Rat odontoblasts may use glutamate to signal dentin injury.

Accumulating evidence indicates that odontoblasts act as sensor cells, capable of triggering action potentials in adjacent pulpal nociceptive axons, suggesting a paracrine signaling via a currently unknown mediator. Since glutamate can mediate signaling by non-neuronal cells, and peripheral axons may express glutamate receptors (GluR), we hypothesized that the expression of high levels of glutamate, and of sensory receptors in odontoblasts, combined with an expression of GluR in adjacent pulpal axons, is the morphological basis for odontoblastic sensory signaling. To test this hypothesis, we investigated the expression of glutamate, the thermo- and mechanosensitive ion channels transient receptor potential vanilloid 1 (TRPV1), transient receptor potential ankyrin 1 (TRPA1), and TWIK-1-related K+channel (TREK-1), and the glutamate receptor mGluR5, in a normal rat dental pulp, and following dentin injury. We also examined the glutamate release from odontoblast in cell culture. Odontoblasts were enriched with glutamate, at the level as high as in adjacent pulpal axons, and showed immunoreactivity for TRPV1, TRPA1, and TREK-1. Pulpal sensory axons adjacent to odontoblasts expressed mGluR5. Both the levels of glutamate in odontoblasts, and the expression of mGluR5 in nearby axons, were upregulated following dentin injury. The extracellular glutamate concentration was increased significantly after treating of odontoblast cell line with calcium permeable ionophore, suggesting glutamate release from odontoblasts. These findings lend morphological support to the hypothesis that odontoblasts contain glutamate as a potential neuroactive substance that may activate adjacent pulpal axons, and thus contribute to dental pain and hypersensitivity.

Bite force measurement in awake rats.

This report describes the implementation of bite force measurement in awake rats and software instruments (Spike 2 script programs) that quantify and analyze the bite force data. One script program employs user-defined control of threshold bite force, which allows an easy adjustment of target force prior to training the rat. Furthermore, the interactive program allows on-line control of threshold bite force at anytime during the training session. Upon detection of the bite force crossing the threshold, it automatically triggers the external water delivery system for reinforcement. Another script program detects successful biting attempts, compiles times stamps and force level for each attempted bite, and calculates the total number of bites, success rate and mean bite force per training session. Using the new methodology, we trained five adult rats to produce the bite force of 1300 g. Our results demonstrated that all rats achieved the target force with a similar time course and exhibited little variability in success rate and mean bite force. The script programs provided instant review and analyses of the captured data. These techniques simplify assessment of bite force in behaving rats.