Role of neurotrophins in cholinergic-neurone function in the adult and aged CNS

Biomarkers in the diagnosis of neurodegenerative diseases

Biomarkers are molecules that behave as of biological states. Ideally, they should have high sensitivity, specificity, and accuracy in reflecting the total disease burden. The review discusses the current status of biomarkers used in neurological disorders. Neurodegenerative diseases are a heterogeneous group disorders characterized by progressive loss of structure and function of the central nervous system or peripheral nervous system. The review discusses the main biomarkers that have predictive value for describing clinical etiology, pathophysiology, and intervention strategies. Preciseness and reliability are one of important requirement for good biomarker. As a result of the analysis of literature data, it was revealed that beta-amyloid, total tau protein and its phosphorylated forms are the first biochemical biomarkers of neurodegenerative diseases measured in cerebrospinal fluid, but these markers are dependent upon invasive lumbar puncture and therefore it’s a cumbersome process for patients. Among the various biomarkers of neurodegenerative diseases, special attention is paid to miRNAs. MicroRNAs, important biomarkers in many disease states, including neurodegenerative disorders, make them promising candidates that may lead to identify new therapeutic targets. Conclusions. Biomarkers of neurological disease are present optimal amount in the cerebrospinal fluid but they are also present in blood at low levels. The data obtained reveal the predictive value of molecular diagnostics of neurodegenerative disorders and the need for its wider use.

Retrograde Axonal Transport of Neurotrophins in Basal Forebrain Cholinergic Neurons

Axonal transport is key for the survival and function of all neurons. This process is especially important in basal forebrain cholinergic neurons due to their extremely long and diffuse axonal projections. These neurons are critical for learning and memory and degenerate rapidly in age-related neurodegenerative disorders like Alzheimer's and Parkinson's disease. The vulnerability of these neurons to age-related neurodegeneration may be partially attributed to their reliance on retrograde axonal transport for neurotrophic support. Unfortunately, little is known about the molecular biology underlying the retrograde transport dynamics of these neurons due to the difficulty associated with their maintenance in vitro. Here, we outline a protocol for culturing primary rodent basal forebrain cholinergic neurons in microfluidic chambers, devices designed specifically for the study of axonal transport in vitro. We outline protocols for labeling neurotrophins and tracking neurotrophin transport in these neurons. Our protocols can also be used to study axonal transport in other types of primary neurons such as cortical and hippocampal neurons.

Serum BDNF as a Potential Biomarker of Alzheimer's Disease: Verification Through Assessment of Serum, Cerebrospinal Fluid, and Medial Temporal Lobe Atrophy

There is an urgent need to establish blood biomarkers for Alzheimer's disease (AD). Although it has been speculated that brain-derived neurotrophic factor (BDNF) is associated with AD, whether it can be used as a blood biomarker has yet to be determined. We used serum, cerebrospinal fluid (CSF), and medial temporal lobe atrophy from patients with AD to evaluate the association of BDNF with AD and assess its severity. For the blood analysis, 66 participants [21 normal controls (NCs) with normal cognitive function, 22 patients with mild cognitive impairment (MCI) due to AD, and 23 patients with AD] were included. For the CSF analysis, 30 participants were included. Magnetic resonance imaging, including a voxel-based specific regional analysis system for AD, and a Mini Mental State Examination were performed. Serum levels of BDNF and CSF levels of amyloid-β₄₂, total tau, and phosphorylated tau were measured using ELISA. Serum BDNF levels were significantly lower in the MCI due to AD group than in the NC group (p = 0.037). Although there was no significant difference in the AD group, there was a downward trend compared to the NC group. Serum BDNF levels were positively correlated with CSF Aβ₄₂ levels (r = 0.49, p = 0.005). There was a significant correlation between serum BDNF levels and medial temporal lobe atrophy. Decreased serum BDNF can potentially be used as a biomarker for early AD detection. Early detection of AD with a less invasive blood test is very beneficial, as it allows for intervention before dementia progresses.

Nerve growth factor is expressed and stored in central neurons of adult zebrafish

Nerve growth factor (NGF), a member of the neurotrophin family, was initially described as neuronal survival and growth factor, but successively has emerged as an active mediator in many essential functions in the central nervous system of mammals. NGF is synthesized as a precursor pro-NGF and is cleaved intracellularly into mature NGF. However, recent evidence demonstrates that pro-NGF is not a simple inactive precursor, but is also secreted outside the cells and can exert multiple roles. Despite the vast literature present in mammals, studies devoted to NGF in the brain of other vertebrate models are scarce. Zebrafish is a teleost fish widely known for developmental genetic studies and is well established as model for translational neuroscience research. Genomic organization of zebrafish and mouse NGF is highly similar, and zebrafish NGF protein has been reported in mature and two-precursors forms. To add further knowledge on neurotrophic factors in vertebrate brain models, we decided to determine the NGF mRNA and protein distribution in the adult zebrafish brain and to characterize the phenotype of NGF-positive cells. NGF mRNA was visualized by in situ hybridization on whole-mount brains. NGF protein distribution was assessed on microtomic sections by using an antiserum against NGF, able to recognize pro-NGF in adult zebrafish brain as demonstrated also in previous studies. To characterize NGF-positive cells, anti-NGF was employed on microtomic slides of aromatase B transgenic zebrafish (where radial glial cells appeared fluorescent) and by means of double-immunolabeling against NGF/proliferative cell nuclear antigen (PCNA; proliferation marker) and NGF/microtube-associated protein2 (MAP2; neuronal marker). NGF mRNA and protein were widely distributed in the brain of adult zebrafish, and their pattern of distribution of positive perikaryal was overlapping, both in males and females, with few slight differences. Specifically, the immunoreactivity to the protein was observed in fibers over the entire encephalon. MAP2 immunoreactivity was present in the majority of NGF-positive cells, throughout the zebrafish brain. PCNA and aromatase B cells were not positive to NGF, but they were closely intermingled with NGF cells. In conclusion, our study demonstrated that mature neurons in the zebrafish brain express NGF mRNA and store pro-NGF.

