Senile plaques and cerebral amyloid angiopathy in an aged California sea lion (Zalophus californianus)

Senile plaques (SPs) and cerebral amyloid angiopathy (CAA) consisting of beta-amyloid (A beta) are major features in the brain of Alzheimer's disease (AD) patients and elderly humans and animals. In this study, we report the finding of SPs and CAA in an aged sea lion (30 years), which is the first demonstration of AD-related pathological changes in a marine animal. Histologically, SPs were observed at the cerebral cortex, most frequently at the frontal lobe, with two morphologically different types: the small round type and the large granular type. Only the small round SPs were positive for Congo red staining. The SPs were equally immunoreactive to A beta 40 and A beta 42 and were mainly composed of A beta with an N-terminal pyroglutamate residue at position 3. Amyloid depositions at vessel walls were noted at the meninges and within the parenchyma. Interestingly, double immunofluorescence staining for A beta 40 and A beta 42 showed that the two subtypes were deposited segmentally in different parts of the vessel walls. The lesions observed in the sea lion suggest that A beta deposition is widely present in various animal species, including marine mammals; however, the peculiar deposits similar to cotton wool plaques and the specific pattern of CAA are characteristic features of this animal.