Intrahippocampal injections of antiserum to nerve growth factor inhibit sympathohippocampal sprouting

Noradrenergic sympathetic sprouting and cholinergic reinnervation maintains non-amyloidogenic processing of AβPP

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) plaques, hyperphosphorylated tau neurofibrillary tangles, and cholinergic dysfunction. Cholinergic degeneration can be mimicked in rats by lesioning medial septum cholinergic neurons. Hippocampal cholinergic denervation disrupts retrograde nerve growth factor (NGF) transport, leading to its accumulation, which subsequently triggers sprouting of noradrenergic sympathetic fibers from the superior cervical ganglia into hippocampus. Previously we reported that coincident with noradrenergic sprouting is the partial reinnervation of hippocampus with cholinergic fibers and the maintenance of a M1 muscarinic acetylcholine receptor (M1 mAChR) dependent long-term depression at CA3-CA1 synapses that is lost in the absence of sprouting. These findings suggest that sympathetic sprouting and the accompanying cholinergic reinnervation maintains M1 mAChR function. Importantly, noradrenergic sympathetic and cholinergic sprouting have been demonstrated in human postmortem AD hippocampus. Furthermore, M1 mAChRs are a recent focus as a therapeutic target for AD given their role in cognition and non-amyloidogenic processing of amyloid-β protein precursor (AβPP). Here we tested the hypotheses that noradrenergic sympathetic sprouting is triggered by NGF, that sprouting maintains non-amyloidogenic AβPP processing, and that sprouting is prevented by intrahippocampal Aβ42 infusion. We found that NGF stimulates sprouting, that sprouting maintains non-amyloidogenic AβPP processing, and that Aβ42 is not only toxic to central cholinergic fibers innervating hippocampus but it prevents and reverses noradrenergic sympathetic sprouting and the accompanying cholinergic reinnervation. These findings reiterate the clinical implications of sprouting as an innate compensatory mechanism and emphasize the importance of M1 mAChRs as an AD therapeutic target.

Brain-directed autoantibodies levels in the serum of Rett syndrome patients

Increased titer of brain-directed autoantibodies (AAB) may represent a risk for brain development in children with Rett syndrome (RTT). The aims of this work were to study the levels of brain-directed AAB, mainly nerve growth factor (NGF) and S-100 protein AAB, to analyze morphological features of brain labeling by AAB produced in RTT patients, and to correlate with clinical manifestation. The increased titer of anti-NGF AAB, but not of anti-S100 AAB has been determined in the blood of RTT patients. The blood from five RTT girls was investigated repeatedly (two to four times) within 0.5-3 years. In these RTT patients the level of anti-NGF AAB was stable, not depending on the stage of illness, so individual stability of anti-NGF AAB levels have been detected. However, the negative correlation between the level of these AAB and severity of disease has been found: girls with the milder course of illness (with relative preservation of speech and locomotor functions, later disease onset, and later development of regressive symptoms) were characterized by the higher levels of AAB. The study also revealed immunohistochemical labeling of neuronal population with serum from RTT patients. Serum AAB from RTT cases labeled the cytoplasm and apical dendrites of pyramidal neurons in the neocortex and hippocampus, neurons in basal ganglia and brain stem, but not in the cerebellum of rats. Our results show the presence of brain-directed AAB in blood serum of RTT patients, which suggests an autoimmune component in pathogenesis of RTT.

Hippocampal sympathetic ingrowth occurs following 192-IgG-Saporin administration

Electrolytic lesions of the medial septal region leads to an unusual neuronal reorganization in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the cholinergically denervated areas of the hippocampus. Since these lesions disrupt cells and fibers of passage which are non-cholinergic, there has been a debate whether Hippocampal Sympathetic Ingrowth is due only to cholinergic denervation of the hippocampus. Using the intraseptal administration of 192-IgG-Saporin, a specific cholinergic neurotoxin, we have found that hippocampal sympathetic ingrowth occurs in the cholinergically denervated hippocampus at 4, 8 and 12 weeks post Saporin injection. These results clearly suggest that hippocampal sympathetic ingrowth is due to the specific loss of the cholinergic projection from the medial septum.

Changes in the serum levels of autoantibody to nerve growth factor in patients with schizophrenia

Studies were performed on 54 patients with different types of schizophrenia-paranoid (8), recurrent-progressive (30), and slowly progressive (16), with ICD-10 rubrics F20.00 and F20.01, F20.22 and F20.02, and F21 respectively. An immunoenzyme method was used to demonstrate that schizophrenia patients had elevated levels of autoantibody to nerve growth factor, by a factor of 1.5 compared with a group of 70 healthy subjects. The autoantibody level was related to the stage of disease: during the active phase, there was a significant increase compared with patients in remission (1.38 +/- 0.26 and 0.92 +/- 0.25 U respectively). There were no differences between variants with different disease courses. The authors suggest that the data obtained here indicate that the autoantibody level can be used as a measure of the activity of the disease process.

Absence of the p75 neurotrophin receptor alters the pattern of sympathosensory sprouting in the trigeminal ganglia of mice overexpressing nerve growth factor

Sympathetic axons invade the trigeminal ganglia of mice overexpressing nerve growth factor (NGF) (NGF/p75(+/+) mice) and surround sensory neurons having intense NGF immunolabeling; the growth of these axons appears to be directional and specific (). In this investigation, we provide new insight into the neurochemical features and receptor requirements of this sympathosensory sprouting. Using double-antigen immunohistochemistry, we demonstrate that virtually all (98%) trigeminal neurons that exhibit a sympathetic plexus are trk tyrosine kinase receptor (trkA)-positive. In addition, the majority (86%) of those neurons enveloped by sympathetic fibers is also calcitonin gene-related peptide (CGRP)-positive; a smaller number of plexuses (14%) surrounded other somata lacking this neuropeptide. Our results show that sympathosensory interactions form primarily between noradrenergic sympathetic efferents and the trkA/CGRP-expressing sensory somata. To assess the contribution of the p75 neurotrophin receptor (p75(NTR)) in sympathosensory sprouting, a hybrid strain of mice was used that overexpresses NGF but lacks p75(NTR) expression (NGF/p75(-/-) mice). The trigeminal ganglia of NGF/p75(-/-) mice, like those of NGF/p75(+/+) mice, have increased levels of NGF protein and display a concomitant ingrowth of sympathetic axons. In contrast to the precise pattern of sprouting seen in the ganglia of NGF/p75(+/+) mice, sympathetic axons course randomly throughout the ganglionic neuropil of NGF/p75(-/-) mice, forming few perineuronal plexuses. Our results indicate that p75(NTR) is not required to initiate or sustain the growth of sympathetic axons into the NGF-rich trigeminal ganglia but rather plays a role in regulating the directional patterns of axon growth.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Learning impairment and cholinergic deafferentation after cortical nerve growth factor deprivation

