BDNF and central nervous system cancer: Through the use of in vivo optogenetic control of cortical neuronal activity in patient-derived pediatric glioblastoma xenograft models in mice expressing the excitatory opsin channelrhodopsin-2, it was demonstrated that neurons stimulate glioma growth through paracrine signaling mediated by Brain-Derived Neurotrophic Factor (BDNF) and the soluble synaptic adhesion protein neuroligin-3 (NLGN3) [10–12].