Ontogeny of immobility reactions elicited by clamping, bandaging, and maternal transports in rats

Wistar neonate rats assume a characteristic posture when being transported by the mother. This carrying posture is normally elicited by the pressure given by the mother's teeth on the pup's neck. By clamping or bandaging the neck and head an immobility reflex with flexion of body and limbs resembling the carrying posture is elicited when pups are in a supine position. On the contrary, by bandaging or by lightly clamping the pups in a prone position, a dorsiflexion with extension of forelimbs is elicited. Both clamping or bandaging inhibits contact and air righting. After a period of immobility bursts of activity follow. The characteristics of all the reactions described above depend on the age of the developing pups. It seems that the immobility reflex with ventroflexion of the body is a behavior used initially by pups to facilitate carrying by the mother, and by both pups and adults as a defense against predators. The posture adopted by the pups bandaged in the neck in a prone position is very similar to the posture they adopt while suckling from the mother. It is postulated that the weight of the mother when lying over the pups plus the pressure on the paws caused by their prone position, could be the stimulus that normally produces the suckling posture.