A dual mechanism linking NGF/proNGF imbalance and early inflammation to Alzheimer's disease neurodegeneration in the AD11 anti-NGF mouse model

The neurotrophin Nerve Growth Factor (NGF) is essential for the maintenance and differentiation of basal forebrain cholinergic neurons. Since basal forebrain cholinergic neurons represent one major neuronal population affected and progressively degenerating in Alzheimer's disease (AD), interest has grown for NGF as a potential therapeutic agent in neurodegenerative disorders linked to aging, particularly for AD. However, no evidence was available, to link, in a cause-effect manner, deficits in NGF signalling to the broader activation in the Alzheimer's cascade, besides cholinergic deficits. The phenotypic analysis of the AD11 anti-NGF transgenic mouse, obtained by the "neuroantibodies" phenotypic protein knock out strategy, allowed demonstrating a direct causal link between NGF deprivation and AD pathology. Since then, extensive mechanistic studies on the AD11 model provided a new twist to the concept that alterations in NGF transport and signalling play a crucial role in sporadic Alzheimer's neurodegeneration, leading to the hypothesis of "Neurotrophic imbalance" as an upstream driver for sporadic AD. The results obtained with the AD11 anti-NGF mice highlight the fact that the particular mode of NGF neutralization, with an NGF antibody expressed in the brain, selectively interfering with mature NGF versus unprocessed proNGF, plays a major role in the mechanism of neurodegeneration, and could lead to new insights into the mechanisms of human sporadic AD. Here, we will review (1) the renewed neurotrophic imbalance hypothesis for AD and (2) the mechanisms underlying the neurodegenerative phenotype of AD11 anti-NGF mice.     

大鼠骨髓间质多能成体祖细胞系统移植治疗脑缺血性损伤的研究

目的 探讨骨髓间质分离的多能成体祖细胞（MAPCs）,通过系统移植方式（尾静脉注入）进入大鼠脑组织内及修复受损的神经功能.方法 采用改良Nagasaway与Zea Longa等线栓法建立大鼠脑缺血再灌注模型,并将大鼠随机分为对照组（n=40）和MAPCs组（n=40）.将在体外纯化、增殖和已用5-溴脱氧尿苷（BrdU）处理过的MAPCs经尾静脉注射入大鼠体内.采用行为学评定、免疫荧光技术、RT-PCR和免疫电镜等方法识别移行入大鼠脑组织内的MAPCs分化的神经元样细胞及其功能表达.结果 （1）MAPCs能移行入大鼠脑组织内并在大脑中动脉阻断（MCAO）的同侧海马区分化为神经元样细胞,免疫荧光双重标记染色显示BrdU、神经元特异性烯醇化酶（NSE）表达阳性;（2）与对照组比较,在MAPCs移植组（MAPCs组）,MCAO所致的大鼠行为损伤明显恢复,神经生长因子（NGF）表达水平明显升高（P＜0.05）;（3）电镜下观察到MAPCs所分化的神经样细胞与其它神经细胞形成突触联系.结论 MAPCs能经血液途径进入脑缺血灶微环境中,分化为神经样细胞并有效地修复大鼠MCAO所致的神经功能缺失症状.因此,MAPCs有望成为中枢神经系统疾病自体移植治疗的最佳候选干细胞之一.     

