Cholinesterases during development of the avian nervous system

Transcriptomic and metabolomic analyses of the ovaries of Taihe black-bone silky fowls at the peak egg-laying and nesting period

The poor reproductive performance of most local Chinese chickens limits the economic benefits and output of related enterprises. As an excellent local breed in China, Taihe black-bone silky fowl is in urgent need of our development and utilization. In this study, we performed transcriptomic and metabolomic analyses of the ovaries of Taihe black-bone silky fowls at the peak egg-laying period (PP) and nesting period (NP) to reveal the molecular mechanisms affecting reproductive performance. In the transcriptome, we identified five key differentially expressed genes (DEGs) that may affect the reproductive performance of Taihe black-bone silky fowl: BCHE, CCL5, SMOC1, CYTL1, and SCIN, as well as three important pathways: the extracellular region, Neuroactive ligand-receptor interaction and Cytokine-cytokine receptor interaction. In the metabolome, we predicted three important ovarian significantly differential metabolites (SDMs): LPC 20:4, Bisphenol A, and Cortisol. By integration analysis of transcriptome and metabolome, we identified three important metabolite-gene pairs: "LPC 20:4-BCHE", "Bisphenol A-SMOC1", and "Cortisol- SCIN". In summary, this study contributes to a deeper understanding of the regulatory mechanism of egg production in Taihe black-bone silky fowl and provides a scientific basis for improving the reproductive performance of Chinese local chickens.

Functional characterization of the schizophrenia associated gene AS3MT identifies a role in neuronal development

Genome-wide association studies (GWAS) have identified multiple genomic regions associated with schizophrenia, although many variants reside in noncoding regions characterized by high linkage disequilibrium (LD) making the elucidation of molecular mechanisms challenging. A genomic region on chromosome 10q24 has been consistently associated with schizophrenia with risk attributed to the AS3MT gene. Although AS3MT is hypothesized to play a role in neuronal development and differentiation, work to fully understand the function of this gene has been limited. In this study we explored the function of AS3MT using a neuronal cell line (SH-SY5Y). We confirm previous findings of isoform specific expression of AS3MT during SH-SY5Y differentiation toward neuronal fates. Using CRISPR-Cas9 gene editing we generated AS3MT knockout SH-SY5Y cell lines and used RNA-seq to identify significant changes in gene expression in pathways associated with neuronal development, inflammation, extracellular matrix formation, and RNA processing, including dysregulation of other genes strongly implicated in schizophrenia. We did not observe any morphological changes in cell size and neurite length following neuronal differentiation and MAP2 immunocytochemistry. These results provide novel insights into the potential role of AS3MT in brain development and identify pathways through which genetic variation in this region may confer risk for schizophrenia.

Serum cholinesterase may independently predict prognosis in non-small-cell lung cancer

Background

Serum cholinesterase (ChE) was found to be involved in cancer initiation and progression. However, the survival association between serum ChE and non-small cell lung cancer (NSCLC) has not been extensively discussed. In the present study, we aim to elevate the role of ChE in overall survival (OS) of NSCLC patients.

Methods

A total of 961 histologically confirmed NSCLC patients diagnosed between 2013 and 2018 in a provincial cancer hospital in southwestern China were retrospectively selected. Relevant information, such as histological type, clinical stage, chemotherapy, smoking status, body mass index (BMI), important serum indicators (albumin, neutrophil-to-lymphocyte ratio, ChE), date of death of the patients was extracted from the computerized hospital information system. Univariate and multivariate Cox proportional hazards models were used to determine the association between baseline serum ChE measured at the diagnosis and the OS of NSCLC patients.

Results

The median of baseline ChE (7700 units/liter) was used as a cut-off to dichotomize NSCLC patients. After controlling for possible confounding factors, serum ChE at diagnosis was significantly associated with OS of NSCLC: patients with higher level of ChE were observed a better prognosis (hazard ratio, HR: 0.77, 95% CI: 0.67–0.93, p = 0.006). Subgroup analysis revealed significant ChE-OS association for NSCLC patients: with lower systemic inflammation level (baseline NLR < 2.95, HR: 0.71, 95% CI: 0.56–0.89, p = 0.003), of adenocarcinoma (HR: 0.66, 95% CI: 0.54–0.80, p < 0.001), in advanced stage (HR: 0.77, 95% CI: 0.66–0.92, p < 0.01), and received chemotherapy (HR: 0.75, 95% CI: 0.59–0.96, p < 0.02).

Conclusion

Baseline ChE may have independent prognostic value for NSCLC patients. Longitudinal studies should be performed to corroborate this finding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09212-0.

High-Throughput Screening and Molecular Dynamics Simulation of Natural Product-like Compounds against Alzheimer's Disease through Multitarget Approach

Alzheimer’s disease (AD) is a progressive neurological disorder that affects 50 million people. Despite this, only two classes of medication have been approved by the FDA. Therefore, we have planned to develop therapeutics by multitarget approach. We have explored the library of 2029 natural product-like compounds for their multi-targeting potential against AD by inhibiting AChE, BChE (cholinergic pathway) MAO-A, and MOA-B (oxidative stress pathway) through in silico high-throughput screening and molecular dynamics simulation. Based on the binding energy of these target enzymes, approximately 189 compounds exhibited a score of less than −10 kcal/mol against all targets. However, none of the control inhibitors exhibited a binding affinity of less than −10 kcal/mol. Among these, the top 10 hits of compounds against all four targets were selected for ADME-T analysis. As a result, only F0850-4777 exhibited an acceptable range of physicochemical properties, drug-likeness, pharmacokinetics, and suitability for BBB permeation with high GI-A and non-toxic effects. The molecular dynamics study confirmed that F0850-4777 remained inside the binding cavity of targets in a stable conformation throughout the simulation and Prime-MM/GBSA study revealed that van der Waals’ energy (ΔG_vdW) and non-polar solvation or lipophilic energy (ΔG_{Sol_Lipo}) contribute favorably towards the formation of a stable protein–ligand complex. Thus, F0850-4777 could be a potential candidate against multiple targets of two pathophysiological pathways of AD and opens the doors for further confirmation through in vitro and in vivo systems.

