Conserved role of dopamine in the modulation of behavior

Ferrostatin-1 mitigates cellular damage in a ferroptosis-like environment in Caenorhabditis elegans

Although iron (Fe) is the most biologically abundant transition metal, it is highly toxic when it accumulates as Fe2+, forming a labile Fe pool and favoring the Fenton reaction. This oxidative scenario leads to a type of caspase-independent programmed cell death, referred to as ferroptosis, where following processes take place: (i) Fe2+ overload, (ii) glutathione peroxidase 4 inactivation, (iii) lipid peroxidation, and (iv) glutathione depletion. The present study sought to evaluate the consequences of Fe2+ administration on ferroptosis induction in Caenorhabditis elegans. We demonstrated higher mortality, increased lipid peroxidation, reduced glutathione peroxidase activity, and morphological damage in dopaminergic neurons upon Fe2+ overload. Pharmacological intervention at the level of lipid peroxidation with ferrostatin-1 (250 μM) mitigated the damage and returned the biochemical parameters to basal levels, revealing the potential of this therapeutical approach. Finally, to assess the relationship between ferroptosis and dopamine in a Parkinsonian background, we evaluated the UA44 worm strain which overexpresses the alpha-synuclein protein in cherry-labeled dopaminergic neurons. We demonstrated that Fe2+ administration reduced lethality associated with similar alterations in biochemical and dopaminergic morphological parameters in wild-type animals. These experiments provide mechanistic-based evidence on the efficacy of a pharmacological approach to mitigate the physiological, biochemical, and morphological consequences of Fe2+ overload. At the same time, they encourage further research on the impact of the combined effects resulting from the genetic background and dopamine signaling in a Parkinsonian phenotype.

Effects of Chronic Exposure to Low Doses of Rotenone on Dopaminergic and Cholinergic Neurons in the CNS of Hemigrapsus sanguineus

Rotenone, as a common pesticide and insecticide frequently found in environmental samples, may be present in aquatic habitats worldwide. Exposure to low concentrations of this compound may cause alterations in the nervous system, thus contributing to Parkinsonian motor symptoms in both vertebrates and invertebrates. However, the effects of chronic exposure to low doses of rotenone on the activity of neurotransmitters that govern motor functions and on the specific molecular mechanisms leading to movement morbidity remain largely unknown for many aquatic invertebrates. In this study, we analyzed the effects that rotenone poisoning exerts on the activity of dopamine (DA) and acetylcholine (ACh) synthesis enzymes in the central nervous system (CNS) of Asian shore crab, Hemigrapsus sanguineus (de Haan, 1835), and elucidated the association of its locomotor behavior with Parkinson's-like symptoms. An immunocytochemistry analysis showed a reduction in tyrosine hydroxylase (TH) in the median brain and the ventral nerve cord (VNC), which correlated with the subsequent decrease in the locomotor activity of shore crabs. We also observed a variation in cholinergic neurons' activity, mostly in the ventral regions of the VNC. Moreover, the rotenone-treated crabs showed signs of damage to ChAT-lir neurons in the VNC. These data suggest that chronic treatment with low doses of rotenone decreases the DA level in the VNC and the ACh level in the brain and leads to progressive and irreversible reductions in the crab's locomotor activity, life span, and changes in behavior.

Cannabidiol and Tetrahydrocannabinol Antinociceptive Activity is Mediated by Distinct Receptors in Caenorhabditis elegans

Cannabis has gained popularity in recent years as a substitute treatment for pain following the risks of typical treatments uncovered by the opioid crisis. The active ingredients frequently associated with pain-relieving effects are the phytocannabinoids Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), but their effectiveness and mechanisms of action are still under research. In this study, we used Caenorhabditis elegans, an ideal model organism for the study of nociception that expresses mammal ortholog cannabinoid (NPR-19 and NPR-32) and vanilloid (OSM-9 and OCR-2) receptors. Here, we evaluated the antinociceptive activity of THC and CBD, identifying receptor targets and several metabolic pathways activated following exposure to these molecules. The thermal avoidance index was used to phenotype each tested C. elegans experimental group. The data revealed for the first time that THC and CBD decreases the nocifensive response of C. elegans to noxious heat (32-35 °C). The effect was reversed 6 h post- CBD exposure but not for THC. Further investigations using specific mutants revealed CBD and THC are targeting different systems, namely the vanilloid and cannabinoid systems, respectively. Proteomic analysis revealed differences following Reactome pathways and gene ontology biological process database enrichment analyses between CBD or THC-treated nematodes and provided insights into potential targets for future drug development.

The influence of internal pressure and neuromuscular agents on C. elegans biomechanics: an empirical and multi-compartmental in silico modelling study

The function of a specific tissue and its biomechanics are interdependent, with pathologies or ageing often being intertwined with structural decline. The biomechanics of Caenorhabditis elegans, a model organism widely used in pharmacological and ageing research, has been established as biomarker for healthy ageing. However, the properties of the constituent tissues, and their contribution to the overall mechanical characteristics of the organism, remain relatively unknown. In this study we investigated the biomechanics of healthy C. elegans cuticle, muscle tissue, and pseudocoelom using a combination of indentation experiments and in silico modelling. We performed stiffness measurements using an atomic force microscope. To approximate the nematode's cylindrical body we used a novel three-compartment nonlinear finite element model, enabling us to analyse of how changes in the elasticity of individual compartments affect the bulk stiffness. We then fine-tuned the parameters of the model to match the simulation force-indentation output to the experimental data. To test the finite element model, we modified distinct compartments experimentally. Our in silico results, in agreement with previous studies, suggest that hyperosmotic shock reduces stiffness by decreasing the internal pressure. Unexpectedly, treatment with the neuromuscular agent aldicarb, traditionally associated with muscle contraction, reduced stiffness by decreasing the internal pressure. Furthermore, our finite element model can offer insights into how drugs, mutations, or processes such as ageing target individual tissues.

