Phasic/tonic glial GABA differentially transduce for olfactory adaptation and neuronal aging.

Phasic (fast) and tonic (sustained) inhibition of γ-aminobutyric acid (GABA) are fundamental for regulating day-to-day activities, neuronal excitability, and plasticity. However, the mechanisms and physiological functions of glial GABA transductions remain poorly understood. Here, we report that the AMsh glia in Caenorhabditis elegans exhibit both phasic and tonic GABAergic signaling, which distinctively regulate olfactory adaptation and neuronal aging. Through genetic screening, we find that GABA permeates through bestrophin-9/-13/-14 anion channels from AMsh glia, which primarily activate the metabolic GABAB receptor GBB-1 in the neighboring ASH sensory neurons. This tonic action of glial GABA regulates the age-associated changes of ASH neurons and olfactory responses via a conserved signaling pathway, inducing neuroprotection. In addition, the calcium-evoked, vesicular glial GABA release acts upon the ionotropic GABAA receptor LGC-38 in ASH neurons to regulate olfactory adaptation. These findings underscore the fundamental significance of glial GABA in maintaining healthy aging and neuronal stability.

The Voltage-Gated Calcium Channel EGL-19 Acts on Glia to Drive Olfactory Adaptation.

Calcium channelopathies have been strongly linked to cardiovascular, muscular, neurological and psychiatric disorders. The voltage-gated calcium channels (VGCC) are vital transducers of membrane potential changes to facilitate the dynamics of calcium ions and release of neurotransmitter. Whether these channels function in the glial cell to mediate calcium variations and regulate behavioral outputs, is poorly understood. Our results showed that odorant and mechanical stimuli evoked robust calcium increases in the amphid sheath (AMsh) glia from C. elegans, which were largely dependent on the L-Type VGCC EGL-19. Moreover, EGL-19 modulates the morphologies of both ASH sensory neurons and AMsh glia. Tissue-specific knock-down of EGL-19 in AMsh glia regulated sensory adaptability of ASH neurons and promoted olfactory adaptation. Our results reveal a novel role of glial L-Type VGCC EGL-19 on olfaction, lead to improved understanding of the functions of VGCCs in sensory transduction.

Protocol for glial Ca2+ imaging in C. elegans following chemical, mechanical, or optogenetic stimulation.

Caenorhabditis elegans is an exceptionally transparent model to analyze calcium (Ca2+) signals, but available protocols for neuronal Ca2+ imaging may not be suitable for studying glial cells. Here, we present a detailed protocol for glial Ca2+ imaging in C. elegans following three different approaches including chemical, mechanical, and optogenetic stimulation. We also provide the details for imaging analysis using Image-J. For complete details on the use and execution of this protocol, please refer to Duan et al. (2020).

Molecular Strategies for Intensity-Dependent Olfactory Processing in Caenorhabditis elegans.

Various odorants trigger complex animal behaviors across species in both quality- and quantity-dependent manners. However, how the intensity of olfactory input is encoded remains largely unknown. Here we report that isoamyl alcohol (IAA) induces bi-directional currents through a Gα- guanylate cyclase (GC)- cGMP signaling pathway in Caenorhabditis elegans olfactory neuron amphid wing "C" cell (AWC), while two opposite cGMP signaling pathways are responsible for odor-sensing in olfactory neuron amphid wing "B" cell (AWB): (1) a depolarizing Gα (GPA-3)- phosphodiesterase (PDE) - cGMP pathway which can be activated by low concentrations of isoamyl alcohol (IAA), and (2) a hyperpolarizing Gα (ODR-3)- GC- cGMP pathway sensing high concentrations of IAA. Besides, IAA induces Gα (ODR-3)-TRPV(OSM-9)-dependent currents in amphid wing "A" cell (AWA) and amphid neuron "H" cell with single ciliated sensory ending (ASH) neurons with different thresholds. Our results demonstrate that an elaborate combination of multiple signaling machineries encode the intensity of olfactory input, shedding light on understanding the molecular strategies on sensory transduction.

