Mirko Witte

Characterizing VIP Neurons in the Barrel Cortex of VIPcre/tdTomato Mice Reveals Layer-Specific Differences

Neocortical GABAergic interneurons have a profound impact on cortical circuitry and its information processing capacity. Distinct subgroups of inhibitory interneurons can be distinguished by molecular markers, such as parvalbumin, somatostatin, and vasoactive intestinal polypeptide (VIP). Among these, VIP-expressing interneurons sparked a substantial interest since these neurons seem to operate disinhibitory circuit motifs found in all major neocortical areas. Several of these recent studies used transgenic Vip-ires-cre mice to specifically target the population of VIP-expressing interneurons. This makes it necessary to elucidate in detail the sensitivity and specificity of Cre expression for VIP neurons in these animals. Thus, we quantitatively compared endogenous tdTomato with Vip fluorescence in situ hybridization and αVIP immunohistochemistry in the barrel cortex of VIPcre/tdTomato mice in a layer-specific manner. We show that VIPcre/tdTomato mice are highly sensitive and specific for the entire population of VIP-expressing neurons. In the barrel cortex, approximately 13% of all GABAergic neurons are VIP expressing. Most VIP neurons are found in layer II/III (∼60%), whereas approximately 40% are found in the other layers of the barrel cortex. Layer II/III VIP neurons are significantly different from VIP neurons in layers IV–VI in several morphological and membrane properties, which suggest layer-dependent differences in functionality.

Nicotine reverses hypofrontality in animal models of addiction and schizophrenia.

The prefrontal cortex (PFC) underlies higher cognitive processes that are modulated by nicotinic acetylcholine receptor (nAChR) activation by cholinergic inputs. PFC spontaneous default activity is altered in neuropsychiatric disorders, including schizophrenia—a disorder that can be accompanied by heavy smoking. Recently, genome-wide association studies (GWAS) identified single-nucleotide polymorphisms (SNPs) in the human CHRNA5 gene, encoding the α5 nAChR subunit, that increase the risks for both smoking and schizophrenia. Mice with altered nAChR gene function exhibit PFC-dependent behavioral deficits, but it is unknown how the corresponding human polymorphisms alter the cellular and circuit mechanisms underlying behavior. Here we show that mice expressing a human α5 SNP exhibit neurocognitive behavioral deficits in social interaction and sensorimotor gating tasks. Two-photon calcium imaging in awake mouse models showed that nicotine can differentially influence PFC pyramidal cell activity by nAChR modulation of layer II/III hierarchical inhibitory circuits. In α5-SNP-expressing and α5-knockout mice, lower activity of vasoactive intestinal polypeptide (VIP) interneurons resulted in an increased somatostatin (SOM) interneuron inhibitory drive over layer II/III pyramidal neurons. The decreased activity observed in α5-SNP-expressing mice resembles the hypofrontality observed in patients with psychiatric disorders, including schizophrenia and addiction. Chronic nicotine administration reversed this hypofrontality, suggesting that administration of nicotine may represent a therapeutic strategy for the treatment of schizophrenia, and a physiological basis for the tendency of patients with schizophrenia to self-medicate by smoking.

Intracortical Network Effects Preserve Thalamocortical Input Efficacy in a Cortex Without Layers.

Layer IV (LIV) of the rodent somatosensory cortex contains the somatotopic barrel field. Barrels receive much of the sensory input to the cortex through innervation by thalamocortical axons from the ventral posteromedial nucleus. In the reeler mouse, the absence of cortical layers results in the formation of mispositioned barrel-equivalent clusters of LIV fated neurons. Although functional imaging suggests that sensory input activates the cortex, little is known about the cellular and synaptic properties of identified excitatory neurons of the reeler cortex. We examined the properties of thalamic input to spiny stellate (SpS) neurons in the reeler cortex with in vitro electrophysiology, optogenetics, and subcellular channelrhodopsin-2-assisted circuit mapping (sCRACM). Our results indicate that reeler SpS neurons receive direct but weakened input from the thalamus, with a dispersed spatial distribution along the somatodendritic arbor. These results further document subtle alterations in functional connectivity concomitant of absent layering in the reeler mutant. We suggest that intracortical amplification mechanisms compensate for this weakening in order to allow reliable sensory transmission to the mutant neocortex.

