Pruritus In Mice Research Articles

Sex-related differences in SLIGRL-induced pruritus in mice

AimsPruritus is a common symptom of skin diseases, and is associated with impaired sleep quality and a considerable reduction in the patient's quality of life. Recently, it was reported that there are sex-specific differences in scratching behavior in chronic pruritus patients. Namely, female chronic pruritus patients scratch more and have significantly more scratch lesions than male patients. However, few animal studies have examined sex-related differences in scratching behavior. Thus, the present work investigated sex-related differences in animal pruritus using pruritogens, which are often used to create experimental animal models of itching. Main methodsAcute pruritus was induced in ICR mice by a single intradermal injection of histamine, 4-methylhistamine, serotonin, compound 48/80, substance P (SP), or the proteinase-activated receptor-2 (PAR-2)-activating peptide SLIGRL-NH2. Chronic pruritus was induced by 5weeks of the repeated application of 2,4,6-trinitro-1-chlorobenzene (TNCB) to BALB/c mice. Key findingsFemale mice showed significantly higher scratching counts in SLIGRL-NH2-induced pruritus than male mice. Conversely, there was no obvious sex-related difference in scratching behavior for the other pruritogens examined. SignificanceThese results indicate that sex-related differences may exist in the pruritogen-responsive neurons that transmit the itch signal induced by SLIGRL-NH2, but not by histamine or 5-HT.

TLR3 deficiency impairs spinal cord synaptic transmission, central sensitization, and pruritus in mice

Itch, also known as pruritus, is a common, intractable symptom of several skin diseases, such as atopic dermatitis and xerosis. TLRs mediate innate immunity and regulate neuropathic pain, but their roles in pruritus are elusive. Here, we report that scratching behaviors induced by histamine-dependent and -independent pruritogens are markedly reduced in mice lacking the Tlr3 gene. TLR3 is expressed mainly by small-sized primary sensory neurons in dorsal root ganglions (DRGs) that coexpress the itch signaling pathway components transient receptor potential subtype V1 and gastrin-releasing peptide. Notably, we found that treatment with a TLR3 agonist induces inward currents and action potentials in DRG neurons and elicited scratching in WT mice but not Tlr3(-/-) mice. Furthermore, excitatory synaptic transmission in spinal cord slices and long-term potentiation in the intact spinal cord were impaired in Tlr3(-/-) mice but not Tlr7(-/-) mice. Consequently, central sensitization-driven pain hypersensitivity, but not acute pain, was impaired in Tlr3(-/-) mice. In addition, TLR3 knockdown in DRGs also attenuated pruritus in WT mice. Finally, chronic itch in a dry skin condition was substantially reduced in Tlr3(-/-) mice. Our findings demonstrate a critical role of TLR3 in regulating sensory neuronal excitability, spinal cord synaptic transmission, and central sensitization. TLR3 may serve as a new target for developing anti-itch treatment.

Topical Cholecystokinin Depresses Itch-Associated Scratching Behavior in Mice

Cholecystokinin (CCK) serves as a gastrointestinal hormone and also functions as a neuropeptide in the central nervous system (CNS). CCK may be a downregulator in the CNS, as represented by its anti-opioid properties. The existence of CCK in the peripheral nervous system has also been reported. We investigated the suppressive effects of various CCKs on peripheral pruritus in mice. The clipped backs of ICR mice were painted with CCK synthetic peptides and injected intradermally with substance P (SP). The frequency of SP-induced scratching was reduced significantly by topical application of sulfated CCK8 (CCK8S) and CCK7 (CCK7S), but not by nonsulfated CCK8, CCK7, or CCK6. Dermal injection of CCK8S also suppressed the scratching frequency, suggesting that dermal cells as well as epidermal keratinocytes (KCs) are the targets of CCKs. As determined using real-time PCR, mRNA for CCK2R, one of the two types of CCK receptors, was expressed highly in mouse fetal skin-derived mast cells (FSMCs) and moderately in ICR mouse KCs. CCK8S decreased in vitro compound 48/80-promoted degranulation of FSMCs with a transient elevation of the intracellular calcium concentration. These findings suggest that CCK may exert an antipruritic effect via mast cells and that topical CCK may be clinically useful for pruritic skin disorders.

