Heritability of symptoms in an experimental model of neuropathic pain.

Male and female rats underwent transection and ligation of the sciatic and saphenous nerves, and the development of autonomy was monitored. The deafferented animals were then interbred, always selecting males and females that expressed relatively high and, alternatively, relatively low levels of autotomy. Offspring were similarly operated and interbred. By the sixth generation of selective breeding, lines were achieved in which autotomy was consistently high (HA) or consistently low (LA). There was no indication of sex linkage. Thermal and mechanical nocifensive responsiveness co-selected with propensity to express autotomy following nerve injury: response thresholds were lower in HA than in LA rats. F1 hybrids formed by crossing homozygous HA and LA animals showed low levels of autotomy, similar to LA stock. This indicates recessive inheritance of the autotomy trait. Backcrossing F1 hybrids onto the LA line yielded a low autotomy phenotype in almost all cases; backcrossing F1 hybrids onto HA stock yielded about 50% high autotomy and 50% low autotomy. These ratios are consistent with simple mendelian inheritance of a single gene. Taken together, the data suggest that autotomy is inherited as a single-gene autosomal recessive trait.