What types of neocortical GABAergic neurons do really exist

The neocortex is regarded as the brain structure responsible for mediating higher brain functions, like conscious perception of sensory signals, learning and memory or programming of goal-directed behavior. Cortical circuits that enable these functions are formed by, first, a larger population of excitatory so-called principal cells (i.e., glutamatergic pyramidal cells; ca. 80–85 %), which issue long-distance projections, in addition to local recurrent collaterals, which form the major part of local cortical excitatory circuits. A second, smaller population of inhibitory also called local or short-axoned interneurons (i.e., GABAergic neurons; ca. 15–20 %), however, contribute heavily to intracortical microcircuits too. They can be subdivided by their location in specific areas, layers, or columns, which possess specific input–output relationships, but also in terms of morphology, electrophysiology, molecular expression profiles, and subcellular target specificity. Here it is proposed that, at present, in the rodent neocortex this population of GABAergic neurons can be reasonably divided into six different types, mainly due to their unique axonal patterns and subcellular target specificity: (i) axo-axonic cells, (ii) basket cells, (iii) Martinotti cells, (iv) bipolar/bitufted cells, (v) neurogliaform cells, and (vi) projection neurons. These different types of GABAergic neurons strongly govern the working of cortical circuits for meaningful behavior by feed-forward and feedback inhibition as well as disinhibition. Thus, they keep excitation in check, perform gain modulation, and open temporal or spatial windows for input control or output generation.

Welche Typen von neokortikalen GABAergen Nervenzellen existieren wirklich?@@@What types of neocortical GABAergic neurons do really exist?

Der Neokortex wird als diejenige Struktur im Gehirn angesehen, die für die Programmierung höherer Hirnfunktionen wie bewusster Wahrnehmung von Sinneseindrücken, Lernen und Gedächtnis sowie Ausführung von zielgerichtetem Verhalten verantwortlich ist. Kortikale Schaltkreise, die diese Funktionen ermöglichen, werden erstens durch eine größere Population von erregenden, sogenannten Prinzipalneuronen (i.e., glutamaterge Pyramidenzellen; ca. 80–85 %) gebildet, die langreichweitige Projektionen aufbauen. Allerdings geben sie aber auch lokale Kollateralen ab, welche den Hauptanteil der lokalen exzitatorischen Schaltkreise ausmachen. Eine zweite, mit 15–20 % deutlich kleinere Population von inhibitorischen oder lokalen Interneuronen (i.e. GABAergen Nervenzellen) trägt ebenfalls sehr ausgiebig zum Aufbau kortikaler Mikroschaltkreise bei. Diese Population kann entsprechend ihrer Lokalisation in spezifischen Arealen, Schichten oder Kolumnen, die alle spezifische Input-Output-Eigenschaften aufweisen, aber auch entsprechend ihrer Morphologie, Elektrophysiologie oder Molekülexpression und subzellulärer Zielzellspezifität weiter unterteilt werden. In dieser Übersichtsarbeit schlagen wir vor, dass im Neokortex von Nagern diese Population von GABAergen Neuronen sinnvollerweise in drei Subpopulationen und in sechs verschiedene Grundtypen eingeteilt werden kann und zwar auf Grund ihrer eigenständigen Axonverteilungsmuster und ihrer subzellulären Zielzellspezifität: i) Axo-axonische (Chandelier) Zellen, ii) Korbzellen, iii) Martinotti-Zellen, iv) Bipolar/doppeltgebüschelte Zellen, v) Neurogliaforme Zellen und vi) Projektionsneurone. Diese verschiedenen Typen von GABAergen Neuronen beeinflussen grundlegend die Arbeitsweise der kortikalen Schaltkreise für sinnvolles Verhalten dadurch, dass sie Vorwärts- und Rückwärtshemmung sowie Disinhibition ausüben. Damit halten sie übermäßige Erregung in Schach, modulieren den Wirksamkeitsgrad der neuronalen Informationsverarbeitung und öffnen räumliche wie auch zeitliche Fenster für Inputkontrolle oder Aktionspotenzialgenerierung. The neocortex is regarded as the brain structure responsible for mediating higher brain functions, like conscious perception of sensory signals, learning and memory or programming of goal-directed behavior. Cortical circuits that enable these functions are formed by, first, a larger population of excitatory so-called principal cells (i.e. glutamatergic pyramidal cells; ca. 80–85 %), which issue long-distance projections, in addition to local recurrent collaterals, which form the major part of local cortical excitatory circuits. A second, smaller population of inhibitory also called local or short-axoned interneurons (i.e. GABAergic neurons; ca. 15–20 %), however, contribute heavily to intracortical microcircuits, too. They can be subdivided by their location in specific areas, layers or columns, which possess specific input-output relationships, but also in terms of morphology, electrophysiology, molecular expression profiles and subcellular target specificity. Here it is proposed that, at present, in the rodent neocortex this population of GABAergic neurons can be reasonably divided into six different types, mainly due to their unique axonal patterns and subcellular target specificity: (i) axo-axonic cells, (ii) basket cells, (iii) Martinotti cells, (iv) bipolar/bitufted cells, (v) neurogliaform cells and (vi) projection neurons. These different types of GABAergic neurons strongly govern the working of cortical circuits for meaningful behavior by feedforward and feedback inhibition as well as disinhibition. Thus, they keep excitation in check, perform gain modulation and open temporal or spatial windows for input control or output generation.