INCB38579 is a novel, potent and selective histamine H4 receptor antagonist with activity in rodent models of inflammatory pain (117.28)

Abstract The histamine H4 receptor (H4) has been considered as an attractive therapeutic target for a number of diseases, such as allergy, asthma, atopic dermatitis and inflammatory pain. INCB38579 is a novel human and rodent active H4 receptor antagonist, with at least 50-fold selectivity over the human H1, H2 and H3 receptors and good pharmacokinetic properties in rats and mice. The compound potently inhibits histamine binding to and signaling through recombinant human and mouse H4 and blocks histamine-induced migration of human and mouse dendritic cells, as well as cell shape change and migration of human eosinophils. This novel H4 inhibitor is efficacious in blocking histamine-induced pruritus in mice and carrageenan-induced acute inflammatory pain in rats. Interestingly, when examined in a formalin pain model, INCB38579 could significantly reduce the relatively long lasting inflammation associated pain. A good correlation between the predicted protein binding adjusted potency from in vitro studies and the analgesic effect in vivo was observed. These results suggest that INCB38579 can serve as a useful tool for pharmacologic characterization of H4 and further supports the hypothesis that the H4 receptor is a target for the development of new therapeutics for various inflammatory diseases.

Acetaminophen enhances pruritus in a mouse model of contact dermatitis induced by suboptimal concentration of hapten

Acetaminophen (APAP) is one of the most commonly used drugs worldwide to reduce fever, particularly in children. It is generally considered to be a safe drug. However, a number of studies have shown that regular use of APAP increases the risk of developing allergic diseases. Nonetheless, no animal models have been used to investigate these findings. Therefore, we aimed to create an animal model of APAP-induced pruritus in mice. APAP (0.25% and 0.5%) was administered via drinking water daily from infancy, and a suboptimal concentration of 2,4,6-trinitrochlorobenzene (TNCB) was applied repeatedly to each ear three times a week for 7 weeks to evoke chronic allergic contact dermatitis. Neither 0.25% nor 0.5% APAP was overtly hepatotoxic after 73 days of daily administration. Repeated challenge with TNCB evoked increase in the number of scratching bouts compared to day 1. This increase in the number of scratching bouts was significant in 0.25% and 0.5% APAP groups but not in the group treated with TNCB alone. Daily administration of 0.5% APAP significantly increased in the number of scratching bouts compared to TNCB alone on day 29. This animal model will be useful for investigating the mechanism underlying the increased risk of development of eczema caused by regular APAP use and for examining safer and more effective therapy with APAP.

Putative mechanism of the itch–scratch circle: Repeated scratching decreases the cutaneous level of prostaglandin D 2, a mediator that inhibits itching

In atopic dermatitis, scratching of the skin as a reaction to itching causes injury to the skin, which, in turn, further increases the itching resulting in the establishment of the so-called itch–scratch circle. We have shown that prostaglandin (PG) D 2 plays an inhibitory role against pruritus in mice with atopic-like dermatitis; therefore, we examined the relationship between scratching and the cutaneous PGD 2 level using an artificial scratching model with a wire brush. Mechanical scratching induced a temporary increase of the skin PGs levels (PGE 2, PGD 2, 6-ketoPGF 1 α , PGF 2 α ). The skin PGD 2 level and the ability of PGD 2 production decreased at 48 h after repeated scratch, compared to that of normal skin, not so after single scratch. Immunohistochemical analysis and Western blotting revealed a decrease in the levels of cyclooxygenase-1 (COX-1) and hematopoietic PGD synthase in mechanically scratched skin. The reduced ability of the skin for PGD 2 production following mechanical scratching could be caused by this decrease in the expression levels of COX-1 and PGD 2 synthase. The results suggest that repeated scratching in mice decreases the ability of the skin to produce PGD 2, which is an endogenous mediator that inhibits pruritus, resulting in the establishment of the itch–scratch circle.

Spinal c-fos expression associated with spontaneous biting in a mouse model of dry skin pruritus

As a model of dry skin pruritus in mice, one hind paw was treated twice daily with a mixture of acetone/diethylether/water (AEW); controls received water only. A protective collar prevented the animals from accessing the treatment area. At 16 days, the collar was removed and AEW-treated mice exhibited marked biting of the treated paw; the number and cumulative duration of bites was significantly greater than in controls. After 3 additional treatment days (collars intact), animals were perfused for c-fos immunohistochemistry. There was significantly more fos-like immunoreactivity in the ipsilateral lumbar spinal cord of AEW-treated animals, with the majority in superficial laminae. It is proposed that biting of the dry skin reflects pruritus, and that neurons predominantly in superficial laminae of the dorsal horn may signal itch sensation.