经尾静脉注入大鼠骨髓间充质多能成体祖细胞向脑缺血灶微环境中的移行及效应

BACKGROUND： Multipotent adult progenitor cells （MAPCs） from the bone marrow have been shown to differentiate into neurons.
OBJECTIVE： To observe migration, survival, and neuronal-like differentiation of MAPCs by tail vein injection. DESIGN, TIME AND SETTING： Randomized, controlled experiment of neural tissue engineering was performed at the Laboratory for Cardio-Cerebrovascular Disease, Hospital of Integrated Traditional and Western Medicine, Tongji Medical College of Huazhong University of Science and Technology between September 2006 and August 2007. MATERIALS： Eighty Sprague Dawley rats, 3-6 months old, underwent cerebral ischemia/reperfusion by thread technique, and were randomly divided into model and MAPCs groups （n = 40）. METHODS： Mononuclear cells were harvested from bone marrow using the FicolI-Paque density gradient centrifugation method. After removing CD45 and glycophorin A-positive cells （GLYA＋） with immunomagnetic beads, CD45 GLYA adult progenitor cells were labeled with bromodeoxyuridine （5-bromo-2-deoxyuridine, BrdU）. A total of 1 mL cell suspension, containing 5 × 10^6 MAPCs, was injected into the MAPCs group through the tail vein. A total of 1 mL normal saline was injected into the model rats.
MAIN OUTCOME MEASURES： After 60 days, BrdU and neuron-specific enolase double-positive cells were observed using immunofluorescence. Cell morphology was observed under electron microscopy, and nerve growth factor mRNA was measured through RT-PCR. In addition, rat neurological functions were measured with behavioral tests.
RESULTS： Immunofluorescence revealed that MAPCs positive for BrdU and neuron specific enolase were found surrounding the ischemic focus in the MAPCs group. Microscopic observation suggested that MAPCs-derived neuronal-like cells connected with other nerve cells to form synapses. Compared with the model animals, the level of nerve growth factor mRNA was significantly upregulated in rats injected with MAPCs （P 〈 0.05）. In addition, rats in the MAPCs group performed better in behavioral tests than the model group on days 28 and 60 （P 〈 0.05）.
CONCLUSION： Transplanted MAPCs migrated to the ischemic region, survived, and differentiated into neuronal-like cells, resulting in stimulation of nerve growth factor mRNA and improved neurological function in ischemic rats.     

Neurotrophin receptors and selective loss of cholinergic neurons in Alzheimer disease

The most consistent neuropathological finding in Alzheimer disease (AD) is the loss of cholinergic neurons of the nucleus basalis of Meynert (NbM). Using immunohistochemistry, we have previously shown that cholinergic neurons located in the ventral striatum were affected, whereas those of the caudate nucleus, putamen, and mesencephalon were spared. Since cholinergic neurons that degenerate in AD are sensitive to NGF and those that are spared are not, it has been hypothesized that the loss of neurotrophins receptors may play a role in the death of cholinergic neuronsin AD. Using immunohistochemistry, we have detected the presence of TrkA on most cholinergic neurons from the NbM, on some from those of the striatum, but not on those of the mesencephalon in the human brain. In AD patients, the number of neurons that expressed TrkA was markedly decreased in the NbM very likely as a consequence of cholinergic neuronal loss. In the striatum, despite the loss of high-affinity NGF binding prevously reported, no loss of TrkA was observed. Taken together, these results suggest a decreased expression of NGF receptors on the striatal cholinergic neurons in AD. This loss may contribute, when it reaches a crucial threshold, to the death of cholinergic neurons occurring in AD.     

Neurotrophin receptors and selective loss of cholinergic neurons in Alzheimer disease

The most consistent neuropathological finding in Alzheimer disease (AD) is the loss of cholinergic neurons of the nucleus basalis of Meynert (NbM). Using immunohistochemistry, we have previously shown that cholinergic neurons located in the ventral striatum were affected, whereas those of the caudate nucleus, putamen, and mesencephalon were spared. Since cholinergic neurons that degenerate in AD are sensitive to NGF and those that are spared are not, it has been hypothesized that the loss of neurotrophins receptors may play a role in the death of cholinergic neuronsin AD. Using immunohistochemistry, we have detected the presence of TrkA on most cholinergic neurons from the NbM, on some from those of the striatum, but not on those of the mesencephalon in the human brain. In AD patients, the number of neurons that expressed TrkA was markedly decreased in the NbM very likely as a consequence of cholinergic neuronal loss. In the striatum, despite the loss of high-affinity NGF binding prevously reported, no loss of TrkA was observed. Taken together, these results suggest a decreased expression of NGF receptors on the striatal cholinergic neurons in AD. This loss may contribute, when it reaches a crucial threshold, to the death of cholinergic neurons occurring in AD.     

Transplantation of NGF secreting primary monocytes counteracts NMDA-induced cell death of rat cholinergic neurons in vivo

Cholinergic neurons of the basal forebrain degenerate in Alzheimer's disease. Nerve growth factor (NGF) is so far the most potent molecule to counteract this neurodegeneration; however, the delivery of NGF into the brain is very difficult. The aim of the present study was to observe, if transplanted primary monocytes secreting NGF may counteract N-methyl-D-aspartate (NMDA)-induced cell death of cholinergic neurons of the basal nucleus of Meynert (nBM) in vivo. Monocytes were purified by indirect magnetic separation from rat blood. Recombinant NGF was introduced into cells using the novel protein-delivery reagent BioPORTERtrade mark and secretion of NGF was measured by ELISA. Monocytes secreted approximately 4000 pg NGF/day/1 x 10(6) cells. Injection of monocytes onto organotypic brain slices of the nBM in vitro protected cholinergic neurons against cell death. When monocytes were transplanted in vivo into the lateral ventricle, the cells survived for up to 7 days and counteracted the NMDA-induced cell death of cholinergic neurons. In conclusion, primary monocytes secreting recombinant NGF are useful to deliver NGF directly into the brain.     