Neural mechanisms of dopamine function in learning and memory in Caenorhabditis elegans

Research into learning and memory over the past decades has revealed key neurotransmitters that regulate these processes, many of which are evolutionarily conserved across diverse species. The monoamine neurotransmitter dopamine is one example of this, with countless studies demonstrating its importance in regulating behavioural plasticity. However, dopaminergic neural networks in the mammalian brain consist of hundreds or thousands of neurons, and thus cannot be studied at the level of single neurons acting within defined neural circuits. The nematode Caenorhabditis elegans (C. elegans) has an experimentally tractable nervous system with a completely characterized synaptic connectome. This makes it an advantageous system to undertake mechanistic studies into how dopamine encodes lasting yet flexible behavioural plasticity in the nervous system. In this review, we synthesize the research to date exploring the importance of dopaminergic signalling in learning, memory formation, and forgetting, focusing on research in C. elegans. We also explore the potential for dopamine-specific fluorescent biosensors in C. elegans to visualize dopaminergic neural circuits during learning and memory formation in real-time. We propose that the use of these sensors in C. elegans, in combination with optogenetic and other light-based approaches, will further illuminate the detailed spatiotemporal requirements for encoding behavioural plasticity in an accessible experimental system. Understanding the key molecules and circuit mechanisms that regulate learning and forgetting in more compact invertebrate nervous systems may reveal new druggable targets for enhancing memory storage and delaying memory loss in bigger brains.

The peptide Acein promotes dopamine secretion through clec-126 to extend the lifespan of elderly C. elegans

Dopamine plays a crucial role in regulating brain activity and movement and modulating human behavior, cognition and mood. Regulating dopamine signaling may improve cognitive abilities and physical functions during aging. Acein, a nonapeptide of sequence H-Pro-Pro-Thr-Thr-Thr-Lys-Phe-Ala-Ala-OH is able to stimulate dopamine secretion in the brain. By using genetic editing and lifespan investigation in C. elegans, we showed that the lack of the C-type lectin domain-containing protein clec-126 significantly suppressed the aging phenotype and prolonged lifespan, while overexpression of clec-126 promoted aging-related phenotypes and accelerated the aging process. We examined the aging phenotype of C. elegans and showed that Acein could induce a decrease in clec-126 expression, prolonging the lifespan of aged C. elegans. The mechanism proceeds through the Acein-induced stimulation of dopamine secretion that ameliorates motor function decline and extends the healthy lifespan of aged C. elegans. In addition, we also observed an increase in brood number. Our study has shown that Acein regulates dopamine secretion and has good antiaging activity by decreasing clec-126 expression.

The worm Adult Activity Test (wAAT): A de novo mathematical model for detecting acute chemical effects in Caenorhabditis elegans

We have adapted a semiautomated method for tracking Caenorhabditis elegans spontaneous locomotor activity into a quantifiable assay by developing a sophisticated method for analyzing the time course of measured activity. The 16-h worm Adult Activity Test (wAAT) can be used to measure C. elegans activity levels for efficient screening for pharmacological and toxicity-induced effects. As with any apical endpoint assay, the wAAT is mode of action agnostic, allowing for detection of effects from a broad spectrum of response pathways. With caffeine as a model mild stimulant, the wAAT showed transient hyperactivity followed by reversion to baseline. Mercury chloride (HgCl2 ) produced an early dose-response hyperactivity phase followed by pronounced hypoactivity, a behavior pattern we have termed a toxicant "escape response." Methylmercury chloride (meHgCl) produced a similar pattern to HgCl2 , but at much lower concentrations, a weaker hyperactivity response, and more pronounced hypoactivity. Sodium arsenite (NaAsO2 ) and dimethylarsinic acid (DMA) induced hypoactivity at high concentrations. Acute toxicity, as measured by hypoactivity in C. elegans adults, was ranked: meHgCl > HgCl2  > NaAsO2  = DMA. Caffeine was not toxic with the wAAT at tested concentrations. Methods for conducting the wAAT are described, along with instructions for preparing C. elegans Habitation Medium, a liquid nutrient medium that allows for developmental timing equivalent to that found with C. elegans grown on agar with OP50 Escherichia coli feeder cultures. A de novo mathematical parametric model for adult C. elegans activity and the application of this model in ranking exposure toxicity are presented.

