Selective antibody-induced cholinergic cell and synapse loss produce sustained hippocampal and cortical hypometabolism with correlated cognitive deficits

Basal Forebrain Atrophy, Cortical Thinning, and Amyloid-β Status in Parkinson's disease-Related Cognitive Decline

BACKGROUND

Degeneration of the cortically-projecting cholinergic basal forebrain (cBF) is a well-established pathologic correlate of cognitive decline in Parkinson's disease (PD). In Alzheimer's disease (AD) the effect of cBF degeneration on cognitive decline was found to be mediated by parallel atrophy of denervated cortical areas.

OBJECTIVES

To examine whether the association between cBF degeneration and cognitive decline in PD is mediated by parallel atrophy of cortical areas and whether these associations depend on the presence of comorbid AD pathology.

METHODS

We studied 162 de novo PD patients who underwent serial 3 T magnetic resonance imaging scanning (follow-up: 2.33 ± 1.46 years) within the Parkinson's Progression Markers Initiative. cBF volume and regional cortical thickness were automatically calculated using established procedures. Individual slopes of structural brain changes and cognitive decline were estimated using linear-mixed models. Associations between longitudinal cBF degeneration, regional cortical thinning, and cognitive decline were assessed using regression analyses and mediation effects were assessed using nonparametric bootstrap. Complementary analyses assessed the effect of amyloid-β biomarker positivity on these associations.

RESULTS

After controlling for global brain atrophy, longitudinal cBF degeneration was highly correlated with faster cortical thinning (PFDR  < 0.05), and thinning in cBF-associated cortical areas mediated the association between cBF degeneration and cognitive decline (rcBF-MoCA  = 0.30, P < 0.001). Interestingly, both longitudinal cBF degeneration and its association with cortical thinning were largely independent of amyloid-β status.

CONCLUSIONS

cBF degeneration in PD is linked to parallel thinning of cortical target areas, which mediate the effect on cognitive decline. These associations are independent of amyloid-β status, indicating that they reflect proper features of PD pathophysiology. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Bisphenol-A Neurotoxic Effects on Basal Forebrain Cholinergic Neurons In Vitro and In Vivo

The widely used plasticizer bisphenol-A (BPA) is well-known for producing neurodegeneration and cognitive disorders, following acute and long-term exposure. Although some of the BPA actions involved in these effects have been unraveled, they are still incompletely known. Basal forebrain cholinergic neurons (BFCN) regulate memory and learning processes and their selective loss, as observed in Alzheimer's disease and other neurodegenerative diseases, leads to cognitive decline. In order to study the BPA neurotoxic effects on BFCN and the mechanisms through which they are induced, 60-day old Wistar rats were used, and a neuroblastoma cholinergic cell line from the basal forebrain (SN56) was used as a basal forebrain cholinergic neuron model. Acute treatment of rats with BPA (40 µg/kg) induced a more pronounced basal forebrain cholinergic neuronal loss. Exposure to BPA, following 1- or 14-days, produced postsynaptic-density-protein-95 (PSD95), synaptophysin, spinophilin, and N-methyl-D-aspartate-receptor-subunit-1 (NMDAR1) synaptic proteins downregulation, an increase in glutamate content through an increase in glutaminase activity, a downregulation in the vesicular-glutamate-transporter-2 (VGLUT2) and in the WNT/β-Catenin pathway, and cell death in SN56 cells. These toxic effects observed in SN56 cells were mediated by overexpression of histone-deacetylase-2 (HDAC2). These results may help to explain the synaptic plasticity, cognitive dysfunction, and neurodegeneration induced by the plasticizer BPA, which could contribute to their prevention.

Are We Inviting Another Attendee to the Temporal Lobe Epilepsy Party?

Role of the Nucleus Basalis as a Key Network Node in Temporal Lobe Epilepsy

González HFJ, Narasimhan S, Johnson GW, et al. Neurology. 2021;96(9):e1334-e1346. doi:https://doi.org/10.1212/WNL.0000000000011523

Objective:

To determine whether the nucleus basalis of Meynert (NBM) may be a key network structure of altered functional connectivity in temporal lobe epilepsy (TLE), we examined functional magnetic resonance imaging (fMRI) with network-based analyses.

Methods:

We acquired resting state fMRI in 40 adults with TLE and 40 matched healthy control participants. We calculated functional connectivity of NBM and used multiple complementary network-based analyses to explore the importance of NBM in TLE networks without biasing our results by our approach. We compared patients to controls and examined associations of network properties with disease metrics and neurocognitive testing.

Results:

We observed marked decreases in connectivity between NBM and the rest of the brain in patients with TLE (0.91 ± 0.88, mean ± SD) versus controls (1.96 ± 1.13, P < .001, t test). Larger decreases in connectivity between NBM and fronto-parietal-insular regions were associated with higher frequency of consciousness-impairing seizures (r = −0.41, P = .008, Pearson). A core network of altered nodes in TLE included NBM ipsilateral to the epileptogenic side and bilateral limbic structures. Furthermore, normal community affiliation of ipsilateral NBM was lost in patients, and this structure displayed the most altered clustering coefficient of any node examined (3.46 ± 1.17 in controls vs 2.23 ± 0.93 in patients). Abnormal connectivity between NBM and subcortical arousal community was associated with modest neurocognitive deficits. Finally, a logistic regression model incorporating connectivity properties of ipsilateral NBM successfully distinguished patients from control datasets with moderately high accuracy (78%).

Conclusions:

These results suggest that while NBM is rarely studied in epilepsy, it may be one of the most perturbed network nodes in TLE, contributing to widespread neural effects in this disabling disorder.

