GABAergic inhibitory feedback from the cerebellum onto the inferior olivary (IO) nucleus plays an... more GABAergic inhibitory feedback from the cerebellum onto the inferior olivary (IO) nucleus plays an important role in olivo-cerebellar function. In this study we characterized the physiology, subunit composition, and spatial distribution of ␥-aminobutyric acid-A (GABA A) receptors in the IO nucleus. Using brain stem slices, we identified two types of IO neuron response to local pressure application of GABA, depending on the site of application: a slow desensitizing response at the soma and a fast desensitizing response at the dendrites. The dendritic response had a more negative reversal potential than did the somatic response, which confirmed their spatial origin. Both responses showed voltage dependence characterized by an abrupt decrease in conductance at negative potentials. Interestingly, this change in conductance occurred in the range of potentials wherein subthreshold membrane potential oscillations usually occur in IO neurons. Immunostaining IO sections with antibodies for GABA A receptor subunits ␣1, ␣2, ␣3, ␣5, 2/3, and ␥2 and against the postsynaptic anchoring protein gephyrin complemented the electrophysiological observation by showing a differential distribution of GABA A receptor subtypes in IO neurons. A receptor complex containing ␣22/3␥2 subunits is clustered with gephyrin at presumptive synaptic sites, predominantly on distal dendrites. In addition, diffuse ␣3, 2/3, and ␥2 subunit staining on somata and in the neuropil presumably represents extrasynaptic receptors. Combining electrophysiology with immunocytochemistry, we concluded that ␣22/3␥2 synaptic receptors generated the fast desensitizing (dendritic) response at synaptic sites whereas the slow desensitizing (somatic) response was generated by extrasynaptic ␣32/3␥2 receptors.
Proceedings of the National Academy of Sciences of the United States of America, Oct 15, 1996
Simultaneous recordings from the soma and apical dendrite of layer V neocortical pyramidal cells ... more Simultaneous recordings from the soma and apical dendrite of layer V neocortical pyramidal cells of young rats show that, for any location of current input, an evoked action potential (AP) always starts at the axon and then propagates actively, but decrementally, backward into the dendrites. This back-propagating AP is supported by a low density (kNa =-4 mS/cm2) of rapidly inactivating voltage
Exploring the organization and function of local inhibitory networks is an essential step on the ... more Exploring the organization and function of local inhibitory networks is an essential step on the way to understand the principles of brain operation. We show here that molecular layer inhibitory interneurons of the guinea pig cerebellar cortex are organized as local networks, generating synchronous activity. Simultaneous recording from two adjacent interneurons revealed a direct current flow between synchronized pairs of neurons. Blocking inhibitory or excitatory synaptic transmission did not alter the synchronization. The electrotonic coupling coefficient (average 0.1) depended mainly on the input resistance of the postsynaptic cell, indicating a homogenous coupling resistance between different pairs. A presynaptic action potential generated a short, attenuated spikelet in the postsyn-aptic cell. The passive current flow was amplified by voltagedependent intrinsic currents to create a reciprocal interplay between the presynaptic and postsynaptic cells. This interplay results in a time window for synchronization that is wider than expected from the duration of the spikelet. Intracellular staining with biocytin revealed high incidence of dye coupling. Furthermore, the interneurons located superficially in the molecular layer tend to form larger networks compared with the inner interneurons. We propose that weakly coupled inhibitory networks can generate loosely synchronous activity, which results from the interaction of electrical coupling and intrinsic currents.
NM Gerrits, TJH Ruigrok and CI De Zeeuw (Eds.) Progress in Brain Research, Vo| 124 2000 Elsevier ... more NM Gerrits, TJH Ruigrok and CI De Zeeuw (Eds.) Progress in Brain Research, Vo| 124 2000 Elsevier Science BV. All rights reserved. CHAPTER 8 Unravelling cerebellar circuitry: an optical imaging study Dana Cohen and Yosef Yarom* Department of Neut~ gbiology, Life ...
