Sensory Afferents Use Different Coding Strategies for Heat and Cold

Publication date: 15 May 2018
Source:Cell Reports, Volume 23, Issue 7
Author(s): Feng Wang, Erik Bélanger, Sylvain L. Côté, Patrick Desrosiers, Steven A. Prescott, Daniel C. Côté, Yves De Koninck
Primary afferents transduce environmental stimuli into electrical activity that is transmitted centrally to be decoded into corresponding sensations. However, it remains unknown how afferent populations encode different somatosensory inputs. To address this, we performed two-photon Ca²⁺ imaging from thousands of dorsal root ganglion (DRG) neurons in anesthetized mice while applying mechanical and thermal stimuli to hind paws. We found that approximately half of all neurons are polymodal and that heat and cold are encoded very differently. As temperature increases, more heating-sensitive neurons are activated, and most individual neurons respond more strongly, consistent with graded coding at population and single-neuron levels, respectively. In contrast, most cooling-sensitive neurons respond in an ungraded fashion, inconsistent with graded coding and suggesting combinatorial coding, based on which neurons are co-activated. Although individual neurons may respond to multiple stimuli, our results show that different stimuli activate distinct combinations of diversely tuned neurons, enabling rich population-level coding.

Graphical abstract

Teaser

Wang et al. imaged thousands of mouse DRG neurons in vivo. They found the majority of small neurons to be polymodal. Furthermore, heat is encoded in a graded fashion by both individual and the population of neurons, whereas cold is encoded by the population of neurons using a combinatorial strategy.


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