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

Enhanced learning in mice parallels vector-mediated nerve growth factor expression in hippocampus

Spatial learning requires the integrity of the nerve growth factor (NGF)-responsive septohippocampal pathway. Loss of a single NGF allele at the mouse NGF locus (heterozygous null, ngf(+/-)) reduces septohippocampal NGF levels and NGF-regulated cholinergic neurotransmitter enzymes and results in spatial learning deficits in adult animals. A herpes simplex virus (HSV) amplicon vector was utilized to locally deliver NGF to the hippocampus of mice heterozygous and wild type (ngf(+/+)) at the NGF gene locus. NGF gene transfer produced transient increases in NGF protein levels and choline acetyltransferase activity in both ngf(+/-) and ngf(+/+) mice. However, spatial learning capability was improved only in ngf(+/-) mice. In aggregate, these findings suggest that amplicon-directed expression of NGF in subjects with baseline septohippocampal dysfunction can correct spatial learning deficits.

Comparison of site specific injections into the basal forebrain on water maze and radial arm maze performance in the male rat after immunolesioning with 192 IgG saporin

In this study we investigated the effects of 192 IgG saporin injections into the medial septal area (MSA), or nucleus basalis magnocellularis (NBM), and combined injections into the MSA and NBM, on the water maze and radial arm maze performance in the male rat. The results of the present study reveal a dissociation between the effects of 192 IgG saporin injections into the basal forebrain on the performance of two tasks of spatial learning in the rat. Bilateral injections of 192 IgG saporin into the NBM, MSA or combined MSA/NBM failed to disrupt water maze performance when compared to controls. In contrast, injections of 192 IgG saporin into the MSA, NBM or MSA/NBM induced mild impairments on a radial arm maze task. Overall, the disruption of spatial learning observed in this study however was relatively mild compared to deficits in spatial learning reported using less selective lesions of the cholinergic basal forebrain. Consequently, the results of this study suggest that a selective reduction in cholinergic transmission in the basal forebrain is by itself, insufficient to account for the functional impairments observed in spatial learning in the rat. Although our data does support the use of 192 IgG saporin as a selective cholinergic toxin in the basal forebrain, it further suggests that assessment of spatial learning in the rat following 192 IgG saporin lesions of the basal forebrain in combination with lesions to other neurotransmitter systems, may be a more viable approach to the elucidation of the neuropathological mechanisms that are associated with the cognitive deficits seen in Alzheimer's Disease.

Effects of nerve growth factor on acetylcholinesterase activity of the proximal stump of the transected sciatic nerve

28 rats were studied. They were divided into four groups of 7 rats of each one-day control animals (Group A), seven-day control animals (Group B), one-day nerve growth factor (NGF)-treated animals (Group C) and seven-day NGF-treated animals (Group D). In all animals, the right sciatic nerve was explored and completely transected using microscissors under a microscope. In NGF-treated animals, NGF (0.1 mg/kg NGF) was injected subcutaneously. In control animals, there was a statistically significant decrease in AChE activity in the proximal stump of the transected sciatic nerve at 7-day measurements (p < 0.05). In the NGF-treated groups, mean AChE activity in the proximal stump of the transected sciatic nerve was decreased at the 7-day measurement. AChE activity difference between control and NGF-treated groups, measured on the 7th day, are statistically significant (p < 0.01). These results demonstrate the effect of NGF on the cholinergic system.

Comparison of site-specific injections into the basal forebrain on water maze and radial arm maze performance in the male rat after immunolesioning with 192 IgG saporin

In this study, we investigated the effects of 192 IgG saporin injections into the medial septal area (MSA), or nucleus basalis magnocellularis (NBM), and combined injections into the MSA and NBM, on water maze and radial arm maze performance in the male rat. The results of the present study reveal a dissociation between the effects of 192 IgG saporin injections into the basal forebrain on the performance of two tasks of spatial learning in the rat. Bilateral injections of 192 IgG saporin into the NBM, MSA or combined MSA/NBM failed to disrupt water maze performance when compared to controls. In contrast, injections of 192 IgG saporin into the MSA, NBM or MSA/NBM induced mild impairments on a radial arm maze task. Overall, the disruption of spatial learning observed in this study was, however, relatively mild compared to deficits in spatial learning reported using less selective lesions of the cholinergic basal forebrain. Consequently, the results of this study suggest that a selective reduction in cholinergic transmission in the basal forebrain is, by itself, insufficient to account for the functional impairments observed in spatial learning in the rat. Although our data do support the use of 192 IgG saporin as a selective cholinergic toxin in the basal forebrain, they further suggests that assessment of spatial learning in the rat following 192 IgG saporin lesions of the basal forebrain in combination with lesions to other neurotransmitter systems, may be a more viable approach to the elucidation of the neuropathological mechanisms that are associated with the cognitive deficits seen in Alzheimer's disease.

