Characteristics of sensory neuronal groups in CGRP-cre-ER reporter mice: Comparison to Nav1.8-cre, TRPV1-cre and TRPV1-GFP mouse lines

Abstract

Peptidergic sensory neurons play a critical role in nociceptive pathways. To precisely define the function and plasticity of sensory neurons in detail, new tools such as transgenic mouse models are needed. We employed electrophysiology and immunohistochemistry to characterize in detail dorsal root ganglion (DRG) neurons expressing an inducible CGRPcre-ER (CGRP-cre+); and compared them to DRG neurons expressing Nav1.8cre (Nav1.8-cre+), TRPV1cre (TRPV1-cre+) and TRPV1-GFP (V1-GFP+). Tamoxifen effectively induced CGRPcre-ER production in DRG. ≈87% of CGRPcre-ER-expressing neurons were co-labeled CGRP antibody. Three small and two medium-large-sized (5HT3a+/NPY2R- and NPY2R+) neuronal groups with unique electrophysiological profiles were CGRP-cre+. Nav1.8-cre+ neurons were detected in all CGRP-cre+ groups, as well as in 5 additional neuronal groups: MrgprD+/TRPA1-, MrgprD+/TRPA1+, TRPV1+/CGRP-, vGLUT3+ and ≈30% of trkC+ neurons. Differences between TRPV1cre and Nav1.8cre reporters were that unlike TRPV1-cre+, Nav1.8-cre+ expression was detected in non-nociceptive vGLUT3+ and trkC+ populations. Many TRPV1-cre+ neurons did not respond to capsaicin. In contrast, V1-GFP+ neurons were in 4 groups, each of which was capsaicin-sensitive. Finally, none of the analyzed reporter lines showed cre-recombination in trkB+, calbindin+, 70% of trkC+ or parvalbumin+ neurons, which together encompassed ≈20% of Nav1.8-cre- DRG neurons. The data presented here increases our knowledge of peptidergic sensory neuron characteristics, while showing the efficiency and specificity manipulation of peptidergic neurons by the CGRPcre-ER reporter. We also demonstrate that manipulation of all C- and A-nociceptors is better achieved with TRPV1-cre reporter. Finally, the described approach for detailed characterization of sensory neuronal groups can be applied to a variety of reporter mice.

Sensitization of small‐diameter sensory neurons is controlled by TRPV1 and TRPA1 association

“…1,4,9,27,41 Pain conditions trigger plasticity of sensory neurons via transcriptional, translational, and posttranslational mechanisms. Accordingly, sensory neuron subgroups have distinct transcriptomes, biochemical makeup, electrophysiology profiles and functions in naïve animals and humans.…”

“…1 Interestingly, recent single-cell data suggest that there are two types of MrgprA3 + DRG neurons: a first MrgprA3 + subgroup has both TRPV1 and TRPA1, while a second MrgprA3 + subgroup, which is represented by lesser number of neurons, express only TRPV1. 46 Recent single-cell RNA-sequencing data 27 and electrophysiology profiling of DRG sensory neurons 4 showed that there are two distinct MrgprD + subgroups (S4 and S5) representing C-mechano-heat and C-mechanosensitive nociceptors 46 . The second subgroup is MrgprD + DRG neurons, which are itch-sensing neurons 45 and also encode C-mechano-heat nociceptors.…”

“…S1-S3 groups represent peptidergic sensory neurons, S4-S6 are non-peptidergic neurons, and S7 is non-nociceptive C-fiber low-threshold mechanoreceptors ( Figure 1A). 4 Sequencing data indicate that vGLUT3 + sensory neurons (ie, S7) have TRPA1 mRNA 1 ; however, no TRPA1 responses were recorded from these neurons. 4 Sequencing data indicate that vGLUT3 + sensory neurons (ie, S7) have TRPA1 mRNA 1 ; however, no TRPA1 responses were recorded from these neurons.…”

“…Medium-tolarge mouse DRG sensory neurons do not respond to TRPA1 or TRPV1 agonists at concentrations used in this study. 4 Therefore, S7 and medium-to-large sensory neuron groups were not considered further in this study. 4 Therefore, S7 and medium-to-large sensory neuron groups were not considered further in this study.…”

“…Through a combination of single-cell sequencing 1,27 and electrophysiology, 4 seven small sensory neuron subgroups were identified using a variety of reporter mice ( Figure 1A). S1-S3 groups represent peptidergic sensory neurons, S4-S6 are non-peptidergic neurons, and S7 is non-nociceptive C-fiber low-threshold mechanoreceptors ( Figure 1A).…”