Dynamic regulation of the cholinergic system in the spinal central nervous system

Loss of ctnnd2b affects neuronal differentiation and behavior in zebrafish

Delta-catenin (CTNND2) is an adhesive junction associated protein belonging to the family of p120 catenins. The human gene is located on the short arm of chromosome 5, the region deleted in Cri-du-chat syndrome (OMIM #123450). Heterozygous loss of CTNND2 has been linked to a wide spectrum of neurodevelopmental disorders such as autism, schizophrenia, and intellectual disability. Here we studied how heterozygous loss of ctnnd2b affects zebrafish embryonic development, and larvae and adult behavior. First, we observed a disorganization of neuronal subtypes in the developing forebrain, namely the presence of ectopic isl1-expressing cells and a local reduction of GABA-positive neurons in the optic recess region. Next, using time-lapse analysis, we found that the disorganized distribution of is1l-expressing forebrain neurons resulted from an increased specification of Isl1:GFP neurons. Finally, we studied the swimming patterns of both larval and adult heterozygous zebrafish and observed an increased activity compared to wildtype animals. Overall, this data suggests a role for ctnnd2b in the differentiation cascade of neuronal subtypes in specific regions of the vertebrate brain, with repercussions in the animal's behavior.

Developmental Neurotoxicity of Difenoconazole in Zebrafish Embryos

Difenoconazole is a type of triazole fungicide that is widely used in the treatment of plant diseases. Triazole fungicides have been shown in several studies to impair the development of the nervous system in zebrafish embryos. There is still little known about difenoconazole-induced neurotoxicity in fish. In this study, zebrafish embryos were exposed to 0.25, 0.5, and 1 mg/L of difenoconazole solution until 120 h post-fertilization (hpf). The difenoconazole-exposed groups showed concentration-dependent inhibitory tendencies in heart rate and body length. Malformation rate and spontaneous movement of zebrafish embryos increased, and the locomotor activity decreased in the highest exposure group. The content of dopamine and acetylcholine was reduced significantly in difenoconazole treatment groups. The activity of acetylcholinesterase (AChE) was also increased after treatment with difenoconazole. Furthermore, the expression of genes involved in neurodevelopment was remarkably altered, which corresponded with the alterations of neurotransmitter content and AChE activity. These results indicated that difenoconazole might affect the development of the nervous system through influencing neurotransmitter levels, enzyme activity, and the expression of neural-related genes, ultimately leading to abnormal locomotor activity in the early stages of zebrafish.

Mitigation of nicotine-induced developmental effects by 24-epibrassinolide in zebrafish

Nicotine is a highly addictive substance that can cause teratogenic impacts in the embryo through redox-dependent pathways. As antioxidants, naturally occurring chemicals can protect cells from redox imbalance. The purpose of this study was to evaluate the effectiveness of 24-epibrassinolide (24-EPI), a natural brassinosteroid with well-known antioxidant properties, in protecting zebrafish embryos against nicotine's teratogenic effects. For 96 h, embryos (2 h post-fertilization - hpf) were exposed to 100 μM nicotine, co-exposed with 24-EPI (0.01, 0.1, and 1 μM), and 24-EPI alone (1 μM). Lethal and sublethal developmental characteristics were evaluated during exposure. Biochemical tests were performed at the conclusion of the exposure, and distinct behavioural paradigms were analysed 24 h later. Nicotine exposure resulted in a higher proportion of larvae with deformities, which were decreased following co-exposure to 24-EPI. Nicotine exposure also caused an increase in oxidative stress as observed by the increased activity of superoxide dismutase and catalase accompanied by an increase in the malondialdehyde levels. Besides, metabolic changes were noticed as observed by the increased lactate dehydrogenase activity that were hypothesised to be associated to nicotine-induced hypoxia which may be responsible for the increased oxidative damage. In addition, locomotor deficits were observed as well as a decrease in the acetylcholinesterase activity denoting nicotine-induced cognitive dysfunction. However, co-exposure to 24-EPI alleviated behavioural deficits and improved nicotine-induced emotional states. Overall, and although further studies are required to clarify these effects, 24-EPI showed promising ameliorative properties against the teratogenic effects induced by nicotine.

