Cerebral neurogenesis is induced by intranasal administration of growth factors

Nasal Model Experiments Show That a Collimated Fluid Delivers Precise Doses to the Human Olfactory Cavity in the Side-Laying Position

The nasal administration of therapeutic fluids and vaccines is used to treat allergic rhinitis, sinusitis, congestion, coronaviruses and even Alzheimer's disease. In the latter, the drug must reach the olfactory region, so it finds its way into the central nervous system. Effective administration techniques able to reach the olfactory region are challenging due to the tortuous anatomy of the nasal cavity, and are frequently evaluated in vitro using transparent anatomical models. Here, the liquid distribution inside a 3D printed human nasal cavity is quantified for model fluids resulting from the discharge of a 1-mL syringe with either a spray-generating nozzle, and a straight tip emitting a collimated fluid stream. Experiments using two model fluids with different viscosities suggest that a simple, correctly positioned straight tip attached to a syringe is able to efficiently deliver most of a therapeutic fluid in the human olfactory region in the side-laying position, avoiding the adoption of head-back and head-down positions that can be difficult for patients in the age range typical of Alzheimer's disease. Furthermore, we demonstrate by computer simulations that the conclusion is valid within a wide range of parameters.

Multi-omics delineate growth factor network underlying exercise effects in an Alzheimer's mouse model

Physical exercise represents a primary defense against age-related cognitive decline and neurodegenerative disorders like Alzheimer's disease (AD). To impartially investigate the underlying mechanisms, we conducted single-nucleus transcriptomic and chromatin accessibility analyses (snRNA-seq and ATAC-seq) on the hippocampus of mice carrying AD-linked NL-G-F mutations in the amyloid precursor protein gene (APPNL-G-F) following prolonged voluntary wheel-running exercise. Our study reveals that exercise mitigates amyloid-induced changes in both transcriptomic expression and chromatin accessibility through cell type-specific transcriptional regulatory networks. These networks converge on the activation of growth factor signaling pathways, particularly the epidermal growth factor receptor (EGFR) and insulin signaling, correlating with an increased proportion of immature dentate granule cells and oligodendrocytes. Notably, the beneficial effects of exercise on neurocognitive functions can be blocked by pharmacological inhibition of EGFR and the downstream phosphoinositide 3-kinases (PI3K). Furthermore, exercise leads to elevated levels of heparin-binding EGF (HB-EGF) in the blood, and intranasal administration of HB-EGF enhances memory function in sedentary APPNL-G-F mice. These findings offer a panoramic delineation of cell type-specific hippocampal transcriptional networks activated by exercise and suggest EGF-related growth factor signaling as a druggable contributor to exercise-induced memory enhancement, thereby suggesting therapeutic avenues for combatting AD-related cognitive decline.

The effect of intra-nasal co-treatment with insulin and growth factor-rich serum on behavioral defects, hippocampal oxidative-nitrosative stress, and histological changes induced by icv-STZ in a rat model

Impaired insulin and growth factor functions are thought to drive many alterations in neurodegenerative diseases like dementia and seem to contribute to oxidative stress and inflammatory responses. Recent studies revealed that nasal growth factor therapy could induce neuronal and oligodendroglia protection in rodent brain damage induction models. Impairment of several growth factors signaling was reported in neurodegenerative diseases. So, in the present study, we examined the effects of intranasal co-treatment of insulin and a pool of growth factor-rich serum (GFRS) which separated from activated platelets on memory, and behavioral defects induced by intracerebroventricular streptozotocin (icv-STZ) rat model also investigated changes in the hippocampal oxidative-nitrosative state and histology. We found that icv-STZ injection (3 mg/kg bilaterally) impairs spatial learning and memory in Morris Water Maze, leads to anxiogenic-like behavior in the open field arena, and induces oxidative-nitrosative stress, neuroinflammation, and neuronal/oligodendroglia death in the hippocampus. GFRS (1µl/kg, each other day, 9 doses) and regular insulin (4 U/40 µl, daily, 18 doses) treatments improved learning, memory, and anxiogenic behaviors. The present study showed that co-treatment (GFRS + insulin with respective dose) has more robust protection against hippocampal oxidative-nitrosative stress, neuroinflammation, and neuronal/oligodendroglia survival in comparison with the single therapy. Memory and behavioral improvements in the co-treatment of insulin and GFRS could be attributed to their effects on neuronal/oligodendroglia survival and reduction of neuroinflammation in the hippocampus.

Human preterm colostrum stimulates outgrowth in neurogenic tissue

BACKGROUND

The olfactory bulb has a key role for nasal delivery of drugs to the brain by its access from the nasal mucosa and its connection to the subventricular zone. The aim of this study was to investigate the neuromodulatory capacity of human milk of premature infants on the olfactory bulb.

METHODS

Olfactory bulbs from P1 mice were embedded in a collagen I gel and incubated with DMEM supplemented with the aqueous phase of human colostrum (Col) of five mothers after very preterm birth, mature milk (Mat) of the same mothers or without supplement (Ctrl). After 7 days, the neurite outgrowth was quantified. Proteome analysis of the milk samples was performed using unlabeled mass spectrometry.

RESULTS

Outgrowth increased significantly in bulbs exposed to Col but not when exposed to Mat. Mass spectrometry revealed profound differences in the proteome of Col versus Mat. Among 21 upregulated proteins in Col were proteins involved in neurite outgrowth, axon guidance, neuromodulation and longevity.

CONCLUSIONS

A high bioactivity of human preterm colostrum on murine neonatal neurogenic tissue is demonstrated to be associated with a proteome profoundly differing from mature milk.

IMPACT

The hypothesis has been raised that neonatal brain damage in a preterm infant could potentially be ameliorated by intranasal application of maternal breast milk. In an in-vitro model using neonatal murine olfactory bulb explants a significant stimulatory effect by human preterm colostrum is observed. Proteomics reveals upregulated neuroactive proteins in human colostrum compared to mature milk. A confirmation of this exploratory study would indicate that preterm colostrum stimulates neurogenic tissue. Early intranasal colostrum application might attenuate perinatal loss of neurogenic tissue thereby contributing to reducing complications such as cerebral palsy.

