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Cell Rep. 2018 May 15;23(7):2001-2013. doi: 10.1016/j.celrep.2018.04.065.

Sensory Afferents Use Different Coding Strategies for Heat and Cold.

Author information

1
CERVO Brain Research Centre, Québec Mental Health Institute, Quebec City, QC, Canada.
2
CERVO Brain Research Centre, Québec Mental Health Institute, Quebec City, QC, Canada; Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec City, QC, Canada.
3
CERVO Brain Research Centre, Québec Mental Health Institute, Quebec City, QC, Canada; Department of Physics, Physical Engineering, and Optics, Laval University, Quebec City, QC, Canada.
4
Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, ON, Canada; Department of Physiology and the Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada.
5
CERVO Brain Research Centre, Québec Mental Health Institute, Quebec City, QC, Canada; Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec City, QC, Canada; Department of Physics, Physical Engineering, and Optics, Laval University, Quebec City, QC, Canada.
6
CERVO Brain Research Centre, Québec Mental Health Institute, Quebec City, QC, Canada; Center for Optics, Photonics and Lasers (COPL), Laval University, Quebec City, QC, Canada; Department of Psychiatry and Neuroscience, Laval University, Quebec City, QC, Canada. Electronic address: yves.dekoninck@neuro.ulaval.ca.

Abstract

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.

KEYWORDS:

combinatorial sensory coding; graded coding; in vivo two-photon imaging; somatosensory afferent polymodality; thermoception

PMID:
29768200
DOI:
10.1016/j.celrep.2018.04.065
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