Butyrylcholinesterase and the control of synaptic responses in acetylcholinesterase knockout mice

Contributions of Non-Neuronal Cholinergic Systems to the Regulation of Immune Cell Function, Highlighting the Role of α7 Nicotinic Acetylcholine Receptors

Loewi's discovery of acetylcholine (ACh) release from the frog vagus nerve and the discovery by Dale and Dudley of ACh in ox spleen led to the demonstration of chemical transmission of nerve impulses. ACh is now well-known to function as a neurotransmitter. However, advances in the techniques for ACh detection have led to its discovery in many lifeforms lacking a nervous system, including eubacteria, archaea, fungi, and plants. Notably, mRNAs encoding choline acetyltransferase and muscarinic and nicotinic ACh receptors (nAChRs) have been found in uninnervated mammalian cells, including immune cells, keratinocytes, vascular endothelial cells, cardiac myocytes, respiratory, and digestive epithelial cells. It thus appears that non-neuronal cholinergic systems are expressed in a variety of mammalian cells, and that ACh should now be recognized not only as a neurotransmitter, but also as a local regulator of non-neuronal cholinergic systems. Here, we discuss the role of non-neuronal cholinergic systems, with a focus on immune cells. A current focus of much research on non-neuronal cholinergic systems in immune cells is α7 nAChRs, as these receptors expressed on macrophages and T cells are involved in regulating inflammatory and immune responses. This makes α7 nAChRs an attractive potential therapeutic target.

Exploration of a library of piperonylic acid-derived hydrazones possessing variable aryl functionalities as potent dual cholinesterase and monoamine oxidase inhibitors

A library of piperonylic acid-derived hydrazones possessing variable aryl moiety was synthesized and investigated for their multifunctional properties against cholinesterases (ChEs) and monoamine oxidases (MAOs). The in vitro enzymatic assay results revealed that the tested hydrazones have exhibited excellent cholinesterase inhibition profile. Compound 4i, (E)-N'-(2,3-dichlorobenzylidene)benzo[d][1,3]dioxole-5-carbohydrazide showed promising dual inhibitory profile against AChE (0.048 ± 0.007 μM), BChE (0.89 ± 0.018 μM), and MAO-B (0.95 ± 0.12 μM) enzymes. SAR exploration revealed that the truncation of the linker connecting both the aryl binding sites of the semicarbazone scaffold, by one atom, has relatively suppressed the AChE inhibitory potential. Kinetic studies disclosed that the compound 4i reversibly inhibited AChE enzyme in a competitive manner (Ki = 8.0 ± 0.076 nM), while it displayed a non-competitive and reversible inhibition profile against MAO-B (Ki = 9.6 ± 0.021 µM). Moreover, molecular docking studies of synthesized compounds against ChEs and MAOs provided the crucial molecular features that enable their close association and interaction with the target enzymes. All atomistic simulation studies confirmed the stable association of compound 4i within the active sites of AChE and MAO-B. In addition, theoretical ADMET prediction studies demonstrated the acceptable pharmacokinetic profile of the dual inhibitors. In summary, the attempted lead simplification study afforded a potent dual ChE-MAO-B inhibitor compound that merits further investigation.

An Evolving Technology That Integrates Classical Methods with Continuous Technological Developments: Thin-Layer Chromatography Bioautography

Thin-layer chromatography (TLC) bioautography is an evolving technology that integrates the separation and analysis technology of TLC with biological activity detection technology, which has shown a steep rise in popularity over the past few decades. It connects TLC with convenient, economic and intuitive features and bioautography with high levels of sensitivity and specificity. In this study, we discuss the research progress of TLC bioautography and then establish a definite timeline to introduce it. This review summarizes known TLC bioautography types and practical applications for determining antibacterial, antifungal, antitumor and antioxidant compounds and for inhibiting glucosidase, pancreatic lipase, tyrosinase and cholinesterase activity constitutes. Nowadays, especially during the COVID-19 pandemic, it is important to identify original, natural products with anti-COVID potential compounds from Chinese traditional medicine and natural medicinal plants. We also give an account of detection techniques, including in situ and ex situ techniques; even in situ ion sources represent a major reform. Considering the current technical innovations, we propose that the technology will make more progress in TLC plates with higher separation and detection technology with a more portable and extensive scope of application. We believe this technology will be diffusely applied in medicine, biology, agriculture, animal husbandry, garden forestry, environmental management and other fields in the future.

