18 research outputs found
Complementary Sensory and Associative Microcircuitry in Primary Olfactory Cortex
The three-layered primary olfactory (piriform) cortex is the largest component of the olfactory cortex. Sensory and intracortical inputs converge on principal cells in the anterior piriform cortex (aPC).Wecharacterize organization principles of the sensory and intracortical microcircuitry of layer II and III principal cells in acute slices of rat aPC using laser-scanning photostimulation and fast two-photon population CaÂČâș imaging. Layer II and III principal cells are set up on a superficial-to-deep vertical axis. We found that the position on this axis correlates with input resistance and bursting behavior. These parameters scale with distinct patterns of incorporation into sensory and associative microcircuits, resulting in a converse gradient of sensory and intracortical inputs. In layer II, sensory circuits dominate superficial cells, whereas incorporation in intracortical circuits increases with depth. Layer III pyramidal cells receive more intracortical inputs than layer II pyramidal cells, but with an asymmetric dorsal offset. This microcircuit organization results in a diverse hybrid feedforward/recurrent network of neurons integrating varying ratios of intracortical and sensory input depending on a cellâs position on the superficial-to-deep vertical axis. Since burstiness of spiking correlates with both the cellâs location on this axis and its incorporation in intracortical microcircuitry, the neuronal output mode may encode a given cellâs involvement in sensory versus associative processing
Early Cortical Changes in Gamma Oscillations in Alzheimerâs Disease
The entorhinal cortices in the temporal lobe of the brain are key structures relaying memory related information between the neocortex and the hippocampus. The medial entorhinal cortex (MEC) routes spatial information, whereas the lateral entorhinal cortex (LEC) routes predominantly olfactory information to the hippocampus. Gamma oscillations are known to coordinate information transfer between brain regions by precisely timing population activity of neuronal ensembles. Here, we studied the organization of in vitro gamma oscillations in the MEC and LEC of the transgenic (tg) amyloid precursor protein (APP)-presenilin 1 (PS1) mouse model of Alzheimerâs Disease (AD) at 4â5 months of age. In vitro gamma oscillations using the kainate model peaked between 30â50 Hz and therefore we analyzed the oscillatory properties in the 20â60 Hz range. Our results indicate that the LEC shows clear alterations in frequency and power of gamma oscillations at an early stage of AD as compared to the MEC. The gamma-frequency oscillation slows down in the LEC and also the gamma power in dorsal LEC is decreased as early as 4â5 months in the tg APP-PS1 mice. The results of this study suggest that the timing of olfactory inputs from LEC to the hippocampus might be affected at an early stage of AD, resulting in a possible erroneous integration of the information carried by the two input pathways to the hippocampal subfields.Peer Reviewe
VGLUT2 functions as a differentia marker for hippocampal output neurons
The subiculum is the gatekeeper between the hippocampus and cortical areas. Yet, the lack of a pyramidal cell-specific marker gene has made the analysis of the subicular area very difficult. Here we report that the vesicular-glutamate transporter 2 (VGLUT2) functions as a specific marker gene for subicular burst-firing neurons, and demonstrate that VGLUT2-Cre mice allow for Channelrhodopsin-2 (ChR2)-assisted connectivity analysis
VGLUT2 Functions as a Differential Marker for Hippocampal Output Neurons
The subiculum is the gatekeeper between the hippocampus and cortical areas. Yet, the lack of a pyramidal cell-specific marker gene has made the analysis of the subicular area very difficult. Here we report that the vesicular-glutamate transporter 2 (VGLUT2) functions as a specific marker gene for subicular burst-firing neurons, and demonstrate that VGLUT2-Cre mice allow for Channelrhodopsin-2 (ChR2)-assisted connectivity analysis
Excitatory microcircuits within superficial layers of the medial entorhinal cortex
The distinctive firing pattern of grid cells in the medial entorhinal cortex (MEC) supports its role in the representation of space. It is widely believed that the hexagonal firing field of grid cells emerges from neural dynamics that depends on the local microcircuitry. However, local networks within the MEC are still not sufficiently characterized. Here, applying up to eight simultaneous whole-cell recordings in acute brain slices, we demonstrate the existence of unitary excitatory connections between principal neurons in the superficial layers of the MEC. In particular, we find prevalent feed-forward excitation from pyramidal neurons in layer III and layer II onto stellate cells in layer II, which might contribute to the generation or the inheritance of grid-cell patterns