Synthesis and Initial Characterization of a Selective, Pseudo-irreversible Inhibitor of Human Butyrylcholinesterase as PET Tracer

The enzyme butyrylcholinesterase (BChE) represents a promising target for imaging probes to potentially enable early diagnosis of neurodegenerative diseases like Alzheimer's disease (AD) and to monitor disease progression in some forms of cancer. In this study, we present the design, facile synthesis, in vitro and preliminary ex vivo and in vivo evaluation of a morpholine-based, selective inhibitor of human BChE as a positron emission tomography (PET) tracer with a pseudo-irreversible binding mode. We demonstrate a novel protecting group strategy for 18 F radiolabeling of carbamate precursors and show that the inhibitory potency as well as kinetic properties of our unlabeled reference compound were retained in comparison to the parent compound. In particular, the prolonged duration of enzyme inhibition of such a morpholinocarbamate motivated us to design a PET tracer, possibly enabling a precise mapping of BChE distribution.

Human umbilical cord perivascular cells: A novel source of the organophosphate antidote butyrylcholinesterase

Human butyrylcholinesterase (BChE) is a well-characterized bioscavenger with significant potential as a prophylactic or post-exposure treatment for organophosphate poisoning. Despite substantial efforts, BChE has proven technically challenging to produce in recombinant systems. Recombinant BChE tends to be insufficiently or incorrectly glycosylated, and consequently exhibits a truncated half-life, compromised activity, or is immunogenic. Thus, expired human plasma remains the only reliable source of the benchmark BChE tetramer, but production is costly and time intensive and presents possible blood-borne disease hazards. Here we report a human BChE production platform that produces functionally active, tetrameric BChE enzyme, without the addition of external factors such as polyproline peptides or chemical or gene modification required by other systems. Human umbilical cord perivascular cells (HUCPVCs) are a rich population of mesenchymal stromal cells (MSCs) derived from Wharton's jelly. We show that HUCPVCs naturally and stably secrete BChE during culture in xeno- and serum-free media, and can be gene-modified to increase BChE output. However, BChE secretion from HUCPVCs is limited by innate feedback mechanisms that can be interrupted by addition of miR 186 oligonucleotide mimics or by competitive inhibition of muscarinic cholinergic signalling receptors by addition of atropine. By contrast, adult bone marrow-derived mesenchymal stromal cells neither secrete measurable levels of BChE naturally, nor after gene modification. Further work is required to fully characterize and disable the intrinsic ceiling of HUCPVC-mediated BChE secretion to achieve commercially relevant enzyme output. However, HUCPVCs present a unique opportunity to produce both native and strategically engineered recombinant BChE enzyme in a human platform with the innate capacity to secrete the benchmark human plasma form.

Hepatic cholinesterase of laying hens naturally infected by Salmonella Gallinarum (fowl typhoid)

Salmonella is a facultative intracellular pathogen that may cause foodborne gastroenteritis in humans and animals consisting of over 2000 serovars. The serovar Salmonella Gallinarum is an important worldwide pathogen of poultry. However, little is known on the mechanisms of pathogenesis of Salmonella in chickens. The aim of this study was to evaluate cholinesterase and myeloperoxidase activities in hepatic tissue of laying hens naturally infected by S. Gallinarum. Twenty positive liver samples for S. Gallinarum were collected, in addition to seven liver samples from healthy uninfected laying hens (control group). The right liver lobe was homogenized for analysis of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and myeloperoxidase (MPO), and the left lobe was divided into two fragments, one for histopathology and the other for Salmonella isolation. The results showed changes in AChE and BchE activity in the liver of infected laying hens compared to the control group (P < 0.05), i.e. reduced AChE and increased BChE activities in liver samples. Infected animals showed increased MPO activity compared to healthy animals (P < 0.05). Furthermore, the histopathological findings showed fibrinoid necrosis associated to the infiltration of lymphocytes, plasma cells, macrophages,heterophils in the liver of infected hens. These findings suggest that the inflammatory process was attenuated providing a pro-inflammatory action of both enzyme analyzed in order to reduce the free ACh, a molecule which has an anti-inflammatory action. Therefore, our results lead to the hypothesis that cholinesterase plays an important role on the modulation of immune response against S. Gallinarum with an inflammatory effect, contributing to the response against this bacterium. This study should contribute to a better understanding on the pathogenic mechanisms involved in laying hens infected by S. Gallinarum.

Role of acetylcholinesterase in lung cancer

Acetylcholinesterase (AChE) plays a key role in catalytic hydrolysis of cholinergic neurotransmitters. Intensive research has proven the involvement of this protein in novel functions, such as cell adhesion, differentiation, and proliferation. In addition, several recent studies have indicated that acetylcholinesterase is potentially a marker and regulator of apoptosis. Importantly, AChE is also a promising tumor suppressor. In this review, we briefly summarize the involvement of AChE in apoptosis and cancer, focusing on the role of AChE in lung cancer, as well as the therapeutic consideration of AChE for cancer therapy.

Neuronal AChE splice variants and their non-hydrolytic functions: redefining a target of AChE inhibitors?

AChE enzymatic inhibition is a core focus of pharmacological intervention in Alzheimer's disease (AD). Yet, AChE has also been ascribed non-hydrolytic functions, which seem related to its appearance in various isoforms. Neuronal AChE presents as a tailed form (AChE-T) predominantly found on the neuronal synapse, and a facultatively expressed readthough form (AChE-R), which exerts short to medium-term protective effects. Notably, this latter form is also found in the periphery. While these non-hydrolytic functions of AChE are most controversially discussed, there is evidence for them being additional targets of AChE inhibitors. This review aims to provide clarification as to the role of these AChE splice variants and their interplay with other cholinergic parameters and their being targets of AChE inhibition: AChE-R is particularly involved in the mediation of (anti-)apoptotic events in cholinergic cells, involving adaptation of various cholinergic parameters and a time-dependent link to the expression of neuroprotective factors. The AChE-T C-terminus is central to AChE activity regulation, while isolated AChE-T C-terminal fragments mediate toxic effects via the α7 nicotinic acetylcholine receptor. There is direct evidence for roles of AChE-T and AChE-R in neurodegeneration and neuroprotection, with these roles involving AChE as a key modulator of the cholinergic system: in vivo data further encourages the use of AChE inhibitors in the treatment of neurodegenerative conditions such as AD since effects on both enzymatic activity and the enzyme's non-hydrolytic functions can be postulated. It also suggests that novel AChE inhibitors should enhance protective AChE-R, while avoiding the concomitant up-regulation of AChE-T.