Regulation of immune responses by tuft cells

Tuft cells are rare, secretory epithelial cells that generated scant immunological interest until contemporaneous reports in 2016 linked tuft cells with type 2 immunity in the small intestine. Tuft cells have the capacity to produce an unusual spectrum of biological effector molecules, including IL-25, eicosanoids implicated in allergy (such as cysteinyl leukotrienes and prostaglandin D₂) and the neurotransmitter acetylcholine. In most cases, the extracellular signals controlling tuft cell effector function are unknown, but signal transduction is thought to proceed via canonical, G protein-coupled receptor-dependent pathways involving components of the signalling pathway used by type II taste bud cells to sense sweet, bitter and umami compounds. Tuft cells are ideally positioned as chemosensory sentinels that can detect and relay information from diverse luminal substances via what appear to be stereotyped outputs to initiate both positive and aversive responses through populations of immune and neuronal cells. Despite recent insights, numerous questions remain regarding tuft cell lineage, diversity and effector mechanisms and how tuft cells interface with the immunological niche in the tissues where they reside.

Novel cholinesterase paralogs of Schistosoma mansoni have perceived roles in cholinergic signalling and drug detoxification and are essential for parasite survival

Cholinesterase (ChE) function in schistosomes is essential for orchestration of parasite neurotransmission but has been poorly defined with respect to the molecules responsible. Interrogation of the S. mansoni genome has revealed the presence of three ChE domain-containing genes (Smche)s, which we have shown to encode two functional acetylcholinesterases (AChE)s (Smache1 –smp_154600 and Smache2 –smp_136690) and a butyrylcholinesterase (BChE) (Smbche1 –smp_125350). Antibodies to recombinant forms of each SmChE localized the proteins to the tegument of adults and schistosomula and developmental expression profiling differed among the three molecules, suggestive of functions extending beyond traditional cholinergic signaling. For the first time in schistosomes, we identified ChE enzymatic activity in fluke excretory/secretory (ES) products and, using proteomic approaches, attributed this activity to the presence of SmAChE1 and SmBChE1. Parasite survival in vitro and in vivo was significantly impaired by silencing of each smche, either individually or in combination, attesting to the essential roles of these molecules. Lastly, in the first characterization study of a BChE from helminths, evidence is provided that SmBChE1 may act as a bio-scavenger of AChE inhibitors as the addition of recombinant SmBChE1 to parasite cultures mitigated the effect of the anti-schistosome AChE inhibitor 2,2- dichlorovinyl dimethyl phosphate—dichlorvos (DDVP), whereas smbche1-silenced parasites displayed increased sensitivity to DDVP.

Cholinesterases—aceytlcholinesterases (AChE)s and butyrylcholinesterases (BChE)s—are multi-functional enzymes that play a pivotal role in the nervous system of parasites by regulating neurotransmission through acetylcholine hydrolysis. Herein, we provide a detailed characterization of schistosome cholinesterases using molecular, enzymatic and gene-silencing approaches and show evidence for these molecules having roles in addition to their neuronal function. Further, we demonstrate the importance of these proteins to parasite development and survival through gene knockdown experiments in laboratory animals, providing evidence for the use of these proteins in the development of novel intervention strategies against schistosomiasis.

Expression and Function of the Cholinergic System in Immune Cells

T and B cells express most cholinergic system components—e.g., acetylcholine (ACh), choline acetyltransferase (ChAT), acetylcholinesterase, and both muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively). Using ChAT^BAC-eGFP transgenic mice, ChAT expression has been confirmed in T and B cells, dendritic cells, and macrophages. Moreover, T cell activation via T-cell receptor/CD3-mediated pathways upregulates ChAT mRNA expression and ACh synthesis, suggesting that this lymphocytic cholinergic system contributes to the regulation of immune function. Immune cells express all five mAChRs (M₁–M₅). Combined M₁/M₅ mAChR-deficient (M₁/M_5-KO) mice produce less antigen-specific antibody than wild-type (WT) mice. Furthermore, spleen cells in M₁/M₅-KO mice produce less tumor necrosis factor (TNF)-α and interleukin (IL)-6, suggesting M₁/M₅ mAChRs are involved in regulating pro-inflammatory cytokine and antibody production. Immune cells also frequently express the α2, α5, α6, α7, α9, and α10 nAChR subunits. α7 nAChR-deficient (α7-KO) mice produce more antigen-specific antibody than WT mice, and spleen cells from α7-KO mice produce more TNF-α and IL-6 than WT cells. This suggests that α7 nAChRs are involved in regulating cytokine production and thus modulate antibody production. Evidence also indicates that nicotine modulates immune responses by altering cytokine production and that α7 nAChR signaling contributes to immunomodulation through modification of T cell differentiation. Together, these findings suggest the involvement of both mAChRs and nAChRs in the regulation of immune function. The observation that vagus nerve stimulation protects mice from lethal endotoxin shock led to the notion of a cholinergic anti-inflammatory reflex pathway, and the spleen is an essential component of this anti-inflammatory reflex. Because the spleen lacks direct vagus innervation, it has been postulated that ACh synthesized by a subset of CD4⁺ T cells relays vagal nerve signals to α7 nAChRs on splenic macrophages, which downregulates TNF-α synthesis and release, thereby modulating inflammatory responses. However, because the spleen is innervated solely by the noradrenergic splenic nerve, confirmation of an anti-inflammatory reflex pathway involving the spleen requires several more hypotheses to be addressed. We will review and discuss these issues in the context of the cholinergic system in immune cells.