Altered serum levels of vascular endothelial growth factor and glial-derived neurotrophic factor but not fibroblast growth factor-2 in treatment-naive children with attention deficit/hyperactivity disorder

Background and aim: Recent evidence suggests that growth factors might be involved in the pathophysiology of attention deficit hyperactivity disorder (ADHD). The aim of this study was to determine whether serum levels of brain-derived neurotrophic factor (BDNF), glial-derived neurotrophic factor (GDNF), neurotrophin-3 (NT-3), nerve growth factor (NGF), fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF) were altered in children with ADHD. Methods: Serum levels of BDNF, GDNF, NT-3, NGF, VEGF and FGF-2 were analyzed in 49 treatment- naive children with ADHD and age, gender matched 36 healthy controls using enzyme-linked immunosorbent assay. ADHD symptoms were scored by Du Paul ADHD Rating Scale and Strengths and Difficulties Questionnaire. Results: We found that serum VEGF levels were significantly lower (p < 0.001) and GDNF levels were significantly higher in ADHD group compared to control group (p = 0.003). However, we found no correlations between ADHD symptoms and serum VEGF or GDNF levels. Furthermore, we observed no significant alterations in serum BDNF, NT-3, NGF, FGF-2 levels in children with ADHD. Conclusion: To our knowledge, the present study is the first to examine serum VEGF and FGF-2 levels in children with ADHD. Our results indicate that VEGF and GDNF might be involved in the etiology of ADHD. Further studies are required to determine the role of growth factors in the etiology and consequently in the treatment of ADHD.

Direct and indirect evidences of BDNF and NGF as key modulators in depression: role of antidepressants treatment

PURPOSE

Depression is one of the most prevalent, recurrent and life-threatening mental illnesses. However, the precise mechanism underlying the disorder is not yet clearly understood. It is therefore, essential to identify the novel biomarkers which may help in the development of effective treatment.

METHODS

In this milieu, the profile of the brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) were considered as biomarkers in the light of pathophysiology of depression and its treatment.

RESULTS

Previously, we have reported that BDNF level in the postmortem brain of suicide victims was significantly lower than those of normal controls. We also found decreased BDNF levels in the specific brain regions of the learned helplessness model of depression in rat, and was found to increase normal level following chronic fluoxetine hydrochloride treatment. NGF is another important member of neurotrophin, which is dysregulated in the pathophysiology of depression in some models of peripheral nerve damage and stress. The results shown evidences of the effect of antidepressants on modulating depression via the NGF in preclinical and clinical models of depression, but conflicted, therefore make it currently difficult to affirm the therapeutic role of antidepressants.

CONCLUSIONS

Here, we review some of the preclinical and clinical studies aimed at disclosing the role of BDNF and NGF mediated pathophysiological mechanisms of depression and the new therapeutic approaches targeting those key molecules. In addition, an important link between BDNF, NGF and depression has been discussed in the light of current existing knowledge.

Type 2 diabetes mellitus in the pathophysiology of Alzheimer's disease

Both Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) are two common forms of disease worldwide and many studies indicate that people with diabetes, especially DM, are at higher risk of developing AD. AD is characterized by progressive cognitive decline and accumulation of β-amyloid (Aβ) forming senile plaques. DM is a metabolic disorder characterized by hyperglycemia in the context of insulin resistance and relative lack of insulin. Both diseases also share common characteristics such as loss of cognitive function and inflammation. Inflammation resulting from Aβ further induces production of Aβ_1-42 peptides. Inflammation due to overnutrition induces insulin resistance and consequently DM. Memory deficit and a decrease in GLUT4 and hippocampal insulin signaling have been observed in animal models of insulin resistance. The objective of this review was to show the shared characteristics of AD and DM.

Possible biomarkers modulating haloperidol efficacy and/or tolerability

Haloperidol (HP) is widely used in the treatment of several forms of psychosis. Despite of its efficacy, HP use is a cause of concern for the elevated risk of adverse drug reactions. adverse drug reactions risk and HP efficacy greatly vary across subjects, indicating the involvement of several factors in HP mechanism of action. The use of biomarkers that could monitor or even predict HP treatment impact would be of extreme importance. We reviewed the elements that could potentially be used as peripheral biomarkers of HP effectiveness. Although a validated biomarker still does not exist, we underlined the several potential findings (e.g., about cytokines, HP metabolites and genotypic biomarkers) which could pave the way for future research on HP biomarkers.

Amyloid cascade hypothesis: Pathogenesis and therapeutic strategies in Alzheimer's disease

Alzheimer's disease is an irreversible, progressive neurodegenerative disorder. Various therapeutic approaches are being used to improve the cholinergic neurotransmission, but their role in AD pathogenesis is still unknown. Although, an increase in tau protein concentration in CSF has been described in AD, but several issues remains unclear. Extensive and accurate analysis of CSF could be helpful to define presence of tau proteins in physiological conditions, or released during the progression of neurodegenerative disease. The amyloid cascade hypothesis postulates that the neurodegeneration in AD caused by abnormal accumulation of amyloid beta (Aβ) plaques in various areas of the brain. The amyloid hypothesis has continued to gain support over the last two decades, particularly from genetic studies. Therefore, current research progress in several areas of therapies shall provide an effective treatment to cure this devastating disease. This review critically evaluates general biochemical and physiological functions of Aβ directed therapeutics and their relevance.

Hippocampal dysfunctions caused by cranial irradiation: a review of the experimental evidence

Cranial irradiation (IR) is commonly used for the treatment of brain tumors but may cause disastrous brain injury, especially in the hippocampus, which has important cognition and emotional regulation functions. Several preclinical studies have investigated the mechanisms associated with cranial IR-induced hippocampal dysfunction such as memory defects and depression-like behavior. However, current research on hippocampal dysfunction and its associated mechanisms, with the ultimate goal of overcoming the side effects of cranial radiation therapy in the hippocampus, is still very much in progress. This article reviews several in vivo studies on the possible mechanisms of radiation-induced hippocampal dysfunction, which may be associated with hippocampal neurogenesis, neurotrophin and neuroinflammation. Thus, this review may be helpful to gain new mechanistic insights into hippocampal dysfunction following cranial IR and provide effective strategies for potential therapeutic approaches for cancer patients receiving radiation therapy.

Serum nerve growth factor (NGF) levels in children with attention deficit/hyperactivity disorder (ADHD)

Attention deficit/hyperactivity disorder (ADHD) is the most commonly diagnosed neurobehavioral disorder of childhood. The etiopathogeny of ADHD has not been totally defined. Recent reports have suggested a pathophysiological role of neurotrophins in ADHD. In this study, we evaluated serum levels of nerve growth factor (NGF) in patients with ADHD. The sample population consisted of 44 child or adolescent patients diagnosed with ADHD according to DSM-IV criteria; 36 healthy subjects were included in the study as controls. Venous blood samples were collected, and NGF levels were measured. The mean serum NGF levels of the ADHD patients were significantly higher than those of the controls. Age and gender of the patients were not correlated with serum NGF levels. There were no significant differences in NGF levels among the combined and predominantly inattentive subtypes of ADHD. Our study suggests that there are higher levels of serum NGF in drug naive ADHD patients, and that increased levels of NGF might have an important role in the pathophysiology of ADHD.