Focusing on cellular biomarkers: The endo-lysosomal pathway in Down syndrome

Down syndrome (DS) is the most frequent chromosomal disorder. It is caused by the triplication of human chromosome 21, leading to increased dosage of a variety of genes including APP (Amyloid Precursor Protein). Mainly for this reason, individuals with DS are at high risk to develop Alzheimer's disease (AD). Extensive literature identified various morphological and molecular abnormalities in the endo-lysosomal pathway both in DS and AD. Most studies in this field investigated the causative role of APP (Amyloid Precursor Protein) in endo-lysosomal dysfunctions, thus linking phenotypes observed in DS and AD. In DS context, several lines of evidence and emerging hypotheses suggest that other molecular players and pathways may be implicated in these complex phenotypes. In this review, we outline the normal functioning of endosomal trafficking and summarize the research on endo-lysosomal dysfunction in DS in light of AD findings. We emphasize the role of genes of chromosome 21 implicated in endocytosis to explain endosomal abnormalities and set the limitations and perspectives of models used to explore endo-lysosomal dysfunction in DS and find new biomarkers. The review highlights the complexity of endo-lysosomal dysfunction in DS and suggests directions for future research in the field.

Cystatin C prevents neuronal loss and behavioral deficits via the endosomal pathway in a mouse model of down syndrome

Cystatin C (CysC) plays diverse protective roles under conditions of neuronal challenge. We investigated whether CysC protects from trisomy-induced pathologies in a mouse model of Down syndrome (DS), the most common cause of developmental cognitive and behavioral impairments in humans. We have previously shown that the segmental trisomy mouse model, Ts[Rb(12.1716)]2Cje (Ts2) has DS-like neuronal and behavioral deficiencies. The current study reveals that transgene-mediated low levels of human CysC overexpression has a preventive effect on numerous neuropathologies in the brains of Ts2 mice, including reducing early and late endosome enlargement in cortical neurons and decreasing loss of basal forebrain cholinergic neurons (BFCNs). Consistent with these cellular benefits, behavioral dysfunctions were also prevented, including deficits in nesting behavior and spatial memory. We determined that the CysC-induced neuroprotective mechanism involves activation of the phosphotidylinositol kinase (PI3K)/AKT pathway. Activating this pathway leads to enhanced clearance of accumulated endosomal substrates, protecting cells from DS-mediated dysfunctions in the endosomal system and, for BFCNs, from neurodegeneration. Our findings suggest that modulation of the PI3/AKT pathway offers novel therapeutic interventions for patients with DS.

Immunolocalization of muscarinic M1 receptor in the rat medial prefrontal cortex

The medial prefrontal cortex (mPFC) has been considered to participate in many higher cognitive functions, such as memory formation and spatial navigation. These cognitive functions are modulated by cholinergic afferents via muscarinic acetylcholine receptors. Previous pharmacological studies have strongly suggested that the M1 receptor (M1R) is the most important subtype among muscarinic receptors to perform these cognitive functions. Actually, M1R is abundant in mPFC. However, the proportion of somata containing M1R among cortical cellular types, and the precise intracellular localization of M1R remain unclear. In this study, to clarify the precise immunolocalization of M1R in rat mPFC, we examined three major cellular types, pyramidal neurons, inhibitory neurons, and astrocytes. M1R immunopositivity signals were found in the majority of the somata of both pyramidal neurons and inhibitory neurons. In pyramidal neurons, strong M1R immunopositivity signals were usually found throughout their somata and dendrites including spines. On the other hand, the signal strength of M1R immunopositivity in the somata of inhibitory neurons significantly varied. Some neurons showed strong signals. Whereas about 40% of GAD67‐immunopositive neurons and 30% of parvalbumin‐immunopositive neurons (PV neurons) showed only weak signals. In PV neurons, M1R immunopositivity signals were preferentially distributed in somata. Furthermore, we found that many astrocytes showed substantial M1R immunopositivity signals. These signals were also mainly distributed in their somata. Thus, the distribution pattern of M1R markedly differs between cellular types. This difference might underlie the cholinergic modulation of higher cognitive functions subserved by mPFC.

Glucose metabolism in pediatric traumatic brain injury

Traumatic brain injury is the number one cause of death and disability among the pediatric population in the USA. The heterogeneity of the pediatric population is reflected by both the normal cerebral maturation and the age differences in the causes of TBI, which generate unique age-related pathophysiology responses and recovery profiles. This review will address the normal changes in cerebral glucose metabolism throughout developmental phases and how TBI alters glucose metabolism. Evidence has shown that TBI disrupts the biochemical processing of glucose to energy. This brings to question, "What is the optimal substrate to manage a pediatric TBI patient?" Issues related to glycemic control and alternative substrate metabolism are addressed specifically in regard to pediatric TBI. Research into pediatric glucose metabolism after TBI is limited, and understanding these age-related differences within the pediatric population have great potential to improve support for the injured younger brain.

CNS Gene Therapy and a Nexus of Complexity: Systems and Biology at a Crossroads

Gene therapy is a potentially promising new treatment for neurodegenerative disorders such as Alzheimer's disease (AD), which has been difficult to treat with conventional therapeutics. Viral vector-mediated somatic gene therapy is a rapidly developing methodology for providing never before achieved capability to deliver specific genes to the CNS in a highly localized and controlled manner. With the advent and refinements of this technology one focus is directed to which genes are the most appropriate to select for specific disease indications. Nerve growth factor (NGF), a potent survival factor for critical cell populations that degenerate in AD, has been chosen already for clinical gene therapy trials in human AD patients. Much knowledge about the pathophysiological underpinnings of AD is still lacking to make clear which patients may benefit from a gene therapy approach. Moreover, a detailed understanding of sustained NGF action in the normal and diseased CNS needs to be resolved before conclusions can be drawn regarding the utility of NGF gene therapy. Systematic efforts to acquire this new knowledge should compel clinically and biologically sophisticated efforts to advance gene therapy for neurodegenerative diseases.

