Various Types Of Neurons Research Articles

Whole-cell patch-clamp recordings from morphologically- and neurochemically-identified hippocampal interneurons.

GABAergic inhibitory interneurons play a central role within neuronal circuits of the brain. Interneurons comprise a small subset of the neuronal population (10-20%), but show a high level of physiological, morphological, and neurochemical heterogeneity, reflecting their diverse functions. Therefore, investigation of interneurons provides important insights into the organization principles and function of neuronal circuits. This, however, requires an integrated physiological and neuroanatomical approach for the selection and identification of individual interneuron types. Whole-cell patch-clamp recording from acute brain slices of transgenic animals, expressing fluorescent proteins under the promoters of interneuron-specific markers, provides an efficient method to target and electrophysiologically characterize intrinsic and synaptic properties of specific interneuron types. Combined with intracellular dye labeling, this approach can be extended with post-hoc morphological and immunocytochemical analysis, enabling systematic identification of recorded neurons. These methods can be tailored to suit a broad range of scientific questions regarding functional properties of diverse types of cortical neurons.

Implementing spiking neuron model and spike-timing-dependent plasticity with generalized Laguerre-Volterra models.

To perform large-scale simulations of the brain or build biologically-inspired cognitive architectures, it is essential to have a succinct and flexible model of spiking neurons. The model should be able to capture the nonlinear dynamical properties of various types of neurons and the nonstationary properties such as the spike-timing-dependent plasticity (STDP). In this paper, we propose a generalized Laguerre-Volterra modeling approach for such a task. Due to its built-in nonlinear dynamical terms, the generalized Laguerre-Volterra model (GLVM) can capture various biological processes/mechanisms. Using Laguerre expansion of Volterra kernel technique, the model is fully represented with a small set of coefficients. The calculation of the model variables can be expressed recursively based on only the current and the one-step-before values and thus can be performed efficiently. In addition, we show that, using the same methodology, STDP can be implemented as a specific form of second-order Volterra kernel describing the causal relationship between pairs of input-output spikes and the changes of the feedforward kernels in the GLVMs.

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.

Development of the embryonic and larval peripheral nervous system of Drosophila.

The peripheral nervous system (PNS) of embryonic and larval stage Drosophila consists of diverse types of sensory neurons positioned along the body wall. Sensory neurons, and associated end organs, show highly stereotyped locations and morphologies. Many powerful genetic tools for gene manipulation available in Drosophila make the PNS an advantageous system for elucidating basic principles of neural development. Studies of the Drosophila PNS have provided key insights into molecular mechanisms of cell fate specification, asymmetric cell division, and dendritic morphogenesis. A canonical lineage gives rise to sensory neurons and associated organs, and cells within this lineage are diversified through asymmetric cell divisions. Newly specified sensory neurons develop specific dendritic patterns, which are controlled by numerous factors including transcriptional regulators, interactions with neighboring neurons, and intracellular trafficking systems. In addition, sensory axons show modality specific terminations in the central nervous system, which are patterned by secreted ligands and their receptors expressed by sensory axons. Modality-specific axon projections are critical for coordinated larval behaviors. We review the molecular basis for PNS development and address some of the instances in which the mechanisms and molecules identified are conserved in vertebrate development.

Positive feedback loop between Sox2 and Sox6 inhibits neuronal differentiation in the developing central nervous system

How a pool of undifferentiated neural progenitor cells is maintained in the developing nervous system is an issue that remains unresolved. One of the key transcription factors for self-renewal of these cells is Sox2, the forced expression of which has been shown to inhibit neuronal differentiation in vivo. To dissect the molecular mechanisms of Sox2 activity, a ChIP-on-chip assay has been carried out for Sox2, and multiple candidate direct target genes have been isolated. In this report, we provide evidence indicating that Sox6, which like Sox2 belongs to the SRY-related HMG box transcription factor family, is a bona-fide direct regulatory target of Sox2. In vivo, Sox6 expression is seen with a temporal lag in Sox2-positive neural precursor cells in the ventricular zone, and Sox2 promotes expression of Sox6 as a transcriptional activator. Interestingly, gain- and loss-of-function assays indicate that Sox6 in turn is required for the maintenance of Sox2 expression, suggesting that a positive feedback loop, which functions to inhibit premature neuronal differentiation, exists between the two transcription factors.

