[Peptides of digestive system and brain. Model of the cholecystokinin]

The systemic administration of exogenous cholecystokinin (CCK), (a peptide released into the circulation when nutrients arrive in small intestine) provokes inhibition of food intake in numerous animal species and a sensation of satiation in humans. The mechanism involved requires participation of vagal afferent neurons to transmit information, possibly on gastric distension, to brain stem. Two crucial questions remain unanswered: does peripheral endogenous cholecystokinin transport information necessary for satiation at end of normal meals and if so, how and when is this message coded and deciphered; other studies have demonstrated that very small doses of exogenous cholecystokinin (too low to induce satiation if administrated peripherally) will induce satiety if injected into cerebral ventricles or directly into cerebral parenchyma. This suggest but does not prove that cerebral endogenous CCK also plays a role in satiety. It is not known how the satiating action of centrally-administered CCK is related to that of peripherally-administered CCK. Current studies aim at establishing a coherent schema of neuro-endocrine mechanisms implicated (from the gastrointestinal wall via the brain to a motivated behaviour) in the fact that food taken during a meal induces the end of the latter.