Welche Typen von neokortikalen GABAergen Nervenzellen existieren wirklich

Zusammenfassung Der Neokortex wird als diejenige Struktur im Gehirn angesehen, die für die Programmierung höherer Hirnfunktionen wie bewusster Wahrnehmung von Sinneseindrucken, Lernen und Gedächtnis sowie Ausführung von zielgerichtetem Verhalten verantwortlich ist. Kortikale Schaltkreise, die diese Funktionen ermöglichen, werden erstens durch eine größere Population von erregenden, so genannten Prinzipalneuronen (i.e., glutamaterge Pyramidenzellen; ca. 80-85 %) gebildet, die langreichweitige Projektionen aufbauen. Allerdings geben sie aber auch lokale Kollateralen ab, welche den Hauptanteil der lokalen exzitatorischen Schaltkreise ausmachen. Eine zweite, mit 15-20 % deutlich kleinere Population von inhibitorischen oder lokalen Interneuronen (i.e. GABAergen Nervenzellen) tragt ebenfalls sehr ausgiebig zum Aufbau kortikaler Mikroschaltkreise bei. Diese Population kann entsprechend ihrer Lokalisation in spezifischen Arealen, Schichten oder Kolumnen, die alle spezifische Input-Output-Eigenschaften aufweisen, aber auch entsprechend ihrer Morphologie, Elektrophysiologie oder Molekülexpression und subzellulärer Zielzellspezifität weiter unterteilt werden. In dieser Übersichtsarbeit schlagen wir vor, dass im Neokortex von Nagern diese Population von GABAergen Neuronen sinnvollerweise in drei Subpopulationen und in sechs verschiedene Grundtypen eingeteilt werden kann und zwar auf Grund ihrer eigenständigen Axonverteilungsmuster und ihrer subzellulären Zielzellspezifität: i) Axo-axonische (Chandelier) Zellen, ii) Korbzellen, iii) Martinotti- Zellen, iv) Bipolar/doppeltgebüschelte Zellen, v) Neurogliaforme Zellen und vi) Projektionsneurone. Diese verschiedenen Typen von GABAergen Neuronen beeinflussen grundlegend die Arbeitsweise der kortikalen Schaltkreise für sinnvolles Verhalten dadurch , dass sie Vorwarts- und Rückwartshemmung sowie Disinhibition ausüben. Damit halten sie übermäßige Erregung in Schach, modulieren den Wirksamkeitsgrad der neuronalen Informationsverarbeitung und öffnen räumliche wie auch zeitliche Fenster für Inputkontrolle oder Aktionspotenzialgenerierung.

