A hippokampális théta aktivitás strukturális alapja és szubkortikális modulációja = Structural basis and subcortical modulation of theta activity in the hippocampus

Kimutattuk, hogy a szeptum és a hippokampusz között a HS sejtek szintjén reciprok gátló kapcsolat áll fent. A HS sejtek érzékelik a hippokampális aktivitás szintjét, elsősorban szeptális gátlás alatt állnak és a szeptumon kívül a hippokampusz távoli területeire is vetítenek ezáltal a szeptum és az egész hippokampusz működését összehangolják. A theta aktivitással együtt előforduló gamma aktivitás kialakításában elsősorban a PV tartalmú kosársejtek játszanak szerepet, aktivitásukat, és így a gamma aktivitást opiát receptorok útján szabályozni lehet. A szeptum és a hippokampusz kölcsönhatását vizsgálva kimutattuk, hogy a medialis septum HCN ioncsatornát es/vagy parvalbumin fehérjét kifejező gátlósejtjei vezérlik a hippocampalis theta ritmust. Részletes CA1-es hálózati modell segítségével jóslatokat fogalmaztunk meg a théta és magasabb frekvenciájú oszcillációk lokális mechanizmusaival, kölcsönhatásaival és extrahippokampális modulációjával kapcsolatban. A felszálló szerotoninerg rendszerben kimutattunk egy az eddig ismerteknél gyorsabb, glutamátot használó hatékony moduláció-típus létezését. | We demonstrated that the reciprocal interaction between the medial septum and the hippocampus is realized at the cellular level via the HS cells. They detect the level of hippocampal activity, are under primarily septal inhibitory control and besides the septum they project to remote hippocampal areas, synchronizing the activity of this two regions. The theta concurrnet gamma activity is primarily controlled by the PV containing basket cells. These cells and thus gamma activity can be modulated via opiate receptors. Studying the interaction of t emedial septum and the hippocampus we proven that HCN/PV expressing medial septal inhibitory neurons drive the hippocampal theta rhythm. Simulations of a detailed network model of area CA1 resulted in predictions regarding the local mechanisms, interactions, and extrahippocampal modulation of theta and higher frequency oscillations. We demonstrated a quick, glutamatergic component in the ascending modulatory raphe-hippocapal serotonergic projection

Glutamatergic input from specific sources influences the nucleus accumbens-ventral pallidum information flow

The nucleus accumbens (NAc) is positioned to integrate signals originating from limbic and cortical areas and to modulate reward-related motor output of various goal-directed behaviours. The major target of the NAc GABAergic output neurons is the ventral pallidum (VP). VP is part of the reward circuit and controls the ascending mesolimbic dopamine system, as well as the motor output structures and the brainstem. The excitatory inputs governing this system converge in the NAc from the prefrontal cortex (PFC), ventral hippocampus (vHC), midline and intralaminar thalamus (TH) and basolateral nucleus of the amygdala (BLA). It is unclear which if any of these afferents innervate the medium spiny neurons of the NAc, that project to the VP. To identify the source of glutamatergic afferents that innervate neurons projecting to the VP, a dual-labelling method was used: Phaseolus vulgaris leucoagglutinin for anterograde and EGFP-encoded adenovirus for retrograde tract-tracing. Within the NAc, anterogradely labelled BLA terminals formed asymmetric synapses on dendritic spines that belonged to medium spiny neurons retrogradely labelled from the VP. TH terminals also formed synapses on dendritic spines of NAc neurons projecting to the VP. However, dendrites and dendritic spines retrogradely labelled from VP received no direct synaptic contacts from afferents originating from mPFC and vHC in the present material, despite the large number of fibres labelled by the anterograde tracer injections. These findings represent the first experimental evidence for a selective glutamatergic innervation of NAc neurons projecting to the VP. The glutamatergic inputs of different origin (i.e. mPFC, vHC, BLA, TH) to the NAc might thus convey different types of reward-related information during goal-directed behaviour, and thereby contribute to the complex regulation of nucleus accumbens functions.National Institutes of Health (U.S.) (Grants NS030549 and DA09158)GENADDICT Integrated Project (Grant LSHM-CT-2004-005166)National Office for Research and Technology (Hungary) (Grant CNK77793)Howard Hughes Medical Institute (Grant 55005608

