Cholecystokinin has been proposed to act in a vagally-dependent manner to increase pancreatic exocrine secretion via actions exclusively at peripheral vagal afferent fibers. Recent evidence, however, suggests the CCK-8s may also affect brainstem structures directly. We used an in vivo preparation with the aim 1) investigating whether the actions of intraduodenal casein perfusion to increase pancreatic protein secretion also involved direct actions of CCK at the level of the brainstem; and, if so, 2) determining whether, in the absence of vagal afferent inputs, CCK-8s applied to the dorsal vagal complex (DVC) can also modulate pancreatic exocrine secretion (PES). Sprague-Dawley rats (250-400g) were anesthetized and the common bile-pancreatic duct cannulated to collect PES. Both vagal deafferentation and pretreatment with the CCK-A antagonist lorglumide on the floor of the IV ventricle decreased the casein-induced increase in PES output. CCK-8s microinjection (450pmoles) in the DVC increased significantly PES, the increase was larger when CCK-8s was injected in the left side of the DVC. Protein secretion returned to baseline levels within 30 min. Microinjection of CCK-8s increased PES (although to a lower extent) also in rats that underwent complete vagal deafferentation. These data indicate that, as well as activating peripheral vagal afferents, CCK-8s increases pancreatic exocrine secretion via an action in the DVC. Our data suggest that the CCK-8s induced increase in PES are due mainly to a paracrine effect of CCK, however, a relevant portion of the effects of CCK is due also to an effect of the peptide on brainstem vagal circuits.