Genetic Labeling of Neurons in Mouse Brain

Mammalian central nervous systems consist of highly diverse types of neurons, which are the functional units of neural circuits. To understand the organization, assembly, and function of neural circuits, it is necessary to develop and to improve technologies that allow efficient and robust visualization of neurons in their native environment in vivo. Here we discuss various genetic strategies for achieving specific and robust neuron labeling in mice.

The aging human cochlear nucleus: Changes in the glial fibrillary acidic protein, intracellular calcium regulatory proteins, GABA neurotransmitter and cholinergic receptor

The human auditory system is highly susceptible to environmental and metabolic insults which further affect the biochemical and physiological milieu of the cells that may contribute to progressive, hearing loss with aging. The cochlear nucleus (CN) is populated by morphologically diverse types of neurons with discrete physiological and neurochemical properties. Between the dorsal and the ventral cochlear nucleus (DCN and VCN), the VCN is further sub-divided into the rostral (rVCN) and caudal (cVCN) sub-divisions. Although, information is available on the age related neurochemical changes in the mammalian CN similar reports on human CN is still sparse. The morphometry and semiquantitative analysis of intensity of expression of glial fibrillary acidic protein (GFAP), calcium binding proteins (calbindin, calretinin and parvalbumin), gamma amino butyric acid (GABA) and nicotinic acetyl choline receptor (nAchR) beta 2 immunostaining were carried out in all three sub-divisions of the human CN from birth to 90 years. There was increased GFAP immunoreactivity in decades 2 and 3 in comparison to decade 1 in the CN. But no change was observed in rVCN from decade 4 onwards, whereas intense staining was also observed in decades 5 and 6 in cVCN and DCN. All three calcium binding proteins were highly expressed in early to middle ages, whereas a significant reduction was found in later decades in the VCN. GABA and nAchR beta 2 expressions were unchanged throughout in all the decades. The middle age may represent a critical period of onset and progression of aging changes in the CN and these alterations may add to the deterioration of hearing responses in the old age.

MicroRNA-mediated regulation of the neurogenic-to-gliogenic competence transition of neural stem/progenitor cells

Multipotent neural stem/progenitor cells (NSPCs) produce various types of neurons and glial cells during the development of the central nervous system (CNS); however, NSPCs are not always able to generate all types of neural cells. The formation of complex neural networks relies on proper cytogenesis from NSPCs, which is under strict spatiotemporal regulation by intrinsic and extrinsic mechanisms. The neurogenesis-to-gliogenesis switch, a major event during CNS development, is largely dependent on the cell-autonomous temporal specification of NSPCs. The results of several previous studies suggest that developmental stage-dependent changes in the epigenetic status of proneural and astrocytic genes correlate with the temporal identity transition of developing NSPCs. These changes are related to alterations in the responsiveness of NSPCs to extrinsic neurogenic or gliogenic factors. Here, we discuss our recent findings that microRNA-mediated regulation of competence and relationships between multi-layered mo...

Insulin/IGF-Regulated Size Scaling of Neuroendocrine Cells Expressing the bHLH Transcription Factor Dimmed in Drosophila

Neurons and other cells display a large variation in size in an organism. Thus, a fundamental question is how growth of individual cells and their organelles is regulated. Is size scaling of individual neurons regulated post-mitotically, independent of growth of the entire CNS? Although the role of insulin/IGF-signaling (IIS) in growth of tissues and whole organisms is well established, it is not known whether it regulates the size of individual neurons. We therefore studied the role of IIS in the size scaling of neurons in the Drosophila CNS. By targeted genetic manipulations of insulin receptor (dInR) expression in a variety of neuron types we demonstrate that the cell size is affected only in neuroendocrine cells specified by the bHLH transcription factor DIMMED (DIMM). Several populations of DIMM-positive neurons tested displayed enlarged cell bodies after overexpression of the dInR, as well as PI3 kinase and Akt1 (protein kinase B), whereas DIMM-negative neurons did not respond to dInR manipulations. Knockdown of these components produce the opposite phenotype. Increased growth can also be induced by targeted overexpression of nutrient-dependent TOR (target of rapamycin) signaling components, such as Rheb (small GTPase), TOR and S6K (S6 kinase). After Dimm-knockdown in neuroendocrine cells manipulations of dInR expression have significantly less effects on cell size. We also show that dInR expression in neuroendocrine cells can be altered by up or down-regulation of Dimm. This novel dInR-regulated size scaling is seen during postembryonic development, continues in the aging adult and is diet dependent. The increase in cell size includes cell body, axon terminations, nucleus and Golgi apparatus. We suggest that the dInR-mediated scaling of neuroendocrine cells is part of a plasticity that adapts the secretory capacity to changing physiological conditions and nutrient-dependent organismal growth.