Nitric oxide synthase inhibitors protect against brain and liver damage caused by acute malathion intoxication

OBJECTIVE

To investigate the effect of NG-nitro-l-arginine methyl ester (l-NAME), a non-selective nitric oxide synthase (NOS) inhibitor, and 7-nitroindazole (7-NI), a selective neuronal NOS inhibitor, on oxidative stress and tissue damage in brain and liver and on DNA damage of peripheral blood lymphocytes in malathion intoxicated rats.

METHODS

Malathion (150 mg/kg) was given intraperitoneally (i.p.) along with l-NAME or 7-NI (10 or 20 mg/kg, i.p.) and rats were euthanized 4 h later. The lipid peroxidation product malondialdehyde (MDA), nitric oxide (nitrite), reduced glutathione (GSH) concentrations and paraoxonase-1 (PON-1) activity were measured in both brain and liver. Moreover, the activities of glutathione peroxidase (GPx) acetylcholinesterase (AChE), and butyrylcholinesterase (BChE), total antioxidant capacity (TAC), glucose concentrations were determined in brain. Liver enzyme determination, Comet assay, histopathological examination of brain and liver sections and inducible nitric oxide synthase (iNOS) immunohistochemistry were also performed.

RESULTS

(i) Rats treated with only malathion exhibited increased nitric oxide and lipid peroxidation (malondialdehyde) accompanied with a decrease in GSH content, and PON-1 activity in brain and liver. Glutathione peroxidase activity, TAC, glucose concentrations, AChE and BChE activities were decreased in brain. There were also raised liver aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and increased DNA damage of peripheral blood lymphocytes (Comet assay). Malathion caused marked histopathological changes and increased the expression of iNOS in brain and liver tissues. (ii) In brain of malathion-intoxicated rats, l-NAME or 7-NI resulted in decreased nitrite and MDA contents while increasing TAC and PON1 activity. Reduced GSH and GPx activity showed an increase by l-NAME. AChE activity increased by 20 mg/kg l-NAME and 10 mg/kg 7-NI. AChE activity decreased by the higher dose of 7-NI while either dose of 7-NI resulted in decreased BChE activity. (iii) In liver of malathion-intoxicated rats, decreased MDA content was observed after l-NAME or 7-NI. Nitrite level was unchanged by l-NAME but increased after 7-NI which also resulted in decreased GSH concentration and PON1 activity. Either inhibitor resulted in decreased liver ALT activity. (iv) DNA damage of peripheral blood lymphocytes was markedly inhibited by l-NAME or 7-NI treatment. (v) iNOS expression in brain and liver decreased by l-NAME or 7-NI. (vi) More marked improvement of the histopathological alterations induced by malathion in brain and liver was observed after 7-NI compared with l-NAME.

CONCLUSIONS

In malathion intoxicated rats, the neuronal NOS inhibitor 7-NI and to much less extent l-NAME were able to protect the brain and liver tissue integrity along with improvement in oxidative stress parameters. The decrease in DNA damage of peripheral blood lymphocytes by NOS inhibitors also suggests the involvement of nitric oxide in this process.

Acetylcholinesterase Inhibitors and Drugs Acting on Muscarinic Receptors- Potential Crosstalk of Cholinergic Mechanisms During Pharmacological Treatment

BACKGROUND

Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.

METHODS

We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.

RESULTS

Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.

CONCLUSION

Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.

Unbalanced acetylcholinesterase activity in larynx squamous cell carcinoma

Previous reports have demonstrated that a non-neuronal cholinergic system is expressed aberrantly in airways. A proliferative effect is exerted directly by cholinergic agonists through the activation of nicotinic and muscarinic receptors. In cancer, particularly those related with smoking, the mechanism through which tumour cells respond to aberrantly activated cholinergic signalling is a key question. Fifty paired pieces of larynx squamous cell carcinoma and adjacent non-cancerous tissue were compared in terms of their acetylcholinesterase activity (AChE). The AChE activity in non-cancerous tissues (0.248 ± 0.030 milliunits per milligram of wet tissue; mU/mg) demonstrates that upper respiratory tissues express sufficient AChE activity for controlling the level of acetylcholine (ACh). In larynx carcinomas, the AChE activity decreased to 0.157 ± 0.024 mU/mg (p=0.009). Larynx cancer patients exhibiting low ACh-degrading enzymatic activity had a significantly shorter overall survival (p=0.031). Differences in the mRNA levels of alternatively spliced AChE isoforms and molecular compositions were noted between glottic and supraglottic cancers. Our results suggest that the low AChE activity observed in larynx squamous cell carcinoma may be useful for predicting the outcome of patients.

