The effect of deletion of the orphan G-protein coupled receptor (GPCR) gene MrgE on pain-like behaviours in mice

Background: The orphan GPCR MrgE is one of an extended family of GPCRs that are expressed in dorsal root ganglia (DRG). Based on these expression patterns it has been suggested that GPCRs like MrgE may play a role in nociception however, to date, no direct supporting evidence has emerged. We generated mutant mice lacking MrgE and examined the effects of deletion of this gene in three pain behavioural models. The effect of MrgE gene deletion on expression of Mrgs and genes involved in sensory neurone function was also investigated. Results: The absence of MrgE had no effect on the development of pain responses to a noxious chemical stimulus or an acute thermal stimulus. However, in contrast, the development but not the maintenance of neuropathic pain was affected by deletion of MrgE. The expression of Mrg genes was not significantly affected in the MrgE knockout (KO) mice with the sole exception of MrgF. In addition, the expression of 77 of 84 genes involved in sensory neuron development and function was also unaffected by deletion of MrgE. Of the 7 genes affected by MrgE deletion, 4 have previously been implicated in nociception. Conclusion: The data suggests that MrgE may play a role in selective pain behavioural responses in mice.