Receptor-mediated retrograde transport in CNS neurons after intraventricular administration of NGF and growth factors

Basal forebrain cholinergic system in the dementias: Vulnerability, resilience, and resistance

The basal forebrain cholinergic neurons (BFCN) provide the primary source of cholinergic innervation of the human cerebral cortex. They are involved in the cognitive processes of learning, memory, and attention. These neurons are differentially vulnerable in various neuropathologic entities that cause dementia. This review summarizes the relevance to BFCN of neuropathologic markers associated with dementias, including the plaques and tangles of Alzheimer's disease (AD), the Lewy bodies of diffuse Lewy body disease, the tauopathy of frontotemporal lobar degeneration (FTLD-TAU) and the TDP-43 proteinopathy of FTLD-TDP. Each of these proteinopathies has a different relationship to BFCN and their corticofugal axons. Available evidence points to early and substantial degeneration of the BFCN in AD and diffuse Lewy body disease. In AD, the major neurodegenerative correlate is accumulation of phosphotau in neurofibrillary tangles. However, these neurons are less vulnerable to the tauopathy of FTLD. An intriguing finding is that the intracellular tau of AD causes destruction of the BFCN, whereas that of FTLD does not. This observation has profound implications for exploring the impact of different species of tauopathy on neuronal survival. The proteinopathy of FTLD-TDP shows virtually no abnormal inclusions within the BFCN. Thus, the BFCN are highly vulnerable to the neurodegenerative effects of tauopathy in AD, resilient to the neurodegenerative effect of tauopathy in FTLD and apparently resistant to the emergence of proteinopathy in FTLD-TDP and perhaps also in Pick's disease. Investigations are beginning to shed light on the potential mechanisms of this differential vulnerability and their implications for therapeutic intervention.

Neuroanatomical basis of the nerve growth factor ovulation-induction pathway in llamas†

The objective of the study was to characterize the anatomical framework and sites of action of the nerve growth factor (NGF)-mediated ovulation-inducing system of llamas. The expression patterns of NGF and its receptors in the hypothalamus of llamas (n = 5) were examined using single and double immunohistochemistry/immunofluorescence. We also compare the expression pattern of the P75 receptor in the hypothalamus of llama and a spontaneous ovulator species (sheep, n = 5). Both NGF receptors (TrkA and P75) were highly expressed in the medial septum and diagonal band of Broca, and populations of TrkA cells were observed in the periventricular and dorsal hypothalamus. Unexpectedly, we found NGF immunoreactive cell bodies with widespread distribution in the hypothalamus but not in areas endowed with NGF receptors. The organum vasculosum of the lamina terminalis (OVLT) and the median eminence displayed immunoreactivity for P75. Double immunofluorescence using vimentin, a marker of tanycytes, confirmed that tanycytes were immunoreactive to P75 in the median eminence and in the OVLT. Additionally, tanycytes were in close association with GnRH and kisspeptin in the arcuate nucleus and median eminence of llamas. The choroid plexus of llamas contained TrkA and NGF immunoreactivity but no P75 immunoreactivity. Results of the present study demonstrate sites of action of NGF in the llama hypothalamus, providing support for the hypothesis of a central effect of NGF in the ovulation-inducing mechanism in llamas.

The relationship between gonadotropin releasing hormone and ovulation inducing factor/nerve growth factor receptors in the hypothalamus of the llama

BACKGROUND

A molecule identical to nerve growth factor, with ovulation-inducing properties has been discovered in the seminal plasma of South American camelids (ovulation-inducing factor/nerve growth factor; OIF/NGF). We hypothesize that the ovulatory effect of OIF/NGF is initiated at the level of the hypothalamus, presumably by GnRH neurons. The objective of the present study was to determine the structural relationship between GnRH neurons and neurons expressing high- and low-affinity receptors for NGF (i.e., TrkA and p75, respectively) in the hypothalamus.

METHODS

Mature llamas (n = 4) were euthanized and their hypothalamic tissue was fixed, sectioned, and processed for immunohistochemistry on free-floating sections. Ten equidistant sections per brain were double stained for immunofluorescence detection of TrkA and GnRH, or p75 and GnRH.

RESULTS

Cells immunoreactive to TrkA were detected in most hypothalamic areas, but the majority of cells were detected in the diagonal band of Broca (part of the ventral forebrain) and the supraoptic nuclei and periventricular area. The number of cells immunoreactive to p75 was highest in the diagonal band of Broca and lateral preoptic areas and least in more caudal areas of the hypothalamus (p < 0.05) in a pattern similar to that of TrkA. A low proportion of GnRH neurons were immunoreactive to TrkA (2.5% of total GnRH cells), and no co-localization between GnRH and p75 was detected. GnRH neuron fibers were detected only occasionally in proximity to TrkA immunopositive neurons.

CONCLUSIONS

Results do not support the hypothesis that the effect of OIF/NGF is driven by a direct interaction with GnRH neurons, but rather provide rationale for the hypothesis that interneurons exist in the hypothalamus that mediate OIF/NGF-induced ovulation.

Light on a sensory interface linking the cerebrospinal fluid to motor circuits in vertebrates

The cerebrospinal fluid (CSF) is circulating around the entire central nervous system (CNS). The main function of the CSF has been thought to insure the global homeostasis of the CNS. Recent evidence indicates that the CSF also dynamically conveys signals modulating the development and the activity of the nervous system. The later observation implies that cues from the CSF could act on neurons in the brain and the spinal cord via bordering receptor cells. Candidate neurons to enable such modulation are the cerebrospinal fluid-contacting neurons (CSF-cNs) that are located precisely at the interface between the CSF and neuronal circuits. The atypical apical extension of CSF-cNs bears a cluster of microvilli bathing in the CSF indicating putative sensory or secretory roles in relation with the CSF. In the brainstem and spinal cord, CSF-cNs have been described in over two hundred species by Kolmer and Agduhr, suggesting an important function within the spinal cord. However, the lack of specific markers and the difficulty to access CSF-cNs hampered their physiological investigation. The transient receptor potential channel PKD2L1 is a specific marker of spinal CSF-cNs in vertebrate species. The transparency of zebrafish at early stages eases the functional characterization of pkd2l1⁺ CSF-cNs. Recent studies demonstrate that spinal CSF-cNs detect spinal curvature via the channel PKD2L1 and modulate locomotion and posture by projecting onto spinal interneurons and motor neurons in vivo. In vitro recordings demonstrated that spinal CSF-cNs are sensing pH variations mainly through ASIC channels, in combination with PKD2L1. Altogether, neurons contacting the CSF appear as a novel sensory modality enabling the detection of mechanical and chemical stimuli from the CSF and modulating the excitability of spinal circuits underlying locomotion and posture.