Optical imaging of voltage-sensitive dyes in an isolated cerebellum preparation was used to study... more Optical imaging of voltage-sensitive dyes in an isolated cerebellum preparation was used to study the spatiotemporal functional organization of the inhibitory systems in the cerebellar cortex. Responses to surface stimulation of the cortex reveal two physiologically distinct inhibitory systems, which we refer to as lateral and on-beam inhibition following classical terminology. Lateral inhibition occurs throughout the area responding to a stimulus, whereas on-beam inhibition is confined to the area directly excited by parallel fibers. The time course of the lateral inhibition is twice as long as that of the on-beam inhibition. Both inhibitory responses increase with stimulus intensity, but the lateral inhibition has a lower threshold, and it saturates at lower stimulus intensity. The amplitude of the on-beam inhibition is linearly related to the excitation at the same location, whereas that of the lateral inhibition is linearly related to the excitation at the center of the beam. Repetitive stimulation is required to activate on-beam inhibition, whereas the same stimulus paradigm reveals prolonged depression of the lateral inhibition. We conclude that lateral inhibition reflects the activation of molecular layer interneurons, and its major role is to increase the excitability of the activated area by disinhibition. The on-beam inhibition most likely reflects Golgi cell inhibition of granule cells. However, Purkinje cell collateral inhibition of Golgi cells cannot be excluded. Both possibilities suggest that the role of the on-beam inhibition is to efficiently modulate, in time and space, the mossy fiber input to the cerebellar cortex.
tonic coupling in the inferior olivary (IO) nucleus is assumed to play a crucial role in generati... more tonic coupling in the inferior olivary (IO) nucleus is assumed to play a crucial role in generating the subthreshold membrane potential oscillations in olivary neurons and in synchronizing climbing fiber input into the cerebellar cortex. We studied the strength and spatial distribution of the coupling by simultaneous double patch recordings from olivary neurons in the brain slice preparation. Electrotonic coupling was observed in 50% of the cell pairs. The coupling coefficient (CC), defined as the ratio between voltage responses of the post-and the prejunctional cell, varied between 0.002 and 0.17; most of the pairs were weakly coupled. In more than 75% of the pairs, the CC was Ͻ0.05. The coupling resistance varied between 0.7 to 19.8 G⍀, and 68% of the values fell between 0.7 to 8 G⍀. The difference between the coupling coefficient measured on stimulation of cell 1 or cell 2 of a coupled pair was 27 Ϯ 16%. Direct calculation of the coupling resistance revealed an asymmetry of 24 Ϯ 12%, suggesting a directional preference of coupling. The coupling was voltage independent, although depolarization of either the pre-or the postjunctional neuron reduced the CC. The chance of a cell pair being coupled was 80% in immediate neighboring cells, but dropped to about 30% at a distance of 40 m. No coupled pairs were observed at distances larger than 70 m. In 52% of staining experiments neurobiotin injection into an olivary neuron produced indirect labeling of 1-11 nearby cells with an average of 3.8 Ϯ 2.9. All indirectly labeled cells were found in, or immediately adjacent, to the dendritic field of the directly stained neuron. Two distinct morphological types of olivary neurons, "curly" and "straight" cells, were found. In each case all neurons stained indirectly by dye passage through gap junctions belonged to the same type. Using the physiological data we estimated that each olivary neuron is directly coupled to about 50 neurons. Since somatic recordings may not reveal coupling through remote dendrites, we conclude that each neuron is directly connected to Ն50 neurons forming two distinct networks of curly and straight cells.
Byk et al. Cerebellar Large Scale Calcium Imaging sagittal bands that is preserved in genetically... more Byk et al. Cerebellar Large Scale Calcium Imaging sagittal bands that is preserved in genetically induced disorganized cerebellar cortex. Furthermore, the response, which represents the activation of two sets of climbing fibers inputs, is followed by a prolonged recovery process that indicates the cerebellar involvement in startle response.
