Ciliary neurotrophic factor stimulates neurite outgrowth from spinal cord neurons.

Ciliary neurotrophic factor (CNTF) has been shown to promote the survival of motoneurons, but its effects on axonal outgrowth have not been examined in detail. Since nerve growth factor (NGF) promotes the outgrowth of neurites within the same populations of neurons that depend on NGF for survival, we investigated whether CNTF would stimulate neurite outgrowth from motoneurons in addition to enhancing their survival. We found that CNTF is a powerful promoter of neurite outgrowth from cultured chick embryo ventral spinal cord neurons. An effect of CNTF on neurite outgrowth was detectable within 7 hours, and at a concentration of 10 ng/ml, CNTF enhanced neurite length by about 3- to 4-fold within 48 hours. The neurite growth-promoting effect of CNTF does not appear to be a consequence of its survival-promoting effect. To determine whether the effect of CNTF on spinal cord neurons was specific for motoneurons, we analyzed cell survival and neurite outgrowth for motoneurons labeled with diI, as well as for neurons taken from the dorsal half of the spinal cord, which lacks motoneurons. We found that the effect of CNTF was about the same for motoneurons as it was for neurons from the dorsal spinal cord. The responsiveness of a variety of spinal cord neurons to CNTF may broaden the appeal of CNTF as a candidate for the treatment of spinal cord injury or disease.