The influence of altered head, thorax and pelvis mass on the postnatal development of the air-righting reaction in albino rats.

The experiments were performed on 18 albino newborn rats of both sexes. The postnatal development of the air-righting-reaction (ARR) of the rats was tested for 4 different falling heights (30, 40, 50 and 60 cm) with 3 different loading conditions: artificial alteration of the head, thorax and pelvis mass, respectively. The reaction was analyzed in terms of a three-segment model of the rat (three rotatable parts: head-thorax-pelvis with only one degree of freedom between successive segments). Loading of the head resulted in a delayed development of the first phase of the ARR, whereas loading of the trunk or pelvis slowed the second phase of development. In general, it appears that loading of a body segment results in a delayed development of the rotation of that segment during free fall. Furthermore, loading of a caudal region was associated with an earlier rotation of cranial segments. The completion of the ARR maturation process showed no dependency on either the location or the size of the load, suggesting that the postnatal development of the ARR is pre-programmed.