Dysregulated cholinergic network as a novel biomarker of poor prognostic in patients with head and neck squamous cell carcinoma

BACKGROUND

In airways, a proliferative effect is played directly by cholinergic agonists through nicotinic and muscarinic receptors activation. How tumors respond to aberrantly activated cholinergic signalling is a key question in smoking-related cancer. This research was addressed to explore a possible link of cholinergic signalling changes with cancer biology.

METHODS

Fifty-seven paired pieces of head and neck squamous cell carcinoma (HNSCC) and adjacent non-cancerous tissue (ANCT) were compared for their mRNA levels for ACh-related proteins and ACh-hydrolyzing activity.

RESULTS

The measurement in ANCT of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities (5.416 ± 0.501 mU/mg protein and 6.350 ± 0.599 mU/mg protein, respectively) demonstrated that upper respiratory tract is capable of controlling the availability of ACh. In HNSCC, AChE and BChE activities dropped to 3.584 ± 0.599 mU/mg protein (p = 0.002) and 3.965 ± 0.423 mU/mg protein (p < 0.001). Moreover, tumours with low AChE activity and high BChE activity were associated with shorter patient overall survival. ANCT and HNSCC differed in mRNA levels for AChE-T, α3, α5, α9 and β2 for nAChR subunits. Tobacco exposure had a great impact on the expression of both AChE-H and AChE-T mRNAs. Unaffected and cancerous pieces contained principal AChE dimers and BChE tetramers. The lack of nerve-born PRiMA-linked AChE agreed with pathological findings on nerve terminal remodelling and loss in HNSCC.

CONCLUSIONS

Our results suggest that the low AChE activity in HNSCC can be used to predict survival in patients with head and neck cancer. So, the ChE activity level can be used as a reliable prognostic marker.

Acetylcholinesterase deficiency contributes to neuromuscular junction dysfunction in type 1 diabetic neuropathy

Diabetic neuropathy is associated with functional and morphological changes of the neuromuscular junction (NMJ) associated with muscle weakness. This study examines the effect of type 1 diabetes on NMJ function. Swiss Webster mice were made diabetic with three interdaily ip injections of streptozotocin (STZ). Mice were severely hyperglycemic within 7 days after the STZ treatment began. Whereas performance of mice on a rotating rod remained normal, the twitch tension response of the isolated extensor digitorum longus to nerve stimulation was reduced significantly at 4 wk after the onset of STZ-induced hyperglycemia. This mechanical alteration was associated with increased amplitude and prolonged duration of miniature end-plate currents (mEPCs). Prolongation of mEPCs was not due to expression of the embryonic acetylcholine receptor but to reduced muscle expression of acetylcholine esterase (AChE). Greater sensitivity of mEPC decay time to the selective butyrylcholinesterase (BChE) inhibitor PEC suggests that muscle attempts to compensate for reduced AChE levels by increasing expression of BChE. These alterations of AChE are attributed to STZ-induced hyperglycemia since similar mEPC prolongation and reduced AChE expression were found for db/db mice. The reduction of muscle end-plate AChE activity early during the onset of STZ-induced hyperglycemia may contribute to endplate pathology and subsequent muscle weakness during diabetes.

The AChE membrane-binding tail PRiMA is down-regulated in muscle and nerve of mice with muscular dystrophy by merosin deficiency

Since Duchenne muscular dystrophy was attributed to mutations in the dystrophin gene, more than 30 genes have been found to be causally related with muscular dystrophies, about half of them encoding proteins of the dystrophin-glycoprotein complex (DGC). Through laminin-2, the DGC bridges the muscle cytoskeleton and the extracellular matrix. Decreased levels of PRiMA-linked acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) have been observed in dystrophic muscle and nerve of dystrophin-deficient (mdx) and laminin-2 deficient (Lama2dy) mice. To help explain these observations, the relative content of AChE, BuChE and PRiMA mRNAs were compared in normal and Lama2dy mouse muscle and sciatic nerve. The 17-fold lower level of PRiMA mRNA in Lama2dy muscle explained the deficit in PRiMA-linked ChEs. This would increase acetylcholine availability and, eventually, the desensitization of nicotinic receptors. Abnormal development of the Schwann cells led to peripheral neuropathy in the Lama2dy mouse. Compared with normal nerve, dystrophic nerve displayed 4-fold less AChE-T mRNA, 3-fold more BuChE mRNA and 2.5-fold less PRiMA mRNA, which agreed with the lower AChE activity in dystrophic nerve, its increased BuChE activity and the specific drop in PRiMA-linked BuChE. The widely accepted role of glial cells as the source of BuChE, the observed dysmyelination of Lama2dy nerve and its increased BuChE activity support the idea that BuChE up-regulation is related with the aberrant differentiation of the Schwann cells.

