Although mosquito
allergy induces the release of
histamine, the itch-related response, scratching, is not effectively suppressed by blockade of H1
histamine receptors. To address this question, we examined the effects of neonatal
capsaicin treatment on
allergic reactions and H1
histamine receptor-expressing sensory neurones in mice. Neonatal
capsaicin treatment almost completely abolished
allergy-associated scratching, without effects on plasma extravasation or increase in serum concentrations of
immunoglobulins E and G1. An injection of
edema contents from an animal exhibiting
allergic reaction elicited scratching in naive animals, suggesting the production of pruritogen(s) by
allergic reaction; this production was not suppressed by neonatal
capsaicin treatment. This treatment markedly decreased the number of sensory neurones immunoreactive for TRPV1
capsaicin receptor, with little effect on sensory neurones immunoreactive for
neurofilament 200, a marker of myelinated A-fibre neurones. In addition, there was a trend towards a reduction in numbers of sensory neurones immunoreactive for H1
histamine receptor. The results suggest that
capsaicin-sensitive sensory neurones that lack H1
histamine receptors play a key role in signalling of allergic itch.