A Role of the Choroid Plexus in Transplantation Therapy

The choroid plexuses (CPs) play pivotal roles in the most basic aspects of neural function. Some of the roles of the CP include maintaining the extracellular milieu of the brain by actively modulating chemical exchange between the CSF and brain parenchyma, surveying the chemical and immunological status of the brain, detoxifying the brain, secreting a nutritive “cocktail” of polypeptides, and participating in repair processes following trauma. This diversity of functions suggests that even modest changes in the CP can have far reaching effects. Indeed, changes in the anatomy and physiology of the CP have been linked to several CNS diseases. It is also possible that replacing diseased CP or transplanting healthy CP might be useful for treating acute and chronic brain diseases. Here we describe the wide-ranging functions of the CP, alterations of these functions in aging and neurodegeneration, and recent demonstrations of the therapeutic potential of transplanted CP for neural trauma.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Coronin-1 is a neurotrophin endosomal effector that is required for developmental competition for survival

Retrograde communication from axonal targets to neuronal cell bodies is critical for both the development and function of the nervous system. Much progress has been made in recent years linking long-distance, retrograde signaling to a signaling endosome, yet the mechanisms governing the trafficking and signaling of these endosomes remain mostly uncharacterized. Here we report that in mouse sympathetic neurons, the target-derived nerve growth factor (NGF)-tropomyosin-related kinase type 1 (TrkA, also called Ntrk1) signaling endosome, on arrival at the cell body, induces the expression and recruitment of a new effector protein known as Coronin-1 (also called Coro1a). In the absence of Coronin-1, the NGF-TrkA signaling endosome fuses to lysosomes sixfold to tenfold faster than when Coronin-1 is intact. We also define a new Coronin-1-dependent trafficking event in which signaling endosomes recycle and re-internalize on arrival at the cell body. Beyond influencing endosomal trafficking, Coronin-1 is also required for several NGF-TrkA-dependent signaling events, including calcium release, calcineurin activation and phosphorylation of cAMP responsive element binding protein (CREB). These results establish Coronin-1 as an essential component of a feedback loop that mediates NGF-TrkA endosome stability, recycling and signaling as a critical mechanism governing developmental competition for survival.

Bystander effect on brain tissue of mesoangioblasts producing neurotrophins

Neurotrophic factors (NTFs) are involved in the regulation of neuronal survival and function and, thus, may be used to treat neurological diseases associated with neuronal death. A major hurdle for their clinical application is the delivery mode. We describe here a new strategy based on the use of progenitor cells called mesoangioblasts (MABs). MABs can be isolated from postnatal mesoderm tissues and, because of a high adhesin-dependent migratory capacity, can reach perivascular targets especially in damaged areas. We generated genetically modified MABs producing nerve growth factor (MABs-NGF) or brain-derived neurotrophic factor (MABs-BDNF) and assessed their bystander effects in vitro using PC12 cells, primary cultures, and organotypic cultures of adult hippocampal slices. MABs-NGF-conditioned medium induced differentiation of PC12 cells, while MABs-BDNF-conditioned medium increased viability of cultured neurons and slices. Slices cultured with MABs-BDNF medium also better retained their morphology and functional connections, and all these effects were abolished by the TrkB kinase blocker K252a or the BDNF scavenger TrkB-IgG. Interestingly, the amount of BDNF released by MABs-BDNF produced greater effects than an identical amount of recombinant BDNF, suggesting that other NTFs produced by MABs synergize with BDNF. Thus, MABs can be an effective vehicle for NTF delivery, promoting differentiation, survival, and functionality of neurons. In summary, MABs hold distinct advantages over other currently evaluated approaches for NTF delivery in the CNS, including synergy of MAB-produced NTF with the neurotrophins. Since MABs may be capable of homing into damaged brain areas, they represent a conceptually novel, promising therapeutic approach to treat neurodegenerative diseases.

Oxytocin-messages via the cerebrospinal fluid: behavioral effects; a review

The cerebrospinal fluid (CSF) usually is considered as a protective 'nutrient and waste control' system for the brain. Recent findings suggest, however, that the composition of CSF is actively controlled and may play an influential role in the changes in brain activity, underlying different behavioral states. In the present review, we present an overview of available data concerning the release of oxytocin into the CSF, the location of the oxytocin-receptive brain areas and the behavioral effects of intracerebroventricular oxytocin. About 80% of the oxytocin-receptive areas are located close to the ventricular or subarachnoid CSF, including the hypothalamic 'Behavior Control Column' (L.W.Swanson, 2003). As a conclusion we suggest that 'CSF-oxytocin' contributes considerably to the non-synaptic communication processes involved in hypothalamic-, brainstem- and olfactory brain areas and behavioral states and that the flowing CSF is used as a 'broadcasting system' to send coordinated messages to a wide variety of nearby and distant brain areas.

The regulation of brain states by neuroactive substances distributed via the cerebrospinal fluid; a review

The cerebrospinal fluid (CSF) system provides nutrients to and removes waste products from the brain. Recent findings suggest, however, that in addition, the CSF contains message molecules in the form of actively released neuroactive substances. The concentrations of these vary between locations, suggesting they are important for the changes in brain activity that underlie different brain states, and induce different sensory input and behavioral output relationships.The cranial CSF displays a rapid caudally-directed ventricular flow followed by a slower rostrally-directed subarachnoid flow (mainly towards the cribriform plate and from there into the nasal lymphatics). Thus, many brain areas are exposed to and can be influenced by substances contained in the CSF. In this review we discuss the production and flow of the CSF, including the mechanisms involved in the regulation of its composition. In addition, the available evidence for the release of neuropeptides and other neuroactive substances into the CSF is reviewed, with particular attention to the selective effects of these on distant downstream receptive brain areas. As a conclusion we suggest that (1) the flowing CSF is involved in more than just nutrient and waste control, but is also used as a broadcasting system consisting of coordinated messages to a variety of nearby and distant brain areas; (2) this special form of volume transmission underlies changes in behavioral states.

Progressive postnatal motoneuron loss in mice lacking GDF-15

Growth/differentiation factor-15 (GDF-15) is a widely expressed distant member of the TGF-beta superfamily with prominent neurotrophic effects on midbrain dopaminergic neurons. We show here that GDF-15-deficient mice exhibit progressive postnatal losses of spinal, facial, and trigeminal motoneurons. This deficit reaches a approximately 20% maximum at 6 months and is accompanied by losses of motor axons and significant impairment of rotarod skills. Similarly, sensory neurons in dorsal root ganglia (L4, L5) are reduced by 20%, whereas sympathetic neurons are not affected. GDF-15 is expressed and secreted by Schwann cells, retrogradely transported along adult sciatic nerve axons, and promotes survival of axotomized facial neurons as well as cultured motor, sensory, and sympathetic neurons. Despite striking similarities in the GDF-15 and CNTF knock-out phenotypes, expression levels of CNTF and other neurotrophic factors in the sciatic nerve were unaltered suggesting that GDF-15 is a genuine novel trophic factor for motor and sensory neurons.

Potential of choroid plexus epithelial cell grafts for neuroprotection in Huntington's disease: what remains before considering clinical trials

The choroid plexuses (CPs) help maintain the extracellular milieu of the brain by modulating chemical exchange between the cerebrospinal fluid and brain parenchyma, surveying the chemical and immunological status of the brain, detoxifying the brain, secreting a nutritive "cocktail" of polypeptides, and participating in repair processes following trauma. Based on recent pre-clinical studies in animal models, a novel therapeutic approach has been suggested that involves transplanting CP for treating acute and chronic brain diseases. To date most studies have focused on rodent and primate models of Huntington's disease (HD) with demonstrations that transplants of CP can prevent the behavioral and anatomical consequences of striatal degeneration. Despite the encouraging results that lend support to the possibility of protecting vulnerable neurons in HD, critical basic science issues remain unexamined that limit the translation of the pre-clinical findings into clinical evaluations of CP transplants for HD. Here we briefly outline the logic behind using this novel cell source for transplantation, the pre-clinical data supporting this concept, and most importantly identify several critical, gating issues that remain prior to moving this approach forward in a meaningful clinical manner.