Why has butyrylcholinesterase been retained? Structural and functional diversification in a duplicated gene

While acetylcholinesterase (EC 3.1.1.7) has a clearly defined role in neurotransmission, the functions of its sister enzyme butyrylcholinesterase (EC 3.1.1.8) are more obscure. Numerous mutations, many inactivating, are observed in the human butyrylcholinesterase gene, and the butyrylcholinesterase knockout mouse has an essentially normal phenotype, suggesting that the enzyme may be redundant. Yet the gene has survived for many millions of years since the duplication of an ancestral acetylcholinesterase early in vertebrate evolution. In this paper, we ask the questions: why has butyrylcholinesterase been retained, and why are inactivating mutations apparently tolerated? Butyrylcholinesterase has diverged both structurally and in terms of tissue and cellular expression patterns from acetylcholinesterase. Butyrylcholinesterase-like activity and enzymes have arisen a number of times in the animal kingdom, suggesting the usefulness of such enzymes. Analysis of the published literature suggests that butyrylcholinesterase has specific roles in detoxification as well as in neurotransmission, both in the brain, where it appears to control certain areas and functions, and in the neuromuscular junction, where its function appears to complement that of acetylcholinesterase. An analysis of the mutations in human butyrylcholinesterase and their relation to the enzyme's structure is shown. In conclusion, it appears that the structure of butyrylcholinesterase's catalytic apparatus is a compromise between the apparently conflicting selective demands of a more generalised detoxifier and the necessity for maintaining high catalytic efficiency. It is also possible that the tolerance of mutation in human butyrylcholinesterase is a consequence of the detoxification function. Butyrylcholinesterase appears to be a good example of a gene that has survived by subfunctionalisation.

Different sensitivities of rat skeletal muscles and brain to novel anti-cholinesterase agents, alkylammonium derivatives of 6-methyluracil (ADEMS)

BACKGROUND AND PURPOSE

The rat respiratory muscle diaphragm has markedly lower sensitivity than the locomotor muscle extensor digitorum longus (EDL) to the new acetylcholinesterase (AChE) inhibitors, alkylammonium derivatives of 6-methyluracil (ADEMS). This study evaluated several possible reasons for differing sensitivity between the diaphragm and limb muscles and between the muscles and the brain.

EXPERIMENTAL APPROACH

Increased amplitude and prolonged decay time of miniature endplate currents were used to assess anti-cholinesterase activity in muscles. In hippocampal slices, induction of synchronous network activity was used to follow cholinesterase inhibition. The inhibitor sensitivities of purified AChE from the EDL and brain were also estimated.

KEY RESULTS

The intermuscular difference in sensitivity to ADEMS is partly explained caused by a higher level of mRNA and activity of 1,3-bis[5(diethyl-o-nitrobenzylammonium)pentyl]-6-methyluracildibromide (C-547)-resistant BuChE in the diaphragm. Moreover, diaphragm AChE was more than 20 times less sensitive to C-547 than that from the EDL. Sensitivity of the EDL to C-547 dramatically decreased after treadmill exercises that increased the amount of PRiMA AChE(G4), but not ColQ AChE(A12) molecular forms. The A12 form present in muscles appeared more sensitive to C-547. The main form of AChE in brain, PRiMA AChE(G4), was apparently less sensitive because brain cholinesterase activity was almost three orders of magnitude more resistant to C-547 than that of the EDL.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that ADEMS compounds could be used for the selective inhibition of AChEs and as potential therapeutic tools.

Role of acetylcholinesterase on the structure and function of cholinergic synapses: insights gained from studies on knockout mice

