Increased NGF mRNA expression in denervated rat skin.

Using a coupled reverse transcription and competitive polymerase chain reaction protocol, we have measured Nerve Growth Factor (NGF) mRNA expression in adult rat skin following its denervation. By 2-4 days, levels of NGF mRNA were increased approximately 5-10 fold over levels in innervated skin, remaining increased for up to at least 2 weeks. In situ hybridization carried out on skin samples revealed that the NGF message was expressed not only in the distal nerve pathways but also in non-nerve associated cells, such as dermal fibroblasts, and in the basal epidermal layer. Denervated skin evokes a NGF-dependent collateral sprouting from neighbouring intact sensory axons. The new findings indicate that an increased NGF production is associated with the increased availability of NGF in such skin, and that cutaneous nerves have a role in regulating this NGF production.