Channelrhodopsin-2 (ChR2) is a light-gated, cation-selective ion channel isolated from the green algae Chlamydomonas reinhardtii. Here, we report the generation of transgenic mice that express a ...ChR2-YFP fusion protein in the CNS for in vivo activation and mapping of neural circuits. Using focal illumination of the cerebral cortex and olfactory bulb, we demonstrate a highly reproducible, light-dependent activation of neurons and precise control of firing frequency in vivo. To test the feasibility of mapping neural circuits, we exploited the circuitry formed between the olfactory bulb and the piriform cortex in anesthetized mice. In the olfactory bulb, individual mitral cells fired action potentials in response to light, and their firing rate was not influenced by costimulated glomeruli. However, in piriform cortex, the activity of target neurons increased as larger areas of the bulb were illuminated to recruit additional glomeruli. These results support a model of olfactory processing that is dependent upon mitral cell convergence and integration onto cortical cells. More broadly, these findings demonstrate a system for precise manipulation of neural activity in the intact mammalian brain with light and illustrate the use of ChR2 mice in exploring functional connectivity of complex neural circuits in vivo.
Manipulation of neuronal activity through genetically targeted actuator molecules is a powerful approach for studying information flow in the brain. In these approaches the genetically targeted ...component, a receptor or a channel, is activated either by a small molecule (chemical genetics) or by light from a physical source (optogenetics). We developed a hybrid technology that allows control of the same neurons by both optogenetic and chemical genetic means. The approach is based on engineered chimeric fusions of a light-generating protein (luciferase) to a light-activated ion channel (channelrhodopsin). Ionic currents then can be activated by bioluminescence upon activation of luciferase by its substrate, coelenterazine (CTZ), as well as by external light. In cell lines, expression of the fusion of Gaussia luciferase to Channelrhodopsin-2 yielded photocurrents in response to CTZ. Larger photocurrents were produced by fusing the luciferase to Volvox Channelrhodopsin-1. This version allowed chemical modulation of neuronal activity when expressed in cultured neurons: CTZ treatment shifted neuronal responses to injected currents and sensitized neurons to fire action potentials in response to subthreshold synaptic inputs. These luminescent channelrhodopsins--or luminopsins--preserve the advantages of light-activated ion channels, while extending their capabilities. Our proof-of-principle results suggest that this novel class of tools can be improved and extended in numerous ways.
•Molecular layer interneurons (MLIs) participate in spatially structured networks via chemical and electrical synapses.•Clusters of MLIs converge to control the temporal and spatial pattern of ...Purkinje cell activity in cerebellum.•These MLI circuits mediate a number of behavioral functions, including motor coordination and learning.
Molecular layer interneurons (MLIs) play an important role in cerebellar information processing by controlling Purkinje cell (PC) activity via inhibitory synaptic transmission. A local MLI network, constructed from both chemical and electrical synapses, is organized into spatially structured clusters that amplify feedforward and lateral inhibition to shape the temporal and spatial patterns of PC activity. Several recent in vivo studies indicate that such MLI circuits contribute not only to sensorimotor information processing, but also to precise motor coordination and cognitive processes. Here, we review current understanding of the organization of MLI circuits and their roles in the function of the mammalian cerebellum.
The widespread reciprocal connectivity between the claustrum and the neocortex has stimulated numerous hypotheses regarding its function; all of these suggest that the claustrum acts as a hub that ...connects multiple cortical regions via dense reciprocal synaptic pathways. Although the connectivity between the anterior cingulate cortex (ACC) and the claustrum has been proposed as an important pathway for top-down cognitive control, little is known about the synaptic inputs that drive claustrum cells projecting to the ACC. Here, we used multi-neuron patch clamp recordings, retrograde and anterograde viral labeling, and optogenetics in mouse claustrum to investigate cortical inputs and outputs of ACC-projecting claustrum (CLA-ACC) neurons. Both ipsilateral and contralateral cortical regions were found to provide synaptic input to CLA-ACC neurons. These cortical regions were predominantly frontal and limbic regions and not primary sensorimotor regions. We show that CLA-ACC neurons receive monosynaptic input from the insular cortex, thereby revealing a potential claustrum substrate mediating the Salience Network. In contrast, sensorimotor cortical regions preferentially targeted non CLA-ACC claustrum neurons. Using dual retrograde labeling of claustrum projection neurons, we show selectivity also in the cortical targets of CLA-ACC neurons: whereas CLA-ACC neurons co-projected mainly to other frontal regions, claustrum neurons projecting to primary sensorimotor cortices selectively targeted other sensorimotor regions. Our results show that both cortical inputs to and projections from CLA-ACC neurons are highly selective, suggesting an organization of cortico-claustral connectivity into functional modules that could be specialized for processing different types of information.