BDNF-TrkB signaling and neuroprotection in schizophrenia

Neurotrophins such as brain-derived neurotropic factor (BDNF), play critical role in neuronal survival, synaptic plasticity and cognitive functions. BDNF is known to mediate its action through various intracellular signaling pathways triggered by activation of tyrosine kinase receptor B (TrkB). Evidence from clinical as well pre-clinical studies indicate alterations in BDNF signaling in schizophrenia. Moreover, several antipsychotic drugs have time-dependent effects on BDNF levels in both schizophrenia subjects and animal models of schizophrenia. Given the emerging interest in neuroplasticity in schizophrenia understanding the neuroprotective and cell survival roles of BDNF signaling will enhance our knowledge of its diverse effects, which may lead to more effective treatments for schizophrenia. This article will present an overview of recent findings on the role of BDNF signaling in the pathophysiology and treatment of schizophrenia, with a special focus on its neuroprotective effects.

Reduced neurotrophin receptor tropomyosin-related kinase A expression in human granulosa cells: a novel marker of diminishing ovarian reserve

OBJECTIVE

To determine whether human mural and cumulus granulosa cell neurotrophin and neurotrophin receptor content correlate to ovarian reserve markers.

DESIGN

Prospective, laboratory-based study.

SETTING

Academic assisted reproductive technology (ART) program.

PATIENT(S)

Twenty-three women undergoing ART.

INTERVENTION(S)

Mural and cumulus granulosa cells were collected from women undergoing oocyte retrieval during ART cycles. Relative messenger RNA (mRNA) levels of neurotrophins and their receptors were measured by quantitative reverse transcription-polymerase chain reaction and correlated to serum antimüllerian hormone (AMH) levels and the number of oocytes retrieved.

MAIN OUTCOME MEASURE(S)

Number of oocytes retrieved.

RESULT(S)

Mural and cumulus granulosa cell nerve growth factor receptor tropomyosin-related kinase A (TrkA) mRNA correlated strongly to the number of oocytes retrieved. Similarly, higher serum AMH was associated with higher cumulus granulosa cell TrkA mRNA. Both mural and cumulus granulosa cell p75(NTR)/TrkA ratios were lower in women with higher serum AMH, and the number of oocytes retrieved was greater among women with low p75(NTR)/TrkA ratio. No significant associations were found between brain-derived neurotrophic factor (BDNF) and its specific receptor tropomyosin-related kinase B (TrkB) and ovarian reserve markers. Although BDNF and TrkB expression were higher in cumulus compared with mural granulosa cells, no such association was found between TrkA and granulosa cells. Antimüllerian hormone and cumulus TrkA mRNA, in a model incorporating both, correlated strongly to the number of oocytes retrieved (R(2) = 0.84).

CONCLUSION(S)

Cumulus TrkA and p75(NTR) mRNA correlate to ovarian reserve, whereas BDNF and TrkB are associated with the type of granulosa cell.

Enhanced dendritic spine number of neurons of the prefrontal cortex, hippocampus, and nucleus accumbens in old rats after chronic donepezil administration

In Alzheimer's disease brains, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been observed. These changes are particularly reflected in the decrement of both the dendritic tree and spine number. Donepezil is a potent and selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease. We have studied the effect of oral administration of this drug on the morphology of neuronal cells from the brain of aged rats. We examined dendrites of pyramidal neurons of the PFC, dorsal or ventral hippocampus (VH), and medium spiny neurons of the nucleus accumbens (NAcc). Donepezil (1 mg/kg, vo) was administrated every day for 60 days to rats aged 10 and 18 months. Dendritic morphology was studied by the Golgi-Cox stain procedure followed by Sholl analysis at 12 and 20 months ages, respectively. In all Donepezil-treated rats, a significant increment of the dendritic spines number in pyramidal neurons of the PFC and dorsal hippocampus was observed. However, pyramidal neurons of the VH and medium spiny cells of the NAcc only showed an increase in the number of their spines in 12-month-old rats. Our results suggest that Donepezil prevents the alterations of the neuronal dendrite morphology caused by aging.

The septo-hippocampal system, learning and recovery of function

We understand this review as an attempt to summarize recent advances in the understanding of cholinergic function in cognition. Such a role has been highlighted in the 1970s by the discovery that dementia patients have greatly reduced cholinergic activity in cortex and hippocampus. A brief anatomical description of the major cholinergic pathways focuses on the basal forebrain and its projections to cortex and hippocampus. From this distinction, compelling evidence suggests that the basal forebrain --> cortex projection regulates the excitability of principal cortical neurons and is thereby critically involved in attention, stimulus detection and memory function, although the biological conditions for these functions are still debated. Similar uncertainties remain for the septo-hippocampal cholinergic system. Although initial lesions of the septum caused memory deficits reminiscent of hippocampal ablations, recent and more refined neurotoxic lesion studies which spared non-cholinergic cells of the basal forebrain failed to confirm these memory impairments in experimental animals despite a near total loss of cholinergic labeling. Yet, a decline in cholinergic markers in aging and dementia still stands as the most central piece of evidence for a link between the cholinergic system and cognition and appear to provide valuable targets for therapeutic approaches.

Family and genetic association studies of bipolar disorder in children

The risk of bipolar disorder (BPD) (15-42%) in first-degree relatives of children with BPD are consistently larger than the 8.7% estimate of recurrence risk of BPD in first-degree relatives of adult BPD cases. There have been no family linkage studies of pediatric BPD, but secondary analyses of adult linkage samples suggest that early-onset BPD both increases the strength of associations in linkage studies. Positive associations with pediatric BPD and the BDNF gene (Vall66), the GAD1 gene (4s2241165), and the dopamine transporter gene (rs41084) have been reported but none of these associations have been replicated in independent samples. The number of informative families examined so far is quite small and studies were vastly underpowered to detect small effects. An adequately powered sample will likely require collaborative ascertainment of cases and families from multiple sites using valid and accepted measures of pediatric BPD.

Family-based association study of the BDNF, COMT and serotonin transporter genes and DSM-IV bipolar-I disorder in children

BACKGROUND

Over the past decade pediatric bipolar disorder has gained recognition as a potentially more severe and heritable form of the disorder. In this report we test for association with genes coding brain-derived neurotrophic factor (BDNF), the serotonin transporter (SLC6A4), and catechol-O-methyltransferase (COMT).

