Review

Authors: Patrice G Guyenet, Douglas A Bayliss

Recent advances have clarified how the brain detects CO2 to regulate breathing (central respiratory chemoreception). These mechanisms are reviewed and their significance is presented in the general context of CO2/pH homeostasis through breathing. At rest, respiratory chemoreflexes initiated at peripheral and central sites mediate rapid stabilization of arterial PCO2 and pH. Specific brainstem neurons (e.g., retrotrapezoid nucleus, RTN; serotonergic) are activated by PCO2 and stimulate breathing. RTN neurons detect CO2 via intrinsic proton receptors (TASK-2, GPR4), synaptic input from peripheral chemoreceptors and signals from astrocytes. Respiratory chemoreflexes are arousal state dependent whereas chemoreceptor stimulation produces arousal. When abnormal, these interactions lead to sleep-disordered breathing. During exercise, central command and reflexes from exercising muscles produce the breathing stimulation required to maintain arterial PCO2 and pH despite elevated metabolic activity. The neural circuits underlying central command and muscle afferent control of breathing remain elusive and represent a fertile area for future investigation.

Topics: Animals; Carbon Dioxide; Chemoreceptor Cells; Homeostasis; Humans; Respiration; Respiratory Center

PubMed: 26335642
DOI: 10.1016/j.neuron.2015.08.001

Review

Authors: Wendy A Valencia-Montoya, Naomi E Pierce, Nicholas W Bellono...

Sensory receptors are at the interface between an organism and its environment and thus represent key sites for biological innovation. Here, we survey major sensory receptor families to uncover emerging evolutionary patterns. Receptors for touch, temperature, and light constitute part of the ancestral sensory toolkit of animals, often predating the evolution of multicellularity and the nervous system. In contrast, chemoreceptors exhibit a dynamic history of lineage-specific expansions and contractions correlated with the disparate complexity of chemical environments. A recurring theme includes independent transitions from neurotransmitter receptors to sensory receptors of diverse stimuli from the outside world. We then provide an overview of the evolutionary mechanisms underlying sensory receptor diversification and highlight examples where signatures of natural selection are used to identify novel sensory adaptations. Finally, we discuss sensory receptors as evolutionary hotspots driving reproductive isolation and speciation, thereby contributing to the stunning diversity of animals.

Topics: Animals; Sensory Receptor Cells; Biological Evolution; Humans; Chemoreceptor Cells

PubMed: 38985841
DOI: 10.1146/annurev-cellbio-120123-112853

Review

Authors: Patrice G Guyenet, Ruth L Stornetta, George M P R Souza...

The ventral surface of the rostral medulla oblongata has been suspected since the 1960s to harbor central respiratory chemoreceptors [i.e., acid-activated neurons that regulate breathing to maintain a constant arterial PCO (PaCO)]. The key neurons, a.k.a. the retrotrapezoid nucleus (RTN), have now been identified. In this review we describe their transcriptome, developmental lineage, and anatomical projections. We also review their contribution to CO homeostasis and to the regulation of breathing automaticity during sleep and wake. Finally, we discuss several mechanisms that contribute to the activation of RTN neurons by COin vivo: cell-autonomous effects of protons; paracrine effects of pH mediated by surrounding astrocytes and blood vessels; and excitatory inputs from other CO-responsive CNS neurons.

Topics: Animals; Carbon Dioxide; Chemoreceptor Cells; Homeostasis; Humans; Hypercapnia; Hypoxia; Medulla Oblongata; Neurons; Respiration; Sleep

PubMed: 31635852
DOI: 10.1016/j.tins.2019.09.002

Authors: Sungmoo Hong, Meejung Ahn, Changjong Moon...

Little is known about the neuronal structure of the vomeronasal organ (VNO), a receptor organ responsible for pheromone perception, in the alpaca (Vicugna pacos). This study was performed to determine the localization of neuronal elements, including protein gene product 9.5 (PGP 9.5), a pan-neuronal marker, olfactory marker protein (OMP), a marker of mature olfactory receptor cells, and phospholipase C beta 2 (PLC-β2), a marker of solitary chemoreceptor cells (SCCs), in the VNO. OMP was identified in receptor cells of the vomeronasal sensory epithelium (VSE), while PGP 9.5 and PLC-β2 were localized in both the VSE and vomeronasal non-sensory epithelium. Collectively, these results suggested that the alpaca VNO possesses SCCs and olfactory receptor cells, which recognize both harmful substances and pheromones.

Topics: Animals; Vomeronasal Organ; Camelids, New World; Male; Olfactory Marker Protein; Phospholipase C beta; Female; Olfactory Receptor Neurons; Chemoreceptor Cells; Ubiquitin Thiolesterase

PubMed: 38508726
DOI: 10.1292/jvms.23-0430

Review

Authors: Denise M Ferkey, Piali Sengupta, Noelle D L'Etoile...

Chemosensory neurons translate perception of external chemical cues, including odorants, tastants, and pheromones, into information that drives attraction or avoidance motor programs. In the laboratory, robust behavioral assays, coupled with powerful genetic, molecular and optical tools, have made Caenorhabditis elegans an ideal experimental system in which to dissect the contributions of individual genes and neurons to ethologically relevant chemosensory behaviors. Here, we review current knowledge of the neurons, signal transduction molecules and regulatory mechanisms that underlie the response of C. elegans to chemicals, including pheromones. The majority of identified molecules and pathways share remarkable homology with sensory mechanisms in other organisms. With the development of new tools and technologies, we anticipate that continued study of chemosensory signal transduction and processing in C. elegans will yield additional new insights into the mechanisms by which this animal is able to detect and discriminate among thousands of chemical cues with a limited sensory neuron repertoire.