Cholinergic basal forebrain (CBF ) neurons have been shown to respond in vivo to exogenous administration of NGF. Although neurotrophins and their receptors are widely expressed in the CNS, little data exist for the physiological significance of endogenous neurotrophin signaling in CNS neurons. To test directly whether cortically derived NGF is functionally required for the cholinergic functions mediated by the cerebral cortex, repeated injections of anti-NGF mAbs were locally applied into the insular cortex (IC) of rats. The biochemical results, using an in vivo microdialysis technique, showed a dramatic lack of extracellular release of acetylcholine after high potassium stimulation compared with controls. Furthermore, by using small injections of the neurotracer fluorogold, we found a corresponding disruption in the connectivity between the IC and the CBF. Behavioral experiments showed that the NGF antibodies applied into the IC produced a significant disruption on the acquisition of conditioned taste aversion and inhibitory avoidance learning. However, the same animals were able to recall the taste aversion when the conditioning trial was established before injections of NGF antibodies. Given these results, it seems that cortical cholinergic functions are actively dependent on locally derived NGF in the adult normal brain, and that the cholinergic activity from the CBF is not necessary for recalling aversive stimuli, but is necessary for the acquisition of aversively motivated conditionings.

Maintenance of sympathetic innervation into the hippocampal formation requires a continuous local availability of nerve growth factor

The sprouting of peripheral sympathetic fibers into the septally denervated hippocampal formation is a well-characterized model of lesion-induced plasticity. While various studies have demonstrated the importance of nerve growth factor for evoking sympathetic sprouting, little is known concerning whether nerve growth factor continues to be required for maintaining innervation once it has occurred. In the present study we have addressed this point by (i) investigating the consequences of withdrawing exogenous nerve growth factor support from rats in which sympathetic innervation was enhanced by a nerve growth factor infusion and (ii) using blocking antibodies to interfere with the actions of endogenous nerve growth factor. The results of this investigation clearly indicate that a continuous supply of nerve growth factor (either exogenous or endogenous) is required to maintain sympathetic innervation within the hippocampal formation. Evidence is also provided demonstrating that the nerve growth factor must be made available locally within a given region to evoke and maintain the sympathetic innervation within this location. Axonal rearrangement within the developing and adult brain is believed to be an important mechanism underlying learning and memory is crucial for lesion-related plasticity. In various experimental paradigms, nerve growth factor has been shown to be an important cue for initiating axonal remodeling. In the current study, we have demonstrated that once such rearrangements have taken place, nerve growth factor may also be required to maintain them.

A nerve growth factor peptide retards seizure development and inhibits neuronal sprouting in a rat model of epilepsy

Kindling, an animal model of epilepsy wherein seizures are induced by subcortical electrical stimulation, results in the upregulation of neurotrophin mRNA and protein in the adult rat forebrain and causes mossy fiber sprouting in the hippocampus. Intraventricular infusion of a synthetic peptide mimic of a nerve growth factor domain that interferes with the binding of neurotrophins to their receptors resulted in significant retardation of kindling and inhibition of mossy fiber sprouting. These findings suggest a critical role for neurotrophins in both kindling and kindling-induced synaptic reorganization.

Hippocampal sympathetic ingrowth and cholinergic denervation uniquely alter muscarinic receptor subtypes in the hippocampus

Following cholinergic denervation of the hippocampus by medial septal lesions, and unusual neuronal reorganization occurs, in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. Previously, we have found that both hippocampal sympathetic ingrowth (HSI) and cholinergic denervation (CD), alone, altered the total number and affinity of muscarinic cholinergic receptors (mAChR). In this study, we utilized the muscarinic antagonist [3H]Pirenzepine, in combination with membrane radioligand binding techniques, to determine the effects of HSI and CD on hippocampal M1 and M1 + M3 mAChR subtypes, 4 weeks after MS lesions. In both the dorsal and ventral hippocampus, HSI was found to markedly diminish the number of M1 AChRs, while CD was found to increase the number of M1 AChRs. Neither treatment affected the affinity of the M1 AChR. However, when M1 + M3 binding was assessed, CD was found to decrease the affinity in both hippocampal regions, without altering the number of receptors. Neither affinity nor number of M1 + M3 receptors was altered by HSI. The results of this study suggest that both cholinergic denervation and hippocampal sympathetic ingrowth uniquely affect hippocampal muscarinic receptors.

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.

