A noncholinergic action of acetylcholinesterase (AChE) in the brain: from neuronal secretion to the generation of movement

Cholinergic dysfunction in isolated rapid eye movement sleep behaviour disorder links to impending phenoconversion

BACKGROUND AND PURPOSE

Most patients with isolated rapid eye movement sleep behaviour disorder (iRBD) progress to a parkinsonian alpha-synucleinopathy. However, time to phenoconversion shows great variation. The aim of this study was to investigate whether cholinergic and dopaminergic dysfunction in iRBD patients was associated with impending phenoconversion.

METHODS

Twenty-one polysomnography-confirmed iRBD patients underwent baseline 11C-donepezil and 6-Fluoro-(18F)-l-3,4-dihydroxyphenylalanine (18F-DOPA) positron emission tomography (PET). Potential phenoconversion was monitored for up to 8 years. PET images were analysed according to patients' diagnoses after 3 and 8 years using linear regression. Time-to-event analysis was made with Cox regression, dividing patients into low and high tracer uptake groups.

RESULTS

Follow-up was accomplished in 17 patients. Eight patients progressed to either Parkinson's disease (n = 4) or dementia with Lewy bodies (n = 4), while nine remained non-phenoconverters. Compared with non-phenoconverters, 8-year phenoconverters had lower mean 11C-donepezil uptake in the parietal (p = 0.032) and frontal cortex (p = 0.042), whereas mean 11C-donepezil uptake in 3-year phenoconverters was lower in the parietal cortex (p = 0.005), frontal cortex (p = 0.025), thalamus (p = 0.043) and putamen (p = 0.049). Phenoconverters within 3 years and 8 years had lower 18F-DOPA uptake in the putamen (p < 0.001). iRBD patients with low parietal 11C-donepezil uptake had a 13.46 (95% confidence interval 1.42;127.21) times higher rate of phenoconversion compared with those with higher uptake (p = 0.023). iRBD patients with low 18F-DOPA uptake in the most affected putamen were all phenoconverters with higher rate of phenoconversion (p = 0.0002).

CONCLUSIONS

These findings suggest that cortical cholinergic dysfunction, particularly within the parietal cortex, could be a biomarker candidate for predicting short-term phenoconversion in iRBD patients. This study aligns with previous reports suggesting dopaminergic dysfunction is associated with forthcoming phenoconversion.

Rodent Models of Alzheimer's Disease: Past Misconceptions and Future Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no effective treatments, not least due to the lack of authentic animal models. Typically, rodent models recapitulate the effects but not causes of AD, such as cholinergic neuron loss: lesioning of cholinergic neurons mimics the cognitive decline reminiscent of AD but not its neuropathology. Alternative models rely on the overexpression of genes associated with familial AD, such as amyloid precursor protein, or have genetically amplified expression of mutant tau. Yet transgenic rodent models poorly replicate the neuropathogenesis and protein overexpression patterns of sporadic AD. Seeding rodents with amyloid or tau facilitates the formation of these pathologies but cannot account for their initial accumulation. Intracerebral infusion of proinflammatory agents offer an alternative model, but these fail to replicate the cause of AD. A novel model is therefore needed, perhaps similar to those used for Parkinson's disease, namely adult wildtype rodents with neuron-specific (dopaminergic) lesions within the same vulnerable brainstem nuclei, 'the isodendritic core', which are the first to degenerate in AD. Site-selective targeting of these nuclei in adult rodents may recapitulate the initial neurodegenerative processes in AD to faithfully mimic its pathogenesis and progression, ultimately leading to presymptomatic biomarkers and preventative therapies.

The gene expression landscape of the human locus coeruleus revealed by single-nucleus and spatially-resolved transcriptomics

Norepinephrine (NE) neurons in the locus coeruleus (LC) make long-range projections throughout the central nervous system, playing critical roles in arousal and mood, as well as various components of cognition including attention, learning, and memory. The LC-NE system is also implicated in multiple neurological and neuropsychiatric disorders. Importantly, LC-NE neurons are highly sensitive to degeneration in both Alzheimer's and Parkinson's disease. Despite the clinical importance of the brain region and the prominent role of LC-NE neurons in a variety of brain and behavioral functions, a detailed molecular characterization of the LC is lacking. Here, we used a combination of spatially-resolved transcriptomics and single-nucleus RNA-sequencing to characterize the molecular landscape of the LC region and the transcriptomic profile of LC-NE neurons in the human brain. We provide a freely accessible resource of these data in web-accessible and downloadable formats.

Progression of brain cholinergic dysfunction in patients with isolated rapid eye movement sleep behavior disorder

BACKGROUND

Reduced cortical acetylcholinesterase activity, as measured by 11 C-donepezil positron emission tomography (PET), has been reported in patients with isolated rapid eye movement (REM) sleep behavior disorder (iRBD). However, its progression and clinical implications have not been fully investigated. Here, we explored the relationship between longitudinal changes in brain acetylcholinesterase activity and cognitive function in iRBD.

METHODS

Twelve iRBD patients underwent 11 C-donepezil PET at baseline and after 3 years. PET images were interrogated with statistical parametric mapping (SPM) and a regions of interest (ROI) approach. Clinical progression was assessed with the Movement Disorder Society-Unified Parkinson's Disease Rating Scale-Part III (MDS-UPDRS-III). Cognitive function was rated using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA).

RESULTS

From baseline to follow-up, the mean 11 C-donepezil distribution volume ratio (DVR) decreased in the cortex (p = 0.006), thalamus (p = 0.013), and caudate (p = 0.013) ROI. Despite no significant changes in the group mean MMSE or MoCA scores being observed, individually, seven patients showed a decline in their scores on these cognitive tests. Subgroup analysis showed that only the subgroup of patients with a decline in cognitive scores had a significant reduction in mean cortical 11 C-donepezil DVR.

CONCLUSIONS

Our results show that severity of brain cholinergic dysfunction in iRBD patients increases significantly over 3 years, and those changes are more severe in those with a decline in cognitive test scores.

[18F]FEOBV positron emission tomography may not be a suitable method to measure parasympathetic denervation in patients with Parkinson's disease

INTRODUCTION

The peripheral autonomic nervous system may be involved years before onset of motor symptoms in some patients with Parkinson's disease (PD). Specific imaging techniques to quantify the cholinergic nervous system in peripheral organs are an unmet need. We tested the hypothesis that patients with PD display decreased [¹⁸F]FEOBV uptake in peripheral organs - a sign of parasympathetic denervation.

METHODS

We included 15 PD patients and 15 age- and sex matched healthy controls for a 70 min whole-body dynamic positron emission tomography (PET) acquisition. Compartmental modelling was used for tracer kinetic analyses of adrenal gland, pancreas, myocardium, spleen, renal cortex, muscle and colon. Standard uptake values (SUV) at 60-70 min post injection were also extracted for these organs. Additionally, SUVs were also determined in the total colon, prostate, parotid and submandibular glands.

RESULTS

We found no statistically significant difference of [¹⁸F]FEOBV binding parameters in any organs between patients with PD and healthy controls, although trends were observed. The pancreas SUV showed a 14% reduction in patients (P = 0.021, not statistically significant after multiple comparison correction). We observed a trend towards lower SUVs in the pancreas, colon, adrenal gland, and myocardium of PD patients with versus without probable REM sleep behavior disorder.

CONCLUSION

[¹⁸F]FEOBV PET may not be a sensitive marker for parasympathetic degeneration in patients with PD.

