Distinct Sets Of Neurons Research Articles

Context-dependent operation of neural circuits underlies a navigation behavior in Caenorhabditis elegans

The nervous system evaluates environmental cues and adjusts motor output to ensure navigation toward a preferred environment. The nematode Caenorhabditis elegans navigates in the thermal environment and migrates toward its cultivation temperature by moving up or down thermal gradients depending not only on absolute temperature but on relative difference between current and previously experienced cultivation temperature. Although previous studies showed that such thermal context-dependent opposing migration is mediated by bias in frequency and direction of reorientation behavior, the complete neural pathways-from sensory to motor neurons-and their circuit logics underlying the opposing behavioral bias remain elusive. By conducting comprehensive cell ablation, high-resolution behavioral analyses, and computational modeling, we identified multiple neural pathways regulating behavioral components important for thermotaxis, and demonstrate that distinct sets of neurons are required for opposing bias of even single behavioral components. Furthermore, our imaging analyses show that the context-dependent operation is evident in sensory neurons, very early in the neural pathway, and manifested by bidirectional responses of a first-layer interneuron AIB under different thermal contexts. Our results suggest that the contextual differences are encoded among sensory neurons and a first-layer interneuron, processed among different downstream neurons, and lead to the flexible execution of context-dependent behavior.

Choice for Drug or Natural Reward Engages Largely Overlapping Neuronal Ensembles in the Infralimbic Prefrontal Cortex.

Cue-reward associations form distinct memories that can drive appetitive behaviors and are involved in craving for both drugs and natural rewards. Distinct sets of neurons, so-called neuronal ensembles, in the infralimbic area (IL) of the medial prefrontal cortex (mPFC) play a key role in alcohol seeking. Whether this ensemble is specific for alcohol or controls reward seeking in general remains unclear. Here, we compared IL ensembles formed upon recall of drug (alcohol) or natural reward (saccharin) memories in male Wistar rats. Using an experimental framework that allows identification of two distinct reward-associated ensembles within the same animal, we found that cue-induced seeking of either alcohol or saccharin activated ensembles of similar size and organization, whereby these ensembles consist of largely overlapping neuronal populations. Thus, the IL seems to act as a general integration hub for reward seeking behavior, but also contains subsets of neurons that encode for the different rewards.SIGNIFICANCE STATEMENT Cue-reward associations form distinct memories that can act as drivers of appetitive behaviors and are involved in craving for natural rewards as well as for drugs. Distinct sets of neurons, so-called neuronal ensembles, in the infralimbic area of the mPFC play a key role in cue-triggered reward seeking. However, it is unclear whether these ensembles act as broadly tuned controllers of approach behavior or represent the learned associations between specific cues and rewards. Using an experimental framework that allows identification of two distinct reward-associated ensembles within the same animal we find largely overlapping neuronal populations. Repeated activation by two distinct events could reflect the linking of the two memory traces within the same neuron.

Let there be light: A tutorial on optogenetics.

The nervous system of the human brain consists of diverse types of neurons that are interconnected. The enormous number and heterogeneity of neurons and their connections has made understanding the brain a difficult task, and it has long been a dream in basic and clinical neuroscience to be able to not only read the brain?s neuronal activity but also to have control over distinct sets of neurons.

