Effects of intraventricular transplantation of NGF-secreting cells on cholinergic basal forebrain neurons after partial immunolesion

The aim of the present study was to examine the effects of nerve growth factor on brain cholinergic function after a partial immunolesion to the rat cholinergic basal forebrain neurons (CBFNs) by 192 IgG-saporin. Two weeks after intraventricular injections of 1.3 μg of 192 IgG-saporin, about 50% of CBFNs were lost which was associated with 40-60% reductions of choline acetyltransferase (ChAT) and high-affinity choline uptake (HACU) activities throughout the basal forebrain cholinergic system. Two groups of lesioned animals received intraventricular transplantations of mouse 3T3 fibroblasts retrovirally transfected with either the rat NGF gene (3T3(NGF+)) or the retrovirus alone (3T3(NGF-)) and were sacrificed eight weeks later. In vivo production of NGF by 3T3(NGF+) cells was confirmed by NGF immunohistochemistry on the grafts and NGF immunoassay on cerebrospinal fluid (CSF) samples. Both ChAT and HACU activities returned to normal control levels in the basal forebrain and cortex after 3T3(NGF+) transplants, whereas no recovery was observed in 3T3(NGF-) transplanted animals. There was a 25% increase in the size of remaining CBFNs and an increased staining intensity for NGF immunoreactivity in these cells after NGF treatments. Acetylcholinesterase (AChE) histochemistry revealed that the optical density of AChE-positive fibers in the cerebral cortex and hippocampus were reduced by about 60% in immunolesioned rats which were completely restored by 3T3(NGF+) grafts. In addition, decreases in growth-associated protein (GAP)- 43 immunoreactivity after immunolesion and increases in synaptophysin immunoreactivity after 3T3(NGF+) grafts were observed in the hippocampus. Our results further confirm the notion that transfected NGF-secreting cells are useful in long-term in vivo NGF treatment and NGF can up-regulate CBFN function. They also highly suggest that NGF induces terminal sprouting from remaining CBFNs.