CCK and development of mother preference in sheep: a neonatal time course study.

We investigated the effects of a CCK-A receptor antagonist on the development of mother preference. Lambs received 2-NAP either at birth or 6, or 12 h later. Controls were given saline. When tested at 24 h of age, lambs receiving 2-NAP at birth or 6 h later did not display mother preference unlike controls and lambs which were given 2-NAP at 12 h. The effect of the antagonist persisted at 48 h of age in lambs treated at birth. This suggests that endogenous CCK participates in the development of mother preference only in the first few hours following birth.