Organohalogen contaminants and metabolites in cerebrospinal fluid and cerebellum gray matter in short-beaked common dolphins and Atlantic white-sided dolphins from the western North Atlantic.

Concentrations of several congeners and classes of organohalogen contaminants (OHCs) and/or their metabolites, namely organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), hydroxylated-PCBs (OH-PCBs), methylsulfonyl-PCBs (MeSO(2)-PCBs), polybrominated diphenyl ether (PBDE) flame retardants, and OH-PBDEs, were measured in cerebrospinal fluid (CSF) of short-beaked common dolphins (n = 2), Atlantic white-sided dolphins (n = 8), and gray seal (n = 1) from the western North Atlantic. In three Atlantic white-sided dolphins, cerebellum gray matter (GM) was also analyzed. The levels of OCs, PCBs, MeSO(2)-PCBs, PBDEs, and OH-PBDEs in cerebellum GM were higher than the concentrations in CSF. 4-OH-2,3,3',4',5-pentachlorobiphenyl (4-OH-CB107) was the only detectable OH-PCB congener present in CSF. The sum (Sigma) OH-PCBs/Sigma PCB concentration ratio in CSF was approximately two to three orders of magnitude greater than the ratio in cerebellum GM for dolphins.

Volumetric neuroimaging of the atlantic white-sided dolphin (Lagenorhynchus acutus) brain from in situ magnetic resonance images.

The structure and development of the brain are extremely difficult to study in free-ranging marine mammals. Here, we report measurements of total white matter (WM), total gray matter (GM), cerebellum (WM and GM), hippocampus, and corpus callosum made from magnetic resonance (MR) images of fresh, postmortem brains of the Atlantic white-sided dolphin (Lagenorhynchus acutus) imaged in situ (i.e., the brain intact within the skull, with the head still attached to the body). WM:GM volume ratios of the entire brain increased from fetus to adult, illustrating the increase in myelination during ontogeny. The cerebellum (WM and GM combined) of subadult and adult dolphins ranged from 13.8 to 15.0% of total brain size, much larger than that of primates. The corpus callosum mid-sagittal area to brain mass ratios (CCA/BM) ranged from 0.088 to 0.137, smaller than in most mammals. Dolphin hippocampal volumes were smaller than those of carnivores, ungulates, and humans, consistent with previous qualitative results assessed from histological studies of the bottlenose dolphin brain. These quantitative measurements of white matter, gray matter, corpus callosum, and hippocampus are the first to be determined from MR images for any cetacean species. We establish here an approach for accurately determining the size of brain structures from in situ MR images of stranded, dead dolphins. This approach can be used not only for comparative and developmental studies of marine mammal brains but also for investigation of the potential impacts of natural and anthropogenic chemicals on neurodevelopment and neuroanatomy in exposed marine mammal populations.

Neuroanatomy of the subadult and fetal brain of the Atlantic white-sided dolphin (Lagenorhynchus acutus) from in situ magnetic resonance images.

This article provides the first anatomically labeled, magnetic resonance imaging (MRI) -based atlas of the subadult and fetal Atlantic white-sided dolphin (Lagenorhynchus acutus) brain. It differs from previous MRI-based atlases of cetaceans in that it was created from images of fresh, postmortem brains in situ rather than extracted, formalin-fixed brains. The in situ images displayed the classic hallmarks of odontocete brains: fore-shortened orbital lobes and pronounced temporal width. Olfactory structures were absent and auditory regions (e.g., temporal lobes and inferior colliculi) were enlarged. In the subadult and fetal postmortem MRI scans, the hippocampus was identifiable, despite the relatively small size of this structure in cetaceans. The white matter tracts of the fetal hindbrain and cerebellum were pronounced, but in the telencephalon, the white matter tracts were much less distinct, consistent with less myelin. The white matter tracts of the auditory pathways in the fetal brains were myelinated, as shown by the T2 hypointensity signals for the inferior colliculus, cochlear nuclei, and trapezoid bodies. This finding is consistent with hearing and auditory processing regions maturing in utero in L. acutus, as has been observed for most mammals. In situ MRI scanning of fresh, postmortem specimens can be used not only to study the evolution and developmental patterns of cetacean brains but also to investigate the impacts of natural toxins (such as domoic acid), anthropogenic chemicals (such as polychlorinated biphenyls, polybrominated diphenyl ethers, and their hydroxylated metabolites), biological agents (parasites), and noise on the central nervous system of marine mammal species.