Trophic-factor modulation of cortical acetylcholinesterase reappearance following transection of the medial cholinergic pathway in the adult rat

Laminar patterns of cortical acetylcholinesterase (AChE) activity are reestablished in the adult, pharmacologically unmanipulated rat following axotomy of the medial cholinergic pathway. The extent to which trophic and/or growth promoting or inhibiting agents modulate AChE fiber reappearance is not fully understood. Such studies, however, would further clarify possible roles for these agents in neuronal plasticity in response to injury, as well as in plastic processes associated with normative functions. In the present experiments, we explored trophic modulation by intracortically infusing nerve growth factor (NGF) or somatostatin into cingulate cortex at a site distal to transection of the medial cholinergic pathway. Comparisons were made with sham-operated or noninfused transected controls, as well as with transected animals infused with renin or antibodies against NGF. Administration began 2 days after axotomy and continued at successive 3-day intervals for 4 weeks. It was found that, proximal to the lesion site, NGF increased and somatostatin decreased optical density of AChE; the number of AChE-containing fibers was unaltered compared to controls. Distal to the knife cut, both NGF and somatostatin increased number of AChE fibers but did not alter overall AChE optical density. Nonetheless, NGF produced an increase in the number of intensely staining puncta both proximal and distal to the cut. Neither renin nor anti-NGF antibodies produced statistically significant effects on optical density or number of fibers at any cortical locus studied. We conclude that NGF and somatostatin have opposite effects on the expression of AChE: whereas NGF increases AChE levels, somatostatin inhibits AChE accumulation in proximal fibers, perhaps by actions on synthesis or transport. Fiber proliferation, which only occurred distally, was affected positively by both NGF and somatostatin, indicating that neurite-promoting effects produced by both agents are confined to tissue regions where neurite extension is stimulated by axotomy. Increases in AChE-positive puncta produced by NGF, however, were not confined to regions of fiber proliferation.

Hippocampal sympathetic ingrowth and cholinergic denervation alter hippocampal muscarinic cholinergic receptors

Cholinergic denervation of the hippocampus by medial septal (MS) lesions results in the ingrowth of peripheral sympathetic fibers, originating from the superior cervical ganglia, into the hippocampus. To determine the effect of hippocampal sympathetic ingrowth (HSI) [3H]-QNB (L-quinuclidinyl [benzilic-4,4(n)] binding was assessed in the dorsal and ventral hippocampus four weeks after MS lesions. In dorsal hippocampus, HSI was found to significantly increase the number (Bmax) of [3H]-QNB binding sites and to normalize the decrease in affinity found in animals with MS lesions plus ganglionectomy (i.e., no ingrowth). In ventral hippocampus, HSI was found to normalize the increased number of binding sites and decreased affinity found in animals with MS lesions without ingrowth. No effect on either Kd or Bmax was found in animals that had undergone ganglionectomy with sham MS lesions. These results suggest that HSI can induce changes in hippocampal muscarinic cholinergic receptors.

The neurotrophins and their receptors: structure, function, and neuropathology

The neurotrophins are a family of polypeptides that promote differentiation and survival of select peripheral and central neurons. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, and neurotrophin-5 are included in this group. In recent years, tremendous advances have been made in the study of these factors. This has stimulated our review of the field, characterizing the neurotrophins from initial isolation to molecular analysis. The review also discusses their synthesis, localization, and responsive tissues, in both the periphery and CNS. The complex receptor interactions of the neurotrophins are also analyzed, as are putative signal transduction mechanisms. Discussion of the observed and postulated involvement in neuropathological disorders leads to the conclusion that the neurotrophins are involved in the function and dysfunction of the nervous system.

Nova, the paraneoplastic Ri antigen, is homologous to an RNA-binding protein and is specifically expressed in the developing motor system

Paraneoplastic opsoclonus-ataxia, a disorder of motor control, develops in breast or lung cancer patients who harbor an antibody (Ri) that recognizes their tumors and a nuclear neuronal protein of 55 kd. We have characterized a gene, Nova, encoding an antigen recognized by the Ri antibody. Nova encodes a novel, highly conserved protein, homologous to the RNA-binding protein hnRNP K, the yeast splicing protein MER1, and a motif in several retroviral proteases. Northern blot analysis detects Nova transcripts only in brain, and several alternatively spliced forms are present in brain and tumor cells. Nova expression is restricted to the ventral brain stem and spinal cord in E18 mice. Since Nova encodes a target antigen in the motor disorder paraneoplastic opsoclonus-ataxia that is expressed in the developing subcortical motor system, it is a likely participant in both the pathogenesis of paraneoplastic opsoclonus-ataxia and the developmental biology of the motor system. The homology between Nova and hnRNP K suggests that Nova regulates RNA splicing or metabolism in a specific subset of developing neurons.

Pathogenesis of mesial temporal sclerosis

A relationship between epilepsy and damage to mesial temporal structures has long been recognized. Recent advances have clarified somewhat the issue of whether the pathological changes seen in mesial temporal sclerosis represent the cause or the effect of seizures. This paper reviews mesial temporal sclerosis from an historical perspective and summarizes recent developments in the fields of excitotoxicity, selective vulnerability, and synaptic reorganization as they pertain to the pathogenesis of mesial temporal sclerosis.

Female circulating sex hormones and hippocampal sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, via medial septal (MS) lesions, sympathetic fibers, originating from the superior cervical ganglia, growth into the hippocampus. Previous studies have demonstrated a sexually dimorphic effect of this neuronal rearrangement on recovery of a spatial-learning task, with this rearrangement being detrimental in male but protective in female rats. Circulating male sex hormones were found to interact with this effect in male animals. In this study we assessed the role of circulating female sex hormones on the behavioral and biochemical effects of hippocampal sympathetic ingrowth (HSI). For the behavioral studies female rats underwent either sham ovariectomy (sham OVARX) or OVARX and were taught a standard radial-8-arm maze task. Following attainment of criterion, animals underwent one of three surgical procedures: sham surgery; MS lesions+sham ganglionectomy (MS); HSI group; MS lesions+ganglionectomy (MSGx). As in our previous study, animals with HSI (i.e. MS group) were found to recover learning faster (in fact, these animals did not differ from controls) than animals with MS lesions without HSI. Gonadal status did not affect this behavioral recovery. For the biochemical studies hippocampal norepinephrine (NE) and choline acetyltransferase (ChAT) were measured in animals sham OVARX and OVARX, 8-12 weeks after the neurosurgical procedure. MS lesions (i.e. MSGx; MS) were found to reduce ChAT activity, regardless of circulating sex hormones. In controls NE levels were similar between OVARX and sham OVARX. NE levels were markedly elevated in the OVARX MS group compared to all other groups including sham OVARX. In the MSGx groups, NE levels were reduced compared to controls, while comparisons between these groups revealed a significant reduction in NE levels in the OVARX MSGx group compared to sham OVARX MSGx group. These studies suggest that female circulating sex hormones interact with brain injury in a very complex manner. However, this interaction does not appear to mediate the changes in behavior observed after HSI.

