Eberhard H. Buhl

Bio: Eberhard H. Buhl is an academic researcher from University of Oxford. The author has contributed to research in topics: Postsynaptic potential & Excitatory postsynaptic potential. The author has an hindex of 24, co-authored 29 publications receiving 7491 citations. Previous affiliations of Eberhard H. Buhl include University of Leeds & Mansfield University of Pennsylvania.

Synchronization of neuronal activity in hippocampus by individual GABAergic interneurons

Abstract: SYNCHRONIZATION of neuronal activity is fundamental in the operation of cortical networks. With respect to an ongoing synchronized oscillation, the precise timing of action potentials is an attractive candidate mechanism for information coding. Networks of inhibitory interneurons have been proposed to have a role in entraining cortical, synchronized 40-Hz activity. Here we demonstrate that individual GABAergic interneurons can effectively phase spontaneous firing and subthreshold oscillations in hippocampal pyramidal cells at 0 frequencies (4-7 Hz). The efficiency of this entrainment is due to interaction of GABAA-receptor-mediated hyperpolarizing synaptic events with intrinsic oscillatory mechanisms tuned to this frequency range in pyramidal cells. Moreover, this GABAergic mechanism is sufficient to synchronize the firing of pyramidal cells. Thus, owing to the divergence of each GABAergic interneuron, more than a thousand pyramidal cells may share a common temporal reference established by an individual interneuron.

Diverse sources of hippocampal unitary inhibitory postsynaptic potentials and the number of synaptic release sites

Abstract: Dual intracellular recordings from microscopically identified neurons in the hippocampus reveal that the synaptic terminals of three morphologically distinct types of interneuron act through GABAA receptors. Each type of interneuron forms up to 12 synaptic contacts with a postsynaptic principal neuron, but each interneuron innervates a different domain of the surface of the postsynaptic neuron. Different kinetics of the postsynaptic effects, together with the strategic placement of synapses, indicate that these GABAergic interneurons serve distinct functions in the cortical network.

Proximally Targeted GABAergic Synapses and Gap Junctions Synchronize Cortical Interneurons

Abstract: Networks of GABAergic interneurons are implicated in synchronizing cortical activity at gamma frequencies (30-70 Hz). Here we demonstrate that the combined electrical and GABAergic synaptic coupling of basket cells instantaneously entrained gamma-frequency postsynaptic firing in layers 2/3 of rat somatosensory cortex. This entrainment was mediated by rapid curtailment of gap junctional coupling potentials by GABAA receptor-mediated IPSPs. Electron microscopy revealed spatial proximity of gap junctions and GABAergic synapses on somata and dendrites. Electrical coupling alone entrained postsynaptic firing with a phase lag, whereas unitary GABAergic connections were ineffective in gamma-frequency phasing. These observations demonstrate precise spatiotemporal mechanisms underlying action potential timing in oscillating interneuronal networks.

A high degree of spatial selectivity in the axonal and dendritic domains of physiologically identified local-circuit neurons in the dentate gyrus of the rat hippocampus

Abstract: The axonal and dendritic domains of neurons with extensive, locally arborizing axons were delineated in the dentate gyrus of the rat hippocampus. In horizontally cut slice preparations neurons were briefly recorded and subsequently filled with biocytin when one or several of the following physiological properties were observed: (i) high-amplitude short-latency spike afterhyperpolarization; (ii) lack of spike frequency adaptation; (iii) high firing rate in response to depolarizing current. In a sample of 14 neurons, sufficient dendritic and/or axonal detail was recovered to identify them as non-principal cells, i.e. non-granule, non-mossy cells. Five distinct types of cells were recognized, based on the spatial distribution of dendrites, presumably reflecting the availability of afferents, and on the basis of the highly selective distribution of their axon terminals, indicating synaptic target selectivity. They are: (1) the hilar cell forming a dense axonal plexus in the commissural and association pathway terminal field (HICAP cell; horizontal axon extent 1.6 mm) in the inner one-third of the molecular layer, and having dendrites extending from the hilus to the top of the molecular layer; (2) the hilar cell with its axon ramifying in the perforant path terminal field (HIPP cell, horizontal axon extent 2.0 mm) in the outer two-thirds of the molecular layer, whereas its spiny dendrites were restricted to the hilus; (3) the molecular layer cell with its dendritic and axonal domains confined to the perforant path terminal zone (MOPP cell, horizontal extent of axon 2.0 mm); (4) the dentate basket cell (horizontal axon extent 0.9 mm) had most of its axon concentrated in the granule cell layer, the remainder being localized in the inner molecular layer and hilus; (5) the hilar chandelier cell, or axo-axonic cell (horizontal axon extent 1.1 mm), densely innervating the granule cell layer with fascicles of radially oriented terminal rows, and also forming an extensive plexus in the hilus. The three cell types having their somata in the hilus projected to granule cells at the same septo-temporal level where their cell bodies were located. The results demonstrate that there is a spatially selective innervation of the granule cells by at least five distinct types of dentate neurons, which terminate in several instances in mutually exclusive domains. Their dendrites may have access to all (HICAP cell) or only a few (e.g. HIPP and MOPP cell) of the hippocampal afferents. This arrangement provides a framework for independent interaction between the output of local circuit neurons and subsets of excitatory afferents providing input to principal cells.

Glutamate Receptor Ion Channels: Structure, Regulation, and Function

Abstract: The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

Interneurons of the neocortical inhibitory system.

Abstract: Mammals adapt to a rapidly changing world because of the sophisticated cognitive functions that are supported by the neocortex. The neocortex, which forms almost 80% of the human brain, seems to have arisen from repeated duplication of a stereotypical microcircuit template with subtle specializations for different brain regions and species. The quest to unravel the blueprint of this template started more than a century ago and has revealed an immensely intricate design. The largest obstacle is the daunting variety of inhibitory interneurons that are found in the circuit. This review focuses on the organizing principles that govern the diversity of inhibitory interneurons and their circuits.

Modulation of Oscillatory Neuronal Synchronization by Selective Visual Attention

Abstract: In crowded visual scenes, attention is needed to select relevant stimuli. To study the underlying mechanisms, we recorded neurons in cortical area V4 while macaque monkeys attended to behaviorally relevant stimuli and ignored distracters. Neurons activated by the attended stimulus showed increased gamma-frequency (35 to 90 hertz) synchronization but reduced low-frequency (<17 hertz) synchronization compared with neurons at nearby V4 sites activated by distracters. Because postsynaptic integration times are short, these localized changes in synchronization may serve to amplify behaviorally relevant signals in the cortex.