Nigrostriatal alterations in bone morphogenetic protein receptor II dominant negative mice.

BACKGROUND: We previously demonstrated that exogenous application of bone morphogenetic protein 7 (BMP7) reduced 6-hydroxydopamine-mediated neurodegeneration in a rodent model of Parkinson's disease. The purpose of this study is to examine the endogenous neurotrophic properties of BMP Receptor II in dopaminergic neurons of the nigrostriatal pathway. METHODS: Adult male BMPRII dominant negative (BMPRIIDN) mice and their wild type controls (WT) were placed in the activity chambers for 3 days to monitor locomotor activity. Animals were sacrificed for tyrosine hydroxylase (TH) immunostaining. A subgroup of BMPRIIDN and WT mice were injected with high doses of methamphetamine (MA) and were sacrificed for terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) histochemistry at 4 days after injection. RESULTS: BMPRIIDN mice had lower locomotor activity than the WT. There is a significant decrease in TH neuronal number in substantia nigra compacta, TH fiber density in the substantia nigra reticulata, and TH immunoreactivity in striatum in the BMPRIIDN mice, suggesting that deficiency in endogenous BMP signaling reduces dopaminergic innervation and motor function in the nigrostriatal pathway. Administration of MA increased TUNEL labeling in the substantia nigra in the BMPRIIDN mice. CONCLUSIONS: Endogenous BMPs have trophic effects on nigrostriatal dopaminergic neurons. Deficiency in BMP signaling increases vulnerability to insults induced by high doses of MA.

BMP enhances transcriptional responses to NGF during PC12 cell differentiation.

Bone morphogenetic proteins (BMPs) enhance neurite outgrowth in nerve growth factor (NGF)-stimulated PC12 cells. To investigate the mechanism of this potentiating effect, real-time PCR was used to analyze the expression of 45 selected genes. A robust increase in expression of 10 immediate early genes including Egr1-4, Hes1, Junb, Jun and Fos was observed already after 1 h treatment with NGF alone. NGF plus BMP4 further increased these transcripts at 1 h and activated 18 additional genes. BMP4 alone induced Smad6, Mtap1b and Hes1. Egr3 was the gene most strongly upregulated by NGF and BMP4. However, luciferase assays showed that the cloned Egr3 proximal promoter was not involved in the BMP4 potentiation. Blocking Egr3 and Junb function by dominant-negative constructs reduced neurite outgrowth under stimulating conditions, proving that activation of members of both the Egr and Jun families is necessary for maximal PC12 cell response to NGF and BMP4.

Bone morphogenetic protein signalling in NGF-stimulated PC12 cells.

Bone morphogenetic proteins (BMPs) are shown to potentiate NGF-induced neuronal differentiation in PC12 phaeochromocytoma cells grown on collagen under low-serum conditions. Whereas, cell bodies remained rounded in control medium or with only BMPs present, addition of BMP4 or BMP6 robustly increased the neuritogenic effect of NGF within 2 days. NGF-increased phosphorylation of p44(Erk1) and p42(Erk2) between 2 and 24h was unaffected by addition of BMP6. PC12 cells transfected with the SBE(4x)-luc reporter showed that BMP4 significantly increased receptor-activated Smad activity. Expression of constitutively active BMP receptor ALK2 activating Smad1 and Smad5 resulted in a strong increase in the SBE(4x)-luc reporter response. Adding the inhibitory Smad7 drastically reduced this signal. In contrast to wild-type (wt) Smad5, a Smad5 variant lacking five Erk phosphorylation sites in the linker region (designated Smad5/5SA) showed a strong background transcriptional activity. A fusion construct (Gal4-Smad5/5SA) was also highly transcriptionally active. Addition of the MEK inhibitor U0126 to PC12 cells expressing Gal4-Smad5/wt did not increase background transcriptional activity. However, upon activation by constitutively active ALK2 both Gal4-Smad5/wt and Gal4-Smad5/5SA strongly stimulated transcription. The data show that serine residues of the linker region of Smad5 reduce spontaneous transcriptional activity and that NGF-activated Erk does not antagonise BMP signalling at this site. Hence, NGF and BMP signals are likely to interact further downstream at the transcriptional level in neuronal differentiation of the PC12 cells.

Vascular endothelial growth factor improves functional outcome and decreases secondary degeneration in experimental spinal cord contusion injury.

