Stability of immunocytochemical reactivity of neuronal substances following delayed fixation

The rates of deterioration of immunocytochemical staining for 4 peptide and 2 neuronal antigens were studied on human, guinea pig and rat colon and urinary bladder. It was found that if the fixation started within 10 h after surgery or death, little change was seen in the pattern and intensity of the immunostains. When fixation was further delayed, the immunostaining gradually deteriorated in quality and decreased in quantity until, when fixation was delayed for 60-72 h, most of the original immunostaining was absent. The deterioration rates of the neuronal antigens in the urinary bladder were slower than in the colon and all antigens were preserved for longer at 4 degrees C than at 20 degrees C. The deterioration curves produced from the present findings provide a standard for comparison with the immunostaining results obtained on tissues where fixation is delayed.