p38MAPK and GFAP are Upregulated by MO Tooth Pulp Stimulation

Objectives: p38MAPK has been reported to be involved in nociceptive processing as well as playing important roles in cellular responses to external stress. Recent studies have shown that activation of microglia and astrocyte may have a key role in the development of central sensitization. The purpose of this study was to elucidate the glial cell immediate response to pulpal nerve excitation by allyl-isothiocyanate (MO) application.

Methods: Pentobarbital sodium anesthetized SD male rats weighing 300g were used, and the pulp of the left maxillary first molar was exposed, and MO (0.5 ěl) was applied to stimulate pulpal nerves. Animals were sacrificed at 10, 20, 30, and 60 min after the MO application (n=3 each), and the bilateral V spinal nuclei (Vi/Vc border) and thalamus were dissected out and immediately processed to extract mRNA. RT-PCR analysis for p38MAPK and astrocyte glial fibrillary acidic protein (GFAP) was performed.

Results: p38MAPK mRNA expression was recognized in the ipsilateral Vi/Vc border of the V spinal nucleus at 30 min and in the contralateral thalamus at 30 and 60 min after the MO application. GFAP mRNA was recognized at all time points in both the ipsilateral Vi/Vc border of the V spinal nucleus and the contralateral thalamus and remarkably increased in the Vi/Vc border at 30 and 60 min and in thalamus at 60min.

Conclusion: Astrocytic and microglial metabolic processes may be involved in the sensitization of dorsal horn nociceptive neurons that is dependent on NMDA and purinergic receptor mechanisms. We showed the upregulation of p38MAPK and GFAP mRNA in the Vi/Vc border of V spinal nucleus and also in the thalamus following MO tooth pulp application. This preliminary study suggests the activation of two kinds of gilal cells immediately after MO pulp stimulation, which might play an important role in sustained pulpal inflammatory pain.