1. The electrophysiological properties of motoneurones in the dorsal motor nucleus of the vagus i... more 1. The electrophysiological properties of motoneurones in the dorsal motor nucleus of the vagus in the guinea-pig were studied at different times following cervical vagotomy. The results were compared both to normal neurones and to results obtained at the same time from intact neurones located in the contralateral nucleus. 2. The input resistances of axotomized neurones are significantly higher than those of normal neurones (66 + 29 compared to 45 + 17 MQ2). This difference was seen during the first month following axotomy without any sign of a time-dependent process. On the other hand, no change in resting potential was observed. 3. Significant reduction in action potential amplitude was observed 1 month after axotomy (from 97-8 + 8 to 87 + 7 mV) and was followed by slow recovery lasting more than 1 year. Neither the Na+ conductance nor the voltage-dependent K+ conductance responsible for the fast rise and fall of the action potential, respectively, were affected by axotomy. 4. One month after axotomy the action potential duration in axotomized neurones was found to be shorter than that of normal neurones (09±+0-1 ms compared to 11 +0-04 ms). We show that this decrease in duration reflects a reduction in the depolarizing hump on the falling phase of the action potential, which is known to express the Ca2+ conductance activated during the action potential. A slow recovery of the spike duration was observed, although an age-dependent reduction in duration was also observed in neurones in the contralateral nucleus. 5. Two K+ conductances, the Ca2+-dependent and the A type, decrease 1 month after axotomy and follow a similar time course of recovery to that of the reduction in action potential duration and amplitude. 6. The firing pattern of axotomized neurones undergoes profound alteration, manifested as an increase in firing duration as a response to a rectangular current pulse. Examination of these alterations reveals that the reduction in both K+ conductances is responsible for the observed changes. 7. The results are discussed within the framework of the degenerative response known to take place in the nucleus following axotomy. We hypothesize that the observed phenomena reflect an increase in intracellular Ca2+ concentration which, in turn, inactivates the Ca2+ and K+ conductances. Furthermore this rise in intracellular Ca2+ may eventually be responsible for cell death.
Publisher Summary This chapter discusses the model of analog and digital processing in single ner... more Publisher Summary This chapter discusses the model of analog and digital processing in single nerve cells that comprises the network. This approach requires the construction of detailed models that incorporate knowledge of neuronal morphology and physiology as well as synaptic architecture. A morphologically and physiologically characterized dendritic tree of a cerebellar Purkinje cell (PC), as well as for a reconstructed axon from the cat somatosensory cortex is demonstrated. The reconstruction of PC cell was performed utilizing a computer-driven system, neuron tracing system (NTS), and it does not include the dendritic spines that account for more than 50% of the total dendritic area of these cells. The study also highlights several general principles which include the single nerve cell can function as a network of almost independent subunits and voltage attenuation resulting from dendritic structure implies that the site of the synaptic input is functionally significant.
Simultaneous patch clamp recordings from the soma and dendrites of neocortical pyramidal neurons ... more Simultaneous patch clamp recordings from the soma and dendrites of neocortical pyramidal neurons of young rats show that, independent of the synaptic input location, the sodium action potential (AP) always starts at the soma and is then carried along the axon, but also propagates backward decrementally into the dendritic tree1. This back-propagating AP is supported by a low density (\({\bar g_{Na}} = \sim 4mS/c{m^2}\) mS/cm2) of Na+ in the dendrites and soma membrane of the pyramidal neurons.
Neuronal interactions mediated by alteration of the extracellular K + concentration [K + ] o occu... more Neuronal interactions mediated by alteration of the extracellular K + concentration [K + ] o occur between populations as well as among single neurones in very restricted regions. The interactions mediated by K + ions may range from low efficacy ones (in which the effects of increased [K + ] o around the non-active cells can be recorded only after massive activity of a large population of neurones) to very effective interactions (in which a single action potential in a neurone is sufficient to produce a depolarization of several mV in a second one). Such efficient K +-mediated interactions cannot be unequivocally distinguished by shape, amplitude or time course from postsynaptic responses induced by chemical or electrotonic synapses. We review here experiments which demonstrate various levels of interactions mediated by changes in potassium ion concentration. The giant axons (Gax) and non-giant axons from the central nervous system of the cockroach Periplaneta americana were used. The types of interactions discussed are: (a) pathological interactions among populations of neurones induced by the convulsant drug picrotoxin; (b) restricted and limited interactions which are the consequence of the combination of the special geometry of Gaxs and increases in extracellular K + ; and finally, (c) local and efficient interactions among Gaxs which are postulated to be mediated by K + ions. The experiments described in this review, as well as others, demonstrate that the extracellular spaces in the CNS serve as predetermined pathways for K +-mediated neuronal communication. When the extracellular space between two adjacent neurones is very small, the K +-mediated interaction may resemble the PSPs of chemical or electrotonic synapses. It is possible that because of this resemblance, other K +-mediated interactions in the CNS have not been identified as such.