Cognitive Correlates of Basal Forebrain Atrophy and Associated Cortical Hypometabolism in Mild Cognitive Impairment

Degeneration of basal forebrain (BF) cholinergic nuclei is associated with cognitive decline, and this effect is believed to be mediated by neuronal dysfunction in the denervated cortical areas. MRI-based measurements of BF atrophy are increasingly being used as in vivo surrogate markers for cholinergic degeneration, but the functional implications of reductions in BF volume are not well understood. We used high-resolution MRI, fluorodeoxyglucose-positron emission tomography (PET), and neuropsychological test data of 132 subjects with mild cognitive impairment (MCI) and 177 cognitively normal controls to determine associations between BF atrophy, cortical hypometabolism, and cognitive deficits. BF atrophy in MCI correlated with both impaired memory function and attentional control deficits, whereas hippocampus volume was more specifically associated with memory deficits. BF atrophy was also associated with widespread cortical hypometabolism, and path analytic models indicated that hypometabolism in domain-specific cortical networks mediated the association between BF volume and cognitive dysfunction. The presence of cortical amyloid pathology, as assessed using AV45-PET, did not significantly interact with the observed associations. These data underline the potential of multimodal imaging markers to study structure-function-cognition relationships in the living human brain and provide important in vivo evidence for an involvement of the human BF in cortical activity and cognitive function.

Basal Forebrain Cholinergic Deficits Reduce Glucose Metabolism and Function of Cholinergic and GABAergic Systems in the Cingulate Cortex

PURPOSE

Reduced brain glucose metabolism and basal forebrain cholinergic neuron degeneration are common features of Alzheimer's disease and have been correlated with memory function. Although regions representing glucose hypometabolism in patients with Alzheimer's disease are targets of cholinergic basal forebrain neurons, the interaction between cholinergic denervation and glucose hypometabolism is still unclear. The aim of the present study was to evaluate glucose metabolism changes caused by cholinergic deficits.

MATERIALS AND METHODS

We lesioned basal forebrain cholinergic neurons in rats using 192 immunoglobulin G-saporin. After 3 weeks, lesioned animals underwent water maze testing or were analyzed by ¹⁸F-2-fluoro-2-deoxyglucose positron emission tomography.

RESULTS

During water maze probe testing, performance of the lesioned group decreased with respect to time spent in the target quadrant and platform zone. Cingulate cortex glucose metabolism in the lesioned group decreased, compared with the normal group. Additionally, acetylcholinesterase activity and glutamate decarboxylase 65/67 expression declined in the cingulate cortex.

CONCLUSION

Our results reveal that spatial memory impairment in animals with selective basal forebrain cholinergic neuron damage is associated with a functional decline in the GABAergic and cholinergic system associated with cingulate cortex glucose hypometabolism.

Selective transfection of microglia in the brain using an antibody-based non-viral vector

There are currently few approaches to transiently manipulate the expression of specific proteins in microglia of the brain. An antibody directed against an extracellular epitope of scavenger receptor class B, type I (SR-BI) was found to be selectively taken up by these cells in the brain. Other antibodies tested were not internalised by microglia. A vector was produced by linking the SR-BI antibody to polyethyleneimine and binding a DNA plasmid encoding green fluorescent protein. Infusions of this vector into the hippocampus produced a widespread transfection of cells, more than 80% of which were immunoreactive for microglial/macrophage markers. Transfection was not detected in cells expressing markers for astrocytes or neurons. Reporter gene expression was most prominent near the infusion site but was seen in tissue up to 4mm away. DNA bound to polyethyleneimine alone or to a vector containing a different antibody did not produce transfection in the brain. Single injections of the vector containing the SR-BI antibody into the brain also resulted in transfection of microglia, albeit with lower efficiency. Vector modifications to promote lysis of endosomes or entry of DNA into the nucleus did not increase efficiency. The findings clearly demonstrate the capacity of the SR-BI antibody to selectively target brain microglia. This approach offers considerable potential to deliver DNA and other molecules capable of modifying the function of these cells in vivo.

Neuroprotective effect of Liuwei Dihuang decoction on cognition deficits of diabetic encephalopathy in streptozotocin-induced diabetic rat

ETHNOPHARMACOLOGICAL RELEVANCE

Liuwei Dihuang decoction (LWDHD) is a well-known prescription of traditional Chinese medicine (TCM) and consists of six crude drugs including Rehmannia glutinosa Libosch. (family: Scrophulariaceae), Cornus officinalis Sieb. (family: Cornaceae), Dioscorea oppositifolia L. (family: Dioscoreaceae), Paoenia ostii (family: Paeoniaceae), Alisma orientale (G. Samuelsson) Juz (family: Alismataceae) and Poria cocos (Schw.) Wolf (family: Polyporaceae). It has been used for the treatment of "Kidney-Yin" deficiency syndrome in clinic in China for a long time. Recent studies found that LWDHD had a potential benefit for the treatment of diabetic complications. The aim of the present study is to investigate the neuroprotective effect of LWDHD on memory and cognition deficits in streptozotocin (STZ)-induced diabetic encephalopathy (DE) rats.

MATERIALS AND METHODS

Adult male Sprague Dawley (SD) rats were fed with high-glucose-fat diet for 50 days and then received an intraperitoneal injection of STZ (40 mg/kg) to induce DE model. Morris water maze test was used to evaluate the memory and cognition capability of DE rats. Choline acetyltransferase (ChAT), acetylcholinesterase (AChE), Na(+)-K(+)-ATP enzyme, iNOS and GSH kits were used to determine their activities or content in hippocampus. TUNEL staining, immunohistochemistry and Congo red staining were conducted to evaluate the apoptosis, caspase-3 protein expression, insulin-like growth factors 1 (IGF-1) and brain derived neurophic factor (BDNF) expressions, as well as Aβ deposition.