METHODS

Bipolar-I affected offspring triads (N = 173) were drawn from 522 individuals with 2 parents in 332 nuclear families recruited for genetic studies of pediatric psychopathology at the Clinical and Research Program in Pediatric Psychopharmacology and Adult ADHD at Massachusetts General Hospital.

RESULTS

We failed to identify an association with the val66 allele in BDNF (OR = 1.23, p = 0.36), the COMT-l allele (OR = 1.27, p = 0.1), or the HTTLPR short allele (OR = 0.87, p = 0.38).

CONCLUSION

Our study suggests that the markers examined thus far in COMT and SLC6A4 are not associated with pediatric bipolar disorder and that if the val66met marker in BDNF is associated with pediatric bipolar disorder the magnitude of the association is much smaller than first reported.

Expression of GDNF transgene in astrocytes improves cognitive deficits in aged rats

Glial cell line-derived neurotrophic factor (GDNF) was assayed for its neurotrophic effects against the neuronal atrophy that causes cognitive deficits in old age. Aged Fisher 344 rats with impairment in the Morris water maze received intrahippocampal injections at the dorsal CA1 area of either a lentiviral vector encoding human GDNF or the same vector encoding human green fluorescent protein as a control. Recombinant lentiviral vectors constructed with human cytomegalovirus promotor and pseudotyped with lyssavirus Mokola glycoprotein specifically transduced the astrocytes in vivo. Astrocyte-secreted GDNF enhanced neuron function as shown by local increases in synthesis of the neurotransmitters acetylcholine, dopamine and serotonin. This neurotrophic effect led to cognitive improvement of the rats as early as 2 weeks after gene transduction. Spatial learning and memory testing showed a significant gain in cognitive abilities due to GDNF exposure, whereas control-transduced rats kept their performance at the chance level. These results confirm the broad spectrum of the neurotrophic action of GDNF and open new gene therapy possibilities for reducing age-related neurodegeneration.

Decreased expression of Sprouty2 in the dorsolateral prefrontal cortex in schizophrenia and bipolar disorder: a correlation with BDNF expression

Background

Current theories on the pathophysiology of schizophrenia suggest altered brain plasticity such as decreased neural proliferation and migration, delayed myelination, and abnormal synaptic modeling, in the brain of subjects with schizophrenia. Though functional alterations in BDNF, which plays important role in neuroplasticity, are implicated in many abnormalities found in schizophrenia, the regulatory mechanism(s) involved in the abnormal signaling of BDNF in schizophrenia is not clear. The present study investigated whether Sprouty2, a regulator of growth factor signaling, is abnormally expressed in schizophrenia, and is associated with the changes in BDNF mRNA in this disorder. The potential effect of antipsychotic drugs on Sprouty2 expression was tested in adult rats.

Methods and Findings

Sprouty2 and BDNF gene expression were analyzed in dorsolateral prefrontal cortex samples from the Stanley Array Collection. Quantitative real-time PCR analysis of RNA in 100 individuals (35 with schizophrenia, 31 with bipolar disorder, and 34 psychiatrically normal controls) showed significantly decreased expression of Sprouty2 and BDNF in both schizophrenia and bipolar disorder. Moreover, a significant correlation between these two genes existed in control, schizophrenia and bipolar subjects. Long-term treatment with antipsychotic drugs, haloperidol and olanzapine, showed differential effects on both Sprouty2 and BDNF mRNA and protein levels in the frontal cortex of rats.

Conclusion

These findings demonstrating decreased expression of Sprouty2 associated with changes in BDNF, suggest the possibility that these decreases are secondary to treatment rather than to factors that are significant in the disease process of either schizophrenia and/or bipolar disorder. Further exploration of Sprouty2-related signal transduction pathways may be helpful to design novel treatment strategies for these disorders.

Brain-derived neurotropic factor/TrkB signaling in the pathogenesis and novel pharmacotherapy of schizophrenia

The role of neurotropins, predominantly brain-derived neurotropic factor (BDNF), has been implicated in the pathophysiology as well as treatment outcome of schizophrenia. Both human and rodent studies indicate that the beneficial effects of antipsychotic drugs are mediated, at least in part, through BDNF and its receptor, TrkB. This review will discuss the available data on the levels of BDNF and TrkB in subjects with schizophrenia and in animals with and without conventional antipsychotics. The data concerning the impact of the antipsychotic drugs on BDNF/TrkB signaling will also be discussed. More importantly, this review will provide future perspective on BDNF/TrkB signaling as a novel molecular target to correct the pathogenesis and improve the long-term clinical outcome by treatments with conventional and adjunctive drugs.

The length of hippocampal cholinergic fibers is reduced in the aging brain

Cholinergic deficits occur in the aged hippocampus and they are significant in Alzheimer's disease. Using stereological and biochemical approaches, we characterized the cholinergic septohippocampal pathway in old (24 months) and young adult (3 months) rats. The total length of choline acetyltransferase (ChAT)-positive fibers in the dorsal hippocampus was significantly decreased by 32% with aging (F((1,9))=20.94, p=0.0014), along with the levels of synaptophysin, a presynaptic marker. No significant changes were detected in ChAT activity or in the amounts of ChAT protein, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tropomyosin related kinase receptor (Trk) A, TrkB, or p75 neurotrophin receptor (p75(NTR)) in the aged dorsal hippocampus. The number and size of ChAT-positive neurons and the levels of ChAT activity, NGF and BDNF were not statistically different in the septum of aged and young adult rats. This study suggests that substantial synaptic loss and cholinergic axonal degeneration occurs during aging and reinforces the importance of therapies that can protect axons and promote their growth in order to restore cholinergic neurotransmission.

Neurotrophins in the dentate gyrus

Since the discovery of nerve growth factor (NGF) in the 1950s and brain-derived neurotrophic factor (BDNF) in the 1980s, a great deal of evidence has mounted for the roles of neurotrophins (NGF; BDNF; neurotrophin-3, NT-3; and neurotrophin-4/5, NT-4/5) in development, physiology, and pathology. BDNF in particular has important roles in neural development and cell survival, as well as appearing essential to molecular mechanisms of synaptic plasticity and larger scale structural rearrangements of axons and dendrites. Basic activity-related changes in the central nervous system (CNS) are thought to depend on BDNF modulation of synaptic transmission. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders. In this chapter, I review neurotrophin structure, signal transduction mechanisms, localization and regulation within the nervous system, and various potential roles in disease. Modulation of neurotrophin action holds significant potential for novel therapies for a variety of neurological and psychiatric disorders.