DAG-sensitive and Ca(2+) permeable TRPC6 channels are expressed in dentate granule cells and interneurons in the hippocampal formation

Members of the transient receptor potential (TRP) cation channel family play important roles in several neuronal functions. To understand the precise role of these channels in information processing, their presence on neuronal elements must be revealed. In this study, we investigated the localization of TRPC6 channels in the adult hippocampal formation. Immunostainings with a specific antibody, which was validated in Trpc6 knockout mice, showed that in the dentate gyrus, TRPC6 channels are strongly expressed in granule cells. Immunogold staining revealing the subcellular localization of TRPC6 channels clarified that these proteins were predominantly present on the membrane surface of the dendritic shafts of dentate granule cells, and also in their axons, often associated with intracellular membrane cisternae. In addition, TRPC6 channels could be observed in the dendrites of some interneurons. Double immunofluorescent staining showed that TRPC6 channels were present in the dendrites of hilar interneurons and hippocampal interneurons with horizontal dendrites in the stratum oriens expressing mGlu1a receptors, whereas parvalbumin immunoreactivity was revealed in TRPC6-expressing dendrites with radial appearance in the stratum radiatum. Electron microscopy showed that the immunogold particles depicting TRPC6 channels were located on the surface membranes of the interneuron dendrites. Our results suggest that TRPC6 channels are in a key position to alter the information entry into the trisynaptic loop of the hippocampal formation from the entorhinal cortex, and to control the function of both feed-forward and feed-back inhibitory circuits in this brain region

Retino‐cortical stimulus frequency‐dependent gamma coupling: evidence and functional implications of oscillatory potentials

Long‐range gamma band EEG oscillations mediate information transmission between distant brain regions. Gamma band‐based coupling may not be restricted to cortex‐to‐cortex communication but may include extracortical parts of the visual system. The retinogram and visual event‐related evoked potentials exhibit time‐locked, forward propagating oscillations that are candidates of gamma oscillatory coupling between the retina and the visual cortex. In this study, we tested if this gamma coupling is present as indicated by the coherence of gamma‐range (70–200 Hz) oscillatory potentials (OPs) recorded simultaneously from the retina and the primary visual cortex in freely moving, adult rats. We found significant retino‐cortical OP coherence in a wide range of stimulus duration (0.01–1000 msec), stimulus intensity (800–5000 mcd/mm2), interstimulus interval (10–400 msec), and stimulus frequency (0.25–25 Hz). However, at low stimulus frequencies, the OPs were time‐locked, flickering light at 25 Hz entrained continuous OP coherence (steady‐state response, SSR). Our results suggest that the retina and the visual cortex exhibit oscillatory coupling at high‐gamma frequency with precise time locking and synchronization of information transfer from the retina to the visual cortex, similar to cortico‐cortical gamma coupling. The temporal fusion of retino‐cortical gamma coherence at stimulus rates of theater movies may explain the mechanism of the visual illusion of continuity. How visual perception depends on early transformations of ascending sensory information is incompletely understood. By simultaneous measurement of flash‐evoked potentials in the retina and the visual cortex in awake, freely moving rats, we demonstrate for the first time that time‐locked gamma oscillatory potentials exhibit stable retino‐cortical synchrony across a wide range of stimulus parameters and that the temporal continuity of coherence changes with stimulus frequency according to the expected change in the visual illusion of continuity.The retina and the visual cortex exhibit oscillatory coupling at high‐gamma frequency with precise time locking and synchronization of information transfer from the retina to the visual cortex, similar to cortico‐cortical gamma coupling. The temporal fusion of retino‐cortical gamma coherence at stimulus rates of theater movies may explain the mechanism of the visual illusion of continuity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134072/1/phy212986.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134072/2/phy212986_am.pd

Divergent in vivo activity of non-serotonergic and serotonergic VGluT3-neurones in the median raphe region

