The chandelier neuron in schizophrenia

Markers of GABA neurotransmission between chandelier neurons and their synaptic targets, the axon initial segment (AIS) of pyramidal neurons, are altered in the dorsolateral prefrontal cortex (DLPFC) of subjects with schizophrenia. For example, immunoreactivity for the GABA membrane transporter (GAT1) is decreased in presynaptic chandelier neuron axon terminals, whereas immunoreactivity for the GABA(A) receptor α2 subunit is increased in postsynaptic AIS. These alterations are most marked in cortical layers 2-3. In addition, other determinants of the function of chandelier cell-pyramidal neuron synapses, such as ankyrin-G (which regulates the recruitment of sodium channels to the AIS), are also selectively altered in superficial layer pyramidal neurons in subjects with schizophrenia. Each of these components of chandelier cell-pyramidal neuron connectivity exhibits distinctive developmental trajectories in the primate DLPFC, suggesting that disturbances in these trajectories could contribute to the pathogenesis of schizophrenia. Recent findings that inputs from neocortical chandelier neurons are excitatory provide new ideas about the role of this circuitry in the pathophysiology of cortical dysfunction in schizophrenia.     

Classification and function of GABAergic interneurons of the mammalian cerebral cortex

GABAergic interneurons make up about 20% of neurons in the cortex and are a heterogeneous group of cells. In recent years it has become clear that different populations of interneurons not only provide the balance of excitation and inhibition in neural networks but are also critically important for generation of rhythmic activity, successful processing of sensory information, implementation of synaptic plasticity and a number of other functions. We examine current approaches to classification of interneurons and review the properties and the functional role of basket cells, chandelier cells, neurogliaform interneurons, Martinotti cells, and some other classes of interneurons based on morphological, immunohistochemical, electrophysiological and optogenetic studies. Besides, we consider the opportunities of the selective impact on target population of interneurons and review the data on the role of different types of interneurons in the pathogenesis of epilepsy and schizophrenia.     

Three groups of interneurons account for nearly 100% of neocortical GABAergic neurons

An understanding of the diversity of cortical GABAergic interneurons is critical to understand the function of the cerebral cortex. Recent data suggest that neurons expressing three markers, the Ca2+-binding protein parvalbumin (PV), the neuropeptide somatostatin (SST), and the ionotropic serotonin receptor 5HT3a (5HT3aR) account for nearly 100% of neocortical interneurons. Interneurons expressing each of these markers have a different embryological origin. Each group includes several types of interneurons that differ in morphological and electrophysiological properties and likely have different functions in the cortical circuit. The PV group accounts for ～40% of GABAergic neurons and includes fast spiking basket cells and chandelier cells. The SST group, which represents ～30% of GABAergic neurons, includes the Martinotti cells and a set of neurons that specifically target layerIV. The 5HT3aR group, which also accounts for ～30% of the total interneuronal population, is heterogeneous and includes all of the neurons that express the neuropeptide VIP, as well as an equally numerous subgroup of neurons that do not express VIP and includes neurogliaform cells. The universal modulation of these neurons by serotonin and acetylcholine via ionotropic receptors suggests that they might be involved in shaping cortical circuits during specific brain states and behavioral contexts.     

大鼠海马脑中枝形吊灯样中间神经元的形态与电生理学特征

在大鼠海马脑片标本上,用微电极记录并标记了４个枝形吊灯样中间,约占所记录到的３９个中间神经元的１０％,与蓝状中间神经元显著不同之处是,这４个神经元均对细胞内去极化电流表现出不同程度的放电频率适应现象,用细胞内注射ｂｉｏｃｙｔｉｎ的方法证实,蓝状中间神经元轴突终末主要分布在锥体在颗粒细胞层,与这些细胞胞体形成接触,而４个枝形吊灯样中间神经元的轴突终末增高度选择性分布在锥体和颗粒细胞轴突始段区,上述结     

Preparation of Parasagittal Slices for the Investigation of Dorsal-ventral Organization of the Rodent Medial Entorhinal Cortex

