Contact Hypersensitivity to Oxazolone Provokes Vulvar Mechanical Hyperalgesia in Mice

Abstract

The interplay among pain, allergy and dysregulated inflammation promises to yield significant conceptual advances in immunology and chronic pain. Hapten-mediated contact hypersensitivity reactions are used to model skin allergies in rodents but have not been utilized to study associated changes in pain perception in the affected skin. Here we characterized changes in mechanical hyperalgesia in oxazolone-sensitized female mice challenged with single and repeated labiar skin exposure to oxazolone. Female mice were sensitized with topical oxazolone on their flanks and challenged 1-3 times on the labia. We then measured mechanical sensitivity of the vulvar region with an electronic pressure meter and evaluated expression of inflammatory genes, leukocyte influx and levels of innervation in the labiar tissue. Oxazolone-sensitized mice developed vulvar mechanical hyperalgesia after a single labiar oxazolone challenge. Hyperalgesia lasted up to 24 hours along with local influx of neutrophils, upregulation of inflammatory cytokine gene expression, and increased density of cutaneous labiar nerve fibers. Three daily oxazolone challenges produced vulvar mechanical hyperalgesic responses and increases in nerve density that were detectable up to 5 days post-challenge even after overt inflammation resolved. This persistent vulvar hyperalgesia is resonant with vulvodynia, an understudied chronic pain condition that is remarkably prevalent in 18-60 year-old women. An elevated risk for vulvodynia has been associated with a history of environmental allergies. Our pre-clinical model can be readily adapted to regimens of chronic exposures and long-term assessment of vulvar pain with and without concurrent inflammation to improve our understanding of mechanisms underlying subsets of vulvodynia and to develop new therapeutics for this condition.

Mast cells: Versatile gatekeepers of pain

“…We adapted an established model of mast cell-dependent contact hypersensitivity to topically applied hapten oxazolone [53], and found increased vulvar tactile sensitivity in oxazolone (Ox)-sensitized female mice after single and repeated labiar skin challenges with Ox [54]. Female ND4 Swiss mice were sensitized with topical oxazolone on their flanks and challenged 1–3 times on the labia on day 5 or day 5–7, respectively.…”

“…Female ND4 Swiss mice were sensitized with topical oxazolone on their flanks and challenged 1–3 times on the labia on day 5 or day 5–7, respectively. After a single challenge, heightened mechanical sensitivity of the ano-genital ridge lasted 24 hours and accompanied hyperinnervation, neutrophil influx, and increased expression of inflammatory cytokine genes in the labiar tissue [54]. Three daily oxazolone challenges produced vulvar mechanical hyperalgesic responses and increases in nerve density that were detectable up to 5 days post-challenge even after overt inflammation (neutrophil influx and upregulation of inflammatory cytokine transcripts) had resolved.…”

“…Until recently, itch and pain have been difficult to distinguish on a behavioral basis in rodents. In our studies, we defined pain (nociceptive) responses as licking or jumping following mechanical stimulation [54]. Licking of the affected region or wiping it with forepaws has been shown to correlate with pain sensation, while biting correlated more with itch [58, 59].…”

Stress and Chronic Pelvic Pain

“…61 Recently, other animal models have investigated various characteristics of vulvodynia such as peripheral nerve sprouting under low estrogenic conditions, 188 vulvar allodynia following repeated vulvovaginal fungal infection, 189 and oxazolone-induced delayed-type contact hypersensitivity of the vulva. 190 Women with vulvodynia have also shown defective regulation of the inflammatory response related to downstream activation of the HPA axis. Vulvodynia patients have increased mast cell degranulation and infiltration within vestibular biopsies when compared to controls.…”

Clonal differences in IgE antibodies affect cutaneous anaphylaxis-associated thermal sensitivity in mice

“…While IgE/Ag-provoked pain has previously not been demonstrated in mice, Lavich et al showed an IgE/Ag-induced transient thermal hyperalgesic response in the hind paws of rats [14]. IgE-dependent, mast cell-driven allergic contact hypersensitivity to the hapten oxazolone has also been shown to induce a persistent tactile sensitivity at the site of challenge [15]. …”