Fibers immunoreactive for nerve growth factor receptor in adult rat cortex and hippocampus mimic the innervation pattern of AChE-positive fibers

Numerous reports have indicated that nerve growth factor (NGF) exerts neurotrophic effects on the cholinergic neurons of the basal forebrain. Receptors for NGF (NGFR) have been demonstrated on cholinergic perikarya in the medial septum, diagonal band of Broca, and basal nucleus of Meynert. These neurons provide the major cholinergic innervation to the cerebral cortex and hippocampus, and previous studies have shown that their terminal plexuses also possess NGFR. However, these studies have shown only isolated examples of immunoreactive fibers. In the present paper we confirm and extend the observation of the presence of NGFR immunoreactivity in the hippocampus and cortex of adult rat by showing the entire plexus and demonstrating that the plexus is strikingly similar to the pattern of cholinergic innervation. Fibers stained for acetylcholinesterase (AChE) and NGFR immunoreactivity were found in all layers of the parietal cortex. Within the hippocampus, fibers were observed in all regions, but were most dense in the strata oriens, pyramidale, and radiatum of hippocampal subfields CA1 and CA3. Particularly intense staining was found throughout the dentate gyrus. Partial transections of the fimbria-fornix, which disrupt fibers projecting from the medial septum to the hippocampus, concomitantly abolish the innervation pattern of both NGFR and AChE. These results provide additional evidence that NGFR are associated with septohippocampal and basocortical cholinergic fibers.