Electrophysiological and ultrastructural studies were performed on phrenic nerve-hemidiaphragm preparations isolated from wild-type and acetylcholinesterase (AChE) knockout (KO) mice to determine the compensatory mechanisms manifested by the neuromuscular junction to excess acetylcholine (ACh). The diaphragm was selected since it is the primary muscle of respiration, and it must adapt to allow for survival of the organism in the absence of AChE. Nerve-elicited muscle contractions, miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) were recorded by conventional electrophysiological techniques from phrenic nerve-hemidiaphragm preparations isolated from 1.5- to 2-month-old wild-type (AChE(+/+)) or AChE KO (AChE(-/-)) mice. These recordings were chosen to provide a comprehensive assessment of functional alterations of the diaphragm muscle resulting from the absence of AChE. Tension measurements from AChE(-/-) mice revealed that the amplitude of twitch tensions was potentiated, but tetanic tensions underwent a use-dependent decline at frequencies below 70 Hz and above 100 Hz. MEPPs recorded from hemidiaphragms of AChE(-/-) mice showed a reduction in frequency and a prolongation in decay (37%) but no change in amplitude compared to values observed in age-matched wild-type littermates. In contrast, MEPPs recorded from hemidiaphragms of wild-type mice that were exposed for 30 min to the selective AChE inhibitor 5-bis(4-allyldimethyl-ammoniumphenyl)pentane-3-one (BW284C51) exhibited a pronounced increase in amplitude (42%) and a more marked prolongation in decay (76%). The difference between MEPP amplitudes and decays in AChE(-/-) hemidiaphragms and in wild-type hemidiaphragms treated with BW284C51 represents effective adaptation by the former to a high ACh environment. Electron microscopic examination revealed that diaphragm muscles of AChE(-/-) mice had smaller nerve terminals and diminished pre- and post-synaptic surface contacts relative to neuromuscular junctions of AChE(+/+) mice. The morphological changes are suggested to account, in part, for the ability of muscle from AChE(-/-) mice to function in the complete absence of AChE.

Localization of butyrylcholinesterase at the neuromuscular junction of normal and acetylcholinesterase knockout mice

At the mouse neuromuscular junction (NMJ), there are two distinct cholinesterases (ChE): acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Until now, it has been difficult to determine the precise localization of BChE at the NMJ. In this study, we use a modification of Koelle's method to stain AChE and BChE activity. This method does not interfere with fluorescent co-staining, which allows precise co-localization of ChE and other synaptic molecules at the NMJ. We demonstrate that AChE and BChE exhibit different localization patterns at the mouse NMJ. AChE activity is present both in the primary cleft and in the secondary folds, whereas BChE activity appears to be almost absent in the primary cleft and to be concentrated in subsynaptic folds. The same localization for BChE is observed in the AChE-knockout (KO) mouse NMJ. Collagenase treatment removed AChE from the primary cleft, but not from secondary folds in the wild-type mouse, whereas in the AChE-KO mouse, BChE remains in the secondary folds. After peripheral nerve injury and regeneration, BChE localization is not modified in either normal or KO mice. In conclusion, specific localization of BChE in the secondary folds of the NMJ suggests that this enzyme is not a strict surrogate of AChE and that the two enzymes have two different roles.

Contributions of selective knockout studies to understanding cholinesterase disposition and function

The complete knockout of the acetylcholinesterase gene (AChE) in the mouse yielded a surprising phenotype that could not have been predicted from deletion of the cholinesterase genes in Drosophila, that of a living, but functionally compromised animal. The phenotype of this animal showed a sufficient compromise in motor function that precluded precise characterization of central and peripheral nervous functional deficits. Since AChE in mammals is encoded by a single gene with alternative splicing, additional understanding of gene expression might be garnered from selected deletions of the alternatively spliced exons. To this end, transgenic strains were generated that deleted exon 5, exon 6, and the combination of exons 5 and 6. Deletion of exon 6 reduces brain AChE by 93% and muscle AChE by 72%. Deletion of exon 5 eliminates AChE from red cells and the platelet surface. These strains, as well as knockout strains that selectively eliminate the AChE anchoring protein subunits PRiMA or ColQ (which bind to sequences specified by exon 6) enabled us to examine the role of the alternatively spliced exons responsible for the tissue disposition and function of the enzyme. In addition, a knockout mouse was made with a deletion in an upstream intron that had been identified in differentiating cultures of muscle cells to control AChE expression. We found that deletion of the intronic regulatory region in the mouse essentially eliminated AChE in muscle and surprisingly from the surface of platelets. The studies generated by these knockout mouse strains have yielded valuable insights into the function and localization of AChE in mammalian systems that cannot be approached in cell culture or in vitro.

Developmental aspects of the cholinergic system

Beyond its importance in sustaining or modulating different aspects of the activity of the central nervous system (CNS), the cholinergic system plays important roles during development. In the current review, we focus on the developmental aspects associated with major components of the cholinergic system: Acetylcholine, choline acetyltransferase, vesicular acetylcholine transporter, high-affinity choline transporter, acetylcholinesterase, nicotinic and muscarinic receptors. We describe when and where each one of these components is first identified in the CNS and the changes in their levels that occur during the course of prenatal and postnatal development. We also describe how these components are relevant to many events that occur during the development of the CNS, including progenitor cells proliferation and differentiation, neurogenesis, gliogenesis, neuronal maturation and plasticity, axonal pathfinding, regulation of gene expression and cell survival. It will be noticed that evidence regarding the developmental aspects of the cholinergic system comes mostly from studies that used agonists, such as nicotine, and antagonists, such as hemicholinium-3. Studies using immunohistochemistry and genetically altered mice also provided valuable information.

