Quantitative analysis of ubiquitin-immunoreactivity in the midbrain periaqueductal gray matter with regard to the causes of death in forensic autopsy

The aim of the present study was to examine Ub-immunoreactivity in the midbrain periaqueductal gray matter (PGM), which is involved in pain processing and modulation, in forensic autopsy cases (n=273) in relation to the causes of death: acute deaths from blunt injuries (n=75), sharp weapon injuries (n=36), fatal asphyxiation (n=22), drownings (n=16: freshwater, n=9; saltwater, n=7), fire fatalities (n=64), poisoning (n=12), hyperthermia (n=5), hypothermia (n=5), delayed deaths from blunt head injury (n=8), acute cardiac deaths (n=24), and acute cerebrovascular strokes (n=6). The Ub-immunoreactivity was clearly observed in the nuclei of the PGM neurons, showing no postmortem interference or age-dependency. A higher value was observed in blunt injuries, fire fatalities and also in saltwater drowning, hyperthermia and delayed head injury deaths. These findings suggest a complicated mechanism for the ubiquitination of PGM neurons, to which multiple factors including the intensity and duration of pains possibly under alert consciousness, traumatic and metabolic neurodegeneration may contribute.