Proceedings of the National Academy of Sciences of the United States of America, Dec 8, 1998
The discrepancy between the structural longitudinal organization of the parallel-fiber system in ... more The discrepancy between the structural longitudinal organization of the parallel-fiber system in the cerebellar cortex and the functional mosaic-like organization of the cortex has provoked controversial theories about the f low of information in the cerebellum. We address this issue by characterizing the spatiotemporal organization of neuronal activity in the cerebellar cortex by using optical imaging of voltage-sensitive dyes in isolated guinea-pig cerebellum. Parallel-fiber stimulation evoked a narrow beam of activity, which propagated along the parallel fibers. Stimulation of the mossy fibers elicited a circular, nonpropagating patch of synchronized activity. These results strongly support the hypothesis that a beam of parallel fibers, activated by a focal group of granule cells, fails to activate the Purkinje cells along most of its length. It is thus the ascending axon of the granule cell, and not its parallel branches, that activates and defines the basic functional modules of the cerebellar cortex. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Increased extracellular levels of ascorbate in striatum after middle cerebral artery occlusion in... more Increased extracellular levels of ascorbate in striatum after middle cerebral artery occlusion in the rat monitored by intracerebral microdialysis.
The electrical connectivity in the inferior olive (IO) nucleus plays an important role in generat... more The electrical connectivity in the inferior olive (IO) nucleus plays an important role in generating well-timed spiking activity. Here we combined electrophysiological and computational approaches to assess the functional organization of mice IO nucleus. Spontaneous fast and slow subthreshold events were commonly encountered during in vitro recordings. We show that the fast events represent a regenerative response in unique excitable spine-like structures in the axon hillock, whereas the slow events reflect the electrical connectivity between neurons ('spikelets'). Recordings from cell pairs revealed the synchronized occurrence of distinct groups of spikelets; their rate and distribution enabled an accurate estimation of the number of connected cells and is suggestive of a clustered organization. This study thus provides a new perspective on the functional and structural organization of the olivary nucleus, insights into two different subthreshold nonsynaptic events, and a novel experimental and theoretical approach to the study of electricallycoupled networks. .
Cerebellar inhibitory interneurons respond to parallel fiber input with a characteristic train of... more Cerebellar inhibitory interneurons respond to parallel fiber input with a characteristic train of action potentials. Here we show that the characteristics of these trains reflect the intrinsic properties of the interneurons. In in vitro cerebellar slices, the response of these neurons to synaptic-like current resembles their in vivo response to parallel fiber input-a train of action potentials characterized by a gradual increase in interspike interval and spike amplitude. A large variability in spike timing, or jitter, was observed, the last action potential emerging from a slow depolarizing wave that lasted beyond the synaptic current and was prevented by either TTX or membrane hyperpolarization. While response duration was weakly dependent on current intensity, the variability of the overall duration was closely related to the variability of the timing of the last action potential. Blocking the Ca 2ϩ currents or partial blockade of the delayed rectifier (TEA 2 mM) decreased the excitability, leading to a decrease in the duration and variability of the response and increasing its dependence on stimulus intensity. Increased duration and variability was observed in the presence of Cs ϩ ions (5 mM) that blocked an h-like current. We conclude that a persistent Na ϩ current governs the duration of the response, whereas the synaptic current and the spiking mechanism shape its pattern. The large variability between trials is due to the stochastic nature of the persistent Na ϩ current. Thus unless precise timing is achieved by a network of interconnected neurons, these results vote against temporal coding as a player in the cerebellar computational processing.
Proceedings of the National Academy of Sciences of the United States of America, Mar 3, 2009
Complex movements require accurate temporal coordination between their components. The temporal a... more Complex movements require accurate temporal coordination between their components. The temporal acuity of such coordination has been attributed to an internal clock signal provided by inferior olivary oscillations. However, a clock signal can produce only time intervals that are multiples of the cycle duration. Because olivary oscillations are in the range of 5-10 Hz, they can support intervals of Ϸ100-200 ms, significantly longer than intervals suggested by behavioral studies. Here, we provide evidence that by generating nonzero-phase differences, olivary oscillations can support intervals shorter than the cycle period. Chronically implanted multielectrode arrays were used to monitor the activity of the cerebellar cortex in freely moving rats. Harmaline was administered to accentuate the oscillatory properties of the inferior olive. Olivaryinduced oscillations were observed on most electrodes with a similar frequency. Most importantly, oscillations in different recording sites retained a constant phase difference that assumed a variety of values in the range of 0-180°, and were maintained across large global changes in the oscillation frequency. The inferior olive may thus underlie not only rhythmic activity and synchronization, but also temporal patterns that require intervals shorter than the cycle duration. The maintenance of phase differences across frequency changes enables the olivo-cerebellar system to replay temporal patterns at different rates without distortion, allowing the execution of tasks at different speeds.