Visualization and Estimation of Nasal Spray Delivery to Olfactory Mucosa in an Image-Based Transparent Nasal Model

Background: Nose-to-brain (N2B) drug delivery offers unique advantages over intravenous methods; however, the delivery efficiency to the olfactory region using conventional nasal devices and protocols is low. This study proposes a new strategy to effectively deliver high doses to the olfactory region while minimizing dose variability and drug losses in other regions of the nasal cavity. Materials and Methods: The effects of delivery variables on the dosimetry of nasal sprays were systematically evaluated in a 3D-printed anatomical model that was generated from a magnetic resonance image of the nasal airway. The nasal model comprised four parts for regional dose quantification. A transparent nasal cast and fluorescent imaging were used for visualization, enabling detailed examination of the transient liquid film translocation, real-time feedback on input effect, and prompt adjustment to delivery variables, which included the head position, nozzle angle, applied dose, inhalation flow, and solution viscosity. Results: The results showed that the conventional vertex-to-floor head position was not optimal for olfactory delivery. Instead, a head position tilting 45-60° backward from the supine position gave a higher olfactory deposition and lower variability. A two-dose application (250 mg) was necessary to mobilize the liquid film that often accumulated in the front nose following the first dose administration. The presence of an inhalation flow reduced the olfactory deposition and redistributed the sprays to the middle meatus. The recommended olfactory delivery variables include a head position ranging 45-60°, a nozzle angle ranging 5-10°, two doses, and no inhalation flow. With these variables, an olfactory deposition fraction of 22.7 ± 3.7% was achieved in this study, with insignificant discrepancies in olfactory delivery between the right and left nasal passages. Conclusions: It is feasible to deliver clinically significant doses of nasal sprays to the olfactory region by leveraging an optimized combination of delivery variables.

Identification of early neurodegenerative pathways in progressive multiple sclerosis

Progressive multiple sclerosis (MS) is characterized by unrelenting neurodegeneration, which causes cumulative disability and is refractory to current treatments. Drug development to prevent disease progression is an urgent clinical need yet is constrained by an incomplete understanding of its complex pathogenesis. Using spatial transcriptomics and proteomics on fresh-frozen human MS brain tissue, we identified multicellular mechanisms of progressive MS pathogenesis and traced their origin in relation to spatially distributed stages of neurodegeneration. By resolving ligand-receptor interactions in local microenvironments, we discovered defunct trophic and anti-inflammatory intercellular communications within areas of early neuronal decline. Proteins associated with neuronal damage in patient samples showed mechanistic concordance with published in vivo knockdown and central nervous system (CNS) disease models, supporting their causal role and value as potential therapeutic targets in progressive MS. Our findings provide a new framework for drug development strategies, rooted in an understanding of the complex cellular and signaling dynamics in human diseased tissue that facilitate this debilitating disease.

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

Liquid Film Translocation Significantly Enhances Nasal Spray Delivery to Olfactory Region: A Numerical Simulation Study

Previous in vivo and ex vivo studies have tested nasal sprays with varying head positions to enhance the olfactory delivery; however, such studies often suffered from a lack of quantitative dosimetry in the target region, which relied on the observer’s subjective perception of color changes in the endoscopy images. The objective of this study is to test the feasibility of gravitationally driven droplet translocation numerically to enhance the nasal spray dosages in the olfactory region and quantify the intranasal dose distribution in the regions of interest. A computational nasal spray testing platform was developed that included a nasal spray releasing model, an airflow-droplet transport model, and an Eulerian wall film formation/translocation model. The effects of both device-related and administration-related variables on the initial olfactory deposition were studied, including droplet size, velocity, plume angle, spray release position, and orientation. The liquid film formation and translocation after nasal spray applications were simulated for both a standard and a newly proposed delivery system. Results show that the initial droplet deposition in the olfactory region is highly sensitive to the spray plume angle. For the given nasal cavity with a vertex-to-floor head position, a plume angle of 10° with a device orientation of 45° to the nostril delivered the optimal dose to the olfactory region. Liquid wall film translocation enhanced the olfactory dosage by ninefold, compared to the initial olfactory dose, for both the baseline and optimized delivery systems. The optimized delivery system delivered 6.2% of applied sprays to the olfactory region and significantly reduced drug losses in the vestibule. Rheological properties of spray formulations can be explored to harness further the benefits of liquid film translocation in targeted intranasal deliveries.

Current Nanoparticle Approaches in Nose to Brain Drug Delivery and Anticancer Therapy - A Review

Nanoparticles (NPs) are unique may be organic or inorganic, play a vital role in the development of drug delivery targeting the central nervous system (CNS). Intranasal drug delivery has shown to be an efficient strategy with attractive application for drug delivery to the CNS related diseases, such as Parkinson's disease, Alzheimer 's disease and brain solid tumors. Blood brain barrier (BBB) and blood-cerebrospinal fluid barriers are natural protective hindrances for entry of drug molecules into the CNS. Nanoparticles exhibit excellent intruding capacity for therapeutic agents and overcome protective barriers. By using nanotechnology based NPs targeted, drug delivery can be improved across BBB with discharge drugs in a controlled manner. NPs confer safe from degradation phenomenon. Several kinds of NPs are used for nose to the brain (N2B) enroute, such as lipidemic nanoparticles, polymeric nanoparticles, inorganic NPs, solid lipid NPs, dendrimers. Among them, popular lipidemic and polymeric NPs are discussed, and their participation in anti-cancer activity has also been highlighted in this review.

Epidermal Growth Factor in the CNS: A Beguiling Journey from Integrated Cell Biology to Multiple Sclerosis. An Extensive Translational Overview

This article reviews the wealth of papers dealing with the different effects of epidermal growth factor (EGF) on oligodendrocytes, astrocytes, neurons, and neural stem cells (NSCs). EGF induces the in vitro and in vivo proliferation of NSCs, their migration, and their differentiation towards the neuroglial cell line. It interacts with extracellular matrix components. NSCs are distributed in different CNS areas, serve as a reservoir of multipotent cells, and may be increased during CNS demyelinating diseases. EGF has pleiotropic differentiative and proliferative effects on the main CNS cell types, particularly oligodendrocytes and their precursors, and astrocytes. EGF mediates the in vivo myelinotrophic effect of cobalamin on the CNS, and modulates the synthesis and levels of CNS normal prions (PrP^Cs), both of which are indispensable for myelinogenesis and myelin maintenance. EGF levels are significantly lower in the cerebrospinal fluid and spinal cord of patients with multiple sclerosis (MS), which probably explains remyelination failure, also because of the EGF marginal role in immunology. When repeatedly administered, EGF protects mouse spinal cord from demyelination in various experimental models of autoimmune encephalomyelitis. It would be worth further investigating the role of EGF in the pathogenesis of MS because of its multifarious effects.

Proneurotrophins Induce Apoptotic Neuronal Death After Controlled Cortical Impact Injury in Adult Mice

The p75 neurotrophin receptor (p75NTR) can regulate multiple cellular functions including proliferation, survival, and apoptotic cell death. The p75NTR is widely expressed in the developing brain and is downregulated as the nervous system matures, with only a few neuronal subpopulations retaining expression into adulthood. However, p75NTR expression is induced following damage to the adult brain, including after traumatic brain injury, which is a leading cause of mortality and disability worldwide. A major consequence of traumatic brain injury is the progressive neuronal loss that continues secondary to the initial trauma, which ultimately contributes to cognitive decline. Understanding mechanisms governing this progressive neuronal death is key to developing targeted therapeutic strategies to provide neuroprotection and salvage cognitive function. In this study, we demonstrate that a cortical impact injury to the sensorimotor cortex elicits p75NTR expression in apoptotic neurons in the injury penumbra, confirming previous studies. To establish whether preventing p75NTR induction or blocking the ligands would reduce the extent of secondary neuronal cell death, we used a noninvasive intranasal strategy to deliver either siRNA to block the induction of p75NTR, or function-blocking antibodies to the ligands pro-nerve growth factor and pro-brain-derived neurotrophic factor. We demonstrate that either preventing the induction of p75NTR or blocking the proneurotrophin ligands provides neuroprotection and preserves sensorimotor function.

