Motilin excites neurons in the cerebral cortex and spinal cord

The 22 amino acid polypeptide motilin was tested by iontophoretic application onto neurons in the rat cerebral cortex and by perfusion over the isolated hemisected toad spinal cord. Motilin (25--150 nA) excited identified cortico-spinal neurons and other deep spontaneously firing cortical cells. Excitation developed relatively rapidly and lasted for up to 60 sec after the application. Motilin was a potent excitant (threshold concentration 2.5 x 10(-9) M) of neurons in the amphibian spinal cord, eliciting a depolarization of dorsal root terminals and motoneurons. Its effects were substantially reduced after tetrodotoxin, suggesting a primary site of action on spinal cord interneurons.