Selegiline Induces Neuronal Phenotype and Neurotrophins Expression in Embryonic Stem Cells

The antiaging effect of selegiline was reported by several investigators; therefore, there is a growing interest in the potential use of stem cell therapy in aging. In this investigation, selegiline was used to induce neuronal differentiation in undifferentiated pluripotent embryonic stem cells (ESCs). The results show that selegiline can induce neuronal phenotype associated with neurotrophic factor expression. Morphologic and immunohistochemical techniques were used to evaluate the differentiation of the CCE cells, Cresyl violet for the morphologic study, anti-synaptophysin and antityrosine hydroxylase antibodies for characterizing the neuronal phenotype of ESCs, and RT-PCR to study the neurotrophins. The results showed that selegiline can induce dose-dependent ESC differentiation into neurons. Moreover, selegiline can induce neurotrophin expression. This study suggests the potential use of combined selegiline and stem cell therapy to improve deficits in neurodegenerative diseases in aging.

Cognitive effects of SL65.0155, a serotonin 5-HT4 receptor partial agonist, in animal models of amnesia

Given that several data suggest the involvement of serotonergic (5-HT) system, particularly the serotonin 5-HT(4) receptors, in memory processes; this study was undertaken to investigate the role of serotonin 5-HT(4) receptors in different experimental models of amnesia in male Swiss mice or in male Sprague-Dawley rats, tested in learning and memory tasks. Amnesia was induced in mice by intracerebroventricular (i.c.v.) injection of beta-amyloid 1-42 fragment (BAP 1-42; 400 pmol/mouse) or of galanin (GAL) 1-29 (3 microg/mouse). Another group of animals was exposed to carbon monoxide (CO). Treatments were made 14 days, 15 min or 8 days prior to the learning trial of a step-through passive avoidance paradigm, respectively. Latency to re-enter the dark box appeared to be reduced in all treatment groups. Intraperitoneal (i.p.) administration of SL65.0155 (5-(8-amino-7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-3-[1-(2-phenylethyl)-4-piperidinyl]-1,3,4-oxadiazol-2(3H)-one-monohydrochloride), a serotonin 5-HT(4) receptor partial agonist (1 mg/kg/day), for 7 days prior to the learning trial, inhibited the amnesic effect of both peptides increasing the latency to re-enter the dark box also in mice exposed to CO. In rats with ibotenate-induced lesions of the nucleus basalis magnocellularis (NBM) or prenatally exposed to methylazoxymethanol (MAM), SL65.0155 (1 mg/kg/day, i.p.) administered for 7 days, improved the learning and memory capacity in animals tested in shuttle-box active avoidance and radial maze tests. These findings give further support to the hypothesis of SL65.0155 cognition-enhancing activity across a range of tasks.

Serum BDNF, TNF-alpha and IL-1beta levels in dementia patients: comparison between Alzheimer's disease and vascular dementia

Neurotrophins such as the brain-derived neurotrophic factor (BDNF) are reportedly related to the pathogenesis of Alzheimer's disease (AD). Several studies have revealed an alteration in BDNF expression in the postmortem brains of AD patients. BDNF has great potential as a therapeutic agent because of its ability to cross the blood-brain barrier and due to its wide in vivo distribution. However, little is known about in vivo BDNF in dementia patients. Moreover, the immunological function of neurotrophins such as BDNF has received great interest. Therefore, we investigated the serum levels of BDNF and cytokines such as TNF-alpha and IL-1beta in dementia patients by the enzyme-linked immunosorbent assay (ELISA). The following subjects were included in this study: 60 AD patients, 60 vascular dementia (VaD) patients and 33 healthy controls. AD and VaD patients were matched for age, gender and severity of dementia. Serum BDNF levels in AD patients were significantly lower than those in VaD patients and controls. TNF-alpha and IL-1beta levels showed no significant difference among the three groups. In the dementia groups, neither the TNF-alpha nor the IL-1beta levels correlated with the BDNF levels. Our results suggest that BDNF may play a pathological role in some cases of AD.

Possible role of nerve growth factor in the pathogenesis of alcohol dependence

BACKGROUND

Recent studies have raised the possibility that nerve growth factor (NGF) is abnormally regulated in the central nervous system (CNS) of animal models of chronic ethanol treatment. The goals of this study were to determine whether prolonged alcohol consumption is associated with the plasma NGF levels and to assess the effect of a positive family history of alcohol dependence on plasma NGF levels in the alcohol-dependent patients.

METHODS

We used the enzyme-linked immunosorbent assay (ELISA) to determine the concentrations of peripheral NGF in patients with alcohol dependence and in a control group.

RESULTS

The plasma NGF concentrations in the alcohol-dependent patients were significantly lower than in the controls (71.9 vs 110.5 pg/mL, respectively). Moreover, the alcohol-dependent patients with positive family histories showed a greater decrease in their NGF levels than those subjects with negative family histories (64.7 vs 83.3 pg/mL, respectively).

CONCLUSIONS

Our study suggests that the NGF levels may be a trait marker for the development of alcohol dependence.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Immunological aetiology of major psychiatric disorders: evidence and therapeutic implications

Historically, immunological research in psychiatry was based on empirical findings and early epidemiological studies indicating a possible relationship between psychiatric symptoms and acute infectious diseases. However, aetiopathological explanations for psychiatric disorders are no longer closely related to acute infection. Nevertheless, immune hypotheses have been discussed in schizophrenia, affective disorders and infantile autism in the last decades. Although the variability between the results of the epidemiological studies conducted to date is strikingly high, there is still some evidence that the immune system might play a role in the aetiopathogenesis of these three psychiatric diseases, at least in subgroups of patients. In anxiety disorders immunological research is still very much in its infancy, and the few and inconsistent data of immune changes in these patients are believed to reflect the influence of short- or long-term stress exposure. Nevertheless, there are also some hints raising the possibility that autoimmune mechanisms could interrupt neurotransmission, which would be of significance in certain patients with anxiety and panic disorders. Drug and alcohol (ethanol) dependence are not believed to be primarily influenced by an immunological aetiology. On the other hand, immune reactions due to different drugs of abuse and alcohol may directly or indirectly influence the course of concomitant somatic diseases. In different organic brain disorders the underlying somatic disease is defined as a primary immune or autoimmune disorder, for instance HIV infection or systemic lupus erythematosus (SLE). For other neurodegenerative disorders, such as Alzheimer's disease, immunoaetiopathological mechanisms are supported by experimental and clinical studies. Treatment strategies based on immune mechanisms have been investigated in patients with schizophrenia and affective disorders. Furthermore, some antipsychotics and most antidepressants are known to have direct or indirect effects on the immune system. Different immunotherapies have been used in autism, including transfer factor, pentoxifylline, intravenous immunoglobulins and corticosteroids. Immunosuppressive and/or immunomodulating agents are well established methods for treating the neuropsychiatric sequelae of immune or autoimmune disorders, for example AIDS and SLE. Therapeutic approaches in Alzheimer's disease also apply immunological methods such as strategies of active/passive immunisation and NSAIDs. Considering the comprehensive interactive network between mind and body, future research should focus on approaches linking targets of the different involved systems.