Active and peripheral anionic sites of acetylcholinesterase have differential modulation effects on cell proliferation, adhesion and neuritogenesis in the NG108-15 cell line

The classical enzymatic role of acetylcholinesterase (AChE) is to terminate impulse transmission at cholinergic synapses through rapid hydrolysis of acetylcholine (ACh). Inactivation of this enzyme's catalytic site is the primary mechanism of acute toxicity of OP insecticides (e.g. parathion, chlorpyrifos). There is now sufficient evidence to suggest that AChE has a neurotrophic function that may be altered by organophosphate (OP) exposure, resulting in defects of neuronal growth and development, though the clarification of the mechanisms involved require further in vitro investigation. In the present study, the mouse neuroblastoma×rat glioma hybrid NG108-15 cell line was used to investigate the differential effects between inhibition of the catalytic site and peripheral anionic site (PAS) of acetylcholinesterase (AChE) on cell adhesion, proliferation and neuritogenesis, in the presence and absence of human red blood cell (hRBC) AChE (ED3.1.1.7). AChE active-site inhibitor paraoxon (PO; 0.1-1.0μM), when added to NG108-15 cells grown on AChE-coated plates, had no effect on cell proliferation, but exerted a significant reduction in strongly adherent viable cells accompanied by mostly short process formations, with 18% of cells considered to be neuritogenic, similar to that observed on uncoated plates. In contrast, PO had no significant effect on cell adhesion and proliferation of NG108-15 cells on uncoated plates. The PAS-ligand thioflavin-T (Th-T; 0.5-25μM), however, decreased cell adhesion and proliferation, on both uncoated and ACh-E coated plates, with less magnitude on AChE-coated plates. Taken together, these results suggest that strong cell adherence and neuritogenesis are sensitive to PO in this cell culture model, with no impact on proliferation, in the presence of membrane bound AChE-coating, while there is no sensitivity to PO on uncoated plates. On the other hand, binding of Th-T directly to the PAS affects both cell adherence and proliferation, with less magnitude in the presence of membrane-bound AChE. The current study indicates that PO is deleterious in neural development during critical periods of strong cell adhesion and differentiation, interfering with AChE trophic function.

Altered magnetic resonance images of brain and social behaviors of hatchling, and expression of thyroid hormone receptor βmRNA in cerebellum of embryos after Methimazole administration

RATIONALE AND OBJECTIVES

The effects of low thyroid hormone level during embryogenesis on MRI of the brain and social behaviors of hatchlings were examined using "fertilized hen's egg-embryo-chick" system.

METHODS AND RESULTS

Control and hatchlings treated with methimazole (20 μmol/egg), which hatched 3 days later than controls were examined. The results are as follows: 1. The MRI examination of the midsagittal section of the brain on hatch day showed that the sizes, by T1- and ADC values by diffusion-weighted images, of the optic lobe and cerebellum of the MMI-hatchlings were significantly bigger than those of the controls. 2. The social behaviors on post-hatch day 3 were based on the following tests: (a) Aggregation test: The speed of four chicks, individually isolated by cardboard barriers in a box, to make a group upon the removal of barriers. (b) Belongingness tests: The speed of a chick isolated at a corner to join the group of three chicks placed at the opposite corner. (c) Vocalization test: The number of decibel produced by a chick isolated at a corner using a sound meter. These tests demonstrated that MMI-hatchlings took longer times and had weaker vocalization than the controls, significantly. 3. Upregulation of THRβ mRNA after MMI treatment suggested that THR was necessary for cerebellum development.

CONCLUSIONS

The MMI exposure during the last week of embryogenesis possibly delayed the myelination of certain brain regions and impaired the social behaviors of hatchlings. The chick embryos can be easily induced with hypothyroidism without maternal influences, and the hatchling's behaviors were analyzed using a video camera. The present method will be useful for assessing the effects of unfavorable influences during embryogenesis on social behaviors in later life.

Biochemical and molecular characterisation of acetylcholinesterase in four field populations of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis, is a major pest that infects fruits and agricultural products worldwide. The latest resistance monitoring of B. dorsalis from mainland China has identified high levels of resistance to insecticides. In this study, the biochemical and molecular characteristics of acetylcholinesterase (AChE) in four field populations of B. dorsalis are investigated.

RESULTS

Among the four populations, the DG population and its purified AChE were found to be the least susceptible to malathion and five inhibitors, whereas the KM population and its purified AChE were the most susceptible. The highest catalytic activity of purified AChE was found for the KM population, and the catalytic activity of the DG population was the lowest. Among developmental stages, the AChE purified from larvae was found to be the most insusceptible to inhibitors, but its catalytic activity was the highest. Sequence analysis of the cDNA encoding AChE showed that some residue differences existed. However, no significant differences in expression levels of the AChE gene among populations and developmental stages were detected.

CONCLUSION

The results suggest that the decrease in susceptibility of B. dorsalis was mainly caused by decrease in AChE activity, and they provide a broad view on the relation between AChE and resistance.

Copy number variation in ACHE/EPHB4 (7q22) and in BCHE/MME (3q26) genes in sporadic breast cancer

Gene amplifications and deletions are common changes in human cancer cells. Previous studies indicate that the regions, where the ACHE (7q22) and BCHE (3q26.1-q26.2) genes are localized, are suffering such structural modifications in breast cancer. Therefore, the products of these genes, acetylcholinesterase and butyrylcholinesterase, respectively, are related to the process of cell differentiation and proliferation, as well as apoptosis. This study also included two other genes involved in tumorigenesis, the EPHB4 (7q22.1) and MME (3q21-27). The aim of this study was to verify amplification and/or deletion in the ACHE, BCHE, EPHB4 and MME genes in 32 samples of sporadic breast cancer. The gene alterations were detected using real-time PCR and determined by relative quantification with the standard curve method. All samples presented genetic alterations, showing a higher tendency for amplification of the ACHE (62.5% vs. 37.5%; p>0.1) and EPHB4 (53.13% vs. 46.88%; p>0.5) genes, and for deletions of the BCHE and MME genes (56.25% vs. 43.75% for both; p>0.5). A positive correlation was found between alterations in ACHE-EPHB4 and BCHE-MME pairs (r(s) = 0.5948; p = 0.0004; r(s) = 0.3581; p = 0.0478, respectively) indicating that these changes comprise a wide region. In conclusion, the results suggest that these genomic regions may contain important genes for this pathology, such as the oncogenes MET (7q31) and PIK3CA (3q26), and thus being interesting targets for future studies in breast cancer research.