Characterization of a Bioactive Peptide T14 in the Human and Rodent Substantia Nigra: Implications for Neurodegenerative Disease

The substantia nigra is generally considered to show significant cell loss not only in Parkinson's but also in Alzheimer's disease, conditions that share several neuropathological traits. An interesting feature of this nucleus is that the pars compacta dopaminergic neurons contain acetylcholinesterase (AChE). Independent of its enzymatic role, this protein is released from pars reticulata dendrites, with effects that have been observed in vitro, ex vivo and in vivo. The part of the molecule responsible for these actions has been identified as a 14-mer peptide, T14, cleaved from the AChE C-terminus and acting at an allosteric site on alpha-7 nicotinic receptors, with consequences implicated in neurodegeneration. Here, we show that free T14 is co-localized with tyrosine hydroxylase in rodent pars compacta neurons. In brains with Alzheimer's pathology, the T14 immunoreactivity in these neurons increases in density as their number decreases with the progression of the disease. To explore the functional implications of raised T14 levels in the substantia nigra, the effect of exogenous peptide on electrically evoked neuronal activation was tested in rat brain slices using optical imaging with a voltage-sensitive dye (Di-4-ANEPPS). A significant reduction in the activation response was observed; this was blocked by the cyclized variant of T14, NBP14. In contrast, no such effect of the peptide was seen in the striatum, a region lacking the T14 target, alpha-7 receptors. These findings add to the accumulating evidence that T14 is a key signaling molecule in neurodegenerative disorders and that its antagonist NBP14 has therapeutic potential.

In vivo vesicular acetylcholine transporter density in human peripheral organs: an [18F]FEOBV PET/CT study

Background

The autonomic nervous system is frequently affected in some neurodegenerative diseases, including Parkinson’s disease and Dementia with Lewy bodies. In vivo imaging methods to visualize and quantify the peripheral cholinergic nervous system are lacking. By using [¹⁸F]FEOBV PET, we here describe the peripheral distribution of the specific cholinergic marker, vesicular acetylcholine transporters (VAChT), in human subjects. We included 15 healthy subjects aged 53–86 years for 70 min dynamic PET protocol of peripheral organs. We performed kinetic modelling of the adrenal gland, pancreas, myocardium, renal cortex, spleen, colon, and muscle using an image-derived input function from the aorta. A metabolite correction model was generated from venous blood samples. Three non-linear compartment models were tested. Additional time-activity curves from 6 to 70 min post injection were generated for prostate, thyroid, submandibular-, parotid-, and lacrimal glands.

Results

A one-tissue compartment model generated the most robust fits to the data. Total volume-of-distribution rank order was: adrenal gland > pancreas > myocardium > spleen > renal cortex > muscle > colon. We found significant linear correlations between total volumes-of-distribution and standard uptake values in most organs.

Conclusion

High [¹⁸F]FEOBV PET signal was found in structures with known cholinergic activity. We conclude that [¹⁸F]FEOBV PET is a valid tool for estimating VAChT density in human peripheral organs. Simple static images may replace kinetic modeling in some organs and significantly shorten scan duration.

Clinical Trial Registration Trial registration: NCT, NCT03554551. Registered 31 May 2018. https://clinicaltrials.gov/ct2/show/NCT03554551?term=NCT03554551&draw=2&rank=1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00889-9.

Study protocol of the DUtch PARkinson Cohort (DUPARC): a prospective, observational study of de novo Parkinson's disease patients for the identification and validation of biomarkers for Parkinson's disease subtypes, progression and pathophysiology

Background

Parkinson’s Disease (PD) is a heterogeneous, progressive neurodegenerative disorder which is characterized by a variety of motor and non-motor symptoms. To date, no disease modifying treatment for PD exists. Here, the study protocol of the Dutch Parkinson Cohort (DUPARC) is described. DUPARC is a longitudinal cohort study aimed at deeply phenotyping de novo PD patients who are treatment-naïve at baseline, to discover and validate biomarkers for PD progression, subtypes and pathophysiology.

Methods/design

DUPARC is a prospective cohort study in which 150 de novo PD subjects will be recruited through a collaborative network of PD treating neurologists in the northern part of the Netherlands (Parkinson Platform Northern Netherlands, PPNN). Participants will receive follow-up assessments after 1 year and 3 years, with the intention of an extended follow-up with 3 year intervals. Subjects are extensively characterized to primarily assess objectives within three major domains of PD: cognition, gastrointestinal function and vision. This includes brain magnetic resonance imaging (MRI); brain cholinergic PET-imaging with fluoroethoxybenzovesamicol (FEOBV-PET); brain dopaminergic PET-imaging with fluorodopa (FDOPA-PET); detailed neuropsychological assessments, covering all cognitive domains; gut microbiome composition; intestinal wall permeability; optical coherence tomography (OCT); genotyping; motor and non-motor symptoms; overall clinical status and lifestyle factors, including a dietary assessment; storage of blood and feces for additional analyses of inflammation and metabolic parameters. Since the start of the inclusion, at the end of 2017, over 100 PD subjects with a confirmed dopaminergic deficit on FDOPA-PET have been included.

Discussion

DUPARC is the first study to combine data within, but not limited to, the non-motor domains of cognition, gastrointestinal function and vision in PD subjects over time. As a de novo PD cohort, with treatment naïve subjects at baseline, DUPARC provides a unique opportunity for biomarker discovery and validation without the possible confounding influences of dopaminergic medication.

Trial registration

NCT04180865; registered retrospectively, November 28th 2019.

Regional vesicular acetylcholine transporter distribution in human brain: A [18 F]fluoroethoxybenzovesamicol positron emission tomography study

Prior efforts to image cholinergic projections in human brain in vivo had significant technical limitations. We used the vesicular acetylcholine transporter (VAChT) ligand [¹⁸ F]fluoroethoxybenzovesamicol ([¹⁸ F]FEOBV) and positron emission tomography to determine the regional distribution of VAChT binding sites in normal human brain. We studied 29 subjects (mean age 47 [range 20-81] years; 18 men; 11 women). [¹⁸ F]FEOBV binding was highest in striatum, intermediate in the amygdala, hippocampal formation, thalamus, rostral brainstem, some cerebellar regions, and lower in other regions. Neocortical [¹⁸ F]FEOBV binding was inhomogeneous with relatively high binding in insula, BA24, BA25, BA27, BA28, BA34, BA35, pericentral cortex, and lowest in BA17-19. Thalamic [¹⁸ F]FEOBV binding was inhomogeneous with greatest binding in the lateral geniculate nuclei and relatively high binding in medial and posterior thalamus. Cerebellar cortical [¹⁸ F]FEOBV binding was high in vermis and flocculus, and lower in the lateral cortices. Brainstem [¹⁸ F]FEOBV binding was most prominent at the mesopontine junction, likely associated with the pedunculopontine-laterodorsal tegmental complex. Significant [¹⁸ F]FEOBV binding was present throughout the brainstem. Some regions, including the striatum, primary sensorimotor cortex, and anterior cingulate cortex exhibited age-related decreases in [¹⁸ F]FEOBV binding. These results are consistent with prior studies of cholinergic projections in other species and prior postmortem human studies. There is a distinctive pattern of human neocortical VChAT expression. The patterns of thalamic and cerebellar cortical cholinergic terminal distribution are likely unique to humans. Normal aging is associated with regionally specific reductions in [¹⁸ F]FEOBV binding in some cortical regions and the striatum.

Oxidative stress and autonomic nervous system functions in restless legs syndrome

BACKGROUND

Oxidative stress has been implicated in over 100 disorders in recent years; however, the situation in restless legs syndrome (RLS) has not been studied yet.

METHODS

Fifty patients with RLS not medicated for RLS and 50 sex- and age-matched, healthy controls and controls with no pathology except mild iron deficiency or iron deficiency anaemia were enrolled. Patients with secondary RLS other than iron deficiency were excluded. Total oxidant status (TOS), total antioxidant status (TAS), oxidative stress index (OSI), arylesterase (ARE), paraoxonase (PON), stimulated paraoxonase (stim-PON), lipid hydroperoxides (LOOHs), acetyl cholinesterase (AChE) and butyryl cholinesterase (BuChE) were measured. Heart rate variability (HRV) analysis was performed.

