AbstractAim  To localize interleukin‐1 receptor type I (IL‐1RI) in rat dental pulp and trigeminal ganglion (TG) and to test the hypothesis that pulpal inflammation increases neuronal expression of IL‐1RI.Methodology  Female Wistar rats were subjected to unilateral pulp exposures in the maxillary and mandibular first molars, whereas the contralateral jaws served as untreated controls. Seven days later the animals were transcardiacally perfused and the jaws and the TGs were removed and prepared for immunohistochemistry. Immunoreactivity for IL‐1RI was examined alone (DAB) and together with calcitonin gene‐related peptide (CGRP), neuropeptide Y (NPY), CD31 or CD34 by multiple‐labelling immunofluorescence. Quantification of IL‐1RI‐immunoreactive (‐IR) cells in the maxillary and mandibular division of the ganglion was performed in parasagittal immunoreacted sections of the right and left TGs. Data were analysed with Mann–Whitney Rank Sum test (P < 0.05).Results  Interleukin‐1 receptor type I was found on sensory (CGRP‐IR) and sympathetic (NPY‐IR) nerve fibres and on blood vessels (CD31‐ and CD34‐IR) in the dental pulp. It was also localized on sensory neurons and axons in the TG. Pulpal inflammation significantly increased the expression of IL‐1RI in the TG (P < 0.001).Conclusions  The localization of IL‐1RI on sensory nerve fibres and its up‐regulation in TG neurons during pulpal inflammation may imply a direct effect of IL‐1 in pulpal nociception. The presence of IL‐1RI on sympathetic nerve fibres and on blood vessels may indicate a vasoactive role of the same cytokine in the pulp.