Spinal cord injury leads to acute local ischemia, which may contribute to secondary degeneration. Hypoxia stimulates angiogenesis through a cascade of events, involving angiogenesis stimulatory substances, such as vascular endothelial growth factor (VEGF). To test the importance of angiogenesis for functional outcome and wound healing in spinal cord injury VEGF165 (proangiogenic), Ringer's (control) or angiostatin (antiangiogenic) were delivered locally immediately after a contusion injury produced using the NYU impactor and a 25 mm weight-drop. Rats treated with VEGF showed significantly improved behavior up to 6 weeks after injury compared with control animals, while angiostatin treatment lead to no statistically significant changes in behavior outcome. Furthermore, VEGF-treated animals had an increased amount of spared tissue in the lesion center and a higher blood vessel density in parts of the wound area compared with controls. These effects were unlikely to be due to increased cell proliferation as determined by bromo-deoxy-uridine-labeling. Moreover, VEGF treatment led to decreased levels of apoptosis, as revealed by TUNEL assays. In situ hybridization demonstrated presence of mRNA for VEGF receptors Flt-1, fetal liver kinase-1, neuropilin-1 and -2 in several important cellular compartments of the spinal cord. The different experiments indicate that beneficial effects seen by acute VEGF delivery was attributable to protection/repair of blood vessels, decreased apoptosis and possibly also by other additional effects on glial cells or certain neuron populations.

NGF, NT-3 and Trk C mRNAs, but not TrkA mRNA, are upregulated in the paraventricular structures in experimental hydrocephalus.

OBJECTS: This study was designed to detect possible alterations in the expression of neurotrophins and trks in kaolin-induced hydrocephalus by in situ hybridization. METHODS AND RESULTS: Sixteen rats were treated by injection of 25 mg kaolin suspended in 0.1 ml of physiological saline into the cisterna magna. Four rats were injected with saline and served as controls. The kaolin-treated rats were divided into two groups studied 1 and 4 weeks after treatment. Rats were anesthetized and killed, and their brains were rapidly dissected and frozen. DNA oligonucleotide probes for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and trkA, trkB, and C were labeled with [(35)S]dATP using terminal deoxyribonucleotidyl transferase for in situ hybridization. Hydrocephalic brains were also classified according to the degree of ventricular enlargement. The results observed were as follows. (1) The medial septal and striatal NGF mRNA levels increased with severity in animals. (2) Hippocampal trkB and BDNF mRNA levels increased with time in animals with moderate ventricular enlargement. (3) Expression of hippocampal trkB, trkC, and NT-3 mRNA increased in animals with moderate ventricular enlargement, while it apparently decreased in the large ventricular enlargement group reaching normal ranges. (4) In the corpus callosum there was an apparent increase in NGF, NT-3 and trkC mRNA, but not in trkA, in hydrocephalic animals. NT-3 EIA confirmed the presence of NT-3 protein increases in corpus callosum. It is therefore possible that simultaneous NGF, NT-3, and trkC receptor upregulation occurred in glial elements of the white matter. CONCLUSIONS: These results demonstrate that neurotrophins and their receptors are overexpressed in many damaged structures of the severely hydrocephalic brain. There were discrepancies in the distribution of NGF and trkA mRNA, and we hypothesize that NGF mRNA in the damaged white matter structure might be due to the reduced availability of other receptors, such as the low-affinity NGF receptors.

Intracerebroventricular infusion of nerve growth factor induces pain-like response in rats.

New strategies have recently been developed where infusion of neurotrophic factors into the brain can rescue different neuronal populations. However, negative side effects have been observed in clinical trials infusing nerve growth factor (NGF) into the lateral ventricle in man, namely pain. Little is known about pain behavior in animals after intracerebroventricular (i.c.v.) neurotrophic injections. Thus, we have examined the effects of i.c.v. infusion of NGF for 2 weeks on the behavioral response of rats to mechanical, cold and heat stimulation. Seven micrograms/day of NGF elicited a significant decrease in vocalization threshold to mechanical stimulation and a significantly increased response to cold and heat stimuli as compared with control. The concentration of NGF in cerebrospinal fluid (CSF) was significantly increased as compared with non-allodynic rats. The enhanced responses to mechanical and heat, but not to cold, stimulation were significantly reduced by CP-99994, a selective antagonist to tachykinin NK-1 receptors. When NGF was infused into the brain parenchyma (striatum, cortex and septum) no allodynic nor hyperalgesic responses could be detected. These results indicate that in rats i.c.v. but not intraparenchymal infusion of NGF induce mechanical and cold allodynia as well as heat hyperalgesia, which is mediated, at least in part, by activation of NK-1 receptors.

