorhynchus)
In order to achieve an optimal fixation of the brain, it was fundamental to:
Summary
Accepted: 19 January 2022In the course of evolution, cetaceans have undergone modifications with respect to their ancestral terrestrial status. Throughout the phylogenesis, the cetaceans’ sphlancnocraniums lengthened in order to obtain a greater hydrodynamic body shape, the upper airways (the blowhole) migrated dorsally, while the neurocranium shortened (Figure 1). The brain does not diminish its size; it folds over itself and acquires a “boxing glove” shape, due to the lack of most of the olfactory structures in the frontal lobes and the pronounced width of the temporal lobe (Figure 2, right). One of the most eminent transformations occurred in the toothed whales (odontocetes) in their size, structure, and neuroanatomical organization. A unique characteristic of the toothed whales is the exceptionally large size of the brain, in some species both in absolute and in relative terms [2], and the extremely dense folding of the neocortex [3]
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