Cobalamin deficiency-induced down-regulation of p75-immunoreactive cell levels in rat central nervous system

We investigated immunoreactivity for p75 neurotrophin receptor (NTR) in the spinal cord white matter and septum of rats made cobalamin-deficient (Cbl-D) by means of total gastrectomy or a Cbl-D diet. Cbl deficiency down-regulates p75NTR-immunoreactive cell levels in spinal cord white matter and septum with different time courses. On the whole, the spinal cord white matter seems to be more affected in terms of p75NTR-immunoreactive cells, most of which are astrocytes. The p75NTR-immunoreactive cell levels in the spinal cord white matter and septum normalized in rats treated with Cbl (scheme b) and killed 4 months after total gastrectomy. However, Western blot analysis of p75NTR in the spinal cords of Cbl-D rats shows increased p75NTR protein levels, which are resistant to Cbl replacement. These findings demonstrate that a neurotrophic vitamin (Cbl) positively regulates the levels of a neurotrophic receptor (p75NTR) (at least in terms of immunohistochemistry) in rat central nervous system, although the underlying mechanism(s) are still unknown.

Diversity in the surface morphology of adjacent epithelial cells of the choroid plexus: an ultrastructural analysis

It is generally known that the luminal surface of the choroidal epithelial cells is covered with a luxuriant coat of slender microvilli and cilia. However, extensive ultrastructural studies on the surface morphology of choroidal epithelial cells are lacking. This study, therefore, is focused on the detailed surface morphology of the choroid plexus of the lateral ventricle of adult Wistar rats using transmission and scanning electron microscopy. The animals were anesthetized, perfused with 0.9% oxygenated saline followed by 3% gluteraldehyde and the choroid plexus was processed for routine electron microscopy. The results of the ultrastructural observations presented in this study show that even the neighboring choroidal epithelial cells may express distinct morphology. In addition to the usually described morphology of choroidal epithelial cells, in this study, the presence of cells with uniform small blebs, crenulated or doughnut shaped structures, large mature blebs, or cells with an extensive network of fibers were observed. Although, dissimilar surface morphology of adjacent choroidal epithelial cells may indicate their distinct functional status, further studies are necessary to understand the physiological relevance of the varied surface morphology of choroidal epithelial cells.

GDNF applied to the MPTP-lesioned nigrostriatal system requires TGF-beta for its neuroprotective action

GDNF is a potent neurotrophic factor for nigrostriatal dopaminergic neurons in vitro and in animal models of Parkinson's disease (PD), but has largely failed when tested in therapeutic applications in human PD. We report here that GDNF requires transforming growth factor-beta (TGF-beta) to elicit its neurotrophic activity. Lesioning the mouse nigrostriatal system with MPTP significantly upregulates striatal TGF-beta2 mRNA levels. As expected, GDNF protects against the destructive effects of MPTP, including losses of TH-ir nigral neurons, striatal dopamine and TH-ir fibers. Application of antibodies neutralizing all three TGF-beta isoforms to the MPTP-lesioned striatum abolishes the neurotrophic effect of GDNF. We show that TGF-beta antibodies are not toxic and do not interfere with retrograde transport of iodinated GDNF, suggesting that TGF-beta antibodies do not impair internalization and retrograde trafficking of GDNF. We conclude that striatal TGF-beta may be essential for permitting exogenous GDNF to act as a neuroprotective factor.

Impact of cell type and density on nerve growth factor distribution and bioactivity in 3-dimensional collagen gel cultures

Local delivery of protein agents is potentially important in many tissue engineering systems. In this report, we evaluate an experimental system for measuring the rate of nerve growth factor (NGF) transport and biological activity within a 3-dimensional, tissue-like environment. Fetal brain cells or PC12 cells were suspended throughout collagen gel cultures; controlled-release matrices were used to control the spatial and temporal pattern of NGF release. Experimentally measured concentration profiles were compared to profiles predicted by a mathematical model encompassing diffusion and first-order elimination. Our results suggest that NGF moves through gels by diffusion while being eliminated at a rate that depends on cell density. Since diffusion and elimination also govern protein transport in brain tissue, the collagen gel serves as a model system that replicates the main features of transport in the brain and, therefore, can be used to identify new strategies that enhance NGF distribution in the central nervous system. As an example of the utility of this biophysical model, we demonstrate that implantation of multiple controlled-release matrices can broaden NGF distribution in gel cultures; this broadening was accompanied by a significant increase in cellular biological activity. This approach may be useful in customizing NGF distribution throughout degenerating or damaged central nervous system tissue while minimizing toxicity to surrounding healthy tissue.

Increased spinal cord NGF levels in rats with cobalamin (vitamin B12) deficiency

We have recently demonstrated that the neuropathological morphological alterations caused by cobalamin (Cbl) deficiency in the rat central nervous system are related to the vitamin's inability to modulate the synthesis of some neurotoxic and neurotrophic agents in opposite directions. In the present study, we measured nerve growth factor (NGF) levels in the spinal cord (SC) and cerebrospinal fluid (CSF) of rats made Cbl-deficient (Cbl-D) by means of total gastrectomy (TG) or a Cbl-D diet. In both cases, Cbl deficiency increased SC and CSF NGF levels after the appearance of myelinolytic lesions in the SC white matter (SCWM) (i.e. after the second post-TG month), and these changes were normalised by Cbl treatment in the 4-month-totally-gastrectomised (TGX) rats. Intracerebroventricular (i.c.v.) anti-NGF-antibody treatment prevented the onset of the myelinolytic SCWM lesions in the 2-month-TGX rats (i.e. when SC and CSF NGF levels are still normal) and normalised the ultrastructure of the SCWM in the 4-month-TGX rats, which was however worsened by the i.c.v. administration of NGF. These findings demonstrate that: (i) Cbl deficiency increases SC and CSF NGF levels; and (ii) endogenous NGF seems to play a noxious role in the progression of rat Cbl-D central neuropathy.

Detection of beta-endorphin in the cerebrospinal fluid after intrastriatal microinjection into the rat brain

We have investigated to what extent microinjected beta-endorphin could migrate from the rat brain parenchyma into the CSF compartment. Exogenous rat beta-endorphin (0.1 nmol) was microinjected into the left striatum 1 mm from the lateral ventricle in anesthetized male rats. CSF samples were collected at different time points up to 2 h post-injection from a catheter affixed to the atlanto-occipital membrane of the cisterna magna. Radioimmunoassay and mass spectrometry were performed on the CSF samples, and brain sections were immunostained for beta-endorphin and mu-opioid receptors. The beta-endorphin injected rats showed a marked increase in beta-endorphin immunoreactive (IR) material in the CSF, with a peak at 30-45 min post-injection, and this beta-endorphin-IR material existed mainly as the intact beta-endorphin peptide. The immunohistochemistry results revealed the appearance of distinct beta-endorphin-IR cell bodies in the globus pallidus and the bed nucleus of stria terminalis supracapsular part, regions distant from the injection site, at 2 h post-injection of exogenous beta-endorphin. The beta-endorphin-IR in several of the globus pallidus cell bodies colocalized with the mu-opioid receptor-IR at the cell surface. These findings show that upon delivery of synthetic beta-endorphin, there is a significant intracerebral spread of the injected peptide, reaching regions far from the site of injection via diffusion in the extracellular space and flow in the cerebrospinal fluid. This may be of relevance when interpreting studies based on intracerebral injections of peptides, and advances our knowledge regarding the migration of compounds within the brain.