Localized expression of BMP and GDF mRNA in the rodent brain.

Expression of BMP- and GDF-related factors within the transforming growth factor-beta (TGF-beta) superfamily was examined in the rat and mouse brain by in situ hybridization. Strong signals were obtained in neurons for GDF-1 and GDF-10. GDF-1 is expressed at postnatal day 6 in the cerebral cortex, hippocampal CA1 through CA3 neurons, while only weakly expressed by cells in the dentate gyrus. Granule cells and neurons in the polymorph layer of the dentate gyrus are GDF-1-positive, as are the majority of neurons in the cortex. GDF-10 shows a distinct pattern of expression: At P6, strong labelling was seen in the superficial layers of cortex, notably in the posterior cingulate cortex, and in CA3 and dentate gyrus. From postnatal day 21, GDF-1 expression is strong in the hippocampus, cortex, and thalamic nuclei, while GDF-10 expression becomes restricted to the granule cell layer in the dentate gyrus. In contrast, OP-1 expression is restricted throughout development to cells of the medial habenular nucleus, choroid plexus, and leptomeninges. The markedly different expression patterns of these BMPs suggest they serve separate functions in the brain.

Increased expression of glial cell line-derived neurotrophic factor mRNA in muscle biopsies from patients with amyotrophic lateral sclerosis.

The expression of glial cell line-derived neurotrophic factor (GDNF) mRNA and brain-derived neurotrophic factor (BDNF) mRNA were studied in muscle biopsies from five patients with amyotrophic lateral sclerosis (ALS), six patients with other neuromuscular diseases and eight healthy control persons. All five patients with ALS had higher GDNF mRNA expressions in their biopsies than the healthy control group (almost a three fold increase). Among the other patients only one, who had a rapidly progressing toxic polyneuropathy, showed a GDNF mRNA expression above those of the controls. The BDNF mRNA expressions in the biopsies from the ALS patients were in the same range as those from the healthy controls, although the mean value of the ALS patients was higher. The only biopsy that showed a markedly higher BDNF mRNA expression was taken from one patient with progressive muscular atrophy. These results suggest that increased GDNF mRNA expression in muscle is an unspecific response to ongoing denervation and that this response is maintained in ALS, at least temporarily. If increased GDNF mRNA in muscle proves to be a constant finding in ALS the rationale for the use of GDNF as a therapeutic agent in ALS must be questioned.

The neurotrophins NGF and NT-3 reduce sensory neuronal loss in adult rat after peripheral nerve lesion.

The effect of three different neurotrophins on axotomy-induced death of adult rat sensory neurons was examined. The ventral branch of the 13th spinal nerve was transected and the corresponding neurons in the 13th thoracic (T13) dorsal root ganglion (DRG) were pre-labelled with Fast Blue (FB). For a period of 4 weeks, animals received either no treatment, continuous intrathecal infusion of phosphate buffer, nerve growth factor (NGF), neurotrophin-3 (NT-3), or brain-derived neurotrophic factor (BDNF). Labelled neurons remaining after this period were counted. Inert, or no treatment, resulted in extensive loss of the DRG neurons. BDNF application was virtually non-effective, while NGF or NT-3 resulted in a greater number of FB-labelled neurons compared to normal controls. This suggests that NGF and NT-3 are survival factors for adult sensory neurons with a therapeutic potential in peripheral nerve injuries.

Use of an internal ribosome entry site for bicistronic expression of Cre recombinase or rtTA transactivator.

Conditional gene targeting depends on tissue and time specificity of recombination events. Endogenous promoters are often used to drive various transgenic constructs. To avoid the problems associated with reconstituting a specific expression pattern in transgenic animals by this method, we tested the internal ribosome entry site of the encephalomyocarditis virus, to enable linkage of the Cre recombinase or rtTA trans-activator to 3' untranslated ends of endogenous genes. Here we report that these constructs function effectively in COS cells. The data suggest that these cassettes will be appropriate for 3' targeting of mouse genes.