A Tailored Thermosensitive PLGA-PEG-PLGA/Emulsomes Composite for Enhanced Oxcarbazepine Brain Delivery via the Nasal Route

The use of nanocarrier delivery systems for direct nose to brain drug delivery shows promise for achieving increased brain drug levels as compared to simple solution systems. An example of such nanocarriers is emulsomes formed from lipid cores surrounded and stabilised by a corona of phospholipids (PC) and a coating of Tween 80, which combines the properties of both liposomes and emulsions. Oxcarbazepine (OX), an antiepileptic drug, was entrapped in emulsomes and then localized in a poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymer thermogel. The incorporation of OX emulsomes in thermogels retarded drug release and increased its residence time (MRT) in rats. The OX-emulsome and the OX-emulsome-thermogel formulations showed in vitro sustained drug release of 81.1 and 53.5%, respectively, over a period of 24 h. The pharmacokinetic studies in rats showed transport of OX to the systemic circulation after nasal administration with a higher uptake in the brain tissue in case of OX-emulsomes and highest MRT for OX-emulsomal-thermogels as compared to the IN OX-emulsomes, OX-solution and Trileptal® suspension. Histopathological examination of nasal tissues showed a mild vascular congestion and moderate inflammatory changes around congested vessels compared to saline control, but lower toxic effect than that reported in case of the drug solution.

Heparin-Binding Epidermal Growth Factor-Like Growth Factor as a Critical Mediator of Tissue Repair and Regeneration

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family. It contains an EGF-like domain as well as a heparin-binding domain that allows for interactions with heparin and cell-surface heparan sulfate. Soluble mature HB-EGF, a ligand of human epidermal growth factor receptors 1 and 4, is cleaved from the membrane-associated pro-HB-EGF by matrix metalloproteinase or a disintegrin and metalloproteinase in a process called ectodomain shedding. Signaling through human epidermal growth factor receptors 1 and 4 results in a variety of effects, including cellular proliferation, migration, adhesion, and differentiation. HB-EGF levels increase in response to different forms of injuries as well as stimuli, such as lysophosphatidic acid, retinoic acid, and 17β-estradiol. Because it is widely expressed in many organs, HB-EGF plays a critical role in tissue repair and regeneration throughout the body. It promotes cutaneous wound healing, hepatocyte proliferation after partial hepatectomy, intestinal anastomosis strength, alveolar regeneration after pneumonectomy, neurogenesis after ischemic injury, bladder wall thickening in response to urinary tract obstruction, and protection against ischemia/reperfusion injury to many cell types. Additionally, innovative strategies to deliver HB-EGF to sites of organ injury or to increase the endogenous levels of shed HB-EGF have been attempted with promising results. Harnessing the reparatory properties of HB-EGF in the clinical setting, therefore, may produce therapies that augment the treatment of various organ injuries.

The Adult Ventricular-Subventricular Zone (V-SVZ) and Olfactory Bulb (OB) Neurogenesis

A large population of neural stem/precursor cells (NSCs) persists in the ventricular-subventricular zone (V-SVZ) located in the walls of the lateral brain ventricles. V-SVZ NSCs produce large numbers of neuroblasts that migrate a long distance into the olfactory bulb (OB) where they differentiate into local circuit interneurons. Here, we review a broad range of discoveries that have emerged from studies of postnatal V-SVZ neurogenesis: the identification of NSCs as a subpopulation of astroglial cells, the neurogenic lineage, new mechanisms of neuronal migration, and molecular regulators of precursor cell proliferation and migration. It has also become evident that V-SVZ NSCs are regionally heterogeneous, with NSCs located in different regions of the ventricle wall generating distinct OB interneuron subtypes. Insights into the developmental origins and molecular mechanisms that underlie the regional specification of V-SVZ NSCs have also begun to emerge. Other recent studies have revealed new cell-intrinsic molecular mechanisms that enable lifelong neurogenesis in the V-SVZ. Finally, we discuss intriguing differences between the rodent V-SVZ and the corresponding human brain region. The rapidly expanding cellular and molecular knowledge of V-SVZ NSC biology provides key insights into postnatal neural development, the origin of brain tumors, and may inform the development regenerative therapies from cultured and endogenous human neural precursors.

Intranasal gene delivery for treating Parkinson's disease: overcoming the blood-brain barrier

INTRODUCTION

Developing a disease-modifying gene therapy for Parkinson's disease (PD) has been a high priority for over a decade. However, due to the inability of large biomolecules to cross the blood-brain barrier (BBB), the only means of delivery to the brain has been intracerebral infusion. Intranasal administration offers a non-surgical means of bypassing the BBB to deliver neurotrophic factors, and the genes encoding them, directly to the brain.

AREAS COVERED

This review summarizes: i) evidence demonstrating intranasal delivery to the brain of a number of biomolecules having therapeutic potential for various CNS disorders; and ii) evidence demonstrating neuroprotective efficacy of a subset of biomolecules specifically for PD. The intersection of these two spheres represents the area of opportunity for development of new intranasal gene therapies for PD. To that end, our laboratory showed that intranasal administration of glial cell line-derived neurotrophic factor (GDNF), or plasmid DNA nanoparticles encoding GDNF, provides neuroprotection in a rat model of PD, and that the cells transfected by the nanoparticle vector are likely to be pericytes.

EXPERT OPINION

A number of genes encoding neurotrophic factors have therapeutic potential for PD, but few have been tested by the intranasal route and shown to be neuroprotective in a model of PD. Intranasal delivery provides a largely unexplored, promising approach for development of a non-invasive gene therapy for PD.

BBB-targeting, protein-based nanomedicines for drug and nucleic acid delivery to the CNS

The increasing incidence of diseases affecting the central nervous system (CNS) demands the urgent development of efficient drugs. While many of these medicines are already available, the Blood Brain Barrier and to a lesser extent, the Blood Spinal Cord Barrier pose physical and biological limitations to their diffusion to reach target tissues. Therefore, efforts are needed not only to address drug development but specially to design suitable vehicles for delivery into the CNS through systemic administration. In the context of the functional and structural versatility of proteins, recent advances in their biological fabrication and a better comprehension of the physiology of the CNS offer a plethora of opportunities for the construction and tailoring of plain nanoconjugates and of more complex nanosized vehicles able to cross these barriers. We revise here how the engineering of functional proteins offers drug delivery tools for specific CNS diseases and more transversally, how proteins can be engineered into smart nanoparticles or 'artificial viruses' to afford therapeutic requirements through alternative administration routes.

Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease

Besides the presence of amyloid beta (Aβ) plaques and neurofibrillary tangles, neurogenesis and synaptic plasticity are markedly impaired in Alzheimer's disease (AD) possibly contributing to cognitive impairment. In this context, neurotrophic factors serve as a promising therapeutic approach via utilization of regenerative capacity of brain to shift the balance from neurodegeneration to neural regeneration. However, besides more conventional "bystander" effect, to what extent can neurotrophic compounds affect underlying AD pathology remains questionable. Here we investigated the effect of chronic oral treatment with a ciliary neurotrophic factor (CNTF) derived peptidergic compound, P021 (Ac-DGGL(A)G-NH2), on disease pathology both at moderate and severe stages in a transgenic mouse model of AD. 3xTg-AD and wild type female mice were treated for 12months with P021 or vehicle diet starting at 9-10months of age. A significant reduction in abnormal hyperphosphorylation and accumulation of tau at known major AD neurofibrillary pathology associated sites was observed. The effect of P021 on Aβ pathology was limited to a significant decrease in soluble Aβ levels and a trend towards reduction in Aβ plaque load in CA1 region of hippocampus, consistent with reduction in Aβ generation and not clearance. This disease modifying effect was probably via increased brain derived neurotrophic factor (BDNF) expression mediated decrease in glycogen synthase kinase-3-β (GSK3β) activity we found in P021 treated 3xTg-AD mice. P021 treatment also rescued deficits in cognition, neurogenesis, and synaptic plasticity in 3xTg-AD mice. These findings demonstrate the potential of the neurotrophic peptide mimetic as a disease modifying therapy for AD.

Precision nanomedicine in neurodegenerative diseases

The treatment of neurodegenerative diseases remains a tremendous challenge due to the limited access of molecules across the blood-brain barrier, especially large molecules such as peptides and proteins. As a result, at most, a small percentage of a drug that is administered systemically will reach the central nervous system in its active form. Currently, research in the field focuses on developing safer and more effective approaches to deliver peptides and proteins into the central nervous system. Multiple strategies have been developed for this purpose. However, noninvasive approaches, such as nanostructured protein delivery carriers and intranasal administration, seem to be the most promising strategies for the treatment of chronic diseases, which require long-term interventions. These approaches are both target-specific and able to rapidly bypass the blood-brain barrier. In this Perspective, we detail some of these strategies and discuss some of the potential pitfalls and opportunities in this field. The next generation strategies will most likely be more cell-type-specific. Devising these strategies to target the brain may ultimately become a novel therapeutic modality to treat neurodegenerative diseases.

Intranasal epidermal growth factor treatment rescues neonatal brain injury

There are no clinically relevant treatments available that improve function in the growing population of very preterm infants (less than 32 weeks' gestation) with neonatal brain injury. Diffuse white matter injury (DWMI) is a common finding in these children and results in chronic neurodevelopmental impairments. As shown recently, failure in oligodendrocyte progenitor cell maturation contributes to DWMI. We demonstrated previously that the epidermal growth factor receptor (EGFR) has an important role in oligodendrocyte development. Here we examine whether enhanced EGFR signalling stimulates the endogenous response of EGFR-expressing progenitor cells during a critical period after brain injury, and promotes cellular and behavioural recovery in the developing brain. Using an established mouse model of very preterm brain injury, we demonstrate that selective overexpression of human EGFR in oligodendrocyte lineage cells or the administration of intranasal heparin-binding EGF immediately after injury decreases oligodendroglia death, enhances generation of new oligodendrocytes from progenitor cells and promotes functional recovery. Furthermore, these interventions diminish ultrastructural abnormalities and alleviate behavioural deficits on white-matter-specific paradigms. Inhibition of EGFR signalling with a molecularly targeted agent used for cancer therapy demonstrates that EGFR activation is an important contributor to oligodendrocyte regeneration and functional recovery after DWMI. Thus, our study provides direct evidence that targeting EGFR in oligodendrocyte progenitor cells at a specific time after injury is clinically feasible and potentially applicable to the treatment of premature children with white matter injury.

[Clinical diagnosis of the olfactory nerve transport function]

Nasal administration of macromolecular drugs (peptides, nanoparticles) has a possibility to enable a drug delivery system beyond the blood brain barrier via olfactory nerve transport. Basic research on nasal drug delivery to the brain has been well studied. However, evaluation of the olfactory nerve transport function in patients with olfactory disorders has yet to be done, although such an evaluation is important in selecting candidates for clinical trials. Current olfactory function tests are useful for the analysis of olfactory thresholds in olfaction-impaired patients. However, the usefulness of using the increase in olfactory thresholds in patients as an index for evaluating olfactory nerve damage has not been confirmed because of the difficulty in directly evaluating the viability of the peripheral olfactory nerves. Nasally administered thallium-201 migrates to the olfactory bulb, as has been shown in healthy volunteers. Furthermore, transection of olfactory nerve fibers in mice significantly decreases migration of nasally administered thallium-201 to the olfactory bulb. The migration of thallium-201 to the olfactory bulb is reduced in patients with impaired olfaction due to head trauma, upper respiratory tract infections, and chronic rhinosinusitis, relative to the values in healthy volunteers. Nasally administrating thallium-201 followed by single photon emission computed tomography, X-ray computed tomography and magnetic resonance imaging might be useful in choosing candidates for clinical trials of nasal drug delivery methods to the brain.

Drug penetration across the blood-brain barrier: an overview

The brain is one of the most protected organs in the body. There are two key barriers that control the access of endogenous substances and xenobiotics (drugs or toxins) to the CNS. These physiological structures are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier. The BBB represents the main determinant of the effective delivery of drugs to the CNS. Good access through the BBB is essential if the target site is located within the CNS or, in contrast, can be a disadvantage if adverse reactions occur at central level. The development of new drugs targeted to the CNS requires a better knowledge of the factors affecting BBB permeation as well as in vitro and in silico predictive tools to optimize screening, and to reduce the attrition rate at later stages of drug development. This review discusses the particular characteristics of the biology and physiology of the BBB with respect to the permeation and distribution of drugs into the brain. The factors affecting rate, extent and distribution into the brain are discussed and a brief description of the in silico, in vitro, in situ and in vivo methods used to measure BBB transport are presented. Finally, the lastest proposals and strategies to enhance transport across the BBB of new CNS drugs are summarized.

Venlafaxine loaded chitosan NPs for brain targeting: pharmacokinetic and pharmacodynamic evaluation

The purpose of the present investigation was to prepare venlafaxine (VLF) loaded chitosan nanoparticles (NPs) to enhance the uptake of VLF to brain via intranasal (i.n.) delivery. VLF loaded chitosan NPs were prepared and characterized for particle size, size distribution, zeta potential, encapsulation efficiency and in vitro drug release. In order to investigate the localization of chitosan NPs in brain and other organs qualitatively confocal laser scanning microscopy technique was carried out using rhodamine-123 (ROD-123) as marker. The levels of VLF in plasma and brain tissues were also determined, the brain/blood ratios of VLF for VLF (i.v.), VLF (i.n.), VLF chitosan NPs (i.n.) were 0.0293, 0.0700 and 0.1612, respectively, at 0.5h, indicative of better brain uptake of VLF chitosan NPs. The higher drug transport efficiency (508.59) and direct transport percentage (80.34) of VLF chitosan NPs as compared to other formulations suggest its better efficacy in treatment of depression.