Computation in the brain relies on neurons responding appropriately to their synaptic inputs. Neurons differ in their complement and distribution of membrane ion channels that determine how they respond to synaptic inputs. However, the relationship between these cellular properties and neuronal function in behaving animals is not well understood. One approach to this problem is to investigate topographically organized neural circuits in which the position of individual neurons maps onto information they encode or computations they carry out¹. Experiments using this approach suggest principles for tuning of synaptic responses underlying information encoding in sensory and cognitive circuits^2,3.The topographical organization of spatial representations along the dorsal-ventral axis of the medial entorhinal cortex (MEC) provides an opportunity to establish relationships between cellular mechanisms and computations important for spatial cognition. Neurons in layer II of the rodent MEC encode location using grid-like firing fields^4-6. For neurons found at dorsal positions in the MEC the distance between the individual firing fields that form a grid is on the order of 30 cm, whereas for neurons at progressively more ventral positions this distance increases to greater than 1 m. Several studies have revealed cellular properties of neurons in layer II of the MEC that, like the spacing between grid firing fields, also differ according to their dorsal-ventral position, suggesting that these cellular properties are important for spatial computation^2,7-10.Here we describe procedures for preparation and electrophysiological recording from brain slices that maintain the dorsal-ventral extent of the MEC enabling investigation of the topographical organization of biophysical and anatomical properties of MEC neurons. The dorsal-ventral position of identified neurons relative to anatomical landmarks is difficult to establish accurately with protocols that use horizontal slices of MEC^7,8,11,12, as it is difficult to establish reference points for the exact dorsal-ventral location of the slice. The procedures we describe enable accurate and consistent measurement of location of recorded cells along the dorsal-ventral axis of the MEC as well as visualization of molecular gradients^2,10. The procedures have been developed for use with adult mice (> 28 days) and have been successfully employed with mice up to 1.5 years old. With adjustments they could be used with younger mice or other rodent species. A standardized system of preparation and measurement will aid systematic investigation of the cellular and microcircuit properties of this area.     

Blanes cells mediate persistent feedforward inhibition onto granule cells in the olfactory bulb

Inhibitory local circuits in the olfactory bulb play a critical role in determining the firing patterns of output neurons. However, little is known about the circuitry in the major plexiform layers of the olfactory bulb that regulate this output. Here we report the first electrophysiological recordings from Blanes cells, large stellate-shaped interneurons located in the granule cell layer. We find that Blanes cells are GABAergic and generate large I(CAN)-mediated afterdepolarizations following bursts of action potentials. Using paired two-photon guided intracellular recordings, we show that Blanes cells have a presumptive axon and monosynaptically inhibit granule cells. Sensory axon stimulation evokes barrages of EPSPs in Blanes cells that trigger long epochs of persistent spiking; this firing mode was reset by hyperpolarizing membrane potential steps. Persistent firing in Blanes cells may represent a novel mechanism for encoding short-term olfactory information through modulation of tonic inhibitory synaptic input onto bulbar neurons.     

Ionic conductance mechanisms contributing to the electrophysiological properties of neurons.

Neurons have a multiplicity of ionic conductance mechanisms, the interactions of which determine in part the response of a neuron to chemical and electrical synaptic interactions, firing patterns, excitability, membrane potential and action-potential waveform. Several papers published in the past year have provided important new information on the role that ionic conductance mechanisms play in determining the electrophysiological properties of neurons, and how subtle differences can contribute to considerable variability of response.     

Functional Integration of Human Neural Precursor Cells in Mouse Cortex

This study investigates the electrophysiological properties and functional integration of different phenotypes of transplanted human neural precursor cells (hNPCs) in immunodeficient NSG mice. Postnatal day 2 mice received unilateral injections of 100,000 GFP+ hNPCs into the right parietal cortex. Eight weeks after transplantation, 1.21% of transplanted hNPCs survived. In these hNPCs, parvalbumin (PV)-, calretinin (CR)-, somatostatin (SS)-positive inhibitory interneurons and excitatory pyramidal neurons were confirmed electrophysiologically and histologically. All GFP+ hNPCs were immunoreactive with anti-human specific nuclear protein. The proportions of PV-, CR-, and SS-positive cells among GFP+ cells were 35.5%, 15.7%, and 17.1%, respectively; around 15% of GFP+ cells were identified as pyramidal neurons. Those electrophysiologically and histological identified GFP+ hNPCs were shown to fire action potentials with the appropriate firing patterns for different classes of neurons and to display spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs). The amplitude, frequency and kinetic properties of sEPSCs and sIPSCs in different types of hNPCs were comparable to host cells of the same type. In conclusion, GFP+ hNPCs produce neurons that are competent to integrate functionally into host neocortical neuronal networks. This provides promising data on the potential for hNPCs to serve as therapeutic agents in neurological diseases with abnormal neuronal circuitry such as epilepsy.     