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•Frontal and limbic cortical regions preferentially target CLA-ACC neurons•Sensorimotor cortical regions preferentially targeted non CLA-ACC claustrum neurons•An Insula-CLA-ACC pathway is described, which may underlie the Salience Network•CLA-ACC neurons mainly co-project to other frontal cortical regions
Using a combination of electrophysiology and anatomical tracing, Chia et al. show that both cortical inputs to and projections from CLA-ACC neurons are highly selective, suggesting that cortico-claustral connectivity is organized as functional modules, specialized in processing different types of information.
The cerebellum and anxiety Chin, Pei Wern; Augustine, George J
Frontiers in cellular neuroscience,
02/2023, Letnik:
17
Journal Article
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Although the cerebellum is traditionally known for its role in motor functions, recent evidence points toward the additional involvement of the cerebellum in an array of non-motor functions. One such ...non-motor function is anxiety behavior: a series of recent studies now implicate the cerebellum in anxiety. Here, we review evidence regarding the possible role of the cerebellum in anxiety-ranging from clinical studies to experimental manipulation of neural activity-that collectively points toward a role for the cerebellum, and possibly a specific topographical locus within the cerebellum, as one of the orchestrators of anxiety responses.
Purkinje cells (PCs) of the cerebellar cortex are necessary for controlling movement with precision, but a mechanistic explanation of how the activity of these inhibitory neurons regulates motor ...output is still lacking. We used an optogenetic approach in awake mice to show for the first time that transiently suppressing spontaneous activity in a population of PCs is sufficient to cause discrete movements that can be systematically modulated in size, speed, and timing depending on how much and how long PC firing is suppressed. We further demonstrate that this fine control of movement kinematics is mediated by a graded disinhibition of target neurons in the deep cerebellar nuclei. Our results prove a long-standing model of cerebellar function and provide the first demonstration that suppression of inhibitory signals can act as a powerful mechanism for the precise control of behavior.
Synapsins cluster synaptic vesicles (SVs) to provide a reserve pool (RP) of SVs that maintains synaptic transmission during sustained activity. However, it is unclear how synapsins cluster SVs. Here ...we show that either liquid-liquid phase separation (LLPS) or tetramerization-dependent cross-linking can cluster SVs, depending on whether a synapse is excitatory or inhibitory. Cell-free reconstitution reveals that both mechanisms can cluster SVs, with tetramerization being more effective. At inhibitory synapses, perturbing synapsin-dependent LLPS impairs SV clustering and synchronization of gamma-aminobutyric acid (GABA) release, while preventing synapsin tetramerization does not. At glutamatergic synapses, the opposite is true: synapsin tetramerization enhances clustering of glutamatergic SVs and mobilization of these SVs from the RP, while synapsin LLPS does not. Comparison of inhibitory and excitatory transmission during prolonged synaptic activity reveals that synapsin LLPS serves as a brake to limit GABA release, while synapsin tetramerization enables rapid mobilization of SVs from the RP to sustain glutamate release.
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•Synapsins cluster synaptic vesicles by liquid-liquid phase separation and by tetramerization•Synapsin-dependent liquid-liquid phase separation clusters vesicles at GABAergic synapses•Synapsin tetramerization cross-links vesicles at glutamatergic synapses•These synapsin-dependent processes confer different properties on GABA and glutamate release
Song and Augustine examine how synaptic vesicles cluster in presynaptic terminals. They find that different types of synapses employ the same protein in different ways: at inhibitory synapses, synapsin-dependent liquid-liquid phase separation sequesters synaptic vesicles, while synapsin tetramers cross-link synaptic vesicles at glutamatergic synapses.