KEY POINTS: *Median raphe is a key subcortical modulatory centre involved in several brain functions e.g. regulation of sleep-wake cycle, emotions and memory storage. *A large proportion of median raphe neurones are glutamatergic and implement a radically different mode of communication than serotonergic cells, but their in vivo activity is unknown. *We provide the first description of the in vivo, brain state-dependent firing properties of median raphe glutamatergic neurones identified by immunopositivity for the vesicular glutamate transporter type 3 (VGluT3) and serotonin (5HT). Glutamatergic populations (VGluT3+/5HT- and VGluT3+/5HT+)were compared to the purely serotonergic (VGluT3-/5HT+) and VGluT3-/5HT- neurones. *VGluT3+/5HT+ neurones fired similar to VGluT3-/5HT+ cells, whereas significantly diverged from the VGluT3+/5HT- population. Activity of the latter subgroup resembled the spiking of VGluT3-/5HT- cells, except their diverging response to sensory stimulation. *The VGluT3+ population of the median raphe may broadcast rapidly varying signals on top of a state-dependent, tonic modulation. ABSTRACT: Subcortical modulation is crucial for information processing in the cerebral cortex. Besides the canonical neuromodulators, glutamate has recently been identified as a key cotransmitter of numerous monoaminergic projections. In the median raphe, a pure glutamatergic neurone population projecting to limbic areas was also discovered with a possibly novel, yet undetermined function. Here, we report the first functional description of the vesicular glutamate transporter type 3 (VGluT3)-expressing median raphe neurones. Since there is no appropriate genetic marker for the separation of serotonergic (5HT+) and non-serotonergic (5HT-) VGluT3+ neurones, we utilised immunohistochemistry after recording and juxtacellular labelling in anaesthetised rats. VGluT3+/5HT- neurones fired faster, more variably and were permanently activated during sensory stimulation, as opposed to the transient response of the slow firing VGluT3-/5HT+ subgroup. VGluT3+/5HT- cells were also more active during hippocampal theta. In addition, the VGluT3-/5HT- population - putative GABAergic cells - resembled the firing of VGluT3+/5HT- neurones, but without significant reaction to the sensory stimulus. Interestingly, the VGluT3+/5HT+ group - spiking slower than the VGluT3+/5HT- population - exhibited a mixed response i.e. the initial transient activation was followed by sustained elevation of firing. Phase coupling to hippocampal and prefrontal slow oscillations was found in VGluT3+/5HT- neurones, also differentiating them from the VGluT3+/5HT+ subpopulation. Taken together, glutamatergic neurones in the median raphe may implement multiple, highly divergent forms of modulation in parallel: a slow, tonic mode interrupted by sensory-evoked rapid transients and a fast one, capable of conveying complex patterns influenced by sensory inputs. This article is protected by copyright. All rights reserved

Az endocannabinoid-mediált szignalizáció funkciója a hippocampus neuronhálózatainak normális és kóros működéseiben = The role of endocannabinoid-mediated signaling in normal and pathological operations os hippocampal circuits

Az OTKA pályázat támogatásával az elmúlt négy évben alapvető felismeréseket tettünk egy új kémiai szignálrendszer, az endokannabinoid rendszer molekuláris és anatómiai szerveződéséről, élettani és kórélettani jelentőségéről. Kimutattuk, hogy az endokannabinoid rendszer egy specializált jelátviteli rendszer, amelynek feladata, hogy a szinapszisok működését a preszinaptikus és a posztszinaptikus idegsejt aktivitásának függvényében szabályozza. Elsőként írtuk le egy endokannabinoid molekula, a 2-arachidonilglicerol kulcsszerepét ebben a folyamatban, és feltártuk, hogy milyen molekuláris mechanizmusok szabályozzák keletkezését és lebontását. Igazoltuk, hogy ez a kémiai szignálrendszer számos agyterületen (agykéregben, hippocampusban, nucleus accumbensben, a ventrális tegmentális areában) megtalálható. Élettani kísérleteink alapján az endokannabinoidok egy negatív visszacsatolási folyamat közvetítői a szinapszisokban. Ezzel párhuzamosan felfedeztük, hogy az endokannabinoid rendszer működési zavarai kulcsszerepet játszhatnak a temporális lebeny eredetű epilepsziában, valamint a szorongásos és poszttraumatikus stressz-okozta panaszok hátterében is megtalálhatók. Ezek az eredményeink egyben új molekuláris gyógyszercélpontokat jelölnek ki, amelyek számos idegrendszeri megbetegedésben vezethetnek hatékonyabb és szelektívebb farmakoterápia kidolgozásához. | During the last four years, our research group has reached fundamental milestones in the understanding of a new chemical messenger system, the so-called endocannabinoid system. We have uncovered the molecular and anatomical organization of endocannabinoid signaling and provided clues for its physiological and pathophysiological importance. We have shown that the endocannabinoid system is a specialized signaling machinery, which controls the efficacy synaptic transmission as a function of the activity of presynaptic and postsynaptic neurons. We have described for the first time that 2-arachidonoylglycerol is a key player in this process, and uncovered the basic mechanisms in its biosynthesis and degradation. We have provided evidence that this chemical signaling mechanism is a conserved feature of several types of synapses in various brain regions, for example in the neocortex, hippocampus, nucleus accumbens and the ventral tegmental area. We have shown that this system is involved in a negative feed-back regulation of transmitter release, and described its impairment in the human epileptic hippocampus, as well as its contribution to anxiety and post-traumatic stress disorder in animal models. These findings unravel new drug targets, whereby they could open novel therapeutic approaches for a more efficient and selective treatment of several brain disorders

