Cellular localization of nerve growth factor-like immunoreactivity in adult rat brain: Quantitative and immunohistochemical study

Abstract

To elucidate the role and the mechanism of action of nerve growth factor in the adult central nervous system, we investigated the localization of nerve growth factor-like immunoreactivity in adult rat brain, both quantitatively and immunohistochemically, using polyclonal anti-nerve growth factor immunoglobulin G. We raised rabbit polyclonal anti-mouse nerve growth factor antibody with an extremely high titer as 10 −9 determined by an enzyme immunoassay. The affinity-purified anti-nerve growth factor immunoglobulin G specifically recognized nerve growth factor with no cross-reaction to recombinant brain-derived neurotrophic factor and neurotrophin-3 evaluated by an enzyme immunoassay. We quantified nerve growth factor content in each layer of the adult rat cerebral cortex and in each small piece (0.225 mg wet weight tissue) of the diencephalon, brainstem and cerebellum with a highly sensitive two-site enzyme immunoassay. Nerve growth factor content was unevenly distributed in the cerebral cortex (dense in layers II/III and V/VI and sparse in layers I and IV). Moderate to high levels of nerve growth factor were registered in the habenular nuclei, zona incerta, ventral tegmental area, substantia nigra, locus coeruleus, ventral cochlear nucleus, trapezoid body, lateral vestibular nucleus, cerebellar nuclei and paraflocculus. Immunohistochemically, the nerve growth factor-like immunoreactivity was found in the cell bodies, dendrites and axons of adult rat central neurons, not only in the cerebral cortex, hippocampus and basal forebrain, but also in the diencephalon, brainstem and cerebellum. The population of neurons with nerve growth factor-like immunoreactivity was limited, but unexpectedly widespread, and the density of these cells correlated well with the content determined by an enzyme immunoassay in the present and a previous study [Nishio T. et al. (1992) Expl Neurol. 116, 76–84]. The monoamine neurons, including dopaminergic, noradrenergic and serotonergic neurons, showed intense nerve growth factor-like immunoreactivity, indicating that the central monoaminergic neuronal system may also be involved in the nerve growth factor trophic system. To visualize nerve growth factor transported in the axons and to enhance the immunostaining in the nerve growth factor-producing cells, we injected colchicine, a potent inhibitor of microtubule polymerization and a blocker of axoplasmic transport, into the lateral ventricle of adult Wistar rat brain. Colchicine treatment enhanced the intensities of nerve growth factor-like immunoreactivity in the axons and cell bodies, especially in the axon hillocks and the proximal axons of the nerve growth factor-producing neurons. This observation may suggest the existence of an orthograde axonal transport system for nerve growth factor in the central neurons. These results suggest that nerve growth factor may exist in widespread populations of adult central neurons, including the monoaminergic neurons, and may exert a trophic effect on these neurons through not only a retrograde manner but also an orthograde manner of transport.