Brain, aging and neurodegeneration: role of zinc ion availability

Actual fields of research in neurobiology are not only aimed at understanding the different aspects of brain aging but also at developing strategies useful to preserve brain compensatory capacity and to prevent the onset of neurodegenerative diseases. Consistent with this trend much attention has been addressed to zinc metabolism. In fact, zinc acts as a neuromodulator at excitatory synapses and has a considerable role in the stress response and in the functionality of zinc-dependent enzymes contributing to maintaining brain compensatory capacity. In particular, the mechanisms that modulate the free zinc pool are pivotal for safeguarding brain health and performance. Alterations in zinc homeostasis have been reported in Parkinson's and Alzheimer's disease as well as in transient forebrain ischemia, seizures and traumatic brain injury, but little is known regarding aged brain. There is much evidence that that age-related changes, frequently associated to a decline in brain functions and impaired cognitive performances, could be related to dysfunctions affecting the intracellular zinc ion availability. A general agreement emerges from studies of humans' and rodents' old brains about an increased expression of metallothionein (MT) isoforms I and II, but dyshomogenous results are reported for MT-III, and it is still uncertain whether these proteins maintain in aging the protective role, as it occurs in adult/young age. At the same time, there is considerable evidence that amyloid-beta deposition in Alzheimer's disease is induced by zinc, but the pathological significance and the causes of this phenomenon are still an open question. The scientific debate on the role of zinc and of some zinc-binding proteins in aging and neurodegenerative disorders, as well as on the beneficial effect of zinc supplementation in aged brain and neurodegeneration, is extensively discussed in this review.

Nutrients as trophic factors in neurons and the central nervous system: role of retinoic acid

In multicellular organisms, death, survival, proliferation, and differentiation of a given cell depend on signals produced by neighboring and/or distant cells, resulting in the coordinated development and function of the various tissues. In the nervous system, control of cell survival and differentiation is achieved through the action of a distinct group of polypeptides collectively known as neurotrophic factors. Recent findings support the view that trophic factors also are involved in the response of the nervous system to acute injury. By contrast, nutrients are not traditionally viewed as potential trophic factors; however, there is increasing evidence that at least some influence neuronal differentiation. During development the brain is responsive to variations in nutrient supply, and this increased sensitivity or vulnerability of the brain to nutrient supply may reappear during neuronal repair, a period during which a rapid membrane resynthesis and reestablishment of synthetic pathways occur. To further evaluate the potential of specific nutrients to act as pharmacologic agents in the repair of injured neurons, the effects of retinoic acid, an active metabolite of vitamin A, and its role as a trophic factor are discussed. This literature review is intended to provide background information regarding the effect of retinoic acid on the cholinergic phenotype and the differentiation of these neurons and to explain how it may promote neuronal repair and survival following injury.

Role of melatonin in neurodegenerative diseases

The pineal product melatonin has remarkable antioxidant properties. It scavenges hydroxyl, carbonate and various organic radicals, peroxynitrite and other reactive nitrogen species. Melatonyl radicals formed by scavenging combine with and, thereby, detoxify superoxide anions in processes terminating the radical reaction chains. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and glutathione reductase, and by augmenting glutathione levels. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases, e.g., Alzheimer's disease. Melatonin has been shown to be effective in arresting neurodegenerative phenomena seen in experimental models of Alzheimer's disease, Parkinsonism and ischemic stroke. Melatonin preserves mitochondrial homeostasis, reduces free radical generation, e.g., by enhancing mitochondrial glutathione levels, and safeguards proton potential and ATP synthesis by stimulating complex I and IV activities. Therapeutic trials with melatonin have been effective in slowing the progression of Alzheimer's disease but not of Parkinson's disease. Melatonin's efficacy in combating free radical damage in the brain suggests that it may be a valuable therapeutic agent in the treatment of cerebral edema after traumatic brain injury.

Differential effects of typical and atypical antipsychotics on nerve growth factor and choline acetyltransferase expression in the cortex and nucleus basalis of rats

Previously we reported that chronic exposure to haloperidol (HAL), but not the atypical antipsychotics risperidone (RISP) or clozapine (CLOZ), resulted in reductions in brain choline acetyltransferase (ChAT) immunoreactivity and impaired water maze task performance in rats. In the present study, we compared the effects of these antipsychotic drugs on the expression of nerve growth factor (NGF) as well ChAT the in the rat cortex and nucleus basalis of Meynert (NBM) in an effort to determine the underlying mechanism for the differential drug effects observed previously. We also evaluated the effects of these compounds in a crossover design to evaluate specific neurochemical consequences of switching between typical and atypical antipsychotics, a common practice observed in the clinical setting. Male Wistar rats (250-300 g) were exposed to HAL (2.0 mg/kg/day), RISP (2.5 mg/kg/day), or CLOZ (20 mg/kg/day) for 45 days or a pre-treatment regimen consisting of administering either RISP/HAL (i.e., RISP followed by HAL) or CLOZ/HAL, or a post-treatment regimen consisting of administering: HAL/RISP or HAL/CLOZ. The duration of each treatment in the crossover study was also 45 days. NGF and ChAT immunoreactivity were measured by quantitative immunohistochemistry in some sub-cerebral cortical regions and NBM after drug exposures. NGF protein was also measured by an enzyme-linked ImmunoSorbent assay (ELISA) in rat sensorimotor cortex. The results indicated that HAL (but not RISP or CLOZ) significantly reduced NGF levels in some sub-cortical regions and ChAT immunoreactivity in both cortex and NBM. However, pre-treatment with CLOZ prevented the HAL-associated decreases in NGF and ChAT, while post-treatment with either RISP or CLOZ (i.e., after the administration of HAL) appeared to restore NGF and ChAT to control levels. These data indicate that antipsychotic drugs exert dissimilar effects on the levels of NGF and ChAT in the brain, which may contribute to their differential effects on cognitive function. The crossover data further suggest that certain atypical antipsychotic drugs (e.g., clozapine) may have the potential to prevent or reverse the deleterious effects of HAL on important neurochemical substrates of cognitive function.