Dopaminergic modulation by quercetin: In silico and in vivo evidence using Caenorhabditis elegans as a model

Quercetin is a flavonol widely distributed in plants and has various described biological functions. Several studies have reported on its ability to restore neuronal function in a wide variety of disease models, including animal models of neurodegenerative disorders such as Parkinson's disease. Quercetin per se can act as a neuroprotector/neuromodulator, especially in diseases related to impaired dopaminergic neurotransmission. However, little is known about how quercetin interacts with the dopaminergic machinery. Here we employed the nematode Caenorhabditis elegans to study this putative interaction. After observing behavioral modulation, mutant analysis and gene expression in C. elegans upon exposure to quercetin at a concentration that does not protect against MPTP, we constructed a homology-based dopamine transporter protein model to conduct a docking study. This led to suggestive evidence on how quercetin may act as a dopaminergic modulator by interacting with C. elegans' dopamine transporter and alter the nematode's exploratory behavior. Consistent with this model, quercetin controls C. elegans behavior in a way dependent on the presence of both the dopamine transporter (dat-1), which is up-regulated upon quercetin exposure, and the dopamine receptor 2 (dop-2), which appears to be mandatory for dat-1 up-regulation. Our data propose an interaction with the dopaminergic machinery that may help to establish the effects of quercetin as a neuromodulator.

Chronic toxicity of broflanilide in Daphnia magna: changes in molting, behavior, and gene expression

Broflanilide is a novel pesticide used in agriculture that binds to unique receptors on pests; however, the widespread use of broflanilide has led to toxicity in Daphnia magna. At present, little information on the potential threats broflanilide imposes on D. magna is available. Therefore, the present study examined the chronic toxicity of broflanilide in D. magna by comparing changes in molting, neurotransmitter function, and behavior. The results showed that broflanilide caused chronic toxicity in D. magna at a concentration of 8.45 μg/L, and growth, development, reproduction, and the development of offspring were affected. In addition, broflanilide affected the molting of D. magna by significantly inhibiting the expression of chitinase, ecdysteroid, and related genes. Broflanilide also affected the expression of γ-glutamic acid, glutamine, gamma-aminobutyric acid, 5-hydroxytryptamine, 5-hydroxytryptophan, dopa, and dopamine. Furthermore, the swimming distance and speed of D. magna were reduced. Taken together, the results demonstrate the chronic toxicity and exposure risk of broflanilide in D. magna.

Effects of a New Natural Catechol-O-methyl Transferase Inhibitor on Two In Vivo Models of Parkinson's Disease

A tetrahydroisoquinoline identified in Mucuna pruriens ((1R,3S)-6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline-1,3-dicarboxylic acid, compound 4) was synthesized and assessed for its in vitro pharmacological profile and in vivo effects in two animal models of Parkinson's disease. Compound 4 inhibits catechol-O-methyltransferase (COMT) with no affinity for the dopaminergic receptors or the dopamine transporter. It restores dopamine-mediated motor behavior when it is co-administered with L-DOPA to C. elegans worms with 1-methyl-4-phenylpyridinium-damaged dopaminergic neurons. In a 6-hydroxydopamine rat model of Parkinson's disease, its co-administration at 30 mg/kg with L-DOPA enhances the effect of L-DOPA with an intensity similar to that of tolcapone 1 at 30 mg/kg but for a shorter duration. The effect is not dose-dependent. Compound 4 seems not to cross the blood-brain barrier and thus acts as a peripheral COMT inhibitor. COMT inhibition by compound 4 further validates the traditional use of M. pruriens for the treatment of Parkinson's disease, and compound 4 can thus be considered as a promising drug candidate for the development of safe, peripheral COMT inhibitors.

Acute toxicity of broflanilide on neurosecretory system and locomotory behavior of zebrafish (Danio rerio)

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC₅₀) of 0.76 mg/L. However, its effect on fish behavior and the underlying mechanisms are still unclear. The present study evaluated the effects of broflanilide on the zebrafish brain over a 96-h exposure by comparing the histopathological changes and relative expression of targeted genes with the behavioral metrics. The results of the toxicity test showed that broflanilide could cause deformities, such as deformation of the operculum and spinal curvature, at 0.6, 0.82 and 1.15 mg/L. Results also showed tissue damage and apoptosis in the cerebellum under 0.27 and 0.6 mg/L exposure. Additionally, broflanilide affected the neurotransmitters, metabolites and transcripts of genes associated with dopamine, gamma-aminobutyric acid expression. and the signaling pathways in zebrafish brains at 0.60 mg/L after 1 h and 96 h of exposure, while the levels of glutamate, glutamate decarboxylase, GABA transaminase, nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) were also inhibited at 0.27 mg/L after 96 h of exposure. The accumulated swimming distance was significantly longer and the average speed was significantly faster than the control at 0.27 and 0.6 mg/L after 1-h of exposure, while these metrics were lowered at 0.6 mg/L after 96 h of exposure. The study results demonstrates that broflanilide affects the zebrafish brain, neurotransmitters and associated fish behaviors. This study also provides deeper insight into the mechanistic understanding of the effects of broflanilide on the zebrafish brain.

Exposome, Molecular Pathways and One Health: The Invertebrate Caenorhabditis elegans

Due to its preferred habitats in the environment, the free-living nematode Caenorhabditis elegans has become a realistic target organism for pollutants, including manufactured nanoparticles. In the laboratory, the invertebrate animal model represents a cost-effective tool to investigate the molecular mechanisms of the biological response to nanomaterials. With an estimated number of 22,000 coding genes and short life span of 2-3 weeks, the small worm is a giant when it comes to characterization of molecular pathways, long-term low dose pollutant effects and vulnerable age-groups. Here, we review (i) flows of manufactured nanomaterials and exposition of C. elegans in the environment, (ii) the track record of C. elegans in biomedical research, and (iii) its potential to contribute to the investigation of the exposome and bridge nanotoxicology between higher organisms, including humans. The role of C. elegans in the one health concept is taken one step further by proposing methods to sample wild nematodes and their molecular characterization by single worm proteomics.

