Abstract Apoptosis similar to that seen in Alzheimer’s disease patients was found in the brain of aged dogs by the TUNEL method of detecting in situ DNA fragmentation. Apoptosis was observed in both neurons and glial cells, and was morphologically characterized by round and swollen cytoplasm and aggregated nuclear chromatin, al- though these changes were slight. Neurons and astrocytes in the gray matter and oligodendrocytes in the white mat- ter were affected. The number of ApopTag-positive brain cells increased slightly with age, but was not correlated to the number of senile plaques. A good correlation between the number of ApopTag-positive cells and the dementia in- dex was clearly found. The present study indicates that brain cell apoptosis could account for dementia in aged dogs and suggested that aged dogs may be useful as a sim- plified animal model for Alzheimer’s disease in man. Key words Apoptosis · Dementia · Dogs · Senile plaques · TUNEL method Introduction Senile plaques of both diffuse and amyloid types, as seen in patients with Alzheimer’s disease (AD) [3, 17, 19] and amyloid angiopathy have been found in the brains of aged dogs (more than 9 years old) [31]. However, neurofibril- lary tangles (NFT), which may directly account for de- mentia in AD, have not been observed in the brains of aged dogs [32, 37] or other aged animals [10, 21, 22, 24, 25, 28, 33], except for sheep [23] and the Asiatic brown bear [5]. Neuronal cell loss is another histopathological hall- mark of human dementia conditions [14, 30]. Recently, apoptotic neuronal cell death was detected in the brains of AD patients [6, 14, 29]. However, only a weak correlation between cell death and NFT and no relation between cell death and senile plaques were reported. This suggests the possibility that apoptotic neuronal cell death, and not se- nile plaques or NFT, is responsible for AD dementia. Moreover, amyloid β protein (Aβ), which is a major com- ponent of mature senile plaques, and amyloid angiopathy have been shown to be toxic in primary neuronal cultures [4, 7, 15, 16, 18, 35, 40] and PC12 cells [1, 2, 13, 39], and this neuronal cell death is likely to occur, at least in part, via apoptosis in vitro [36]. Therefore, we decided to investigate apoptosis in the brains of aged dogs. Very recently, a dementia index for dogs was proposed by Uchino et al. [34]. In the present study, we found brain cell apoptosis in aged dogs and ex- amined the correlation between apoptosis and clinical de- mentia. Materials and methods General neuropathology Fifty-five canine brains obtained at autopsy were used in this study. Thirteen dogs, aged 13–24 years, had been clinically evalu- ated for dementia before death using the index proposed by Uchino et al. [34] (Tables 1, 2); the remaining 42 dogs, aged from 1 month to 18 years old, were not evaluated for dementia. The postmortem time in the study ranged from 1 to 24 h. The brains were fixed in 10% neutral buffered formalin and routinely embedded in paraffin. Sections, 6 μm thick, from the mid part of the brain including the cerebral cortex, medulla, hippocampus and thalamus were stained with hematoxylin and eosin, Congo red and periodic acid methenamine silver (PAM) staining. Wijit Kiatipattanasakul · Shin-ichiro Nakamura · Mokbul M. Hossain · Hiroyuki Nakayama · Tomiya Uchino · Seigou Shumiya · Naoaki Goto · Kunio Doi Apoptosis in the aged dog brain Acta Neuropathol (1996) 92 : 242–248 © Springer-Verlag 1996 Received: 25 January 1996 / Revised, accepted: 15 March 1996 REGULAR PAPER W. Kiatipattanasakul · S. Nakamura · M. M, Hossain · H. Nakayama · K. Doi () Department of Veterinary Pathology, Faculty of Agriculture, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113, Japan Tel.: 81-3-38112-2111, ext. 5400; Fax: 81-3-5800-6919 T. Uchino Veterinary ME Research Center, 482-3 Ina, Akiruno, Tokyo 190-01, Japan S. Shumiya Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi-ku, Tokyo 173, Japan N. Goto Shin-Nippon Biomedical Laboratories, 2-7-7 Shinkawa, Chu-ou-ku, Tokyo 104, Japan