DETERMINANTS OF EMOTIONALITY IN THE RAT

A total of 112 rats (56 males and 56 females) is used to investigate the effects of some antecedent factors upon the defecation and ambulation scores derived from Hall's open‐field test of emotionality, given under precisely standardized conditions. Conditions of rearing and husbandry are similarly constant, except where systematically varied for experimental purposes. The results show that neither defecation nor ambulation is affected by systematic ‘gentling’. Sexual experience does not affect defecation, but increases ambulation significantly, and this effect appears due, among females, to the experience of suckling a litter. Previous experience of the same test at earlier ages decreases defecation among young rats, but not among older ones, while ambulation is unaffected throughout. The effect of ageing itself upon defecation is seen as a decrease among older rats only, young ones being unaffected: conversely, its effect upon ambulation is an increase among young ones only. The previously reported sex difference in response is confirmed; no interaction between this sex difference and any of the experimental variables was detected. It is concluded that these findings further support the status of defecation, as observed in this test, as a measure of an emotional response.