Long-lasting effect of systemically administrated caerulein on monoaminergic neuronal pathways in rat brain.

The effect of systemically administrated cholecystokinin analog, caerulein, on monoaminergic neurons was examined in discrete regions of rat brain. A single injection of caerulein (400 micrograms/kg, i.p.) significantly elevated 5-hydroxyindoleacetic acid (5HIAA) levels in the prefrontal cortex lateral field, nucleus accumbens, tuberculum olfactorium and striatum after 2 hours, together with a significant increase in striatal serotonin (5HT). Moreover, the time-course study showed that the caerulein-induced increase in both 5HIAA and 5HT levels lasted even for 24 hours, and their levels tended to recover to the control values gradually. This time-dependent change was not found in the other monoamines and their metabolites. These results suggest a long-lasting action of caerulein on 5HT neurons in specific regions of rat brain.