Expression of olfactory receptor genes in non-olfactory tissues in the developing and adult zebrafish

Since the discovery of olfactory receptor (OR) genes, their expression in non-olfactory tissues have been reported in rodents and humans. For example, mouse OR23 (mOR23) is expressed in sperm and muscle cells and has been proposed to play a role in chemotaxis and muscle migration, respectively. In addition, mouse mesencephalic dopaminergic neurons express various ORs, which respond to corresponding ligands. As the OR genes comprise the largest multigene family of G protein-coupled receptors in vertebrates (over 400 genes in human and 1000 in rodents), it has been difficult to categorize the extent of their diverse expression in non-olfactory tissues making it challenging to ascertain their function. The zebrafish genome contains significantly fewer OR genes at around 140 genes, and their expression pattern can be easily analyzed by carrying out whole mount in situ hybridization (ISH) assay in larvae. In this study, we found that 31 out of 36 OR genes, including or104-2, or108-1, or111-1, or125-4, or128-1, or128-5, 133-4, or133-7, or137-3 are expressed in various tissues, including the trunk, pharynx, pancreas and brain in the larvae. In addition, some OR genes are expressed in distinct brain regions such as the hypothalamus and the habenula in a dynamic temporal pattern between larvae, juvenile and adult zebrafish. We further confirmed that OR genes are expressed in non-olfactory tissues by RT-PCR in larvae and adults. These results indicate tight regulation of OR gene expression in the brain in a spatial and temporal manner and that the expression of OR genes in non-olfactory tissues are conserved in vertebrates. This study provides a framework to start investigating the function of ORs in the zebrafish brain.

Different developmental insecticide exposure windows trigger distinct locomotor phenotypes in the early life stages of zebrafish

Due to their extensive use and high biological activity, insecticides largely contribute to loss of biodiversity and environmental pollution. The regulation of insecticides by authorities is mainly focused on lethal concentrations. However, sub-lethal effects such as alterations in behavior and neurodevelopment can significantly affect the fitness of individual fish and their population dynamics and therefore deserve consideration. Moreover, it is important to understand the impact of exposure timing during development, about which there is currently a lack of relevant knowledge. Here, we investigated whether there are periods during neurodevelopment of fish, which are particularly vulnerable to insecticide exposure. Therefore, we exposed zebrafish embryos to six different insecticides with cholinergic mode of action for 24 h during different periods of neurodevelopment and measured locomotor output using an age-matched behavior assay. We used the organophosphates diazinon and dimethoate, the carbamates pirimicarb and methomyl as well as the neonicotinoids thiacloprid and imidacloprid because they are abundant in the environment and cholinergic signaling plays a major role during key processes of neurodevelopment. We found that early embryonic motor behaviors, as measured by spontaneous tail coiling, increased upon exposure to most insecticides, while later movements, measured through touch-evoked response and a light-dark transition assay, rather decreased for the same insecticides and exposure duration. Moreover, the observed effects were more pronounced when exposure windows were temporally closer to the performing of the respective behavioral assay. However, the measured behavioral effects recovered after a short period, indicating that none of the exposure windows chosen here are particularly critical, but rather that insecticides acutely interfere with neuronal function at all stages as long as they are present. Overall, our results contribute to a better understanding of risks posed by cholinergic insecticides to fish and provide an important basis for the development of safe regulations to improve environmental health.

Cholinergic deficiency in the cholinergic system as a pathogenetic link in the formation of various syndromes in COVID-19

According to recent data, several mechanisms of viral invasion of the central nervous system (CNS) have been proposed, one of which is both direct penetration of the virus through afferent nerve fibers and damage to the endothelium of cerebral vessels. It has been proven that the SARS-CoV-2 virus affects pathologically not only the human cardiorespiratory system but is also associated with a wide range of neurological diseases, cerebrovascular accidents, and neuromuscular pathologies. However, the observed post-COVID symptom complex in patients, manifested in the form of headache, "fog in the head," high temperature, muscle weakness, lowering blood pressure, does it make us think about the pathophysiological mechanisms that contribute to the development of this clinical picture? One possible explanation is a disruption in the signaling of the acetylcholine system (AChS) in the body. Viral invasions, and in particular COVID-19, can negatively affect the work of the AChS, disrupting its coordination activities. Therefore, the main goal of this literature review is to analyze the information and substantiate the possible mechanisms for the occurrence of post-COVID syndrome in people who have had COVID-19 from the standpoint of AChS dysfunctions.

Novel Chromone-Containing Allylmorpholines Induce Anxiolytic-like and Sedative Effects in Adult Zebrafish

Chromone-containing allylmorpholines (CCAMs) are a novel class of compounds that have demonstrated acetyl- and butyryl-cholinesterase-inhibiting and N-methyl-D-aspartate (NMDA) receptor-blocking properties in vitro, but their in vivo pharmacological activity remains underexplored. In this work, we evaluated the psychotropic activity of five different CCAMs (1 (9a), 2 (9j), 3 (9l), 4 (33a), and 5 (33b)) using the novel tank test (NTT) and light/dark box (LDB) test in adult zebrafish. The CCAMs were screened in the NTT at a range of concentrations, and they were found to induce a dose-dependent sedative effect. Compound 4 (33a) was also evaluated using the LDB test, and it was found to have anxiolytic-like properties at low concentrations. To assess the potential contribution of the glutamate and cholinergic mechanisms in the effects of the CCAMs, we conducted experiments with pre-exposure to putative antagonists, NMDA and biperiden. Neither biperiden nor NMDA were able to diminish or cancel the effects of the CCAMs, countering the in vitro data obtained in previous studies. The apparent discrepancy could be related to the specifics of CCAM metabolism or to the interspecies differences between the putative target proteins, possibly due to the relatively low identity percentage of their sequences. Although further research in mammals is required in order to establish their pharmacological properties, novel CCAMs may represent an appealing group of psychoactive drug candidates.