Nerve growth factor immunoreactivity and sympathetic sprouting in the rat hippocampal formation

Several lines of evidence support a role for nerve growth factor (NGF) in the sympathetic sprouting response that occurs following septal cholinergic denervation of the rat hippocampal formation. The present study was undertaken to compare the distribution of NGF-like immunoreactivity and the topography of sympathetic sprouting in rats receiving medial septal lesions. Comparisons were made using adjacent sections of the hippocampal formation stained either for NGF-like immunoreactivity or for NGF receptor-immunoreactivity (p75, to visualize sympathetic fibers). p75-immunoreactive sympathetic axons were localized within the same regions exhibiting NGF-like staining, i.e., the hilus of the dentate gyrus and stratum lucidum in the CA3 area. Furthermore, the sympathetic fibers that invaded the hippocampal formation exhibited NGF-like immunostaining. These results provide additional evidence in support of NGF's role in this collateral sprouting response in the mature rat CNS.

Expression of nerve growth factor, p75, and trk in the somatosensory and motor cortices of mature rats: evidence for local trophic support circuits

Neurotrophins such as nerve growth factor (NGF) are critical for the maintenance of CNS neurons. We determined the expression of NGF and the neurotrophin receptors p75 and trk in the somatosensory and motor cortices of mature rats with immunohistochemical techniques. Sections of mature rat cortex were processed immunohistochemically with primary antibodies directed against NGF, p75, or trk. The distribution of immunoreactive elements was examined, and stereological techniques were used to determine the density and size of immunoreactive cell bodies. Some sections processed for trk immunoreactivity were examined with an electron microscope. From the size and morphology of the labeled cells, it appeared that only neurons in the gray matter were NGF-positive. NGF was detected in one-third of the neurons in layers II-III, V, and VI of both somatosensory cortex and motor cortex; however, fewer than 1 in 12 of the layer IV neurons was NGF-positive. With the notable exception of layer V, few cell bodies (2-10% of the total population) were p75- or trk-immunoreactive. Layer Vb was replete with receptor-positive cell bodies; more than one-third of the layer Vb neurons were p75- or trk-positive. All labeled cells appeared to be pyramidal neurons. The distribution of p75 labeling with the two anti-p75 antibodies was indistinguishable. In addition, the neuropil in the supragranular laminae was p75- or trk-positive. Electron microscopy showed that trk immunoreactivity was also expressed by dendrites. Only rarely were immunoreactive axons detected. In summary, NGF is expressed by cortical neurons throughout cortex, and neurotrophin receptors are widely produced by postsynaptic targets. Thus, NGF appears to participate in an intracortical autoregulatory system. The strong expression of neurotrophin receptors by pyramidal neurons in layer Vb (the origin of brainstem and spinal cord projections) suggests that the neurotrophins are especially critical for the regulation of corticofugal projection systems.

Sprouting of central noradrenergic fibers in the dentate gyrus following combined lesions of its entorhinal and septal afferents

Virtually all of the afferents to the hippocampal formation undergo collateral sprouting after removal of adjacent afferent systems. However, the central noradrenergic (NA) afferents, which demonstrate a remarkable propensity for regeneration and sprouting in other regions of the brain, have not been found to sprout in the denervated hippocampal formation. The present study was designed to determine if the pattern of innervation by NA fibers in the dentate gyrus of adult rats can be altered by interruption of the other major afferents. The innervation pattern of NA fibers was examined in the dentate gyrus 4 weeks after removal of the ipsilateral and/or contralateral entorhinal afferents and/or transection of the fimbria-fornix and supracallosal stria. The noradrenergic identity of the fibers was indicated by immunoreactivity for dopamine beta hydroxylase (DBH) and peripheral sympathetic fibers were demonstrated by immunoreactivity for nerve growth factor receptor (NGFr), which did not stain cholinergic fibers in this application. In control brains, the noradrenergic innervation of the dentate molecular layer was light and uniform across the width of the layer. Transection of the perforant path (ipsilateral entorhinal afferents) or ventral hippocampal commissure (contralateral entorhinal afferents) resulted in a significant increase in innervation density in the outer half of the molecular layer, and the combination of these two lesions produced the greatest increase. In those brains with transection of the ipsilateral and contralateral entorhinal afferents, the denervated dentate gyrus had a nearly twofold increase in density of DBH-immunoreactive fibers within the outer half of the molecular layer. These fibers tended to course parallel to the pial surface rather that perpendicular as in control sections. Transection of the fimbria-fornix alone had no affect on the innervation pattern of DBH-ir fibers in the molecular layer. When the fimbria-fornix was transected in combination with both of the other lesions, an overall increase in innervation density occurred, but there was no further increase in the difference between the inner and outer halves of the molecular layer. No NGFr-immunoreactive fibers were observed in the molecular layer in any of the brains, indicating that the DBH-immunoreactive fibers in this region were not of peripheral origin. It is concluded that removal of the ipsi- and contralateral entorhinal afferents to the dentate gyrus results in the sprouting of central NA fibers in the outer half of the molecular layer.