Antibody to NGF inhibits collateral sprouting of septohippocampal fibers following entorhinal cortex lesion in adult rats

We have used an antiserum raised against mouse 2.5S NGF to examine the involvement of endogenous neurotrophins in the collateral sprouting of septohippocampal fibers in the adult rat brain. The antiserum was administered intraventricularly. Immunocytochemical techniques indicated that the injected antibodies penetrated into brain tissue that included the basal forebrain, cortex, striatum, corpus callosum, and hippocampus. Unilateral lesioning of the entorhinal cortex was done to evoke the sprouting of the cholinergic septohippocampal fibers. At 8 days postlesion, the sprouting was much advanced, as evidenced by an increase in density of the acetylcholinesterase (AChE) staining in the outer molecular layer (OML) of the dentate gyrus and by the associated increase in the absolute number of AChE-positive fibers in the OML. As well, there was a widening of the inner molecular layer (IML), interpreted as being due to sprouting of noncholinergic axons in that region. In rats injected daily with anti-NGF or anti-NGF Fab fragments, no increase in AChE density, or in the population of AChE-positive fibers, was observed in the OML. In contrast, the widening of the IML seemed to be unaffected by the anti-NGF treatment. No changes were observed in the AChE related parameters in the dentate gyrus of nonlesioned animals treated similarly for 8 days with anti-NGF; there was, however, a decrease of choline acetyltransferase (ChAT) immunostaining in the ChAT-positive cells of the basal forebrain. Our findings and the confirmation that our polyclonal anti-NGF also recognizes other members of the NGF neurotrophin family, specifically brain-derived neurotrophic factor and neurotrophin-3, indicate that at least one of these neurotrophins plays a key role in the collateral sprouting of the cholinergic septohippocampal fibers (but not that presumed to occur within the IML) following an entorhinal cortex lesion.

Graft-derived cholinergic reinnervation of the hippocampus prevents a lasting increase of hippocampal noradrenaline concentration induced by septohippocampal damage in rats

Long-Evans female rats sustained aspirative lesions of the septohippocampal pathways and, 2 weeks later, received into the dorsal hippocampus grafts prepared from the septal area (rich in cholinergic neurons; Group Sep) or from the mesencephalic raphe (poor in cholinergic neurons; Group Rap) of rat fetuses. Lesion-only (Group Les) and virtually intact (Group Sham) rats served as controls. Between 9.5 and 10.5 months after grafting surgery, we found the lesions to decrease choline acetyltransferase activity (ChAT), high affinity synaptosomal uptake of [3H]choline (HACU) and serotonin concentration ([5-HT]), as well as to increase the noradrenaline concentration ([NA]) in the dorsal hippocampus. Raphe grafts increased [5-HT] to 456% of normal, but had only weak or no effects on the other lesion-induced modifications in brain neurochemistry. Septal grafts dramatically increased ChAT activity and HACU, enhanced [5-HT], and reduced [NA] to near-normal levels. We also found a significant negative correlation between HACU and [NA] in rats with lesions, whether grafted or not. These data show that grafts providing the denervated hippocampus with a new cholinergic innervation might be able to exert inhibitory effects on the lesion-induced increase of [NA]. Since such an increase is indicative of sympathetic sprouting, the finding of reduced [NA] in rats with graft-derived cholinergic reinnervation of the hippocampus is in line with the hypothesis that hippocampal cholinergic denervation plays a crucial role in the induction of sympathetic sprouting. However, our data do not allow to distinguish whether grafts rich in cholinergic neurons inhibited the sympathetic sprouting itself, or rather reduced the NA content of sprouted fibers.

Decrease of pre-synaptic noradrenergic fiber density in rat hippocampus after transient ischemia

The selective loss of hippocampal CA-1 pyramidal neurons has been reported not to be accompanied by damage to presynaptic terminals in the stratum radiatum as shown by electron microscopic observations. However, we examined changes in the tyrosine hydroxylase (TH) immunoreactive fibers following transient ischemia in rats using an immunohistochemical method 1, 3, 7 and 30 days after ischemia. The present study indicates that ischemic neuronal injury spreads to pre-synaptic fibers after the disappearance of the post-synaptic CA-1 pyramidal neurons.

In vitro cell cultures as a model of the basal forebrain

The basal forebrain has attracted considerable attention because of its putative role in complex functions such as learning, memory and behavioral state control as well as its vulnerability in neurological disorders such as Alzheimer's Disease (AD). The finding that nerve growth factor provides trophic support for the cholinergic basal forebrain neurons has stimulated further interest in understanding trophic interactions of basal forebrain neurons as well as in possible trophic factor therapeutic strategies for disease states. Our laboratory has utilized primary cell cultures and developed immortalized central nervous system cell lines to study the trophic interactions that establish and maintain the septohippocampal pathway, a basal forebrain component which plays an essential role in cognitive function and is prominently affected in AD. The results of our primary cell culture studies have demonstrated the importance of trophic signals elaborated by the hippocampus in mediating the development of septal cholinergic neurons. Nerve growth factor plays an important role in this process, but it cannot account for all of the trophic signals elaborated by authentic hippocampal target cells. The development by this laboratory of clonal cell lines of septal and hippocampal lineage offers the prospect of investigating both the response to and elaboration of neural trophic signals at a more precise level of resolution than can be achieved with primary cultures. The technology and information that is generated from the engineering of such cell lines will also serve as a strategy to study trophic interactions in other brain circuits in future years, and to investigate possible changes or dysfunctions that occur neurological diseases.