Optical Imaging of Intrinsic Neural Signals and Simultaneous MicroECoG Recording Using Polyimide Implants

This paper presents the simultaneous use of intrinsic optical signal imaging (iOS) and micro-electrocorticography (μECoG) techniques by introducing a transparent polymer based microelectrode array into the optical recording chamber used in vivo functional mapping experiments in anaesthetized cat. The robustness of its site impedance was proven in electrochemical impedance spectroscopy. To demonstrate the feasibility of the combined optical-electrical recording, we have run several stimulus protocols and measured the evoked optical and electrical responses of the visual cortex

Cell Surface Protein mRNAs Show Differential Transcription in Pyramidal and Fast-Spiking Cells as Revealed by Single-Cell Sequencing

The prefrontal cortex (PFC) plays a key role in higher order cognitive functions and psychiatric disorders such as autism, schizophrenia, and depression. In the PFC, the two major classes of neurons are the glutamatergic pyramidal (Pyr) cells and the GABAergic interneurons such as fast-spiking (FS) cells. Despite extensive electrophysiological, morphological, and pharmacological studies of the PFC, the therapeutically utilized drug targets are restricted to dopaminergic, glutamatergic, and GABAergic receptors. To expand the pharmacological possibilities as well as to better understand the cellular and network effects of clinically used drugs, it is important to identify cell-type-selective, druggable cell surface proteins and to link developed drug candidates to Pyr or FS cell targets. To identify the mRNAs of such cell-specific/enriched proteins, we performed ultra-deep single-cell mRNA sequencing (19 685 transcripts in total) on electrophysiologically characterized intact PFC neurons harvested from acute brain slices of mice. Several selectively expressed transcripts were identified with some of the genes that have already been associated with cellular mechanisms of psychiatric diseases, which we can now assign to Pyr (e.g., Kcnn2, Gria3) or FS (e.g., Kcnk2, Kcnmb1) cells. The earlier classification of PFC neurons was also confirmed at mRNA level, and additional markers have been provided

Local apoptotic-like mechanisms underlie complement-mediated synaptic pruning

C1q, a member of the immune complement cascade, is implicated in the selective pruning of synapses by microglial phagocytosis. C1q-mediated synapse elimination has been shown to occur during brain development, while increased activation and complement-dependent synapse loss is observed in neurodegenerative diseases. However, the molecular mechanisms underlying C1q-controlled synaptic pruning are mostly unknown. This study addresses distortions in the synaptic proteome leading to C1q-tagged synapses. Our data demonstrated the preferential localization of C1q to the presynapse. Proteomic investigation and pathway analysis of C1q-tagged synaptosomes revealed the presence of apoptotic-like processes in C1q-tagged synapses, which was confirmed experimentally with apoptosis markers. Moreover, the induction of synaptic apoptotic-like mechanisms in a model of sensory deprivation-induced synaptic depression led to elevated C1q levels. Our results unveiled that C1q label-based synaptic pruning is triggered by and directly linked to apoptotic-like processes in the synaptic compartment