Ultrasonic response of CBA newborn mice to bedding odour

A drop in ambient temperature which increases thermogenesis is the fundamen tal factor stimulating ultrasonic vocalization in newborn rodents. Neonatal mice modify ultrasonic calling in response to olfactory cues. When removed from the nest and cooled, CBA-strain mouse pups produced ultrasonic calls an the 3rd, 5th and 7th days of life. The presence of conspecific bedding a ffected their ultrasonic vocalization. The number and duration of calls wer e higher in 3-day-old CBA pups exposed to bedding of C57BL lactating female s than in newborns tested in the presence of bedding from CBA lactating fem ales. This indicates that CBA pups discriminate between the odours of the t wo genotypes. The influence of postnatal experiences on the ability to diff erentiate odours was investigated. Three-day-old CBA mice nursed by their o wn mothers vocalized at higher frequencies than did newborns fostered by C5 7BL lactating females. It is suggested that ultrasonic vocalization in CBA pups is affected by genetic factors and postnatal environmental conditions.