Cross-fostering does not alter the differential sensitivity of Fischer and Lewis rats to central neurotensin-induced locomotion and hypothermia

A cross-fostering paradigm was used to determine whether the differential locomotor and hypothermic responses to neurotensin (NT) in Fischer (F344) and Lewis (LEW) rats are mediated by the post-natal environment. From post-natal day (PD) 1 to PD 21, male pups from each strain were assigned to a same-strain dam (in-fostered) or were cross-fostered, and at adulthood were implanted with a guide cannula over the lateral ventricle. They were then tested for locomotion and hypothermia following injection of vehicle, 0.18, 1.8 or 18 nmol of NT or D-Tyr[11]NT. In-fostered LEW, but not F344, displayed a strong dose-orderly hypothermic response to NT and to D-Tyr[11]NT while in-fostered F344, but not LEW, rats displayed strong locomotor responses to D-Tyr[11]NT. Cross-fostering had no effect on D-Tyr[11]NT-induced locomotor responses in either strain; it had no effect also on NT- and D-Tyr[11]NT-induced hypothermia in F344 rats while it slightly increased the sensitivity to NT in LEW rats. The results show that these NT-mediated actions are not influenced by cross-fostering or the pre-weaning environment.