The effect of gonadal steroids on the behavioral and biochemical effects of hippocampal sympathetic ingrowth

Following cholinergic denervation of the hippocampal formation, via medial septal lesions, sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. Previous studies have demonstrated a detrimental effect of these fibers on recovery of a spatial-learning task in male but not female animals. In this study we assessed the role of circulating male sex hormones on the behavioral and biochemical effects of hippocampal sympathetic ingrowth (HSI). For the behavioral studies male Sprague-Dawley rats underwent either sham gonadectomy or gonadectomy and were taught a standard radial 8-arm maze task. Following attainment of criterion animals underwent one of three surgical procedures: sham surgery, MS lesions, MS lesions + ganglionectomy. MS lesions, regardless of the presence of HSI, were found to severely impair reacquisition of the task in both sham-gonadectomized and gonadectomized animals. As expected, in the sham-gonadectomized group, MSGx animals reacquired the task faster than the MS group. However, gonadectomy was found to block the detrimental effect of HSI on behavior. For the biochemical studies hippocampal norepinephrine (NE) and choline acetyltransferase (ChAT) were measured eight weeks after surgery in sham-gonadectomized and gonadectomized animals. MS lesions were found to significantly reduce the ChAT activity, regardless of circulating sex hormones. Gonadectomy was found to significantly reduce the level of NE associated with HSI, while having no effect on central NE in CON or MSGx animals. These studies suggest that circulating male sex hormones can influence both the behavioral and biochemical processes associated with HSI.

Purification and characterization of Fab fragments from anti-mouse NGF polyclonal antibodies

A functional role for Nerve Growth Factor (NGF) in the peripheral nervous system is well-documented, but a similar case for NGF in the central nervous system remains to be established. One approach to answering this question would be the availability of high-affinity monospecific Fab fragments obtained against NGF. In the present studies we describe the preparation and characterization of such Fab fragments from anti-mouse NGF polyclonal antibodies. Following their purification by the use of a NGF Sepharose-coupled affinity column, the Fab fragments were examined for biological competence in several ways. In vitro, the anti-Fab fragments blocked the neuronotrophic activity of NGF, as measured by the survival of chicken embryonic day 8 dorsal root ganglion neurons. In vivo, these Fab fragments, when administered systemically to neonatal rats, produced a decrease of noradrenaline levels in two sympathetically innervated organs, the heart and the spleen. These findings suggest that affinity purified Fab fragments of anti-NGF antibodies can be a useful tool for studying the physiological function of NGF in the nervous system.

Brief seizure episodes induce long-term potentiation and mossy fibre sprouting in the hippocampus

Much of our present understanding of the cellular mechanisms of learning and memory derives from studies on the hippocampus in which long-term potentiation (LTP) of synaptic transmission is produced by a train of high-frequency electrical stimulation or by potassium channel blockers. The hippocampus is also a seizure-prone region and recent studies have revealed that brief seizure episodes produce remarkably long-lasting changes which are reminiscent of 'classical' LTP. A brief seizure episode also sets in motion a cascade of events that includes changes in gene expression, sprouting of fibres and the establishment of new synaptic contacts. This paper reviews this use-dependent structural rearrangement of the neuronal network and discusses its possible role in epilepsy and as a model of plasticity in the adult nervous system.

Does the Kunitz domain from the Alzheimer's amyloid beta protein precursor inhibit a kallikrein responsible for post-translational processing of nerve growth factor precursor?

Alternative splicing of the Alzheimer's amyloid beta protein precursor (ABPP) message leads to the production of several variants of this precursor polypeptide. Two of these variants contain a domain that is highly homologous to members of the Kunitz class of protease inhibitors. In order to initiate a study of the physiological role of this domain, we have produced active ABPP Kunitz inhibitor by constructing and expressing a synthetic gene in E. coli. Nerve growth factor (NGF) deficiency has been suggested as a possible cause of the neural degeneration characteristic of Alzheimer's disease, and trypsin and gamma-NGF are the two enzymes that have been shown to be capable of processing beta-NGF precursor to active, mature beta-NGF in vitro, therefore, the specificity of purified recombinant ABPP Kunitz inhibitor was analyzed with respect to these two proteases. Binding of isolated ABPP Kunitz domain both to trypsin (Ki,app less than 10 nM and to gamma-NGF (Ki,app = 300 nM) was observed. This difference in binding to the two proteases correlates with the approximately 20-fold higher rate observed for in vitro processing of the beta-NGF precursor by trypsin compared to processing by gamma-NGF, indicating that perhaps the inhibitor mimics the interaction of the beta-NGF precursor with proteases. The kallikrein actually responsible for beta-NGF precursor processing in vivo is unknown, but these results suggest that it is capable of being significantly inhibited by exposure to the ABPP Kunitz domain.

Catecholamine reinnervation of supraoptic nucleus after deafferenting mechanical lesions and superior cervical ganglionectomy: histofluorescence and functional assessments in young adult and aged rats

Catecholaminergic innervation of the hypothalamic vasopressin (VP)-secreting supraoptic nucleus (SON) was examined at selected intervals after deafferenting neurosurgical lesions, with respect to potential contribution of peripheral vascular sympathetic fibers. Young adult (3 months) and aged (20 months) male F344 rats were subjected to mechanical knife-cut lesion just caudal and medial to the SON, superior cervical ganglionectomy (SCGx), or both surgeries. SON and lesion sites were assessed at 4, 14, 30 or 45 days after surgery, by CA histofluorescence. Functional evaluation in rats subjected to chronic lesions consisted of monitoring water balance (water consumption and urine volumes, and urine osmolality and VP content) in individual rats for presurgical and postsurgical intervals. Histofluorescence evaluation showed that SCGx did not affect the overall SON fluorescence pattern, although a minor sympathetic contribution to that pattern was discerned by comparing SON in rats subjected to lesion alone vs SCGx + lesion. Morphological reinnervation of SON was accomplished at 30 days in young rats, and 45 days in aged rats, after both lesion and SCGx. In young rats, histofluorescence density 30 days after deafferentation was denser than the innervation pattern seen in intact (sham-lesioned) animals, while reinnervation at 45 days postsurgically in aged rats only approximated the presurgical pattern. Vasopressin excretion and corresponding water conservation measures were compromised by SON deafferentation at both ages; excreted VP levels and water balance did not rebound to presurgical values at chronic postsurgical intervals in either young or aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

NGF-dependent sprouting and regeneration in the hippocampus

While a variety of sprouting and regenerative responses have been investigated in the hippocampus, the cellular and molecular events responsible for these plastic responses have not been determined. One transmitter system, the cholinergic system, shows several distinct responses to damage in the septohippocampal circuit. Present evidence strongly supports a role for nerve growth factor (NGF) in these responses. NGF is not only important for the survival of the adult cholinergic neurons, but can also induce regrowth of the damaged fibers given an appropriate substratum for growth. These reparative effects of NGF can manifest themselves in functional recovery in the aged rat and the young rat with fimbria-fornix lesions. Finally, a role for glia cells is proposed to clarify how NGF availability may be regulated during the degenerative and regenerative events. While all plasticity events certainly cannot be explained by the coincidence of NGF and the cholinergic system, their interaction may provide a template for other transmitter/trophic factor interactions.