RESULTS

TOS, ARE and AChE were increased (P = 0·018, P < 0·001 and P < 0·001, respectively), whereas LOOHs were decreased (P < 0·001) in RLS group. TAS, OSI, PON and stim-PON were comparable. Erythrocyte sedimentation rate (ESR) and mean platelet volume (MPV) were increased (P = 0·021 and P = 0·037, respectively) in RLS group. HRV triangular index (HRVi) was lower (P = 0·012) in RLS group. Other HRV parameters were similar.

CONCLUSIONS

Increased AChE and decreased LOOHs, which were influenced by increased PON1, were considered as indicators of efforts towards the protection of dopaminergic activity in central nervous system in RLS group. Increased ESR, MPV and low HRVi indicate elevated sympathetic activity in RLS group. Elevated sympathetic activity might be beneficial in relieving RLS symptoms, also causing increases in TOS. The evidence we found regarding oxidative stress and autonomic nervous system might be seminal in RLS treatment.

Co-localization of PRiMA with acetylcholinesterase in cholinergic neurons of rat brain: an immunocytochemical study

In the central nervous system, acetylcholinesterase (AChE) is present in a tetrameric form that is anchored to membranes via a proline-rich membrane anchor (PRiMA). Previously it has been found that principal cholinergic neurons in the brain express high concentrations of AChE enzymic activity at their neuronal membranes. The aim of this study was to use immunocytochemical methods to determine the distribution of PRiMA in these neurons in the rat brain. Confocal laser and electron microscopic investigations showed that PRiMA immunoreactivity is associated with the membranes of the somata, dendrites and axons of cholinergic neurons in the basal forebrain, striatum and pedunculopontine nuclei, i.e. the neurons that innervate forebrain and brainstem structures. In these neurones, PRiMA also co-localizes with AChE immunoreactivity at the plasma membrane. PRiMA label was absent from neighboring GABAergic neurons, and from other neurons of the brain known to express high levels of AChE enzymic activity including cranial nerve motor neurons and dopaminergic neurons of the substantia nigra zona compacta. A strong association of AChE with PRiMA at the plasma membrane is therefore a feature specific to principal cholinergic neurons that innervate the central nervous system.

Impact of detergents on the activity of acetylcholinesterase and on the effectiveness of its inhibitors

Acetylcholinesterase (AChE) plays a central role in the development of Alzheimer's disease: AChE inhibition for preventing the characteristic dwindling of acetylcholine levels constitutes the current standard treatment for the disorder. Amongst the diverse risk factors contributing to the degenerative process, high cholesterol causes a reduction in the effectiveness of the otherwise therapeutic inhibitors of AChE. Our biochemical study on the activity of AChE elucidates the effect of amphiphilic molecules on the activity and kinetics of AChE, and sheds light onto the nature of the impact of these amphiphilic molecules on enzyme-inhibitor interactions. Using kinetic studies we discovered that detergents alter the enzymatic activity of AChE through an uncompetitive mechanism. Additional experiments using AChE inhibitors (amphiphilic procaine hydrochloride, hydrophobic tetrabutylammonium bromide) in the absence or presence of detergent further illustrate the detergent-enzyme-solvent interactions. The results contribute to the understanding of the importance of hydrophobic-lipophilic interactions for the correct function of AChE and its inhibitors. We present a model system for the study of lipid-related alterations in the activity of isolated AChE in the central nervous system. This model may also be used to assess and predict the effectiveness of AChE inhibitors, which are traditionally used for the treatment of cognitive impairment, under pathological (high-cholesterol) conditions.

Cholinergic dysfunction in temporal lobe epilepsy

The entorhinal cortex-hippocampus complex is believed to be the site of origin of seizure activity in the majority of patients with temporal lobe epilepsy (TLE). Both these regions are enriched with cholinergic innervation, which plays a key role in the normal control of neuronal excitability and in higher cognitive processes. In TLE, anatomical and functional changes occur in all cellular components of the local neural circuit. Thus, while it is not surprising that cholinergic functions are altered in the epileptic temporal lobe, the exact nature and role of these changes in the pathogenesis of the disease are not known. In this report, we summarize the scientific background and experimental data supporting a "cholinergic hypothesis of TLE." We conclude that while the exact role of cholinergic dysfunction in TLE is not known, there is a firm basis for suggesting that changes in the expression of key cholinergic proteins-and the associated cholinergic dysfunction-are key factors in the basic mechanisms underlying TLE.

Morphine-induced place preference: Involvement of cholinergic receptors of the ventral tegmental area

In the present study, the effects of intra-ventral tegmental area injections of cholinergic agents on morphine-induced conditioned place preference were investigated by using an unbiased 3-day schedule of place conditioning design in rats. The conditioning treatments with subcutaneous injections of morphine (0.5-7.5 mg/kg) induced a significant dose-dependent conditioned place preference for the drug-associated place. Intra-ventral tegmental area injection of an anticholinesterase, physostigmine (2.5 and 5 microg/rat) or nicotinic acetylcholine receptor agonist, nicotine (0.5 and 1 microg/rat) with an ineffective dose of morphine (0.5 mg/kg) elicited a significant conditioned place preference. Furthermore, intra-ventral tegmental area administration of muscarinic acetylcholine receptor antagonist, atropine (1-4 microg/rat) or nicotinic acetylcholine receptor antagonist, mecamylamine (5 and 7.5 microg/rat) dose-dependently inhibited the morphine (5 mg/kg)-induced place preference. Atropine or mecamylamine reversed the effect of physostigmine or nicotine on morphine response respectively. The injection of physostigmine, but not atropine, nicotine or mecamylamine, into the ventral tegmental area alone produced a significant place aversion. Moreover, intra-ventral tegmental area administration of the higher doses of physostigmine or atropine, but not nicotine or mecamylamine decreased the locomotor activity. We conclude that muscarinic and nicotinic acetylcholine receptors in the ventral tegmental area may critically mediate the rewarding effects of morphine.

Termination and beyond: acetylcholinesterase as a modulator of synaptic transmission

Termination of synaptic transmission by neurotransmitter hydrolysis is a substantial characteristic of cholinergic synapses. This unique termination mechanism makes acetylcholinesterase (AChE), the enzyme in charge of executing acetylcholine breakdown, a key component of cholinergic signaling. AChE is now known to exist not as a single entity, but rather as a combinatorial complex of protein products. The diverse AChE molecular forms are generated by a single gene that produces over ten different transcripts by alternative splicing and alternative promoter choices. These transcripts are translated into six different protein subunits. Mature AChE proteins are found as soluble monomers, amphipatic dimers, or tetramers of these subunits and become associated to the cellular membrane by specialized anchoring molecules or members of other heteromeric structural components. A substantial increasing body of research indicates that AChE functions in the central nervous system go far beyond the termination of synaptic transmission. The non-enzymatic neuromodulatory functions of AChE affect neurite outgrowth and synaptogenesis and play a major role in memory formation and stress responses. The structural homology between AChE and cell adhesion proteins, together with the recently discovered protein partners of AChE, predict the future unraveling of the molecular pathways underlying these multileveled functions.

Review of Growth Inhibitory Peptide as a biotherapeutic agent for tumor growth, adhesion, and metastasis

This review surveys the biological activities of an alpha-fetoprotein (AFP) derived peptide termed the Growth Inhibitory Peptide (GIP), which is a synthetic 34 amino acid segment produced from the full length 590 amino acid AFP molecule. The GIP has been shown to be growth-suppressive in both fetal and tumor cells but not in adult terminally-differentiated cells. The mechanism of action of this peptide has not been fully elucidated; however, GIP is highly interactive at the plasma membrane surface in cellular events such as endocytosis, cell contact inhibition and cytoskeleton-induced cell shape changes. The GIP was shown to be growth-suppressive in nine human tumor types and to suppress the spread of tumor infiltrates and metastases in human and mouse mammary cancers. The AFP-derived peptide and its subfragments were also shown to inhibit tumor cell adhesion to extracellular matrix (ECM) proteins and to block platelet aggregation; thus it was expected that the GIP would inhibit cell spreading/migration and metastatic infiltration into host tissues such as lung and pancreas. It was further found that the cyclic versus linear configuration of GIP determined its biological and anti-cancer efficacy. Genbank amino acid sequence identities with a variety of integrin alpha/beta chain proteins supported the GIP's linkage to inhibition of tumor cell adhesion and platelet aggregation. The combined properties of tumor growth suppression, prevention of tumor cell-to-ECM adhesion, and inhibition of platelet aggregation indicate that tumor-to-platelet interactions present promising targets for GIP as an anti-metastatic agent. Finally, based on cholinergic studies, it was proposed that GIP could influence the enzymatic activity of membrane acetylcholinesterases during tumor growth and metastasis. It was concluded that the GIP derived from full-length AFP represents a growth inhibitory motif possessing instrinsic properties that allow it to interfere in cell surface events such as adhesion, migration, metastasis, and aggregation of tumor cells.

