Implant of mAb MNAC13-secreting cells in the rat brain significantly reduces the number of cholinergic basal forebrain neurons. The cholinergic phenotype of P9 (A–C) and P16 (D–F) rat basal forebrain neurons was determined by immunoreactivity for ChAT after the intraventricular implant at P2 of cells secreting the anti-TrkA MNAC13 antibody (B,E), the anti-NGF αD11 antibody (C, F), or of control myeloma cells (A,D). Note the marked reduction of the number of ChAT-positive neurons in MNAC13-implanted rats (B). Scale bar, 75 μm.