Pain
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Randomized Controlled Trial
The association of acetazolamide infusion with headache and cranial artery dilation in healthy volunteers.
The carbonic anhydrase inhibitor acetazolamide causes extracellular acidosis and dilatation of cerebral arterioles. In this study, we tested the hypothesis that acetazolamide also may induce headache and dilatation of cranial arteries. In a randomized double-blind crossover study design, 12 young healthy women were allocated to injection of 1 g acetazolamide or placebo on 2 separate days. ⋯ Compared to placebo, arterial circumference increased after acetazolamide in the basilar artery (P=.002) as well as the cerebral (P=.003), cavernous (P=.002), and cervical (P=.005) parts of the internal carotid artery, but no other extracranial arteries changed after acetazolamide. In conclusion, acetazolamide caused immediate and delayed headache as well as dilatation of intracranial arteries in healthy volunteers. It is possible that extracellular acidosis induced by acetazolamide causes sensitization of cephalic perivascular nociceptors, which, in combination with vasodilatation, leads to delayed headache.
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Although classical trigeminal neuralgia (CTN) is frequently caused by neurovascular contact (NVC) at the trigeminal root entry zone (REZ), both anatomical and MRI studies have shown that NVC of the trigeminal nerve frequently occurs in individuals without CTN. To assess the accuracy of MRI in distinguishing symptomatic from asymptomatic trigeminal NVC, we submitted to high-definition MRI the series of CTN patients referred to our outpatient service between June 2011 and January 2013 (n=24), and a similar number of age-matched healthy controls. Two neuroradiologists, blinded to the clinical data, evaluated whether the trigeminal nerve displayed NVC in the REZ or non-REZ, whether it was dislocated by the vessel or displayed atrophy at the contact site, and whether the offending vessel was an artery or a vein. ⋯ When REZ contact and nerve atrophy coexisted, both specificity and positive predictive value rose to 100%. Meta-analysis showed that REZ NVC was detected in 76% of symptomatic and 17% of asymptomatic nerves (P<.0001), whereas anatomical changes were detected in 52% of symptomatic and 9% of asymptomatic nerves (P<.0001). In conclusion, trigeminal REZ NVC, as detected by MRI, is highly likely to be symptomatic when it is associated with anatomical nerve changes.
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Dysregulation of the immune system may play a role in chronic pain, although study findings are inconsistent. This cross-sectional study examined whether basal inflammatory markers and the innate immune response are associated with the presence and severity of chronic multisite musculoskeletal pain. Data were used on 1632 subjects of the Netherlands Study of Depression and Anxiety. ⋯ For some LPS-stimulated inflammatory markers, we did find elevated levels in subjects with chronic multisite musculoskeletal pain both before and after adjustment for covariates. Pain severity was not associated with inflammation within chronic pain subjects. An enhanced innate immune response in chronic multisite musculoskeletal pain may be examined as a potential biomarker for the onset or perpetuation of chronic pain.
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Unlike most classical analgesics, botulinum toxin type A (BoNT/A) does not alter acute nociceptive thresholds, and shows selectivity primarily for allodynic and hyperalgesic responses in certain pain conditions. We hypothesized that this phenomenon might be explained by characterizing the sensory neurons targeted by BoNT/A in the central nervous system after its axonal transport. BoNT/A's central antinociceptive activity following its application into the rat whisker pad was examined in trigeminal nucleus caudalis (TNC) and higher-level nociceptive brain areas using BoNT/A-cleaved synaptosomal-associated protein 25 (SNAP-25) and c-Fos immunohistochemistry. ⋯ BoNT/A reduced the c-Fos activation in TNC, locus coeruleus, and periaqueductal gray. Present experiments suggest that BoNT/A alters the nociceptive transmission at the central synapse of primary afferents. Targeting of TRPV1-expressing neurons might be associated with observed selectivity of BoNT/A action only in certain types of pain.
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Serotonin (5-HT) plays pivotal roles in the pathogenesis of postinfectious irritable bowel syndrome (PI-IBS), and luminal 5-HT time-dependently modulates visceral nociception. We found that duodenal biopsies from PI-IBS patients exhibited increased 5-HT and decreased anandamide levels and that decreased anandamide was associated with abdominal pain severity, indicating a link between 5-HT and endocannabinoid signaling pathways in PI-IBS. To understand this, we investigated the role of endocannabinoids in 5-HT modulation of visceral nociception in a rat model. ⋯ Daily pretreatment with CB1 agonists or anandamide from day 3 attenuated 5-HT-induced hyperalgesia. These data suggest that vagal 5-HT3R-mediated duodenal anandamide release contributes to acute luminal 5-HT-induced antinociception via CB1 signaling, whereas decreased anandamide is associated with hyperalgesia upon chronic 5-HT treatment. Further understanding of peripheral vagal anandamide signaling may provide insights into the mechanisms underlying 5-HT-related IBS.