Neurons in the mammalian CNS receive 104-105 synaptic inputs onto their dendritic tree. Each of t... more Neurons in the mammalian CNS receive 104-105 synaptic inputs onto their dendritic tree. Each of these inputs may fire spontaneously at a rate of a few spikes per second. Consequently, the cell is bombarded by several hundred synapses in each and every millisecond. An extreme example is the cerebellar Purkinje cell (PC) receiving approximately 100,000 excitatory synapses from the parallel fibers (p.f.s) onto dendritic spines covering the thin dendritic branchlets. What is the effect of the p.f.s activity on the integrative capabilities of the PC? This question is explored theoretically using analytical cable models as well as compartmental models of a morphologically and physiologically characterized PC from the guinea pig cerebellum. The input of individual p.f.s was moaeled as a transient conductance change, peaking at 0.4 nS with a rise time of 0.3 msec and a reversal potential of f60 mV relative to rest. We found that already at a firing frequency of a few spikes per second the membrane conductance is several times larger than the membrane conductance in the absence of synaptic activity. As a result, the cable properties of the PC significantly change; the most sensitive parameters are the system time constant (70) and the steady-state attenuation factor from dendritic terminal to soma. The implication is that the cable properties of central neurons in freely behaving animals are different from those measured in slice preparation or in anesthetized animals, where most of the synaptic inputs are inactive. We conclude that, because of the large conductance increase produced by the background activity of the p.f.s, the activity of the PC will be altered from this background level either when the p.f.s change their firing frequency for a period of several tens of milliseconds or when a large population of the p.f.s fires during a narrow time window.
GABAergic inhibitory feedback from the cerebellum onto the inferior olivary (IO) nucleus plays an... more GABAergic inhibitory feedback from the cerebellum onto the inferior olivary (IO) nucleus plays an important role in olivo-cerebellar function. In this study we characterized the physiology, subunit composition, and spatial distribution of ␥-aminobutyric acid-A (GABA A) receptors in the IO nucleus. Using brain stem slices, we identified two types of IO neuron response to local pressure application of GABA, depending on the site of application: a slow desensitizing response at the soma and a fast desensitizing response at the dendrites. The dendritic response had a more negative reversal potential than did the somatic response, which confirmed their spatial origin. Both responses showed voltage dependence characterized by an abrupt decrease in conductance at negative potentials. Interestingly, this change in conductance occurred in the range of potentials wherein subthreshold membrane potential oscillations usually occur in IO neurons. Immunostaining IO sections with antibodies for GABA A receptor subunits ␣1, ␣2, ␣3, ␣5, 2/3, and ␥2 and against the postsynaptic anchoring protein gephyrin complemented the electrophysiological observation by showing a differential distribution of GABA A receptor subtypes in IO neurons. A receptor complex containing ␣22/3␥2 subunits is clustered with gephyrin at presumptive synaptic sites, predominantly on distal dendrites. In addition, diffuse ␣3, 2/3, and ␥2 subunit staining on somata and in the neuropil presumably represents extrasynaptic receptors. Combining electrophysiology with immunocytochemistry, we concluded that ␣22/3␥2 synaptic receptors generated the fast desensitizing (dendritic) response at synaptic sites whereas the slow desensitizing (somatic) response was generated by extrasynaptic ␣32/3␥2 receptors.