Erratum to: What types of neocortical GABAergic neurons do really exist?

Prof. Dr. J. F. Staiger Center for Anatomy, Institute for Neuroanatomy University Medical Center Gottingen Kreuzbergring 36, 37075 Gottingen jochen.staiger@med.uni-goettingen.de Jochen F. Staiger1,2 · Martin Mock2 · Alvar Proenneke2 · Mirko Witte2 1 Center for Anatomy, Institute for Neuroanatomy, University Medical Center Gottingen, Gottingen, Germany 2 Institute for Neuroanatomy, University Medical Center, Georg-August-University, Gottingen, Germany

Presynaptic and postsynaptic origin of multicomponent extracellular waveforms at the endbulb of Held-spherical bushy cell synapse

Extracellular signals from the endbulb of Held–spherical bushy cell (SBC) synapse exhibit up to three component waves (‘P’, ‘A’ and ‘B’). Signals lacking the third component (B) are frequently observed but as the origin of each of the components is uncertain, interpretation of this lack of B has been controversial: is it a failure to release transmitter or a failure to generate or propagate an action potential? Our aim was to determine the origin of each component. We combined single‐ and multiunit in vitro methods in Mongolian gerbils and Wistar rats and used pharmacological tools to modulate glutamate receptors or voltage‐gated sodium channels. Simultaneous extra‐ and intracellular recordings from single SBCs demonstrated a presynaptic origin of the P‐component, consistent with data obtained with multielectrode array recordings of local field potentials. The later components (A and B) correspond to the excitatory postsynaptic potential (EPSP) and action potential of the SBC, respectively. These results allow a clear interpretation of in vivo extracellular signals. We conclude that action potential failures occurring at the endbulb–SBC synaptic junction largely reflect failures of the EPSP to trigger an action potential and not failures of synaptic transmission. The data provide the basis for future investigation of convergence of excitatory and inhibitory inputs in modulating transmission at a fully functional neuronal system using physiological stimulation.

Presynaptic and postsynaptic origin of multicomponent extracellular waveforms at the endbulb of Held-spherical bushy cell synapse: Complex waveforms at endbulb of Held-SBC synapses

Extracellular signals from the endbulb of Held–spherical bushy cell (SBC) synapse exhibit up to three component waves (‘P’, ‘A’ and ‘B’). Signals lacking the third component (B) are frequently observed but as the origin of each of the components is uncertain, interpretation of this lack of B has been controversial: is it a failure to release transmitter or a failure to generate or propagate an action potential? Our aim was to determine the origin of each component. We combined single‐ and multiunit in vitro methods in Mongolian gerbils and Wistar rats and used pharmacological tools to modulate glutamate receptors or voltage‐gated sodium channels. Simultaneous extra‐ and intracellular recordings from single SBCs demonstrated a presynaptic origin of the P‐component, consistent with data obtained with multielectrode array recordings of local field potentials. The later components (A and B) correspond to the excitatory postsynaptic potential (EPSP) and action potential of the SBC, respectively. These results allow a clear interpretation of in vivo extracellular signals. We conclude that action potential failures occurring at the endbulb–SBC synaptic junction largely reflect failures of the EPSP to trigger an action potential and not failures of synaptic transmission. The data provide the basis for future investigation of convergence of excitatory and inhibitory inputs in modulating transmission at a fully functional neuronal system using physiological stimulation.