The development of cholecystokinin in the interpeduncular nucleus of rats

This study describes the development and late disappearance of cholecystokinin-like immunoreactivity (CCK-LI) in the interpeduncular nucleus (IPN) of rats. Between one and 7 days of age, CCK-positive fiber labeling was sparse and restricted to the lateral subnuclei of the caudal IPN. By 28 days of age the density of CCK-positive fibers increased and labeling was found in the lateral, rostral and apical subnuclei, and medial to the dorsolateral subnuclei. At 35 days of age CCK-LI fiber labeling was absent in the lateral subnuclei and medial to the dorsolateral subnuclei. No additional changes in fiber labeling were observed after 35 days of age. These results suggest that significant anatomical or biochemical reorganization may occur in projections to the IPN between 28 and 35 days of age.