The Neural Basis of Localized Thermosensation in the tobacco hornworm, Manduca sexta.
- Thermosensing in animals is the ability to detect temperature or temperature changes. Survival often depends on being able to discriminate thermal events and to locate such stimuli. Although the molecular events associated with thermal transduction have been studied intensely, the encoding of thermal stimuli remains poorly understood at the level of neural circuits. Here, we describe for the first... read moretime behavioral and neural responses to local thermal stimuli in the invertebrate Manduca sexta evoked using a novel stimulation technique. Discrete and quantifiable thermal stimuli were delivered to the larval body wall using a low power infrared laser. As the stimulus intensity was increased, Manduca responded with a localized muscular twitch while high intensity stimuli that increased cuticle temperatures above 50°C elicited a defensive strike response indicating the activation of nociceptive neural transduction pathways. The activity of afferent sensory neurons in the body wall was monitored using an extracellular suction electrode on the lateral branch of the dorsal nerve of a reduced body preparation. Brief thermal stimuli evoked a rapid and transient increase in spike activity. Neural firing frequencies increased in response to a high heat thermal stimulus across the entire surface of the segmental body wall. We found the activity of these neurons to encode the initial rise in temperature within 10-20 ms of stimulus onset rather than the absolute temperature parameter of the stimulus. Findings from this work will enable further work into the neural circuits that underlie temperature sensation in invertebrates.read less