Abstract
Histochemical and ultrastructural studies of the muscle coat of the oesophagus from ICRC/HiCri mice (with megaoesophagus) and DBA/2fNCri mice (normal oesophagus) were carried out. The striking observation from histochemical studies was the presence of smooth muscle in the abdominal segment of the oesophagus from ICRC mouse in contrast to the control strain where smooth muscle was present only in the lowermost portion adjoining the stomach. Ultrastructural studies of the oesophageal wall from 5and 10-day-old ICRC mice revealed an apparently normal muscle coat. In 3-month-old ICRC mice the upper abdominal segment of the oesophagus showed several abnormalities of smooth muscle fibres and paucity of plexus tissue accompanied by interstitial collagen deposition. The abnormalities were more severe in 1-year-old animals and were seen throughout the abdominal segment. From this study it is suggested that the primary cause of megaoesophagus in ICRC mice is neurogenic and not myogenic.