How Brain Waves Help Us Make Sense of Speech

Understanding a sentence that someone else utters may seem effortless to you, but it's actually a complex process because you have to parse that sentence into many parts to understand what it means. Speech consists of a hierarchy of components that each takes place on a different timescale. Speech cues such as intonation occur on a relatively long timescale, unfolding over hundreds of milliseconds. At the other end of the spectrum is the phoneme—the smallest unit of speech—which lasts only tens of milliseconds. Gross and co-workers show that hierarchical speech patterns (top) entrain hierarchical wave frequencies in the brain (bottom). Similarly, distinct sets of neurons in the brain fire rhythmically at different rates, and these oscillations can also be arranged in a hierarchy. For instance, slow delta-wave oscillations can influence the magnitude of faster theta oscillations, which in turn can alter the amplitude of even faster gamma oscillations. Rhythmic brain activity plays an important role in a variety of cognitive processes, including attention, memory, and decision-making. A new study published in PLOS Biology now offers insights into the important role that neural oscillations play in speech perception. Joachim Gross, Simon Garrod, and co-workers report novel evidence that hierarchically organized neural oscillations allow people to parse the hierarchical components of speech. The findings not only provide a more complete understanding of the role of brain oscillations in cognition, but they also reveal that people can efficiently understand speech by simultaneously processing different speech components on various timescales. Gross and his team used a brain imaging technique called magnetoencephalography to record neural activity in 22 volunteers while they listened to a seven-minute real-life story. The researchers found that neural oscillations were arranged in a hierarchy: delta oscillations influenced the magnitude of theta oscillations, which in turn affected the amplitude of gamma oscillations. These hierarchical oscillations matched the hierarchical components of speech. Slow delta-wave oscillations in brain regions that process auditory information were in sync with slow rhythmic changes in speech, corresponding to the timescale of prosody—the rhythm, stress, and intonation of speech. This temporal alignment was more pronounced in the right hemisphere of the brain than in the left hemisphere. Meanwhile, the magnitude of fast gamma-wave oscillations in auditory brain areas was influenced by changes in speech that took place on a relatively short timescale, corresponding to syllables. This effect was stronger in the left hemisphere than in the right hemisphere. Collectively, these findings are consistent with a theory called “asymmetric sampling in time” (AST), which proposes that the right hemisphere preferentially processes information over longer timescales, whereas the left hemisphere shows a bias for processing information over shorter timescales. Gross and his collaborators then examined how brain oscillations were affected by variations in speech over time. Speech is not strictly periodic; sometimes people unexpectedly stop talking or begin to talk more quickly. The researchers found that sudden, large changes in the physical features of speech reset the timing of oscillations in auditory brain areas, helping to sync up important speech events with oscillatory brain activity. This finding illustrates how oscillations adapt to changes in the rhythm of speech, allowing the brain to continue to efficiently process speech even when the physical features abruptly change. Taken together, the findings show that hierarchically organized brain oscillations work in concert to track speech components occurring at different timescales, helping to convert a continuous speech stream into meaningful internal representations. Gross J, Hoogenboom N, Thut G, Schyns P, Panzeri S, et al. (2013) Speech Rhythms and Multiplexed Oscillatory Sensory Coding in the Human Brain. doi:10.1371/journal.pbio.1001752

Cell lineage and cis‐regulation for a unique GABAergic/glycinergic neuron type in the larval nerve cord of the ascidian Ciona intestinalis

The tunicate Ciona intestinalis larva has a simple central nervous system (CNS), consisting of fewer than 400 cells, which is homologous to the vertebrate CNS. Recent studies have revealed neuronal types and networks in the larval CNS of C. intestinalis, yet their cell lineage and the molecular mechanism by which particular types of neurons are specified and differentiate remain poorly understood. Here, we report cell lineage origin and a cis-regulatory module for the anterior caudal inhibitory neurons (ACINs), a putative component of the central pattern generator regulating swimming locomotion. The vesicular GABA⁄ glycine transporter gene Ci-VGAT, a specific marker for GABAergic ⁄ glycinergic neurons, is expressed in distinct sets of neurons, including ACINs of the tail nerve cord and others in the brain vesicle and motor ganglion. Comparative genomics analysis between C. intestinalis and Ciona savignyi and functional analysis in vivo identified the cis-regulatory module responsible for Ci-VGAT expression in ACINs. Our cell lineage analyses inferred that ACINs derive from A11.116 cells, which have been thought to solely give rise to glial ependymal cells of the lateral wall of the nerve cord. The present findings will provide a solid basis for future studies addressing the molecular mechanism underlying specification of ACINs, which play a critical role in controlling larval locomotion

The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications

IntroductionAcoels are microscopic marine worms that have become the focus of renewed debate and research due to their placement at the base of the Bilateria by molecular phylogenies. To date, Isodiametra pulchra is the most promising “model acoel” as it can be cultured and gene knockdown can be performed with double-stranded RNA. Despite its well-known morphology data on the nervous system are scarce. Therefore we examined this organ using various microscopic techniques, including histology, conventional histochemistry, electron microscopy, and immunocytochemistry in combination with CLSM and discuss our results in light of recently established phylogenies.ResultsThe nervous system of Isodiametra pulchra consists of a bilobed brain with a dorsal posterior commissure, a frontal ring and tracts, four pairs of longitudinal neurite bundles, as well as a supramuscular and submuscular plexus. Serotonin-like immunoreactivity (SLI) is displayed in parts of the brain, the longitudinal neurite bundles and a large part of the supramuscular plexus, while FMRFamide-like immunoreactivity (RFLI) is displayed in parts of the brain and a distinct set of neurons, the longitudinal neurite bundles and the submuscular plexus. Despite this overlap SLI and RFLI are never colocalized. Most remarkable though is the presence of a distinct functional neuro-muscular system consisting of the statocyst, tracts, motor neurons and inner muscles, as well as the presence of various muscles that differ with regard to their ultrastructure and innervation.ConclusionsThe nervous system of Isodiametra pulchra consists of an insunk, bilobed brain, a peripheral part for perception and innervation of the smooth body-wall musculature as well as tracts and motor neurons that together with pseudostriated inner muscles are responsible for steering and quick movements. The insunk, bilobed brains with two to three commissures found in numerous acoels are homologous and evolved from a ring-commissural brain that was present in the stem species of acoelomorphs. The acoelomorph brain is bipartite, consisting of a Six3/6-dependend animal pole nervous system that persists throughout adulthood and an axial nervous system that does not develop by exhibiting a staggered pattern of conserved regulatory genes as in other bilaterians but by a nested pattern of these genes. This indicates that acoelomorphs stem from an ancestor with a simple brain or with a biphasic life cycle.

