Brain ageing in mice leads to the progressive appearance of degenerative granular structures frequently referred to as “PAS granules” because of their positive staining with periodic acid-Schiff (PAS). It has been reported that these granules contain neo-epitopes that can be recognised by natural IgM auto-antibodies, and proposed that they intervene in a brain cleaning mechanism. Some preliminary studies seem to indicate that these neo-epitopes are also present in other structures than PAS granules, so the aim of this work has been to study and characterize the presence of neo-epitopes in mice brain. Brains from ICR-CD1 and senescence-accelerated mouse prone-8 (SAMP8) mice aged 3, 6 and 12 months of age were processed and criosectioned, obtaining coronal sections including the hippocampal zone. Immunofluorescence and PAS staining were performed on these sections. Staining shows that, besides hippocampal PAS granules, other brain structures are labeled with IgM or are IgM+. Among them, some astrocytes generally located in the vicinity of the ventricles, and also some granular structures nearby which are not stained with the PAS staining. The number of IgM+ astrocytes increases with age, whereas the number of IgM+ PAS- granular structures decreases. So, we conclude that the presence of neo-epitopes in the mice brain is not restricted to the previously described PAS granules, but can also be found in astrocytes and PAS- granular structures. The relationship between these structures and their function is still under study.