Modulation of the induction of long-term potentiation in the hippocampus

High frequency stimulation in the guinea pig hippocampus or on the rabbit cerebral cortical surface results in a release of substances that produce, when applied, LTP in the CA1 area of guinea pig hippocampal slices. The substances collected from the neocortex also induce neurite growth in PC-12 cells. The samples collected during the tetanic stimulation of the neocortex contained increased concentrations of glycine, and various other amino acids that are being identified, as well as peptides. Whether the release of the substances is from neurons or from glia is being investigated. Tetanic stimulations of stratum radiatum in the guinea pig hippocampus that induce LTP in CA1 neurons also cause large and prolonged depolarization of glial cells in the CA1 apical dendritic area. Artificial depolarization of glial cells during the activation of stratum radiatum results in LTP of the CA1 neuronal EPSP. It is, therefore, suggested that glial depolarization is involved as one of the steps in the induction of LTP. We speculate that the depolarization results in the release of substances into the extracellular space and that these substances are involved in directly or indirectly modulating the NMDA receptor-coupled channels as well as in producing trophic effects to induce structural changes in the synapses that are thought to be associated with the establishment and maintenance of LTP.

Function of neurotrophic factors in the adult and aging brain and their possible use in the treatment of neurodegenerative diseases

This review summarizes the current knowledge of characterized neurotrophic factors, including nerve growth factor (NGF) which serves as paradigmatic example when studying novel molecules. Special consideration is given to the function of neurotrophic factors in the adult and aging brain. Strategies are discussed for the eventual development of pharmacological applications of these molecules in the treatment of neurodegenerative diseases.

Evidence for a physiological role of nerve growth factor in the central nervous system of neonatal rats

Forebrain cholinergic neurons have been shown to respond in vivo to administration of nerve growth factor (NGF) with a prominent and selective increase of choline acetyltransferase (ChAT) activity. This has suggested that NGF can act as a trophic factor for these neurons. To test this hypothesis directly, anti-NGF antibodies (and their Fab fragments) were intracerebroventricularly injected into neonatal rats to neutralize endogenously occurring NGF. The anti-NGF antibody administration produced a decrease of ChAT activity in the hippocampus, septal area, cortex, and striatum of rat pups. This finding was substantiated by a concomitant decrease of immunopositive staining for ChAT in the septal area. These effects indicate that the occurrence of endogenous NGF in the CNS is physiologically relevant for regulating the function of forebrain cholinergic neurons.

Noradrenergic innervation does not affect chronic regulation of [125I]pindolol receptors in fetal rat brain transplants or host neocortex

Fetal (E15-16) somatosensory cortex (n = 15) or cerebellum (n = 9) were placed into the somatosensory cortex (SmI) of adult rat hosts to study the relative importance of tissue origin versus host milieu on graft beta-adrenoceptor regulation. Autoradiographic studies of [125I]pindolol ([125I]pin) binding in the presence of 3 microM serotonin were performed as an index of beta-receptor binding in both intact hosts and those with ipsilateral locus coeruleus (LC) lesions and/or ipsilateral superior cervical ganglionectomy. [125I]pin binding within fetal grafts was highly variable with areas of highest specific binding in cortical grafts (Kd = 209 +/- 30 pM, Bmax = 106 +/- 7 (fmol/mg protein) being comparable to host cortex (Kd = 211 +/- 41 pM, Bmax = 111 +/- 9 fmol/mg protein). Average total binding in whole cortical grafts was 73% and in cerebellar grafts was 60% of that in comparable adult cortex. Host cortex had 66-73% and cerebellum had 4-8% beta 1-receptors while cortical grafts had 59% and cerebellar grafts had 43% beta 1-receptors as determined by competitive binding with ICI 89406 and 118551. Noradrenergic fibers derived from both the host LC and superior cervical ganglion grew into fetal cortical grafts. Binding to high affinity uptake sites ([3H]desmethylimipramine, [3H]DMI) on noradrenergic terminals in cerebellar grafts was 28% higher than that in cortical grafts; superior cervical ganglionectomy decreased [3H]DMI binding in cortical grafts by 37% but had no effect on cerebellar grafts. Neither ganglionectomy nor LC lesions affected total specific binding or binding to beta-receptor subtypes in the grafts or host cortex 3-6 months after removal. Therefore, anatomic site of origin appeared to be the predominant factor in determining the development of beta-adrenoceptors in fetal cortical tissue. In ectopically placed cerebellar grafts, beta-receptor subtypes did not develop comparably to host cerebellar receptors suggesting that host milieu may be of critical importance in receptor development in this tissue.

