naloxone and Temporomandibular-Joint-Disorders

To investigate whether the protective effect of testosterone on the development of temporomandibular joint (TMJ) nociception in male rats is mediated by the activation of central opioid mechanisms.. Experiments were performed on 156 male Wistar rats. A pharmacologic approach was used to assess the ability of opioid receptor antagonists infused into the dorsal portion of the brainstem and adjacent to the caudal component (subnucleus caudalis) of the spinal trigeminal nucleus to block the protective effect of testosterone in male rats. The TMJ injection of 0.5% formalin was used as a nociceptive stimulus. One-way or two-way ANOVA was used for data analyses.. The injection of 0.5% formalin into the TMJ induced a significant nociceptive behavior in gonadectomized male rats (P < .05), but not in naïve, sham, and testosterone-replaced gonadectomized rats, confirming that testosterone prevents the development of TMJ nociception. The injection of either the nonselective opioid receptor antagonist naloxone (15 μg) or the simultaneous injection of the μ-opioid receptor antagonist Cys2, Tyr3, Orn5, Pen7amide (CTOP, 30 μg) and the κ-opioid receptor antagonist Nor-Binaltorphimine (Nor-BNI, 90 μg) significantly increased the 0.5% formalin-induced behavioral response in sham and testosterone-replaced gonadectomized rats (P < .05) but had no effect in gonadectomized rats. However, the injection of each selective opioid receptor antagonist alone or the simultaneous injection of μ- or κ- and δ-opioid receptor antagonists had no effect.. These findings indicate that the protective effect of endogenous testosterone on the development of TMJ nociception in male rats is mediated by the activation of central opioid mechanisms. Furthermore, the coactivation of central μ- and κ-opioid receptors is necessary for testosterone to protect male rats from developing TMJ nociception.

Topics: Animals; Brain Stem; Facial Pain; Formaldehyde; Male; Naloxone; Naltrexone; Narcotic Antagonists; Nociception; Nociceptive Pain; Orchiectomy; Rats; Rats, Wistar; Receptors, Opioid, kappa; Receptors, Opioid, mu; Somatostatin; Temporomandibular Joint; Temporomandibular Joint Disorders; Testosterone; Trigeminal Caudal Nucleus

This study describes a novel method for direct subarachnoid drug delivery to the medullary dorsal horn region of rats, without introducing a catheter. The reliability of the method was demonstrated by a pharmacological validation; that is, morphine administration to the medullary region blocked the nociceptive response to formalin injected in the temporomandibular joint (TMJ) region, an effect that was prevented by co-administration of naloxone. The method proposed offers many advantages over the existing methods for medullary drug delivery with catheter implantation. It is easy to be employed, it does not induce any sign of motor impairment, and it does not require the neck surgery performed to implant a catheter in the medullary dorsal horn region. Therefore, it is a useful method for subarachnoid drug delivery in behavioral trigeminal pain studies, particularly when nociceptive behavioral measures that require normal neck muscle activity to occur, such as head withdraw or head flinch, are evaluated.

Topics: Analgesics, Opioid; Animals; Arthralgia; Drug Delivery Systems; Head Movements; Male; Medulla Oblongata; Microinjections; Morphine; Naloxone; Narcotic Antagonists; Neck Muscles; Neurosurgical Procedures; Nociceptors; Pain Measurement; Rats; Rats, Wistar; Subarachnoid Space; Syringes; Temporomandibular Joint Disorders; Trigeminal Caudal Nucleus