Rescue of synaptic failure and alleviation of learning and memory impairments in a trisomic mouse model of down syndrome

Down syndrome (DS) is caused by the triplication of ∼240 protein-coding genes on chromosome 21 and is the most prevalent form of developmental disability. This condition results in abnormalities in many organ systems, as well as in intellectual retardation. Many previous efforts to understand brain dysfunction in DS have indicated that cognitive deficits are coincident with reduced synaptic plasticity and decreased neuronal proliferation. One therapeutic strategy for optimizing the microenvironment for neuronal proliferation and synaptic plasticity in the brain is the use of neurotrophins to restore the homeostasis of the brain biochemical milieu. Here, we show that peripheral administration of Peptide 6, an 11-mer corresponding to an active region of ciliary neurotrophic factor, amino acid residues 146 to 156, can inhibit learning and memory impairments in Ts65Dn mice, a trisomic mouse model of DS. Long-term treatment with Peptide 6 enhanced the pool of neural progenitor cells in the hippocampus and increased levels of synaptic proteins crucial for synaptic plasticity. These findings suggest a therapeutic potential of Peptide 6 in promoting functional neural integration into networks, thereby strengthening biologic substrates of memory processing.

A Role for the Cannabinoid 1 Receptor in Neuronal Differentiation of Adult Spinal Cord Progenitors in vitro is Revealed through Pharmacological Inhibition and Genetic Deletion

In contrast to the adult brain, the adult spinal cord is a non-neurogenic environment. Understanding how to manipulate the spinal cord environment to promote the formation of new neurons is an attractive therapeutic strategy for spinal cord injury and disease. The cannabinoid 1 receptor (CB1R) has been implicated as a modulator of neural progenitor cell proliferation and fate specification in the brain; however, no evidence exists for modulation of adult spinal cord progenitor cells. Using adult rat spinal cord primary cultures, we demonstrated that CB1R antagonism with AM251 significantly decreased the number of Nestin(+) cells, and increased the number of βIII tubulin(+) and DCX(+) cells, indicative of neuronal differentiation. AM251’s effect was blocked by co-application of the CB1R agonists, WIN 55, 212-2, or ACEA. Consistent with our hypothesis, cultures, and spinal cord slices derived from CB1R knock-out (CB1−/−) mice had significantly higher levels of DCX(+) cells compared to those derived from wild type (CB1+/+) mice, indicative of enhanced neuronal differentiation in CB1−/− spinal cords. Moreover, AM251 promoted neuronal differentiation in CB1+/+, but not in CB1−/− cultures. Since CB1R modulates synaptic transmission, and synaptic transmission has been shown to influence progenitor cell fate, we evaluated whether AM251-induced neuronal differentiation was affected by chronic inactivity. Either the presence of the voltage-dependent sodium channel blocker tetrodotoxin (TTX), or the removal of mature neurons, inhibited the AM251-induced increase in DCX(+) cells. In summary, antagonism or absence of CB1R promotes neuronal differentiation in adult spinal cords, and this action appears to require TTX-sensitive neuronal activity. Our data suggest that the previously detected elevated levels of endocannabinoids in the injured adult spinal cord could contribute to the non-neurogenic environment and CB1R antagonists could potentially be used to enhance replacement of damaged neurons.

Opportunities and challenges in developing Alzheimer disease therapeutics

Alzheimer disease (AD) is a chronic, progressive disorder with an average disease progression of 7-10 years. However, the histopathological hallmark lesions of this disease, the extracellular Aβ plaques and the intraneuronal neurofibrillary tangles, start as early as childhood in the affected individuals. AD is multifactorial and probably involves many different etiopathogenic mechanisms. Thus, while AD offers a wide window of opportunity that practically includes the whole life span of the affected individuals, and numerous therapeutic targets, the multifactorial nature of this disease also makes the selection of the therapeutic targets an immensely challenging task. In addition to β-amyloidosis and neurofibrillary degeneration, the AD brain also is compromised in its ability to regenerate by enhancing neurogenesis and neuronal plasticity. An increasing number of preclinical studies in transgenic mouse models of AD show that enhancement of neurogenesis and neuronal plasticity can reverse cognitive impairment. Development of both drugs that can inhibit neurodegeneration and drugs that can increase the regenerative capacity of the brain by enhancing neurogenesis and neuronal plasticity are required to control AD.

Heterogeneity and Fgf dependence of adult neural progenitors in the zebrafish telencephalon

Adult telencephalic neurogenesis is a conserved trait of all vertebrates studied. It has been investigated in detail in rodents, but very little is known about the composition of neurogenic niches and the cellular nature of progenitors in nonmammalian vertebrates. To understand the components of the progenitor zones in the adult zebrafish telencephalon and the link between glial characteristics and progenitor state, we examined whether canonical glial markers are colocalized with proliferation markers. In the adult zebrafish telencephalon, we identify heterogeneous progenitors that reside in two distinct glial domains. We find that the glial composition of the progenitor zone is linked to its proliferative behavior. Analyzing both fast-cycling proliferating cells as well as slowly cycling progenitors, we find four distinct progenitor types characterized by differential expression of glial markers. Importantly, a significant proportion of progenitors do not display typical radial glia characteristics. By blocking or activating Fgf signaling by misexpression of a dominant negative Fgf-receptor 1 or Fgf8a, respectively, we find that ventral and dorsal progenitors in the telencephalon also differ in their requirement for Fgf signaling. Together with data on the expression of Fgf signaling components in the ventricular zone of the telencephalon, this suggests that Fgf signaling directly regulates proliferation of specific subsets of adult telencephalic progenitors in vivo. Taken together our results show that adult neural progenitor cells are heterogeneous with their respect to distribution into two distinct glial domains and their dependence upon Fgf signaling as a proliferative cue in the zebrafish telencephalon.

Pharmacologic reversal of neurogenic and neuroplastic abnormalities and cognitive impairments without affecting Aβ and tau pathologies in 3xTg-AD mice

In addition to the occurrence of numerous neurofibrillary tangles and Aβ plaques, neurogenesis and neuronal plasticity are markedly altered in Alzheimer disease (AD). Although the most popular therapeutic approach has been to inhibit neurodegeneration, another is to promote neurogenesis and neuronal plasticity by utilizing the regenerative capacity of the brain. Here we show that, in a transgenic mouse model of AD, 3xTg-AD mice, there was a marked deficit in neurogenesis and neuroplasticity, which occurred before the formation of any neurofibrillary tangles or Aβ plaques and was associated with cognitive impairment. Furthermore, peripheral administration of Peptide 6, an 11-mer, which makes an active region of ciliary neurotrophic factor (CNTF, amino acid residues 146-156), restored cognition by enhancing neurogenesis and neuronal plasticity in these mice. Although this treatment had no detectable effect on Aβ and tau pathologies in 9-month animals, it enhanced neurogenesis in dentate gyrus, reduced ectopic birth in the granular cell layer, and increased neuronal plasticity in the hippocampus and cerebral cortex. These findings, for the first time, demonstrate the possibility of therapeutic treatment of AD and related disorders by peripheral administration of a peptide corresponding to a biologically active region of CNTF.