Effects of beta-catenin on dendritic morphology and simulated firing patterns in cultured hippocampal neurons

Beta-catenin is an intracellular signaling molecule that has been shown to be important in activity-dependent dendritic morphogenesis. Here, we investigate the detailed morphological changes elicited in dendritic arbors of cultured hippocampal neurons by overexpression of beta-catenin, and we simulate the electrophysiological consequences of these changes. Compared to control neurons, cells overexpressing beta-catenin have dendritic arbors with significantly greater surface area and more branches, as well as different topological characteristics. To investigate possible effects of beta-catenin expression on the electrophysiological properties of neurons, we converted confocal images of neurons expressing beta-catenin into computational simulator formats using parameters that evenly distributed voltage-dependent channels across the cells' membranes. In simulated current clamp experiments, somata were injected with a normalized current such that the observed electrophysiological differences in the neurons would be due only to morphological differences. We found that the morphology of beta-catenin-expressing neurons contributes to significantly smaller action potential amplitude and greater sensitivity than seen in control neurons. As a consequence, beta-catenin-expressing neurons tended to exhibit higher spike rates and needed less excitation to induce firing. These findings show that beta-catenin, by modifying dendritic arborization, could have profound influences on the electrophysiological behavior of neurons.     

Globus Pallidus External Segment Neuron Classification in Freely Moving Rats: A Comparison to Primates

Globus Pallidus external segment (GPe) neurons are well-characterized in behaving primates. Based on their firing properties, these neurons are commonly divided into two distinct groups: high frequency pausers (HFP) and low frequency bursters (LFB). However, no such characterization has been made for behaving rats. The current study characterizes and categorizes extracellularly recorded GPe neurons in freely moving rats, and compares these results to those obtained by extracellular recordings in behaving primates using the same analysis methods. Analysis of our data recorded in rats revealed two distinct neuronal populations exhibiting firing-pattern characteristics that are similar to those obtained in primates. These characteristic firing patterns are conserved between species although the firing rate is significantly lower in rats than in primates. Significant differences in waveform duration and shape were insufficient to create a reliable waveform-based classification in either species. The firing pattern analogy may emphasize conserved processing properties over firing rate per-se. Given the similarity in GPe neuronal activity between human and non-human primates in different pathologies, our results encourage information transfer using complementary studies across species in the GPe to acquire a better understanding of the function of this nucleus in health and disease.     

Subthalamic Nucleus High-Frequency Stimulation Restores Altered Electrophysiological Properties of Cortical Neurons in Parkinsonian Rat

Electrophysiological recordings performed in parkinsonian patients and animal models have confirmed the occurrence of alterations in firing rate and pattern of basal ganglia neurons, but the outcome of these changes in thalamo-cortical networks remains unclear. Using rats rendered parkinsonian, we investigated, at a cellular level in vivo, the electrophysiological changes induced in the pyramidal cells of the motor cortex by the dopaminergic transmission interruption and further characterized the impact of high-frequency electrical stimulation of the subthalamic nucleus, a procedure alleviating parkinsonian symptoms. We provided evidence that a lesion restricted to the substantia nigra pars compacta resulted in a marked increase in the mean firing rate and bursting pattern of pyramidal neurons of the motor cortex. These alterations were underlain by changes of the electrical membranes properties of pyramidal cells including depolarized resting membrane potential and increased input resistance. The modifications induced by the dopaminergic loss were more pronounced in cortico-striatal than in cortico-subthalamic neurons. Furthermore, subthalamic nucleus high-frequency stimulation applied at parameters alleviating parkinsonian signs regularized the firing pattern of pyramidal cells and restored their electrical membrane properties.     

