Immunocytochemical localization of the neurokinin 1 receptor in rat dental pulp

Abstract

The dentin-pulp complex is a peripheral end-organ supplied by dense sensory nerve fibers. Substance P, a representative neuropeptide widely distributed in the dental pulp, has been reported to play roles in pain transmission and the amplification of inflammation. We analyzed here the expression of the neurokinin 1 (NK1) receptor, preferentially activated by substance P, using immunocytochemistry in rat dental pulp at both the light and electron microscopic levels. Conspicuous NK1 receptor immunoreactivity was found in the odontoblasts; immunolabelings were present at their plasma membrane and endosomal structures, especially in their cytoplasmic processes. Immunoreactions for NK1 receptor were also detectable in a part of the nerve terminals associated with the cytoplasmic processes of the odontoblasts. Furthermore, the endothelial cells of capillaries and post-capillary venules and the fibroblasts were labeled with the NK1 receptor in the subodontoblast layer. These findings suggest that pulpal cells and nerve fibers are targets for substance P that mediate multiple functions, including a vasoactive function and the regulation of vascular permeability as well as the modulation of pain transmission.

Peripheral Mechanisms of Dental Pain: The Role of Substance P

“…NK1 and NK2 receptors have been reported in odontoblast as well as in enamel forming cells (ameloblasts). As expected NK1 receptor is abundantly present on capillaries and smaller blood vessels, and both NK1 and NK2 receptors are densely distributed on the capillary plexus subjacent to dentin [27]. …”

“…A few studies have characterized the presence of NK receptors in rodent and human teeth [27, 28]. Animal studies identified the expression pattern of the tachykinin receptors NK1, NK2, and NK3 in different types of hard tissue cells, epithelial cells, fibroblasts, endothelium, and blood vessel walls in teeth and supporting oral tissues.…”

“…NK1 and NK2 receptors were also shown on fibroblasts in the periodontal ligament and in the pulp [27]. Substance P receptors have been reported also in human pulp tissue, although the methods used for their evaluation, radioreceptor assay, did not allow to measure which type of receptor (NK1, NK,2 or NK3) was primarily present [28].…”

“…Sensory fibers terminate near blood vessels, and SP receptors are present in high concentrations in this tissue [27, 28]. In healthy tissues, basal SP release plays a key role in the maintenance of tissue homeostasis; on the other hand, massive release of this molecule due to external stimuli induces a vasodilator response followed by a long-lasting increase in blood flow [7].…”

An Insight Into Neurophysiology of Pulpal Pain: Facts and Hypotheses

“…It can be speculated that NK1 is the receptor most involved in physiological conditions, while NK1 and NK2 become involved in pathological conditions because of the higher SP concentrations [37]. Kido et al [38], 2005, using immunocytochemical studies in rat dental pulp, reported that NK1 receptors were present in odontoblasts and ameloblasts and were abundant on capillaries and smaller blood vessels, and both NK1 and NK2 receptors were found on the capillary plexus subjacent to the dentin. Substance P receptors have also been reported in human pulp tissue, although the methods used for their evaluation, the radioreceptor assay, did not allow investigators to measure which type of receptor (NK1, NK2, or NK3) was primarily present [39].…”