Division of Labor for Division: Inhibitory Interneurons with Different Spatial Landscapes in the Olfactory System

Normalizing neural responses by the sum of population activity allows the nervous system to adjust its sensitivity according to task demands, facilitating intensity-invariant information processing. In this issue of Neuron, two studies, Kato etal. (2013) and Miyamichi etal. (2013), suggest that parvalbumin-positive interneurons in the olfactory bulb play a role in this process.

Novel genes upregulated when NOTCH signalling is disrupted during hypothalamic development

BackgroundThe generation of diverse neuronal types and subtypes from multipotent progenitors during development is crucial for assembling functional neural circuits in the adult central nervous system. It is well known that the Notch signalling pathway through the inhibition of proneural genes is a key regulator of neurogenesis in the vertebrate central nervous system. However, the role of Notch during hypothalamus formation along with its downstream effectors remains poorly defined.ResultsHere, we have transiently blocked Notch activity in chick embryos and used global gene expression analysis to provide evidence that Notch signalling modulates the generation of neurons in the early developing hypothalamus by lateral inhibition. Most importantly, we have taken advantage of this model to identify novel targets of Notch signalling, such as Tagln3 and Chga, which were expressed in hypothalamic neuronal nuclei.ConclusionsThese data give essential advances into the early generation of neurons in the hypothalamus. We demonstrate that inhibition of Notch signalling during early development of the hypothalamus enhances expression of several new markers. These genes must be considered as important new targets of the Notch/proneural network.

Adult neural stem cells: plastic or restricted neuronal fates?

During embryonic development, the telencephalon is specified along its axis through morphogenetic gradients, leading to the positional-dependent generation of multiple neuronal types. After embryogenesis, however, the fate of neuronal progenitors becomes more restricted, and they generate only a subset of neurons. Here, we review studies of postnatal and adult neurogenesis, challenging the notion that fixed genetic programs restrict neuronal fate. We hypothesize that the adult brain maintains plastic neural stem cells that are capable of responding to changes in environmental cues and generating diverse neuronal types. Thus, the limited diversity of neurons generated under normal conditions must be actively maintained by the adult milieu.

T-Type Ca2+Channels in Normal and Abnormal Brain Functions

Low-voltage-activated T-type Ca(2+) channels are widely expressed in various types of neurons. Once deinactivated by hyperpolarization, T-type channels are ready to be activated by a small depolarization near the resting membrane potential and, therefore, are optimal for regulating the excitability and electroresponsiveness of neurons under physiological conditions near resting states. Ca(2+) influx through T-type channels engenders low-threshold Ca(2+) spikes, which in turn trigger a burst of action potentials. Low-threshold burst firing has been implicated in the synchronization of the thalamocortical circuit during sleep and in absence seizures. It also has been suggested that T-type channels play an important role in pain signal transmission, based on their abundant expression in pain-processing pathways in peripheral and central neurons. In this review, we will describe studies on the role of T-type Ca(2+) channels in the physiological as well as pathological generation of brain rhythms in sleep, absence epilepsy, and pain signal transmission. Recent advances in studies of T-type channels in the control of cognition will also be briefly discussed.

