As many fibers and varicosities were labeled with GFP in L2 and L5, it seems likely that infection with AAV–BDNF or AAV–NT-3 resulted in the release of these neurotrophins onto cells of the CPG in L2 (Jakeman et al., 1998; Blits et al., 2003) and motoneurons in L5, which are known to express both TrkB and TrkC receptors (Yan et al., 1997; Copray & Kernell, 2000), whose excitability was tested directly. Here, NTRK2 is linked to infection.