VGLUT2 functions as a differential marker for hippocampal output neurons
The subiculum is the gatekeeper between the hippocampus and cortical areas. Yet, the lack of a pyramidal cell-specific marker gene has made the analysis of the subicular area very difficult. Here we report that the vesicular-glutamate transporter 2 (VGLUT2) functions as a specific marker gene for subicular burst-firing neurons, and demonstrate that VGLUT2-Cre mice allow for Channelrhodopsin-2 (ChR2)-assisted connectivity analysis
Layer 3 Pyramidal Cells in the Medial Entorhinal Cortex Orchestrate Up-Down States and Entrain the Deep Layers Differentially
Up-down states (UDS) are synchronous cortical events of neuronal activity during non-REM sleep. The medial entorhinal cortex (MEC) exhibits robust UDS during natural sleep and under anesthesia. However, little is known about the generation and propagation of UDS-related activity in the MEC. Here, we dissect the circuitry underlying UDS generation and propagation across layers in the MEC using both in vivo and in vitro approaches. We provide evidence that layer 3 (L3) MEC is crucial in the generation and maintenance of UDS in the MEC. Furthermore, we find that the two sublayers of the L5 MEC participate differentially during UDS. Our findings show that L5b, which receives hippocampal output, is strongly innervated by UDS activity originating in L3 MEC. Our data suggest that L5b acts as a coincidence detector during information transfer between the hippocampus and the cortex and thereby plays an important role in memory encoding and consolidation
Mikroschaltkreise des entorhinalen Cortex
Neuronal microcircuits are the fundamental units of brain functions. Such
microcircuits are at the interface between the elementary building blocks,
namely excitatory and inhibitory neurons and functional neuronal networks. The
structure of neuronal microcircuits matures over development and stabilizes in
the adult. Developmental or environmental insults often result in misconnected
circuits. By studying normal or misconnected neuronal microcircuits one can
better understand the underlying functions in physiological or pathological
(neurodegenerative diseases) conditions. In my doctoral thesis, I aimed to
understand the functional microcircuitry of the entorhinal cortex, in
particular the medial entorhinal cortex (mEC), in normal functions and
disease. Past research has focused mainly on the anatomical circuitry of the
entorhinal cortex. However, recent in vivo work has revealed the functional
relevance of the entorhinal cortex as an independent computational unit
serving a key role in spatial navigation and not simply an information hub
between the cortex and hippocampus. The chronological gap between structural
and functional studies has led to many open questions. In addition the mEC has
been implicated heavily in Alzheimerâs disease, temporal lobe epilepsy (TLE),
Schizophrenia and many other neuropsychiatric disorders. In chapters 1 and 2,
I introduce the concept of a neuronal microcircuit and emphasize the need to
understand it both at the structural and functional levels. Further, I
introduce the mECâs role in spatial navigation and pathophysiology and the
importance of looking at the underlying microcircuitry which might further our
understanding in these directions. In chapter 3, I discuss the available
techniques for studying neuronal microcircuitry, introduce the fast-scanning
photostimulation software and in depth compare its performance to the other
standard techniques and software available. By mapping the intralaminar
synaptic connectivity of Layer 2 stellate cells (L2S) of the mEC as a model
cell, the applicability, resolution and repeatability of the software was
validated. Further, the detection algorithm for distinguishing photo-induced
events from background events was tested and proven to be capable of
faithfully differentiating between the two kinds of photo-induced events â the
direct responses and the synaptic inputs. In chapter 4, the main findings of
the functional microcircuitry of the two projection neurons in the L2 mEC â
Layer 2 stellate cell (L2S) and the Layer 2 pyramidal cell (L2P) â are
presented. Results reveal the existence of excitatory microcircuits with a
cell-typeâspecific separation of intralaminar recurrent connections and
ascending interlaminar feedback connections as well as modular organization.
