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Genetics,
2018]
Sleep is crucial for survival and well-being. This behavioral and physiological state has been studied in all major genetically accessible model animals, including rodents, fish, flies, and worms. Genetic and optogenetic studies have identified several neurons that control sleep, making it now possible to compare circuit mechanisms across species. The "motor" of sleep across animal species is formed by neurons that depolarize at the onset of sleep to actively induce this state by directly inhibiting wakefulness. These sleep-inducing neurons are themselves controlled by inhibitory or activating upstream pathways, which act as the "drivers" of the sleep motor: arousal inhibits "sleep-active" neurons whereas various sleep-promoting "tiredness" pathways converge onto sleep-active neurons to depolarize them. This review provides the first overview of sleep-active neurons across the major model animals. The occurrence of sleep-active neurons and their regulation by upstream pathways in both vertebrate and invertebrate species suggests that these neurons are general and ancient components that evolved early in the history of nervous systems.
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Parasite,
1994]
Organelles and neurons of nematodes involved in sensing chemical signals present in the environment are described. Laser ablation of neurons has helped assign them a specific function. Genetic mutational analysis has led to the identification of genes controlling the behavior of the worms and/or some cellular properties of the chemosensory neurons. Some conclusions on the general organization and functioning of chemoreception in nematodes can be drawn.
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Dev Neurobiol,
2020]
Cilia are microtubule-based organelles that display diversity in morphology, ultrastructure, protein composition, and function. The ciliary microtubules of C. elegans sensory neurons exemplify this diversity and provide a paradigm to understand mechanisms driving ciliary specialization. Only a subset of ciliated neurons in C. elegans are specialized to make and release bioactive extracellular vesicles (EVs) into the environment. The cilia of extracellular vesicle releasing neurons have distinct axonemal features and specialized intraflagellar transport that are important for releasing EVs. In this review, we discuss the role of the tubulin code in the specialization of microtubules in cilia of EV releasing neurons.
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Front Neuroanat,
2022]
Studies on sexual dimorphism in the structure and function of the nervous system have been pivotal to understanding sex differences in behavior. Such studies, especially on invertebrates, have shown the importance of neurons specific to one sex (sex-specific neurons) in shaping sexually dimorphic neural circuits. Nevertheless, recent studies using the nematode C. elegans have revealed that the common neurons that exist in both sexes (sex-shared neurons) also play significant roles in generating sex differences in the structure and function of neural circuits. Here, we review the anatomical and functional differences in the sex-shared neurons of C. elegans. These sexually dimorphic characteristics include morphological differences in neurite projection or branching patterns with substantial changes in synaptic connectivity, differences in synaptic connections without obvious structural changes, and functional modulation in neural circuits with no or minimal synaptic connectivity changes. We also cover underlying molecular mechanisms whereby these sex-shared neurons contribute to the establishment of sexually dimorphic circuits during development and function differently between the sexes.
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[
Curr Biol,
2000]
To make the most of a small number of neurons, the nematode olfactory system includes neurons that are bilaterally symmetrical in morphology, but differ in the sets of genes they express. An intriguing recent example is the axon contact-mediated asymmetry in expression of the
str-2 odorant receptor gene.
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Ciba Found Symp,
1993]
The small soil nematode Caenorhabditis elegans has only 302 neurons in its entire nervous system, so it is possible to analyse the functions of individual neurons in the animal's behaviour. We are using behavioural, cellular and genetic analyses of chemotactic responses to find out how olfactory behaviour patterns are generated and regulated. Single chemosensory neurons in C. elegans can recognize several different attractive odorants that are distinguished by the animal. Distinct sets of chemosensory neurons detect high and low concentrations of a single odorant. Odorant responses adapt after prolonged exposure to an odorant; this adaptation is odorant specific and reversible. Mutants with defects in odorant responses have been identified. Some genes appear to be necessary for the development or function of particular kinds of sensory neurons. Other genes have effects that suggest that they participate in odorant reception or signal transduction.
