STRAIN DIFFERENCES IN THE CONTROL INCIDENCES OF MORPHOLOGICAL ABNORMALITIES IN THE RAT WHOLE-EMBRYO CULTURE

Since the animal supplier to this laboratory stopped carrying the rat strain used for the previous 7 yr, a number of other strains from this supplier were tested to determine their suitability for use in the whole embryo culture system. The in vitro development from prenatal days 9.5 to 11.5 of rat conceptuses of the strain Kfm:WSA (A) was compared with that of strains Ibm: WSA (B), HanIbm: WIST (C) and Ibm: RORO (D) cultured under identical methodological conditions. The parameters for conceptal growth (yolk-sac diameter, embryonic crown-rump and head lengths) after 48 hr of culture of strains A, B and D were similar. These measurements were smaller in the conceptuses of strain C than in those of strain A, but embryonic differentiation (morphological score and somite numbers) was not delayed in comparison with strain A. The overall frequencies of conceptuses with dysmorphogenic events in strains A and B were 3.1 and 4.4%, respectively. In contrast, in strains C and D 30.0 and 22.6% of the conceptuses assessed had morphologically abnormal features. Both values were statistically significantly higher than the incidence in strain A. The types and frequencies of anomalies observed were different in the different strains tested. The results from conceptuses of strain B (derived from strain A) indicate that this strain is suitable for the culture model established in this laboratory, whereas strains C and D are not useful without methodological changes or adaptations. This study indicates that strain differences should be kept in mind when setting up the whole embryo culture system.