Potentiating interactions between morphogenetic protein and neurotrophic factors in developing neurons.

mRNA for bone morphogenetic protein receptor type II (BMPR-II) was mapped to different neurons in peripheral ganglia and spinal cord of the chicken embryo. The expression of this serine/threonine kinase receptor partially overlaps with that of tyrosine kinase receptors Trk and Ret. Biological activities of osteogenic protein-1 (OP-1), a documented ligand for BMPR-II, were tested in explanted embryonic chicken ganglia and dissociated ganglionic neurons. OP-1 had only a limited stimulatory effect on neuronal survival. However, OP-1 combined with either neurotrophin-3 (NT-3, a relative of nerve growth factor) or glial cell line-derived neurotrophic factor (GDNF) potentiated neuronal survival three- to fourfold. We also show that OP-1 strongly potentiates nerve fiber outgrowth from ganglia stimulated with NT-3 or GDNF. Signaling by BMPR-II in neurons may potentiate the tyrosine kinase pathway activated by NT-3 and GDNF. The data suggest that morphogenetic proteins may modulate neurotrophic activities during neuronal development and plasticity.

Intracerebroventricular infusion of nerve growth factor in three patients with Alzheimer's disease.

Nerve growth factor (NGF) is important for the survival and maintenance of central cholinergic neurons, a signalling system impaired in Alzheimer's disease. We have treated 3 patients with Alzheimer's disease with a total of 6.6 mg NGF administered continuously into the lateral cerebral ventricle for 3 months in the first 2 patients and a total of 0.55 mg for 3 shorter periods in the third patient. The patients were extensively evaluated with clinical, neuropsychological, neurophysiological and neuroradiological techniques. Three months after the NGF treatment ended, a significant increase in nicotine binding was found in several brain areas in the first 2 patients and in the hippocampus in the third patient as studied by positron emission tomography. A clear cognitive amelioration could not be demonstrated, although a few neuropsychology tests showed slight improvements. The amount of slow-wave cortical activity as studied by electroencephalography was reduced in the first 2 patients. Two negative side effects occurred with NGF treatment: first, a dull, constant back pain was observed in all 3 patients, which in 1 patient was aggravated by axial loading resulting in sharp, shooting pain of short duration. When stopping the NGF infusion, the pain disappeared within a couple of days. Reducing the dose of NGF lessened the pain. Secondly, a marked weight reduction during the infusion with a clear weight gain after ending the infusion was seen in the first 2 patients. We conclude from this limited trial that, while long-term intracerebroventricular NGF administration may cause certain potentially beneficial effects, the intraventricular route of administration is also associated with negative side effects that appear to outweigh the positive effects of the present protocol. Alternative routes of administration, and/or lower doses of NGF, perhaps combined with low doses of other neurotrophic factors, may shift this balance in favor of positive effects.

A non-invasive system for delivering neural growth factors across the blood-brain barrier: a review.

Intraventricular administration of nerve growth factor (NGF) in rats has been shown to reduce age-related atrophy of central cholinergic neurons and the accompanying memory impairment, as well as protect these neurons against a variety of perturbations. Since neurotrophins do not pass the blood-brain barrier (BBB) in significant amounts, a non-invasive delivery system for this group of therapeutic molecules needs to be developed. We have utilized a carrier system, consisting of NGF covalently linked to an anti-transferrin receptor antibody (OX-26), to transport biologically active NGF across the BBB. The biological activity of this carrier system was tested using in vitro bioassays and intraocular transplants; we were able to demonstrate that cholinergic markers in both developing and aged intraocular septal grafts were enhanced by intravenous delivery of the OX-26-NGF conjugate. In subsequent experiments, aged (24 months old) Fischer 344 rats received intravenous injections of the OX-26-NGF conjugate for 6 weeks, resulting in a significant improvement in spatial learning in previously impaired rats, but disrupting the learning ability of previously unimpaired rats. Neuroanatomical analyses showed that OX-26-NGF conjugate treatment resulted in a significant increase in cholinergic cell size as well as an upregulation of both low and high affinity NGF receptors in the medial septal region of rats initially impaired in spatial learning. Finally, OX-26-NGF was able to protect striatal cholinergic neurons against excitotoxicity and basal forebrain cholinergic neurons from degeneration associated with chemically-induced loss of target neurons. These results indicate the potential utility of the transferrin receptor antibody delivery system for treatment of neurodegenerative disorders with neurotrophic substances.

BMPR-II expression and OP-1 effects in developing chicken retinal explants.

