The expression of bradykinin B₁ receptors on primary sensory neurones that give rise to small caliber sciatic nerve fibres in rats

The bradykinin B₁ receptor has been considered as an important mediator for inflammatory pain. In the present study, we have investigated the fibre types of sciatic nerve primary sensory neurones that express B₁ receptors by retrograde tracing in combination with immunohistochemical staining, or double-immunohistochemical staining. Approximately 12% of the A-fibre dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of fluorescein isothiocyanate-conjugated cholera toxin B subunit, were B₁ receptor-immunoreactive. Over 70% of the small diameter dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of tetramethylrhodamine isothiocyanate-conjugated wheat germ agglutinin, were B₁ receptor-immunoreactive. Over 50% of the (predominantly non-peptidergic) C-fibre dorsal root ganglion neurones, retrogradely labelled from an intra-sciatic nerve injection of fluorescein isothiocyanate-conjugated Bandeiraea simplicifolia isolectin B4, were B₁ receptor-immunoreactive. When calcitonin gene-related peptide, which is contained mainly in small caliber C- and Aδ-fibre primary afferents, and B₁ receptors were stained with a double-immunofluorescent method, over 80% of the calcitonin gene-related peptide-positive dorsal root ganglion neurones were B₁ receptor-immunoreactive. From these results we suggest that B₁ receptors are predominantly expressed by small diameter primary afferent neurones that give rise to sciatic nerve fibres, which include both peptidergic and non-peptidergic C-fibres and Aδ-fibres. Since peripheral nociceptive information is primarily transmitted by C- and Aδ-fibres, B₁ receptors may be involved in the modulation of nociceptive transduction or transmission.