Proceedings of the National Academy of Sciences of the United States of America, Oct 15, 1996
Simultaneous recordings from the soma and apical dendrite of layer V neocortical pyramidal cells ... more Simultaneous recordings from the soma and apical dendrite of layer V neocortical pyramidal cells of young rats show that, for any location of current input, an evoked action potential (AP) always starts at the axon and then propagates actively, but decrementally, backward into the dendrites. This back-propagating AP is supported by a low density (kNa =-4 mS/cm2) of rapidly inactivating voltage
Exploring the organization and function of local inhibitory networks is an essential step on the ... more Exploring the organization and function of local inhibitory networks is an essential step on the way to understand the principles of brain operation. We show here that molecular layer inhibitory interneurons of the guinea pig cerebellar cortex are organized as local networks, generating synchronous activity. Simultaneous recording from two adjacent interneurons revealed a direct current flow between synchronized pairs of neurons. Blocking inhibitory or excitatory synaptic transmission did not alter the synchronization. The electrotonic coupling coefficient (average 0.1) depended mainly on the input resistance of the postsynaptic cell, indicating a homogenous coupling resistance between different pairs. A presynaptic action potential generated a short, attenuated spikelet in the postsyn-aptic cell. The passive current flow was amplified by voltagedependent intrinsic currents to create a reciprocal interplay between the presynaptic and postsynaptic cells. This interplay results in a time window for synchronization that is wider than expected from the duration of the spikelet. Intracellular staining with biocytin revealed high incidence of dye coupling. Furthermore, the interneurons located superficially in the molecular layer tend to form larger networks compared with the inner interneurons. We propose that weakly coupled inhibitory networks can generate loosely synchronous activity, which results from the interaction of electrical coupling and intrinsic currents.
NM Gerrits, TJH Ruigrok and CI De Zeeuw (Eds.) Progress in Brain Research, Vo| 124 2000 Elsevier ... more NM Gerrits, TJH Ruigrok and CI De Zeeuw (Eds.) Progress in Brain Research, Vo| 124 2000 Elsevier Science BV. All rights reserved. CHAPTER 8 Unravelling cerebellar circuitry: an optical imaging study Dana Cohen and Yosef Yarom* Department of Neut~ gbiology, Life ...
Optical imaging of voltage-sensitive dyes in an isolated cerebellum preparation was used to study... more Optical imaging of voltage-sensitive dyes in an isolated cerebellum preparation was used to study the spatiotemporal functional organization of the inhibitory systems in the cerebellar cortex. Responses to surface stimulation of the cortex reveal two physiologically distinct inhibitory systems, which we refer to as lateral and on-beam inhibition following classical terminology. Lateral inhibition occurs throughout the area responding to a stimulus, whereas on-beam inhibition is confined to the area directly excited by parallel fibers. The time course of the lateral inhibition is twice as long as that of the on-beam inhibition. Both inhibitory responses increase with stimulus intensity, but the lateral inhibition has a lower threshold, and it saturates at lower stimulus intensity. The amplitude of the on-beam inhibition is linearly related to the excitation at the same location, whereas that of the lateral inhibition is linearly related to the excitation at the center of the beam. Repetitive stimulation is required to activate on-beam inhibition, whereas the same stimulus paradigm reveals prolonged depression of the lateral inhibition. We conclude that lateral inhibition reflects the activation of molecular layer interneurons, and its major role is to increase the excitability of the activated area by disinhibition. The on-beam inhibition most likely reflects Golgi cell inhibition of granule cells. However, Purkinje cell collateral inhibition of Golgi cells cannot be excluded. Both possibilities suggest that the role of the on-beam inhibition is to efficiently modulate, in time and space, the mossy fiber input to the cerebellar cortex.
