Figure 1.

OPRM1-positive and OPRM1-negative human nociceptors express OPRD1 while OPRK1 is expressed in satellite glial cells

(A) Overall schematic of experimental design for 4-Plex in situ hybridization studies. The major nociceptive ion channel TRPV1 is paired with the major analgesic receptor (μ-opioid, OPRM1) and a series of genes coding for algesic and analgesic mediators.

(B) Scanned image of a complete section from human L3 DRG hybridized for the heat- and inflammation-activated channel TRPV1 (green), the μ-opioid (OPRM1) (magenta), δ-opioid (OPRD1) (yellow), and κ-opioid receptor (OPRK1) (orange). Note the strong expression and high prevalence of neuronal TRPV1 expression which tends to obscure the signal from the other genes at this magnification.

(C) Enlargement showing the multiple neuronal signals. Representative neurons are labeled i–iv and are characterized further in (H).

(D) Percentage of 1,280 DRG neurons expressing each individual transcript. Note the comparatively low neuronal expression of OPRK1.

(E) Percentage of DRG neurons expressing the most common transcript combinations, which defines populations i–iv. Bar graphs in (D) and (E) show mean, standard deviation (SD), and individual values from four independent tissue donors.

(F) Single-neuron example demonstrating the expression of OPRK1 in satellite glial cells surrounding the neuron, as detected by the standard probe (yellow) and, as a technical replicate, the custom probe (red). The large fluorescent patch, “L,” is lipofuscin. See also Figures S4 and S5.

(G) The preponderance of neurons that are surrounded by OPRK1 (κ-opioid receptor) expressing satellite cells.

(H) Individual channel and multi-channel microscopy images of representative neurons for each population (i–iv, as in C) and the corresponding populations’ cell size distribution. Scale bar, 25 μm.

(I) Percentages of nociceptors showing low, medium, or high expression levels for TRPV1 and each opioid receptor transcript averaged across the 4 tissue donors.