HIV-associated neurocognitive disorder: pathogenesis and therapeutic opportunities

Human immunodeficiency virus type 1 (HIV) infection presently affects more that 40 million people worldwide, and is associated with central nervous system (CNS) disruption in at least 30% of infected individuals. The use of highly active antiretroviral therapy has lessened the incidence, but not the prevalence of mild impairment of higher cognitive and cortical functions (HIV-associated neurocognitive disorders) as well as substantially reduced a more severe form dementia (HIV-associated dementia). Furthermore, improving neurological outcomes will require novel, adjunctive therapies that are targeted towards mechanisms of HIV-induced neurodegeneration. Identifying such molecular and pharmacological targets requires an understanding of the events preceding irreversible neuronal damage in the CNS, such as actions of neurotoxins (HIV proteins and cellular factors), disruption of ion channel properties, synaptic damage, and loss of adult neurogenesis. By considering the specific mechanisms and consequences of HIV neuropathogenesis, unified approaches for neuroprotection will likely emerge using a tailored, combined, and non-invasive approach.

Epigenetics, hippocampal neurogenesis, and neuropsychiatric disorders: unraveling the genome to understand the mind

In mature, differentiated neurons in the central nervous system (CNS), epigenetic mechanisms--including DNA methylation, histone modification, and regulatory noncoding RNAs--play critical roles in encoding experience and environmental stimuli into stable, behaviorally meaningful changes in gene expression. For example, epigenetic changes in mature hippocampal neurons have been implicated in learning and memory and in a variety of neuropsychiatric disorders, including depression. With all the recent (and warranted) attention given to epigenetic modifications in mature neurons, it is easy to forget that epigenetic mechanisms were initially described for their ability to promote differentiation and drive cell fate in embryonic and early postnatal development, including neurogenesis. Given the discovery of ongoing neurogenesis in the adult brain and the intriguing links among adult hippocampal neurogenesis, hippocampal function, and neuropsychiatric disorders, it is timely to complement the ongoing discussions on the role of epigenetics in mature neurons with a review on what is currently known about the role of epigenetics in adult hippocampal neurogenesis. The process of adult hippocampal neurogenesis is complex, with neural stem cells (NSCs) giving rise to fate-restricted progenitors and eventually mature dentate gyrus granule cells. Notably, neurogenesis occurs within an increasingly well-defined "neurogenic niche", where mature cellular elements like vasculature, astrocytes, and neurons release signals that can dynamically regulate neurogenesis. Here we review the evidence that key stages and aspects of adult neurogenesis are driven by epigenetic mechanisms. We discuss the intrinsic changes occurring within NSCs and their progeny that are critical for neurogenesis. We also discuss how extrinsic changes occurring in cellular components in the niche can result in altered neurogenesis. Finally we describe the potential relevance of epigenetics for understanding the relationship between hippocampal neurogenesis in neuropsychiatric disorders. We propose that a more thorough understanding of the molecular and genetic mechanisms that control the complex process of neurogenesis, including the proliferation and differentiation of NSCs, will lead to novel therapeutics for the treatment of neuropsychiatric disorders.

A symphony of signals conducts early and late stages of adult neurogenesis

Neurogenesis is continually occurring in two regions within the mammalian central nervous system (CNS) and increasing evidence suggests that it is important for selective learning and memory. How this plasticity is maintained in isolated niches within mature networks has been extensively studied in recent years, and a large body of evidence has accumulated describing many different regulatory factors and points of regulation. In this review, we attempt to organize the current research by summarizing findings affecting early neurogenesis: during proliferation, fate commitment and migration, versus late neurogenesis: including dendritic development, synaptic integration, and survival. We discuss the roles of three different classes of factors regulating early and late phases of neurogenesis: intrinsic factors, extrinsic factors, and neurotransmitters. Finally, we suggest that neurotransmitters may act upstream from extracellular other factors and cell-intrinsic mechanisms by coupling network activity to the niche microenvironment and intracellular machinery to ultimately regulate neurogenesis.

Intranasal delivery of erythropoietin plus insulin-like growth factor-I for acute neuroprotection in stroke. Laboratory investigation

OBJECT

Individually, the cytokines erythropoietin (EPO) and insulin-like growth factor-I (IGF-I) have both been shown to reduce neuronal damage significantly in rodent models of cerebral ischemia. The authors have previously shown that EPO and IGF-I, when administered together, provide acute and prolonged neuroprotection in cerebrocortical cultures against N-methyl-D-aspartate-induced apoptosis. The aim of this study was to determine whether intranasally applied EPO plus IGF-I can provide acute neuroprotection in an animal stroke model and to show that intranasal administration is more efficient at delivering EPO plus IGF-I to the brain when compared with intravenous, subcutaneous, or intraperitoneal administration.

METHODS

The EPO and IGF-I were administered intranasally to mice that underwent transient middle cerebral artery occlusion (MCAO). Stroke volumes were measured after 1 hour of MCAO and 24 hours of reperfusion. To evaluate the long-term effects of this treatment, behavioral outcomes were assessed at 3, 30, 60, and 90 days following MCAO. Radiography and liquid scintillation were used to visualize and quantify the uptake of radiolabeled 125I-EPO and 125I-IGF-I into the mouse brain after intranasal, intravenous, subcutaneous, or intraperitoneal administration.

RESULTS

Intranasal administration of EPO plus IGF-I reduced stroke volumes within 24 hours and improved neurological function in mice up to 90 days after MCAO. The 125I-EPO and 125I-IGF-I were found in the brain within 20 minutes after intranasal administration and accumulated within the injured areas of the brain. In addition, intranasal administration delivered significantly higher levels of the applied 125I-EPO and 125I-IGF-I to the brain compared with intravenous, subcutaneous, or intraperitoneal administration.

CONCLUSIONS

The data demonstrate that intranasal EPO plus IGF-I penetrates into the brain more efficiently than other drug delivery methods and could potentially provide a fast and efficient treatment to prevent chronic effects of stroke.

