Regional differences in the development of cholecystokinin-like activity in rat brain.

The postnatal development of cholecystokinin (CCK) in rat brain was studied by radioimmunoassay and bioassay of tissue extracts. Marked differences were found in the patterns of development in different regions of the brain. In the cerebellum and brainstem of newborn rats the concentrations of CCK8-like immunoreactivity were 40-100% those in adults, whereas in more rostral regions the concentrations were 1-10% of those in adults. Between 0 and 14 days in concentrations of CCK-like activity measured by radioimmunoassay increased up to 30-fold in hypothalamus, cortex and olfactory bulb; in the cortex there were further increases up to 42 days. Cortical CCK was also measured by bioassay on rabbit gall bladder in vitro; bioactivity was identified in foetuses, and after birth showed a similar pattern of increase to that measured by radioimmunoassay. Immunoreactive material in extracts of neonatal cerebellum, brainstem and cortex was identified as CCK8 on the basis of cross-reactivity with different antisera, and chromatographic properties on gel filtration. The results raise the possibility of different rates of maturation of central CCKergic systems.