The present invention relates to the discovery of a novel molecular pathway involved in long-term hyperexcitability of sensory neurons, which, in higher animals, is associated with persistent pain. It is based on the discovery that, following injury to an axon of a neuron, an increase in nitric oxide synthase activity results in increased nitric oxide production, which, in turn, activates guanylyl cyclase, thereby increasing levels of cGMP. Increased cGMP results in activation of protein kinase G ("PKG"), which then is retrogradely transported along the axon to the neuron cell body, where it phosphorylates MAPKerk.