L2Ss display more intralaminar recurrent connectivity; in comparison, L2Ps
receive a larger fraction of the ascending interlaminar feedback connectivity
from deep layers of the mEC, constituting the hippocampal feedback loop.
Ascending interlaminar feedback connections to L2 are spatially organized in
modules with distinct properties for the two cell types. Neuronal synchrony is
an inherent property of neuronal microcircuits. Brain rhythms of different
temporal frequencies, especially gamma oscillations, have been attributed
important roles in binding information from several brain areas. In chapter 5,
a model for studying the role of mEC microcircuitry in neuronal synchrony and
excitability is assessed, the molecular mechanisms behind such synchrony and
pathological consequences of hyperexcitability. From the results, we conclude
that GluK2 containing kainate receptors are crucial players in the kainate-
induced gamma oscillations in the superficial layers of the mEC. Layer 3
pyramidal cells (L3Ps) contain KARs that are limited to the somatodendritic
region. The specific expression and distribution of GluK2 containing KARs on
L3Ps might render them sensitive to seizure related insults as is often seen
in animal models of TLE (eg: kainate model, pilocarpine model etc.). Since
epilepsy can result from hyperexcitable neuronal networks, there are more than
one way and region where and how this might occur. As an outlook, from another
study that I was involved in, we propose the role of a novel mediator of
synaptic transmission, PRG-1 (plasticity related gene-1) in modulating
excitability in neuronal networks. PRG-1 is found exclusively at glutamatergic
synapses on the postsynaptic side and modulates synaptic transmission. Genetic
deletion of PRG-1 results in severe hyperexcitability (chapter 5) in the
hippocampus leading to pathological seizures. Taken together these findings
reveal the importance of studying the functional microcircuitry of a cortical
region in normal and pathological conditions. The cell-type specific and
modular organization of inputs upon the L2S and L2P further the knowledge as
to how information is transferred within the local microcircuitry of the
entorhinal cortex. The deep layer inputs have been implicated to be of pivotal
importance for the L2 cells to perform its role in spatial navigation. Here,
we provide the first direct functional evidence for the existence of such
input to the L2 cells. Secondly, the characterization of the KARs on L3Ps is a
step forward to understand the KAR-mediated synaptic transmission and its
contribution towards neuronal synchrony and excitability in the mEC. Further,
the identification of a novel mediator of excitability at the synapse, PRG-1,
show a critical way in which neuronal networks are finely tuned. The balance
between excitation and inhibition is needed to maintain the integrity of
neuronal microcircuits. In conclusion, my doctoral thesis makes a contribution
towards understanding the functional microcircuitry in the medial entorhinal
cortex and answers questions explaining the role of microcircuit-forming
synapses in physiological and pathophysiological conditions.Neuronale Mikroschaltkreise bilden die elementaren Einheiten von
Hirnfunktionen. Solche Mikroschaltkreise verbinden die elementaren Bausteine,
dh. erregende und inhibitorische Neurone zu funktionalen neuronalen
Netzwerken. Die Struktur neuronaler Mikroschaltkreise reift wÀhrend der
Entwicklung und stabilisiert sich im adulten Organismus. Entwicklungs- oder
umgebungsbedingte BeeintrĂ€chtigungen haben oft fehlerhaft verknĂŒpfte
KreislĂ€ufe zur Folge. Die Betrachtung normaler und falsch verknĂŒpfter
Mikroschaltkreise ermöglicht das bessere VerstÀndnis der zugrunde liegenden
Funktionen unter physiologischen oder pathologischen (neuropsychiatrischen
Krankheiten) Bedingungen. Das Ziel meiner Doktorarbeit ist das VerstÀndnis des
funktionalen Mikroschaltkreises des entorhinalen Cortex, ins Besondere des
medialen entorhinalen Cortex (mEC), in seiner gesunden Funktion und auch im
Zusammenhang mit Krankheiten. FrĂŒhere Studien konzentrierten sich
hauptsÀchlich auf die anatomische Verschaltung des entorhinalen Cortex.