Cholinergic Modulation of Locomotor Circuits in Vertebrates

Locomotion is a basic motor act essential for survival. Amongst other things, it allows animals to move in their environment to seek food, escape predators, or seek mates for reproduction. The neural mechanisms involved in the control of locomotion have been examined in many vertebrate species and a clearer picture is progressively emerging. The basic muscle synergies responsible for propulsion are generated by neural networks located in the spinal cord. In turn, descending supraspinal inputs are responsible for starting, maintaining, and stopping locomotion as well as for steering and controlling speed. Several neurotransmitter systems play a crucial role in modulating the neural activity during locomotion. For instance, cholinergic inputs act both at the spinal and supraspinal levels and the underlying mechanisms are the focus of the present review. Much information gained on supraspinal cholinergic modulation of locomotion was obtained from the lamprey model. Nicotinic cholinergic inputs increase the level of excitation of brainstem descending command neurons, the reticulospinal neurons (RSNs), whereas muscarinic inputs activate a select group of hindbrain neurons that project to the RSNs to boost their level of excitation. Muscarinic inputs also reduce the transmission of sensory inputs in the brainstem, a phenomenon that could help in sustaining goal directed locomotion. In the spinal cord, intrinsic cholinergic inputs strongly modulate the activity of interneurons and motoneurons to control the locomotor output. Altogether, the present review underlines the importance of the cholinergic inputs in the modulation of locomotor activity in vertebrates.

Metal contamination and heat stress impair swimming behavior and acetylcholinesterase activity in embryo-larval stages of the Mediterranean mussel, Mytilus galloprovincialis

Behavioral parameters are increasingly considered sensitive and early bioindicators of toxicity in aquatic organisms. A video-tracking tool was specifically developed to monitor the swimming behaviour of D-larvae of the Mediterranean mussel, Mytilus galloprovincialis, in controlled laboratory conditions. Both maximum and average swimming speeds and trajectories were recorded. We then investigated the impact of copper and silver with or without a moderate rise of temperature on swimming behavior and acetylcholinesterase (AChE) activity of mussel D-larvae and the possible mechanistic link between both biological responses. Our results showed that copper and/or silver exposure, as well as temperature increase, disrupts the swimming behavior of mussel larvae which could compromise their dispersal and survival. In addition, the combined effect of temperature and metals significantly (p < 0.05) increased AChE activity in mussel larvae. Pearson's correlation analysis was performed and results showed that the AChE activity is positively correlated with maximum speeds (r = 0.71, p < 0.01). This study demonstrates the value of behavioral analyzes of aquatic invertebrates as a sensitive and integrate marker of the effects of stressors.

Neuro- and Cardiovascular Activities of Montivipera bornmuelleri Snake Venom

Simple Summary

Snake venoms are rich in molecules acting on different biological systems, and they are responsible for the complications following snake bite envenoming. These bioactive molecules are of interest in pharmaceutical industries as templates for drug design. Different biological activities of Montivipera bornmuelleri snake venom have been already studied; however, the venom’s activity on the nervous system has not yet been studied, and its effect on the cardiovascular system needs further investigation. Herein, we show that this venom induces toxicity on the nervous system and disrupts the cardiovascular system, highlighting a broad spectrum of biological activities.

Abstract

The complications following snake bite envenoming are due to the venom’s biological activities, which can act on different systems of the prey. These activities arise from the fact that snake venoms are rich in bioactive molecules, which are also of interest for designing drugs. The venom of Montivipera bornmuelleri, known as the Lebanon viper, has been shown to exert antibacterial, anticancer, and immunomodulatory effects. However, the venom’s activity on the nervous system has not yet been studied, and its effect on the cardiovascular system needs further investigation. Because zebrafish is a convenient model to study tissue alterations induced by toxic agents, we challenged it with the venom of Montivipera bornmuelleri. We show that this venom leads to developmental toxicity but not teratogenicity in zebrafish embryos. The venom also induces neurotoxic effects and disrupts the zebrafish cardiovascular system, leading to heartbeat rate reduction and hemorrhage. Our findings demonstrate the potential neurotoxicity and cardiotoxicity of M. bornmuelleri’s venom, suggesting a multitarget strategy during envenomation.