Topics: Animals; Behavior, Animal; Caenorhabditis elegans; Chemoreceptor Cells; Neuronal Plasticity; Signal Transduction

PubMed: 33693646
DOI: 10.1093/genetics/iyab004

Authors: Evan Lamb, Michael J Trimble, Linda L McCarter...

Motile bacteria are proficient at finding optimal environments for colonization. Often, they use chemotaxis to sense nutrient availability and dangerous concentrations of toxic chemicals. For many bacteria, the repertoire of chemoreceptors is large, suggesting they possess a broad palate with respect to sensing. However, knowledge of the molecules detected by chemotaxis signal transduction systems is limited. Some bacteria, like Vibrio parahaemolyticus, are social and swarm in groups on surfaces. This marine bacterium and human pathogen secretes the S signal autoinducer, which cues degradation of intracellular c-di-GMP leading to transcription of the swarming program. Here, we report that the S signal also directs motility at a behavioral level by serving as a chemoattractant. The data demonstrate that V. parahaemolyticus senses the S signal using SscL and SscS, homologous methyl-accepting chemotaxis proteins. SscL is required by planktonic bacteria for S signal chemotaxis. SscS plays a role during swarming, and mutants lacking this chemoreceptor swarm faster and produce colonies with more deeply branched swarming fronts than the wild type or the sscL mutant. Other Vibrio species can swim toward the S signal, suggesting a recruitment role for this cell-cell communication molecule in the context of polymicrobial marine communities.

Topics: Bacterial Proteins; Cell Communication; Cell Movement; Chemoreceptor Cells; Chemotaxis; Membrane Proteins; Signal Transduction; Vibrio parahaemolyticus

PubMed: 30938898
DOI: 10.1111/mmi.14256

Review

Authors: Shuangyu Bi, Luhua Lai

Bacteria use chemotaxis signaling pathways to sense environmental changes. Escherichia coli chemotaxis system represents an ideal model that illustrates fundamental principles of biological signaling processes. Chemoreceptors are crucial signaling proteins that mediate taxis toward a wide range of chemoeffectors. Recently, in deep study of the biochemical and structural features of chemoreceptors, the organization of higher-order clusters in native cells, and the signal transduction mechanisms related to the on-off signal output provides us with general insights to understand how chemotaxis performs high sensitivity, precise adaptation, signal amplification, and wide dynamic range. Along with the increasing knowledge, bacterial chemoreceptors can be engineered to sense novel chemoeffectors, which has extensive applications in therapeutics and industry. Here we mainly review recent advances in the E. coli chemotaxis system involving structure and organization of chemoreceptors, discovery, design, and characterization of chemoeffectors, and signal recognition and transduction mechanisms. Possible strategies for changing the specificity of bacterial chemoreceptors to sense novel chemoeffectors are also discussed.

Topics: Chemoreceptor Cells; Chemotaxis; Directed Molecular Evolution; Escherichia coli; Escherichia coli Proteins; Signal Transduction

PubMed: 25374297
DOI: 10.1007/s00018-014-1770-5

Review

Authors: Christoph Schneider

Chemosensory processes are integral to the physiology of most organisms. This function is typically performed by specialized cells that are able to detect input signals and to convert them to an output dedicated to a particular group of target cells. Tuft cells are cholinergic chemosensory epithelial cells capable of producing immunologically relevant effector molecules. They are scattered throughout endoderm-derived hollow organs and function as sensors of luminal stimuli, which has been best studied in mucosal barrier epithelia. Given their epithelial origin and broad distribution, and based on their interplay with immune pathways, tuft cells can be considered a prototypical example of how complex multicellular organisms engage innate immune mechanisms to modulate and optimize organ physiology. In this review, I provide a concise overview of tuft cells and discuss how these cells influence organ adaptation to dynamic luminal conditions.

Topics: Animals; Chemoreceptor Cells; Epithelial Cells; Humans; Immunity, Innate

PubMed: 34635955
DOI: 10.1007/s00424-021-02630-2

Review

Authors: Jennifer L Pluznick, Michael J Caplan

In order to assess the status of the volume and composition of the body fluid compartment, the kidney monitors a wide variety of chemical and physical parameters. It has recently become clear that the kidney's sensory capacity extends well beyond its ability to sense ion concentrations in the forming urine. The kidney also keeps track of organic metabolites derived from a surprising variety of sources and uses a complex interplay of physical and chemical sensing mechanisms to measure the rate of fluid flow in the nephron. Recent research has provided new insights into the nature of these sensory mechanisms and their relevance to renal function.

Topics: Adenylyl Cyclases; Animals; Bicarbonates; Chemoreceptor Cells; Cilia; Fatty Acids, Volatile; Humans; Kidney; Mechanoreceptors; Succinic Acid

PubMed: 25280495
DOI: 10.2215/CJN.00730114

Review

Authors: L B Buck

Topics: Animals; Chemoreceptor Cells; Genetic Variation

PubMed: 8521462
DOI: 10.1016/0092-8674(95)90110-8