The choroid plexus in the rise, fall and repair of the brain

The choroid plexuses (CPs) are involved in the most-basic aspects of neural function including maintaining the extracellular milieu of the brain by actively modulating chemical exchange between the CSF and brain parenchyma, surveying the chemical and immunological status of the brain, detoxifying the brain, secreting a nutritive "cocktail" of polypeptides and participating in repair processes following trauma. This diversity of functions may mean that even modest changes in the CP can have far-reaching effects. Indeed, changes in the anatomy and physiology of the CP have been linked to aging and several CNS diseases. It is also possible that replacing diseased or transplanting healthy CP might be useful for treating acute and chronic brain diseases. This review focuses on the wide-ranging and under-appreciated functions of the CP, alterations of these functions in aging and neurodegeneration, and recent demonstrations of the therapeutic potential of transplanted CP for neural trauma.

The choroid plexus: function, pathology and therapeutic potential of its transplantation

The choroid plexus (CP) produces cerebrospinal fluid (CSF) and forms the blood-CSF barrier. However, the CP may have additional functions in the CNS beyond these traditional roles. Preclinical and clinical studies in ageing and neurodegeneration demonstrate anatomical and physiological changes in CP, suggesting roles in normal and pathological conditions and potentially endogenous repair processes following trauma. One of the broadest functions of the CP is establishing and maintaining the extracellular milieu throughout the brain and spinal cord, in part by secreting numerous growth factors into the CSF. The endogenous secretion of growth factors raises the possibility that transplantable CP might enable delivery of these molecules to the brain, while avoiding the conventional molecular and genetic alterations associated with modifying cells to secrete selected products. This review describes some of the anatomical and functional changes of CP in ageing and neurodegeneration, and recent demonstrations of the therapeutic potential of transplanted CP for neural trauma.

The Choroid Plexus‐Cerebrospinal Fluid System: From Development to Aging

The function of the cerebrospinal fluid (CSF) and the tissue that secretes it, the choroid plexus (CP), has traditionally been thought of as both providing physical protection to the brain through buoyancy and facilitating the removal of brain metabolites through the bulk drainage of CSF. More recent studies suggest, however, that the CP-CSF system plays a much more active role in the development, homeostasis, and repair of the central nervous system (CNS). The highly specialized choroidal tissue synthesizes trophic and angiogenic factors, chemorepellents, and carrier proteins, and is strategically positioned within the ventricular cavities to supply the CNS with these biologically active substances. Through polarized transport systems and receptor-mediated transcytosis across the choroidal epithelium, the CP, a part of the blood-CSF barrier (BCSFB), controls the entry of nutrients, such as amino acids and nucleosides, and peptide hormones, such as leptin and prolactin, from the periphery into the brain. The CP also plays an important role in the clearance of toxins and drugs. During CNS development, CP-derived growth factors, such as members of the transforming growth factor-beta superfamily and retinoic acid, play an important role in controlling the patterning of neuronal differentiation in various brain regions. In the adult CNS, the CP appears to be critically involved in neuronal repair processes and the restoration of the brain microenvironment after traumatic and ischemic brain injury. Furthermore, recent studies suggest that the CP acts as a nursery for neuronal and astrocytic progenitor cells. The advancement of our knowledge of the neuroprotective capabilities of the CP may therefore facilitate the development of novel therapies for ischemic stroke and traumatic brain injury. In the later stages of life, the CP-CSF axis shows a decline in all aspects of its function, including CSF secretion and protein synthesis, which may in themselves increase the risk for development of late-life diseases, such as normal pressure hydrocephalus and Alzheimer's disease. The understanding of the mechanisms that underlie the dysfunction of the CP-CSF system in the elderly may help discover the treatments needed to reverse the negative effects of aging that lead to global CNS failure.

Increased proNGF levels in subjects with mild cognitive impairment and mild Alzheimer disease

Nerve growth factor (NGF) is critical for the regulation, differentiation, and survival of basal forebrain cholinergic neurons that degenerate in the late stage of Alzheimer disease (AD). The precursor of NGF (proNGF) is the predominant form of NGF in brain and is increased in end stage AD. To determine whether this increase in proNGF is an early or late change during the progression of cognitive decline, we used Western blotting to measure the relative amounts of proNGF protein in the parietal cortex from subjects clinically classified with no cognitive impairment (NCI; n = 20), mild cognitive impairment (MCI; n = 20), or mild to moderate AD (n = 19). We found that proNGF increased during the prodromal stage of AD. The amount of proNGF protein was 1.4-fold greater in the MCI group as compared to NCI, and was 1.6-fold greater in mild-moderate AD as compared to NCI, similar to our previous findings of a 2-fold increase in end stage AD. There was a negative correlation between proNGF levels and Mini Mental Status Examination (MMSE) score, demonstrating that the accumulation of proNGF is correlated with loss of cognitive function. These findings demonstrate that proNGF levels increase during the preclinical stage of AD and may reflect an early biological marker for the onset of AD.

Evaluation of the neurorestorative effects of the murine beta-nerve growth factor infusions in old rat with cognitive deficit

The nerve growth factor (NGF) is known to participate in the regulation of the expression levels and activity of the choline acetyltransferase (ChAT) in the nervous system. This enzyme is sensitive to the degenerative changes found in Alzheimer's disease (AD). We compared the effectiveness of intraparenchymal (ip) and intracerebroventricular (icv) administration of the murine beta-NGF (beta-NGFm) produced in our laboratories, through the determination of the expression levels and activity of the ChAT, and the evaluation of behavioral recovery in aged rat with cognitive deficit. Our results indicated that icv infusion of beta-NGFm stimulates the expression levels of ChAT gene in the striatum of old rats. Remarkable losses in the ChAT activity were observed in the septum and striatum of old rats. Exogenous administration of beta-NGFm produced a significant increase of ChAT activity in these brain regions differentially according to the administration pathway. The behavioral studies demonstrated that the administration pathway is an important factor in order to obtain the best results for a neurorestorative treatment.

Insulin-like growth factor-1 and post-ischemic brain injury

Insulin-like growth factor-1 (IGF-1) is a naturally occurring neurotrophic factor that plays an important role in promoting cell proliferation and differentiation during normal brain development and maturation. The present review examines recent evidence that endogenous IGF-1 also plays a significant role in recovery from insults such as hypoxia-ischemia and that giving additional exogenous IGF-1 can actively ameliorate damage. It is now well established that neurons and other cell types die many hours or even days after initial injury due to activation of programmed cell death pathways. IGF-1 and its binding proteins and receptors are intensely induced within damaged brain regions following brain injury, suggesting a possible a role for IGF-1 in brain recovery. Exogenous administration of IGF-1 within a few hours after brain injury is now known to be protective in both gray and white matter and leads to improved somatic function. In contrast, pre-treatment is ineffective, likely reflecting limited intracerebral penetration of IGF-1 into the uninjured brain. The neuroprotective effects of IGF-1 are mediated by IGF-1 receptors and its binding proteins and are specific to particular cellular phenotypes and brain regions. The window of opportunity for treatment with IGF-1 is limited to a few hours after normothermic brain injury, reflecting its specific actions on early, intracellular events in the apoptotic cascade. However, injury-associated mild post-hypoxic hypothermia, which delays the development of cell death, can shift and dramatically extend the window of opportunity for delayed treatment with IGF-1. Such a combined approach is likely to be essential for any clinical treatment.