Behavioral phenotyping of heterozygous acetylcholinesterase knockout (AChE+/-) mice showed no memory enhancement but hyposensitivity to amnesic drugs

Decrease in the expression or activity of acetylcholinesterase (AChE) enzymatic activity results in increased cholinergic tonus in the brain and periphery, with concomitant regulations of nicotinic and muscarinic receptors expression. We generated AChE knockout mice and characterized the behavioral phenotype of heterozygous animals, focusing on learning and memory functions. Male and female, AChE+/- and AChE+/+ littermate controls (129 sv strain) were tested at 5-9 weeks of age. AChE activity was significantly decreased in the hippocampus and cortex of AChE+/- mice, but butyrylcholinesterase activity was preserved. AChE+/- mice failed to show any difference in terms of locomotion, exploration and anxiety parameters in the open-field test. Animals were then tested for place learning in the water-maze. They were trained using a 'sustained acquisition' protocol (3 swim trials per day) or a 'mild acquisition' protocol (2 swim trials per day) to locate an invisible platform in fixed position (reference memory procedure). Then, during 3 days, they were trained to locate the platform in a variable position (working memory procedure). Learning profiles and probe test performances were similar for AChE+/- and AChE+/+ mice. Mice were then treated with the muscarinic receptor antagonist scopolamine (0.5, 5 mg/kg) 20 min before each training session. Scopolamine impaired learning at both doses in AChE+/+ mice, but only at the highest dose in AChE+/- mice. Moreover, the intracerebroventricular injection of amyloid-beta25-35 peptide, 9 nmol, 7 days before water-maze acquisition, failed to induce learning deficits in AChE+/- mice, but impaired learning in AChE+/+ controls. The peptide failed to be toxic in forebrain structures of AChE+/- mice, since an increase in lipid peroxidation levels was measured in the hippocampus of AChE+/+ but not AChE+/- mice. We conclude that the increase in cholinergic tonus observed in AChE+/- mice did not result in increased memory functions but allowed a significant prevention of the deleterious effects of muscarinic blockade or amyloid toxicity.

Mechanisms of cardiac muscle insensitivity to a novel acetylcholinesterase inhibitor C-547

We compared the effects of the novel acetylcholinesterase (AChE) inhibitor C-547 on action potential configuration and sinus rhythm in the isolated right atrium preparation of rat with those of armin and neostigmine. Both armin (10(-7), 10(-6), and 10(-5) M) and neostigmine (10(-7), 10(-6), and 5 x 10(-6) M) produced a marked decrease in action potential duration and slowing of sinus rate. These effects were abolished by atropine and are attributable to the accumulation of acetylcholine in the myocardium. The novel selective AChE inhibitor C-547 (10(-9) to 10(-7) M), an alkylammonium derivative of 6-methyluracil, had no such effects. The inhibition constant of C-547 on cardiac AChE is 40-fold higher than that on extensor digitorum longus muscle AChE. These results suggest that C-547 might be employed to treat diseases such as myasthenia gravis or Alzheimer disease, without having unwanted effects on the heart.

Influence of differential expression of acetylcholinesterase in brain and muscle on respiration

A mouse strain with a deleted acetylcholinesterase (AChE) gene (AChE knockout) shows a decreased inspiration time and increased tidal volume and ventilation .To investigate the respective roles of AChE in brain and muscle, we recorded respiration by means of whole-body plethysmography in knockout mice with tissue selective deletions in AChE expression. A mouse strain with the anchoring domains of AChE deleted (del E5+6 knockout mice) has very low activity in the brain and neuromuscular junction, but increased monomeric AChE in serum. A mouse strain with deletion of the muscle specific region of AChE (del i1RR knockout mice) exhibits no expression in muscle, but unaltered expression in the central nervous system. Neither strain exhibits the pronounced phenotypic traits observed in the complete AChE knockout strain. A third strain lacking the anchor molecule PRiMA, has no functional AChE and butyrylcholinesterase (BChE) in brain and an unaltered respiratory function. BChE inhibition by bambuterol decreases tidal volume and body temperature in del E5+6 and i1RR knockout strains, but not in PRiMA deletion or wild-type controls. We find that: (1) deletion of the full AChE gene is required for a pronounced alteration in respiratory phenotype, (2) BChE is involved in respiratory muscles contraction and temperature control in del E5+6 and i1RR knockout mice, and (3) AChE expression requiring a gene product splice to either exons 5 and 6 or regulated by intron1 influences temperature control.