RESULTS

The treatment with LWDHD (1 and 2g/kg, p.o., once daily, 30 days) could significantly reduce the escape latency time and path length, and obviously enhance the spent time in the target quadrant and platform crossings in Morris water maze test compared with model group (P<0.05, P<0.01). LWDHD could also significantly decrease the level of fasting blood glucose, increase Na(+)-K(+)-ATP enzyme and ChAT activities, enhance remarkedly GSH level while decrease significantly AChE and iNOS activities in hippocampus (P<0.05, P<0.01). Furthermore, TUNEL staining, Congo red staining and immunohistochemistry showed that LWDHD significantly improved the expressions of IGF-1 and BDNF, attenuated the neural apoptosis, overexpression of caspase-3 and Aβ deposition in the hippocampus and cerebral cortex of STZ-induced DE rats (P<0.01).

CONCLUSION

Our findings suggested that LWDHD had a neuroprotective effect on DE rats. LWDHD may be of benefit in the treatment of DE.

Cortical metabolic deficits in a rat model of cholinergic basal forebrain degeneration

Evidence indicates that the degeneration of basal forebrain cholinergic neurons may represent an important factor underlying the progressive cognitive decline characterizing Alzheimer's disease (AD). However, the nature of the relationship between cholinergic depletion and AD is not fully elucidated. This study aimed at clarifying some aspects of the relation existing between deficits in cerebral energy metabolism and degeneration of cholinergic system in AD, by investigating the neuronal metabolic activity of several cortical areas after depletion of basal forebrain cholinergic neurons. In cholinergically depleted rats, we evaluated the neuronal metabolic activity by assaying cytochrome oxidase (CO) activity in frontal, parietal and posterior parietal cortices at four different time-points after unilateral injection of 192 IgG-saporin in the nucleus basalis magnocellularis. Unilateral depletion of cholinergic cells in the basal forebrain induced a bilateral decrease of metabolic activity in all the analyzed areas. Frontal and parietal cortices showed decreased metabolic activity even 3 days after the lesion, when the cholinergic degeneration was still incomplete. In posterior parietal cortex metabolic activity decreased only 7 days after the lesion. The possible molecular mechanisms underlying these findings were also investigated. Real-time PCR showed an increase of CO mRNA levels at 3, 7 and 15 days after the lesion both in frontal and parietal cortices, followed by normalization at 30 days. Western Blot analysis did not show any change in CO protein levels at any time-point after the lesion. Our findings support a link between metabolic deficit and cholinergic hypofunctionality characterizing AD pathology. The present model of cholinergic hypofunctionality provides a useful means to study the complex mechanisms linking two fundamental and interrelated phenomena characterizing AD from the early stages.

Metabolic syndrome--from the neurotrophic hypothesis to a theory

Metabolic syndrome (MetS) is a complex and heterogeneous disease characterized by central obesity, impaired glucose metabolism, dyslipidemia, arterial hypertension, insulin resistance and high-sensitivity C-reactive protein. In 2006, a neurotrophic hypothesis of the etiopathogenesis of MetS was launched. This hypothesis considered the neurotrophins a key factor in MetS development. Chronic inflammatory and/or psychoemotional distress provoke a series of neuroimmunoendocrine interactions such as increased tissue and plasma levels of proinflammatory cytokines and neurotrophins, vegetodystonia, disbalance of neurotransmitters, hormones and immunity markers, activation of the hypothalamo-pituitary-adrenal axis, insulin resistance, and atherosclerosis. An early and a late clinical stage in the course of MetS are defined. Meanwhile, evidence of supporting results from the world literature accumulates. This enables the transformation of the definition of the neurotrophic hypothesis into a neurotrophic theory of MetS. The important role of two neurotrophic factors, i.e. the nerve growth factor and brain-derived neurotrophic factor as well as of the proinflammatory cytokines, neurotransmitters, adipokines and, especially, of leptin for the development of MetS, obesity and type 2 diabetes mellitus is illustrated. There are reliable scientific arguments that the metabotrophic deficit due to reduced neurotrophins could be implicated in the pathogenesis of MetS, type 2 diabetes mellitus, and atherosclerosis as well. A special attention is paid to the activity of the hypothalamo-pituitary-adrenal axis after stress. The application of the neurotrophic theory of MetS could contribute to the etiological diagnosis and individualized management of MetS by eliminating the chronic distress, hyponeurotrophinemia and consequent pathology. It helps estimating the risk, defining the prognosis and implementing the effective prevention of this socially significant disease as evidenced by the dramatic recent growth of the world publication output on this interdisciplinary topic.

Repeated mild traumatic brain injury: mechanisms of cerebral vulnerability

Among the 3.5 million annual new head injury cases is a subpopulation of children and young adults who experience repeated traumatic brain injury (TBI). The duration of vulnerability after a single TBI remains unknown, and biomarkers have yet to be determined. Decreases in glucose metabolism (cerebral metabolic rate of glucose [CMRglc]) are consistently observed after experimental and human TBI. In the current study, it is hypothesized that the duration of vulnerability is related to the duration of decreased CMRglc and that a single mild TBI (mTBI) increases the brain's vulnerability to a second insult for a period, during which a subsequent mTBI will worsen the outcome. Postnatal day 35 rats were given sham, single mTBI, or two mTBI at 24-h or 120-h intervals. (14)C-2-deoxy-D-glucose autoradiography was conducted at 1 or 3 days post-injury to calculate CMRglc. At 24 h after a single mTBI, CMRglc is decreased by 19% in both the parietal cortex and hippocampus, but approached sham levels by 3 days post-injury. When a second mTBI is introduced during the CMRglc depression of the first injury, the consequent CMRglc is depressed (36.5%) at 24 h and remains depressed (25%) at 3 days. In contrast, when the second mTBI is introduced after the metabolic recovery of the first injury, the consequent CMRglc depression is similar to that seen with a single injury. Results suggest that the duration of metabolic depression reflects the time-course of vulnerability to second injury in the juvenile brain and could serve as a valuable biomarker in establishing window of vulnerability guidelines.