Crosstalk between neurons and glia through G-protein coupled receptors: Insights from Caenorhabditis elegans

The past decades have witnessed a dogmatic shift from glia as supporting cells in the nervous system to their active roles in neurocentric functions. Neurons and glia communicate and show bidirectional responses through tripartite synapses. Studies across species indicate that neurotransmitters released by neurons are perceived by glial receptors, which allow for gliotransmitter release. These gliotransmitters can result in activation of neurons via neuronal GPCR receptors. However, studies of these molecular interactions are in their infancy. Caenorhabditis elegans has a conserved neuron-glia architectural repertoire with molecular and functional resemblance to mammals. Further, glia in C. elegans can be manipulated through ablation and mutations allowing for deciphering of glial dependent processes in vivo at single glial resolutions. Here, we will review recent findings from vertebrate and invertebrate organisms with a focus on how C. elegans can be used to advance our understanding of neuron-glia interactions through GPCRs.

Developmental lead exposure affects dopaminergic neuron morphology and modifies basal slowing response in Caenorhabditis elegans: effects of ethanol

Lead (Pb) and ethanol (EtOH) are neurotoxicants that affect the dopaminergic (DAergic) system. We first sought to assess the morphology of the DAergic neurons in the Caenorhabditis elegans BY200 strain. The results demonstrated dose-dependent damage in these neurons induced by developmental Pb exposure. Secondly, transgenic worms exposed to 24μM Pb and administered with 200mM EtOH were evaluated in the basal slowing response (BSR). Pb induced impairment in the BSR in the wild-type strain that did not improve in response to EtOH, an effect also observed in strains that lack the DOP-1, DOP-2, and DOP-3 receptors. The animals that overexpress tyrosine hydroxylase (TH), or lack the vesicular transport (VMAT) showed a Pb-induced impairment in the BSR that seemed to improve after EtOH. Interestingly, a dramatic impairment in the BSR was observed in the Pb group in strains lacking the DOP-4 receptor, resembling the response of the TH-deficient strain, an effect that in both cases showed a non-significant reversal by EtOH. These results suggest that the facilitatory effect of EtOH on the impaired BSR observed in Pb-exposed null mutant strains may be the result of a compensatory effect in the altered DAergic synapse present in these animals.

Invited review: Unearthing the mechanisms of age-related neurodegenerative disease using Caenorhabditis elegans

As human life expectancy increases, neurodegenerative diseases present a growing public health threat, for which there are currently few effective treatments. There is an urgent need to understand the molecular and genetic underpinnings of these disorders so new therapeutic targets can be identified. Here we present the argument that the simple nematode worm Caenorhabditis elegans is a powerful tool to rapidly study neurodegenerative disorders due to their short lifespan and vast array of genetic tools, which can be combined with characterization of conserved neuronal processes and behavior orthologous to those disrupted in human disease. We review how pre-existing C. elegans models provide insight into human neurological disease as well as an overview of current tools available to study neurodegenerative diseases in the worm, with an emphasis on genetics and behavior. We also discuss open questions that C. elegans may be particularly well suited for in future studies and how worms will be a valuable preclinical model to better understand these devastating neurological disorders.

Neurotoxicity induced by toluene: In silico and in vivo evidences of mitochondrial dysfunction and dopaminergic neurodegeneration

Toluene is an air pollutant widely used as an organic solvent in industrial production and emitted by fossil fuel combustion, in addition to being used as a drug of abuse. Its toxic effects in the central nervous system have not been well established, and how and which neurons are affected remains unknown. Hence, this study aimed to fill this gap by investigating three central questions: 1) How does toluene induce neurotoxicity? 2) Which neurons are affected? And 3) What are the long-term effects induced by airborne exposure to toluene? To this end, a Caenorhabditis elegans model was employed, in which worms at the fourth larval stage were exposed to toluene in the air for 24 h in a vapor chamber to simulate four exposure scenarios. After the concentration-response curve analysis, we chose scenarios 3 (E3: 792 ppm) and 4 (E4: 1094 ppm) for the following experiments. The assays were performed 1, 48, or 96 h after removal from the exposure environments, and an irreversible reduction in neuron fluorescence and morphologic alterations were observed in different neurons of exposed worms, particularly in the dopaminergic neurons. Moreover, a significant impairment in a dopaminergic-dependent behavior was also associated with negative effects in healthspan endpoints, and we also noted that mitochondria may be involved in toluene-induced neurotoxicity since lower adenosine 5'-triphosphate (ATP) levels and mitochondrial viability were observed. In addition, a reduction of electron transport chain activity was evidenced using ex vivo protocols, which were reinforced by in silico and in vitro analysis, demonstrating toluene action in the mitochondrial complexes. Based on these findings model, it is plausible that toluene neurotoxicity can be initiated by complex I inhibition, triggering a mitochondrial dysfunction that may lead to irreversible dopaminergic neuronal death, thus impairing neurobehavioral signaling.

