Mrgprd-expressing polymodal nociceptive neurons innervate most known classes of substantia gelatinosa neurons.
The Mas-related G-protein-coupled receptor D (Mrgprd) marks a distinct subset of sensory neurons that transmit polymodal nociceptive information from the skin epidermis to the substantia gelatinosa (SG, lamina II) of the spinal cord. Moreover, Mrgprd-expressing (Mrgprd(+)) neurons are required for the full expression of mechanical but not thermal nociception. While such anatomical and functional specificity suggests Mrgprd(+) neurons might synapse with specific postsynaptic targets in the SG, precisely how Mrgprd(+) neurons interface with spinal circuits is currently unknown. To study circuit connectivity, we genetically targeted the light-activated ion channel Channelrhodopsin-2-Venus (ChR2-Venus) to the Mrgprd locus. In these knock-in mice, ChR2-Venus was localized to nonpeptidergic Mrgprd(+) neurons and axons, while peptidergic CGRP(+) neurons were not significantly labeled. Dissociated Mrgprd(+) DRG neurons from mice expressing one or two copies of ChR2-Venus could be activated in vitro as evidenced by light-evoked currents and action potentials. In addition, illumination of Mrgprd-ChR2-Venus(+) axon terminals in spinal cord slices evoked EPSCs in half of all SG neurons. Within this subset, Mrgprd(+) neurons were monosynaptically connected to most known classes of SG neurons, including radial, tonic central, transient central, vertical, and antenna cells. This cellular diversity ruled out the possibility that Mrgprd(+) neurons innervate a dedicated class of SG neuron. Our findings set broad constraints on the types of spinal neurons that process afferent input from Mrgprd(+) polymodal nociceptors.
Wang
Hong
H
Department of Cell and Molecular Physiology, University of North Carolina Neuroscience Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Zylka
Mark J
MJ
D000818:Animals; D001703:Biophysics; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002478:Cells, Cultured; D000075402:Channelrhodopsins; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000528:radiation effects; D005727:Ganglia, Spinal / Q000166:cytology; D049452:Green Fluorescent Proteins / Q000235:genetics; D066298:In Vitro Techniques; D037102:Lectins / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009415:Nerve Net / Q000166:cytology / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D018408:Patch-Clamp Techniques; D010775:Photic Stimulation / Q000379:methods; D043562:Receptors, G-Protein-Coupled / Q000235:genetics; D011984:Sensory Receptor Cells / Q000145:classification* / Q000502:physiology*; D013376:Substantia Gelatinosa / Q000166:cytology*
D000075402:Channelrhodopsins; D037102:Lectins; C497098:Mrgprd protein, mouse; D043562:Receptors, G-Protein-Coupled; D049452:Green Fluorescent Proteins; D015740:Calcitonin Gene-Related Peptide