Effect of bite-raised condition on the hippocampal cholinergic system of aged SAMP8 mice

Occlusal disharmony induces chronic stress, which results in learning deficits in association with the morphologic changes in the hippocampus, e.g., neuronal degeneration and increased hypertrophied glial fibrillary acidic protein-positive cells. To investigate the mechanisms underlying impaired hippocampal function resulting from occlusal disharmony, we examined the effects of the bite-raised condition on the septohippocampal cholinergic system by assessing acetylcholine release in the hippocampus and choline acetyltransferase immunoreactivity in the medial septal nucleus in aged SAMP8 mice that underwent the bite raising procedure. Aged bite-raised mice showed decreased acetylcholine release in the hippocampus and a reduced number of choline acetyltransferase-immunopositive neurons in the medial septal nucleus compared to age-matched control mice. These findings suggest that the bite-raised condition in aged SAMP8 mice enhances the age-related decline in the septohippocampal cholinergic system, leading to impaired learning.

The cannabinergic system is implicated in the upregulation of central NGF protein by psychotropic drugs

RATIONALE

Studies on the regulation of nerve growth factor (NGF) levels by psychotropics are limited in scope and the mechanism(s) remain elusive which merit further elucidation.

OBJECTIVES

We aimed to perform a more comprehensive investigation on the possible effects of pharmacologically heterogeneous groups of psychotropic drugs on NGF contents in the brain regions involved in the modulation of emotions. As a mechanistic approach, we looked at the role of the cannabinergic system which is linked to depression and/or antidepressant effect and appears to interact with neurotrophin signaling.

METHODS

Following psychotropic treatment, NGF or endocannabinoid (eCB) contents were quantified by Bio-Rad protein assay and isotope-dilution liquid chromatography/mass spectrometry, respectively. In case of any significant change, the effects of pretreatment with the CB(1) receptor neutral antagonist AM4113 were investigated.

RESULTS

Single injection of nortriptyline, isocarboxazid, citalopram, diazepam, risperidone (2.5, 5, and 10 mg/kg, each), and fluphenazine (0.25, 0.5, and 1 mg/kg) into rats did not alter NGF or eCB contents. Following 4-week treatment, all drugs except diazepam elevated NGF or eCB levels in dose-dependent and brain region-specific fashion. Pretreatment with the highest dose of AM4113 (5.6 mg/kg) prevented psychotropic-induced NGF or eCB elevation. AM4113 had no effect by itself.

CONCLUSIONS

The cannabinergic system is implicated in the mechanisms of action of certain psychotropic drugs including the upregulation of brain NGF levels. This provides a better understanding of the pathophysiological mechanisms underlying neuropsychiatric disorders, leading to novel drug design.

Reduced serum concentrations of nerve growth factor, but not brain-derived neurotrophic factor, in chronic cannabis abusers

Chronic cannabis use produces effects within the central nervous system (CNS) which include deficits in learning and attention tasks and decreased brain volume. Neurotrophins, in particular nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), are proteins that serve as survival factors for CNS neurons. Deficits in the production and utilization of these proteins can lead to CNS dysfunctions including those associated with cannabis abuse. In this study we measured by enzyme-linked immunosorbent assay (ELISA) the NGF and BDNF serum levels in two groups of subjects: cannabis-dependent patients and healthy subjects. We found that NGF serum levels were significantly reduced in cannabis abusers as compared to healthy subjects. These findings indicate that NGF may have a role in the central action of cannabis and potentially in the neurotoxicity induced by this drug. These data also suggest that chronic cannabis consumption may be a risk factor for developing psychosis among drug users.

Septal grafts restore cognitive abilities and amyloid precursor protein metabolism

Cortical cholinergic loss and amyloidogenic processing of the beta-amyloid precursor protein (APP), may functionally interact in Alzheimer's disease. However, it is still unknown whether biological restoration of regulatory cholinergic inputs affects APP metabolism in vivo. Rats immunolesioned with 192 IgG-saporin exhibited severe acquisition deficits in place navigation that were paralleled by a dramatic loss of terminal cholinergic innervation and by marked changes in the regional expression of APP-like immunoreactivity. Moreover, in these animals, we observed a drastic reduction of soluble APP (sAPP) and a concomitant increase of the unsoluble, membrane-bound fraction (mAPP). Notably, at about 6 months post-surgery, lesioned animals implanted with reinnervating cholinergic-rich septal tissue grafts exhibited fairly normal spatial navigation abilities, as well as cortical and hippocampal APP levels that were restored up to normal or near-normal values. APP levels correlated significantly with lesion- or graft-induced changes in cholinergic innervation density, and both these measures correlated with performance in the spatial navigation task. Thus, integrity of ascending cholinergic inputs may be required to prevent amyloidogenic processing of APP in vivo and to modulate cognitive performance.