Microplastics and Their Impact on Reproduction-Can we Learn From the C. elegans Model?

Biologically active environmental pollutants have significant impact on ecosystems, wildlife, and human health. Microplastic (MP) and nanoplastic (NP) particles are pollutants that are present in the terrestrial and aquatic ecosystems at virtually every level of the food chain. Moreover, recently, airborne microplastic particles have been shown to reach and potentially damage respiratory systems. Microplastics and nanoplastics have been shown to cause increased oxidative stress, inflammation, altered metabolism leading to cellular damage, which ultimately affects tissue and organismal homeostasis in numerous animal species and human cells. However, the full impact of these plastic particles on living organisms is not completely understood. The ability of MPs/NPs to carry contaminants, toxic chemicals, pesticides, and bioactive compounds, such as endocrine disrupting chemicals, present an additional risk to animal and human health. This review will discusses the current knowledge on pathways by which microplastic and nanoplastic particles impact reproduction and reproductive behaviors from the level of the whole organism down to plastics-induced cellular defects, while also identifying gaps in current knowledge regarding mechanisms of action. Furthermore, we suggest that the nematode Caenorhabditis elegans provides an advantageous high-throughput model system for determining the effect of plastic particles on animal reproduction, using reproductive behavioral end points and cellular readouts.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.

Manganese exposure during early larval stages of C. elegans causes learning disability in the adult stage

Manganese (Mn), even though an essential trace element, causes neurotoxicity in excess. In adults, over-exposure to Mn causes clinical manifestations, including dystonia, progressive bradykinesia, disturbance of gait, slurring, and stuttering of speech. These symptoms are mainly because of Mn-associated oxidative stress and degeneration of dopamine neurons in the central nervous system. Children with excessive Mn exposure often show learning disabilities but rarely show symptoms associated with dopaminergic neuron dysfunction. It is unclear why Mn exposure shows distinctive clinical outcomes in developing brains versus adult brains. Studies on nematode C. elegans have demonstrated that it is an excellent model to elucidate Mn-associated toxicity in the nervous system. In this study, we chronically exposed Mn to L1 larval stage of the worms to understand the effects on dopamine neurons and cognitive development. The worms showed modified behavior to exogenous dopamine compared to the control. The dopamine neurons showed resistance to neurodegeneration on repeated Mn exposure during the adult stage. As observed in mammalian systems, these worms showed significantly low olfactory adaptive learning and memory. This study shows that C. elegans alters adaptive developmental plasticity during Mn overexposure, modifying its sensitivity towards the metal ion and leads to remodeling in its innate learning behavior.

Genome-Wide Transcriptional Responses of Marine Nematode Litoditis marina to Hyposaline and Hypersaline Stresses

Maintenance of osmotic homeostasis is essential for all organisms, especially for marine animals in the ocean with 3% salinity or higher. However, the underlying molecular mechanisms that how marine animals adapt to high salinity environment compared to their terrestrial relatives, remain elusive. Here, we investigated marine animal’s genome-wide transcriptional responses to salinity stresses using an emerging marine nematode model Litoditis marina. We found that the transthyretin-like family genes were significantly increased in both hyposaline and hypersaline conditions, while multiple neurotransmitter receptor and ion transporter genes were down-regulated in both conditions, suggesting the existence of conserved strategies for response to stressful salinity environments in L. marina. Unsaturated fatty acids biosynthesis related genes, neuronal related tubulins and intraflagellar transport genes were specifically up-regulated in hyposaline treated worms. By contrast, cuticle related collagen genes were enriched and up-regulated for hypersaline response. Given a wide range of salinity tolerance of the marine nematodes, this study and further genetic analysis of key gene(s) of osmoregulation in L. marina will likely provide important insights into biological evolution and environmental adaptation mechanisms in nematodes and other invertebrate animals in general.

Increased dopaminergic neurotransmission results in ethanol dependent sedative behaviors in Caenorhabditis elegans

Ethanol is a widely used drug, excessive consumption of which could lead to medical conditions with diverse symptoms. Ethanol abuse causes dysfunction of memory, attention, speech and locomotion across species. Dopamine signaling plays an essential role in ethanol dependent behaviors in animals ranging from C. elegans to humans. We devised an ethanol dependent assay in which mutants in the dopamine autoreceptor, dop-2, displayed a unique sedative locomotory behavior causing the animals to move in circles while dragging the posterior half of their body. Here, we identify the posterior dopaminergic sensory neuron as being essential to modulate this behavior. We further demonstrate that in dop-2 mutants, ethanol exposure increases dopamine secretion and functions in a DVA interneuron dependent manner. DVA releases the neuropeptide NLP-12 that is known to function through cholinergic motor neurons and affect movement. Thus, DOP-2 modulates dopamine levels at the synapse and regulates alcohol induced movement through NLP-12.

