Introduction Chronic itch has been drawing much attention due to its clinical significance and the complexity of its mechanisms. To facilitate the development of anti-itch strategies, it is necessary to investigate the key players in itch sensation under chronic itch conditions. Several members of the Mrgpr family were identified as itch receptors that detect cutaneous pruritogens in primary sensory neurons. However, the role of Mrgprs in chronic itch conditions has not been well described. Methods Scratching behaviors of WT and Mrgpr-clusterΔ−/− mice were examined in dry skin model and contact dermatitis model to examine the role of Mrgpr genes in mediating chronic itch sensation. Scratching behaviors of the mice were also examined in allergic itch model. Real-time PCR were performed to examine the expression level of MrgprA3 and MrgprC11 under naïve and dry skin conditions. The MrgprA3+ itch-sensing fibers were labeled by tdTomato fluorescence in Mrgpra3GFP-Cre; ROSA26tdTomato mice, and the morphology and density of those fibers in the epidermis were analyzed under dry skin condition. Results We showed that deleting a cluster of Mrgpr genes in mice reduced scratching behavior severely under two chronic itch conditions, namely dry skin and contact dermatitis, and the allergic itch condition. Moreover, the gene expressions of itch receptors MrgprA3 and MrgprC11 in dorsal root ganglia (DRG) were upregulated significantly under dry skin condition. Consistently, the percentage of MrgprA3+ itch-sensing neurons was increased as well. We also observed hyperinnervation of MrgprA3+ itch-sensing fibers in the epidermis of the skin under dry skin condition. Discussion We demonstrate that Mrgprs play important roles in mediating chronic itch and allergic itch. These findings enrich our knowledge of itch mechanism and may lead to the development of novel therapeutic approach to combat itch.

Central venous catheter (CVC) related complications are a common cause of morbidity among home parenteral nutrition (HPN) patients. A substantial number of patients on HPN carry out their own CVC care after a period of training. At St Mark's Hospital, London in 2009 a change in the method of training for HPN patients to carry out their own CVC care was instituted with more patients completing their training at home. In June 2010 a cohort of self-caring HPN patients were tested on their knowledge of CVC care as part of their routine clinic visit. This was prompted by the failure to recognise serious CVC complications in a small number of long term HPN patients.Patients were asked to answer seven questions on systemic CVC infections, exit site infections, CVC fractures, CVC occlusion, central vein thrombosis and hydration levels, both over and under hydrated. The scores for patients trained before and after 2009 were compared. The number of CVC related complications per patient was obtained from the St Mark's HPN database. The number of days on HPN was calculated.A total of 70 patients completed the questions representing 44 % of the total self caring HPN patients. The mean age was 50. The median knowledge score was 72 % (range 24-96 %). There was no significant difference between knowledge score and training before or after 2009 (P = 0.055). There was a significant correlation between HPN days and number of CVC complications (r = 0.373, P = 0.001) and a significant negative correlation between age and knowledge score (r = -0.241, p = 0.044). There was no correlation between knowledge score and the number of CVC complications (r = 0.016, P = 0.896).In this small cohort study of self caring HPN patients the overall infection rate was low (0.98 infections per 1000 HPN days) and patients scored well in their knowledge test (72%). This is not a validated scoring system, but reflects our training practice. We have demonstrated that there has been a significant increase in CVC infection rates at a time when there was a change in the training process for these patients. There was no difference in knowledge of complications in those trained before and after 2009, with no correlation between knowledge score and complication rate. The lack of association between knowledge and complications could be confounded by the fact that patients who develop complications have more experiential knowledge. We are concerned that the move towards home training of HPN patients may be less effective, as reflected in the increase CVC infection rates that we have observed. This merits further investigation.

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