Pain
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The transient receptor potential vanilloid receptor type-1 (TRPV1) is critically involved in peripheral nociceptive processes of somatic and visceral pain. However, the role of the capsaicin receptor in the brain regarding visceral pain remains elusive. ⋯ Notably, intracerebral TRPV1 antagonism by SB 366791 significantly reduced chemical and inflammatory spontaneous abdominal nocifensive responses, as observed by reduced expressions of nociceptive facial grimacing, illustrating the affective component of pain. In addition to the established role of cerebral TRPV1 in anxiety, fear, or emotional stress, we demonstrate here for the first time that TRPV1 in the brain modulates visceral nociception by interfering with the affective component of abdominal pain.
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Randomized Controlled Trial
Peripheral opioid receptor blockade increases postoperative morphine demands - a randomized, double-blind, placebo-controlled trial.
Experimental studies suggest that a large proportion of opioid analgesia can be mediated by peripheral opioid receptors. This trial examined the contribution of such receptors to clinical analgesia induced by intravenous morphine. We hypothesized that the selective blockade of peripheral opioid receptors by methylnaltrexone (MNX) would increase the patients' demand for morphine to achieve satisfactory postoperative pain relief. ⋯ Secondary endpoints were similar in all groups (P>.05). Thus, a significant proportion of analgesia produced by systemically administered morphine is mediated by peripheral opioid receptors. Drugs that selectively activate such receptors should have the potential to produce powerful clinical pain relief.
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Central sensitization elicits pain hypersensitivity and is thought to be causally implicated in painful temporomandibular disorder (TMD). This causal inference is based on cross-sectional evidence that people with TMD have greater sensitivity than controls to noxious stimuli. We tested this inference in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) prospective cohort study of 3258 adults with no lifetime history of TMD when enrolled (visit 1). ⋯ Among first-onset case patients, visit 2 PPTs were modest predictors of persistent TMD (OR=1.36, P=.002). In this longitudinal study, PPTs reduced when TMD developed then rebounded when TMD resolved. However, premorbid PPTs poorly predicted TMD incidence, countering the hypothesis that PPTs signify mechanisms causing first-onset TMD.