Effects of Postmortem Delay and Temperature on Neurotransmitter Receptor Binding in a Rat Model of the Human Autopsy Process

Studies of neurotransmitter and drug receptor alterations in neurodegenerative disorders have contributed to our understanding of the pathophysiology of these conditions. The effect of postmortem delay in freezing tissue after death and prolonged storage of tissue prior to analysis on receptor binding assays are potential artifacts that may limit interpretation of the effects of disease on receptor populations. We used a rat model of the human autopsy process to study the effects of increasing postmortem delay and storage time on N-methylscopolamine (NMS), p-aminoclonidine (PAC), flunitrazepam (FLU), and spiperone binding in a variety of rat brain regions. The rat brains were cooled using a temperature-controlled environment and thermistor probe to follow cooling curves obtained in human brain. Brains were cooled to either room temperature (22 degrees C) or refrigerator temperature (4 degrees C). For three of the four receptors, receptor binding decreased as postmortem delay before freezing increased, particularly in tissue cooled to room temperature. Unlike binding at other receptor sites, FLU binding increased with increasing postmortem delay to freezing. Different effects on KD and Bmax were noted for each ligand studied. No effects of the freezing process itself or storage at -80 degrees C were detectable.