Membrane and firing properties of avian medial vestibular nucleus neuronsin vitro

The intrinsic membrane and firing properties of medial vestibular nucleus (MVN) neurons were investigated in slices of the chick brainstem using intracellular recording and current injection. Avian MVN neurons fired spontaneous action potentials with very regular interspike intervals. The rapid repolarization of all action potentials was followed by an after-hyperpolarization. Intracellular injection of steps of hyperpolarizing current revealed both an inward rectification of the membrane potential during the step and a rebound depolarization following the offset of the step. In some neurons, the rebound depolarization resulted in bursts of action potentials. Steps of depolarizing current applied to spontaneously active neurons evoked increases in firing rate that were higher at the onset of the step than during the steady-state response. The relationship between current and firing rate was linear. The membrane and firing properties of avian MVN neurons were distributed continuously across the population of recorded neurons. These properties appear identical to those of rodent MVN neurons, suggesting that the composition and distribution of ion channels in the MVN neuronal membrane has been highly conserved across vertebrate species.Abbreviations MVN medial vestibular nucleus - VOR vestibulo-ocular reflex - AHP after-hyperpolarization     

Small Modifications to Network Topology Can Induce Stochastic Bistable Spiking Dynamics in a Balanced Cortical Model

Directed random graph models frequently are used successfully in modeling the population dynamics of networks of cortical neurons connected by chemical synapses. Experimental results consistently reveal that neuronal network topology is complex, however, in the sense that it differs statistically from a random network, and differs for classes of neurons that are physiologically different. This suggests that complex network models whose subnetworks have distinct topological structure may be a useful, and more biologically realistic, alternative to random networks. Here we demonstrate that the balanced excitation and inhibition frequently observed in small cortical regions can transiently disappear in otherwise standard neuronal-scale models of fluctuation-driven dynamics, solely because the random network topology was replaced by a complex clustered one, whilst not changing the in-degree of any neurons. In this network, a small subset of cells whose inhibition comes only from outside their local cluster are the cause of bistable population dynamics, where different clusters of these cells irregularly switch back and forth from a sparsely firing state to a highly active state. Transitions to the highly active state occur when a cluster of these cells spikes sufficiently often to cause strong unbalanced positive feedback to each other. Transitions back to the sparsely firing state rely on occasional large fluctuations in the amount of non-local inhibition received. Neurons in the model are homogeneous in their intrinsic dynamics and in-degrees, but differ in the abundance of various directed feedback motifs in which they participate. Our findings suggest that (i) models and simulations should take into account complex structure that varies for neuron and synapse classes; (ii) differences in the dynamics of neurons with similar intrinsic properties may be caused by their membership in distinctive local networks; (iii) it is important to identify neurons that share physiological properties and location, but differ in their connectivity.     

Identification of a Group of GABAergic Neurons in the Dorsomedial Area of the Locus Coeruleus

The locus coeruleus (LC)-norepinephrine (NE) system in the brainstem plays a critical role in a variety of behaviors is an important target of pharmacological intervention to several neurological disorders. Although GABA is the major inhibitory neurotransmitter of LC neurons, the modulation of LC neuronal firing activity by local GABAergic interneurons remains poorly understood with respect to their precise location, intrinsic membrane properties and synaptic modulation. Here, we took an optogenetic approach to address these questions. Channelrhodopsin (ChR2) in a tandem with the yellow fluorescent protein (YFP) was expressed in GABAergic neurons under the control of glutamic acid decarboxylase 2 (GAD2) promoter. Immediately dorsomedial to the LC nucleus, a group of GABAergic neurons was observed. They had small soma and were densely packed in a small area, which we named the dorsomedial LC or dmLC nucleus. These GABAergic neurons showed fast firing activity, strong inward rectification and spike frequency adaptation. Lateral inhibition among these GABAergic neurons was observed. Optostimulation of the dmLC area drastically inhibited LC neuronal firing frequency, expanded the spike intervals, and reset their pacemaking activity. Analysis of the light evoked inhibitory postsynaptic currents (IPSCs) indicated that they were monosynaptic. Such light evoked IPSCs were not seen in slices where this group of GABAergic neurons was absent. Thus, an isolated group of GABAergic neurons is demonstrated in the LC area, whose location, somatic morphology and intrinsic membrane properties are clearly distinguishable from adjacent LC neurons. They interact with each and may inhibit LC neurons as well as a part of local neuronal circuitry in the LC.     

