Meeting Abstract
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 innocuous thermal stimuli remains poorly understood at the level of neural circuits. This can be readily addressed using insects as tractable models because their sensory neurons are identifiable and located peripherally. Here, we describe for the first time behavioral and neural responses to local thermal stimuli in the invertebrate Manduca sexta evoked using a novel stimulation technique. After coating the outer cuticle with a dark pigment, discrete and quantifiable thermal stimuli can be delivered to the underlying sensory neurons using a low power infrared laser. As the stimulus intensity was increased Manduca responded with increasingly vigorous but local muscular activity. High levels of thermal stimulation elicited a defensive strike response indicating the activation of nociceptive neural transduction pathways similar to those previously described for strong mechanical stimuli. To determine how thermal stimulation is encoded, the activity of afferent neurons was monitored using an extracellular suction electrode on the dorsal nerve of a reduced body preparation. Brief thermal stimuli evoked a transient increase in spike activity. Waveform and cluster analysis of these spikes suggests that only a small number of neurons in the body wall respond to non-damaging temperature changes and that they encode both the duration and intensity of the stimulus.
