Evidence for the importance of these signaling pathways in experimental brain injury is growing. Activation of multiple components of the Fas death receptor signaling pathway have been found in rat and mouse models of motor neuron degeneration [188] and blocking Fas death receptor signaling by genetic means affords protection in these models [188]. Neuron degeneration caused by target deprivation in vivo appears to be driven in part by a death receptor-dependent pathway [18].