Lipid signature of neural tissues of marine and terrestrial mammals: consistency across species and habitats.
Marine mammals are exposed to O2-limitation and increased N2 gas concentrations as they dive to exploit habitat and food resources. The lipid-rich tissues (blubber, acoustic, neural) are of particular concern as N2 is five times more soluble in lipid than in blood or muscle, creating body compartments that can become N2 saturated, possibly leading to gas emboli upon surfacing. We characterized lipids in the neural tissues of marine mammals to determine whether they have similar lipid profiles compared to terrestrial mammals. Lipid profiles (lipid content, lipid class composition, and fatty acid signatures) were determined in the neural tissues of 12 cetacean species with varying diving regimes, and compared to two species of terrestrial mammals. Neural tissue lipid profile was not significantly different in marine versus terrestrial mammals across tissue types. Within the marine species, average dive depth was not significantly associated with the lipid profile of cervical spinal cord. Across species, tissue type (brain, spinal cord, and spinal nerve) was a significant factor in lipid profile, largely due to the presence of storage lipids (triacylglycerol and wax ester/sterol ester) in spinal nerve tissue only. The stability of lipid signatures within the neural tissue types of terrestrial and marine species, which display markedly different dive behaviors, points to the consistent role of lipids in these tissues. These findings indicate that despite large differences in the level of N2 gas exposure by dive type in the species examined, the lipids of neural tissues likely do not have a neuroprotective role in marine mammals.