23 SummaryThe occurrence of megaoesophagus in (CRC/ HiCri mice afforded opportunities to study the genetics and histology of this condition. The anomaly was found to be inherited as a recessive character. Histology indicated abnormality in the myenteric plexus. Keywords: Megaoesophagus; MiceJCRC/HiCri is a large-sized albino strain of mice which has been maintained at the Cancer Research Institute since 1957. It was originally obtained from the Haffkine Institute, Bombay, as a random-bred colony which on inbreeding developed mammary tumours and leukaemia. Megaoesophagus was observed from the fifteenth generation onwards. Later, owing to inbreeding, the anomaly was observed in all animals irrespective of whether mammary tumours or leukaemia occurred in them. Another subline without mammary tumours (ICRC/HiCrif) was developed by fostering (Shirke & Pai, 1978). Even in this strain all mice revealed a grossly dilated oesophagus on postmortem examination. The disease was not observed in 12 other strains of mice which were bred under the same conditions and fed the same diet. All these strains, which are maintained in an air-conditioned animal house, are healthy and free from infection. The occurrence of this abnormality in both males and females suggested that the condition was inherited. This study was therefore undertaken to investigate the mode of inheritance and histopathology of this condition. Materials and methodsThe strains of mice used were ICRC/HiCri with megaoesophagus and DBN2fNCri which did not have an oesophageal abnormality. The average adult body weights of the 20 male and 20 female JCRC mice investigated were 30·6 ± 0·7 g and 26·9 ± 0·6 g respectively. The average life span of ICRC mice is 12·8 ± 0·5 months (mean ± SE; n = 30). Breeding experiments between JCRC and DBA mice were carried out for genetic studies. The histology of the oesophagus was studied in animals of both sexes ranging from newborn to 1 year old. A total of 75 mice were investigated.Longitudinal and transverse sections (6 !-lm thick) of formalin-fixed paraffin-embedded tissues were stained with haematoxylin and eosin (H&E). A few sections were also stained with phosphotungstic acid-haematoxylin. Results GeneticsAs seen from the breeding experiments summarized in Table 1, the appearance of a normal oesophagus in all the FI hybrids between ICRC and DBA mice indicated that megaoesophagus is a recessive condition. The proportions from the intercross and backcross matings gave ratios which did not differ significantly from the expected values of 3: 1 and I: 1 respectively.In addition, all offspring from incrosses of ICRC mice developed megaoesophagus.These data indicate that megaoesophagus occurred in mice that were homozygous for an autosomal recessive gene. This recessive allele showed a wide range of expression from a slightly enlarged to a dilated oesophagus.
The first histologically confirmed case of carcinoma of the horn in a bilaterally cryptorchid Malvi bull, detected during an epidemiological survey, is reported. Examinations of 78,024 bullocks and 1,468 bulls, belonging to 7 different Zebu breeds revealed horn cancer in 793 bullocks and 1 cryptorchid bull but not in a normal bull. Histologically cryptorchid testes were devoid of spermatogenesis and had hyperplasia of Leydig cells. The remnant of castrated testes had only seminiferous tubules with coagulative necrosis and were devoid of spermatogenesis and Leydig cells. The significant difference in the incidence of HC in bullocks and cows and its absence in bulls is discussed in the light of the role of hormone in the causation of HC.
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 5- and 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.
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