Intranasal insulin administration: a method for dissociating central and peripheral effects of insulin

Animal studies have demonstrated the effects of insulin on central nervous system (CNS) functions such as cognition and control of adiposity, but human studies of insulin's CNS effects are more difficult to interpret. Peripheral insulin administration, which increases CNS insulin levels, is associated with increased insulin-stimulated glucose disposal and the release of counter-regulatory hormones--events that can confound CNS results. However, intranasal insulin administration results in direct insulin transport from the nasal cavity to the CNS via intraneuronal and extraneuronal pathways. Recent studies from independent groups of investigators have demonstrated functional, cognitive and adiposity changes following acute and chronic intranasal administration in humans. Available evidence suggests that intranasal insulin administration is safe in humans. Thus, this approach may provide the opportunity to dissociate the central and peripheral effects of insulin. Furthermore, intranasal insulin administration may offer a novel treatment strategy for disorders associated with central insulin abnormalities, such as diabetes and neurodegenerative diseases.