Mammalian Thermosensation: A Product of Two Lines of Aversive Input

Abstract

Detection of environmental temperature is essential for survival as it allows for attraction to optimal, as well as avoidance of potentially dangerous temperatures. Normally, mammals are able to detect subtle variation in a broad range of temperatures. However, upon injury or with chronic pain syndromes, innocuous temperatures can become extremely painful. In this study we look at the neuronal inputs responsible for both innocuous and noxious temperature sensation. Recently, we generated mutant mice that are insensate to all thermal cues. These mice lack various sensory cells including those that express TRPV1, TRPM8 and Mrgprd. To dissect the thermosensory functional roles of these cell types, we engineered mice where these cell populations can be conditionally ablated with diphtheria toxin treatment. Our data show that non-overlapping, aversive inputs from TRPM8 and TRPV1 neurons are responsible for accurate temperature sensation from 0°C to 50°C. In addition, we find that avoidance of extreme temperatures is the result of an additional population of nociceptors that express Mrgprd, and that these responses are likely mediated through sensing of tissue damage rather than temperature. Together these studies give us a better understanding of how humans and other mammals are able to navigate a wide range of environments effectively and safely. The data show how only few types of neurons can encompass the full range of mammalian temperature sensation.