Cholinergic system during the progression of Alzheimer's disease: therapeutic implications

Alzheimer's disease (AD) is characterized by a progressive phenotypic downregulation of markers within cholinergic basal forebrain (CBF) neurons, frank CBF cell loss and reduced cortical choline acetyltransferase activity associated with cognitive decline. Delaying CBF neurodegeneration or minimizing its consequences is the mechanism of action for most currently available drug treatments for cognitive dysfunction in AD. Growing evidence suggests that imbalances in the expression of NGF, its precursor proNGF and the high (TrkA) and low (p75(NTR)) affinity NGF receptors are crucial factors underlying CBF dysfunction in AD. Drugs that maintain a homeostatic balance between TrkA and p75(NTR) may slow the onset of AD. A NGF gene therapy trial reduced cognitive decline and stimulated cholinergic fiber growth in humans with mild AD. Drugs treating the multiple pathologies and clinical symptoms in AD (e.g., M1 cholinoceptor and/or galaninergic drugs) should be considered for a more comprehensive treatment approach for cholinergic dysfunction.     

Stem cell therapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder which impairs the memory and intellectual abilities of the affected individuals. Loss of episodic as well as semantic memory is an early and principal feature. The basal forebrain cholinergic system is the population of neurons most affected by the neurodegenerative process. Extracellular as well as intracellular deposition of beta-amyloid or Abeta (Abeta) protein, intracellular formation of neurofibrillary tangles and neuronal loss are the neuropathological hallmarks of AD. In the last few years, hopes were raised that cell replacement therapy would provide cure by compensating the lost neuronal systems. Stem cells obtained from embryonic as well as adult tissue and grafted into the intact brain of mice or rats were mostly followed by their incorporation into the host parenchyma and differentiation into functional neural lineages. In the lesioned brain, stem cells exhibited targeted migration towards the damaged regions of the brain, where they engrafted, proliferated and matured into functional neurones. Neural precursor cells can be intravenously administered and yet migrate into brain damaged areas and induce functional recovery. Observations in animal models of AD have provided evidence that transplanted stem cells or neural precursor cells (NPCs) survive, migrate, and differentiate into cholinergic neurons, astrocytes, and oligodendrocytes with amelioration of the learning/memory deficits. Besides replacement of lost or damaged cells, stem cells stimulate endogenous neural precursors, enhance structural neuroplasticity, and down regulate proinflammatory cytokines and neuronal apoptotic death. Stem cells could also be genetically modified to express growth factors into the brain. In the last years, evidence indicated that the adult brain of mammals preserves the capacity to generate new neurons from neural stem/progenitor cells. Inefficient adult neurogenesis may contribute to the pathogenesis of AD and other neurodegenerative disorders. An attempt at mobilizing this endogenous pool of resident stem-like cells provides another attractive approach for the treatment of AD. Studies in patients with AD indicated decreased hippocampal volume derived by neurodegeneration. Intriguingly, many drugs including antidepressants, lithium, acetyl cholinesterase inhibitors, and ginkgo biloba, were able to enhance the impaired neurogenesis in this disease process. This paved the way towards exploring the possible pharmacological manipulation of neurogenesis which would offer an alternative approach for the treatment of AD.     

