After transection of the sciatic nerve there is a dramatic increase in both
galanin/
galanin message-associated peptide-like immunoreactivities and preprogalanin
messenger RNA levels in rat and mouse lumbar 4 and 5 dorsal root ganglion neurons. There is strong evidence that after nerve injury
leukemia inhibitor factor is a key molecule in the control of
peptide expression both in sympathetic neurons and in dorsal root ganglion neurons, although the cells of origin of endogenous
leukemia inhibitory factor remain to be established. We have therefore studied the effect of
leukemia inhibitory factor on
galanin expression in 72 h cultured dorsal root ganglion neurons from normal mice,
leukemia inhibitory factor-deficient and heterozygous mice with immunohistochemistry and in situ hybridization. In cultures of
leukemia inhibitory factor-deficient (-/-) mice only 13% of the dorsal root ganglion neurons expressed
galanin message-associated peptide and in cultures from heterozygous (+/-) and wild-type (+/+) mice the corresponding figures were, respectively, 24 and 40%. After addition of
leukemia inhibitory factor (10 or 50 ng/ml) to the culture medium, the number of neurons expressing
galanin message-associated peptide was increased (up to 41%) in cultures from (-/-) animals after the high concentration and reached similar values in cultures from heterozygous animals incubated with the low concentration. These findings were supported by parallel analysis of prepro-
galanin messenger RNA levels, where similar transcript levels and effects in the various cultures were observed in the non-radioactive in situ hybridization experiments. These results support the hypothesis that
leukemia inhibitory factor is an important regulator of
galanin/
galanin message-associated peptide expression following
axotomy, and may therefore be involved in the defence mechanisms against
neuropathic pain at the level of dorsal root ganglion neurons.