Serum cholinesterases are differentially regulated in normal and dystrophin-deficient mutant mice

The cholinesterases, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) (pseudocholinesterase), are abundant in the nervous system and in other tissues. The role of AChE in terminating transmitter action in the peripheral and central nervous system is well understood. However, both knowledge of the function(s) of the cholinesterases in serum, and of their metabolic and endocrine regulation under normal and pathological conditions, is limited. This study investigates AChE and BChE in sera of dystrophin-deficient mdx mutant mice, an animal model for the human Duchenne muscular dystrophy (DMD) and in control healthy mice. The data show systematic and differential variations in the concentrations of both enzymes in the sera, and specific changes dictated by alteration of hormonal balance in both healthy and dystrophic mice. While AChE in mdx-sera is elevated, BChE is markedly diminished, resulting in an overall cholinesterase decrease compared to sera of healthy controls. The androgen testosterone (T) is a negative modulator of BChE, but not of AChE, in male mouse sera. T-removal elevated both BChE activity and the BChE/AChE ratio in mdx male sera to values resembling those in healthy control male mice. Mechanisms of regulation of the circulating cholinesterases and their impairment in the dystrophic mice are suggested, and clinical implications for diagnosis and treatment are considered.

A soluble acetylcholinesterase provides chemical defense against xenobiotics in the pinewood nematode

The pinewood nematode genome encodes at least three distinct acetylcholinesterases (AChEs). To understand physiological roles of the three pinewood nematode AChEs (BxACE-1, BxACE-2, and BxACE-3), BxACE-3 in particular, their tissue distribution and inhibition profiles were investigated. Immunohistochemistry revealed that BxACE-1 and BxACE-2 were distributed in neuronal tissues. In contrast, BxACE-3 was detected from some specific tissues and extracted without the aid of detergent, suggesting its soluble nature unlike BxACE-1 and BxACE-2. When present together, BxAChE3 significantly reduced the inhibition of BxACE-1 and BxACE-2 by cholinesterase inhibitors. Knockdown of BxACE-3 by RNA interference significantly increased the toxicity of three nematicidal compounds, supporting the protective role of BxACE-3 against chemicals. In summary, BxACE-3 appears to have a non-neuronal function of chemical defense whereas both BxACE-1 and BxACE-2 have classical neuronal function of synaptic transmission.

Three acetylcholinesterases of the pinewood nematode, Bursaphelenchus xylophilus: insights into distinct physiological functions

Acetylcholinesterase (AChE) plays a key role in postsynaptic transmission in most animals. Nematodes encode multiple AChEs, implying its functional diversity. To explore physiological functions of multiple AChEs, three distinct AChEs (BxACE-1, BxACE-2, and BxACE-3) were identified and characterized from the pinewood nematode. Sequencing comparison with Torpedo AChE and Caenorhabditis elegans ACEs identified choline-binding site, catalytic triad functional site, three internal disulfide bonds and aromatic residues for the catalytic gorge. Transcriptional profiling by quantitative real-time PCR revealed that BxACE-3 is more actively transcribed than BxACE-1 (2-3 times) and BxACE-2 (9-18 times) in both propagative and dispersal stages. The three BxACEs were functionally expressed using baculovirus system. Kinetic analysis of in vitro-expressed BxACEs revealed that the substrate specificity was highest in BxACE-1 whereas the catalytic efficiency was highest in BxACE-2. In inhibition assay, BxACE-3 showed the lowest inhibition rate. Taken together, it appears that both BxACE-1 and BxACE-2 play common but non-overlapping roles in synaptic transmission, whereas BxACE-3 may have non-neuronal functions. The current findings should provide valuable insights into the evolutionary process and various physiological roles of AChE.

Amplification and deletion of the ACHE and BCHE cholinesterase genes in sporadic breast cancer

Increasing evidence supports the involvement of acetylcholinesterase and butyrylcholinesterase in cell proliferation control and differentiation, reinforcing the hypothesis that these enzymes might have an influence in tumorigenesis. It has already been shown that the cholinesterase genes are structurally altered or aberrantly expressed in a variety of tumor types. In this study, amplifications and deletions in the ACHE and BCHE genes were investigated in sporadic breast tumors using real-time polymerase chain reaction and the relative quantification method. The majority of the tumor tissues showed a notable number of both deletions and amplifications: 65.7% and 22.9%, respectively, in BCHE and 45.7% and 31.4%, respectively, in ACHE. Deletion of the ACHE gene was significantly correlated with amplification of the protooncogene ERBB2. Tumor size was significantly higher when the ACHE gene was amplified, and the total number of alterations (amplifications plus deletions) of the BCHE gene was positively correlated with tumor malignancy grade.

Effects of glucocorticoid on brain acetylcholinesterase of developing chick embryos

AIM

Fetal exposure to excessive or deficient glucocorticoids may alter the programming in differentiation and maturation of various tissues including the brain and nervous system, leading to dysfunctions later in life. For further exploration of this possibility, we established an animal model using developing chick embryos.

METHODS

(i) Reverse-transcription polymerase chain reaction was used to determine the expression of glucocorticoid receptor mRNA in the brain of chick embryos. (ii) Embryos on day 15 were administered betamethasone or mifepristone and their cerebrum, cerebellum and optic lobe were investigated to determine the activity of acetylcholinesterase.

RESULTS

(i) Glucocorticoid receptor mRNA was shown to be present in the cerebrum, cerebellum and optic lobe. (ii) After the administration of betamethasone, acetylcholinesterase activities in the cerebrum, cerebellum and optic lobe on day 19 were 1.5- to 2-fold higher than those of untreated control. Weights of body and brain parts were 0.65-0.75-fold relative to control values. However, these differences were less noticeable on day 22. (iii) Administration of mifepristone before treatment with betamethasone prevented high-dose betamethasone-induced changes in acetylcholinesterase activity and bodyweights on day 19. Administration of mifepristone alone did not induce differences from the control.

CONCLUSIONS

The cerebrum, cerebellum and optic lobe of chick embryos could be influenced by glucocorticoids because of the presence of glucocorticoid receptor mRNA. Although the effects observed after treatment with excess glucocorticoids (even no effects after mifepristone treatment) were transitory, they may alter the developmental program in ways that could result in lasting change and influence behavioral activities after hatching.

Neurobehavioral teratogenicity of sarin in an avian model

Nerve gas organophosphates like sarin are likely to be used in urban terrorism, leading to widespread exposures of pregnant women and young children. Here, we established a model for sarin neurobehavioral teratogenicity in the developing chick so as to explore the consequences of apparently subtoxic sarin exposure and the mechanisms underlying synaptic and behavioral deficits. Chicken eggs were injected with sarin (2, 6 and 12 microg/kg) on incubation days 2 and 6, treatments that did not decrease hatching and did not evoke dysmorphology. After hatching the chicks were tested for filial imprinting and neurochemical markers known to be critical for imprinting. Imprinting was reduced at 2 and 6 microg/kg but not at the highest dose. Acetylcholinesterase and choline acetyltransferase were unaffected but sarin reduced the concentration of the high-affinity choline transporter, the rate-limiting factor in acetylcholine utilization. The concentration of PKC isoforms was assessed in the imprinting-related intermediate part of the medial hyperstriatum ventrale, the region most closely associated with cholinergic function in imprinting behavior. Sarin reduced the concentration of all isoforms (alpha, beta, gamma) with a similar, biphasic dose-response curve to that seen for behavioral performance, a relationship noted in previous work with organophosphate pesticides. Our results indicate that otherwise subtoxic exposures to sarin produce neurodevelopmental deficits; since we utilized a chick model, which is devoid of maternal confounds that are present in mammalian development, the adverse effects of sarin are mediated directly in the developing organism.