Polymodal Functionality of C. elegans OLL Neurons in Mechanosensation and Thermosensation.

Sensory modalities are important for survival but the molecular mechanisms remain challenging due to the polymodal functionality of sensory neurons. Here, we report the C. elegans outer labial lateral (OLL) sensilla sensory neurons respond to touch and cold. Mechanosensation of OLL neurons resulted in cell-autonomous mechanically-evoked Ca2+ transients and rapidly-adapting mechanoreceptor currents with a very short latency. Mechanotransduction of OLL neurons might be carried by a novel Na+ conductance channel, which is insensitive to amiloride. The bona fide mechano-gated Na+-selective degenerin/epithelial Na+ channels, TRP-4, TMC, and Piezo proteins are not involved in this mechanosensation. Interestingly, OLL neurons also mediated cold but not warm responses in a cell-autonomous manner. We further showed that the cold response of OLL neurons is not mediated by the cold receptor TRPA-1 or the temperature-sensitive glutamate receptor GLR-3. Thus, we propose the polymodal functionality of OLL neurons in mechanosensation and cold sensation.

Sensory Glia Detect Repulsive Odorants and Drive Olfactory Adaptation.

Glia are typically considered as supporting cells for neural development and synaptic transmission. Here, we report an active role of a glia in olfactory transduction. As a polymodal sensory neuron in C. elegans, the ASH neuron is previously known to detect multiple aversive odorants. We reveal that the AMsh glia, a sheath for multiple sensory neurons including ASH, cell-autonomously respond to aversive odorants via G-protein-coupled receptors (GPCRs) distinct from those in ASH. Upon activation, the AMsh glia suppress aversive odorant-triggered avoidance and promote olfactory adaptation by inhibiting the ASH neuron via GABA signaling. Thus, we propose a novel two-receptor model where the glia and sensory neuron jointly mediate adaptive olfaction. Our study reveals a non-canonical function of glial cells in olfactory transduction, which may provide new insights into the glia-like supporting cells in mammalian sensory procession.

Serotonergic neuron ADF modulates avoidance behaviors by inhibiting sensory neurons in C. elegans.

Serotonin plays an essential role in both the invertebrate and vertebrate nervous systems. ADF, an amphid neuron with dual ciliated sensory endings, is considered to be the only serotonergic sensory neuron in the hermaphroditic Caenorhabditis elegans. This neuron is known to be involved in a range of behaviors including pharyngeal pumping, dauer formation, sensory transduction, and memory. However, whether ADF neuron is directly activated by environmental cues and how it processes these information remains unknown. In this study, we found that ADF neuron responds reliably to noxious stimuli such as repulsive odors, copper, sodium dodecyl sulfonate (SDS), and mechanical perturbation. This response is mediated by cell-autonomous and non-cell autonomous mechanisms. Furthermore, we show that ADF can modulate avoidance behaviors by inhibiting ASH, an amphid neuron with single ciliated ending. This work greatly furthers our understanding of 5-HT's contributions to sensory information perception, processing, and the resulting behavioral responses.

OSM-9 and an amiloride-sensitive channel, but not PKD-2, are involved in mechanosensation in C. elegans male ray neurons.

Mechanotransduction is crucial for touch sensation, hearing, proprioception, and pain sensing. In C. elegans, male ray neurons have been implicated to be involved in the mechanosensation required for mating behavior. However, whether ray neurons directly sense mechanical stimulation is not yet known, and the underlying molecular mechanisms have not been identified. Using in vivo calcium imaging, we recorded the touch-induced calcium responses in male ray neurons. Our data demonstrated that ray neurons are sensitive to mechanical stimulation in a neurotransmitter-independent manner. PKD-2, a putative sensor component for both mechanosensation and chemosensation in male-specific neurons, was not required for the touch-induced calcium responses in RnB neurons, whereas the TRPV channel OSM-9 shaped the kinetics of the responses. We further showed that RnB-neuron mechanosensation is likely mediated by an amiloride-sensitive DEG/ENaC channel. These observations lay a foundation for better understanding the molecular mechanisms of mechanosensation.

