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Updated: Apr 12, 2026
Cheek Injection Model for Simultaneous Measurement of Pain and Itch-related Behaviors
Published on: September 27, 2019
Mechanisms Underlying the Scratching Behavior Induced by the Activation of Proteinase-Activated Receptor-4 in Mice
Eliziane S Patricio1, Robson Costa2, Claudia P Figueiredo2
1Department of Pharmacology, Centre of Biological Sciences, Universidade Federal de Santa Catarina, Florianópolis, Brazil.
Abstract:
A role for proteinase-activated receptor-4 (PAR-4) was recently suggested in itch sensation. Here, we investigated the mechanisms underlying the pruriceptive actions of the selective PAR-4 agonist AYPGKF-NH2 (AYP) in mice. Dorsal intradermal (i.d.) administration of AYP elicited intense scratching behavior in mice, which was prevented by the selective PAR-4 antagonist (pepducin P4pal-10). PAR-4 was found to be coexpressed in 32% of tryptase-positive skin mast cells, and AYP caused a 2-fold increase in mast cell degranulation. However, neither the treatment with cromolyn nor the deficiency of mast cells (WBB6F1-Kit(W/Wv) mice) was able to affect AYP-induced itch. PAR-4 was also found on gastrin-releasing peptide (GRP)-positive neurons (pruriceptive fibers), and AYP-induced itch was reduced by the selective GRP receptor antagonist RC-3095. In addition, AYP evoked calcium influx in ∼1.5% of cultured DRG neurons also sensitive to TRPV1 (capsaicin) and/or TRPA1 (AITC) agonists. Importantly, AYP-induced itch was reduced by treatment with either the selective TRPV1 (SB366791), TRPA1 (HC-030031), or NK1 (FK888) receptor antagonists. However, genetic loss of TRPV1, but not of TRPA1, diminished AYP-induced calcium influx in DRG neurons and the scratching behavior in mice. These findings provide evidence that PAR-4 activation by AYP causes pruriceptive itch in mice via a TRPV1/TRPA1-dependent mechanism.
Insights
Proteinase-activated receptor-4 (PAR-4) activation triggers itch in mice. This itch involves gastrin-releasing peptide (GRP) neurons and relies on TRPV1 channels, not mast cells, for its sensory pathway.
Area of Science:
- Neuroscience
- Dermatology
- Pharmacology
Background:
- Proteinase-activated receptor-4 (PAR-4) has been implicated in itch sensation.
- The specific mechanisms by which PAR-4 contributes to itch are not fully understood.
Purpose of the Study:
- To investigate the underlying mechanisms of PAR-4 agonist-induced pruriceptive actions in mice.
- To elucidate the role of mast cells, GRP neurons, and ion channels in PAR-4 mediated itch.
Main Methods:
- Administration of a selective PAR-4 agonist (AYPGKF-NH2) and antagonist (pepducin P4pal-10) in mice.
- Assessment of mast cell degranulation, GRP receptor antagonism, and calcium influx in dorsal root ganglion (DRG) neurons.
- Evaluation of the effects of TRPV1, TRPA1, and NK1 receptor antagonists and genetic knockouts on AYP-induced itch.
Main Results:
- Intradermal PAR-4 agonist induced significant scratching behavior, blocked by the PAR-4 antagonist.
- PAR-4 was coexpressed in mast cells, but mast cell degranulation or deficiency did not affect AYP-induced itch.
- AYP-induced itch was reduced by GRP receptor antagonism and by TRPV1, TRPA1, and NK1 receptor antagonists.
- Genetic deletion of TRPV1, but not TRPA1, reduced AYP-induced calcium influx and scratching behavior.
Conclusions:
- PAR-4 activation by AYP elicits pruriceptive itch in mice.
- The mechanism involves GRP-positive neurons and is dependent on TRPV1 and TRPA1 channels.
- Mast cells do not play a significant role in PAR-4 mediated itch in this model.