The aryl acylamidase activity is much more sensitive to Alzheimer drugs than the esterase activity of acetylcholinesterase in chicken embryonic brain

The appearance of cholinergic trait often precedes synaptogenesis, indicating the involvement of cholinesterase proteins in nervous system development, particularly so acetylcholinesterase (AChE). In addition to AChE's acclaimed esterase activity, its lesser known non-cholinergic functions have gained much attention, because of AChE protein expression in areas other than cholinergic innervations; one such function could be exerted by its associated aryl acylamidase (AAA) activity. In this study, an attempt has been made in profiling esterase and AAA activities of AChE at different developmental stages of the chick embryo, e.g. at embryonic day 6 (E6), E9, E12, E15 and E18. AAA activity showed a correlated expression with esterase activity at all stages, but the relative ratios of AAA to esterase activity were higher at younger stages. The inhibition of AAA activity was shown to be more sensitive towards Huperzine, Donepezil whereas inhibition of esterase activity was sensitive to Tacrine and DFP. Remarkably, the major Alzheimer drugs- Huperzine and Donepezil, much more strongly inhibited AAA activity of AChE at younger developmental stages whose IC50 values are 0.01 muM and 0.1 muM respectively. In the case of BW284c51, inhibition was more pronounced at older stages and IC50 value was 0.1 muM. Since in Alzheimer's disease (AD), embryonic forms of AChE have been reported to reappear, a possible role of AAA activity in the pathogenesis of AD should be considered.

Developmental neurotoxic effects of chlorpyrifos on acetylcholine and serotonin pathways in an avian model

The developmental neurotoxicity of organophosphates such as chlorpyrifos (CPF) involves multiple mechanisms that ultimately compromise the function of specific neurotransmitter systems, notably acetylcholine (ACh) and serotonin (5-hydroxytryptamine, 5HT). Studies in mammalian models incorporate both direct effects on brain development and indirect effects mediated through maternal physiology and maternal/neonatal interactions. We examined the effects of CPF in an avian model, which does not share these potential confounds. Chick eggs were injected with CPF (10 or 20 mg/kg) on incubation days 2 and 6 and markers of ACh and 5HT systems were examined at hatching. The higher dose caused a reduction in cholinesterase activity but there was no consistent downregulation of m(2)-muscarinic ACh receptors as would have been expected from ACh hyperstimulation. Both doses evoked significant reductions in the presynaptic high-affinity choline transporter, the rate-limiting factor in ACh biosynthesis, as monitored by binding of hemicholinium-3. Choline acetyltransferase, a constitutive marker for ACh terminals, was unaffected. This suggests that CPF reduces ACh presynaptic activity rather than compromising the development of ACh projections per se. CPF exposure also reduced the expression of cerebrocortical 5HT(1A) receptors. These effects in the chick model recapitulate many of the actions of early gestational CPF exposure in rats, and thus suggest that CPF exerts direct actions on the immature brain to compromise the development of ACh and 5HT pathways.

Control of cell proliferation by neurotransmitters in the developing vertebrate retina

In the developing vertebrate retina, precise coordination of retinal progenitor cell proliferation and cell-cycle exit is essential for the formation of a functionally mature retina. Unregulated or disrupted cell proliferation may lead to dysplasia, retinal degeneration or retinoblastoma. Both cell-intrinsic and -extrinsic factors regulate the proliferation of progenitor cells during CNS development. There is now growing evidence that in the developing vertebrate retina, both slow and fast neurotransmitter systems modulate the proliferation of retinal progenitor cells. Classic neurotransmitters, such as GABA (gamma-amino butyric acid), glycine, glutamate, ACh (acetylcholine) and ATP (adenosine triphosphate) are released, via vesicular or non-vesicular mechanisms, into the immature retinal environment. Furthermore, these neurotransmitters signal through functional receptors even before synapses are formed. Recent evidence indicates that the activation of purinergic and muscarinic receptors may regulate the cell-cycle machinery and consequently the expansion of the retinal progenitor pool. Interestingly, GABA and glutamate appear to have opposing roles, inducing retinal progenitor cell-cycle exit. In this review, we present recent findings that begin to elucidate the roles of neurotransmitters as regulators of progenitor cell proliferation at early stages of retinal development. These studies also raise several new questions, including how these neurotransmitters regulate specific cell-cycle pathways and the mechanisms by which retinal progenitor cells integrate the signals from neurotransmitters and other exogenous factors during vertebrate retina development.

Localization, specific activity, and molecular forms of acetylcholinesterase in developmental stages of the cestode Mesocestoides corti

The nervous system of flatworms is quite simple although there is increasing evidence indicating that it is chemically complex. Studies of the nervous system in these animals have only been performed in the larval stage or in the adult worms, which are easy to obtain in nature, while the description of the nervous system in developing stages of these organisms is missing. Mesocestoides corti is a parasitic platyhelminth whose larvae can be induced in vitro to develop to adult, sexually mature worms, opening the possibility of studying the nervous system of a flatworm in different stages of development. Here, we describe the presence, activity, location, and molecular forms of acetylcholinesterase (AChE) in different stages of development of M. corti, from the larvae to adult forms of this endoparasite, obtained in in vitro cultures after induction of the larval stage with trypsin. Our results point to AChE as a molecular marker of the nervous system in platyhelminthes. The change in molecular forms of this enzyme and the increase in its activity during development from larvae to adult worm may reflect the presence of a more complex nervous system, necessary to adjust and coordinate the movement of a much bigger structure. A relationship between the development of the reproductive apparatus in segmented and adult worms with a more complex nervous system in these stages is also apparent. Finally, our study opens the possibility of applying anti-AChE as more effective therapeutic strategies against cestode parasites.