A Time Course Analysis of the Electrophysiological Properties of Neurons Differentiated from Human Induced Pluripotent Stem Cells (iPSCs)

Many protocols have been designed to differentiate human embryonic stem cells (ESCs) and human induced pluripotent stem cells (iPSCs) into neurons. Despite the relevance of electrophysiological properties for proper neuronal function, little is known about the evolution over time of important neuronal electrophysiological parameters in iPSC-derived neurons. Yet, understanding the development of basic electrophysiological characteristics of iPSC-derived neurons is critical for evaluating their usefulness in basic and translational research. Therefore, we analyzed the basic electrophysiological parameters of forebrain neurons differentiated from human iPSCs, from day 31 to day 55 after the initiation of neuronal differentiation. We assayed the developmental progression of various properties, including resting membrane potential, action potential, sodium and potassium channel currents, somatic calcium transients and synaptic activity. During the maturation of iPSC-derived neurons, the resting membrane potential became more negative, the expression of voltage-gated sodium channels increased, the membrane became capable of generating action potentials following adequate depolarization and, at day 48–55, 50% of the cells were capable of firing action potentials in response to a prolonged depolarizing current step, of which 30% produced multiple action potentials. The percentage of cells exhibiting miniature excitatory post-synaptic currents increased over time with a significant increase in their frequency and amplitude. These changes were associated with an increase of Ca²⁺ transient frequency. Co-culturing iPSC-derived neurons with mouse glial cells enhanced the development of electrophysiological parameters as compared to pure iPSC-derived neuronal cultures. This study demonstrates the importance of properly evaluating the electrophysiological status of the newly generated neurons when using stem cell technology, as electrophysiological properties of iPSC-derived neurons mature over time.     

Effect of moxonidine on putative sympathetic neurons in the rostral ventrolateral medulla of the rat

We used an intracellular recording technique in vitro to investigate the effects of moxonidine on neurons in the rostral ventrolateral medulla (RVLM) with electrophysiological properties similar to premotor sympathetic neurons in vivo. These neurons were classified as firing regularly and irregularly, according to previous reports. Moxonidine is a sympathoinhibitory and antihypertensive agent that is thought to be a ligand of alpha(2)-adrenergic receptors and imidazoline type-1 receptors in the RVLM. Moxonidine (2-10 microM) was applied to the perfusate on 4 irregularly firing neurons, and 2 regularly firing neurons. Moxonidine (2 microM) produced only minor depolarization in 2 of these neurons. However, on 4 tested neurons, moxonidine (10 microM) elicited a profound inhibitory effect with hyperpolarization (near -20 mV); these neurons practically ceased firing. These changes were partially reversible. The results would indicate that neurons in the RVLM, recorded in vitro and with similar electrophysiological characteristics to a group of neurons previously identified in vivo in the same bulbar region as barosensitive premotor sympathetic neurons, can be modulated by imidazoline-derivative adrenergic agonists. These results could help to understand the hypotensive effects of moxonidine.     

Conditional Probability Analyses of the Spike Activity of Single Neurons

With the objective of separating stimulus-related effects from refractory effects in neuronal spike data, various conditional probability analyses have been developed. These analyses are introduced and illustrated with examples based on electrophysiological data from auditory nerve fibers. The conditional probability analyses considered here involve the estimation of the conditional probability of a firing in a specified time interval (defined relative to the time of the stimulus presentation), given that the last firing occurred during an earlier specified time interval. This calculation enables study of the stimulus-related effects in the spike data with the time-since-the-last-firing as a controlled variable. These calculations indicate that auditory nerve fibers “recover” from the refractory effects that follow a firing in the following sense: after a “recovery time” of approximately 20 msec, the firing probabilities no longer depend on the time-since-the-last-firing. Probabilities conditional on this minimum time since the last firing are called “recovered probabilities.” The recovered probabilities presented in this paper are contrasted with the corresponding poststimulus time histograms, and the differences are related to the refractory properties of the nerve fibers.     

