Pain sensitivity and vasopressin analgesia are mediated by a gene-sex-environment interaction

Abstract

Quantitative trait locus mapping of chemical/inflammatory pain in the mouse identified the Avpr1a gene, which encodes the vasopressin-1A receptor (V1AR), as being responsible for strain-dependent pain sensitivity to formalin and capsaicin. A genetic association study in humans revealed the influence of a single nucleotide polymorphism (rs10877969) in AVPR1A on capsaicin pain levels, but only in male subjects reporting stress at the time of testing. The analgesic efficacy of the vasopressin analog desmopressin revealed a similar interaction between the drug and acute stress, as desmopressin inhibition of capsaicin pain was only observed in nonstressed subjects. Additional experiments in mice confirmed the male-specific interaction of V1AR and stress, leading to the conclusion that vasopressin activates endogenous analgesia mechanisms unless they have already been activated by stress. These findings represent, to the best of our knowledge, the first explicit demonstration of analgesic efficacy depending on the emotional state of the recipient, and illustrate the heuristic power of a bench-to-bedside-to-bench translational strategy.

Fig. 1

Haplotype mapping localizes Nociq2 to a region of distal chromosome 10 upstream of Avpr1a. Bars in graph a show mean (± SEM) % positive samples in the late-phase formalin test of 16 inbred mouse strains (n=10–26/strain). Two contrasting haplotypes (b; light vs. dark squares) were noted in many SNPs in the 3.4-Mb linked region in the CGD1 SNP data set . c) An exhaustive analysis (by 100-kb segments) of SNPs within this region revealed high percentages of non-polymorphic SNPs among the 16 strains tested. Of SNPs showing polymorphisms, those with perfect correspondence (“perfect”) as defined in b were found only from 121.7–121.8 Mb, just upstream from Avpr1a (121.886 Mb), and from 122.1–122.3 Mb, upstream or within Ppm1h (122.115 Mb).

Fig. 2

Functional evidence for Avpr1a's involvement in pain. a) Formalin pain-resistant A/J mice display significantly higher basal expression of Avpr1a than pain-sensitive B6 mice in various loci. A strong trend (p=0.13) towards significance was seen in the periaqueductal gray (PAG). Bars represent mean (± SEM) mRNA expression in arbitrary units compared to the housekeeping gene, Gapdh; n=3–4 mice/strain. *p<0.05; ***p<0.001. b) As predicted, Avpr1a^−/− mice (−/−) display more late-phase formalin pain behavior than wildtype mice (+/+); heterozygous mice (+/−) were intermediate. Bars represent mean (± SEM) % positive samples (n=9–17 mice/genotype); *p<0.05 compared to +/+. c) Unique among a variety of other pain modalities examined , Avpr1a^−/− mice (−/−) display increased capsaicin pain behavior. Bars represent mean (± SEM) time spent licking the injected paw (s) (n=12–14 mice/genotype); *p<0.05 compared to +/+.

Fig. 3

Genetic association of a SNP within AVPR1A (rs10877969) to capsaicin pain ratings. Because of the paucity of subjects with GG genotypes (n=12), they were grouped with AG heterozygotes (n=33) for statistical comparison to AA homozygotes (n=59). a) No association of rs10877969 to overall capsaicin VAS scores. Bars represent mean (± SEM) VAS score averaged over the 50-min testing period. b) Subjective stress ratings (0–10 scale) in the subset of subjects (n=61) in which these data were collected, stratified by genotype. c) Genotype at rs10877969 interacts with stress to affect capsaicin pain in male subjects. Bars represent mean (± SEM) VAS score. The stress groups were defined as those above and below the means shown in b. ***p<0.001 compared to analogous AA group. d) No significant effect of stress (p=0.21) or genotype (p=0.14) on capsaicin pain in female subjects. Bars as in c.

Fig. 4

Evidence for the interaction of stress with desmopressin analgesia in 38 human subjects. a) Numerical rating scale (NRS) ratings of capsaicin pain (0–100) at 10-min intervals for desmopressin versus saline reveal that the overall effect of desmopressin (DES) was non-significant. Symbols represent mean (± SEM) NRS score. b) The order of drug administration interacted significantly with drug condition, such that desmopressin was highly efficacious in those receiving it in the second session (Veh.→DES), but not among those receiving it in the first session (DES→Veh.). Bars represent mean (± SEM) NRS scores averaged over the 50-min testing period; ***p<0.001 compared to Veh. c) Using a median split, subjects were divided into high- versus low-stress groups, which revealed a significant stress × drug interaction, such that desmopressin produced significant analgesia for low-stress subjects, but no effect of desmopressin emerged among high-stress subjects; *p<0.05 compared to vehicle. Bars as in b. d–g) The correlation of desmopressin analgesia (expressed as saline–desmopressin difference scores in mean NRS scores; positive values represent desmopressin analgesia) with stress levels (0–10) is only seen in male subjects with the TT genotype at rs10877969 within AVPR1A.

Fig. 5

Interaction of AVP/V1AR-mediated analgesia and stress in male mice. a) Male CD-1 mice (n=7 mice/drug/condition) either habituated or not habituated to the testing environment were tested for capsaicin (2.5 μg)-induced pain behavior following s.c. injection of AVP (0.1 mg/kg) or saline (10 ml/kg). Bars represent mean (± SEM) time spent licking the injected paw (s); *p<0.05, **p<0.01. b) Increased capsaicin sensitivity only in non-habituated Avpr1a^-/- mice (−/−) compared to wildtype mice (+/+) (n =4–5 mice/genotype/condition). Bars represent mean (± SEM) time spent licking the injected paw (s); *p<0.05. c) Absence of opioid-mediated (i.e., reversible by 10 mg/kg naloxone) swim stress-induced analgesia in Avpr1a^-/- mice (−/−). Bars represent mean (± SEM) percentage of maximum possible analgesia on the 56 °C hot-plate test (n=6–7 mice/genotype/drug); **p<0.01; ***p<0.001. d) A/J versus B6 strain differences in formalin sensitivity are dependent on habituation. Bars represent mean (± SEM) percentage of positive samples in the late-phase formalin test (n=4–6 mice/genotype/condition); *p<0.05. For analogous female data, see Fig. S8.