Abstract
The present study explored the antinociceptive effects of H3 (R-alpha-methylhistamine) and GABAB (baclofen) receptor ligands in an orofacial model of pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (50 μl, 5 %) in the upper lip region, and the number of jumps and time spent face rubbing was recorded for 40 min. Formalin produced a marked biphasic pain response; first phase, 0–10 min (jumps), and second phase, 15–40 min, (rubbing). Baclofen (50 μg) injected into the rat wiskerpad 5 min before formalin administration suppressed both phases of pain whereas R-alpha-methylhistamine (12.5 μg) abolished the first phase only. Brains were taken immediately after behavioral testing was completed. HPLC/ED analysis showed that 5-hydroxytryptamine (5-HT) turnover was increased in hippocampus, thalamus, and brain stem of all formalin groups, excepting the baclofen group in which the balance of 5-HT metabolism was restored to control values. These findings demonstrate that GABAB receptors represent peripheral targets for analgesia. Consequently, locally administered baclofen may be a useful approach in treating inflammatory trigeminal pain.
Highlights
Pain is the primary reason for patients to visit a physician or dentist, and the diagnosis and management of pain in the face, mouth and jaws have been integral components of dental practice
The present study explored the antinociceptive effects of H3 (R-alpha-methylhistamine) and GABAB receptor ligands in an orofacial model of pain in rats
High levels of DA, dihydroxyphenylacetic acid (DOPAC), HVA, 5-HT, and 5-hydroxyindoleacetic acid (5-HIAA) in the prefrontal cortex were observed between all groups of rats
Summary
Pain is the primary reason for patients to visit a physician or dentist, and the diagnosis and management of pain in the face, mouth and jaws have been integral components of dental practice. For an adequate understanding of the neurological mechanisms underlying dental pain, with the objective of improving pain management, an animal model for dental pain assessment is frequently employed. Such models allow us to manipulate neural pathways for the study of those pathways and search for new treatment options (Raboisson and Dallel 2004; Rusina et al 2010). Activation of the GABAB receptor leads to the blockade of voltage-gated calcium channels, which results in inhibition of presynaptic mediator release as well as the inhibition of postsynaptic neuronal activity by indirect activation of K? A specific agonist of the heterodimeric GABAB receptor, is effectively used in the treatment of rigidity and spasms of skeletal muscles
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