| 1. |
- Bengtsson, Fredrik, et al.
(författare)
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Climbing Fiber Coupling between Adjacent Purkinje Cell Dendrites in Vivo.
- 2009
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Ingår i: Frontiers in Cellular Neuroscience. - : Frontiers Media SA. - 1662-5102. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Climbing fiber discharges within the rat cerebellar cortex have been shown to display synchrony, especially for climbing fibers terminating in the same parasagittal bands. In addition, Purkinje cells which have the smallest rostrocaudal separation also seem to have the highest degree of synchrony. But this has so far only been investigated for distances down to 250 mum. In the present study, we wanted to investigate whether Purkinje cells that are located immediately next to each other display a particularly pronounced synchrony in their climbing fiber discharges. To this end, we used a previously undescribed type of electrophysiological recording, a single electrode, loose patch, dual dendritic recording, from pairs of adjacent Purkinje cells in the decerebrated, non-anesthetized cat. From each recorded dendrite, this technique provided well isolated, unitary calcium spikes, which we found to have a spontaneous activity that was essentially identical with the pattern of spontaneous climbing fiber discharges. By calculating the coupling in firing between the adjacent dendrites, we found that most climbing fiber responses occurred independently of each other and that the probability of coupled discharges was less than 8%. These values are comparable to those obtained in previous studies for Purkinje cells located within the same parasagittal band and show that climbing fiber coupling within a microzone exists also in non-rodent mammalian species. However, since the degree of synchrony of climbing fiber discharge was not particularly pronounced in adjacent Purkinje cells, it seems unlikely that climbing fiber synchrony has pronounced systematic regional variations within the same microzone.
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| 2. |
- Bengtsson, Fredrik, et al.
(författare)
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Ketamine and xylazine depress sensory-evoked parallel fiber and climbing fiber responses.
- 2007
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 98:3, s. 705-1697
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The last few years have seen an increase in the variety of in vivo experiments used for studying cerebellar physiological mechanisms. A combination of ketamine and xylazine has become a particularly popular form of anesthesia. However, because nonanesthetized control conditions are lacking in these experiments, so far there has been no evaluation of the effects of these drugs on the physiological activity in the cerebellar neuronal network. In the present study, we used the mossy fiber, parallel fiber, and climbing fiber field potentials evoked in the nonanesthetized, decerebrated rat to serve as a control condition against which the effects of intravenous drug injections could be compared. All anesthetics were applied at doses required for normal maintenance of anesthesia. We found that ketamine substantially depressed the evoked N3 field potential, which is an indicator of the activity in the parallel fiber synapses (-40%), and nearly completely abolished evoked climbing fiber field potentials (-90%). Xylazine severely depressed the N3 field (-75%) and completely abolished the climbing fiber field (-100%). In a combination commonly used for general anesthesia (20:1), ketamine-xylazine injections also severely depressed the N3 field (-75%) and nearly completely abolished the climbing fiber field (-90%). We also observed that lowered body and surface temperatures (<34 degrees C) resulted in a substantial depression of the N3 field (-50%). These results urge for some caution in the interpretations of studies on cerebellar network physiology performed in animals anesthetized with these drugs
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| 3. |
- Ekerot, Carl-Fredrik, et al.
(författare)
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Synaptic Integration in Cerebellar Granule Cells
- 2008
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Ingår i: Cerebellum. - : Springer Science and Business Media LLC. - 1473-4230. ; 7:4, s. 539-541
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Tidskriftsartikel (refereegranskat)abstract
- To understand the function of cerebellar granule cells, we need detailed knowledge about the information carried by their afferent mossy fibers and how this information is integrated by the granule cells. Recently, we made whole cell recordings from granule cells in the non-anesthetized, decerebrate cats. All recordings were made in the forelimb area of the C3 zone for which the afferent and efferent connections and functional organization have been investigated in detail. Major findings of the study were that the mossy fiber input to single granule cells was modality- and receptive field-specific and that simultaneous activity in two and usually more of the afferent mossy fibers were required to activate the granule cell spike. The high threshold for action potentials and the convergence of afferents with virtually identical information suggest that an important function of granule cells is to increase the signal-to-noise ratio of the mossy fiber-parallel fiber information. Thus a high-sensitivity, noisy mossy fiber input is transformed by the granule cell to a high-sensitivity, low-noise signal.
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| 4. |
- Jörntell, Henrik, et al.
(författare)
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Electrophysiological properties of parallel fiber synapses in vivo
- 2007
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Ingår i: Neural Synapse Research Trends. - 9781600215759 - 1600215750 ; , s. 239-252
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In vitro studies have revealed intriguing properties of parallel fiber synaptic transmisson. Most notably, these synapses have been shown to induce highly variable synaptic responses, have a pronounced paired pulse facilitation and to induce later, variable synaptic responses in their target neurons. In the present study, whole cell recordings from stellate cells and basket cells were made to evaluate the properties of parallel fiber synaptic transmission under non-anesthetized in vivo conditions in decerebrated cats. Electrical parallel fiber stimulation at threshold intensity was used to study the variability as well as the delayed activation of transmission at single parallel fiber synapses. In addition, the synaptic responses to brief manual skin stimulation, which mimicked the natural synaptic activation pattern and evoked intense spike bursts in these neurons, were analyzed to gain clues about the physiological role of these parallel fiber-specific properties. The data suggest that the high variability pronounced paired-pulse facilitation and the delayed responses reported for parallel fiber synapses in vitro are virtually non-existent in vivo.