Cell-type-specific asynchronous modulation of PKA by dopamine in learning

Reinforcement learning models postulate that dopamine (DA) releasing neurons (DANs) encode information about action and action outcome and provide a teaching signal to striatal spiny projection neurons (SPNs) in the form of DA release¹. DA is thought to guide learning via dynamic and differential modulation of protein kinase A (PKA) in each class of SPN². However, the real-time relationship between DA and SPN PKA remains untested in behaving animals. Here, we monitor the activity of DANs, extracellular DA levels, and net PKA activity in SPNs in the nucleus accumbens in mice during learning. We find positive and negative modulation of DA that evolves across training and is both necessary and sufficient to explain concurrent fluctuations in SPN PKA activity. The modulations of PKA in SPNs that express type-1 and type-2 DA receptors are dichotomous such that they are selectively sensitive to increases and decreases in DA, respectively, which occur at different phases of learning. Thus, PKA-dependent pathways in each class of SPNs are asynchronously engaged by positive or negative DA signals during learning.

Caffeine reduces deficits in mechanosensation and locomotion induced by L-DOPA and protects dopaminergic neurons in a transgenic Caenorhabditis elegans model of Parkinson's disease

CONTEXT

L-DOPA is the first-line drug for Parkinson's disease (PD). However, chronic use can lead to dyskinesia. Caffeine, which is a known neuroprotectant, can potentially act as an adjunct to minimise adverse effects of L-DOPA.

OBJECTIVES

This study determined changes in terms of neurodegeneration, locomotion and mechanosensation in Caenorhabditis elegans (Rhabditidae) strain UA57 overexpressing tyrosine hydroxylase (CAT-2) when treated with caffeine, L-DOPA or their combinations.

MATERIALS AND METHODS

Neurodegeneration was monitored via fluorescence microscopy of GFP-tagged dopaminergic neurons in the head and tail regions of C. elegans (n = 20). Meanwhile, mechanosensation and locomotion under vehicle (0.1% DMSO), L-DOPA (60 mM), caffeine (10 mM) or 60 mM L-DOPA + 10 or 20 mM caffeine (60LC10 and 60LC20) treatments were scored for 3 days.

RESULTS

L-DOPA (60 mM) reduced CEP and ADE neurons by 4.3% on day 3, with a concomitant decrease in fluorescence by 44.6%. This correlated with reductions in gentle head (-35%) and nose touch (-40%) responses, but improved locomotion (20-75%) compared with vehicle alone. CEP and ADE neuron counts were preserved with caffeine (10 mM) or 60LC10 (98-100%), which correlated with improved mechanosensation (10-23%) and locomotion (18-76%). However, none of the treatments was able to preserve PDE neuron count, reducing the basal slowing response. Discussion and conclusions: Taken together, we show that caffeine can protect DAergic neurons and can reduce aberrant locomotion and loss of sensation when co-administered with L-DOPA, which can potentially impact PD treatment and warrants further investigation.

Decreased 14-3-3 expression correlates with age-related regional reductions in CNS dopamine and motor function in the pond snail, Lymnaea

Ageing is associated in many organisms with a reduction in motor movements. We have previously shown that the rate of feeding movements of the pond snail, Lymnaea, decreased with age but the underlying cause is not fully understood. Here, we show that dopamine in the cerebro-buccal complex is an important signalling molecule regulating feeding frequency in Lymnaea and that ageing is associated with a decrease in CNS dopamine. A proteomic screen of young and old CNSs highlighted a group of proteins that regulate stress responses. One of the proteins identified was 14-3-3, which can enhance the synthesis of dopamine. We show that the Lymnaea 14-3-3 family exists as three distinct isoforms. The expression of the 29 kDa isoform (14-3-3Lym3) in the cerebro-buccal complex decreased with age and correlated with feeding rate. Using a 14-3-3 antagonist (R18) we were able to reduce the synthesis of L-DOPA and dopamine in ex vivo cerebro-buccal complexes. Together these data suggest that an age-related reduction in 14-3-3 can decrease CNS dopamine leading to a consequential reduction in feeding rate.

Probiotics and Psychobiotics: the Role of Microbial Neurochemicals

In light of recent data, microorganisms should be construed as organisms that are capable of communication and collective behaviors. Microbial communication signals are involved both in interactions among microbial cells within microbial social systems, including the human body-inhabiting microconsortium, and the dialog between the microbiota and the host organism. The microbiota inhabits various niches of the host organism, especially the gastrointestinal (GI) tract. Microorganisms release diverse signal molecules and, in addition, specifically respond to host signals. This enables them to constantly interact with the nervous system including the brain and the immune system of the host organism. Evolutionarily conserved signals that are involved in the communication between microbiota and the host include neuroactive substances (neurochemicals) such as peptides, amino acids, biogenic amines, short-chain fatty acids, and gaseous substances. This ongoing dialog may either stabilize the host's physical and mental health state or, alternatively, cause serious health problems. Attempts are made to correct imbalances in the brain-gut-microbiota axis with probiotics including their subgroup called psychobiotics that release neuroactive substances directly influencing the human brain, psyche, and behavior. A number of recent review works address the microbiota-host system and its communication signals. Some of the publications focus on the involvement of neurochemicals in the bidirectional communication within the host-microbiota system. However, this work concentrates on the impact of bacterial cell components, metabolites, and signal molecules as promising alternatives to the currently widespread probiotics that have both advantages and disadvantages. Such biologically active agents of microbial origin are referred to as postbiotics or, alternatively, metabiotics (the term preferred in this work).