Exposure to Diazinon Alters In Vitro Retinogenesis: Retinospheroid Morphology, Development of Chicken Retinal Cell Types, and Gene Expression

Developing embryos are more vulnerable than adults to acute cholinergic intoxication by anticholinesterases, including organophosphorus pesticides. These agents affect the process of neural development itself, leading to permanent deficits in the architecture of the nervous system. Recent evidence on direct roles of acetylcholinesterase (AChE) on neuronal differentiation provides additional grounds for investigating the developmental toxicity of anticholinesterases. Therefore, the effect of the organophosphate diazinon on the development of chick retinal differentiation was studied by an in vitro reaggregate approach. Reaggregated spheres from dissociated retinal cells of the E6 chick embryo were produced in rotation culture. During the whole culture period of 10 days, experimental cultures were supplemented with different concentrations of the pesticide, from 20 to 120 microM diazinon. The pesticide-treated spheres were reduced in size, and their outer surface was irregular. More importantly, inner structural distortions could be easily traced because the structure of control spheroids can be well characterized by a histotypical arrangement of laminar parts homologous to the normal retina. Acetylcholinesterase activity in diazinon-treated spheres was reduced when compared with controls. As a dramatic effect of exposure to the pesticide, inner plexiform layer (IPL)-like areas in spheroids were not distinguishable anymore. Similarly, photoreceptor rosettes and Müller radial glia were strongly decreased, whereas apoptosis was stimulated. The expression of transcripts for choline-acetyltransferase and muscarinic receptors was affected, revealing an effect of diazinon on the cholinergic system. This further proves the significance of cholinesterases and the cholinergic system for proper nervous system development and shows that further studies of debilitating diazinon actions on development are necessary.

Excessive expression of acetylcholinesterase impairs glutamatergic synaptogenesis in hippocampal neurons

Acetylcholinesterase (AChE) exerts noncatalytic activities on neural cell differentiation, adhesion, and neuritogenesis independently of its catalytic function. The noncatalytic functions of AChE have been attributed to its peripheral anionic site (PAS)-mediated protein-protein interactions. Structurally, AChE is highly homologous to the extracellular domain of neuroligin, a postsynaptic transmembrane molecule that interacts with presynaptic beta-neurexins, thus facilitating synaptic formation and maturation. Potential effects of AChE expression on synaptic transmission, however, remain unknown. Using electrophysiology, immunocytochemistry, and molecular biological approaches, this study investigated the role of AChE in the regulation of synaptic formation and functions. We found that AChE was highly expressed in cultured embryonic hippocampal neurons at early culture days, particularly in dendritic compartments including the growth cone. Subsequently, the expression level of AChE declined, whereas synaptic activity and synaptic proteins progressively increased. Chronic blockade of the PAS of AChE with specific inhibitors selectively impaired glutamatergic functions and excitatory synaptic structures independently of cholinergic activation, while inducing AChE overexpression. Moreover, the PAS blockade-induced glutamatergic impairments were associated with a depressed expression of beta-neurexins and an accumulation of other synaptic proteins, including neuroligins, and were mostly preventable by antisense suppression of AChE expression. Our findings demonstrate that interference with the nonenzymatic features of AChE alters AChE expression, which impairs excitatory synaptic structure and functions.

Spontaneous Waves in the Ventricular Zone of Developing Mammalian Retina

Spontaneous rhythmic waves in the developing mammalian retina are thought to propagate among differentiated neurons in the inner retina (IR) and play an important role in activity-dependent visual development. Here we report a new form of rhythmic Ca2+wave in the ventricular zone (VZ) of the developing rabbit retina. Ca2+imaging from two-photon optical sections near the ventricular surface of the whole-mount retina showed rhythmic Ca2+transients propagating laterally as waves. The VZ waves had a distinctively slow Ca2+dynamics (lasting ∼20 s) but shared a similar frequency and propagation speed with the IR waves. Simultaneous Ca2+imaging in VZ and multi-electrode array recording in the ganglion cell layer (GCL) revealed close spatiotemporal correlation between spontaneous VZ and IR waves, suggesting a common source of initiation and/or regulation of the two waves. Pharmacological studies further showed that all drugs that blocked IR waves also blocked VZ waves. However, the muscarinic antagonist atropine selectively blocked VZ but not IR waves at this developmental stage, indicating that IR waves were not dependent on VZ waves, but VZ waves likely relied on the initiation of IR waves. Eliciting IR waves with puffs of nicotinic or non- N-methyl-d-aspartate agonists in GCL produced atropine-sensitive waves in the VZ, demonstrating a unique, retrograde signaling pathway from IR to VZ. Thus differentiated neurons in the IR use spontaneous, rhythmic waves to send both forward signals to the central visual targets and retrograde messages to the developing cells in the VZ.

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.

Muscle induces neuronal expression of acetylcholinesterase in neuron-muscle co-culture: transcriptional regulation mediated by cAMP-dependent signaling

Presynaptic motor neuron synthesizes and secretes acetylcholinesterase (AChE) at vertebrate neuromuscular junctions. In order to determine the retrograde role of muscle in regulating the expression of AChE in motor neuron, a chimeric co-culture of NG108-15 cell, a cholinergic cell line that resembles motor neuron, with chick myotube was established to mimic the neuromuscular contact in vitro. A DNA construct of human AChE promoter tagged with luciferase (pAChE-Luc) was stably transfected into NG108-15 cells. The co-culture with myotubes robustly stimulated the promoter activity as well as the endogenous expression of AChE in pAChE-Luc stably transfected NG108-15 cells. Muscle extract derived from chick embryos when applied onto pAChE-Luc-expressing NG108-15 cells induced expressions of AChE promoter and endogenous AChE. The cAMP-responsive element mutation on human AChE promoter blocked the muscle-induced AChE transcriptional activity in cultured NG108-15 cells either in co-culturing with myotube or in applying muscle extract. The accumulation of intracellular cAMP and the phosphorylation of cAMP-responsive element-binding protein in cultured NG108-15 cells were stimulated by applied muscle extract. Part of the muscle-induced signaling was mimicked by application of calcitonin gene-related peptide in cultured NG108-15 cells. These results suggest the muscle-induced neuronal AChE expression in the co-culture is mediated by a cAMP-dependent signaling.

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 butyrylcholinesterase in the early development of the brine shrimp (Artemia salina) larvae: a target for phthalate ester embryotoxicity?