A new 18F-labeled fluoroacetylmorpholino derivative of vesamicol for neuroimaging of the vesicular acetylcholine transporter

With the aim of producing selective radiotracers for in vivo imaging of the vesicular acetylcholine transporter (VAChT) using positron mission tomography (PET), here, we report synthesis and analysis of a new class of conformationally constrained vesamicol analogues with moderate lipophilicity. The sequential ring opening on trans-1,4-cyclohexadiene dioxide enabled an approach to synthesize 6-arylpiperidino-octahydrobenzo[1,4]oxazine-7-ols [morpholino vesamicols]. The radiosynthesis of the [18F]fluoroacetyl-substituted derivative ([18F]FAMV) was achieved starting from a corresponding bromo precursor [2-Bromo-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone] and using a modified commercial computer-controlled module system with a radiochemical yield of 27+/-4%, a high radiochemical purity (99%) and a specific activity of 35 GBq/micromol. In competitive binding assays using a PC12 cell line overexpressing VAChT and [3H]-(-) vesamicol, 2-fluoro-1-[7-hydroxy-6-(4-phenyl-piperidin-1-yl)-octahydro-benzo[1,4]oxazin-4-yl]-ethanone (FAMV) demonstrated a high selectivity for binding to VAChT (K(i): 39.9+/-5.9 nM) when compared to its binding to sigma 1/2 receptors (Ki>1500 nM). The compound showed a moderate lipophilicity (logD (pH 7)=1.9) and a plasma protein binding of 49%. The brain uptake of [18F]FAMV was about 0.1% injected dose per gram at 5 min after injection and decreased continuously with time. Notably, an increasing accumulation of radioactivity in the lateral brain ventricles was observed. After 1 h, the accumulation of [18F]FAMV, expressed as ratio to the cerebellum, was 4.5 for the striatum, 2.0 for the cortical and 1.5 for the hippocampal regions, measured on brain slices using ex vivo autoradiography. At the present time, 75% of [18F]FAMV in the plasma was shown to be metabolized to various hydrophilic compounds, as detected by high-performance liquid chromatography. The degradation of [18F]FAMV was also detected in brain extracts as early as 15 min post injection (p.i.) and increased to 50% at 1 h postinjection. In conclusion, although the chemical properties of [18F]FAMV and the selectivity of binding to VAChT appear to be promising indicators of a useful PET tracer for imaging VAChT, a low brain extraction, in combination with only moderate specific accumulation in cholinergic brain regions and an insufficient in vivo stability prevents the application of this compound for neuroimaging in humans.

Resistance is futile: antineuronal autoimmunity in multiple sclerosis

For many years, loss of myelin was considered to be the major cause of neurological dysfunction in multiple sclerosis (MS), a chronic inflammatory, demyelinating disease of the central nervous system. This 'myelinocentric' view of MS was revised recently, after recognition that axonal damage, rather than demyelination, provides a better correlate to clinical symptoms. Nonetheless, current views of MS pathogenesis remain focused on the role of myelin-specific autoimmunity, and the potential contribution of autoimmune responses to axonal and neuronal antigens is ignored. Drawing on experience gained from work with other neurodegenerative diseases, we hypothesize that autoimmunity, particularly pathogenic antibodies to neuronal and axonal antigens, plays a significant role in the development of axonal pathology in MS. This concept offers a new perspective of disease pathogenesis and therapeutic approaches to prevent irreversible axonal loss and chronic disability in MS.

Chronic heroin and cocaine abuse is associated with decreased serum concentrations of the nerve growth factor and brain-derived neurotrophic factor

Chronic cocaine and heroin users display a variety of central nervous system (CNS) dysfunctions including impaired attention, learning, memory, reaction time, cognitive flexibility, impulse control and selective processing. These findings suggest that these drugs may alter normal brain functions and possibly cause neurotoxicity. Neurotrophins are a class of proteins that serve as survival factors for CNS neurons. In particular, nerve growth factor (NGF) plays an important role in the survival and function of cholinergic neurons while brain-derived neurotrophic factor (BDNF) is involved in synaptic plasticity and in the maintenance of midbrain dopaminergic and cholinergic neurons. In the present study, we measured by enzyme-linked immunosorbent assay (ELISA) the NGF and BDNF levels in serum of three groups of subjects: heroin-dependent patients, cocaine-dependent patients and healthy volunteers. Our goal was to identify possible change in serum neurotrophins in heroin and cocaine users. BDNF was decreased in heroin users whereas NGF was decreased in both heroin and cocaine users. These findings indicate that NGF and BDNF may play a role in the neurotoxicity and addiction induced by these drugs. In view of the neurotrophin hypothesis of schizophrenia the data also suggest that reduced level of neurotrophins may increase the risk of developing psychosis in drug users.

Combined damage to entorhinal cortex and cholinergic basal forebrain neurons, two early neurodegenerative features accompanying Alzheimer's disease: effects on locomotor activity and memory functions in rats

In Alzheimer's disease (AD), cognitive decline is linked to cholinergic dysfunctions in the basal forebrain (BF), although the earliest neuronal damage is described in the entorhinal cortex (EC). In rats, selective cholinergic BF lesions or fiber-sparing EC lesions may induce memory deficits, but most often of weak magnitude. This study investigated, in adult rats, the effects on activity and memory of both lesions, alone or in combination, using 192 IgG-saporin (OX7-saporin as a control) and L-N-methyl-D-aspartate to destroy BF and EC neurons, respectively. Rats were tested for locomotor activity in their home cage and for working- and/or reference-memory in various tasks (water maze, Hebb-Williams maze, radial maze). Only rats with combined lesions showed diurnal and nocturnal hyperactivity. EC lesions impaired working memory and induced anterograde memory deficits in almost all tasks. Lesions of BF cholinergic neurons induced more limited deficits: reference memory was impaired in the probe trial of the water-maze task and in the radial maze. When both lesions were combined, performance never improved in the water maze and the number of errors in the Hebb-Williams and the radial mazes was always larger than in any other group. These results (i) indicate synergistic implications of BF and EC in memory function, (ii) suggest that combined BF cholinergic and fiber-sparing EC lesions may model aspects of anterograde memory deficits and restlessness as seen in AD, (iii) challenge the cholinergic hypothesis of cognitive dysfunctions in AD, and (iv) contribute to open theoretical views on AD-related memory dysfunctions going beyond the latter hypothesis.