Inflammation, plasticity and real-time imaging after cerebral ischemia

With an incidence of approximately 350 in 100,000, stroke is the third leading cause of death and a major cause of disability in industrialized countries. At present, although progress has been made in understanding the molecular pathways that lead to ischemic cell death, the current clinical treatments remain poorly effective. There is mounting evidence that inflammation plays an important role in cerebral ischemia. Experimentally and clinically, brain response to ischemic injury is associated with an acute and prolonged inflammatory process characterized by the activation of resident glial cells, production of inflammatory cytokines as well as leukocyte and monocyte infiltration in the brain, events that may contribute to ischemic brain injury and affect brain recovery and plasticity. However, whether the post-ischemic inflammatory response is deleterious or beneficial to brain recovery is presently a matter of debate and controversies. Here, we summarize the current knowledge on the molecular mechanisms underlying post-ischemic neuronal plasticity and the potential role of inflammation in regenerative processes and functional recovery after stroke. Furthermore, because of the dynamic nature of the brain inflammatory response, we highlight the importance of the development of novel experimental approaches such as real-time imaging. Finally, we discuss the novel transgenic reporter mice models that have allowed us to visualize and to analyze the processes such as neuroinflammation and neuronal repair from the ischemic brains of live animals.

The FGF-2/FGFRs neurotrophic system promotes neurogenesis in the adult brain

Neurogenesis occurs in two regions of the adult brain, namely, the subventricular zone (SVZ) throughout the wall of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG) in hippocampal formation. Adult neurogenesis requires several neurotrophic factors to sustain and regulate the proliferation and differentiation of the adult stem cell population. In the present review, we examine the cellular and functional aspects of a trophic system mediated by fibroblast growth factor-2 (FGF-2) and its receptors (FGFRs) related to neurogenesis in the SVZ and SGZ of the adult rat brain. In the SVZ, FGF-2 is expressed in GFAP-positive cells of SVZ but is not present in proliferating precursor cells, which instead express FGFR-1 and FGFR-2, but not FGFR-3 mRNA, although expressed in the SVZ, and FGFR-4. Therefore, it seems that in the SVZ FGF-2 may be released by GFAP-positive cells, different from the precursor cell lineage, and via volume transmission it reaches the proliferating precursor cells. FGFR-1 mRNA is also expressed in the SGZ and is localized in BrdU-labeled precursor cells, whereas FGFR-2 and FGFR-3 mRNA, although expressed in the SGZ, are not located within proliferating precursor cells. An aged-related decline of proliferating precursor cells in the SVZ and DG of old rats has been well documented, and there is the suggestion that in part it could be the consequence of alterations in growth factor expression levels. Thus, the old precursors may respond to growth factors, suggesting that during aging the basic components for neuronal precursor cell proliferation are retained and the capacity to increase neurogenesis after appropriate stimulation is still preserved. In conclusion, the trophic system mediated by FGF-2 and its receptors contributes to create an important micro-environmental niche that promotes neurogenesis in the adult and aged brain.

Intranasal delivery bypasses the blood-brain barrier to target therapeutic agents to the central nervous system and treat neurodegenerative disease

Intranasal delivery provides a practical, non-invasive method of bypassing the blood-brain barrier (BBB) to deliver therapeutic agents to the brain and spinal cord. This technology allows drugs that do not cross the BBB to be delivered to the central nervous system within minutes. It also directly delivers drugs that do cross the BBB to the brain, eliminating the need for systemic administration and its potential side effects. This is possible because of the unique connections that the olfactory and trigeminal nerves provide between the brain and external environment. Intranasal delivery does not necessarily require any modification to therapeutic agents. A wide variety of therapeutics, including both small molecules and macromolecules, can be targeted to the olfactory system and connected memory areas affected by Alzheimer's disease. Using the intranasal delivery system, researchers have reversed neurodegeneration and rescued memory in a transgenic mouse model of Alzheimer's disease. Intranasal insulin-like growth factor-I, deferoxamine, and erythropoietin have been shown to protect the brain against stroke in animal models. Intranasal delivery has been used to target the neuroprotective peptide NAP to the brain to treat neurodegeneration. Intranasal fibroblast growth factor-2 and epidermal growth factor have been shown to stimulate neurogenesis in adult animals. Intranasal insulin improves memory, attention, and functioning in patients with Alzheimer's disease or mild cognitive impairment, and even improves memory and mood in normal adult humans. This new method of delivery can revolutionize the treatment of Alzheimer's disease, stroke, and other brain disorders.

Intranasal delivery of transforming growth factor-beta1 in mice after stroke reduces infarct volume and increases neurogenesis in the subventricular zone

Background

The effect of neurotrophic factors in enhancing stroke-induced neurogenesis in the adult subventricular zone (SVZ) is limited by their poor blood-brain barrier (BBB) permeability.

Intranasal administration is a noninvasive and valid method for delivery of neuropeptides into the brain, to bypass the BBB. We investigated the effect of treatment with intranasal transforming growth factor-β1 (TGF-β1) on neurogenesis in the adult mouse SVZ following focal ischemia. The modified Neurological Severity Scores (NSS) test was used to evaluate neurological function, and infarct volumes were determined from hematoxylin-stained sections. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) labeling was performed at 7 days after middle cerebral artery occlusion (MCAO). Immunohistochemistry was used to detect bromodeoxyuridine (BrdU) and neuron- or glia-specific markers for identifying neurogenesis in the SVZ at 7, 14, 21, 28 days after MCAO.

Results

Intranasal treatment of TGF-β1 shows significant improvement in neurological function and reduction of infarct volume compared with control animals. TGF-β1 treated mice had significantly less TUNEL-positive cells in the ipsilateral striatum than that in control groups. The number of BrdU-incorporated cells in the SVZ and striatum was significantly increased in the TGF-β1 treated group compared with control animals at each time point. In addition, numbers of BrdU- labeled cells coexpressed with the migrating neuroblast marker doublecortin (DCX) and the mature neuronal marker neuronal nuclei (NeuN) were significantly increased after intranasal delivery of TGF-β1, while only a few BrdU labeled cells co-stained with glial fibrillary acidic protein (GFAP).

Conclusion

Intranasal administration of TGF-β1 reduces infarct volume, improves functional recovery and enhances neurogenesis in mice after stroke. Intranasal TGF-β1 may have therapeutic potential for cerebrovascular disorders.

Intranasally delivered bFGF enhances neurogenesis in adult rats following cerebral ischemia

Basic fibroblast growth factor (bFGF) is a very important mitogenic factor with proved neurogenesis effects in the central nervous system. Intranasal administration can bypass blood-brain barrier and deliver drugs into the brain directly. We investigated whether intranasal administration of bFGF at later time points after ischemia could promote adult neurogenesis and improve neurologic functions. Rats received bFGF or saline intranasally once daily for 6 consecutive days, starting at 1 day after transient middle cerebral artery occlusion (MCAO). Bromodeoxyuridine (BrdU) was injected at 5 and 6 days after MCAO. Rats were killed at 7 or 28 days after MCAO. Neurogenesis was assessed by immunostaining for BrdU and cell type-specific markers. Neurological functions were evaluated by the modified Neurological Severity Scores. Compared with the control animals, intranasal administration of bFGF improved behavioral recovery without affecting infarct size, and enhanced proliferation of progenitor cells in the subventricular zone and the subgranular zone of the dentate gyrus (DG). Furthermore, the new proliferated cells could differentiate into neurons (BrdU+NeuN+ cells) in the striatum and DG at 28 days after MCAO. Intranasal administration of bFGF offers a non-invasive alternative for the treatment of stroke.

