Histochemical characteristics and distribution of lipofuscin and polyglucosan bodies in the brain of dogs more than 10 years old

The ageing process is accompanied by numerous changes in the brain of dogs, such as accumulation of amyloid, fibrosis of blood vessel walls and meninges, accumulation of lipofuscin, and the presence of polyglucosan bodies (PGBs), satellitosis and neuronophagia. In this study, the presence of lipofuscin and PGBs in various parts of the brain in dogs of different sexes and ages was examined. For this purpose, brain samples were stained using haematoxylin eosin, modified Ziehl Neelsen and Periodic acid Schiff (PAS) methods. Lipofuscin was visualised by Ziehl Neelsen and PAS methods of specific staining on the same brain tissue segments. Lipofuscin had accumulated in 93% of old (more than 10 years old) dog brains, mostly in neurons of the medulla oblongata. The percentage of age-related lipofuscin pigment in other examined brain tissue segments was lower than in the medulla oblongata. There was a small difference in the percentage of lipofuscin-positive individuals between the two staining methods. The presence of PGBs was established by the PAS method for the vast majority (about 93%) of the old dogs (more than 10 years old), while PGBs were not detected in the group of young dogs (up to 5 years old). However, PGBs occurred in all examined segments of the dog’s brain tissues (for each of the tissue types, from 90% to 93% of dogs were positive for PGBs). The results obtained the oldest dogs (15 years old) harboured PGBs both extracellularly and intracellularly, while in other dogs, only extracellular PGBs were seen. Lipofuscin was accumulated mostly in large neurons of olivary nuclei of the medulla oblongata. PGBs were confirmed in all examined segments of the brain tissue of dogs more than 10 years old. This is one of the numerous indications that old dogs could be a very good animal model for studying the normal ageing process or neurodegenerative diseases.