Intrahippocampal injections of antiserum to nerve growth factor inhibit sympathohippocampal sprouting

Persistence of sympathetic ingrowth fibers in aged rat hippocampus

Sympathetic fibers appear in the rat hippocampus following interruption of the septal-hippocampal pathway. The current study examined the relative ability of young (3 month) and old (24 month) rats to produce sympathetic ingrowth fibers. Sympathetic ingrowth was present in the hippocampus of young adult rats 2 months after fimbria/fornix transection. The aged rats either lacked, or had very limited, hippocampal ingrowth two months after fimbria/fornix transections. In contrast, aged rats which had fimbria/fornix transections as young adults had extensive hippocampal ingrowth fibers. The topographical distribution of ingrowth fibers in the hippocampal formation was similar in young 3-month-old rats and rats which were lesioned young and sacrificed when aged. Counts of sympathetic fibers found similar numbers of hippocampal ingrowth fibers at both of the post-operative ages. Thus, although aged animals were acutely impaired in their ability to initiate the ingrowth response, the sympathetic fibers which were established at a young age persisted into senescence.

Developmental changes of nerve growth factor and its mRNA in the rat hippocampus: comparison with choline acetyltransferase

Previous experiments have demonstrated that in the septo-hippocampal system choline acetyltransferase (ChAT) is induced by nerve growth factor (NGF) (Gnahn et al. (1983) Dev. Brain Res. 9, 45-52) and that hippocampal NGF and mRNANGF levels are correlated with the density of cholinergic innervation (Korsching et al. (1985) EMBO J. 4, 1389-1393). In the present investigation we have compared the developmental changes of ChAT, NGF, and mRNANGF levels in this system. During the postnatal development of the hippocampus the time courses of NGF and ChAT were well correlated including the most rapid increase between P12 and P14. This increase in hippocampal NGF was preceded by a corresponding increase in mRNANGF. The developmental changes in hippocampal NGF levels were also closely reflected by corresponding changes in the septum. This, together with previous observations (Korsching et al., 1985) that the adult septum, in spite of relatively high NGF levels, does not contain measurable quantities of mRNANGF, suggests that the NGF levels in the septum are determined by the quantity of NGF transported retrogradely from the field of innervation rather than by local synthesis. During the prenatal period hippocampal NGF levels were relatively high, whereas the mRNANGF was below the level of detection. Since the ingrowth of septal fibers, and with that also the removal of NGF by retrograde transport, begins around birth, the relatively high prenatal NGF levels probably result from an accumulation produced by a small copy number of mRNANGF prior to the removal of NGF by retrograde axonal transport. It is concluded that the correlation of the developmental changes in NGF and mRNANGF with the ChAT activity in the hippocampus further supports the concept of a physiological role of NGF in the central nervous system.

Basal forebrain magnocellular neurons stain for nerve growth factor receptor: correlation with cholinergic cell bodies and effects of axotomy

Recent evidence has demonstrated the presence of nerve growth factor (NGF) in areas of the central nervous system characterized by cholinergic innervation. We report that a unique population of rat basal forebrain magnocellular neurons that project to the cortex and hippocampus are immunoreactive to a monoclonal antibody to the NGF receptor. Removal of target contact results in a time-dependent loss or shrinkage of cells in the basal forebrain that stain for NGF receptor and acetylcholinesterase, suggesting that under normal conditions, basal forebrain cholinergic neurons utilize NGF for trophic support.

Nerve growth factor protein level increases in the adult rat hippocampus after a specific cholinergic lesion

Nerve growth factor (NGF) is the best-characterized neurotrophic substance and has recently been shown to influence cholinergic neurons in the basal forebrain. Hippocampus and neocortex, the primary targets for these central neurons, have further been found to contain high levels of NGF. Using enzyme immunoassay and acetylcholine esterase (AChE) histochemistry we have now studied the levels of NGF and AChE after a specific cholinergic lesion, transection of the fimbria fornix comprising the major cholinergic input to hippocampus. Fimbriectomy in adult rats led to a marked decrease in AChE-positive nerve terminals in both hippocampus and neocortex 10 days later, and to an increase (40%) of NGF protein concentration in hippocampus. thirty days after surgery, NGF had returned to control levels and remained there after 90 days. Removal of superior cervical ganglion did not alter the results. The density of cholinergic terminals in both hippocampus and neocortex increased with time (90 days) after fimbrial transection. The results support the idea that cholinergic neurons in the basal forebrain take up and retrogradely transport NGF from their target areas and suggest that transection of the pathway interrupts the transport thereby increasing NGF distal to the lesion. The return of NGF to control levels probably reflects reestablished cholinergic contracts in the hippocampus.

Studies on the expression of the beta nerve growth factor (NGF) gene in the central nervous system: level and regional distribution of NGF mRNA suggest that NGF functions as a trophic factor for several distinct populations of neurons

Beta nerve growth factor (NGF), a target-derived protein necessary for survival and development of sympathetic and sensory neurons, can also affect subpopulations of neurons in the central nervous system (CNS). Using a blot hybridization assay capable of detecting 10 fg of mRNA, we measured the levels of NGF mRNA in the major brain regions, including those innervated by NGF-responsive neurons. NGF mRNA was detected unambiguously in each major region of the CNS. The levels were comparable to those in sympathetic effector organs. Discrete areas contained very different amounts of NGF mRNA. Up to 40-fold differences were seen, a range comparable to the differences between richly and sparsely innervated sympathetic effector organs. The highest concentrations of NGF mRNA were found in the cortex and hippocampus, which are the major targets of the NGF-responsive cholinergic neurons of the basal forebrain nuclei. Significant amounts of NGF mRNA were also found in areas that contain the central processes of NGF-responsive sensory neurons, such as the pons, medulla, and spinal cord. The presence of NGF mRNA in these areas suggests that brain NGF may act as a target-derived trophic factor for both populations of neurons. NGF mRNA was also found in the striatum, suggesting that locally derived NGF may act there as a trophic factor for a recently identified population of NGF-responsive cholinergic local circuit neurons. However, high levels of NGF mRNA were also found in some regions, such as the diencephalon, that have no relation to any identified population of NGF-responsive neurons. This suggests that there may be additional populations of NGF-responsive neurons in the CNS that have not yet been discovered.