Stem cell review series: role of neurogenesis in age-related memory disorders

Neuroplasticity is characterized by growth and branching of dendrites, remodeling of synaptic contacts, and neurogenesis, thus allowing the brain to adapt to changes over time. It is maintained in adulthood but strongly repressed during aging. An age-related decline in neurogenesis is particularly pronounced in the two adult neurogenic areas, the subventricular zone and the dentate gyrus. This age-related decline seems to be attributable mainly to limited proliferation, associated with an age-dependent increase in quiescence and/or a lengthening of the cell cycle, and is closely dependent on environmental changes. Indeed, when triggered by appropriate signals, neurogenesis can be reactivated in senescent brains, thus confirming the idea that the age-related decrease in new neuron production is not an irreversible, cell-intrinsic process. The coevolution of neurogenesis and age-related memory deficits--especially regarding spatial memory--during senescence supports the idea that new neurons in the adult brain participate in memory processing, and that a reduction in the ability to generate new neurons contributes to the appearance of memory deficits with advanced age. Furthermore, the age-related changes in hippocampal plasticity and function are under environmental influences that can favor successful or pathological aging. A better understanding of the mechanisms that regulate neurogenesis is necessary to develop new therapeutic tools to cure or prevent the development of memory disorders that may appear during the course of aging in some individuals.

Antidepressants and Cdk inhibitors: releasing the brake on neurogenesis?

It is now clear that neurogenesis occurs in the brain of adult mammals. Many studies have attempted to establish relationships among neurogenesis, depression and the mechanism of action of antidepressant drugs. Therapeutic effects of antidepressants appear to be linked to increased neurogenesis in the hippocampus. Cdk inhibitors are expressed in multiple brain regions, presumably maintaining quiescence in differentiated neurons. Recently, the abundant expression of p21(Cip1) was found in neuroblasts and in newly developing neurons in the subgranular zone of the hippocampus, a region where adult neurogenesis occurs. Chronic treatment with the tricyclic antidepressant imipramine markedly decreased p21(Cip1) mRNA and protein levels and stimulated neurogenesis in this region. These results suggest that p21(Cip1) restrains neurogenesis in the hippocampus, and antidepressant-induced stimulation of neurogenesis might be a consequence of decreased p21(Cip1) expression, with the subsequent release of neuronal progenitor cells from the blockade of proliferation. These findings suggest the potential for new therapeutic strategies for the treatment of depression that target cell cycle proteins. However, there is a possibility that long-term stimulation of neurogenesis might exhaust the proliferation potentials of neuronal progenitors.

A diacylglycerol lipase-CB2 cannabinoid pathway regulates adult subventricular zone neurogenesis in an age-dependent manner

The subventricular zone (SVZ) is a major site of neurogenesis in the adult. We now show that ependymal and proliferating cells in the adult mouse SVZ express diacylglycerol lipases (DAGLs), enzymes that synthesise a CB1/CB2 cannabinoid receptor ligand. DAGL and CB2 antagonists inhibit the proliferation of cultured neural stem cells, and the proliferation of progenitor cells in young animals. Furthermore, CB2 agonists stimulate progenitor cell proliferation in vivo, with this effect being more pronounced in older animals. A similar response was seen with a fatty acid amide hydrolase (FAAH) inhibitor that limits degradation of endocannabinoids. The effects on proliferation were mirrored in changes in the number of neuroblasts migrating from the SVZ to the olfactory bulb (OB). In this context, CB2 antagonists reduced the number of newborn neurons appearing in the OB in the young adult animals while CB2 agonists stimulated this in older animals. These data identify CB2 receptor agonists and FAAH inhibitors as agents that can counteract the naturally observed decline in adult neurogenesis that is associated with ageing.

Intranasal HB-EGF administration favors adult SVZ cell mobilization to demyelinated lesions in mouse corpus callosum

In the adult rodent brain, the subventricular zone (SVZ) represents a special niche for neural stem cells; these cells proliferate and generate neural progenitors. Most of these migrate along the rostral migratory stream to the olfactory bulb, where they differentiate into interneurons. SVZ-derived progenitors can also be recruited spontaneously to damaged brain areas to replace lost cells, including oligodendrocytes in demyelinated lesions. In this study, we searched for factors able to enhance this spontaneous recruitment of endogenous progenitors. Previous studies have suggested that epidermal growth factor (EGF) could stimulate proliferation, migration, and glial differentiation of SVZ progenitors. In the present study we examined EGF influence on endogenous SVZ cell participation to brain repair in the context of demyelinated lesions. We induced a focal demyelinated lesion in the corpus callosum by lysolecithin injection and showed that intranasal heparin-binding epidermal growth factor (HB-EGF) administration induces a significant increase in SVZ cell proliferation together with a stronger SVZ cell mobilization toward the lesions. Besides, HB-EGF causes a shift of SVZ-derived progenitor cell differentiation toward the astrocytic lineage. However, due to the threefold increase in cell recruitment by EGF treatment, the absolute number of SVZ-derived oligodendrocytes in the lesion of treated mice is higher than in controls. These results suggest that enhancing SVZ cell proliferation could be part of future strategies to promote SVZ progenitor cell mobilization toward brain lesions.

Delivery of interferon-beta to the monkey nervous system following intranasal administration

We determined the nervous system targeting of interferon-beta1b (IFN-beta1b), a 20 kDa protein used to treat the relapsing-remitting form of multiple sclerosis, following intranasal administration in anesthetized, adult cynomolgus monkeys. Five animals received an intranasal bolus of [(125)I]-labeled IFN-beta1b, applied bilaterally to the upper nasal passages. Serial blood samples were collected for 45 min, after which the animals were euthanized by transcardial perfusion-fixation. High resolution phosphor imaging of tissue sections and gamma counting of microdissected tissue were used to obtain the distribution and concentration profiles of [(125)I]-IFN-beta1b in central and peripheral tissues. Intranasal administration resulted in rapid, widespread targeting of nervous tissue. The olfactory bulbs and trigeminal nerve exhibited [(125)I]-IFN-beta1b levels significantly greater than in peripheral organs and at least one order of magnitude higher than any other nervous tissue area sampled. The basal ganglia exhibited highest [(125)I]-IFN-beta1b levels among CNS regions other than the olfactory bulbs. Preferential IFN-beta1b distribution to the primate basal ganglia is a new finding of possible clinical importance. Our study suggests both IFN-beta and IFN-alpha, which share the same receptor, may be bound with relatively high affinity in these structures, possibly offering new insight into a neurovegetative syndrome induced by IFN-alpha therapy and suspected to involve altered dopamine neurotransmission in the basal ganglia. Most importantly, our results suggest intranasally applied macromolecules may bypass the blood-brain barrier and rapidly enter the primate CNS along olfactory- and trigeminal-associated extracellular pathways, as shown previously in the rat. This is the first study to finely detail the central distribution of a labeled protein after intranasal administration in non-human primates.