Analysis of emotional defecation under severe and mild stress — evidence for genotype-situation interaction

Abstract

LEVELS of emotionality in mice and rats have been correlated with a number of autonomic responses; one of the most common measures being defecation at the time of the experiment. Hall suggested the use of defecation scores as an index of emotionality and provided the first comprehensive data on heritability of this trait. Since then, a number of reports have appeared on the subject (Broadhurst; Broadhurst and Eysenck; Henderson; Lindzey, Winston and Whitney; Tellegen; Thompson; Tobach and Schneirla. Fuller and Thompson have discussed the complexity of the relation between defecation and different measures of emotionality. They have pointed to discrepancies between the results of Lindzey and of Thompson, concluding that “Although there may be a genetic basis for frequency and amount of defecation in a mildly stressful situation … results point up sharply to the dependence of genetic models on the situation used.” In the study reported here further information is provided on the problem of interactions between situations and genotype as it relates to defecation responsivity, observed in two inbred strains of mice, their hybrid offspring and backcrosses tested in two controlled situations differing in the amount of stress. The purpose of the research was to test whether (1) autonomic responsivity as measured by defecation score, may in a given genotype vary with the test situation, while (2) different genotypes may show differential defecation rates within a given experimental condition. Information was also sought on the question of heritability of the defecation phenotype. Since the defecation scores were measures of the animals' responses in two entirely different situations of stress, heritability need not be the same for both defecation scores.