Differential localization of acetylcholinesterase in neuronal and non-neuronal cells

Acetylcholinesterase (AChE) expression is regulated in cell types at the transcriptional and translational levels. In this study, we characterized and compared AChE catalytic activity, mRNA, protein expression, and protein localization in a variety of neuronal (SH-SY5Y neuroblastoma and primary cerebellar granule neurons (CGN)) and non-neuronal (LLC-MK2, HeLa, THP-1, and primary astrocytes) cell types. All cell lines expressed AChE catalytic activity; however the levels of AChE-specific activity were higher in neuronal cells than in the non-neuronal cell types. CGN expressed significantly more AChE activity than SH-SY5Y cells. All cell lines analyzed expressed AChE protein at equivalent levels, as well as mRNA splice variants. Localization of AChE was characterized by immunofluorescence and confocal microscopy. SH-SY5Y, CGN, and nerve-growth factor-differentiated PC-12 cells exhibited a pattern of AChE localization characterized as diffuse in the cytoplasm and punctate staining along neurites and on the plasma membrane. The localization in HeLa, LLC-MK2, fibroblasts, and undifferentiated PC-12 cells was significantly different than in neuronal cells-AChE was intensely localized in the perinuclear region, without staining near or on the plasma membrane. Based on the evidence presented here, we hypothesize that the presence of AChE protein doesn't correlate with catalytic activity, and the diffuse cytoplasmic and plasma membrane localization of AChE is a property of neuronal cell types.

Characterization of acetylcholinesterase expression and secretion during osteoblast differentiation

Although best known for its role in cholinergic signalling, a substantial body of evidence suggests that acetylcholinesterase (AChE) has multiple biological functions. Previously, we and others identified AChE expression in areas of bone that lacked expression of other neuronal proteins. More specifically, we identified AChE expression at sites of new bone formation suggesting a role for AChE as a bone matrix protein. We have now characterised AChE expression, secretion and adhesive function in osteoblasts. Using Western blot analysis, we identified expression of two AChE species in osteoblastic cells, a major species of 68 kDa and less abundant species of approximately 55 kDa. AChE colocalised with the Golgi apparatus in osteoblastic cells and was identified in osteoblast-conditioned medium. Further analyses revealed differentiation-dependent secretion by osteoblasts, with AChE secretion levels corresponding with alkaline phosphatase activity. AChE expression by osteoblastic cells was also found to be regulated by mechanical strain both in vitro and in vivo. Finally, we investigated the possibility of a functional role for AChE in osteoblast adhesion. Using specific inhibitors, blockade of sites thought to be responsible for AChE adhesive properties caused a concentration-dependent decrease in osteoblastic cell adhesion, suggesting that AChE is involved in regulating cell-matrix interactions in bone.

Postnatal development of the basolateral complex of rabbit amygdala: a stereological and histochemical study

The aim of the study was to estimate developmental changes in the rabbit basolateral complex (BLC) by stereological and histochemical methods. Material consisted of 45 brains of New Zealand rabbits (aged from 2 to 180 days, P2 to P180) of both sexes, divided into nine groups. The following parameters were estimated: volume of the cerebral hemisphere; volume of the whole BLC and of particular BLC nuclei; neuronal density and total number of neurons in these nuclei. Developmental changes in acetylcholinesterase (AChE) activity in the BLC were also examined. The volume of the cerebral hemisphere increased until P30, whereas volumes of nuclei increased for longer--until P90. The density of neurons in all nuclei studied reached the level characteristic for an adult animal at about P30. The total number of neurons in the dorsolateral division of the lateral nucleus (Ldl) stabilized the earliest--between P30 and P60, whereas in the ventromedial division of the lateral nucleus (Lvm), basomedial (BM) and basolateral (BL) nuclei the number stabilized later--between P60 and P90. AChE activity appears minimal in the BLC on P2, reaches a maximum on P30 and then decreases to the level characteristic of an adult animal on P60. AChE activity was greater in BL than in other nuclei in all age groups. Reaching adult AChE activity 1 month earlier than the total number of neurons in the BLC may indicate a role of the cholinergic system in BLC maturation.

Axon terminals possessing α2C-adrenergic receptors densely innervate neurons in the rat lateral spinal nucleus which respond to noxious stimulation

The lateral spinal nucleus (LSN) in the rat spinal cord contains projection neurons that are densely innervated by peptidergic varicosities which probably originate from spinal interneurons. The alpha2C-adrenoceptor (alpha2C-AR) is present on axon terminals in this nucleus and therefore norepinephrine is likely to modulate input to LSN neurons. We investigated the involvement of LSN neurons in nociceptive transmission and their relationship with axons that possess alpha2C-ARs. Double-labeling immunostaining experiments showed that alpha2C-ARs are present on axon terminals of excitatory and inhibitory interneurons that frequently contain colocalised peptides. Electron microscopy revealed that alpha2C-AR terminals are presynaptic to dendrites and somata of LSN neurons and predominantly form asymmetric synapses. We retrogradely labeled LSN neurons that project to the caudal ventrolateral medulla and combined this with induction of c-Fos expression by peripheral noxious thermal stimulation along with immunolabelling for the alpha2C-AR and the substance P (neurokinin-1) receptor. This enabled us to identify neuronkinin-1 projection neurons in the LSN that express c-Fos and to determine if such cells receive contacts from alpha2C-AR terminals. The results show that some LSN neurons are activated by noxious stimulation and that this input is likely to be modulated by norepinephrine acting on alpha2C-ARs which are present on axon terminals that are presynaptic to LSN neurons.

Brain cholinesterases: II. The molecular and cellular basis of Alzheimer's disease

Currently available evidence demonstrates that cholinesterases (ChEs), owing to their powerful enzymatic and non-catalytic actions, unusually strong electrostatics, and exceptionally ubiquitous presence and redundancy in their capacity as the connector, the organizer and the safeguard of the brain, play fundamental role(s) in the well-being of cells, tissues, animal and human lives, while they present themselves adequately in quality and quantity. The widespread intracellular and extracellular membrane networks of ChEs in the brain are also subject to various insults, such as aging, gene anomalies, environmental hazards, head trauma, excessive oxidative stress, imbalances and/or deficits of organic constituents. The loss and the alteration of ChEs on the outer surface membranous network may initiate the formation of extracellular senile plaques and induce an outside-in cascade of Alzheimer's disease (AD). The alteration in ChEs on the intracellular compartments membranous network may give rise to the development of intracellular neurofibrillary tangles and induce an inside-out cascade of AD. The abnormal patterns of glycosylation and configuration changes in ChEs may be reflecting their impaired metabolism at the molecular and cellular level and causing the enzymatic and pharmacodynamical modifications and neurotoxicity detected in brain tissue and/or CSF of patients with AD and in specimens in laboratory experiments. The inflammatory reactions mainly arising from ChEs-containing neuroglial cells may facilitate the pathophysiologic process of AD. It is proposed that brain ChEs may serve as a central point rallying various hypotheses regarding the etio-pathogenesis of AD.