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.

Altered neurotrophin receptor function in the developing prefrontal cortex leads to adult-onset dopaminergic hyperresponsivity and impaired prepulse inhibition of acoustic startle

BACKGROUND

Survival and differentiation of neurons and the formation and maintenance of synapses in the cerebral cortex may be affected in schizophrenia. Since neurotrophins play an important role in these events, behavioral effects relevant to schizophrenia were investigated in rats that had compromised neurotrophin function during prefrontal cortical development.

METHODS

Neonatal rat pups were injected into the developing prefrontal cortex with a depot preparation of p75 receptor antibody conjugated to saporin. Animals were tested for dopaminergic hyperresponsivity and prepulse inhibition of acoustic startle at 5 or 10 weeks. Neonatal and adult brain sections were examined for morphologic abnormality.

RESULTS

Animals that received neonatal injections of p75 antibody conjugated to saporin showed significantly increased amphetamine-induced locomotion and rearing and impairment of prepulse inhibition of acoustic startle at 10 weeks of age but not at 5 weeks. Examination of adult brain sections revealed apparently normal structure, whereas neonatal brain sections showed apoptotic cells in the developing prefrontal cortex in pups that received p75 antibody conjugated to saporin.

CONCLUSIONS

Compromised p75 neurotrophin receptor function in the developing prefrontal cortex may be associated with the manifestation of adult-onset dopaminergic hyperresponsivity and impaired prepulse inhibition and therefore may be involved in the pathogenesis of schizophrenia.

Neurotrophic factors and CNS disorders: findings in rodent models of depression and schizophrenia

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are proteins involved in neuronal survival and plasticity of dopaminergic, cholinergic and serotonergic neurons in the central nervous system (CNS). Loss of neurons in specific brain regions has been found in depression and schizophrenia, and this chapter summarizes the findings of altered neurotrophins in animal models of those two disorders under baseline condition and following antidepressive and antipsychotic treatments. In a model of depression (Flinders sensitive line/Flinders resistant line; FSL/FRL rats), increased NGF and BDNF concentrations were found in frontal cortex of female, and in occipital cortex of male 'depressed' FSL compared to FRL control rats. Using the same model, the effects of electroconvulsive stimuli (ECS) and chronic lithium treatment on brain NGF, BDNF and glial cell line-derived neurotrophic factors were investigated. ECS and lithium altered the brain concentrations of neurotrophic factors in the hippocampus, frontal cortex, occipital cortex and striatum. ECS mimic the effects of electroconvulsive therapy (ECT) that is an effective treatment for depression and also schizophrenia. Since NGF and BDNF may also be changed in the CNS of animal models of schizophrenia, we investigated whether treatment with antipsychotic drugs (haloperidol, risperidone, and olanzapine) affects the constitutive levels of NGF and BDNF in the CNS. Both typical and atypical antipsychotic drugs altered the regional brain levels of NGF and BDNF. Other studies also demonstrated that these drugs differentially altered neurotrophin mRNAs. Overall, these studies indicate that alteration of brain level of NGF and BDNF could constitute part of the biochemical alterations induced by antipsychotic drugs.

Beta-amyloid modulates tyrosine kinase B receptor expression in SHSY5Y neuroblastoma cells: influence of the antioxidant melatonin

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in humans and is characterized by neuronal loss, neurofibrillary tangles and beta-amyloid deposition. The interaction between neurotrophins and their tyrosine kinase (trk) receptors is important for cellular differentiation and survival. Interestingly, marked reductions in neurotrophins and receptors have been reported in AD. The cause of the decrease in these molecules remains unclear. However, the role of beta-amyloid (A beta) appears central in understanding the mechanisms controlling neurotrophin/trk expression. In this study we exposed SHSY5Y neuroblastoma cells to A beta or hydrogen peroxide and measured the expression of trk B/truncated trk B, and brain-derived neurotrophic factor (BDNF)/NT4 at the protein and molecular level. We show that A beta or hydrogen peroxide (H(2)O(2)) induces oxidative stress and cell cytotoxicity. The exposure of cells to A beta results in an increased trk B expression with a concurrent reduction in truncated trk B levels. H(2)O(2) exposure decreased both trk B and truncated trk B levels at the cell surface. At the molecular level trk B RNA increased in the presence of A beta and was unaffected by H(2)O(2). Similarly, BDNF and NT4 levels increased in the presence of A beta. Pre-treatment of cells with the anti-oxidant melatonin returns trk receptor expression, mRNA and BDNF/NT4 secretion to normal levels. These results are significant as they can help in the planning and implementation of AD treatment strategies involving neurotrophins.

Nerve growth factor in never-medicated first-episode psychotic and medicated chronic schizophrenic patients: possible implications for treatment outcome

Nerve growth factor (NGF) has been found to play a crucial role in the neuroplasticity of predominantly cholinergic neurons in brain development, and neuronal survival following brain injury, which reflect in cognitive performance. Wide ranges of neurodevelopmental abnormalities have been reported in schizophrenic patients, who also show poor cognitive performance. We report plasma NGF levels in never-medicated first-episode psychotic (FEP; N=24) and chronic medicated schizophrenic patients (N=24). NGF levels were determined in plasma by Enzyme-Linked ImmunoSorbent Assay (ELISA). Plasma NGF levels were significantly lower in both FEP and medicated chronic patients as compared to normal subjects (P<0.001). However, NGF levels were significantly higher in chronic schizophrenic patients, which were treated with antipsychotics as compared to FEP (P<0.05). Moreover, NGF levels in chronic patients treated with atypical antipsychotics were markedly higher as compared to patients treated with typical antipsychotics (P<0.05). Lower NGF levels in FEP patients at the onset of psychosis may have implications for the neurodevelopmental abnormalities. However, higher NGF levels in chronic patients treated with atypical antipsychotics may have implications for the treatment outcome.