Low-stringency PCR was used to isolate the chicken homologue of the human bone morphogenetic protein receptor type II (BMPR-II). In situ hybridization localized mRNA expression for this serine/threonine kinase receptor. It was weakly expressed in the vitreal side of the neural retina at E6. In the E7 chicken, fairly strong labelling was found in cells of the internal part of the neural retina. At E9, strong labelling was found in the region of the retinal ganglion cells. Explants of E6 retina exposed to osteogenic protein-1 (OP-1/BMP-7), exhibited dense retinal fibre outgrowth. This suggests that BMPR-II may form a signalling receptor complex important for retinal development. OP-1 and related ligands may serve functions supplementary to those of neurotrophins.

NGF, BDNF, NT3, NT4 and GDNF in tooth development.

Neurotrophic factors have robust effects on development, differentiation, maintenance and regeneration of neurons. In the present study, we have used in situ hybridization to determine the specific sites of gene activity of five neurotrophic factors during tooth development. Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNAs were mainly detected in the dental papilla/pulp in postnatal rats, and the pattern of expression correlated with onset of dental innervation. In contrast, neurotrophin 3 (NT3) and 4 (NT4) mRNA expression patterns were predominantly epithelial and were strongest during early developmental stages when teeth are not yet innervated. Glial cell line-derived neurotrophic factor (GDNF) mRNA was present in dental epithelium at early stages, but later in development, GDNF mRNA expression was mainly mesenchymal and observed in the odontoblast layer and extending into the subodontoblast zone. Our results suggest that both neurotrophins and GDNF may have multiple functions during tooth development. In addition to an influence on the establishment of the dental innervation, neurotrophic substances might have morphogenetic effects such as modulating the proliferation or differentiation of developing epithelial and mesenchymal cells.

Bone morphogenetic proteins and their receptors: potential functions in the brain.

Transforming growth factors-beta (TGF-betas), activins, and bone morphogenetic proteins (BMPs) comprise an evolutionarily well-conserved group of proteins controlling a number of cell differentiation, cell growth, and morphogentic processes during development. The superfamily of TGFbeta-related genes include over 25 members in mammals several of which are expressed in the growing nervous system and serve important functions in regionalizing the early CNS. Cultured nerve cells show different responses to these factors. Recent developments have revealed that TGFbetas, activins, and BMPs selectively signal to the responding cells via different hetero-oligomeric complexes of type I and type II serine/threonine kinase receptors. The adult brain exhibits specific expression patterns of some of these receptors suggesting neuronal functions not only during development but also in the mature brain. In particular, the brain is expressing high levels of bone morphogenetic protein receptor type II (BMPR-II), activin receptor type I (ActR-I), and activin receptor type IIA (ActR-II). This indicates that osteogenic protein-1 (OP-1/BMP-7), BMP-2, and BMP-4 as well as activins may serve functions for brain neurons. Expression of the receptors partially overlaps in populations of neurons and has been shown to be regulated by brain lesions. This suggests that brain neurons may use receptors BMPR-II and ActR-I to sense the presence of BMPs. This may form a system parallel to the neurotrophin Trk tyrosine kinase receptors regulating neuroplasticity and brain repair. The presence of BMPs in brain is not well studied, but preliminary in situ data indicate that the BMP relatives growth/differentiation factor (GDF)-1 and GDF-10 are distinctly but differentially expressed at high levels in neurons expressing BMPR-II and ActR-I. The receptors mediating responses to these two GDFs remain, however, to be defined. Finally, recent data show that the signal from the activated type I serine/threonine kinase receptor is directly transduced to the nucleus by Smad proteins that become incorporated into transcriptional complexes. Preliminary in situ hybridization observations demonstrate the existence of different Smad mRNAs. It is concluded that BMPs and their signaling systems may comprise a novel pathway for control of neural activity and offer means for pharmacological interventions rescuing brain neurons.

West syndrome: cerebrospinal fluid nerve growth factor and effect of ACTH.

West syndrome is a strictly age-limited encephalopathy of early infancy with unknown pathogenesis. It is often progressive, leading to mental retardation. Neurotrophic factors are important for the regulation of neuronal survival and differentiation, and their expression is influenced by hormones. Levels of beta-nerve growth factor in the cerebrospinal fluid were examined by two-site enzyme-linked immunosorbent assay method. Human antigen was used as a standard. We present data on largely normal levels of nerve growth factor in the cerebrospinal fluid of infants with cryptogenic etiology, but low or negligible levels in infants with symptomatic etiology, and very high levels in infants with symptomatic postinfectious etiology. Treatment with ACTH led to a greater increase in patients with a good response than in those with a poor response. Low nerve growth factor in patients with symptomatic infantile spasms possibly reflects massive neuronal death. The regression seen in these infants and their poor response to ACTH therapy may be due in part to lack of growth factors supporting neuron survival. This study, previously only demonstrated in animal models, is the first to depict nerve growth factor gene activity in humans as modulated by steroids.