JĂŒngste in vivo Forschungen offenbarten jedoch die funktionale Relevanz des
entorhinalen Cortex als unabhÀngige Recheneinheit, die bei der rÀumlichen
Orientierung eine SchlĂŒsselrolle einnimmt und keineswegs nur als
Informationsdrehkreuz zwischen Cortex und Hippocampus dient. Die zeitliche
Diskrepanz zwischen strukturellen und funktionalen Studien warf viele offene
Fragen auf. Desweiteren wurde der mEC in Zusammenhang mit Alzheimer,
Temporallappenepilepsie (TLE), Schizophrenie und vielen anderen
neuroentwicklungs- und psychiatrischen Erkrankungen gebracht. In den Kapiteln
1 und 2 leite ich das Konzept des neuronalen Mikroschaltkreises ein und gehe
auf die Notwendigkeit des VerstÀndnisses auf struktureller und funktionaler
Ebene ein. AuĂerdem erlĂ€utere ich die Rolle des mEC bei der rĂ€umlichen
Orientierung und in der Pathophysiologie, sowie die Wichtigkeit die zugrunde
liegenden Mikroschaltkreise zu betrachten, welche unser VerstÀndnis in obigen
ZusammenhĂ€ngen erweitern dĂŒrften. In Kapitel 3 diskutiere ich die zur
Untersuchung neuronaler Mikroschaltkreise verfĂŒgbaren Techniken, stelle die
schnell abtastende Photostimulationssoftware vor und vergleiche deren
Leistungsvermögen mit dem anderer Standardtechniken und Softwares. Die
Anwendbarkeit, Auflösung und Reproduzierbarkeit der Software wurde an Hand der
Kartierung der intralaminaren synaptischen VerknĂŒpfungen der Schicht 2
Sternzellen (L2S) des mEC als Modellzelle bestĂ€tigt. Desweiteren ĂŒberprĂŒfte
ich den Detektionsalgorithmus zur Unterscheidung photo-induzierter Ereignisse
von Hintergrundereignissen und bewies auĂerdem dessen VerlĂ€sslichkeit zwischen
den beiden Arten photo-induzierter Ereignisse, direkte Antworten und
synaptische EingÀnge, zu differenzieren. In Kapitel 4 lege ich die
Kernergebnisse bezĂŒglich der funktionalen Mikroschaltkreise der beiden
Projektionsneuronen der Schicht 2 des mEC, L2S und Schicht 2 Pyramidenzellen
(L2P), dar. Meine Ergebnisse offenbaren das Vorhandensein erregender
Mikroschaltkreise mit einer zelltypspezifischen Trennung zwischen
intralaminaren rekurrenten Verbindungen und aufsteigenden interlaminaren
RĂŒckkopplungsverbindungen sowie eine modulare Organisation. L2S zeigen
hauptsĂ€chlich intralaminare rekurrente VerknĂŒpfungen wohingegen L2P
mehrheitlich Eingang von aufsteigenden interlaminaren
RĂŒckkopplungsverbindungen aus den tiefen Schichten des mEC erhalten. Letztere
bilden den hippocampalen RĂŒckfĂŒhrkreis. Aufsteigende interlaminare
RĂŒckkopplungsverbindungen nach Schicht 2 sind in rĂ€umlichen Modulen
organisiert welche fĂŒr die beiden Zelltypen verschiedene Eigenschaften
aufweisen. Neuronale SynchronitÀt ist eine inherente Eigenschaft neuronaler
Mikroschaltkreise. Hirnrythmen verschiedener zeitlicher Frequenzen, ins
Besondere Gamma Oszillationen, werden wichtige Rollen beim ZusammenfĂŒhren von
Informationen aus verschiedenen Hirnregionen zugeschrieben. In Kapitel 5
beschÀftige ich mich mit einem Modell zur Untersuchung der Rolle von mEC
Mikroschaltkreisen im Zusammenhang mit neuronaler SynchronitÀt und
Erregbarkeit, den zugrunde liegenden molekularen Mechanismen dieser