In vitro sensitivity of cholinesterases and [3H]oxotremorine-M binding in heart and brain of adult and aging rats to organophosphorus anticholinesterases

Organophosphorus (OP) insecticides elicit toxicity via acetylcholinesterase inhibition, allowing acetylcholine accumulation and excessive stimulation of cholinergic receptors. Some OP insecticides bind to additional macromolecules including butyrylcholinesterase and cholinergic receptors. While neurotoxicity from OP anticholinesterases has been extensively studied, effects on cardiac function have received less attention. We compared the in vitro sensitivity of acetylcholinesterase, butyrylcholinesterase and [(3)H]oxotremorine-M binding to muscarinic receptors in the cortex and heart of adult (3 months) and aging (18 months) rats to chlorpyrifos, methyl parathion and their active metabolites chlorpyrifos oxon and methyl paraoxon. Using selective inhibitors, the great majority of cholinesterase in brain was defined as acetylcholinesterase, while butyrylcholinesterase was the major cholinesterase in heart, regardless of age. In the heart, butyrylcholinesterase was markedly more sensitive than acetylcholinesterase to inhibition by chlorpyrifos oxon, and butyrylcholinesterase in tissues from aging rats was more sensitive than enzyme from adults, possibly due to differences in A-esterase mediated detoxification. Relatively similar differences were noted in brain. In contrast, acetylcholinesterase was more sensitive than butyrylcholinesterase to methyl paraoxon in both heart and brain, but no age-related differences were noted. Both oxons displaced [(3)H]oxotremorine-M binding in heart and brain of both age groups in a concentration-dependent manner. Chlorpyrifos had no effect but methyl parathion was a potent displacer of binding in heart and brain of both age groups. Such OP and age-related differences in interactions with cholinergic macromolecules may be important because of potential for environmental exposures to insecticides as well as the use of anticholinesterases in age-related neurological disorders.

Effect of fluoxetine on neuromuscular function in acetylcholinesterase (AChE) knockout mice

Congenital myasthenic syndromes (CMS) are a heterogeneous group of diseases caused by genetic defects affecting neuromuscular transmission. The causal mutations have been described in number of cases. The slow channel myasthenic syndrome (slow-channel-CMS) results in a marked prolongation of channel opening in stimulated receptors (nAChR) and the end plate acetylcholinesterase (AChE) deficiency congenital myasthenic syndrome (ColQ-CMS) results in an increased action of acetylcholine (ACh) at the synapse. Anticholinesterase medication is detrimental in these cases. The successful treatment of slow-channel-CMS patients with the antidepressant serotonin re-uptake inhibitor fluoxetine has been reported. At high concentration it has a non-depolarizing effect on nicotinic receptors. This led us to the idea that fluoxetine could protect AChR from a relative excess of ACh. We investigated the possible use of fluoxetine as treatment in the AChE KO mouse. Treatment at 6 mg/kg from 3 weeks to 2 months increased slightly the daily weight gain but not the final weight at 2 months in AChE-/- mice. Isometric force production of Tibialis anterior in response to electric nerve stimulation was measured in situ in AChE-/- and wild type mice treated or not by fluoxetine. The results show that the maximum twitch force in response to a single nerve stimulation, the maximal tetanic force (P0) in response to repetitive nerve stimulation and the tetanic fade are not changed in AChE-/- mice treated with fluoxetine versus control AChE-/- mice.

Diminished antigen-specific IgG1 and interleukin-6 production and acetylcholinesterase expression in combined M1 and M5 muscarinic acetylcholine receptor knockout mice

Immunological activation of T cells enhances synthesis of acetylcholine (ACh) and transcription of choline acetyltransferase (ChAT), M5 muscarinic ACh receptor (mAChR) and acetylcholinesterase (AChE). Stimulation of mAChRs on T and B cells causes oscillating Ca(2+)-signaling and up-regulation of c-fos expression; moreover, M1 mAChRs play a crucial role in the differentiation of CD8(+) T cells into cytolytic T lymphocytes. Collectively, these findings suggest that immune cell function is regulated by its own cholinergic system. Bearing that in mind, we tested whether immune function can be regulated via mAChR-mediated pathways by immunizing combined M1 and M5 mAChR knockout (M1/M5 KO) and wild-type (WT) C57BL/6JJcl mice with ovalbumin (OVA) and measuring serum IgG1 and IgM 1 wk later. We found that serum levels of total and anti-OVA-specific IgG1 were significantly lower in M1/M5 KO than WT mice, though there was no difference in serum levels of total and anti-OVA-specific IgM between the two genotypes. Secretion of interleukin (IL)-6 from activated spleen cells was significantly reduced in M1/M5 KO mice, whereas there was no significant change in gamma interferon secretion. Expression of AChE mRNA was significantly reduced in activated spleen cells from M1/M5 KO mice. These results suggest that M1 and/or M5 mAChRs are involved in regulating cytokine (e.g., IL-6) production, leading to modulation of antibody class switching from IgM to IgG1, but are not involved in the initial generation of the antibody response. They also support the notion that a non-neuronal cholinergic system is involved in regulating immune cell function.