The phthalate ester insensitive blue-green algae (Synechococcus lividus) were used as a food source to extend the survival of synchronously hatched brine shrimp (Artemia salina) larvae allowing measurement of a reduced toxic response to phthalate esters at late post-hatching stages of development. The maximum acute toxicity due to di-n-butyl phthalate (DNBP) correlated with the expression of a phthalate ester-hydrolyzing enzyme. The purified enzyme was identified as a butyrylcholinesterase due to its rapid inactivation by low concentrations (10(-7)M) of diisopropyl fluorophosphate and inhibition by physostigmine (IC(50)=6 x 10(-7)M) and tetraisopropylpyrophosphoramide (I-OMPA, IC(50)=x 10(-6)M) but not by BW284c5. Apparently competition of the phthalates with the endogenous substrates of the enzyme led to development-dependent toxicity.

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.

Induction of acetylcholinesterase expression during apoptosis in various cell types

Acetylcholinesterase (AChE) plays a key role in terminating neurotransmission at cholinergic synapses. AChE is also found in tissues devoid of cholinergic responses, indicating potential functions beyond neurotransmission. It has been suggested that AChE may participate in development, differentiation, and pathogenic processes such as Alzheimer's disease and tumorigenesis. We examined AChE expression in a number of cell lines upon induction of apoptosis by various stimuli. AChE is induced in all apoptotic cells examined as determined by cytochemical staining, immunological analysis, affinity chromatography purification, and molecular cloning. The AChE protein was found in the cytoplasm at the initiation of apoptosis and then in the nucleus or apoptotic bodies upon commitment to cell death. Sequence analysis revealed that AChE expressed in apoptotic cells is identical to the synapse type AChE. Pharmacological inhibitors of AChE prevented apoptosis. Furthermore, blocking the expression of AChE with antisense inhibited apoptosis. Therefore, our studies demonstrate that AChE is potentially a marker and a regulator of apoptosis.

A Hidden Retinal Regenerative Capacity from the Chick Ciliary Margin is Reactivated In Vitro, that is Accompanied by Down-regulation of Butyrylcholinesterase

The chicken retina has a capacity to regenerate in vivo, which is restricted up to embryonic day 4 (E4). Here we test the proliferative patterns of dissociated chicken cells from the centre retina or the ciliary margin, including pigmented cells, after their transfer into rotation culture. For central cells in culture, the uptake of [3H]thymidine after a short initial rise decreases similarly to their in ovo counterparts. In contrast, marginal cells that have been shown to regenerate up to E9 into retinotypic stratospheroids re-enter a novel and long-lasting phase of in vitro cell division. We have shown previously that cell types of all nuclear layers are produced. Both observations taken together indicate a pronounced self-renewal of multipotent stem cells. Molecularly, the enzyme butyrylcholinesterase, which in other systems has been shown to mark transitory neuronal cells between proliferation and differentiation, is strongly expressed at the ciliary margin over most of the embryonic period. After these cells are transferred into rotation culture, butyrylcholinesterase is down-regulated. Concomitantly, the neuronal differentiation marker acetylcholinesterase increases. We conclude that the regenerative capacity of the chick retina is not lost at E4, but rather remains hidden in the chicken ciliary margin, since it can be reactivated in vitro at least up to E9. We suggest that butyrylcholinesterase may be linked to the regulation of stem cell activity.

Increased expression of intranuclear AChE involved in apoptosis of SK-N-SH cells

Programmed cell death plays an integral role in neurodegenerative diseases such as Alzheimer's disease (AD). Acetylcholinesterase (AChE) was suggested to be neurotoxic in vivo and in vitro and accelerate assembly of amyloid peptide into Alzheimer's fibrils. In our experiments, we found increased AChE expression in apoptotic neuroblastoma SK-N-SH cells after long-term culture. Our results first showed that in apoptotic SK-N-SH cells, AChE aggregated in the nucleus and suppression of AChE expression with antisense oligonucleotide could save the cells from apoptosis. It was also found that caspase-3 activity was parallel with AChE activation in apoptotic SK-N-SH cells. These results suggest that AChE plays an important role in the procession of neuroblastoma cell apoptosis and favor the association between AChE and neuronal apoptosis in AD.

Muscarinic acetylcholine receptors in the normal, developing and regenerating newt retinas

Immunoreactivity for m2 and m4 muscarinic acetylcholine receptors (mAChRs) was demonstrated in the adult newt retina. The m2 mAChR was localized to somata on either side of the inner plexiform layer (IPL), especially ganglion cells, and also distributed into two bands within the IPL. The distal band at a depth of 0-15% IPL co-localized with one of two choline acetyltransferase (ChAT) immunoreactive bands, while the proximal band at 85-100% depth did not overlap with either of the ChAT-ir bands. The m4 mAChR was localized to somata closely apposed to either side of the IPL, probably amacrine cell somata, and no immunoreactivity was detectable throughout the IPL. The time course of appearance of the m2 and m4 mAChRs was examined in both developing and regenerating retinas. Like acetylcholinesterase (AChE), the m2 was first detected in somata located at the most proximal level of the retina well before ChAT-ir cholinergic neurons appeared, while the m4 was detected at the time of appearance of ChAT, in both developing and regenerating retinas. When the outer plexiform layer (OPL) began to form, somata in the horizontal cell layer became transiently immunoreactive to the m2. The discrepancy in distribution of the m2 and ChAT in the IPL suggests that mAChR may play a role other than cholinergic neurotransmission. Furthermore, the similarity in time course of appearance of the m2 and m4, as well as other cholinergic system components [4], in both developing and regenerating retinas would suggest that the mechanisms that control neuronal differentiation during retinal development and regeneration are similar.

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.

Expression of cholinergic system molecules during development of the chick nervous system

There are suggestions of the participation of nicotinic acetylcholine receptors (nAChRs), the acetylcholine degradation enzyme, acetylcholinesterase (AChE), and the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT), in the development of the nervous system. In this study, we aimed at comparing the development of some subunits of the nAChRs, AChE, and ChAT in the chick nervous system by standard immunohistochemical methods. The expression of all molecules investigated here appeared very early in ganglia (embryonic day 3.5-4), persisting into posthatching, except for ChAT, which is not detected after hatching in ganglia. A differential development was observed for nAChR subunits, with these receptors appearing around embryonic day 6 in some sites. The time-course of development of different nAChR subunits revealed several instances of transient expression (such as in the cerebellum), increasing expression (such as in the nucleus spiriformis lateralis), and diminishing expression into posthatching stages (such as in the oculomotor and throclear nuclei). Expression of AChE and ChAT also starts around embryonic day 6 in some structures and follows mainly increasing time-courses in the chick brain. The results of this study reveal a developmentally regulated expression of cholinergic system-related molecules in the chick nervous system and characterize differential time-courses of expression for nAChR subunits, AChE, and ChAT during development.

