Revealing a role of brainstem monoaminergic nuclei on the pronociceptive effect of sleep restriction.

Sleep disturbances and persistent pain conditions are public health challenges worldwide. Although it is well-known that sleep deficit increases pain sensitivity, the underlying mechanisms remain elusive. We have recently demonstrated the involvement of nucleus accumbens (NAc) and anterior cingulate cortex (ACC) in the pronociceptive effect of sleep restriction.

Impact of endogenous analgesia triggered by acupuncture, stress, or noxious stimulation on REM sleep-deprived rats.

Poor sleep increases pain, at least in part, by disrupting endogenous pain modulation. However, the efficacy of endogenous analgesia in sleep-deprived subjects has never been tested. To assess this issue, we chose three different ways of triggering endogenous analgesia: (1) acupuncture, (2) acute stress, and (3) noxious stimulation, and compared their ability to decrease the pronociceptive effect induced by REM-SD (Rapid Eye Movement Sleep Deprivation) with that to decrease inflammatory hyperalgesia in the classical carrageenan model.

5-HT induces temporomandibular joint nociception in rats through the local release of inflammatory mediators and activation of local β adrenoceptors.

The 5-hydroxytryptamine (serotonin, 5-HT) is an important inflammatory mediator found in high levels in the synovial fluid of the temporomandibular joint (TMJ) of patients with inflammatory pain. In this study, we used the nociceptive behavior responses, measured as flinching the head and rubbing the orofacial region, as a nociceptive assay. We demonstrated that the local blockade of the 5-HT₃ receptor and β₁ or β₂-adrenoceptors, the depletion of norepinephrine in the sympathetic terminals and the local inhibition of cyclooxygenase significantly reduced 5-HT-induced TMJ nociception.

Local kappa opioid receptor activation decreases temporomandibular joint inflammation.

In an attempt to decrease central side effects associated with the use of opioids, some strategies have been developed by targeting peripheral opioid receptors. In this context, kappa receptors are of major interest, since, in contrast to other opioid receptors, their activation is not associated with potent peripheral side effects. We have recently demonstrated that local activation of kappa opioid receptors significantly decreases formalin-induced temporomandibular joint nociception; however, whether it also decreases temporomandibular joint inflammation is not known.

Sexual dimorphism on cytokines expression in the temporomandibular joint: the role of gonadal steroid hormones.

Temporomandibular joint pain-related conditions are generally characterized by local inflammation; however, little studies have focused on the role of gonadal hormones in the expression of inflammatory mediators, such as cytokines. Therefore, we asked whether gonadal steroid hormones affect formalin-induced cytokines expression in the rat temporomcandibular joint. The expression of tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and cytokine-induced neutrophil chemoattractant (CINC)-1 was significantly higher in males than in diestrus and proestrus females and was decreased by orchiectomy and restored by testosterone replacement.

Contribution of endogenous opioids to gonadal hormones-induced temporomandibular joint antinociception.

The authors have recently demonstrated that the high serum estradiol level during the proestrus phase of the estrous cycle and that the administration of estradiol or progesterone in ovariectomized female and of testosterone in orchiectomized male rats significantly decrease formalin-induced temporomandibular joint (TMJ) nociception. In this study, the authors investigate the contribution of endogenous opioids to this antinociceptive effect of gonadal hormones in the TMJ formalin test. The opioid receptor antagonist naloxone was administrated either in the surrounding of the trigeminal sensory complex or in the TMJ region.

The influence of sex and ovarian hormones on temporomandibular joint nociception in rats.

Unlabelled: The aim of this study was to investigate the influence of sex and ovarian hormones on formalin- and glutamate-induced temporomandibular joint (TMJ) nociception in rats. The influence of sex and ovarian hormones on the nociceptive behavior induced by formalin or glutamate was virtually the same. The nociceptive behavior of males was similar to that of females in the proestrus phase of the estrous cycle but was significantly lower than that in the diestrus phase.