Occurrence and distribution of different neurochemical markers in the human dental pulp

The occurrence and distribution of neuronal markers in human premolar and molar pulps were studied immunohistochemically. In the apical and central parts of the pulp, evenly distributed, thick neurofilament-immunoreactive nerve bundles predominated, which in many instances accompanied blood vessels. In the coronal parts, especially in the pulp horns, such nerve bundles formed a subodontoblastic plexus, while thin neurofilament-immunoreactive fibres projected into the odontoblastic region. In the coronal parts of the pulp, thin, varicose, calcitonin gene-related peptide (CGRP)- and occasionally substance P-immunoreactive fibres were observed in the pulp-dentine zone and also in the vicinity of blood vessels. Vasoactive intestinal polypeptide (VIP) fibres were distributed in several nerve bundles, while single VIP fibres were seen projecting into the odontoblastic region as well as in the vicinity of blood vessels. Peptide histidine isoleucine amide (PHI)-immunoreactive fibres showed a similar distribution as VIP, but were less common. Furthermore, neuropeptide Y-immunoreactive fibres occurred occasionally around blood vessels in the inner parts of the pulp. Tyrosine hydroxylase-immunoreactive nerve fibres with a varicose appearance were observed in some nerve bundles, but were also frequently seen around and in blood vessels. In premolar pulps obtained from teeth with open apices a less dense neurofilament innervation was seen in the coronal pulp. However, no apparent difference in the occurrence and distribution of the other neuronal markers was found compared to mature teeth. The human dental pulp, thus, seems to have a rich occurrence of neuropeptides and tyrosine hydroxylase in thin, varicose fibres. However, the distribution of the fibres expressing immunoreactivity to these neuronal markers seems to be sparse in comparison to neurofilament-immunoreactive fibres.