Intraventricular NGF infusion in the mature rat brain enhances sympathetic innervation of cerebrovascular targets but fails to elicit sympathetic ingrowth

The ability of peripheral axons to regenerate long distances in the peripheral nervous system (PNS) is well documented; however, examples of axonal elongation within the adult mammalian central nervous system (CNS) are rare. One example of axonal growth in the mature brain is the sprouting of sympathetic axons into the hippocampal formation following disruption of the septohippocampal pathway. A current hypothesis is that elevated hippocampal NGF levels, secondary to loss of retrograde transport by septal neurons, elicits sympathetic ingrowth, In this study, we sought to determine whether elevation of hippocampal NGF activity without septal denervation is sufficient to elicit sympathetic sprouting. Forty-one female rats were infused for two weeks with NGF or cytochrome C in the right lateral ventricle through cannulae connected to an osmotic minipump. In some animals the brains were sectioned and stained for acetylcholinesterase (AChE) activity and norepinephrine histofluorescence; in others, CNS tissue was assayed for nerve growth factor (NGF) content with a two-site ELISA. A Farrand microspectrophotometer was used to measure the intensity of catecholamine fluorescence around the internal carotid artery. The average fluorescence intensity of the sympathetic innervation of the internal carotid artery in the NGF-injected animals was over twice that of vehicle-injected rats indicating that the infused NGF was both accessible to the sympathetic axons and biologically active. However, in none of the cases with elevated hippocampal NGF levels were sympathetic axons observed within the hippocampal formation or any other brain region. These results suggest that simple elevation of brain NGF, while perhaps necessary, is insufficient to permit the growth of sympathetic axons into the mature mammalian CNS.

Sustained elevation in hippocampal NGF-like biological activity following medial septal lesions in the rat

Several laboratories have documented an increase in hippocampal nerve growth factor (NGF) levels, measured with biological or immunological assays, within 1-2 weeks following septal lesions or fimbria/fornix transections. In the present study we have determined the increase in NGF-like biological activity in medium conditioned by hippocampal slices at more prolonged times following medial septal lesion. In contrast to reports based on immunological assays, which demonstrate a transient increase in hippocampal NGF, elevated NGF-like biological activity was present in hippocampal slice-conditioned medium up to one year after a medial septal lesion.

Nerve growth factor receptor and choline acetyltransferase colocalization in neurons within the rat forebrain: response to fimbria-fornix transection

Although it is well known that magnocellular cholinergic basal forebrain neurons are trophically responsive to nerve growth factor (NGF) and contain NGF receptors (NGFr), the exact distribution of forebrain NGFr-immunoreactive neurons and the degree to which cholinergic neurons are colocalized with them have remained in question. In this study we employed a very sensitive double-labelling method and examined in the same tissue section the distribution and cellular features of NGFr-positive and choline acetyltransferase (ChAT)-immunolabelled neurons within the rat basal forebrain. Throughout this region the majority of magnocellular basal forebrain neurons were immunoreactive for both NGFr and ChAT. However, a small percentage of neurons in the ventral portion of the vertical limb of the diagonal band of Broca were immunoreactive only for NGFr, whereas a larger population of magnocellular neurons in the substantia innominata exhibited only ChAT immunoreactivity. No NGFr-immunoreactive cells were found associated with ChAT-positive neurons in the striatum, neocortex, or hippocampus, and no single-labelled NGFr-immunoreactive neurons were found outside the basal forebrain area, except for a large number of positive-labelled cells along the ventricular walls of the third ventricle. In addition to its function in maintaining the normal integrity of the basal forebrain and cholinergic, peripheral sympathetic, and neural-crest-derived sensory neurons, NGF may also have a role in the growth of these neurons after damage to the nervous system. To examine this postulate the hippocampus was denervated of its septal input and examined 8 weeks later. Two populations of neurons were found to have undergone collateral sprouting--namely, the midline magnocellular cholinergic neurons of the dorsal hippocampus and the sympathetic noradrenergic neurons of the superior cervical ganglion. Both of these neuronal populations also stained strongly for NGFr. In contrast, the small intrinsic cholinergic neurons of the hippocampus exhibited neither sprouting response nor staining for NGFr. In view of these results, we suggest that the differing sprouting responses demonstrated by these three neuronal populations may be due to their responsiveness to NGF, as indicated by the presence or absence of NGF receptors.

NGF in CNS: experimental data and clinical implications

The presence of beta-nerve growth factor (NGF) and its cell surface receptor (NGF-R) in the brain has been well established by a variety of experimental techniques in recent years. In particular, the molecular cloning of NGF and NGF-R as well as the development of sensitive two-site ELISA techniques for determining the levels of NGF and antibodies to NGF-R suitable for immunohistochemistry have led to rapid accumulation of data in this field from many laboratories. A main finding is the function of NGF in the cholinergic neurons of the basal forebrain, expressing NGF receptors and responding to the factor by increased activity of choline acetyltransferase, and the production of NGF in cortical areas and hippocampus comprising terminal areas for the cholinergic projections from the basal forebrain. In addition, findings suggest that additional neurons in the brain and spinal cord may utilize NGF, notably during development and possibly also after lesion of the adult CNS. Moreover, observations indicate that endogenous levels of NGF are lowered in the aged rat brain concomitant with losses of NGF-dependent neurons in the basal forebrain. The involvement of NGF in human neurodegenerative diseases is not established but the application of NGF to degenerating cholinergic neurons in Alzheimer patients may prove useful. A promising approach to achieve this goal is the production of biologically active, recombinant NGF.

Nerve growth factor receptors in the central nervous system

Nerve growth factor (NGF) is well known to be involved in the development, survival, and maintenance of sympathetic and neural crest-derived sensory neurons in the peripheral nervous system. Over the last 10-15 years, however, the role of NGF as a necessary trophic substrate for magnocellular cholinergic neurons in the central nervous system (CNS) has emerged. Because the trophic effects of NGF are initiated by its interaction with membrane-bound receptors, the characterization, localization, and function of these specific NGF receptors are essential to understanding the many actions of NGF. The first part of this review will summarize briefly the presence and possible role of NGF in the CNS, with the remainder of the review focusing on what is known about the receptor to NGF.