Firing-rate models for neurons with a broad repertoire of spiking behaviors

Instantaneous firing rates are commonly used to describe either the compound spiking activity of neuron ensembles (population rate) or the trial-averaged response of individual neurons to multiple repetitions of the same stimulus. The dynamics of firing rates is often studied by means of population or firing-rate models. The main motivation for using such models rather than spiking neuron models is to reduce the dimensionality and complexity of the microscopic dynamics to allow analytical tractability, efficient simulation, and intuitive understanding. In most cases, population models have to be treated as purely phenomenological descriptions. Only under simplifying assumptions can they be derived or extracted from the single-neuron dynamics. Previous studies in this field were mainly restricted to homogeneous populations of simple integrate-and-fire neurons which can, to some extent, mimic the rather stereotypical behaviour of regularly firing neurons (e.g., pyramidal cells in the neocortex). Electrophysiological studies have revealed a large diversity of neuron types with different dynamical behaviours, ranging from regular spiking to bursting cells, from accommodating to non-accommodating cells, from integrators to resonators, from depolarization- to hyperpolarization-activated cells, etc. So far, the effect of this neuron-type diversity on the dynamics of neural populations is unclear. Here, we investigate the rate-response characteristics for a variety of neuron types in simulation experiments. To this end, we extend previous work on simple integrate-and-fire neurons [1,2] to the multi-timescale adaptive threshold (MAT) [3] and the Izhikevich model [4]. The model neurons are probed by spike trains modeled as realizations of inhomogeneous Poisson or Gamma point processes with sinusoidally modulated intensity. Average rates, modulation amplitudes and phases of the period-averaged spike responses are measured for a broad range of stimulus, neuron and synapse parameters. The stationary and nonstationary response properties are parameterized by means of nonlinear activation functions and linear filter kernels, respectively, serving as ingredients for simple linear-nonlinear firing rate models. We show that linear-nonlinear rate models can accurately predict the population responses to novel test stimuli for a broad range of parameters and neuron types.

A temporal mechanism that produces neuronal diversity in the Drosophila visual center

The brain consists of various types of neurons that are generated from neural stem cells; however, the mechanisms underlying neuronal diversity remain uncertain. A recent study demonstrated that the medulla, the largest component of the Drosophila optic lobe, is a suitable model system for brain development because it shares structural features with the mammalian brain and consists of a moderate number and various types of neurons. The concentric zones in the medulla primordium that are characterized by the expression of four transcription factors, including Homothorax (Hth), Brain-specific homeobox (Bsh), Runt (Run) and Drifter (Drf), correspond to types of medulla neurons. Here, we examine the mechanisms that temporally determine the neuronal types in the medulla primordium. For this purpose, we searched for transcription factors that are transiently expressed in a subset of medulla neuroblasts (NBs, neuronal stem cell-like neural precursor cells) and identified five candidates (Hth, Klumpfuss (Klu), Eyeless (Ey), Sloppy paired (Slp) and Dichaete (D)). The results of genetic experiments at least explain the temporal transition of the transcription factor expression in NBs in the order of Ey, Slp and D. Our results also suggest that expression of Hth, Klu and Ey in NBs trigger the production of Hth/Bsh-, Run- and Drf-positive neurons, respectively. These results suggest that medulla neuron types are specified in a birth order-dependent manner by the action of temporal transcription factors that are sequentially expressed in NBs.

Cell biology of normal brain aging: synaptic plasticity–cell death

Senescence of the brain seems to be related to increased levels of free oxygen radical (FOR). FOR may damage macromolecular compounds such as: proteins, lipids, and DNA. In the aging brain, increased FOR levels damage DNA, mitochondrial DNA (mtDNA), and nuclear DNA (nDNA). In DNA they damage single and double strands, leading to mutations in mtDNA and nDNA. Damage to mtDNA seems to result in decay of mitochondria, decreased production of ATP, and in the activation of the apoptotic process. In the aging brain, apoptosis does not seem to be activated in wild-type p53-expressing cells because the elevated levels of the p53 protein are no longer accompanied by decreased levels of the Bcl-2 protein and increased levels of the Bax protein. It seems that, in the aging brain, changes in the metabolism of neurons may lead to their decreased numbers in the cerebral and cerebellar cortex, hippocampus, basal nucleus of Meynert, locus ceruleus, and substantia nigra, as well as to decreased numbers of synapses and disturbed stimulation of synaptic plasticity in the senescent brain. Simultaneously, a decrease in neurogenesis in the aging brain may lead to a decline in the maintenance of tissue integrity, function, and regenerative response. Environmental enrichment and physical activity may improve hippocampal neurogenesis and induce neuronal plasticity. The morphological lesions in the senescent brain are undoubtedly followed by a disturbed balance between various types of neurons in the CNS. Nevertheless, the high plasticity of the CNS in humans most probably does not allow for the development of abnormalities in higher functions.