Delivery of neurotrophic factors to the central nervous system: pharmacokinetic considerations

Neurotrophic factors are proteins with considerable potential in the treatment of central nervous system (CNS) diseases and traumatic injuries. However, a significant challenge to their clinical use is the difficulty associated with delivering these proteins to the CNS. Neurotrophic factors are hydrophilic, typically basic, monomeric or dimeric proteins, mostly in the size range of 5 to 30 kDa. Neurotrophic factors potently support the development, growth and survival of neurons, eliciting biological effects at concentrations in the nanomolar to femtomolar range. They are not orally bioavailable and the blood-brain and blood-cerebrospinal fluid barriers severely limit their ability to enter into and act on sites in the CNS following parenteral systemic routes of administration. Most neurotrophic factors have short in vivo half-lives and poor pharmacokinetic profiles. Their access to the CNS is restricted by rapid enzymatic inactivation, multiple clearance processes, potential immunogenicity and sequestration by binding proteins and other components of the blood and peripheral tissues. The development of targeted drug delivery strategies for neurotrophic factors will probably determine their clinical effectiveness for CNS conditions. Achieving significant CNS target site concentrations while limiting systemic exposure and distribution to peripheral sites of action will lessen unwanted pleiotropic effects and toxicity. Local introduction of neurotrophic factors into the CNS intraparenchymally by direct injection/infusion or by implantation of delivery vectors such as polymer matrices or genetically modified cells yields the highest degree of targeting, but is limited by diffusion restrictions and invasiveness. Delivery of neurotrophic factors into the cerebrospinal fluid (CSF) following intracerebroventricular or intrathecal administration is less invasive and allows access to a much wider area of the CNS through CSF circulation pathways. However, diffusional and cellular barriers to penetration into surrounding CNS tissue and significant clearance of CSF into the venous and lymphatic circulation are also limiting. Unconventional delivery strategies such as intranasal administration may offer some degree of CNS targeting with minimal invasiveness. This review presents a summary of the neurotrophic factors and their indications for CNS disorders, their physicochemical characteristics and the different approaches that have been attempted or suggested for their delivery to the CNS. Future directions for further research such as the potential for CNS disease treatment utilising combinations of neurotrophic factors, displacement strategies, small molecule mimetics, chimaeric molecules and gene therapy are also discussed.

Target-derived cardiotrophin-1 and insulin-like growth factor-I promote neurite growth and survival of developing oculomotor neurons

Several trophic factors support the survival of developing motoneurons, but it is not known whether these factors act in a retrograde fashion from the motoneuron target muscle or are derived from other sources. Cardiotrophin-1 (CT-1) and the insulin-like growth factors (IGFs) are candidate target-derived motoneuron survival factors as both are expressed in muscle during naturally occurring motoneuron death and, applied systemically, support the survival of developing motoneurons. By using the embryonic chick oculomotor system, we show that CT-1 and IGF-I promote neurite outgrowth from E13-derived oculomotor explants and are retrogradely transported from muscle to nerve cell body in vivo, and injection of CT-1 or IGF-I into eye muscles increases motoneuron survival by 20 and 30%, respectively, as evidenced by calibrated stereological counting techniques. Pharmacological depletion of endogenous target-derived IGF-I in vivo reduces oculomotor neuron survival by up to 30% in a dose-dependent manner. These results significantly extend previous studies using systemic administration of trophic factors and are the first to demonstrate a target-derived retrograde mechanism of developing motoneuron survival factors.

Relationship between nociceptor activity, peripheral edema, spinal microglial activation and long-term hyperalgesia induced by formalin

To determine whether initial nociceptive inputs caused by subcutaneous injection of formalin into the hindpaw are necessary and/or sufficient for allodynic behavior and microglial activation observed at one week following behavior, we examined Sprague-Dawley rats under five test conditions. Test condition 1. Formalin alone group (six rats), 5% formalin was injected subcutaneously into the dorsal side of the right hind paw. Test condition 2. Bupivacaine/Formalin group (six rats), bupivacaine was injected into the ankle area and into the site of formalin injection 10 min before formalin injection. Test condition 3. Saline/Formalin group (six rats), saline was injected 10min before formalin in the same manner as bupivacaine. Test condition 4. Formalin/Bupivacaine group 1 (six rats), bupivacaine was injected 10 min after formalin. Test condition 5. Formalin/Bupivacaine group 2 (six rats), bupivacaine was injected similarly 1h after formalin. The magnitude of paw edema and paw withdrawal thresholds to mechanical stimuli applied to the plantar surface of the injected paw and on the dorsal surface of the contralateral side were evaluated prior to and one week after formalin injection. The lumbar spinal cord was immunohistochemically processed at one week to assess the expression of a marker for activated microglia. The results showed: (i) pre-treatment with bupivacaine blocked both phases of formalin-evoked pain behaviors and the mechanical allodynia that developed one week post-formalin injection, but did not block microglial activation; (ii) treatment with bupivacaine 1h after formalin injection reduced paw edema and prevented skin ulceration, but one week allodynia and microglial activation were still present; and (iii) prolonged spinal microglial activation was not dependent on acute formalin-induced nociceptor activity, but was strongly associated with the amount of tissue destruction. Our studies suggest that: (i) the central sensitization associated with the phase II of formalin-evoked behaviors and spinal microglial activation are both necessary to permit the development of the long-term hyperalgesia produced by the subcutaneous administration of formalin into the rat's hindpaw; and (ii) acute nociceptive inputs following formalin injection are not necessary for central microglial activation that may be triggered by nerve damage or prolonged signals from peripherally inflamed tissue

Choroid plexus: target for polypeptides and site of their synthesis

Choroid plexus (CP) is an important target organ for polypeptides. The fenestrated phenotype of choroidal endothelium facilitates the penetration of blood-borne polypeptides across the capillary walls. Thus, both circulating and cerebrospinal fluid (CSF)-borne polypeptides can reach their receptors on choroidal epithelium. Several polypeptides have been demonstrated to regulate CSF formation by controlling blood flow to choroid plexus and/or the activity of ion transport in choroidal epithelium. However, many ligand-receptor interactions occurring in the CP are not involved in the regulation of fluid secretion. Increasing evidence suggests that the choroidal epithelium plays an important role in hormonal signaling via a receptor-mediated transport into the brain (e.g., leptin) and helps to clear certain CSF-borne polypeptides (e.g., soluble amyloid beta-protein). Thus, impaired choroidal transport or insufficient clearance of polypeptides may contribute to pathogenesis of systemic or central nervous system (CNS) disorders, such as obesity or Alzheimer's disease. CP epithelium is not only a target but is also a source of neuropeptides, growth factors, and cytokines in the CNS. These polypeptides following their release into the CSF may exert distal, endocrine-like effects on target cells in the brain due to bulk flow of this fluid. Distinct temporal patterns of choroidal expression of several polypeptides are observed during brain development and in various CNS disorders, including traumatic brain injury and ischemia. Therefore, it is proposed that the CP plays an integral role not only in normal brain functioning, but also in the recovery from the injury. This review attempts to critically analyze the available data to support the above hypothesis.