大鼠骨髓间质多潜能成年祖细胞体内移植与多巴胺能神经元分化的研究

目的:探讨骨髓间质分离的多潜能成年祖细胞(MAPCs)通过系统移植(即尾静脉注射)方式进入大鼠脑组织内并修复受损的神经功能。方法:制作实验性帕金森疾病大鼠模型.将在体外纯化、增殖和已用5-溴-2脱氧尿苷(BrdUrd)处理过的多潜能成年祖细胞通过尾静脉注射入帕金森病大鼠体内。三个月后,对受试大鼠进行行为学评定;并应用免疫荧光化学技术和RT-PCR等方法对脑组织内的MAPCs及其分化细胞进行鉴定。结果:多潜能成年祖细胞能移行入大鼠脑组织内并在中脑黑质和纹状体区分化为神经元样细胞.如多巴胺能神经元,免疫荧光染色显示5-溴-2脱氧尿苷、神经元特异性烯醇化酶(NSE)或酪胺酸羟化酶(TH)表达阳性;6-羟多巴诱导的大鼠行为损伤有明显恢复;多巴胺-β-羟化酶(DBH)和多巴胺转运体(DAT)mRNA的表达水平明显升高。结论:骨髓间质分离的多潜能成年祖细胞能通过系统移植方式进入大鼠脑组织内,在中脑微环境中可自主分化为多巴胺能神经细胞并有效地修复6-羟多巴诱导的神经功能缺损。因此,多潜能成年祖细胞有望成为中枢神经系统疾病自体移植治疗的最佳候选干细胞之一。     

β/A4-Amyloid increases nerve growth factor production in rat primary hippocampal astrocyte cultures

Nerve growth factor (NGF), a member of the neurotrophin family, is an essential mediator of neuronal activity and synaptic plasticity of basal forebrain cholinergic neurons (BFCN). In processes of chronic degeneration of BFCN like in Alzheimer's disease (AD), characterized among others by amyloid containing plaques, NGF has been shown to improve cognitive decline and rescue BFCN but also to reduce survival of hippocampal neurons via p75 neurotrophin receptor (p75). Little is known about the mechanisms of NGF regulation in glial cells under pathological conditions in AD. This study investigates the influence of amyloid administration on the NGF protein secretion in rat primary hippocampal astrocytes. Astrocytes were stimulated with "aged" beta/A4-Amyloid (1-40), and NGF was measured in different fractions, such as supernatant, vesicles, and cytosol fraction. Treatment with amyloid at a final concentration of 10 microM for 72 h led to increased NGF protein levels up to 30-fold increase compared to unstimulated controls. This observation may be an endogenous neuroprotective mechanism possibly contributing to a delay of amyloid-dependent loss of cholinergic neurons or contribute to accelerated neuronal death by activation of p75 within Alzheimer pathology.     

Developmental change in the nerve growth factor action from induction of choline acetyltransferase to promotion of cell survival in cultured basal forebrain cholinergic neurons from postnatal rats

Nerve growth factor (NGF), a well-characterized target-derived growth factor, has been postulated to promote neuronal differentiation and survival of the basal forebrain cholinergic neurons. In the present paper, we demonstrate that a developmental change in NGF action occurs in postnatal rat basal forebrain cholinergic neurons in culture. Firstly, NGF acts as maturation factor by increasing choline acetyltransferase (ChAT) activity and acts later as a survival factor. In dissociated cell cultures of septal neurons from early postnatal (P1-4) rats, ChAT activities were increased by the addition of NGF. That is, ChAT activities in P1 septal cells cultured for 7 days was increased 4-fold in the presence of NGF at a concentration of 100 ng/ml. However, the number of the acetylcholinesterase (AChE)-positive neurons was not significantly different between these groups. In contrast, septal neurons from P8 to P14 rats showed different responses to NGF. Although the P14 septal neurons in culture for 7 days without NGF lost about half of the ChAT activity during a 7-day cultivation, cells cultured with NGF retained the activity at the initial level. The number of AChE-positive neurons counted in cultures with NGF was much greater than the number without NGF. These results suggest that, during the early postnatal days, the action of NGF on the septal cholinergic neurons in culture changes from induction of ChAT activity to the promotion of cholinergic neuronal cell survival. During this developmental period in vivo, septal neurons are terminating their projections to the hippocampal formation. Similar NGF-regulated changes in cholinergic neurons were observed in cultured postnatal neurons from vertical limb of diagonal band. An analogy has been pointed out between the neuronal death of the basal forebrain cholinergic neurons and a similar neuronal death in senile dementia, especially Alzheimer's type. The work reported here might present a possibility that NGF could play a role in preventing the loss of the basal forebrain cholinergic neurons in this disease.     

