To test the role of BDNF-TrkB signaling in cholinergic activity-regulated DMG proliferation in the midbrain, we allografted DMG cells in the PPN and administered a TrkB antagonist (Entrectinib) directly to the tumor 30 min prior to optogenetic stimulation using an optofluid cannula for intratumoral drug delivery (Figure 3G). The gene discussed is BDNF; the disease is neoplasm.