Cyto- and chemoarchitecture of basal forebrain cholinergic neurons in the common marmoset (Callithrix jacchus)

The cyto- and chemoarchitecture of basal forebrain cholinergic neurons (BFCN) was investigated in the lower primate, the common marmoset (Callithrix jacchus). A large population of magnocellular, hyperchromic, and choline acetyltransferase (ChAT)-positive neurons was detected in the marmoset basal forebrain. The distribution of these neurons was similar to those in higher primates. Thus, ChAT-positive neurons were observed in the medial septum (Ch2), the vertical (Ch2) and horizontal (Ch3) limbs of the diagonal band of Broca, and the nucleus basalis of Meynert (Ch4). The Ch4 complex was relatively well differentiated and displayed distinct sectors. We detected anterior (Ch4a, with a medial and a lateral subdivision), intermediate (Ch4i, with a dorsal and a ventral subdivision), and posterior (Ch4p) sectors in the marmoset Ch4. The Ch4i was relatively small while the Ch4p was large. Similar to the rodent, the marmoset Ch1 extended quite a distance posteriorly, and the Ch4p displayed a major interstitial component distributed within the globus pallidus, its medullary laminae, and the internal capsule. Virtually all of the marmoset BFCN displayed acetylcholinesterase activity, and low affinity (p75(NTR)) and high affinity (Trk) neurotrophin receptor immunoreactivity. A majority contained immunoreactivity for calbindin-D(28K) and calretinin. Many of the Ch4 neurons also displayed tyrosine hydroxylase immunoreactivity. The BFCN lacked galanin immunoreactivity, but were innervated by galanin-positive fibers. None of the marmoset BFCN were NADPH-d-positive. Thus, the BFCN display major anatomical and biochemical differences in the marmoset when compared with higher primates. The marmoset BFCN also display many characteristics common to other primates. This fact, combined with the relatively short life span of the marmoset, indicates that this species may be ideal for studies of age-related changes in the BFCN.

Serum growth factors and neuroprotective surveillance: focus on IGF-1

The adult brain requires a constant trophic input for appropriate function. Although the main source of trophic factors for mature neurons is considered to arise locally from glial cells and synaptic partners, recent evidence suggests that hormonal-like influences from distant sources may also be important. These include not only relatively well-characterized steroid hormones that cross the brain barriers, but also blood-borne protein growth factors able to cross the barriers and exert unexpected, albeit specific, trophic actions in diverse brain areas. Insulin-like growth factor I (IGF-I) is until now the serum neurotrophic factor whose actions on the adult brain are best-characterized. This is because IGF-I has been known for many years to be present in serum, whereas the presence in the circulation of other more classical neurotrophic factors has only recently been recognized. Thus, new evidence strongly suggests that IGF-I, and other blood-borne neurotrophic factors such as Fibroblast Growth Factor (FGF-2) or the neurotrophins, exert a tonic trophic input on brain cells, providing a mechanism for what we may refer to as neuroprotective surveillance. Protective surveillance includes "first-line" defense mechanisms ranging from blockade of neuronal death after a wide variety of cellular insults to upregulation of neurogenesis when defenses against neuronal death are overcome. Most importantly, surveillance should also encompass modulation of homeostatic mechanisms to prevent neuronal derangement. These will include modulation of basic cellular processes such as metabolic demands and maintainance of cell-membrane potential as well as more complex processes such as regulation of neuronal plasticity to keep neurons able to respond to constantly changing functional demands.

Intracerebral transportation and cellular localisation of insulin-like growth factor-1 following central administration to rats with hypoxic-ischemic brain injury

Insulin-like growth factor-1 (IGF-1) has been shown to be neuroprotective when administered centrally following hypoxic-ischemic (HI) brain injury. However, the cerebral distribution and site of action of IGF-1 after intracerebroventricular (i.c.v.) administration are not known. A unilateral HI brain injury was induced in adult rats by a modified Levine method. Either 3H-IGF-1 alone, or in combination with unlabelled IGF-1, was administered into the lateral ventricle 2 h after injury. The activity of 3H-IGF-1 signal in the potentially injured cortex was compared between two treatment groups using image analysis. The regional distribution and cellular localisation of 3H-IGF-1 were examined autoradiographically in potentially injured hemispheres at 0.5 and 6 h after administration. Tritiated IGF-1 was detected predominantly in the pia mater, perivascular spaces and subcortical white matter tracts 0.5 h after administration and decreased by 6 h (p<0.05). The signals associated with the perivascular spaces and pia mater were not blocked by unlabelled IGF-1, suggesting non-saturable binding in these brain areas. IGF-1 signal was co-localised with IGF binding protein (IGFBP)-2 immunostaining in the white matter tracts where the signal was blocked by unlabelled IGF-1, suggesting competitive association. IGF-1 signal associated with neurons and glia was maximal in the cerebral cortex and less in the CA1-2 subregion of the hippocampus which were blocked by unlabelled IGF-1 (p<0.05). The signals from cortical neurons did not decrease 6 h after administration, suggesting specific and persistent binding to these cells. Our results indicate that centrally administered IGF-1 can be translocated to neurons and glia via the perivascular circulation and the ependymal cell-white matter tract pathways.

Levels of transforming growth factor alpha (TGF-alpha) in human cerebrospinal fluid

In this study, we investigated cerebrospinal fluid of patients with various neurological symptoms for the presence of transforming growth factor alpha (TGF-alpha). 41 samples of cerebrospinal fluid were collected by lumbar puncture performed routinely due to the clinical suspicion of neurological disease from 22 females (age 15-80 years, median 42 years) and from 19 males (age 18-82 years, median 48 years). A highly sensitive and specific radioimmunoassay was used to determine the concentration of TGF-alpha in the samples. The detection limit of the assay was about 200 pg TGF-alpha. There was no cross-reactivity to human EGF. We showed CSF indeed does contain TGFalpha. As TGF-alpha was detected in all 41 samples investigated, this growth factor appears to be a constant component of CSF. The mean concentration was 5.5 ng TGF-alpha (S.D. +/- 2.7 pg/ml, range 1.1 to 13.9 pg/ml). There was no significant correlation between TGF-alpha concentration in CSF and age (r = -0.006) and there was no significant difference between females (mean 5.8+/-3.10 pg/ml) and males (mean 5.2+/-1.96 pg/ml). No diagnosis was over represented in patients with TGF-alpha concentrations above or below 1 S.D. off the mean. However, highest concentrations of TGF-alpha were found in the group of patients with peripheral neurological sensory dysfunctions and polyneuropathy. We conclude that TGF-alpha is not only a constant component of human cerebrospinal fluid in adults but could also be significantly involved in the pathophysiology of various neurological diseases. The earlier hypothesis that TGF-alpha could mainly have a role in brain development needs hence to be re-evaluated.

