[Substance P in the primary sensory neurons innervating the dental pulp in the guinea pig].

Primary sensory trigeminal neurons supplying the dental pulp of incisors in guinea pigs were labelled by retrograde axonal transport. Using an autometallographic intensification procedure, 48 h after injection of wheat germ agglutinin/colloidal gold in the pulp, gold particles were detected in the cytoplasm of the neurons as black granulations. A morphometric study showed a bimodal repartition of the labelled neurons of the ganglion. By submitting ganglion slices to an anti-substance P immunserum revealed by immunocytochemistry, it could be observed that, among the neurons supplying the dental pulp of incisors, the majority of the largest were substance P immunopositive while the smallest were substance P immunonegative. These observations suggest that there could be at least two different populations of nerve fibres supplying the guinea pig incisor dental pulp. Substance P negative neurons could express different neurotransmitters.