Functional Development of Oligodendrocytes and Open-field Behavior in Developing Rats: An Approach Using Monoclonal Antibody to Immature Oligodendrocytes

To examine the relation between functional development of oligodendrocytes and open-field behavior during the postnatal period, a mouse monoclonal antibody termed 14F7, which predominantly labels stage-specific immature oligodendrocytes, was employed. Antibody 14F7 was administered intraperitoneally into male pups on day 3 and 4 after birth. The open-field test was performed on days 12 and 18 of the postnatal period. Horizontal activity increased remarkably with the growth of pups. On day 18, horizontal activity in the group with 14F7 was significantly higher than the control, while there was no significant difference between treatments on day 12. In contrast to the horizontal activity, the frequency of hind leg rearing, vertical activity, in the group with 14F7 was significantly lower than that in the control. On day 12, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in the cerebral cortex were similar between the groups. These activities increased with the growth of pups in both groups. In the 14F7 group on day 18, ChAT activity was the same as the control, whereas AChE activity was significantly lower compared with the control. These results suggest that neonatal exposure to 14F7 induces abnormal neurotransmission by reducing the degradation of acetylcholine and alters the spontaneous activities in developing rats.

Effect of bupivacaine application on cholinesterase activities, total protein- and albumin concentration in serum and cerebrospinal fluid

The rationale of this study was to determine whether Bupivacaine used for spinal anesthesia alters the specific secretory activity of nerve cells and/or the function of the blood/cerebrospinal fluid barrier. Four groups were assessed: (1) patients undergoing spinal anesthesia using Bupivacaine for lower limb surgery, (2) spinal Bupivacaine anesthesia without subsequent surgery, (3) local facet joint infiltration using Bupivacaine, and (4) general anesthesia for lower limb surgery without Bupivacaine application. Cholinesterase activities, total protein- and albumin concentrations in serum as well as in cerebrospinal fluid were significantly decreased after surgical intervention under spinal Bupivacaine anesthesia but remained unchanged following spinal Bupivacaine application without surgery. No significant correlation was found between Bupivacaine dosage and parameter alteration. There was no influence of intrathecal Bupivacaine application on the albumin ratio cerebrospinal fluid/serum, nor was there any significant alteration of total protein- or albumin concentrations and butyrylcholinesterase activity in the serum as a result of local injection of Bupivacaine to facet joints. These serum parameters were reduced after surgery under general anesthesia. Alterations of serum- and cerebrospinal fluid parameters investigated after surgery are not related to Bupivacaine application but to effects linked to operative treatment, i.e. suppressed secretory cell activity or protein depletion owing to blood loss. We conclude that the secretory function of cholinesterase-releasing nerve cells is not affected by spinal application of Bupivacaine. The blood/cerebrospinal fluid barrier remains intact.

Bioactivity of a peptide derived from acetylcholinesterase: electrophysiological characterization in guinea-pig hippocampus

Acetylcholinesterase is well known to have noncholinergic functions. Only recently, however, has the salient part been identified of the molecule responsible for these nonclassical actions, a peptide of 14 amino acids towards the C-terminus of acetylcholinesterase. The aim of this study was to test the bioactivity of this 'acetylcholinesterase-peptide' using intracellular recordings in guinea-pig hippocampal slices. In the presence of tetrodotoxin, acetylcholinesterase-peptide alone affected neither the membrane potential nor the input resistance of CA1 neurons; however, a modulatory action was observed, as a concentration-dependent decrease of N-methyl-d-aspartic acid-induced depolarization. When calcium potentials were elicited by a depolarizing current pulse, application of acetylcholinesterase-peptide increased or reduced the degree of calcium spike firing in, respectively, the presence or absence of the N-methyl-d-aspartic acid antagonist d(-)-2-amino-5-phosphonopentanoic acid. In contrast, a peptide derived from the equivalent region of butyrylcholinesterase, which also hydrolyses acetylcholine, had no effect. In conclusion, acetylcholinesterase-peptide has a selective bioactivity in the hippocampus; it could thus offer new ways of targeting mechanisms of calcium-induced neurotoxicity.

Alternative acetylcholinesterase molecular forms exhibit similar ability to induce neurite outgrowth

Several groups have reported that acetylcholinesterase (AChE), through a mechanism not involving its catalytic activity, may have a role in fiber elongation. These observations were performed on experimental systems in which acetylcholine synthesis was active. Because neurite outgrowth can be modulated by neurotransmitters, we used the N18TG2 neuroblastoma line, which is defective for neurotransmitter production, to evaluate whether AChE may modulate neurite sprouting in nonenzymatic ways. To avoid the possibility that differences between transfected and mock-transfected clones may be due to the selection procedure, N18TG2 cells were previously subcloned, and the FB5 subclone was used for transfections. We performed transfections of FB5 cells with three distinct constructs encoding for the glycosylphosphoinositol-anchored AChE form, the tetrameric AChE form, and a soluble monomeric AChE form truncated in its C-terminus. A morphometric analysis of retinoic acid-differentiated clones was also undertaken. The results revealed that higher AChE expression following transfection brings about a greater ability of the clones to grow fibers with respect to nontransfected or mock-transfected cells irrespective of the used construct. Having observed no differences between the morphology of the transfected clones, we tested the possibility that the culture substrate can affect the capability of the clones to extend fibers. Also in this case we revealed no differences between the clones cultured on uncoated or collagen-pretreated dishes. These data indicate that alternative AChE molecular forms that differ in their C-teminal region exhibit similar ability to induce fiber outgrowth and suggest that the protein region responsible for this role is located in the invariant portion of the AChE molecule.

A non-cholinergic, trophic action of acetylcholinesterase on hippocampal neurones in vitro: molecular mechanisms

In this study neurite outgrowth from cultured hippocampal neurones was increased by addition of acetylcholinesterase acting in a non-cholinergic manner. Only monomeric acetylcholinesterase, a form of acetylcholinesterase dominant in development, increased neurite outgrowth (3-10 U/ml); moreover this effect was not blocked by active site blockers (echothiophate and galanthamine) but was sensitive to the addition of peripheral site blockers (fasciculin and BW284c51). It appears therefore that acetylcholinesterase has alternative, non-cholinergic functions, one of which could be in development, via a peripheral site. The possibility of a causal relationship between neurite outgrowth and calcium influx was explored using a spectrum of acetylcholinesterase variants, inhibitors and calcium channel blockers. Acetylcholinesterase regulation of outgrowth was shown to depend on an influx of extracellular calcium specifically via the L-type voltage-gated calcium channel. In summary, we propose that, independent of its catalytic activity, a selective form of acetylcholinesterase has a role in the development of hippocampal neurones via a selective voltage-gated calcium channel.

Behavioural correlates of the release and subsequent action of acetylcholinesterase secreted in the substantia nigra

Acetylcholinesterase is secreted in the central nervous system (independently of cholinergic transmission) in a non-classic, non-enzymatic capacity. A light-emitting reaction has recently been established that demonstrates release of this protein from the substantia nigra of a guinea pig with a temporal resolution corresponding to real time, i.e. 'on-line'. In this study the technique has been applied to investigate the significance of this novel phenomenon in the generation of specific types of movement. During locomotion a 'pulsatile' release of acetylcholinesterase occurs much more frequently than in other situations. However, these pulses of released acetylcholinesterase are of shorter duration than the respective periods of locomotion that caused them. Furthermore, as episodes of movement are repeated, the release of acetylcholinesterase becomes less likely. These observations suggest that the phenomenon does not simply reflect ongoing movement. Indeed, chewing behaviour is frequently initiated when acetylcholinesterase release occurs during locomotor activity. Hence, acetylcholinesterase released in association with locomotion may favour the onset of further types of movement.