Brain cholinergic vulnerability: Relevance to behavior and disease

The major populations of cholinergic neurons in the brain include two "projection" systems, located in the pontine reticular formation and in the basal forebrain. These two complexes comprise, in part, the anatomical substrates for the "ascending reticular activating system" (ARAS). The pontine cholinergic system relays its rostral influences mainly through thalamic intralaminar nuclei, but it also connects to the basal forebrain and provides a minor innervation of cortex. The basal forebrain cholinergic complex (BFCC) projects directly to cortex and hippocampus, and has a minor connection with the thalamus. Recent data reveal that a parallel system of basal forebrain GABAergic projection neurons innervates cortex/hippocampus in a way that seems to complement the BFCC. Generally, the picture developed from more than 50 years of research is consistent with a "global" influence of these two ascending cholinergic projections on cortical and hippocampal regions. Seemingly, the BFCC acts in tandem or in parallel with the pontine cholinergic projection to activate the electro-encephalogram, increase cerebral blood flow, regulate sleep-wake cycling, and modulate cognitive function. There are quite a number and variety of human brain conditions, notably including Alzheimer's disease, in which degeneration of basal forebrain cholinergic neurons has been documented. Whether the corticopetal GABA system is affected by disease has not been established. Studies of degeneration of the pontine projection are limited, but the available data suggest that it is relatively preserved in Alzheimer's disease. Hypotheses of BFCC degeneration include growth factor deprivation, intracellular calcium dysfunction, amyloid excess, inflammation, and mitochondrial abnormalities/oxidative stress. But, despite considerable research conducted over several decades, the exact mechanisms underlying brain cholinergic vulnerability in human disease remain unclear.

Selective loss of basal forebrain cholinergic neurons by 192 IgG-saporin is associated with decreased phosphorylation of Ser glycogen synthase kinase-3beta

Glycogen synthase kinase-3beta (GSK-3beta) is a multifunctional enzyme involved in a variety of biological events including development, glucose metabolism and cell death. Its activity is inhibited by phosphorylation of the Ser9 residue and up-regulated by Tyr216 phosphorylation. Activated GSK-3beta increases phosphorylation of tau protein and induces cell death in a variety of cultured neurons, whereas phosphorylation of phosphatidylinositol-3 (PI-3) kinase-dependent protein kinase B (Akt), which inhibits GSK-3beta activity, is one of the best characterized cell survival signaling pathways. In the present study, the cholinergic immunotoxin 192 IgG-saporin was used to address the potential role of GSK-3beta in the degeneration of basal forebrain cholinergic neurons, which are preferentially vulnerable in Alzheimer's disease (AD) brain. GSK-3beta co-localized with a subset of forebrain cholinergic neurons and loss of these neurons was accompanied by a transient decrease in PI-3 kinase, phospho-Ser473Akt and phospho-Ser9GSK-3beta levels, as well as an increase in phospho-tau levels, in the basal forebrain and hippocampus. Total Akt, GSK-3beta, tau and phospho-Tyr216GSK-3beta levels were not significantly altered in these brain regions in animals treated with 192 IgG-saporin. Systemic administration of the GSK-3beta inhibitor LiCl did not significantly affect cholinergic marker or phospho-Ser9GSK-3beta levels in control rats but did preclude 192-IgG saporin-induced alterations in PI-3 kinase/phospho-Akt, phospho-Ser9GSK-3beta and phospho-tau levels, and also partly protected cholinergic neurons against the immunotoxin. These results provide the first evidence that increased GSK-3beta activity, via decreased Ser9 phosphorylation, can mediate, at least in part, 192-IgG saporin-induced in vivo degeneration of forebrain cholinergic neurons by enhancing tau phosphorylation. The partial protection of these neurons following inhibition of GSK-3beta kinase activity suggests a possible therapeutic role for GSK-3beta inhibitors in attenuating the loss of basal forebrain cholinergic neurons observed in AD.

Abnormal APP, cholinergic and cognitive function in Ts65Dn Down's model mice

We evaluated Ts65Dn Down's syndrome mice and their littermates (LM) at 1-2, 4, and 12 months of age to determine amyloid precursor protein (APP)-related cellular and biochemical changes associated with cognitive deficits. Ts65Dn mice showed cognitive deficits in the Morris water maze compared to LM mice at 4 and 12 months of age. Ts65Dn, but not LM mice, developed a septohippocampal cholinergic neuronal degeneration of choline acetyltransferase (ChAT)-positive neurons at 12 months of age. These cellular changes were compensated by increases in ChAT enzyme activity of remaining cholinergic terminals in the hippocampus. By 12 months of age, Ts65Dn mice had elevations of APP protein levels in the hippocampus compared to their LM. At this age, both Ts65Dn mice and their LM abnormally responded to cholinergic muscarinic M1 agonist treatment in terms of hippocampal APP, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) levels compared to young adult C57BL/6 mice. In summary, the Ts65Dn mice show developmental and progressive age-related behavioral deficits, hippocampal APP, and cholinergic pathology. The relatively better cognitive spatial performance in LM compared to Ts65Dn mice suggests that high APP levels combined with progressive degeneration of the cholinergic system are critical to the pathology and cognitive deficits seen in Ts65Dn mice.

Time course of behavioral changes following basal forebrain cholinergic damage in rats: Environmental enrichment as a therapeutic intervention

The present experiment was designed to study changes in behavior following immunolesioning of the basal forebrain cholinergic system. Rats were lesioned at 3 months of age by injection of the 192 IgG-saporin immunotoxin into the medial septum area and the nucleus basalis magnocellularis, and then tested at different times after surgery (from days 7-500) on a range of behavioral tests, administered in the following order: a nonmatching-to-position task in a T-maze, an object-recognition task, an object-location task, and an open-field activity test. The results revealed a two-way interaction between post-lesion behavioral testing time and memory demands. In the nonmatching-to-position task, memory deficits appeared quite rapidly after surgery, i.e. at a post-lesion time as short as 1 month. In the object-recognition test, memory impairments appeared only when rats were tested at late post-lesion times (starting at 15 months), whereas in the object-location task deficits were apparent at early post-lesion times (starting from 2 months). Taking the post-operative time into account, one can hypothesize that at the shortest post-lesion times, behavioral deficits are due to pure cholinergic depletion, while as the post-lesion time increases, one can speculate the occurrence of a non-cholinergic system decompensation process and/or a gradual degeneration process affecting other neuronal systems that may contribute to mnemonic impairments. Interestingly, when middle-aged rats were housed in an enriched environment, 192 IgG-saporin-lesioned rats performed better than standard-lesioned rats on both the nonmatching-to-position and the object-recognition tests. Environment enrichment had significant beneficial effects in 192 IgG-saporin-lesioned rats, suggesting that lesioned rats at late post-lesion times (over 1 year) still have appreciable cognitive plasticity.

