Nerve growth factor receptor immunoreactive profiles in the normal, aged human basal forebrain: colocalization with cholinergic neurons.

A monoclonal antibody raised against the receptor for nerve growth factor (NGF) has been used to map the distribution of NGF receptor-containing profiles within the human basal forebrain of four male and three female elderly patients without neurologic or psychiatric illness. Immunohistochemically processed tissue reveals a continuum of NGF receptor-positive neurons located within the medial septum, vertical and horizontal limb nuclei of the diagonal band, and nucleus basalis. NGF receptor-containing neurons are also found within the bed nucleus of the stria terminalis, the anterior commissure, the internal capsule, and the internal and external medullary laminae of the globus pallidus. Virtually all (greater than 95%) NGF receptor-containing neurons colocalize with the specific cholinergic marker choline acetyltransferase (ChAT) or the nonspecific marker acetylcholinesterase (AChE). Conversely, a few cholinergic perikarya are found which are not NGF receptor positive (and vice versa). These findings demonstrate that human basal forebrain neurons on which NGF receptor immunoreactivity is detected are primarily cholinergic and analogous to the nonhuman primate Ch1-Ch4 subgroups of Mesulam et al. (J. Comp. Neurol., 214:170-197, '83). NGF receptor-containing fiber tracts are observed emanating from the medial septum and vertical limb nucleus of the diagonal band coursing medially within the fornix. Another fascicle originating mainly from the nucleus basalis and travelling within the external capsule enroute to the cortex is observed innervating all cortical layers. Comparison of NGF receptor- and ChAT-containing neurons reveals cholinergic perikarya within the striatal complex, whereas virtually no NGF receptor-containing neurons are found in these structures. An occasional displaced NGF receptor-containing neurons is seen in the ventrolateral portion of the putamen and the white matter underlying the nucleus accumbens. These data are discussed in terms of the relationship of NGF receptor- and ChAT-containing neurons within the basal forebrain and in terms of the possible functional significance of NGF in normal and diseased brain.