Reversible schwann cell hyperplasia and sprouting of sensory and sympathetic neurites after intraventricular administration of nerve growth factor

Substantial dysfunction and loss of cholinergic neurons occur in Alzheimer's disease (AD). Nerve growth factor (NGF) is a potent neurotrophic factor for cholinergic basal forebrain neurons, and the use of NGF to stimulate residual dysfunctional cells in AD is being considered. To define the effects of NGF on other cell populations in the brain, NGF was continuously infused into the lateral ventricle of rats for 7 weeks. At the end of treatment, Schwann cell hyperplasia and abundant sensory and sympathetic neurite sprouting were observed in the subpial region of the medulla oblongata and the spinal cord. Following withdrawal of NGF, the Schwann cell hyperplasia and sprouting of sensory and sympathetic neurites disappeared completely. These findings suggest that better temporal and spatial delivery systems for NGF must be explored to limit potential undesirable side effects while maintaining the survival and function of diseased basal forebrain cholinergic neurons.     

The cholinergic system, nerve growth factor and the cytoskeleton

Cholinergic neurons of the basal forebrain provide the major cholinergic innervation to the cortex and hippocampus, and play a key role in memory and attentional processes. Dysfunction of basal forebrain cholinergic neurons (BFCN) is a cardinal feature of Alzheimer's disease (AD) and correlates with cognitive decline. Survival of BFCN neurons depends upon binding of nerve growth factor (NGF), which is synthesized and secreted by cells in the cortex and hippocampus, with high-affinity (TrkA) and low-affinity (p75^NTR) neurotrophin receptors produced within BFCN neurons. NGF released from target cells activates TrkA on axon terminals and triggers activation of PI3K/Akt, MEK/ERK, and PLCγ (phospholipase C) signaling pathways. The signal then travels retrogradely along axon to cell body to promote neuronal survival. However, the nature of the retrograde signal remains mysterious. p75^NTR receptors could mediate a fundamentally different signaling pathway leading to apoptic cell death. Dysfunction of NGF and its receptors has been suggested to underlie the selective degeneration of the BFCN in end stage Alzheimer disease. In this regard, NGF, the founding member of the neurotrophin family, has generated great interest as a potential target for the treatment of AD. This review focuses on NGF-cholinergic dependency, NGF/receptor binding, signal transduction, retrograde transport, regulation of specific cellular endpoints, and the potential involvement of cytoskeleton dysfunction in defected NGF signaling.     

Is there nicotinic modulation of nerve growth factor? Implications for cholinergic therapies in Alzheimer's disease.

Studies on the neurobiology of nerve growth factor (NGF) reveal a diverse range of actions. Through alterations in gene expression, NGF is important in maintaining and regulating the phenotype of neurons that express the high-affinity receptor, trkA. Nerve growth factor also has a rapid action, revealed by its role in pain signaling in bladder and in skin. In the central nervous system (CNS), NGF has an intimate relationship with the cholinergic system. It promotes cholinergic neuron survival after experimental injury but also maintains and regulates the phenotype of uninjured cholinergic neurons. In addition to these effects mediated by gene expression, NGF has a rapid neurotransmitter-like action to regulate cholinergic neurotransmission and neuronal excitability. Consistent with its actions on the cholinergic system, NGF can enhance function in animals with cholinergic lesions and has been proposed to be useful in humans with Alzheimer's disease (AD); however, the problems of CNS delivery and of side effects (particularly pain) limit the clinical efficacy of NGF. Drug treatment strategies to enhance production of NGF in the CNS may be useful in the treatment of AD. Nicotine is one such agent, which, when administered directly to the hippocampus in rats, produces long-lasting elevation of NGF production.     

Neurotrophins: from pathophysiology to treatment in Alzheimer's disease

Alzheimer's disease (AD) is the most common diagnosis among dementia. As increasing longevity results in larger numbers of AD patients and thus rising economic costs, there has been intense research about the pathophysiology and treatment strategies during the last years. Since neurotrophic factors are not only responsible for neuronal development but also critical for the maintenance of neurons, they represent mediators of high interest within the research of neurodegeneration. Thereby, NGF has been identified as a dynamic pattern during the time course of neurodegeneration in AD. Post mortem studies point to a lack of NGF action in early stages of AD. In contrast NGF is found in enhanced concentrations in brains with severe AD partly due to a pathologically altered axonal transport of NGF in the neurons. Therefore, pharmacological interventions strategies focus on an neurotrophin substitution in mild to moderate cases of AD. Intensive research mostly in rodents has recently led to first promising clinical trials of intracerebral neurotrophin application pointing to a growing role of neurotrophins in the establishment of new pharmacological strategies concerning AD.     