Activation of RHO-1 in cholinergic motor neurons competes with dopamine signalling to control locomotion

The small GTPase RhoA plays a crucial role in the regulation of neuronal signalling to generate behaviour. In the developing nervous system RhoA is known to regulate the actin cytoskeleton, however the effectors of RhoA-signalling in adult neurons remain largely unidentified. We have previously shown that activation of the RhoA ortholog (RHO-1) in C. elegans cholinergic motor neurons triggers hyperactivity of these neurons and loopy locomotion with exaggerated body bends. This is achieved in part through increased diacylglycerol (DAG) levels and the recruitment of the synaptic vesicle protein UNC-13 to synaptic release sites, however other pathways remain to be identified. Dopamine, which is negatively regulated by the dopamine re-uptake transporter (DAT), has a central role in modulating locomotion in both humans and C. elegans. In this study we identify a new pathway in which RHO-1 regulates locomotory behaviour by repressing dopamine signalling, via DAT-1, linking these two pathways together. We observed an upregulation of dat-1 expression when RHO-1 is activated and show that loss of DAT-1 inhibits the loopy locomotion phenotype caused by RHO-1 activation. Reducing dopamine signalling in dat-1 mutants through mutations in genes involved in dopamine synthesis or in the dopamine receptor DOP-1 restores the ability of RHO-1 to trigger loopy locomotion in dat-1 mutants. Taken together, we show that negative regulation of dopamine signalling via DAT-1 is necessary for the neuronal RHO-1 pathway to regulate locomotion.

Transcriptome analysis of adult Caenorhabditis elegans cells reveals tissue-specific gene and isoform expression

The biology and behavior of adults differ substantially from those of developing animals, and cell-specific information is critical for deciphering the biology of multicellular animals. Thus, adult tissue-specific transcriptomic data are critical for understanding molecular mechanisms that control their phenotypes. We used adult cell-specific isolation to identify the transcriptomes of C. elegans' four major tissues (or "tissue-ome"), identifying ubiquitously expressed and tissue-specific "enriched" genes. These data newly reveal the hypodermis' metabolic character, suggest potential worm-human tissue orthologies, and identify tissue-specific changes in the Insulin/IGF-1 signaling pathway. Tissue-specific alternative splicing analysis identified a large set of collagen isoforms. Finally, we developed a machine learning-based prediction tool for 76 sub-tissue cell types, which we used to predict cellular expression differences in IIS/FOXO signaling, stage-specific TGF-β activity, and basal vs. memory-induced CREB transcription. Together, these data provide a rich resource for understanding the biology governing multicellular adult animals.

To Do or Not to Do: Dopamine, Affordability and the Economics of Opportunity

Five years ago, we introduced the thrift hypothesis of dopamine (DA), suggesting that the primary role of DA in adaptive behavior is regulating behavioral energy expenditure to match the prevailing economic conditions of the environment. Here we elaborate that hypothesis with several new ideas. First, we introduce the concept of affordability, suggesting that costs must necessarily be evaluated with respect to the availability of resources to the organism, which computes a value not only for the potential reward opportunity, but also the value of resources expended. Placing both costs and benefits within the context of the larger economy in which the animal is functioning requires consideration of the different timescales against which to compute resource availability, or average reward rate. Appropriate windows of computation for tracking resources requires corresponding neural substrates that operate on these different timescales. In discussing temporal patterns of DA signaling, we focus on a neglected form of DA plasticity and adaptation, changes in the physical substrate of the DA system itself, such as up- and down-regulation of receptors or release probability. We argue that changes in the DA substrate itself fundamentally alter its computational function, which we propose mediates adaptations to longer temporal horizons and economic conditions. In developing our hypothesis, we focus on DA D2 receptors (D2R), arguing that D2R implements a form of “cost control” in response to the environmental economy, serving as the “brain’s comptroller”. We propose that the balance between the direct and indirect pathway, regulated by relative expression of D1 and D2 DA receptors, implements affordability. Finally, as we review data, we discuss limitations in current approaches that impede fully investigating the proposed hypothesis and highlight alternative, more semi-naturalistic strategies more conducive to neuroeconomic investigations on the role of DA in adaptive behavior.

Behavioral Phenotyping and Pathological Indicators of Parkinson's Disease in C. elegans Models

Parkinson's disease (PD) is a neurodegenerative disorder with symptoms that progressively worsen with age. Pathologically, PD is characterized by the aggregation of α-synuclein in cells of the substantia nigra in the brain and loss of dopaminergic neurons. This pathology is associated with impaired movement and reduced cognitive function. The etiology of PD can be attributed to a combination of environmental and genetic factors. A popular animal model, the nematode roundworm Caenorhabditis elegans, has been frequently used to study the role of genetic and environmental factors in the molecular pathology and behavioral phenotypes associated with PD. The current review summarizes cellular markers and behavioral phenotypes in transgenic and toxin-induced PD models of C. elegans.