A Drosophila model for alcohol reward

The rewarding properties of drugs contribute to the development of abuse and addiction. Here we present a new assay to investigate the motivational properties of ethanol in the genetically tractable model, Drosophila melanogaster. Flies learn to associate cues with ethanol intoxication and, although transiently aversive, the experience leads to a long-lasting attraction for the ethanol-paired cue, implying that intoxication is rewarding. Temporally blocking transmission in dopaminergic neurons revealed that flies require activation of these neurons to express, but not develop, conditioned preference for ethanol-associated cues. Moreover, flies acquire, consolidate, and retrieve these rewarding memories using distinct sets of neurons of the mushroom body. Finally, mutations in scabrous, encoding a fibrinogen-related peptide that regulates Notch signaling, disrupt the formation of memories for ethanol reward. Our results thus establish that Drosophila can be useful in understanding the molecular, genetic and neural mechanisms underling the rewarding properties of ethanol.

Immunohistochemical localization of calbindin-D28k and calretinin in the brainstem of anuran and urodele amphibians

Calbindin-D28k (CB) and calretinin (CR) are calcium binding proteins present in distinct sets of neurons; they act as buffers regulating the concentration of intracellular calcium. CB and CR immunohistochemistry was studied in the brainstem of anuran and urodele amphibians in combination with other markers (choline acetyltransferase, tyrosine hydroxylase, and nitric oxide synthase), which served to clarify the localization and signature of many cell groups. CR labeled the retinorecipient layers of the optic tectum, and CB and CR labeled distinct tectal cell populations. The two proteins were largely complementary in the torus semicircularis and marked auditory and lateral line sensory regions, depending on the species. CB and CR in the mesencephalic and isthmic tegmentum specified the boundaries of basal and medial longitudinal bands. In the cerebellum, CB labeled Purkinje cells in all species, whereas CR was mainly found in fibers and labeled Purkinje cells only in Rana. In the parabrachial region, CB and CR allowed the distinction of the laterodorsal tegmental nucleus, isthmic nucleus, locus coeruleus, and rostral octavolateral nuclei. The distribution of CB- and CR-immunoreactive cells in the reticular formation and central gray was consistent with the current models of brainstem segmentation in amphibians. CR was found in the auditory fibers and nuclei in Rana and in mechanosensory lateral line fibers in Xenopus and urodeles, whereas CB mainly labeled vestibular fibers and nuclei in all species. These results highlight the anatomical complexity of the amphibian brainstem and help in an understanding of its regional organization that is not cytoarchitectonically evident. J. Comp. Neurol. 515:503–537, 2009. © 2009 Wiley-Liss, Inc.

Immunohistochemical localization of calbindin‐D28k and calretinin in the brainstem of anuran and urodele amphibians

AbstractCalbindin‐D28k (CB) and calretinin (CR) are calcium binding proteins present in distinct sets of neurons; they act as buffers regulating the concentration of intracellular calcium. CB and CR immunohistochemistry was studied in the brainstem of anuran and urodele amphibians in combination with other markers (choline acetyltransferase, tyrosine hydroxylase, and nitric oxide synthase), which served to clarify the localization and signature of many cell groups. CR labeled the retinorecipient layers of the optic tectum, and CB and CR labeled distinct tectal cell populations. The two proteins were largely complementary in the torus semicircularis and marked auditory and lateral line sensory regions, depending on the species. CB and CR in the mesencephalic and isthmic tegmentum specified the boundaries of basal and medial longitudinal bands. In the cerebellum, CB labeled Purkinje cells in all species, whereas CR was mainly found in fibers and labeled Purkinje cells only in Rana. In the parabrachial region, CB and CR allowed the distinction of the laterodorsal tegmental nucleus, isthmic nucleus, locus coeruleus, and rostral octavolateral nuclei. The distribution of CB‐ and CR‐immunoreactive cells in the reticular formation and central gray was consistent with the current models of brainstem segmentation in amphibians. CR was found in the auditory fibers and nuclei in Rana and in mechanosensory lateral line fibers in Xenopus and urodeles, whereas CB mainly labeled vestibular fibers and nuclei in all species. These results highlight the anatomical complexity of the amphibian brainstem and help in an understanding of its regional organization that is not cytoarchitectonically evident. J. Comp. Neurol. 515:503–537, 2009. © 2009 Wiley‐Liss, Inc.