A Systematic RNAi Screen Reveals a Novel Role of a Spindle Assembly Checkpoint Protein BuGZ in Synaptic Transmission in C. elegans.

Synaptic vesicles (SV) store various neurotransmitters that are released at the synapse. The molecular mechanisms of biogenesis, exocytosis, and endocytosis for SV, however, remain largely elusive. In this study, using Complex Object Parametric Analysis and Sorter (COPAS) to monitor the fluorescence of synapto-pHluorin (SpH), we performed a whole-genome RNAi screen in C. elegans to identify novel genetic modulators in SV cycling. One hundred seventy six genes that up-regulating SpH fluorescence and 96 genes that down-regulating SpH fluorescence were identified after multi-round screen. Among these genes, B0035.1 (bugz-1) encodes ortholog of mammalian C2H2 zinc-finger protein BuGZ/ZNF207, which is a spindle assembly checkpoint protein essential for mitosis in human cells. Combining electrophysiology, imaging and behavioral assays, we reveal that depletion of BuGZ-1 results in defects in locomotion. We further demonstrate that BuGZ-1 promotes SV recycling by regulating the expression levels of endocytosis-related genes such as rab11.1. Therefore, we have identified a bunch of potential genetic modulators in SV cycling, and revealed an unexpected role of BuGZ-1 in regulating synaptic transmission.

Ultrasound neuro-modulation chip: activation of sensory neurons in Caenorhabditis elegans by surface acoustic waves.

Ultrasound neuro-modulation has gained increasing attention as a non-invasive method. In this paper, we present an ultrasound neuro-modulation chip, capable of initiating reversal behaviour and activating neurons of C. elegans under the stimulation of a single-shot, short-pulsed ultrasound. About 85.29% ± 6.17% of worms respond to the ultrasound stimulation exhibiting reversal behaviour. Furthermore, the worms can adapt to the ultrasound stimulation with a lower acoustic pulse duration of stimulation. In vivo calcium imaging shows that the activity of ASH, a polymodal sensory neuron in C. elegans, can be directly evoked by the ultrasound stimulation. On the other hand, AFD, a thermal sensitive neuron, cannot be activated by the ultrasound stimulation using the same parameter and the temperature elevation during the stimulation process is relatively small. Consistent with the calcium imaging results, the tax-4 mutants, which are insensitive to temperature increase, do not show a significant difference in avoidance probability compared to the wild type. Therefore, the mechanical effects induced by ultrasound are the main reason for neural and behavioural modulation of C. elegans. With the advantages of confined acoustic energy on the surface, compatible with standard calcium imaging, this neuro-modulation chip could be a powerful tool for revealing the molecular mechanisms of ultrasound neuro-modulation.

Polymodal Responses in C. elegans Phasmid Neurons Rely on Multiple Intracellular and Intercellular Signaling Pathways.

Animals utilize specialized sensory neurons enabling the detection of a wide range of environmental stimuli from the presence of toxic chemicals to that of touch. However, how these neurons discriminate between different kinds of stimuli remains poorly understood. By combining in vivo calcium imaging and molecular genetic manipulation, here we investigate the response patterns and the underlying mechanisms of the C. elegans phasmid neurons PHA/PHB to a variety of sensory stimuli. Our observations demonstrate that PHA/PHB neurons are polymodal sensory neurons which sense harmful chemicals, hyperosmotic solutions and mechanical stimulation. A repulsive concentration of IAA induces calcium elevations in PHA/PHB and both OSM-9 and TAX-4 are essential for IAA-sensing in PHA/PHB. Nevertheless, the PHA/PHB neurons are inhibited by copper and post-synaptically activated by copper removal. Neuropeptide is likely involved in copper removal-induced calcium elevations in PHA/PHB. Furthermore, mechanical stimulation activates PHA/PHB in an OSM-9-dependent manner. Our work demonstrates how PHA/PHB neurons respond to multiple environmental stimuli and lays a foundation for the further understanding of the mechanisms of polymodal signaling, such as nociception, in more complex organisms.