Three-dimensional mapping of cholinergic molecules by confocal laser scanning microscopy in sea urchin larvae

Confocal laser scanning microscopy (CLSM) was used to examine molecules related to the cholinergic neurotransmission system and detected at all the larval stages of Paracentrotus lividus, by histochemical and immunohistochemical methods. CLSM, providing spatial resolution of the cells located both at the larval surface and at depth, allows a complete mapping in a three-dimensional volumetric frame. At early larval stages acetylcholinesterase- as well as choline acetyltransferase-like molecules were found mainly in the gut wall cells, and along the ciliary bands of the arms, together with muscarinic acetylcholine receptors. At perimetamorphic stages, cholinergic molecules were present in the ciliate strands along the arms, in the larval body and in the rudiment. At metamorphosis, positivity to cholinergic molecules translocated to the juvenile, where a high frequency of mAChR- and ChAT-like positive cells was found.

Identification of hybrid cholinesterase forms consisting of acetyl- and butyrylcholinesterase subunits in human glioma

Brain and non-brain tumors contain acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) transcripts and enzyme activity. AChE and BuChE occur in tissues as a set of molecular components, whose distribution in a cyst fluid from a human astrocytoma we investigated. The fluid displayed high BuChE and low AChE activities. Three types of cholinesterase (ChE) tetramers were identified in the fluid by means of sedimentation analyses and assays with specific inhibitors, and their sedimentation coefficients were 11.7S (ChE-I), 11.1S (ChE-II), and 10.5S (ChE-III). ChE-I was unretained, ChE-II was weakly retained and ChE-III was adsorbed to edrophonium-agarose, confirming the AChE nature of the latter. ChE-I and ChE-II tetramers contained BuChE subunits as shown by their binding with an antiserum against BuChE. The ChE activity of the immunocomplexes made with ChE-II and anti-BuChE antibodies decreased with the AChE inhibitor BW284c51, revealing that ChE-II was made of AChE and BuChE subunits, in contrast to ChE-I, which only contained BuChE subunits. The binding of an anti-AChE antibody (AE1) to ChE-II and ChE-III, but not to ChE-I, demonstrated the hybrid composition of ChE-II. A substantial fraction of the AChE tetramers and dimers of astrocytomas and oligodendrogliomas bound both to anti-AChE and anti-BuChE antibodies, which revealed a mixed composition of AChE and BuChE subunits in them. The AChE components of brain, meningiomas and neurinomas were only recognized by AE1. In conclusion, our results demonstrate that aberrant ChE oligomers consisting of AChE and BuChE subunits are generated in astrocytomatous cyst and gliomas but not in brain, meningiomas or neurinomas.

Butyrylcholinesterase in lumbar and ventricular cerebrospinal fluid

OBJECTIVES

This study establishes reference data for human lumbar CSF butyrylcholinesterase (E.C.3.1.1.8.) activity and investigates the enzyme activity in ventricular CSF. We comment on the relationship between CSF butyrylcholinesterase activity and other laboratory parameters.

SUBJECTS AND METHODS

We investigated 64 lumbar CSF samples obtained from a clinically healthy population and 169 ventricular CSF samples collected from 90 neurosurgical patients.

RESULTS

The reference range we recommend for lumbar CSF butyrylcholinesterase activity is 5.4 to 17.0 nmol/min x ml. The majority of ventricular butyrylcholinesterase activities in our patient subset ranged up to 5 nmol/min x ml.

CONCLUSIONS

We established the relative influence of serum and CNS components on total CSF butyrylcholinesterase activity. The CNS fraction predominates the total butyrylcholinesterase activity in normal lumbar CSF. In ventricular CSF enzyme influx from serum outweighs the CNS component.

Acetylcholinesterase in lumbar and ventricular cerebrospinal fluid

BACKGROUND

Soluble acetylcholinesterase (AChE, E.C. 3.1.1.7.) is released by neurons, glial and meningeal cells into the CSF. AChE activity in cerebrospinal fluid (CSF) is altered in various disorders of the nervous system. The objects of this study are to define a reference range for CSF AChE activity in human lumbar CSF, to prove that the enzyme activity does not depend on the blood/CSF barrier function, and to provide information about AChE in ventricular CSF. In addition, drugs used in neurosurgical care have been examined for their in vitro effects on CSF AChE activity to exclude interference with the test system.

METHODS

We tested the AChE activity in 64 lumbar CSF samples collected from a clinically healthy population and in 169 ventricular CSF samples obtained from 90 neurosurgical patients. AChE activity was assayed with our inhibitor-free test procedure.

RESULTS

The reference range determined for lumbar CSF AChE activity is 9.2-24.4 nmol/min per ml. Lumbar CSF AChE activity does not correlate with parameters characterising the status of the blood/CSF barrier. Ventricular puncture is only justified for underlying pathology making it impossible to provide reference data for ventricular CSF. Most measurements reveal ventricular enzyme activity below 4 nmol/min per ml.

CONCLUSION

The results of this study suggest the utility of lumbar CSF AChE activity as a measure of specific secretory function in enzyme releasing cells of the nervous system.

Absence of cholinergic sympathetic innervation from limb muscle vasculature in rats and mice

Although the existence of cholinergic sympathetic vasodilatory innervation in limb muscle vasculature is well established for some species, previous pharmacological studies have failed to reveal the presence of such innervation in rats. Recently, Schafer and colleagues [Schafer, M.K., Eiden, L.E., Weihe, E., 1998. Cholinergic neurons and terminal fields revealed by immunohistochemistry for the vesicular acetylcholine transporter. II. The peripheral nervous system. Neuroscience 84(2), 361-376] reported that vesicular acetylcholine transporter immunoreactivity (VAChT-IR), a marker for cholinergic terminals, is present in the innervation of the microvasculature of rat hindlimb skeletal muscle and concluded that rats possess cholinergic sympathetic innervation of limb muscle vasculature. Because of our interest in identifying targets of cholinergic sympathetic neurons, we have analyzed the transmitter properties of the innervation of muscle vessels in rat and mouse limbs. We found that the innervation of vasculature in muscle is noradrenergic, exhibiting robust catecholamine histofluorescence and immunoreactivity for tyrosine hydroxylase (TH) and the peptide transmitters, neuropeptide Y (NPY) and occasionally vasoactive intestinal peptide (VIP). In contrast, cholinergic phenotypic markers,VAChT-IR and acetylcholinesterase (AChE) activity, are absent. Neuron cell bodies in sympathetic ganglia, retrogradely labeled with injections of tracer into limb muscles, also lacked VAChT but contained TH-IR. The innervation of large extramuscular feed arteries in hindlimbs was also devoid of cholinergic markers, as were the cell bodies of sympathetic neurons innervating extramuscular femoral arteries. These results, like those of previous physiological studies, provide no evidence for the presence of cholinergic sympathetic innervation of muscle vasculature in rats or mice.

Chronic, low-level exposure to the cholinesterase inhibitor DFP. II. Time course of behavioral state changes in rats

Rats were repeatedly administered with low doses of diisopropylfluorophosphate (DFP; 0.2 mg/kg/day, SC), an irreversible cholinesterase (ChE) inhibitor. Control rats received a daily injection of oil vehicle or of saline. Recordings of the sleep-wake states were obtained in the 6 h following 1, 3, 6, 9, 13, 17, and 21 injections, as well as 2, 4, and 19 days after 9-day treatment. DFP administration increased waking at the expense of slow-wave sleep (SWS), but not of paradoxical sleep (PS); as a result, the PS/SWS ratio was strongly enhanced. These changes developed across days, were maximal after six to nine injections, and were then maintained at that level until cessation of treatment. This time course of behavioral state alterations paralleled the time course of ChE inhibition in the mesopontine cholinergic nuclei and the pontine reticular formation described in the companion article. In contrast, after DFP withdrawal, behavioral states returned to control values more rapidly (in 2-4 days) than did ChE activity. These results are discussed regarding the promoting role of cholinergic neurotransmission in brain-activated states.