Amyloid-beta deposition is associated with decreased hippocampal glucose metabolism and spatial memory impairment in APP/PS1 mice

In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double "Swedish" amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss.

Changes in cortical acetyl-CoA metabolism after selective basal forebrain cholinergic degeneration by 192IgG-saporin

The aim of the present study was to reveal whether reduced cortical cholinergic input affects the acetyl-CoA metabolism in cholinoceptive cortical target regions which may play a causative role for the deficits in cerebral glucose metabolism observed in Alzheimer's disease. The effect of cortical cholinergic denervation produced by a single intracerebroventricular application of the cholinergic immunotoxin 192IgG-saporin, on activities of pyruvate dehydrogenase and adenosine triphosphate (ATP)-citrate lyase as well as on the level of synaptoplasmic and mitochondrial acetyl-CoA and acetylcholine release in cortical target regions was studied. Cholinergic lesion produced 83%, 72% and 32% decreases in the activities of choline acetyltransferase, acetylcholinesterase and ATP-citrate lyase in nerve terminals isolated from rat brain cortex, respectively, but no change in pyruvate dehydrogenase activity. Spontaneous and Ca2+-evoked acetylcholine release from synaptosomes was inhibited by 76% and 73%, respectively, following immunolesion. The lesion-induced 39% decrease of acetyl-CoA level in synaptosomal mitochondria was accompanied by 74% increase in synaptoplasmic fraction. Levels of acetyl-CoA and CoASH assayed in fraction of whole brain mitochondria from lesioned cortex were 61% and 48%, respectively, higher as compared to controls. The data suggest a preferential localization of ATP-citrate lyase in cholinergic nerve terminals, where it may contribute to the transport of acetyl-CoA from the mitochondrial to the cytoplasmic compartment. They provide evidence on differential distribution of acetyl-CoA in subcellular compartments of cholinergic and non-cholinergic nerve terminals. There are also indications that cholinergic activity affects acetyl-CoA level and its intracellular distribution in glial and other non-cholinergic cortical cells.

Hippocampal gene expression profiling in spatial discrimination learning

Learning and long-term memory are thought to involve temporally defined changes in gene expression that lead to the strengthening of synaptic connections in selected brain regions. We used cDNA microarrays to study hippocampal gene expression in animals trained in a spatial discrimination-learning paradigm. Our analysis identified 19 genes that showed statistically significant changes in expression when comparing Nai;ve versus Trained animals. We confirmed the changes in expression for the genes encoding the nuclear protein prothymosin(alpha) and the delta-1 opioid receptor (DOR1) by Northern blotting or in situ hybridization. In additional studies, laser-capture microdissection (LCM) allowed us to obtain enriched neuronal populations from the dentate gyrus, CA1, and CA3 subregions of the hippocampus from Nai;ve, Pseudotrained, and spatially Trained animals. Real-time PCR examined the spatial learning specificity of hippocampal modulation of the genes encoding protein kinase B (PKB, also known as Akt), protein kinase C(delta) (PKC(delta)), cell adhesion kinase(beta) (CAK(beta), also known as Pyk2), and receptor protein tyrosine phosphatase(zeta/beta) (RPTP(zeta/beta)). These studies showed subregion specificity of spatial learning-induced changes in gene expression within the hippocampus, a feature that was particular to each gene studied. We suggest that statistically valid gene expression profiles generated with cDNA microarrays may provide important insights as to the cellular and molecular events subserving learning and memory processes in the brain.

Beta-amyloid and cholinergic neurons

It is generally accepted that the crucial events in the pathogeny of Alzheimer's disease (AD) are the increased accumulation of amyloidogenic peptides derived from amyloid precursor protein and the harmful actions of these peptides on neurons, which bring about neurodegeneration. The enhanced beta-amyloid accumulation is known to be caused by mutations of specific genes in patients who suffer from the familial (hereditary) form of AD but who represent just a minor group within the total population of AD patients. The reasons for beta-amyloid accumulation are not known in the much larger group of patients with the sporadic form of the disease. A biochemical feature common to either form of the disease is the preferential atrophy and degeneration of cholinergic neurons, which is probably responsible for much of the cognitive decline characteristic of the disease. We present an overview of recent investigations on the interactions between beta-amyloid and cholinergic neurons.

Changes in the septohippocampal cholinergic system following removal of molar teeth in the aged SAMP8 mouse

We investigated the effect of dysfunctional teeth on age-related changes in the septohippocampal cholinergic system by assessing acetylcholine (ACh) release and choline acetyltransferase (ChAT) activity in the hippocampus and ChAT immunohistochemistry in the medial septal nucleus and the vertical limb of the diagonal band in young-adult and aged SAMP8 mice after removal of their upper molar teeth (molarless condition). Aged molarless mice showed decreased ACh release and ChAT activity in the hippocampus and a reduced number of ChAT-immunopositive neurons in the medial septal nucleus compared to age-matched control mice, whereas these effects were not seen in young-adult mice. The results suggest that the molarless condition in aged SAMP8 mice may enhance an age-related decline in the septohippocampal cholinergic system.