Impact of the NGF maturation and degradation pathway on the cortical cholinergic system phenotype

Cortical cholinergic atrophy plays a significant role in the cognitive loss seen with aging and in Alzheimer's disease (AD), but the mechanisms leading to it remain unresolved. Nerve growth factor (NGF) is the neurotrophin responsible for the phenotypic maintenance of basal forebrain cholinergic neurons in the mature and fully differentiated CNS. In consequence, its implication in cholinergic atrophy has been suspected; however, no mechanistic explanation has been provided. We have previously shown that the precursor of NGF (proNGF) is cleaved extracellularly by plasmin to form mature NGF (mNGF) and that mNGF is degraded by matrix metalloproteinase 9. Using cognitive-behavioral tests, Western blotting, and confocal and electron microscopy, this study demonstrates that a pharmacologically induced chronic failure in extracellular NGF maturation leads to a reduction in mNGF levels, proNGF accumulation, cholinergic degeneration, and cognitive impairment in rats. It also shows that inhibiting NGF degradation increases endogenous levels of the mature neurotrophin and increases the density of cortical cholinergic boutons. Together, the data point to a mechanism explaining cholinergic loss in neurodegenerative conditions such as AD and provide a potential therapeutic target for the protection or restoration of this CNS transmitter system in aging and AD.     

Time window in cholinomimetic ability to rescue long-term potentiation in neurodegenerating anti-nerve growth factor mice

A deficit in cortical cholinergic synaptic transmission is a common feature of cognitive and behavioral impairment observed in neurodegenerative pathologies. AD11 transgenic mice producing blocking antibodies against Nerve Growth Factor (NGF) are characterized by a progressive neurodegenerative phenotype defined by the deposition of amyloid peptide, intracellular neurofibrillary tangles and by a marked cholinergic depletion. We exploited AD11 mice to develop a functional assay to investigate the impact of cholinergic deficit on cortical synaptic plasticity impairment at different neurodegenerative stages. In particular, we investigated the time course of long-term potentiation (LTP) impairment in neocortex of AD11 mice and potential rescue by acute pharmacological treatment with Acetylcholine (ACh) or the cholinergic agonist Galantamine (GAL). We showed that LTP starts being absent in AD11 mice at 2 months, an age corresponding to early neurodegenerative stage characterized by the first observed decrease in number of basal forebrain cholinergic neurons (BFCNs) without overt cortical neurodegeneration. We demonstrated that acute ACh or GAL treatment fully reverts LTP impairment in 2 month old AD11 mice. In contrast, cholinergic treatment failed to recover synaptic plasticity deficit in aged (9-10 months) AD11 mice characterized by a severe cortical neurodegeneration.     

Transplantation of a temperature-sensitive, nerve growth factor-secreting, neuroblastoma cell line into adult rats with fimbria-fornix lesions rescues cholinergic septal neurons

The HT4 cell line was derived from infection of a mouse neuroblastoma cell line with a retrovirus that encoded the temperature-sensitive (ts) mutant of SV40 large T antigen. At nonpermissive temperature, HT4 cells differentiated with neuronal morphology, expressed neuronal antigens, synthesized nerve growth factor (NGF) mRNA, and secreted biologically active NGF in vitro. We sought to establish whether transplanted HT4 cells expressed class I major histocompatibility complex (MHC) antigens, a partial requirement for recognition by cytotoxic T lymphocytes (CTL), and thus be susceptible to xenograft rejection. Differentiated HT4 cells expressed marginally detectable levels of class I MHC antigens, but demonstrated higher levels of class I MHC expression after treatment with interferon-gamma. However, HT4 cells were resistant to direct lysis by perforin, the pore-forming protein of CTLs, and thus may have potential use in xenograft experiments. To address whether HT4 cells secrete NGF in vivo, HT4 cells were transplanted into adults rats with unilateral fimbria-fornix transections. A ts cell line derived from P4 cerebellum, BT1, that does not differentiate with neuronal phenotype or synthesize NGF in vitro, was transplanted as a control. Six weeks posttransplant. HT4 cells had integrated into host CNS without forming tumors. In BT1 transplants, the number of medial septal acetylcholinesterase (AChE)-positive cells was reduced to 26-39% of the contralateral control side, depending on the rostrocaudal level. In HT4 transplants, the number of cholinergic septal neurons was 58-78% of the contralateral side. This percentage was significantly (P less than 0.005) greater than that seen with BT1 transplants, indicating that transplanted HT4 cells secrete NGF in vivo and rescue cholinergic septal neurons following fimbria-fornix transection.