Insights into the Mechanisms Involved in Protective Effects of VEGF-B in Dopaminergic Neurons

Vascular endothelial growth factor-B (VEGF-B), when initially discovered, was thought to be an angiogenic factor, due to its intimate sequence homology and receptor binding similarity to the prototype angiogenic factor, vascular endothelial growth factor-A (VEGF-A). Studies demonstrated that VEGF-B, unlike VEGF-A, did not play a significant role in angiogenesis or vascular permeability and has become an active area of interest because of its role as a survival factor in pathological processes in a multitude of systems, including the brain. By characterization of important downstream targets of VEGF-B that regulate different cellular processes in the nervous system and cardiovascular system, it may be possible to develop more effective clinical interventions in diseases such as Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS), and ischemic heart disease, which all share mitochondrial dysfunction as part of the disease. Here we summarize what is currently known about the mechanism of action of VEGF-B in pathological processes. We explore its potential as a homeostatic protective factor that improves mitochondrial function in the setting of cardiovascular and neurological disease, with a specific focus on dopaminergic neurons in Parkinson's disease.

A proposed resolution to the paradox of drug reward: Dopamine's evolution from an aversive signal to a facilitator of drug reward via negative reinforcement

The mystery surrounding how plant neurotoxins came to possess reinforcing properties is termed the paradox of drug reward. Here we propose a resolution to this paradox whereby dopamine - which has traditionally been viewed as a signal of reward - initially signaled aversion and encouraged escape. We suggest that after being consumed, plant neurotoxins such as nicotine activated an aversive dopaminergic pathway, thereby deterring predatory herbivores. Later evolutionary events - including the development of a GABAergic system capable of modulating dopaminergic activity - led to the ability to down-regulate and 'control' this dopamine-based aversion. We speculate that this negative reinforcement system evolved so that animals could suppress aversive states such as hunger in order to attend to other internal drives (such as mating and shelter) that would result in improved organismal fitness.

Operant conditioning: a minimal components requirement in artificial spiking neurons designed for bio-inspired robot's controller

In this paper, we investigate the operant conditioning (OC) learning process within a bio-inspired paradigm, using artificial spiking neural networks (ASNN) to act as robot brain controllers. In biological agents, OC results in behavioral changes learned from the consequences of previous actions, based on progressive prediction adjustment from rewarding or punishing signals. In a neurorobotics context, virtual and physical autonomous robots may benefit from a similar learning skill when facing unknown and unsupervised environments. In this work, we demonstrate that a simple invariant micro-circuit can sustain OC in multiple learning scenarios. The motivation for this new OC implementation model stems from the relatively complex alternatives that have been described in the computational literature and recent advances in neurobiology. Our elementary kernel includes only a few crucial neurons, synaptic links and originally from the integration of habituation and spike-timing dependent plasticity as learning rules. Using several tasks of incremental complexity, our results show that a minimal neural component set is sufficient to realize many OC procedures. Hence, with the proposed OC module, designing learning tasks with an ASNN and a bio-inspired robot context leads to simpler neural architectures for achieving complex behaviors.

n-butylidenephthalide protects against dopaminergic neuron degeneration and α-synuclein accumulation in Caenorhabditis elegans models of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the second most common degenerative disorder of the central nervous system that impairs motor skills and cognitive function. To date, the disease has no effective therapies. The identification of new drugs that provide benefit in arresting the decline seen in PD patients is the focus of much recent study. However, the lengthy time frame for the progression of neurodegeneration in PD increases both the time and cost of examining potential therapeutic compounds in mammalian models. An alternative is to first evaluate the efficacy of compounds in Caenorhabditis elegans models, which reduces examination time from months to days. n-Butylidenephthalide is the naturally-occurring component derived from the chloroform extract of Angelica sinensis. It has been shown to have anti-tumor and anti-inflammatory properties, but no reports have yet described the effects of n-butylidenephthalide on PD. The aim of this study was to assess the potential for n-butylidenephthalide to improve PD in C. elegans models.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study, we employed a pharmacological strain that expresses green fluorescent protein specifically in dopaminergic neurons (BZ555) and a transgenic strain that expresses human α-synuclein in muscle cells (OW13) to investigate the antiparkinsonian activities of n-butylidenephthalide. Our results demonstrate that in PD animal models, n-butylidenephthalide significantly attenuates dopaminergic neuron degeneration induced by 6-hydroxydopamine; reduces α-synuclein accumulation; recovers lipid content, food-sensing behavior, and dopamine levels; and prolongs life-span of 6-hydroxydopamine treatment, thus revealing its potential as a possible antiparkinsonian drug. n-Butylidenephthalide may exert its effects by blocking egl-1 expression to inhibit apoptosis pathways and by raising rpn-6 expression to enhance the activity of proteasomes.

CONCLUSIONS/SIGNIFICANCE

n-Butylidenephthalide may be one of the effective neuroprotective agents for PD.

The bilaterian forebrain: an evolutionary chimaera

The insect, annelid and vertebrate forebrains harbour two major centres of output control, a sensory-neurosecretory centre releasing hormones and a primordial locomotor centre that controls the initiation of muscular body movements. In vertebrates, both reside in the hypothalamus. Here, we review recent comparative neurodevelopmental evidence indicating that these centres evolved from separate condensations of neurons on opposite body sides ('apical nervous system' versus 'blastoporal nervous system') and that their developmental specification involved distinct regulatory networks (apical six3 and rx versus mediolateral nk and pax gene-dependent patterning). In bilaterian ancestors, both systems approached each other and became closely intermingled, physically, functionally and developmentally. Our 'chimeric brain hypothesis' sheds new light on the vast success and rapid diversification of bilaterian animals in the Cambrian and revises our understanding of brain architecture.