tonic coupling in the inferior olivary (IO) nucleus is assumed to play a crucial role in generati... more tonic coupling in the inferior olivary (IO) nucleus is assumed to play a crucial role in generating the subthreshold membrane potential oscillations in olivary neurons and in synchronizing climbing fiber input into the cerebellar cortex. We studied the strength and spatial distribution of the coupling by simultaneous double patch recordings from olivary neurons in the brain slice preparation. Electrotonic coupling was observed in 50% of the cell pairs. The coupling coefficient (CC), defined as the ratio between voltage responses of the post-and the prejunctional cell, varied between 0.002 and 0.17; most of the pairs were weakly coupled. In more than 75% of the pairs, the CC was Ͻ0.05. The coupling resistance varied between 0.7 to 19.8 G⍀, and 68% of the values fell between 0.7 to 8 G⍀. The difference between the coupling coefficient measured on stimulation of cell 1 or cell 2 of a coupled pair was 27 Ϯ 16%. Direct calculation of the coupling resistance revealed an asymmetry of 24 Ϯ 12%, suggesting a directional preference of coupling. The coupling was voltage independent, although depolarization of either the pre-or the postjunctional neuron reduced the CC. The chance of a cell pair being coupled was 80% in immediate neighboring cells, but dropped to about 30% at a distance of 40 m. No coupled pairs were observed at distances larger than 70 m. In 52% of staining experiments neurobiotin injection into an olivary neuron produced indirect labeling of 1-11 nearby cells with an average of 3.8 Ϯ 2.9. All indirectly labeled cells were found in, or immediately adjacent, to the dendritic field of the directly stained neuron. Two distinct morphological types of olivary neurons, "curly" and "straight" cells, were found. In each case all neurons stained indirectly by dye passage through gap junctions belonged to the same type. Using the physiological data we estimated that each olivary neuron is directly coupled to about 50 neurons. Since somatic recordings may not reveal coupling through remote dendrites, we conclude that each neuron is directly connected to Ն50 neurons forming two distinct networks of curly and straight cells.
Byk et al. Cerebellar Large Scale Calcium Imaging sagittal bands that is preserved in genetically... more Byk et al. Cerebellar Large Scale Calcium Imaging sagittal bands that is preserved in genetically induced disorganized cerebellar cortex. Furthermore, the response, which represents the activation of two sets of climbing fibers inputs, is followed by a prolonged recovery process that indicates the cerebellar involvement in startle response.
1. The electrophysiological properties of motoneurones in the dorsal motor nucleus of the vagus i... more 1. The electrophysiological properties of motoneurones in the dorsal motor nucleus of the vagus in the guinea-pig were studied at different times following cervical vagotomy. The results were compared both to normal neurones and to results obtained at the same time from intact neurones located in the contralateral nucleus. 2. The input resistances of axotomized neurones are significantly higher than those of normal neurones (66 + 29 compared to 45 + 17 MQ2). This difference was seen during the first month following axotomy without any sign of a time-dependent process. On the other hand, no change in resting potential was observed. 3. Significant reduction in action potential amplitude was observed 1 month after axotomy (from 97-8 + 8 to 87 + 7 mV) and was followed by slow recovery lasting more than 1 year. Neither the Na+ conductance nor the voltage-dependent K+ conductance responsible for the fast rise and fall of the action potential, respectively, were affected by axotomy. 4. One month after axotomy the action potential duration in axotomized neurones was found to be shorter than that of normal neurones (09±+0-1 ms compared to 11 +0-04 ms). We show that this decrease in duration reflects a reduction in the depolarizing hump on the falling phase of the action potential, which is known to express the Ca2+ conductance activated during the action potential. A slow recovery of the spike duration was observed, although an age-dependent reduction in duration was also observed in neurones in the contralateral nucleus. 5. Two K+ conductances, the Ca2+-dependent and the A type, decrease 1 month after axotomy and follow a similar time course of recovery to that of the reduction in action potential duration and amplitude. 6. The firing pattern of axotomized neurones undergoes profound alteration, manifested as an increase in firing duration as a response to a rectangular current pulse. Examination of these alterations reveals that the reduction in both K+ conductances is responsible for the observed changes. 7. The results are discussed within the framework of the degenerative response known to take place in the nucleus following axotomy. We hypothesize that the observed phenomena reflect an increase in intracellular Ca2+ concentration which, in turn, inactivates the Ca2+ and K+ conductances. Furthermore this rise in intracellular Ca2+ may eventually be responsible for cell death.
Publisher Summary This chapter discusses the model of analog and digital processing in single ner... more Publisher Summary This chapter discusses the model of analog and digital processing in single nerve cells that comprises the network. This approach requires the construction of detailed models that incorporate knowledge of neuronal morphology and physiology as well as synaptic architecture. A morphologically and physiologically characterized dendritic tree of a cerebellar Purkinje cell (PC), as well as for a reconstructed axon from the cat somatosensory cortex is demonstrated. The reconstruction of PC cell was performed utilizing a computer-driven system, neuron tracing system (NTS), and it does not include the dendritic spines that account for more than 50% of the total dendritic area of these cells. The study also highlights several general principles which include the single nerve cell can function as a network of almost independent subunits and voltage attenuation resulting from dendritic structure implies that the site of the synaptic input is functionally significant.