Morphology,Classification, and Distribution of the Projection Neurons in the Dorsal Lateral Geniculate Nucleus of the Rat

The morphology of confirmed projection neurons in the dorsal lateral geniculate nucleus (dLGN) of the rat was examined by filling these cells retrogradely with biotinylated dextran amine (BDA) injected into the visual cortex. BDA-labeled projection neurons varied widely in the shape and size of their cell somas, with mean cross-sectional areas ranging from 60–340 µm². Labeled projection neurons supported 7–55 dendrites that spanned up to 300 µm in length and formed dendritic arbors with cross-sectional areas of up to 7.0×10⁴ µm². Primary dendrites emerged from cell somas in three broad patterns. In some dLGN projection neurons, primary dendrites arise from the cell soma at two poles spaced approximately 180° apart. In other projection neurons, dendrites emerge principally from one side of the cell soma, while in a third group of projection neurons primary dendrites emerge from the entire perimeter of the cell soma. Based on these three distinct patterns in the distribution of primary dendrites from cell somas, we have grouped dLGN projection neurons into three classes: bipolar cells, basket cells and radial cells, respectively. The appendages seen on dendrites also can be grouped into three classes according to differences in their structure. Short “tufted” appendages arise mainly from the distal branches of dendrites; “spine-like” appendages, fine stalks with ovoid heads, typically are seen along the middle segments of dendrites; and “grape-like” appendages, short stalks that terminate in a cluster of ovoid bulbs, appear most often along the proximal segments of secondary dendrites of neurons with medium or large cell somas. While morphologically diverse dLGN projection neurons are intermingled uniformly throughout the nucleus, the caudal pole of the dLGN contains more small projection neurons of all classes than the rostral pole.     

Quantitative analysis of the structure of neuronal dendritic spines in the striatum using the Leitz-ASM system

Two principal classes of striatum long axonal neurons (sparsely ramified reticular cells and densely ramified dendritic cells) were analyzed quantitatively in four animal species: hedgehog, rabbit, dog and monkey. The cross section area, total dendritic length and the area of dendritic field were measured using "LEITZ-ASM" system. Classes of neurons studied were significantly different in dogs and monkeys, while no differences were noted between hedgehog and rabbit. Reticular neurons of different species varied much more than dendritic ones. Quantitative analysis has revealed the progressive increase in the complexity of dendritic tree in mammals from rabbit to monkey.     

A generalized linear model for estimating spectrotemporal receptive fields from responses to natural sounds

In the auditory system, the stimulus-response properties of single neurons are often described in terms of the spectrotemporal receptive field (STRF), a linear kernel relating the spectrogram of the sound stimulus to the instantaneous firing rate of the neuron. Several algorithms have been used to estimate STRFs from responses to natural stimuli; these algorithms differ in their functional models, cost functions, and regularization methods. Here, we characterize the stimulus-response function of auditory neurons using a generalized linear model (GLM). In this model, each cell's input is described by: 1) a stimulus filter (STRF); and 2) a post-spike filter, which captures dependencies on the neuron's spiking history. The output of the model is given by a series of spike trains rather than instantaneous firing rate, allowing the prediction of spike train responses to novel stimuli. We fit the model by maximum penalized likelihood to the spiking activity of zebra finch auditory midbrain neurons in response to conspecific vocalizations (songs) and modulation limited (ml) noise. We compare this model to normalized reverse correlation (NRC), the traditional method for STRF estimation, in terms of predictive power and the basic tuning properties of the estimated STRFs. We find that a GLM with a sparse prior predicts novel responses to both stimulus classes significantly better than NRC. Importantly, we find that STRFs from the two models derived from the same responses can differ substantially and that GLM STRFs are more consistent between stimulus classes than NRC STRFs. These results suggest that a GLM with a sparse prior provides a more accurate characterization of spectrotemporal tuning than does the NRC method when responses to complex sounds are studied in these neurons.