Embryonic expression of the mRNA for the rat homologue of the fusin/CXCR-4 HIV-1 co-receptor.

We have previously cloned a human receptor recently shown to be a cofactor for entry of T-tropic HIV-1 strains into CD4+ cells, now named fusin. Stromal derived factor-1 (SDF-1) is an endogenous ligand for fusin, also called CXCR-4. Here we show the distribution of fusin/CXCR-4 mRNA during ontogeny in the rat. The onset of mRNA expression is around embryonic day 9 and the mRNA expression is high in the thymus as well as proliferative areas of the brain during development. Our results suggest: (1) that fusin/CXCR-4 might have a dual role in both brain development and the immune system; (2) that SDF-1 has a role in brain development or that additional physiological ligands exist for this receptor; (3) co-expression of CD4 and fusin/CXCR-4 may make fetuses susceptible to HIV infection during development.

Intraventricular injection of NGF, but not BDNF, induces rapid motor activation that is inhibited by nicotinic receptor antagonists.

The acute and subacute effects of intracerebroventricularly (ICV) administered nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) on locomotor activity were evaluated in awake adult rats. Immediately after ICV injection through an implanted cannula, locomotor activity was measured by a computerized system using infrared photocells, which allowed us to record locomotion, motility, and rearing simultaneously. A single dose of 5 microg mouse beta-NGF produced significant increases in horizontal ambulatory components of locomotor activity (locomotion and motility), but not vertical movement (rearing) 30-45 min after ICV administration. These increases lasted for at least 3-4 h. Systemic injection of 2.0 mg/kg mecamylamine, a central nicotinic receptor antagonist, inhibited the hyperactivity induced by NGF. Systemic injection of 0.5 mg/kg scopolamine, a muscarinic receptor antagonist, did not interfere with the NGF effects. Thus, while scopolamine induced marked increases in all three measures of behavior in both NGF and cytochrome-c-treated animals, locomotion and motility remained significantly higher in the NGF group. Immunohistochemistry demonstrated that NGF diffused readily from the ventricular space into brain parenchyma on the injected side and could be visualized 1 h after ICV injection. These results suggest that ICV administration of NGF increases locomotor activity by inducing acetylcholine release, and that nicotinic receptors are involved in the hyperactivity induced by NGF. ICV administration of 5 microg recombinant human BDNF had no significant effect on locomotor activity during the 0- to 4-h period after ICV injection. However, it produced significant decreases in locomotion, motility, and rearing 24-26 h later. Hence ICV administration of BDNF has entirely different effects on animal behavior from those evoked by NGF. While NGF elicits increases in ambulatory behavior within hours, BDNF causes delayed decreases in ambulatory behavior.

Cell death of adult pyramidal CA1 neurons after intraventricular injection of a novel peptide derived from trkA.

Members of the nerve growth factor (NGF) family of neurotrophins bind to the second leucine-rich motif (LRM2) within the extracellular domains of their respective receptors (trkA, trkB, trkC). Small LRM2 peptides have been recently demonstrated to selectively bind the neurotrophins revealing similar complex binding characteristics as full-length receptors. We extend our recent findings, showing that the peptides (A and C) do not block nerve fiber outgrowth through high affinity trk receptors in a ganglia bioassay. Since the highest concentration of neurotrophins [NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3)] is found in the hippocampus, the peptides were injected into the 3rd ventricle of anesthetized adult rats. The (NGF binding) LRM2-A peptide, but not the (BDNF binding) LRM2-B or the (NT-3 binding) LRM2-C peptides, caused severe apoptotic neurodegeneration of hippocampal pyramidal CA1 neurons as revealed by cresyl violet staining and the TUNEL reaction. The degeneration was protected by intrahippocampal injection of NGF-beta and by the non-N-methyl-D-aspartate (NMDA) antagonist CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), indicating a glutamatergic mechanism. In situ hybridization revealed that pyramidal CA1 neurons did not express trkA and p75 receptor mRNA in sham and LRM2-A-lesioned animals. It is concluded that the LRM2-A peptide represents a novel peptide with properties to induce apoptotic cell death of pyramidal CA1 neurons and may be useful as an experimental agent.