Anatomy, three-dimensional reconstructions, and volume estimation of the brain of the Atlantic White-sided Dolphin (Lagenorhynchus acutus) from magnetic resonance images

Thyroid hormones (TH) play an integral role in neuro-development, particularly in the maturation of the corpus callosum, cerebellum, hippocampus, and inner ear. In rodents, it has been shown that persistent organic pollutants (POPs), particularly polychlorinated biphenyls (PCBs), interfere with TH signaling. These pollutants are widespread in the marine environment and biomagnify in marine mammals to very high levels. Brominated flame-retardants have also recently been shown to interfere with the TH system in experimental animals. Although at the present time levels are much lower than PCBs, flame-retardants have been shown to biomagnify in marine mammals. Hence, there is concern that PCBs and flame-retardants with similar mechanisms of toxicity may affect neuro-development of marine mammals.
At the present time, little is known about the variability of absolute and regional brain size within a population of marine mammals and among species. Magnetic resonance (MR) imaging has recently been used by other researchers to study the neuroanatomy of the fetal common dolphin, the bottlenose dolphin, the harbour porpoise, and the beluga whale. The benefit of this technique is the non-destructive and non-invasive acquisition of external and internal brain structure data, which minimizes dissection artifacts and allows more accurate determination of regional brain volumes. We are using MR imaging to better understand brain volume variability in both pinnipeds and odontocetes. Our research plan is to obtain total brain, hippocampus, cerebellum, and cerebral cortex volumes, as well as brain chemical data, in order to test the hypothesis that volume reductions are seen in animals with high levels of thyroid hormone disrupting chemicals. We have devised a detailed imaging and necropsy procedure to begin to assess the neurodevelopmental health effects of thyroid hormone disrupting chemicals in marine mammals, which we review for stranding network participants. In this presentation, we report initial results on the anatomy, three-dimensional reconstructions, and volume estimation of the brain of the Atlantic white-sided dolphin, obtained from MR images. The data collected from these images can also be used for diagnosing gross pathologies of the central nervous system (CNS), including nasitrema infestations, morbillivirus lesions, and trauma. In addition to diagnosing pathologies of the CNS, the data will give insight on the comparative neuroanatomy and evolution of brains in aquatic mammals.