Modulation of acetylcholinesterase and voltage-gated Na(+) channels in choline acetyltransferase- transfected neuroblastoma clones

Neurotransmitters appear early in the developing embryo and may play a role in the regulation of neuronal differentiation. To study potential effects of acetylcholine production in neuronal differentiation, we used the FB5 subclone of N18TG2 murine neuroblastoma cells stably transfected with cDNA for choline acetyltransferase. We tested whether the forced acetylcholine production can modify the expression or the cellular localization of different neuronal markers. We studied the activity, localization, and secretion of acetylcholinesterase in view of its possible role in the modulation of the morphogenetic action of acetylcholine and of its proposed role of a regulator of neurite outgrowth. FB5 cells are characterized by a high level of acetylcholinesterase, predominantly released into the culture medium. Acetylcholinesterase secretion into the medium was lower in choline acetyltransferase-transfected clones than in nontransfected and antisense-transfected controls. Moreover, sequential extraction of acetylcholinesterase revealed that detergent-extracted, i.e., membrane-associated, activity was higher in the transfected clones expressing choline acetyltransferase activity than in both control groups. These observations suggest that a shift occurs in the utilization of acetylcholinesterase in choline acetyltransferase-transfected clones from a secretion pathway to a pathway leading to membrane localization. In addition, the choline acetyltransferase-positive clones showed higher densities of voltage-gated Na(+) channels and enhanced high-affinity choline uptake, suggesting the accomplishment of a more advanced differentiated neuronal phenotype. Finally, binding experiments demonstrated the presence of muscarinic acetylcholine receptors in all examined clones. This observation is consistent with the proposed existence of an autocrine loop, which may be important for the enhancement in the expression of neurospecific traits.

Maturation-dependent effects of chlorpyrifos and parathion and their oxygen analogs on acetylcholinesterase and neuronal and glial markers in aggregating brain cell cultures

An in vitro model, the aggregating brain cell culture of fetal rat telencephalon, has been used to study the maturation-dependent sensitivity of brain cells to two organophosphorus pesticides (OPs), chlorpyrifos and parathion, and to their oxon derivatives. Immature (DIV 5-15) or differentiated (DIV 25-35) brain cells were treated continuously for 10 days. Acetylcholinesterase (AChE) inhibitory potency for the OPs was compared to that of eserine (physostigmine), a reversible AChE inhibitor. Oxon derivatives were more potent AChE inhibitors than the parent compounds, and parathion was more potent than chlorpyrifos. No maturation-dependent differences for AChE inhibition were found for chlorpyrifos and eserine, whereas for parathion and paraoxon there was a tendency to be more effective in immature cultures, while the opposite was true for chlorpyrifos-oxon. Toxic effects, assessed by measuring protein content as an index of general cytotoxicity, and various enzyme activities as cell-type-specific neuronal and glial markers (ChAT and GAD, for cholinergic and GABAergic neurons, respectively, and GS and CNP, for astrocytes and oligodendrocytes, respectively) were only found at more than 70% of AChE inhibition. Immature compared to differentiated cholinergic neurons appeared to be more sensitive to OP treatments. The oxon derivates were found to be more toxic on neurons than the parent compounds, and chlorpyrifos was more toxic than parathion. Eserine was not neurotoxic. These results indicate that inhibition of AChE remains the most sensitive macromolecular target of OP exposure, since toxic effects were found at concentrations in which AChE was inhibited. Furthermore, the compound-specific reactions, the differential pattern of toxicity of OPs compared to eserine, and the higher sensitivity of immature brain cells suggest that the toxic effects and inhibition of AChE are unrelated.

Localization of choline acetyltransferase in the developing and adult turtle retinas

Acetylcholine has important epigenetic roles in the developing retina. In this study, cells that expressed choline acetyltransferase (ChAT), the enzyme that synthesizes acetylcholine, were investigated in embryonic, postnatal, and adult turtle retinas by using immunofluorescence histochemistry. ChAT was present at stage 15 (S15) in cells near the vitreal surface. With the formation of the inner plexiform layer (IPL) at S18, ChAT-immunoreactive (-IR) cells were located in the inner nuclear layer (INL) and the ganglion cell layer (GCL). In the INL, presumed starburst amacrine cells were homogenous in appearance and formed a single row next to the IPL: This pattern was conserved until adulthood. In the GCL, however, there were multiple rows of ChAT-IR cells early in development, and this high density of labeled cells continued during the embryonic stages, until around birth. The high density of ChAT-IR cells in the GCL was due in part to a population of cells that expressed ChAT transiently. In postnatal stages and adult retinas, the presumed starburst amacrine ChAT-IR cells formed two mirror-like rows of homogenous cells on both borders of the IPL. Two cholinergic dendritic strata that were continuous with these cells were observed as early as S18, and their depths in the IPL were relatively stable throughout development. A third population of ChAT-IR cells was observed toward the middle of the INL around S25 and persisted into adulthood. Finally, cells in the outer nuclear layer (ONL) were ChAT-IR during the embryonic stages, were less immunoreactive during the postnatal stages, and were not immunoreactive in the adult retinas.

Colocalization of choline acetyltransferase and gamma-aminobutyric acid in the developing and adult turtle retinas

Acetylcholine and gamma -aminobutyric acid (GABA) are putative neurotransmitters in the adult vertebrate retina. In this study, cells that coexpress choline acetyltransferase (ChAT) and GABA or glutamic acid decarboxylase (GAD) were investigated in turtle retinas from stage 14 (S14) to adulthood by using a double-labeling immunofluorescence technique. ChAT immunoreactivity was observed at S15 and included not only the presumptive starburst cholinergic amacrine cells but also a population in the ganglion cell layer (GCL) that expressed ChAT transiently during the embryonic stages (see the accompanying paper: Nguyen et al. [2000] J. Comp. Neurol. 420:512-526).

Development of the visual system of the chick. I. Cell differentiation and histogenesis

This review summarizes present knowledge on the embryonic development of the avian visual projections, based on the domestic chick as a model system. The reductionist goal to understand formation and function of complex neuroanatomical systems on a causal level requires a synthesis of classic developmental biology with recent advances on the molecular mechanisms of cell differentiation and histogenesis. It is the purpose of this article. We are discussing the processes underlying patterning of the anterior neural tube, when the retina and optic tectum are specified and their axial polarity is determined. Then the development of these structures is described from the molecular to the anatomical level. Following sections deal with the establishment of secondary visual connections, and the developmental interactions between compartments of the retinotectal system. Using this latter pathway, from the retina to the optic tectum, many investigations aimed at mechanisms of axonal pathfinding and connectivity have accumulated a vast body of research, which will be covered by a following review.