Evidence that nerve growth factor influences recent memory through structural changes in septohippocampal cholinergic neurons

We compared, in 4- and 23-month-old Fischer-344 rats, the effects of nerve growth factor (NGF) on basal forebrain cholinergic neurons with behavioral performance in acetylcholine-dependent memory tasks (recent and reference memory). Noncholinergic monoamine markers in target fields of cholinergic neurons were also investigated. We found that NGF has contrasting effects on recent memory in the two age groups in causing improvement in aged rats and deterioration in young rats. In addition, NGF caused significant increase in the size of cholinergic perikarya in all sectors of the basal nucleus complex (BNC). Higher doses of NGF were required to produce hypertrophy in aged animals, a pattern consistent with a lower sensitivity to NGF of aged cholinergic neurons. Analysis of covariance showed that the behavioral effects of NGF were eliminated after covarying out the hypertrophy of cholinergic perikarya. Therefore, NGF causes hypertrophy of cholinergic perikarya regardless of age, and this neurobiological measure correlates with the effects of NGF on recent memory. Reference memory improved moderately only in old rats. This mild effect covaried with an increase in choline acetyltransferase activity in neocortex. Cortical terminal fields of noradrenergic and serotoninergic pathways were not affected by NGF. Taken together, our results indicate that NGF influences recent memory in an age- and transmitter-specific fashion. We postulate that the direct cause of the effects of NGF on memory is not perikaryal hypertrophy per se but rather an increased density of terminals, which always accompanies perikaryal hypertrophy. Although these results continue to support the use of NGF for the treatment of Alzheimer's disease, they raise questions regarding the therapeutic role of NGF for degeneration of BNC neurons occurring in young age.

Distribution and retrograde transport of trophic factors in the central nervous system: functional implications for the treatment of neurodegenerative diseases

Neurotrophins play a crucial role in the maintenance, survival and selective vulnerability of various neuronal populations within the normal and diseased brain. Several families of growth promoting substances have been identified within the central nervous system (CNS) including the superfamily of nerve growth factor related neurotrophin factors, glial derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF). In addition, other non-neuronal growth factors such as fibroblast growth factor (FGF) have also been identified. This article reviews the trophic anatomy of these factors within the CNS. Intraventricular and intraparenchymal injections of exogenous nerve growth factor result in retrograde labeling mainly within the cholinergic basal forebrain. Distribution of brain derived neurotrophic factor (BDNF) following intraventricular injection is minimal due to the binding to the trkB receptor along the ventricular wall. In contrast, intraparenchymal injections of BDNF results in widespread retrograde transport throughout the CNS. BDNF has also been shown to be transported anterogradely within the CNS. Infusion of GDNF into the CNS results in retrograde transport limited to the nigrostriatal pathway. Hippocampal injections of NT-3 retrogradely label mainly basal forebrain neurons. Retrograde transport of radiolabeled CNTF has only been observed in sensory neurons of the sciatic nerve. Following intraventricular and intraparenchymal infusion of radiolabeled bFGF, retrograde neuronal labeling was found in the telecephalon, diencephalon, mesencephalon and pons. In contrast retrograde labeling for aFGF was found only in the hypothalamus and midbrain. Since select neurotrophins traffic anterogradely and retrogradely within the nervous system, these proteins could be used to treat neurological diseases such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis.

Electron microscopic evidence for a cholinergic innervation of GABAergic parvalbumin-immunoreactive neurons in the rat medial septum

The presence of interconnections between cholinergic and parvalbumin (PARV)-containing gamma aminobutyric acid (GABA)ergic septohippocampal projection neurons is still a matter of debate. To search for contacts of cholinergic collateral axon terminals in the septal-diagonal band region the immunotoxin 192IgG-saporin was applied, which was proved to selectively destroy cholinergic basal forebrain neurons. Seven and 10 days after administration of the immunotoxin, choline acetyltransferase immunoreactivity had disappeared, and numerous neuronal somata and dendrites as well as axonal terminals revealed characteristics of electron-lucent degeneration. Electron-dense degeneration was never observed in dendrites and synaptic boutons. Degenerating terminals were found in contact with PARV-immunopositive and PARV-negative neurons. Because only cholinergic cells were degenerating, the terminals should be collaterals from cholinergic neurons. In addition to such contacts, PARV-immunoreactive boutons were seen in contact with PARV-positive and PARV-negative cells, but were not identified at degenerating postsynaptic profiles. As suggested in other studies, cholinergic boutons contacting GABAergic PARV-containing septal projection cells may influence hippocampal theta activity. Furthermore, multiple synaptic connections of both neuronal populations forming the septohippocampal pathway may contribute to their high rate of survival after fimbria-fornix transection.

Localized delivery of proteins in the brain: can transport be customized?

Certain central nervous system (CNS) diseases are characterized by the degeneration of specific cell populations. One strategy for treating neurodegenerative diseases is long-term, controlled delivery of proteins such as epidermal growth factor (EGF) and nerve growth factor (NGF). Since proteins permeate through brain capillaries very slowly, local administration using polymeric implants, continuous infusion pumps, or transplanted, protein-secreting cells may be required to achieve therapeutic concentrations in the tissue. The efficiency of local distribution, and hence effectiveness of local therapy, depends on the rate of protein migration through tissue. The rate of dispersion of molecules in a quiescent, isotropic medium can be characterized by the molecular diffusion coefficient, D, which can be measured by techniques such as quantitative autoradiography, iontophoresis, and fluorescence photobleaching recovery (FPR). These methods are reviewed, with an emphasis on their application to measurement of D for proteins in the brain. Biophysical techniques yield quantitative descriptions of local protein distribution and may enable discrimination of mechanisms of protein transport in the brain. This capability suggests a new paradigm for design of protein therapies, in which proteins and delivery systems are collectively customized to provide sustained protein availability over predetermined volumes of tissue.

Evidence that perihypoglossal neurons involved in vestibular-auditory and gaze control functions respond to nerve growth factor

Nerve growth factor (NGF), which has long been considered to be a trophic factor for peripheral sensory and sympathetic neurons, has been found recently to influence cholinergic neurons in the basal forebrain and neostriatum. In the present study, we provide evidence that brainstem neurons in the perihypoglossal area that relay information from the inner ear and vestibular apparatus to the cerebellum and tectum are responsive to NGF. These neurons, which are located in the nucleus prepositus hypoglossi (NPH), spinal vestibular nucleus, cochlear complex, and gigantocellular and paragigantocellular nuclei of the reticular formation, express functional receptors for NGF and up-regulate the expression of trkA receptors after injection of NGF into targets. In addition, the developmental up-regulation of NGF in the cerebellum coincides with the differentiation of the perihypoglossal nuclei. These results suggest that neurons representing the principal brain relays for auditory and vestibular pathways and perihypoglossal neurons involved in gaze coordination are a novel group of central neurons (besides cholinergic neurons in the basal forebrain and neostriatum) that respond to NGF.

Retrograde degeneration and colchicine protection of basal forebrain cholinergic neurons following hippocampal injections of an immunotoxin against the P75 nerve growth factor receptor

Intracerebroventricular injection of 192 IgG antibody against the p75LNGFR rat low affinity nerve growth factor receptor conjugated with saporin, a ribosome inactivating protein, has been shown to destroy the p75LNGFR-expressing cholinergic neurons of the basal forebrain. We injected this immunotoxin into the hippocampus and studied its retrograde effect upon the cholinergic neurons of the medial septum and the vertical limb of the diagonal band of Broca. Seven days after injection, there was a nearly total depletion of cholinergic axons within the hippocampus. This depletion was associated with a marked and significant decrease in the number of cholinergic neurons of the ipsilateral medial septum and the vertical limb of the diagonal band of Broca. At longer survival times, these changes were more pronounced. Parvalbumin-positive, GABAergic neurons within the same areas of the basal forebrain were not affected by immunotoxin injections. Injections of saporin alone had no effect upon cholinergic neurons. Simultaneous injection of colchicine with the immunotoxin resulted in a significant reduction of retrograde degeneration of cholinergic neurons and relative preservation of hippocampal cholinergic axons. These observations suggest that 192 IgG-saporin is transported retrogradely from the hippocampus to the cholinergic neurons in the medial septum and the vertical limb of the diagonal band of Broca and provide a model for retrograde degeneration of basal forebrain cholinergic neurons following cortically based toxic-pathologic processes.

