Abstract
Although mosquito allergy induces the release of histamine, the itch-related response, scratching, is not effectively suppressed by blockade of H, histamine receptors. To address this question, we examined the effects of neonatal capsaicin treatment on allergic reactions and H, 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 G,. 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 sensor), 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 H, histamine receptor. The results suggest that capsaicin-sensitive sensory neurones that lack H, histamine receptors play a key role in signalling of allergic itch.