Structural roles of acetylcholinesterase variants in biology and pathology

Apart from its catalytic function in hydrolyzing acetylcholine, acetylcholinesterase (AChE) affects cell proliferation, differentiation and responses to various insults, including stress. These responses are at least in part specific to the three C-terminal variants of AChE which are produced by alternative splicing of the single ACHE gene. 'Synaptic' AChE-S constitutes the principal multimeric enzyme in brain and muscle; soluble, monomeric 'readthrough' AChE-R appears in embryonic and tumor cells and is induced under psychological, chemical and physical stress; and glypiated dimers of erythrocytic AChE-E associate with red blood cell membranes. We postulate that the homology of AChE to the cell adhesion proteins, gliotactin, glutactin and the neurexins, which have more established functions in nervous system development, is the basis of its morphogenic functions. Competition between AChE variants and their homologs on interactions with the corresponding protein partners would inevitably modify cellular signaling. This can explain why AChE-S exerts process extension from cultured amphibian, avian and mammalian glia and neurons in a manner that is C-terminus-dependent, refractory to several active site inhibitors and, in certain cases, redundant to the function of AChE-like proteins. Structural functions of AChE variants can explain their proliferative and developmental roles in blood, bone, retinal and neuronal cells. Moreover, the association of AChE excess with amyloid plaques in the degenerating human brain and with progressive cognitive and neuromotor deficiencies observed in AChE-transgenic animal models most likely reflects the combined contributions of catalytic and structural roles.

Choline acetyltransferase and acetylcholinesterase in the normal, developing and regenerating newt retinas

The presence of the choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) was demonstrated in the adult newt retina using immunocytochemical and histochemical techniques. Within the inner plexiform layer (IPL), two ChAT-positive bands were detected at relative depths of 0-15% and 45-60% of the total thickness (100%) of the IPL. AChE-positive band occupied approximately 0-60% of the IPL width with an intensive AChE-positive band at a depth of 20-40% within the IPL. Localizations of maximum ChAT and AChE activity were not exactly the same in the IPL of the mature retina. To elucidate whether retinal regeneration follows the same sequence of cellular differentiation steps that occur in retinal development, we examined the time course of appearance of the cholinergic neurons and AChE activity in both developing and regenerating retinas. The ChAT-positive cells were first detected in the retina just before or at the beginning of the morphological development of the IPL in both developing and regenerating retinas. AChE activity first became detectable in somata located at the most proximal layer of the retina before the ChAT-positive cells could be detected and well before the IPL developed in both developing and regenerating retinas. During subsequent development and regeneration, the outer plexiform layer, the IPL, and somata close to either side of the IPL became AChE-positive. The fact that the time course of the appearance of ChAT and AChE molecules during regeneration was similar to that observed during development suggests that common mechanisms may control both the development and the regeneration of the newt retina.

Evidence for homeostatic adjustments of rat somatosensory cortical neurons to changes in extracellular acetylcholine concentrations produced by iontophoretic administration of acetylcholine and by systemic diisopropylfluorophosphate treatment

We describe the responses of single units in the awake (24 cells) or urethane-anesthetized (37 cells) rat somatosensory cortex during repeated iontophoretic pulses (1.0 s, 85 nA) of acetylcholine, both before and after systemic treatment with the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (i.p., 0.3-0.5 LD50). The time-course of the response to acetylcholine pulses differed among cortical neurons but was characteristic for a given cell. Different time-courses included monophasic excitatory or inhibitory responses, biphasic (excitatory-inhibitory, inhibitory-excitatory, excitatory-excitatory, and inhibitory-inhibitory), and triphasic (excitatory-excitatory-inhibitory, inhibitory-inhibitory-excitatory, and inhibitory-excitatory-inhibitory) responses. Although the sign and time-course of the individual responses remained consistent, their magnitude fluctuated across time; most cells exhibited either an initial increase or decrease in response magnitude followed by oscillations in magnitude that diminished with time, gradually approaching the original size. The time-course of the characteristic response to an acetylcholine pulse appeared to determine direction and rate of change in response magnitude with successive pulses of acetylcholine. Diisopropylfluorophosphate treatment, given 1 h after beginning repeated acetylcholine pulses, often resulted in a gradual increase in spontaneous activity to a slightly higher but stable level. Superimposed on this change in background activity, the oscillations in the response amplitude reappeared and then subsided in a pattern similar to the decay seen prior to diisopropylfluorophosphate treatment. Our results suggest that dynamic, homeostatic mechanisms control neuronal excitability by adjusting the balance between excitatory and inhibitory influences within the cortical circuitry and that these mechanisms are engaged by prolonged increases in extracellular acetylcholine levels caused by repeated pulses of acetylcholine and by acetylcholinesterase inhibition. However, this ability of neurons in the cortical neuronal network to rapidly adjust to changes in extracellular levels of acetylcholine questions the potential efficacy of therapeutic treatments designed to increase ambient levels of acetylcholine as a treatment for Alzheimer's disease or to enhance mechanisms of learning and memory.

Early appearance of acetylcholinergic, serotoninergic, and peptidergic neurons and fibers in the developing human central nervous system

Animal experiments have already shown that neurotransmitters and neuropeptides are not only important for normal functioning of the adult central nervous system (CNS) but are also crucial to its development. However, information on the spatio-temporal distribution of these endogenous substances in the developing human CNS is still scarce. With the use of immunocytochemical staining and a constant supply of properly fixed human abortuses from southern China, an early appearance of acetylcholinesterase, enkephalin, and substance P immunoreactivities was detected first in the spinal cord (weeks 5 to 7 of gestation), then in the brainstem nuclei (weeks 11 to 12). Their overlapping localizations in many regions of the CNS suggest possible interactions among neurons containing these substances, which are in turn important for the proper establishment of the neuronal circuitry. Immunoreactivity for neuropeptide Y appeared initially in the lateral region of upper segments of the spinal cord at week 12 of gestation, then spread latero-medially and cranio-caudally to the sacral region. In the hippocampus, neuropeptide Y neurons appeared from week 15 onwards. Serotoninergic neurons were found in the dorsal raphe nucleus at week 10 and then decreased in number as the fetus grew older. Somatostatin releasing inhibitory factor, vasopressin, and oxytocin were detected in the hypothalamus from weeks 12 to 14 onwards, and monoamine oxidase, succinic dehydrogenase, parvalbumin, calbindin D28K, and vasoactive intestinal peptide were found in the visual cortex at midgestation. The early appearance and the abundance of the neurotransmitters and neuropeptides in the developing CNS indicate that they may play a key role in neuronal differentiation.

Presynaptic muscarinic (M3) receptors reduce excitatory transmission in dopamine neurons of the rat mesencephalon

The effects of carbachol (0.01-30 microM) and muscarine (10-30 microM) on the excitatory synaptic potentials were studied using conventional intracellular recordings from dopaminergic neurons in rat mesencephalic slices. Both muscarinic agonists reversibly reduced the excitatory synaptic potentials, evoked by local electrical stimulation. The EC50 for carbachol was determined to be 4.5 microM. The maximal degree of the excitatory synaptic potentials suppression caused by carbachol and muscarine was around 40% of control. This suppression was completely blocked by the non-specific muscarinic antagonist atropine (1 microM) and the selective M3 antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (1 microM). Other antagonists, preferentially acting at M1, M2 and M4 receptors, were not effective. Furthermore, the acetylcholinesterase inhibitor, physostigmine (50 microM), decreased the amplitude of the excitatory synaptic potentials, indicating that ambient acetylcholine can depress this potential. Direct depolarizing responses to glutamate were not changed by muscarine. In addition, muscarine facilitated the second excitatory synaptic potentials during a paired-pulse protocol. Thus, the effect of the muscarinic agonists is attributable to a presynaptic locus of action. The action of muscarine was not mediated by an N-ethylmaleimide-sensitive G-protein since it was not modified by a treatment of the slices with this agent. The calcium channels blockers, omega-conotoxin GIVA, omega-agatoxin IVA and omega-conotoxin MVIIC did not affect the action of muscarine on the excitatory synaptic potentials. When the potassium currents were reduced by extracellular barium and 4-aminopyridine, the muscarinic agonists still depressed the excitatory synaptic potentials. Our data indicate that presynaptically located M3 receptors modulate the excitatory transmission to midbrain dopaminergic neurons via a N-ethylmaleimide-insensitive G-protein which activates mechanisms neither linked to N-, P-, Q-type calcium channels nor to barium- and 4-aminopyridine-sensitive potassium channels.