Practical aspects of the development of ex vivo and in vivo gene therapy for Parkinson's disease

Current approaches to gene therapy of CNS disorders include grafting genetically modified autologous cells or introducing genetic material into cells in situ using a variety of viral or synthetic vectors to produce and deliver therapeutic substances to specific sites within the brain. Here we discuss issues related to the application of ex-vivo and in-vivo gene therapies as possible treatments for Parkinson's disease. Autologous monkey fibroblasts engineered ex-vivo to express tyrosine hydroxylase were grafted into MPTP-treated monkeys and found to express for up to 4 months. Adeno-associated (AAV) viral vectors expressing beta-galactosidase or tyrosine hydroxylase were introduced into monkey brains to determine the extent of infection and the types of cells infected by the vector at 21 days and 3 months. Gene expression was detected at both time points and was restricted to neurons in the striatum. These experiments demonstrate that two different approaches can be used to deliver proteins into the CNS. However, further technological advances are required to optimize gene delivery, regulation of gene expression, and testing in appropriate functional models before gene therapy can be considered for treating human disease.

Retrograde transport of brain-derived neurotrophic factor (BDNF) following infusion in neo- and limbic cortex in rat: relationship to BDNF mRNA expressing neurons

Brain-derived neurotrophic factor (BDNF) was the second member of the nerve growth factor (NGF) family to be isolated. The ability of BDNF to be retrogradely transported following intraparenchymal infusion represents a unique neurobiological tool to determine the location of putative neuron-specific BDNF-responsive neuronal systems. In the present study, we infused recombinant human (rh) BDNF into the rodent neo- and limbic cortex and used a turkey anti-BDNF antibody to determine specific populations of neurons which retrogradely transport this neurotrophin. Frontal cortex infusion retrogradely labeled neurons within the ipsilateral and contralateral frontal cortex, basal forebrain, lateral hypothalamus, centrolateral, mediodorsal, ventrolateral, ventromedial, ventral posterior, rhomboid, reuniens, and medial geniculate thalamic nuclei, and locus coeruleus. Occipital cortex infusion retrogradely labeled neurons in the frontal, temporal, occipital, and perirhinal cortices as well as the claustrum, basal forebrain, thalamus, epithalamus, hypothalamus, and raphe nuclei. Dorsal hippocampal infusion retrogradely labeled neurons within the septal diagonal band, supramammillary nucleus, and entorhinal cortex and was also transported within various hippocampal subfields. Entorhinal cortex infusion retrogradely labeled neurons within the perirhinal cortex, endopiriform nucleus, piriform cortex, dentate gyrus, presubiculum, parasubiculum, CA1-CA4 fields, amygdaloid nuclei, basal forebrain, thalamus, hypothalamus, periaqueductal gray, raphe nuclei, and locus coeruleus. Amygdala infusion labeled neurons in the endopiriform nucleus, temporal cortex, piriform cortex, paralimbic cortex, hippocampus, subiculum, entorhinal cortex, amygdala, basal forebrain, thalamus, hypothalamus, substantia nigra, pars compacta, raphe, and pontine parabrachial nuclei. In situ hybridization experiments demonstrated that virtually all areas which retrogradely transport BDNF also express its message. Neuroanatomical distributional studies of BDNF will unravel specific central nervous system neurotrophic-responsive systems.

Chronic infusion of nerve growth factor into rat striatum increases cholinergic markers and inhibits striatal neuronal discharge rate

New strategies have recently been developed where infusion of neurotrophic factors into the brain can rescue different populations of neurons. Infusion of nerve growth factor (NGF) has been used in combination with transplants of chromaffin tissue to the striatum in the rat model of Parkinson's disease as well as to patients suffering from Alzheimer's disease. In this study we have evaluated the distribution of recombinant human NGF (rhNGF) in different brain areas and evaluated morphological and electrophysiological effects after continuous infusion for 2 weeks of rhNGF (500 micrograms/ml) into the striatum of normal rats. One week after termination of rhNGF infusion, NGF levels in the infused striata were 10-fold increased while in contralateral striata normal levels were found. Extracellular recordings from striatal neurons revealed a significantly decreased spontaneous firing rate (0.76 +/- 0.07 Hz) in rats infused with rhNGF compared to vehicle-infused control animals (1.36 +/- 0.16 Hz). Local application of rhNGF during recordings showed no direct inhibitory effect of NGF on neuronal discharge rate. Immunohistochemistry, using antibodies against acetyl cholinesterase (AChE) and glial fibrillary acidic protein (GFAP), revealed a 38.7 +/- 7.0% increase in optical density of AChE immunoreactivity close to the NGF source and an increase in GFAP-positive profiles that was restricted close to the implanted dialysis fibre. In situ hybridization showed an increase in mRNAs for choline acetyltransferase, trkA, p75 and muscarinic m2 receptor in the large neurons of rhNGF-infused striatum. Messenger RNAs for m1 and m4 receptors in striatal neurons were not changed. Thus, chronic infusion of rhNGF into the striatum caused a cholinergic hyperinnervation and reduced spontaneous activity of striatal neurons.

Transport and elimination of recombinant human NGF during long-term delivery to the brain

The gene for human nerve growth factor (NGF) has been cloned into a mammalian cell line and large quantities of recombinant human NGF (rhNGF) can now be produced for clinical use, but little is known about the fate of rhNGF following delivery to the brain. In this study, we implanted polymer matrices containing 125I-labeled rhNGF into the brains of adult rats and measured spatial distributions of the released protein for 8 weeks after implantation. NGF content in the tissue was determined by counting gamma radiation in thick (1 mm) sections and by autoradiography of thin (20 microns) sections. For the first several days, the rate of NGF release from the polymer matrix was high (approximately 100 ng/day); maximal NGF concentrations, measured at the polymer-tissue interface, were correspondingly high (> 20 micrograms/ml) though day 4. At later times, the release rate decreased (2-10 ng/day) and lower maximal concentrations were observed (1-10 micrograms/ml). NGF levels were always highest in the tissue sections closest to the polymer; during the 8 weeks of the experiment, NGF levels measured in thick sections decreased 100-fold, from 30 ng/section at day 2 to 0.3 ng/section at day 54. The first 10-fold decrease occurred during the first 10 days of the study; a further 6 weeks was required to achieve the second 10-fold decrease. Throughout the experiment, the majority of NGF remained within a restricted zone around the polymer at all times; the mass of NGF decreased to 10% of the maximal level within 2-3 mm of the polymer matrix. At early times (< 1 week), radiolabel corresponding to > 20 pg of NGF was also detected in regions of the brain further removed from the polymer. Comparison of local rhNGF concentration profiles with a simple mathematical model indicated that rhNGF diffuses through the brain interstitial space and is eliminated with a half-life of approximately 45 min, although elimination appears to be substantially slower in white matter regions. This limited ability of NGF to penetrate and be retained within the brain tissue indicates that NGF will need to be delivered almost directly to the target tissue for efficacy.