The differentiation of sensory neurons of dorsal root ganglia (DRG) has been studied extensively with respect to inductive events that specify neuronal fate [2,3], as well as the involvement of late target-derived neurotrophic factors in the control of neuronal survival [4]. Recent evidence has begun to emerge that target-derived factors are also involved in regulating later aspects of neuronal differentiation [5,6,7]. In particular, genetic experiments have addressed the survival-independent role of neurotrophic factors during development by exploiting strains of mice defective both in neurotrophin signaling and in the function of the proapoptotic gene Bax [8,9]. These studies, for example, have revealed that neurotrophin signaling controls the acquisition of peptidergic traits in nociceptive DRG neurons and the control of target innervation [8,9].