Purkinje cells (PCs) in Crus 1 represent whisker movement via linear changes in firing rate, but the circuit mechanisms underlying this coding scheme are unknown. Here we examine the role of upstream ...inputs to PCs-excitatory granule cells (GCs) and inhibitory molecular layer interneurons-in processing of whisking signals. Patch clamp recordings in GCs reveal that movement is accompanied by changes in mossy fibre input rate that drive membrane potential depolarisation and high-frequency bursting activity at preferred whisker angles. Although individual GCs are narrowly tuned, GC populations provide linear excitatory drive across a wide range of movement. Molecular layer interneurons exhibit bidirectional firing rate changes during whisking, similar to PCs. Together, GC populations provide downstream PCs with linear representations of volitional movement, while inhibitory networks invert these signals. The exquisite sensitivity of neurons at each processing stage enables faithful propagation of kinematic representations through the cerebellum.Cerebellar Purkinje cells (PCs) linearly encode whisker position but the precise circuit mechanisms that generate these signals are not well understood. Here the authors use patch clamp recordings to show that selective tuning of granule cell inputs and bidirectional tuning of interneuron inputs are required to generate the kinematic representations in PCs.
Purkinje cell dendrites convert excitatory climbing fiber input into signals that instruct plasticity and motor learning. Modulation of instructive signaling may increase the range in which learning ...is encoded, yet the mechanisms that allow for this are poorly understood. We found that optogenetic activation of molecular layer interneurons (MLIs) that inhibit Purkinje cells suppressed climbing-fiber-evoked dendritic Ca2+ spiking. Inhibitory suppression of Ca2+ spiking depended on the level of MLI activation and influenced the induction of associative synaptic plasticity, converting climbing-fiber-mediated potentiation of parallel fiber-evoked responses into depression. In awake mice, optogenetic activation of floccular climbing fibers in association with head rotation produced an adaptive increase in the vestibulo-ocular reflex (VOR). However, when climbing fibers were co-activated with MLIs, adaptation occurred in the opposite direction, decreasing the VOR. Thus, MLIs can direct a continuous spectrum of plasticity and learning through their influence on Purkinje cell dendritic Ca2+ signaling.
•Purkinje cell dendritic spiking is suppressed respective to MLI activity levels•Increasing inhibition converts LTD into LTP along a continuous spectrum•MLI activation alters the magnitude and valence of motor learning•Graded climbing fiber Ca2+ signaling by MLIs expands error coding in the cerebellum
By linking inhibitory control of Purkinje cell dendritic Ca2+ signaling to alteration of plasticity and learning, Rowan et al. provide a mechanistic framework by which MLIs influence the ability of climbing fibers to instruct adaptive behavior in the cerebellum.
Channel-Mediated Tonic GABA Release from Glia Lee, Soojung; Yoon, Bo-Eun; Berglund, Ken ...
Science (American Association for the Advancement of Science),
11/2010, Letnik:
330, Številka:
6005
Journal Article
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Synaptic inhibition is based on both tonic and phasic release of the inhibitory transmitter γ-aminobutyric acid (GABA). Although phasic GABA release arises from Ca²⁺-dependent exocytosis from ...neurons, the mechanism of tonic GABA release is unclear. Here we report that tonic inhibition in the cerebellum is due to GABA being released from glial cells by permeation through the Bestrophin 1 (Best1) anion channel. We demonstrate that GABA directly permeates through Best1 to yield GABA release and that tonic inhibition is eliminated by silencing of Best1. Glial cells express both GABA and Best1, and selective expression of Best1 in glial cells, after preventing general expression of Best1, fully rescues tonic inhibition. Our results identify a molecular mechanism for tonic inhibition and establish a role for interactions between glia and neurons in mediating tonic inhibition.
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