SynchronitĂ€t und den pathologischen Folgen von Ăbererregbarkeit. Aus den
Ergebnissen dieser Studien schlussfolgere ich, dass GluK2 enthaltende
Kainatrezeptoren eine SchlĂŒsselrolle bei durch Kainat induzierten
Gammaoszillationen in den oberflÀchlichen Schichten des mEC einnehmen. KARs
der Schicht 3 Pyramidenzellen (L3Ps) sind auf die somatodendritischen Bereiche
beschrÀnkt. Die spezielle Expression und Verteilung von GluK2 enthaltenden
KARs auf L3Ps könnte sie empfĂ€nglich fĂŒr mit epileptischen AnfĂ€llen in
Beziehung stehende krankhafte VerÀnderungen machen, wie sie oft bei
Tiermodellen fĂŒr TLE (z.B. Kainatmodell, Pilokarpinmodell, etc.) beobachtet
werden. Da sich Epilepsie aus ĂŒbererregbaren neuronalen Netzwerken entwickeln
kann, gibt es mehr als einen Weg wie und wo dies erfolgen kann. Als Ausblick
diskutiere ich die Rolle eines neuartigen Vermittlers synaptischer
Ăbertragung, PRG-1 (plasticity related gene-1) bei der Modulation von
Erregbarkeit in neuronalen Netzwerken. Dieser wurde in einer anderen Studie,
an der ich beteiligt war, untersucht. PRG-1 findet sich ausschlieĂlich an
glutamatergen Synapsen auf der postsynaptischen Seite und moduliert die
synaptische Ăbertragung. Genetische Deletion von PRG-1 fĂŒhrt zu schwerer
Ăbererregbarkeit (Kapitel 5) des Hippocampus welche in der Entstehung
pathologischer AnfĂ€lle mĂŒndet. Zusammenfassend zeigen diese Erkenntnisse die
Wichtigkeit funktionale Mikroschaltkreise eines cortikalen Bereichs unter
normalen wie auch unter pathologischen Bedingungen zu untersuchen auf. Die
zelltypspezifische und modulare Organisation von Inputs auf L2S und L2P
erweitern unser Wissen darĂŒber wie Information innerhalb eines lokalen
Mikroschaltkreises des entorhinalen Cortex ĂŒbermittelt wird. Den EingĂ€ngen der
tiefen Schichten wird eine herausragende Rolle fĂŒr L2 Zellen bei deren
Funktion bei der rÀumlichen Orientierung zugeschrieben. Diese Arbeit zeigt die
ersten funktionalen Beweise der Existenz solcher EingÀnge auf L2 Zellen.
Desweiteren ist die Charakterisierung der KARs auf L3Ps ein weiterer Schritt
zum VerstĂ€ndnis KAR-vermittelter synaptischer Ăbertragung und deren Beitrag zu
neuronaler SynchronitÀt und Erregbarkeit im mEC. Die Identifikation eines
neuartigen Mediators der Erregbarkeit von Synapsen, PRG-1, zeigt eine
entscheidende Möglichkeit wie neuronale Netzwerke genau reguliert werden
können. Das Gleichgewicht zwischen Erregung und Inhibition ist notwendig um
die IntegritÀt neuronaler Mikroschaltkreise zu bewahren. In ihrer Gesamtheit
leistet meine Doktorarbeit einen Beitrag zum VerstÀndnis der funktionalen
Mikroschaltkreise im medialen entorhinalen Cortex und beantwortet Fragen zu
dessen Rolle unter physiologischen und pathophysiologischen Bedingungen
Do things have ethics?
This is an open hardware and open software game console developed by hackers in Belgrade. By just looking at the game console itself, you would not see the ethical thinking behind it. This is why, the values of things should be taken into account. Acknowledgements: European Unionâs Horizon 2020 Research and Innovation Programme under Grant Agreement No: 732027