Nerve growth factor receptor immunoreactivity in the nonhuman primate (Cebus apella): distribution, morphology, and colocalization with cholinergic enzymes

A monoclonal antibody raised against the receptor for nerve growth factor (NGF) was used to examine the distribution and morphology of NGF receptor-containing neurons within the central nervous system of Cebus apella monkeys. Most somata demonstrating positive immunoreactivity were localized within the Ch1-4 regions of the basal forebrain. Neurons in the Ch1 region displayed morphological features typical of cholinergic medial septal neurons. These perikarya were primarily vertically oriented (40-50 micron along the vertical axis) with both apical and basal neuritic processes. Magnocellular (40-50 micron) neurons within the Ch2 (vertical limb of the diagonal band), Ch3 (horizontal limb of the diagonal band) and Ch4 (nucleus basalis of Meynert) regions were multipolar and had rounded perikarya that often displayed an eccentric nucleus. Fibers presumably originating from the Ch1-2 regions were observed throughout the fimbria-fornix system and were found to terminate preferentially within the CA1 and CA3 regions of the hippocampal formation and within the dentate gyrus of the hippocampus. An intense fiber network was also observed in the olfactory tubercle and other rhinencephalic structures, presumably originating from the Ch3 region of the basal forebrain. Beaded processes emanating from the Ch4 region primarily coursed within the external capsule and terminated preferentially within layers I, II, and IV of the cerebral cortex. In a pattern similar to that of cortical acetylcholinesterase (AChE) staining, NGF receptor immunopositive fibers were oriented in a tangential plane within the molecular layer of the cortex and in both a radial and tangential fashion within the cortical granular cell layers. In addition to neural innervation, there was an extensive vascular apposition by NGF receptor-containing neurites on both large caliber vessels and microcapillaries. NGF receptor immunoreactivity was extensively, but not exclusively, colocalized with choline acetyltransferase (ChAT) and AChE in the basal forebrain. A small population of cholinergic neurons were observed that were not NGF receptor-immunoreactive. Conversely, a few NGF receptor-containing neurons that were noncholinergic were also observed in this brain region. NGF receptor-containing somata were also identified in the putamen. The number of immunoreactive neurons observed in this structure, however, would not appear to be sufficient to account for the homologous NGF receptor binding densities described in rodents.(ABSTRACT TRUNCATED AT 250 WORDS)

Astrocytes are important for sprouting in the septohippocampal circuit

Damage to the fimbria-fornix, and separately to the perforant path, leads to distinct and dramatic time-dependent increases in glial fibrillary acidic protein immunoreactivity (GFAP-IR) in specific areas of the hippocampal formation. Specifically, fimbria-fornix lesions resulted in an increase in the GFAP-IR in the pyramidal and oriens area of the CA3 as well as the inner molecular layer of the dentate gyrus. In addition, in the septum ipsilateral to the lesion, there was a rapid and robust increase in GFAP-IR in the dorsal lateral quadrant of the septum, but not in the medial region. Only after 30 days did the GFAP-IR reach the medial septum. Following perforant path lesions, there was a selective increase in GFAP-IR in the outer molecular layer of the dentate gyrus. Most of these changes were transient and had disappeared by 30 days postlesion. We speculate that the increase in GFAP-IR in these target areas is a necessary requirement for the sprouting responses that are observed. This hypothesis is supported by the fact that astrocytes secrete NGF in vitro and that NGF activity increases in these target areas following these same lesions. A mechanism for the selective activation of the astrocytes through the initial activation of microglia and secretion of interleukin-1 is postulated.

Intraventricular injection of antiserum to nerve growth factor delays the development of amygdaloid kindling

To investigate the possibility that nerve growth factor (NGF) may play some role in the development of kindling, rabbit anti-NGF serum was injected into the third ventricle on the first 3 days of daily electrical stimulation of the basolateral amygdala. The number of stimulations required to reach full amygdaloid kindling increased significantly in the rat injected with anti-NGF serum compared to that in the rat injected with normal rabbit serum. It was confirmed that anti-NGF serum did not act as an anticonvulsant. The results demonstrate that NGF may be important for the long-lasting neuronal changes induced by daily electrical stimulation of the amygdala.

Transplantation of male mouse submaxillary gland increases survival of axotomized basal forebrain neurons

Transection of the fimbria-fornix results in a loss of magnocellular neurons in the medial septum and vertical limb of the diagonal band (MS/VDB), possibly due to the deprivation of a retrogradely transported trophic substance, such as nerve growth factor (NGF), derived from the hippocampal formation. We have utilized a transplantation model in which grafts of NGF-rich male mouse submaxillary gland were placed in the lateral ventricle adjacent to the MS/VDB of rats with transections of the fimbria-fornix. At 2-4 weeks following transection, animals with grafted submaxillary glands exhibited enhanced survival of MS/VDB neurons, which stained positive for acetylcholinesterase and were immunoreactive for the NGF receptor. These experiments demonstrate that grafts of male mouse submaxillary gland can facilitate the survival of axotomized MS/VDB cholinergic neurons and may therefore prove beneficial in promoting regeneration of damaged neural systems.

Quantification of hippocampal noradrenaline and zinc changes after selective cell destruction

Deafferentation of septo-hippocampal projections results in sprouting of sympathetic noradrenergic (NA) fibers into the hippocampus. To determine whether dentate granule cells are necessary for the initiation and/or direction of this sprouting, both NA intensity and zinc density were microspectrophotometrically quantified at 10 or 30 days after selective neurotoxin lesions of either granule cells or CA3 pyramidal cells, and electrolytic lesions of medial septum. Groups with elevated zinc density at 10 days also had significantly higher NA levels at 30 days. Destruction of granule cells eliminated the rise in zinc and prevented the NA increase. The zinc increase may be related to a nerve growth factor-like protein responsible for the initiation of sympathetic sprouting.

Sympathetic sprouting in the central nervous system: a model for studies of axonal growth in the mature mammalian brain

Sympathetic fibers innervate many peripheral tissues but are normally confined to extracerebral structures within the cranial cavity, e.g. blood vessels. The invasion of the central nervous system by vascular sympathetic axons is a unique example of neuronal plasticity which provides new information concerning the regulation and mechanisms of neuronal sprouting in both the peripheral and central nervous systems. In this paper, the principal findings concerning the conditions under which such sprouting occurs, the mechanisms which may be involved, and the question of its possible function are reviewed. Of special interest is the fact that a nerve growth factor-like brain factor may be involved in this growth response. The principles gleaned from studies of this sprouting phenomenon may be applicable to other models of neuronal plasticity and may have clinical relevance.