Osteoblast-derived acetylcholinesterase: a novel mediator of cell-matrix interactions in bone?

The adhesive interactions that occur between bone cells and the developing matrix during bone formation help guide coupled remodeling and the maintenance of bone mass. Here, we provide evidence that acetylcholinesterase (AChE) is a novel osteoblast-derived mediator of cell-matrix interactions in bone. These findings complement an increasing body of evidence which suggests that AChE, in addition to its role in terminating cholinergic signaling, may be instrumental in regulating cellular differentiation and adhesion. We have shown, using RT-PCR, that osteosarcoma cell lines and primary cultures of osteoblasts express AChE mRNA. Expression appeared to be differentiation-dependent, and restricted to AChE splice variants containing the T subunit (exon 6). Immunofluorescent localization demonstrated that these osteoblastic cells expressed protein for AChE with an intracellular vesicular distribution. Immunohistochemistry on tissue sections confirmed AChE expression by osteoblasts in vivo, and revealed the presence of AChE along cement lines, also identified by enzyme histochemistry. In vitro functional studies indicated that osteoblast-like cells adhered specifically to and spread on AChE substrates, but did not interact with butyrylcholinesterase, a closely related protein. Our evidence strongly implicates AChE as a novel bone matrix protein, capable of mediating cell-matrix interactions, and as such may be a principal participant in organized bone formation and the regulation of remodeling.

Rat locomotion and release of acetylcholinesterase

In the substantia nigra acetylcholinesterase is released from the dopamine cells of the pars compacta independent of cholinergic transmission. In this study the effects of local and systemic amphetamine treatment were compared on acetylcholinesterase release in the rat substantia nigra in relation to concomitant behavior. Acetylcholinesterase release, measured "on-line" with a sensitive chemiluminescent system, was enhanced by amphetamine stimulation administered locally and could not be dissociated from simultaneous amphetamine-induced circling behavior. On the other hand, amphetamine administered systemically resulted in a general increase in locomotor behavior followed by a subsequent increase in acetylcholinesterase release. The alternative scenario of an initial rise in acetylcholinesterase release, subsequently followed by enhanced movement, was never seen. Hence, movement can enhance release of acetylcholinesterase from the substantia nigra, whereas "upstream" local nigral events can affect acetylcholinesterase release and movement simultaneously.

Acetylcholinesterase gene expression in axotomized rat facial motoneurons is differentially regulated by neurotrophins: correlation with trkB and trkC mRNA levels and isoforms

We examined the potential influences of muscle-derived neurotrophins on the acetylcholinesterase (AChE) gene expression of adult rat motoneurons. Seven days after facial nerve transection, both AChE mRNA and enzyme activity levels were markedly reduced in untreated and vehicle-treated facial motoneurons, suggesting positive regulation of motoneuron AChE expression by muscle-derived factors. Because skeletal muscle is a source of neurotrophin-3 (NT-3), NT-4/5, and BDNF, these neurotrophins were individually infused onto the proximal nerve stump for 7 d, beginning at the time of axotomy. The trkB ligands NT-4/5 and BDNF prevented the downregulation of AChE mRNA and enzymatic activity, as determined by in situ hybridization, biochemical assay, and histochemical visualization of enzyme activity. In contrast, NT-3 had limited effects, and NGF was without effect. Because motoneurons normally express both trkB and trkC receptors and the trkC ligand NT-3 is the most abundant muscle-derived neurotrophin, we investigated possible reasons for the limited effects of NT-3. In situ hybridization and reverse transcription-PCR both revealed a downregulation of trkC mRNA in axotomized motoneurons, which contrasted the upregulation of trkB expression. Furthermore, isoforms of trkC were detected carrying insertions within their kinase domains, known to limit certain trkC-mediated signal transduction pathways. Because the changes in trkB and trkC mRNA levels were not significantly altered by neurotrophin infusions, it is unlikely they were induced by loss of muscle-derived neurotrophins. These results demonstrate that NT-4/5 and BDNF stimulate AChE gene expression in motoneurons and support the concept that muscle-derived trkB ligands modulate the cholinergic phenotype of their innervating motoneurons.

Dendritic release of vasopressin and oxytocin

In addition to the release of neurotransmitters from their axon terminals, several neuronal populations are able to release their products from their dendrites. The cell bodies and dendrites of vasopressin- and oxytocin-producing neurones are mainly located within the hypothalamic supraoptic and paraventricular nuclei and neuropeptide release within the magnocellular nuclei has been shown in vitro and in vivo. Local release is induced by a range of physiological and pharmacological stimuli, and is regulated by a number of brain areas; locally released peptides are mainly involved in pre- and postsynaptic modulation of the electrical activity of magnocellular neurones. Spatial and temporal differences between peptide release within the nuclei and that from the distant axonal varicosities indicate that the release mechanisms are at least partially independent, supporting the hypothesis of locally regulated dendritic release of vasopressin and oxytocin. In this respect, magnocellular neurones show similarities to other neuronal populations and thus autoregulation of neuronal activity by dendritic neuromodulator release may be a general phenomenon within the brain.

Motor neurone acetylcholinesterase release precedes neurotoxicity caused by systemic administration of excitatory amino acids and strychnine

We have proposed that neuronal overactivation by either stimulation of excitatory receptors or hypofunction of inhibitory circuits is a cause of excessive acetylcholinesterase (AChE) release, which, in turn, can contribute to ALS/MND pathogenesis. We investigated histochemical and histopathological changes in cell populations of the mouse spinal ventral horn upon in vivo stimulation of glutamate receptors with L-aspartate (ASP, 10-50 mg/kg, intraperitoneal: i.p.), or blockade of glycine receptors with strychnine (STRY, 2 mg/kg, i.p.). ASP in P4-P13 (postnatal age in days) but not in older mice, and STRY irrespective of age, provoked rapid, striking depletions of motor neurone AChE, and appearance of AChE activity in astrocytes. This was followed by recovery of the enzyme in most motor neurones, astrocyte activation and statistically significant changes in: brain macrophage infiltration, loss of interneurones and motor neurones and neuronophagic images including rosettes of glial cells surrounding a central 'ghost-like' motor neurone. Although AChE release preceded the neuropathology found, it is not known if its uptake is a cause of glial activation. However, it has been shown that the enzyme potentiates non-N-metyl-D-aspartate receptors identical to those that mediate astrocyte activation. AChE activity produces protons and choline, possible microglial activators. These are putative routes towards long-lasting neuropathology.

Chronic (-) deprenyl administration increases dendritic arborization in CA3 neurons of hippocampus and AChE activity in specific regions of the primate brain

The mechanism by which (-) deprenyl enhances cognitive function in Alzheimer's disease (AD) is not yet understood. (-) Deprenyl (0.2 mg/kg/day) was administered intramuscularly to adult male monkeys (n = 6) for 25 days. Control monkeys (n = 6) received physiological saline by the same route. The activity of acetylcholinesterase (AChE) in different brain regions and the dendritic arborization in CA3 pyramidal neurons of hippocampus were analysed. (-) Deprenyl-treated monkeys showed a significant increase in the AChE activity by 43% (p < 0.001) in the frontal cortex, by 39% (p < 0.025) in the motor cortex, by 66% (p < 0.001) in the hippocampus and by 26% (p < 0.05) in the striatum compared to controls. The branching points and the intersections of both apical and basal dendrites of CA3 hippocampal pyramidal neurons were also significantly increased in (-) deprenyl-treated monkeys. Enhanced AChE activity may increase dendritic arborization in the hippocampus and it may also play a role in improving cognitive functions observed in AD, following (-) deprenyl treatment.