Identification of In Vivo, Conserved, TAF15 RNA Binding Sites Reveals the Impact of TAF15 on the Neuronal Transcriptome

RNA binding proteins (RBPs) have emerged as major causative agents of amyotrophic lateral sclerosis (ALS). To investigate the function of TAF15, an RBP recently implicated in ALS, we explored its target RNA repertoire in normal human brain and mouse neurons. Coupling high-throughput sequencing of immunoprecipitated and crosslinked RNA with RNA sequencing and TAF15 knockdowns, we identified conserved TAF15 RNA targets and assessed the impact of TAF15 on the neuronal transcriptome. We describe a role of TAF15 in the regulation of splicing for a set of neuronal RNAs encoding proteins with essential roles in synaptic activities. We find that TAF15 is required for a critical alternative splicing event of the zeta-1 subunit of the glutamate N-methyl-D-aspartate receptor (Grin1) that controls the activity and trafficking of NR1. Our study uncovers neuronal RNA networks impacted by TAF15 and sets the stage for investigating the role of TAF15 in ALS pathogenesis.

Inducible gene expression in postmitotic neurons by an in vivo electroporation-based tetracycline system

In vivo electroporation has been widely used to transfect foreign genes into neural progenitors and analyze the function of genes of interest in the developing nervous system. However, it has not been thoroughly examined in the conditional regulation of exogenous genes in postmitotic neurons. Here we show that the combination of in vivo electroporation and the newest version of the tetracycline (Tet)-controlled gene regulatory (Tet-On) system efficiently induced gene expression in various types of neurons in mouse embryonic and postnatal tissues. In pyramidal neurons of the cerebral cortex, tetracycline-responsive element (TRE)-driven gene expression was induced in the presence of doxycycline (Dox). The induction occurred in a dose-dependent manner. The Dox-dependent induction was also observed in cerebellar Purkinje cells and spinal cord neurons. Moreover, the TRE-driven inducible expression of mammalian Barh1 (Mbh1) mimicked the phenotype of the ubiquitous expression of Mbh1 in the spinal cord. These results indicate that the combination of the Tet-On system and in vivo electroporation is useful for analyzing gene function specifically in postmitotic neurons.

A 3D-matrigel/microbead assay for the visualization of mechanical tractive forces at the neurite-substrate interface of cultured neurons

Mechanical properties of neuronal processes contribute to neuronal function, to resistance of fiber tracts against mechanical trauma, and to morphological changes during development and neurodegeneration. Conventional in vitro cell culture systems on inflexible substrates do not allow for the visualization of changing mechanical stress between neurites and their substrate. To solve this problem, we adapted a three-dimensional gel matrix assay to visualize mechanical traction forces at the neurite-substrate interface. We chose matrigel as substrate because in this matrix various types of neurons initially adapt a bipolar morphology while migrating, similar to migrating neurons in vivo. To visualize emerging traction forces between neurites and their substrate, microbeads were embedded into the matrix as visible landmarks. We first analyzed mechanical distortion of matrigel by stepwise movements of a glass pipette tip under control of a micromanipulator to ensure reproducibility of induced bead displacement. The assay was then used to study the effect of the microtubule disrupting drug nocodazole on neuronal processes. By monitoring displacement of matrigel-embedded microbeads, we visualized here for the first time emerging mechanical traction forces between the leading process and the substrate during nocodazole-induced soma translocation. We did not observe bead displacement by processes of aged neurons.

Thalamus-Derived Molecules Promote Survival and Dendritic Growth of Developing Cortical Neurons

The mammalian neocortex is composed of various types of neurons that reflect its laminar and area structures. It has been suggested that not only intrinsic but also afferent-derived extrinsic factors are involved in neuronal differentiation during development. However, the role and molecular mechanism of such extrinsic factors are almost unknown. Here, we attempted to identify molecules that are expressed in the thalamus and affect cortical cell development. First, thalamus-specific molecules were sought by comparing gene expression profiles of the developing rat thalamus and cortex using microarrays, and by constructing a thalamus-enriched subtraction cDNA library. A systematic screening by in situ hybridization showed that several genes encoding extracellular molecules were strongly expressed in sensory thalamic nuclei. Exogenous and endogenous protein localization further demonstrated that two extracellular molecules, Neuritin-1 (NRN1) and VGF, were transported to thalamic axon terminals. Application of NRN1 and VGF to dissociated cell culture promoted the dendritic growth. An organotypic slice culture experiment further showed that the number of primary dendrites in multipolar stellate neurons increased in response to NRN1 and VGF, whereas dendritic growth of pyramidal neurons was not promoted. These molecules also increased neuronal survival of multipolar neurons. Taken together, these results suggest that the thalamus-specific molecules NRN1 and VGF play an important role in the dendritic growth and survival of cortical neurons in a cell type-specific manner.