Insulin excites neurons of the area postrema and causes emesis.

Responses of neurons of the canine area postrema were recorded to ionophoretic application of insulin, apomorphine, leucine-enkephalin and glutamate. Each excited the neurons directly in a dose-dependent fashion. Like apomorphine and leucine enkephalin, which are known to induce emesis by activation of area postrema neurons, insulin given systemically induced emesis in intact dogs but not in animals with area postrema ablations. These results provide further support for a critical role of the area postrema in triggering the emetic reflex, and are the first definitive demonstration of a direct excitatory action of insulin on mammalian neurons.