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| 5. |
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| 6. |
- Jörntell, Henrik, et al.
(författare)
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Mathematical Modeling of Brain Circuitry during Cerebellar Movement Control
- 2009
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Ingår i: Proc. 2009 IEEE International Conference on Robotics and Biomimetics (ROBIO2009), Guilin, China, Dec 19 -23, 2009. ; , s. 98-103
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Konferensbidrag (refereegranskat)abstract
- Reconstruction of movement control properties of the brain could result in many potential advantages for application in robotics. However, a hampering factor so far has been the lack of knowledge of the structure and function of brain circuitry in vivo during movement control. Much more detailed information has recently become available for the area of the cerebellum that controls arm-hand movements. In addition to previously obtained extensive background knowledge of the overall connectivity of the controlling neuronal network, recent studies have provided detailed characterizations of local microcircuitry connectivity and physiology in vivo. In the present study, we study one component of this neuronal network, the cuneate nucleus, and characterize its mathematical properties using system identification theory. The cuneate nucleus is involved in the processing of the sensory feedback evoked by movements. As a substrate for our work, we use a characterization of incoming and outgoing signals of individual neurons during sensory activation as well as a recently obtained microcircuitry characterization for this structure. We find that system identification is a useful way to find suitable mathematical models that capture the properties and transformation capabilities of the neuronal microcircuitry that constitute the cuneate nucleus. Future work will show whether specific aspects of the mathematical properties can be ascribed to a specific microcircuitry and/or neuronal property.
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| 7. |
- Jörntell, Henrik, et al.
(författare)
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Properties of somatosensory synaptic integration in cerebellar granule cells in vivo.
- 2006
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Ingår i: The Journal of Neuroscience. - 1529-2401. ; 26:45, s. 11786-11797
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Tidskriftsartikel (refereegranskat)abstract
- In decerebrated, nonanesthetized cats, we made intracellular whole-cell recordings and extracellular cell-attached recordings from granule cells in the cerebellar C3 zone. Spontaneous EPSPs had large, relatively constant peak amplitudes, whereas IPSPs were small and did not appear to contribute substantially to synaptic integration at a short time scale. In many cases, the EPSPs of individual mossy fiber synapses appeared to be separable by their peak amplitudes. A substantial proportion of our granule cells had small receptive fields on the forelimb skin. Skin stimulation evoked explosive responses in which the constituent EPSPs were analyzed. In the rising phase of the response, our analyses indicated a participation of three to four different mossy fiber synapses, corresponding to the total number of mossy fiber afferents. The cutaneous receptive fields of the driven EPSPs overlapped, indicating an absence of convergence of mossy fibers activated from different receptive fields. Also in granule cells activated by joint movements did we find indications that different afferents were driven by the same type of input. Regardless of input type, the temporal patterns of granule cell spike activity, both spontaneous and evoked, appeared to primarily follow the activity in the presynaptic mossy fibers, although much of the nonsynchronized mossy fiber input was filtered out. In contrast to the prevailing theories of granule cell function, our results suggest a function of granule cells as signal-to-noise enhancing threshold elements, rather than as sparse coding pattern discriminators or temporal pattern generators.
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| 8. |
- Jörntell, Henrik, et al.
(författare)
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Synaptic memories upside down: bidirectional plasticity at cerebellar parallel fiber-purkinje cell synapses.
- 2006
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Ingår i: Neuron. - : Elsevier BV. - 0896-6273. ; 52:2, s. 227-238
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Forskningsöversikt (refereegranskat)abstract
- Information storage in neural circuits depends on activity-dependent alterations in synaptic weights, such as long-term potentiation (LTP) and long-term depression (LTD). Bidirectional synaptic plasticity endows synapses with mechanisms for rapid reversibility, but it remains unclear how it correlates with reversibility in behavioral learning and whether there is a universal synaptic memory mechanism that operates similarly at all types of synapses. A recently discovered postsynaptic form of LTP at cerebellar parallel fiber (PF)-Purkinje cell (PC) synapses provides a reversal mechanism for PF-LTD and enables a fresh look at the implications of bidirectional plasticity in a brain structure that is particularly suitable to correlate cellular to behavioral learning events. Here, we will review recent studies that reveal unique properties of bidirectional cerebellar plasticity and suggest that the induction cascades for cerebellar LTP and LTD provide a mirror image of their counterparts at hippocampal synapses. We will also discuss how PF-LTP helps to explain reversibility observed in cerebellar motor learning.
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| 9. |
- Köhler, Per, et al.
(författare)
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Flexible multi electrode brain-machine interface for recording in the cerebellum.
- 2009
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Ingår i: IEEE Engineering in Medicine and Biology Society. Conference Proceedings. - 1557-170X. ; 1, s. 536-538
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Tidskriftsartikel (refereegranskat)abstract
- A new type of chip based microelectrode for acute electrophysiological recordings in the CNS has been developed. It's designed to be adaptable to a multitude of specific neuronal environments, in this study the cerebellar cortex of rat and cat. Photolithographically patternened SU-8 is used to yield flexible and biocompatible penetrating shanks with gold leads. Electrodes with an impedance of about 300 kOmega at 1kHz have excellent signal to noise ratio in acute recordings in cat cerebellum.
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| 10. |
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