Kinetics of neuronal contribution during the development of a contact allergic reaction

Antigen-induced arthritis in rats is associated with increased growth-associated protein 43-positive intraepidermal nerve fibres remote from the joint

Introduction

Pain in arthritis may be experienced in regions outside the affected joint, and hyperalgesia may even be widespread. The spread of pain is usually attributed to mechanisms in the central nervous system. We investigated whether rats with antigen-induced arthritis (AIA) exhibit peripheral changes in skin innervation remote from the inflamed joint.

Methods

After immunization, unilateral AIA in the knee joint was induced in rats. Intraepidermal nerve fibre density was determined by immunohistochemical staining for protein gene product 9.5 (PGP 9.5) and for nerve fibres expressing calcitonin gene–related peptide (CGRP), substance P (SP), transient receptor potential vanilloid 1 (TRPV1; the heat and capsaicin receptor), β-tubulin, and growth-associated protein 43 (GAP-43; a marker of regenerating nerve fibres) in paw pad skin and back skin. Cluster of differentiation 11b (CD11b)-positive macrophages and CD3-positive T cells were quantified in skin, and macrophages were quantified in the lumbar dorsal root ganglia. In addition, pain-related behaviour was assessed.

Results

Intraepidermal nerve fibre density (PGP 9.5) and the numbers of fibres expressing CGRP, SP, TRPV1, or β-tubulin did not show a significant change in the acute (3 days) or chronic phase (21 days) of AIA compared with control rats that were only immunized. However, paw skin and back skin revealed a significantly higher number of nerve fibres expressing GAP-43 at both the acute and chronic stages of AIA. The skin of arthritic rats in these regions did not contain a greater density of CD11b and CD3 immune cells than the skin of control rats. Enhanced expression of GAP-43 in nerve fibres of the skin was not related to hyperalgesia in the joint, but it accompanied persistent secondary cutaneous hyperalgesia in the skin remote from the inflamed joint.

Conclusions

Although the innervation of the skin remote from the joint did not show significant abnormalities of the other nerve fibre markers, the rapid and persistent increase of GAP-43 expression is conspicuous. The data suggest that immune-mediated arthritis is associated with changes in skin innervation remote from the inflamed joint, although the skin is not inflamed, which may contribute to symptoms in nonarticular tissue remote from the affected joint.

Contact hypersensitivity to oxazolone provokes vulvar mechanical hyperalgesia in mice

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.

Different responses of galanin and calcitonin gene-related peptide to capsaicin stimulation on dorsal root ganglion neurons in vitro

Both galanin (Gal) and calcitonin gene-related peptide (CGRP) are sensory neuropeptides which expressed in dorsal root ganglion (DRG) neurons and are involved in nociceptive processing. Capsaicin (CAP) influences nociceptive processing via influencing the expression of sensory neuropeptides in primary sensory neurons. However, little is known about the alterations of Gal and CGRP expression at the same condition stimulated by CAP. In the present study, primary cultured DRG neurons were used to determine the different responses of Gal and CGRP to CAP stimulation. DRG neurons were cultured for 48 hours and then exposed to CAP (2 μmol/L), capsazepine (CPZ) (2 μmol/L) plus CAP (2 μmol/L), or extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor PD98059 (10 μmol/L) plus CAP (2 μmol/L) for an additional 24hours. The DRG neurons were continuously exposed to culture media as a control. After that, the levels of Gal mRNA and CGRP mRNA of DRG neurons were determined using real time-PCR analysis. Gal and CGRP expression in situ was detected by an immunofluorescent labeling technique. The levels of phosphorylated-ERK1/2 (pERK1/2) protein were detected using a Western blot assay. The results showed that CAP evoked increases of Gal and its mRNA and decreases of CGRP and its mRNA in DRG neurons. Administration of either CPZ or PD98059 blocked the effects of CAP. These data indicate that Gal and CGRP shared different responses to CAP stimulation. Gal and CGRP may have different effects in nociceptive processing during neurogenic inflammation.

Study of the genetic factors predisposing to the development of psoriasis

Many findings confirm the influence of neuropsychic factors on the manifestation and exacerbation of the atopic dermatitis and psoriasis. Nowadays it is assumed that by means of neurotransmitters’ secretion the nervous system can influence different processes, including the immune mediated inflammation, which has the key role in the pathogenesis of such dermatosis. The article hereunder contains comprehensive data on prospective trends of following studies of the nervous regulation participation in the pathogenesis of such dermatosis.