Role of Bmal1 in mediating the cholinergic system to regulate the behavioral rhythm of nocturnal marine molluscs

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The circadian differential expression of AchE was identified using TMT quantitative proteomics;

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It was found that the Ach concentration and the expression levels of AchE and Bmal1 exhibit circadian cosine rhythm;

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The full-length sequences of AchE and nAchR were obtained by cloning technique and made available for phylogenetic analysis;

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The movement distance and duration of abalone increased after the injection of neostigmine methylsulfate as the AchE inhibitor;

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Bmal1 as the core circadian clock gene was proven to bind to AchE and nAchR, thereby regulating the movement behavior of abalone.

The circadian rhythm is one of the most general and important rhythms in biological organisms. In this study, continuous 24-h video recordings showed that the cumulative movement distance and duration of the abalone, Haliotis discus hannai, reached their maximum values between 20:00–00:00, but both were significantly lower between 08:00–12:00 than at any other time of day or night (P < 0.05). To investigate the causes of these diel differences in abalone movement behavior, their cerebral ganglia were harvested at 00:00 (group D) and 12:00 (group L) to screen for differentially expressed proteins using tandem mass tagging (TMT) quantitative proteomics. Seventy-five significantly different proteins were identified in group D vs. group L. The differences in acetylcholinesterase (AchE) expression levels between day- and nighttime and the key role in the cholinergic nervous system received particular attention during the investigation. A cosine rhythm analysis found that the concentration of acetylcholine (Ach) and the expression levels of AchE tended to be low during the day and high at night, and high during the day and low at night, respectively. However, the rhythmicity of the diel expression levels of acetylcholine receptor (nAchR) appeared to be insignificant (P > 0.05). Following the injection of three different concentrations of neostigmine methylsulfate, as an AchE inhibitor, the concentration of Ach in the hemolymph, and the expression levels of nAchR in the cerebral ganglia increased significantly (P < 0.05). Four hours after drug injection, the cumulative movement distance and duration of abalones were significantly higher than those in the uninjected control group, and the group injected with saline (P < 0.05). The expression levels of the core diurnal clock Bmal1 over a 24-h period also tended to be high during the day and low at night. First, a co-immunoprecipitation assay demonstrated the binding between Bmal1 and AchE or nAchR. A dual-luciferase gene test and electrophoretic mobility shift assay showed that Bmal1 bound to the promoter regions of AchE and nAchR. Twenty-four hours after silencing the Bmal1 gene, the expression levels of AchE and nAchR decreased significantly compared to those of the dsEGFP and PBS control groups, further showing that Bmal1 mediates the cholinergic system to regulate the behavioral rhythm of abalone. These findings shed light on the endocrine mechanism regulating the rhythmic behavior of abalone, and provide a reference for understanding the life history adaptation strategies of nocturnal organisms and the proliferation and protection of bottom dwelling economically important organisms.

Possible effects of different doses of 2.1 GHz electromagnetic radiation on learning, and hippocampal levels of cholinergic biomarkers in Wistar rats

The present study evaluated whether short-term exposure to different doses of 2.1 GHz radiofrequency electromagnetic radiation (RF-EMR) has different effects on rats' behaviour and hippocampal levels of central cholinergic biomarkers. Animals were divided into three equal groups namely; group 1 was sham-exposed group, group 2-3 were exposed to 45 V/m and 65 V/m doses of 2.1 GHz frequency for 1 week respectively. Numerical dosimetry simulations were carried out. Object location and Y-maze were used as behavioural tasks. The protein and mRNA expression levels of AChE, ChAT, and VAChT, in the hippocampus were tested using Western Blotting and Real-Time PCR. The impairment performance of rats subjected to 65 V/m dose of 2.1 GHz RF-EMR in both object location and Y-maze tasks was observed. The hippocampal levels of AChE, ChAT, and VAChT, were significantly lower in rats exposed to 65 V/m dose of 2.1 GHz RF-EMR than others. The stronger effect of "65 V/m" dose on both rat's hippocampal-dependent behavioural performances and hippocampal levels of cholinergic biomarkers may be due to the stronger effect of "65 V/m" dose where rats' snouts were located at the nearest distance from the monopole antenna. Furthermore, the simulated SAR values were high for 65 V/m electric-field strengths. For the first time, we report the potential dose-dependent effects of short-term exposure to 2.1 GHz radiation on rat's behavioural performances as well as hippocampal levels of cholinergic biomarkers. Further studies are needed to understand the mechanisms by which RF-EMR influences the function of the central cholinergic system in the brain.