Functional evidence for a transmission of peptides along the olfactory systems into the brain in healthy humans
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Some peptides are known to affect central nervous processing in humans after intravenous and intranasal application. These effects were assumed to be mediated via the peripheral blood. However, this assumption was challenged by the observation that for some peptides the intranasal application was more effective than the intravenous application in evoking central nervous effects. The present study served to test the hypothesis that following intranasal application, peptides exert central nervous effects that are not mediated by peripheral blood. In two experiments in healthy humans vasopressin (AVP) or cholecystokinin (CCK) were administered intranasally and intravenously in doses, comparable with respect to the induced plasma levels in the systemic blood. Cortical event-related potentials (ERPs) served as indicators of central nervous processing. The results indicate that under comparable plasma levels of vasopressin and cholecystokinin following intravenous or intransal administration, pronounced ERP-effects were observed only after intranasal, but not after intravenous application. It is concluded, that peptides can affect the brain via the olfactory or accessory olfactory systems.