Nociceptive neurons respond to multimodal stimuli in Manduca sexta

Abstract

The caterpillar Manduca sexta produces a highly stereotyped strike behavior in response to noxious thermal or mechanical stimuli to the abdomen. This rapid movement is targeted to the site of the stimulus, but the identities of the nociceptive sensory neurons are currently unknown. It is also not known if both mechanical and thermal stimuli are detected by the same neurons. Here we show that the likelihood of a strike increases with the strength of the stimulus and that activity in nerves innervating the body wall increases rapidly in response to noxious stimuli. Both mechanical and thermal stimuli to the dorsal body wall activate the same sensory unit suggesting it represents a multimodal neuron. This is further supported by the effects of rapidly repeated thermal or mechanical stimuli which cause a depression of neuronal responsiveness that is generalized across modalities. Mapping the receptive fields of neurons responding to strong thermal stimuli indicate that these multimodal, nociceptive units are produced by class γ multi-dendritic neurons in the body wall.