Immunohistochemical localization of calbindin‐D28k and calretinin in the brainstem of anuran and urodele amphibians

Calbindin-D28k (CB) and calretinin (CR) are calcium binding proteins present in distinct sets of neurons; they act as buffers regulating the concentration of intracellular calcium. CB and CR immunohistochemistry was studied in the brainstem of anuran and urodele amphibians in combination with other markers (choline acetyltransferase, tyrosine hydroxylase, and nitric oxide synthase), which served to clarify the localization and signature of many cell groups. CR labeled the retinorecipient layers of the optic tectum, and CB and CR labeled distinct tectal cell populations. The two proteins were largely complementary in the torus semicircularis and marked auditory and lateral line sensory regions, depending on the species. CB and CR in the mesencephalic and isthmic tegmentum specified the boundaries of basal and medial longitudinal bands. In the cerebellum, CB labeled Purkinje cells in all species, whereas CR was mainly found in fibers and labeled Purkinje cells only in Rana. In the parabrachial region, CB and CR allowed the distinction of the laterodorsal tegmental nucleus, isthmic nucleus, locus coeruleus, and rostral octavolateral nuclei. The distribution of CB- and CR-immunoreactive cells in the reticular formation and central gray was consistent with the current models of brainstem segmentation in amphibians. CR was found in the auditory fibers and nuclei in Rana and in mechanosensory lateral line fibers in Xenopus and urodeles, whereas CB mainly labeled vestibular fibers and nuclei in all species. These results highlight the anatomical complexity of the amphibian brainstem and help in an understanding of its regional organization that is not cytoarchitectonically evident.

Corazonin- and PDF-immunoreactivities in the cephalic ganglia of termites

Antisera against the pigment-dispersing factor (PDF) and corazonin (Crz) reacted with distinct sets of neurons in the cephalic ganglia of termites. The locations of immunoreactive cells were similar but their numbers differed among the eight species examined: PDF-ir occurred in 0–6 cells in each optic lobe and 1–2 pairs of cells in the subosophageal ganglion (SOG), and Crz-ir in 0–2 pairs of cells in the pars intecerebralis, 3–14 cells in each lateral protocerebrum, and 0–6 pairs of cells in the SOG. Staining patterns were identical in the pseudergates, soldiers, and substitutive reproductives of Prorhinotermes simplex. Workers and soldiers were compared in the remaining 7 species. The only caste divergence was detected in Coptotermes formosanus, in which the soldiers differed from the workers by lack of 4 Crz-ir perikarya in the pars intercerebralis and occasionally also by the absence of 2 Crz-ir perikarya in the SOG. Diurnal changes in PDF-ir and Crz-ir were examined in P. simplex kept under long day (18:6 h light:darkness) or short day (10:14 h) photoperiods. No circadian fluctuations in the distribution or the intensity of immunostaining were found in the pseudergates and soldiers that were sacrificed in 4 h intervals or in the male and female substitutive reproductives examined in 6 h intervals.

Comparative genomics identifies a cis‐regulatory module that activates transcription in specific subsets of neurons in Ciona intestinalis larvae

The larval nervous system of the ascidian Ciona intestinalis exhibits an abstract form of the vertebrate nervous system. The Ci-Galphai1 gene, which encodes a G-protein alpha subunit, is specifically expressed in distinct sets of neurons in C. intestinalis larvae, including papillar neurons of the adhesive organ, ocellus photoreceptor cells, and cholinergic and GABAergic neurons in the central nervous system (CNS). A GFP reporter gene driven by the 4.2-kb 5' flanking region of Ci-Galphai1 recapitulated the endogenous gene expression patterns. Comparative genomic analysis of the Galphai1 gene between C. intestinalis and Ciona savignyi identified an 87-bp highly conserved non-coding sequence located between -3176 and -3090 bp upstream of the gene. Deletion of this conserved upstream sequence resulted in the complete loss of reporter expression in the central nervous system, while reporter expression in the adhesive organ and mesenchyme cells remained unaffected. The conserved upstream sequence can activate gene expression from basal promoters in the brain vesicle, although it requires additional cis-regulatory sequences to fully activate the CNS-specific gene expression. These results suggest that different types of central neurons share a common transcriptional activation mechanism that is different from that of papillar neurons.