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Vet Parasitol,
1999]
Nematode parasites of warm-blooded hosts use chemical and thermal signals in host-finding and in the subsequent resumption of development. The free-living nematode Caenorhabditis elegans is a useful model for investigating the chemo- and thermosensory neurons of such parasites, because the functions of its amphidial neurons are well known from laser microbeam ablation studies. The neurons found in the amphidial channel detect aqueous chemoattractants and repellants; the wing cells-flattened amphidial neurons-detect volatile odorants. The finger cells-digitiform amphidial neurons-are the primary thermoreceptors. Two neuron classes, named ADF and ASI, control entry into the environmentally resistant resting and dispersal dauer larval stage, while the paired ASJ neurons control exit from this stage. Skin-penetrating nematode parasites, i.e. the dog hookworm Ancylostoma caninum, and the threadworm, Strongyloides stercoralis, use thermal and chemical signals for host-finding, while the passively ingested sheep stomach worm, Haemonchus contortus, uses environmental signals to position itself for ingestion. Amphidial neurons presumably recognize these signals. In all species, resumption of development, on entering a host, is probably triggered by host signals also perceived by amphidial neurons. In the amphids of the A. caninum infective larva, there are wing- and finger-cell neurons, as well as neurons ending in cilia-like dendritic processes, some of which presumably recognize a sequence of signals that stimulate these larvae to attach to suitable hosts. The functions of these neurons can be postulated, based on the known functions of their homologs in C. elegans. The threadworm, S. stercoralis, has a complex life cycle. After leaving the host, soil-dwelling larvae may develop either to infective larvae (the life-stage equivalent of dauer larvae) or to free-living adults. As with the dauer larva of C. elegans, two neuron classes control this developmental switch. Amphidial neurons control chemotaxis to a skin extract, and a highly modified amphidial neuron, the lamellar cell, appears to be the primary thermoreceptor, in addition to having chemosensory function. The stomach worm, Haemonchus contortus, depends on ingestion by a grazing host. Once ingested, the infective larva is exposed to profound environmental changes in the rumen. These changes stimulate resumption of development in this species. We hypothesize that resumption of development is under the control of the ASJ neuronal pair. Identification of the neurons that control the infective process could provide the basis for entirely new approaches to parasite control involving interference with development at the time and place of initial host-contact.
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Cell Mol Life Sci,
2017]
Animals survive in harsh and fluctuating environments using sensory neurons to detect and respond to changes in their surroundings. Olfactory sensory neurons are essential for detecting food, identifying danger, and sensing pheromones. The ability to sense a large repertoire of different types of odors is crucial to distinguish between different situations, and is achieved through neuronal diversity within the olfactory system. Here, we review the developmental mechanisms used to establish diversity of olfactory sensory neurons in various model organisms, including Caenorhabditis elegans, Drosophila, and vertebrate models. Understanding and comparing how different olfactory neurons develop within the nervous system of different animals can provide insight into how the olfactory system is shaped in humans.
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Annu Rev Neurosci,
2005]
A current challenge in neuroscience is to bridge the gaps between genes, proteins, neurons, neural circuits, and behavior in a single animal model. The nematode Caenorhabditis elegans has unique features that facilitate this synthesis. Its nervous system includes exactly 302 neurons, and their pattern of synaptic connectivity is known. With only five olfactory neurons, C. elegans can dynamically respond to dozens of attractive and repellant odors. Thermosensory neurons enable the nematode to remember its cultivation temperature and to track narrow isotherms. Polymodal sensory neurons detect a wide range of nociceptive cues and signal robust escape responses. Pairing of sensory stimuli leads to long-lived changes in behavior consistent with associative learning. Worms exhibit social behaviors and complex ultradian rhythms driven by Ca(2+) oscillators with clock-like properties. Genetic analysis has identified gene products required for nervous system function and elucidated the molecular and neural bases of behaviors.
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Neurosci Bull,
2013]
Neurons in the mammalian central nervous system (CNS) cannot regenerate axons after injury. in contrast, neurons in the mammalian peripheral nervous system and in some non-mammalian models, such as C. elegans and Drosophila, are able to regrow axons. Understanding the molecular mechanisms by which these neurons support axon regeneration will help us find ways to enhance mammalian CNS axon regeneration. Here, recent studies in which signaling pathways regulating naturally-occurring axon regeneration that have been identified are reviewed, focusing on how these pathways control gene expression and growth-cone function during axon regeneration.