Peptide activation of a simple neural circuit.

Pupae of the tobacco hornworm moth display a characteristic reflex response to tactile stimulation of sensory hairs located in the gin-trap. The reflex is not functional in the prepupa, but is activated abruptly as the animal enters the pupal stage by the direct action of an identified peptide hormone. The neuronal pathway between the sensory and motor neurons involved in the reflex is not direct, and the site of hormone action was localized to the connection between an interganglionic interneuron, and the motorneurons.