Age-dependent differential regulation of sensory neuropeptides by glial cell line-derived neurotrophic factor

Glial cell line-derived neurotrophic factor markedly enhances survival of neonatal dorsal root sensory neurons in vitro, an effect seen even in the presence of anti-nerve growth factor. Furthermore, it increases levels of substance P, inducing more than a sixfold rise that is maximal at 10 ng/ml. At the same dose, it potentiates the action of nerve growth factor on substance P but not on survival. Neither factor increases somatostatin content in neonatal neurons. Although its effect on substance P diminishes with age, glial cell line-derived neurotrophic factor dramatically increases somatostatin levels in neurons from adult rats. Glial cell line-derived neurotrophic factor is therefore the second trophic factor found to promote survival and regulate substance P in neonatal sensory neurons. More significant is that it is the first and sole neurotrophic factor reported to regulate somatostatin in sensory neurons at any age, with its effect restricted to the adult. These results suggest mechanisms for differential regulation of somatostatin versus substance P in nociceptive pathways.