Agonistic encounters in aged male mouse potentiate the expression of endogenous brain NGF and BDNF: possible implication for brain progenitor cells' activation

The condition of dominance or submission following agonistic encounters in the adult male mouse is known to differentially affect brain nerve growth factor, a neurotrophin playing a role in brain remodeling, in the fine tuning of behaviour and in the regulation of the basal forebrain cholinergic neurons. During development and adult life nerve growth factor regulates brain expression of neurotransmitters and the stimulation of progenitor cells (stem cells) which, under different external stimuli, may differentiate into neuronal and/or glial cells promoting the recovery of the injured brain. However, little information is available for the aged brain. Thus in the present study we investigated the effect of the social status ('dominance' vs. 'submission') in the aged mouse on the presence of nerve growth factor, brain-derived neurotrophic factor, choline acetyltransferase, neuropeptide Y and progenitor cells of selected brain regions. We found that aged dominant mice showed increased brain-derived neurotrophic factor in the subventricular zone and hippocampus and increased choline acetyltransferase in the septum and basal nuclei, which were associated with increased presence of progenitor cells in the subventricular zone. Conversely, in aged subordinate mice the data showed a marked brain increase in nerve growth factor in the subventricular zone and hippocampus, choline acetyltransferase in the septum and basal nuclei and neuropeptide Y in the hippocampus and parietal cortex. The possible functional implications of these findings are discussed.

Pro-brain-derived neurotrophic factor is decreased in parietal cortex in Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) promotes the function and survival of the major neuronal types affected in Alzheimer disease, such as hippocampal, cortical and basal forebrain cholinergic neurons. We and others have demonstrated a reduction in BDNF mRNA expression in Alzheimer's disease hippocampus and cortex, which may help to explain the selective vulnerability of these neurons. Several studies have also shown decreased BDNF protein in Alzheimer's disease. BDNF protein is synthesized as a precursor, proBDNF, which is cleaved to the mature 14-kDa form. We demonstrate here that BDNF exists as a mixture of proBDNF and mature BDNF in all regions tested of human brain. Using Western blotting, we observe a 40% reduction in proBDNF levels in Alzheimer's disease parietal cortex compared to controls. Thus, decreased BDNF protein measured by ELISA and immunohistochemistry likely represents a mixture of the two BDNF forms, and previously reported decreases in BDNF protein may be due, at least in part, to a significant reduction in proBDNF levels. Although the biological activity of proBDNF is unknown, reduced proBDNF may have functional consequences for the selective neuronal degeneration in Alzheimer's disease brain.

Differential effects of cortical neurotrophic factors on development of lateral geniculate nucleus and superior colliculus neurons: anterograde and retrograde actions

Neurotrophins strongly affect visual system development and plasticity. However, the mode of delivery and targets of neurotrophin action are still under debate. For instance, cortical NT-4/5 (neurotrophin 4/5; Ntf4/5) was shown to rescue lateral geniculate nucleus (LGN) neurons from monocular deprivation-induced atrophy suggesting a retrograde action on thalamic afferents. It is still unclear whether LGN neurons respond to NT-4/5 and other neurotrophins during development in animals with normal vision. We now show that infusions of NT-4/5 and NGF (nerve growth factor) into visual cortex at the onset and the peak of the critical period accelerated LGN neuron growth. BDNF (brain-derived neurotrophic factor) was ineffective. The effects of neurotrophin on LGN development were clearly dissociated from the effects at cortical level because soma growth of cortical layer IV and VI neurons was strongly promoted by BDNF. NT-4/5 was only effective at the onset, but no longer at the peak of the critical period suggesting a switch in neurotrophin dependency for these cortical cell classes. To dissociate retrograde and anterograde effects of the TrkB ligands, we analyzed the stratum griseum superficiale (SGS) of the superior colliculus, a target of visual cortical efferents. Indeed, TrkB-expressing inhibitory SGS neurons responded to cortical NT-4/5 infusion with somatic growth. Strikingly, the TrkB-expressing excitatory tectothalamic calbindin neurons in the SGS did not respond. This demonstrated for the first time a selective cell type-specific anterograde action of NT-4/5 and suggested for the LGN that anterograde as well as retrograde effects contribute to soma size regulation. Strikingly, cortical infusion of the cytokine LIF, which affects development of visual cortex neurochemical architecture, transiently inhibited growth of neurons in LGN, cortical layer IV and VI and SGS. In summary, the study presents three important results. First, central neurons regulate soma size development in an age-and ligand-specific fashion. Second, NT-4/5 and NGF accelerate LGN development in rats with normal vision while LIF delays growth. Third, anterogradely transported NT-4/5 effectively promotes neuronal maturation. These differential actions on subcortical neurons may contribute to the different effects of neurotrophins on visual system development and plasticity.

Improvement of spatial learning and memory after adenovirus-mediated transfer of the nerve growth factor gene to aged rat brain

Adenovirus-mediated transfer of the nerve growth factor gene promotes significant recovery of age-related cholinergic neuronal deficits in aged rats, but the effects of such treatment on cognitive dysfunction remain unclear. Herein we report a beneficial effect of first-generation adenovirus-mediated nerve growth factor gene transfer (AdNGF) on the spatial learning and memory of aged rats. The NGF protein was detected by enzyme-linked immunosorbent assay in cerebrospinal fluid as early as 3 days after gene transfer and was expressed for at least 30 days. Escape latency in the Morris water maze hidden-platform test was significantly improved on day 8 postinoculation in memory-impaired rats treated with AdNGF as well as at later testing intervals. Ultimately, the escape latency values for the AdNGF group become indistinguishable from those for aged rats with normal learning capacity. Immunohistochemical analysis of septal cholinergic neurons for choline acetyltransferase (ChAT) showed significant increases in both the number and somal distribution of ChAT-positive cells after inoculation of memory-impaired rats with AdNGF. Improvement in memory performance was positively correlated with increases in both NGF concentration in cerebrospinal fluid (r = 0.73, p = 0.005) and the number of ChAT-staining cells (r = 0.77, p = 0.0022). We conclude that AdNGF can improve cognitive function in memory-impaired aged rats and, with refinements in vector-driven expression of the transgene, may prove suitable for use in humans.

Brain NGF and EGF administration improves passive avoidance response and stimulates brain precursor cells in aged male mice

Nerve growth factor (NGF) has been shown to improve damage in spatial cognition following aging, whereas epidermal growth factor (EGF) is important in brain cell proliferation. It is also known that the adult mammalian central nervous system contains persistent progenitor cells with characteristics of stem cells. These studies suggest that under appropriate external stimuli progenitor cells may generate neuronal and glial cells promoting recovery of the injured nervous system. However, little is known about the presence and responsiveness of progenitor cells in the aged brain. In the present investigation, we studied the effect of brain intracerebroventricular injections of EGF and/or NGF on progenitor cells of the subventricular area (SVZ) in aged male mice to test learning performances in the passive avoidance apparatus. We found that neither NGF nor EGF improved learning responses. However, combined NGF and EGF administration in the brain improved learning responses of aged mice in the passive avoidance when compared with aged matched nontreated controls. These findings resulted to be associated with increased immunopositivity to progenitor cells in the SVZ. The possible functional implications of these data are discussed.