Nerve growth factor‐like immunoreactive profiles in the primate basal forebrain and hippocampal formation

The distribution of nerve growth factor (NGF), the prototypic neurotrophin, within the basal forebrain and hippocampal formation of young adult monkeys and aged humans was characterized with and affinity purified polyclonal β‐NGF antibody raised against mouse β‐NGF. In the basal forebrain of both primates, a granular NGF‐like immunoreactive (ir) reaction product was observed within neurons of the medial septum, nucleus of the diagonal band, and nucleus basalis of Meynert. NGF‐like immunoreactivity exclusively colocalized within p75 NGF receptor (NGFR) containing basal forebrain neurons. The intensity of NGF immunolabeling varied between cell bodies. Many NGF‐ir perikarya were highly immunoreactive. In other basal forebrain neurons, NGF‐like immunoreactivity was either undetectable or minimally expressed. In the hippocampus of both species, NGF‐like immunoreactivity was mainly localized within the hilus of the dentate gyrus and within CA3 and CA2 hippocampal subfields. A marked diminution in NGF‐like staining was seen in CA1. Within the hippocampal formation, NGF‐like immunoreactivity was heaviest within the neuropil of stratum radiatum, intermediate in stratum oriens, and lightest in stratum pyramidal. NGF‐like immunoreactivity was not found within the granule or pyramidal cells of the dentate gyrus and hippocampal formation, respectively. These findings demonstratre the presence of an NGF‐like antigen in association with monkey and human magnocellular basal forebrain neurons and within their hippocampal target sites. This lends support to the hypothesis that NGF is internalized from sources located within target regions of the primate cholinergic basal forebrain neurons and is retrogradely transported to these cell bodies where the NGF trophic effect likely occurs.