Heritability of nociception IV: neuropathic pain assays are genetically distinct across methods of peripheral nerve injury

Prior genetic correlation analysis of 22 heritable behavioral measures of nociception and hypersensitivity in the mouse identified 5 genetically distinct pain types. In the present study, we reanalyzed that dataset and included the results of an additional 9 assays of nociception and hypersensitivity, with the following goals: to replicate the previously identified 5 pain types; to test whether any of the newly added pain assays represent novel genetically distinct pain types; and to test the level of genetic relatedness among 9 commonly used neuropathic pain assays. Multivariate analysis of pairwise correlations between assays shows that the newly added zymosan-induced heat hypersensitivity assay does not conform to the 2 previously identified groups of heat hypersensitivity assays and cyclophosphamide-induced cystitis, the first organ-specific visceral pain model examined, is genetically distinct from other inflammatory assays. The 4 included mechanical hypersensitivity assays are genetically distinct and do not comprise a single pain type as previously reported. Among the 9 neuropathic pain assays including autotomy, chemotherapy, nerve ligation and spared nerve injury assays, at least 4 genetically distinct types of neuropathic sensory abnormalities were identified, corresponding to differences in nerve injury method. In addition, 2 itch assays and Comt genotype were compared to the expanded set of nociception and hypersensitivity assays. Comt genotype was strongly related only to spontaneous inflammatory nociception assays. These results indicate the priority for continued investigation of genetic mechanisms in several assays newly identified to represent genetically distinct pain types.