The vanilloid receptor-1 (VR1) is a ligand-gated, non-selective cation channel expressed predominantly by sensory neurons. VR1 responds to noxious stimuli including capsaicin, the pungent component of chilli peppers, heat and extracellular acidification, and it is able to integrate simultaneous exposure to these stimuli. These findings and research linking capsaicin with nociceptive behaviours (that is, responses to painful stimuli in animals have led to VR1 being considered as important for pain sensation. Here we have disrupted the mouse VR1 gene using standard gene targeting techniques. Small diameter dorsal root ganglion neurons isolated from VR1-null mice lacked many of the capsaicin-, acid- and heat-gated responses that have been previously well characterized in small diameter dorsal root ganglion neurons from various species. Furthermore, although the VR1-null mice appeared normal in a wide range of behavioural tests, including responses to acute noxious thermal stimuli, their ability to develop carrageenan-induced thermal hyperalgesia was completely absent. We conclude that VR1 is required for inflammatory sensitization to noxious thermal stimuli but also that alternative mechanisms are sufficient for normal sensation of noxious heat.

The endogenous cannabinoid anandamide was identi®ed as an agonist for the recombinant human VR1 (hVR1) by screening a large array of bioactive substances using a FLIPR-based calcium assay. Further electrophysiological studies showed that anandamide (10 or 100 mM) and capsaicin (1 mM) produced similar inward currents in hVR1 transfected, but not in parental, HEK293 cells. These currents were abolished by capsazepine (1 mM). In the FLIPR anandamide and capsaicin were full agonists at hVR1, with pEC 50 values of 5.94+0.06 (n=5) and 7.13+0.11 (n=8) respectively. The response to anandamide was inhibited by capsazepine (pK B of 7.40+0.02, n=6), but not by the cannabinoid receptor antagonists AM630 or AM281. Furthermore, pretreatment with capsaicin desensitized the anandamide-induced calcium response and vice versa. In conclusion, this study has demonstrated for the ®rst time that anandamide acts as a full agonist at the human VR1.

The vanilloid receptor-1 (VR1) is a heat-gated ion channel that is responsible for the burning sensation elicited by capsaicin. A similar sensation is reported by patients with esophagitis when they consume alcoholic beverages or are administered alcohol by injection as a medical treatment. We report here that ethanol activates primary sensory neurons, resulting in neuropeptide release or plasma extravasation in the esophagus, spinal cord or skin. Sensory neurons from trigeminal or dorsal root ganglia as well as VR1-expressing HEK293 cells responded to ethanol in a concentration-dependent and capsazepine-sensitive fashion. Ethanol potentiated the response of VR1 to capsaicin, protons and heat and lowered the threshold for heat activation of VR1 from approximately 42 degrees C to approximately 34 degrees C. This provides a likely mechanistic explanation for the ethanol-induced sensory responses that occur at body temperature and for the sensitivity of inflamed tissues to ethanol, such as might be found in esophagitis, neuralgia or wounds.

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WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Overdose with citalopram is associated with QT prolongation and torsades de pointes, whereas this arrhythmia has not been reported after venlafaxine or mirtazapine overdose.• Uncertainty exists concerning the best means of identifying poisoned patients at greatest risk of arrhythmia, and a nomogram comparing QT and heart rate has recently been proposed based on published cases of torsades de pointes.• Few data are available concerning the performance of the nomogram in patients that present to hospital after antidepressant overdose. WHAT THIS STUDY ADDS• After antidepressant overdose patients had a broad range of heart rate and QT values, which were below the nomogram in 98% of cases (95% confidence interval 96, 99%).• Citalopram overdose was associated with a higher proportion of patients with QT values above the nomogram than venlafaxine and mirtazapine overdose, especially in those who had low heart rates.• The nomogram allowed discrimination between the different antidepressant agents and may have a role in predicting arrhythmia in clinical practice. AIMSA QT-heart rate nomogram has recently been proposed as a means of identifying patients at risk of torsades de pointes after antidepressant overdose, based on published cases of drug-induced torsades de pointes. The present study sought to examine the performance of the nomogram in patients who ingest an antidepressant overdose but do not develop arrhythmia. METHODSA retrospective case control study of patients presenting to hospital after overdose of citalopram, mirtazapine and venlafaxine was carried out. The primary outcome variable was QT higher than the nomogram, and was compared with occurrence of QTc (QT corrected by Bazett's formula) greater than Ն440 ms and QTc Ն500 ms, with comparison between drugs. Data are expressed as proportions in each group with 95% confidence intervals. RESULTSThere were 858 electrocardiograms from 541 patients. QT was higher than the nomogram in 2.4% (1.4, 4.1%), whereas QTc was Ն440 ms in 23.1% (95% CI 19.8, 26.8%), and QTc was Ն500 ms in 1.1% (0.5, 2.5%). Citalopram overdose was more likely to be associated with QT higher than the nomogram compared with the other agents (difference 7.0%, 95% CI 2.9, 11.9%, P = 0.001) and more likely to be associated with QTc Ն440 ms (difference = 11.0%, 95% CI 2.6, 19.0%, P = 0.013). CONCLUSIONSThe QT nomogram was associated with a lower false positive rate than widely accepted QTc criteria, and allowed detection of different effects of individual drugs. The nomogram offers potential advantages over QTc criteria and merits further investigation in a clinical setting.