The mRNA-like noncoding RNA Gomafu constitutes a novel nuclear domain in a subset of neurons

Recent transcriptome analyses have revealed that a large body of noncoding regions of mammalian genomes are actually transcribed into RNAs. Our understanding of the molecular features of these noncoding RNAs is far from complete. We have identified a novel mRNA-like noncoding gene, named Gomafu, which is expressed in a distinct set of neurons in the mouse nervous system. Interestingly, spliced mature Gomafu RNA is localized to the nucleus despite its mRNA-like characteristics, which usually act as potent export signals to the cytoplasm. Within the nucleus, Gomafu RNA is detected as numerous spots that do not colocalize with known nuclear domain markers. Gomafu RNA is extremely insoluble and remains intact after nuclear matrix preparation. Furthermore, heterokaryon assays revealed that Gomafu RNA does not shuttle between the nucleus and cytoplasm, but is retained in the nucleus after its transcription. We propose that Gomafu RNA represents a novel family of mRNA-like noncoding RNA that constitutes a cell-type-specific component of the nuclear matrix.

Efficient and cell specific knock-down of gene function in targeted C. elegans neurons

The nematode C. elegans has become an important model for understanding how genes influence behavior. However, in this organism the available approaches for identifying the neuron(s) where the function of a gene is required for a given behavioral trait are time consuming and restricted to non essential genes for which mutants are available. We describe a simple reverse genetics approach for reducing, in chosen C. elegans neurons, the function of genes. The method is based on the expression, under cell specific promoters, of sense and antisense RNA corresponding to a gene of interest. By targeting the genes osm-10, osm-6 and the Green Fluorescent Protein gene, gfp, we show that this approach leads to efficient, heritable and cell autonomous knock-downs of gene function, even in neurons usually refractory to classic RNA interference (RNAi). By targeting the essential and ubiquitously expressed gene, gpb-1, which encodes a G protein β subunit, we identify for the first time two distinct sets of neurons in which the function of gpb-1 is required to regulate two distinct behaviors: egg-laying and avoidance of repellents. The cell specific knock-downs obtained with this approach provide information that is complementary to that provided by the cell specific rescue of loss-of-function mutations and represents a useful new tool for dissecting the role that genes play in selected neurons.

Identification of neuron-specific promoters in Ciona intestinalis.

We isolated 5' flanking regions of four genes, Ci-Galphai1, Ci-arr, Ci-vAChTP, and Ci-vGAT, each of which is expressed in distinct sets of neurons in the central nervous system of the ascidian Ciona intestinalis, and we examined their function by introducing green fluorescent protein (GFP)-fusion constructs into Ciona embryos. The reporter gene driven by the 5' flanking region of Ci-Galphai1, Ci-arr, and Ci-vAChTP recapitulated the endogenous gene expression patterns, while that of Ci-vGAT can drive GFP expression in particular subsets of neurons expressing the endogenous gene. Deletion analysis revealed that the Ci-Galphai1 promoter consists of multiple regulatory modules controlling the expression in different types of cells. The GFP fluorescence enabled visualization of cell bodies and axons of different sets of neurons in ascidian larvae. These promoters can be a powerful tool for studying molecular mechanisms of neuronal development as well as neuron networks and functions in ascidians.

Tachykinin- and leucokinin-related peptides in the nervous system of the blowfly: Immunocytochemical and chromatographical diversity

We are interested in the presence and function in insects of neuropeptides related to the vertebrate tachykinins. Hence, we have used antisera raised against the tachykinins substance P and kassinin, and against the insect neuropeptide leucokinin I, for localization studies and immunochemical analysis of related peptides in the nervous system of the blowfly Phormia terraenovae. In radioimmunoassays (with antisera against kassinin and leucokinin I) used in combination with reverse-phase HPLC, it was shown that the antisera recognize immunoreactive material with distinctly different hydrophobic properties and each antiserum appear to detect several forms of immunochemically related peptides. With immunocytochemistry it was shown that the kassinin and leucokinin antisera each reacted with material in a distinct set of neurons. The leucokinin-immunoreactive material is present both in interneurons and in neurosecretory cells, suggesting roles of native leucokinin-like peptides as neuromodulators in the nervous system and as neurohormones acting on peripheral targets. The kassinin immunoreactivity was seen in interneurons, but could not be conclusively localized in neurosecretory cells, possibly indicating a role only within the nervous system.