Simultaneous patch clamp recordings from the soma and dendrites of neocortical pyramidal neurons ... more Simultaneous patch clamp recordings from the soma and dendrites of neocortical pyramidal neurons of young rats show that, independent of the synaptic input location, the sodium action potential (AP) always starts at the soma and is then carried along the axon, but also propagates backward decrementally into the dendritic tree1. This back-propagating AP is supported by a low density (\({\bar g_{Na}} = \sim 4mS/c{m^2}\) mS/cm2) of Na+ in the dendrites and soma membrane of the pyramidal neurons.
Neuronal interactions mediated by alteration of the extracellular K + concentration [K + ] o occu... more Neuronal interactions mediated by alteration of the extracellular K + concentration [K + ] o occur between populations as well as among single neurones in very restricted regions. The interactions mediated by K + ions may range from low efficacy ones (in which the effects of increased [K + ] o around the non-active cells can be recorded only after massive activity of a large population of neurones) to very effective interactions (in which a single action potential in a neurone is sufficient to produce a depolarization of several mV in a second one). Such efficient K +-mediated interactions cannot be unequivocally distinguished by shape, amplitude or time course from postsynaptic responses induced by chemical or electrotonic synapses. We review here experiments which demonstrate various levels of interactions mediated by changes in potassium ion concentration. The giant axons (Gax) and non-giant axons from the central nervous system of the cockroach Periplaneta americana were used. The types of interactions discussed are: (a) pathological interactions among populations of neurones induced by the convulsant drug picrotoxin; (b) restricted and limited interactions which are the consequence of the combination of the special geometry of Gaxs and increases in extracellular K + ; and finally, (c) local and efficient interactions among Gaxs which are postulated to be mediated by K + ions. The experiments described in this review, as well as others, demonstrate that the extracellular spaces in the CNS serve as predetermined pathways for K +-mediated neuronal communication. When the extracellular space between two adjacent neurones is very small, the K +-mediated interaction may resemble the PSPs of chemical or electrotonic synapses. It is possible that because of this resemblance, other K +-mediated interactions in the CNS have not been identified as such.
Proceedings of the National Academy of Sciences of the United States of America, Dec 8, 1998
The discrepancy between the structural longitudinal organization of the parallel-fiber system in ... more The discrepancy between the structural longitudinal organization of the parallel-fiber system in the cerebellar cortex and the functional mosaic-like organization of the cortex has provoked controversial theories about the f low of information in the cerebellum. We address this issue by characterizing the spatiotemporal organization of neuronal activity in the cerebellar cortex by using optical imaging of voltage-sensitive dyes in isolated guinea-pig cerebellum. Parallel-fiber stimulation evoked a narrow beam of activity, which propagated along the parallel fibers. Stimulation of the mossy fibers elicited a circular, nonpropagating patch of synchronized activity. These results strongly support the hypothesis that a beam of parallel fibers, activated by a focal group of granule cells, fails to activate the Purkinje cells along most of its length. It is thus the ascending axon of the granule cell, and not its parallel branches, that activates and defines the basic functional modules of the cerebellar cortex. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Increased extracellular levels of ascorbate in striatum after middle cerebral artery occlusion in... more Increased extracellular levels of ascorbate in striatum after middle cerebral artery occlusion in the rat monitored by intracerebral microdialysis.
The electrical connectivity in the inferior olive (IO) nucleus plays an important role in generat... more The electrical connectivity in the inferior olive (IO) nucleus plays an important role in generating well-timed spiking activity. Here we combined electrophysiological and computational approaches to assess the functional organization of mice IO nucleus. Spontaneous fast and slow subthreshold events were commonly encountered during in vitro recordings. We show that the fast events represent a regenerative response in unique excitable spine-like structures in the axon hillock, whereas the slow events reflect the electrical connectivity between neurons ('spikelets'). Recordings from cell pairs revealed the synchronized occurrence of distinct groups of spikelets; their rate and distribution enabled an accurate estimation of the number of connected cells and is suggestive of a clustered organization. This study thus provides a new perspective on the functional and structural organization of the olivary nucleus, insights into two different subthreshold nonsynaptic events, and a novel experimental and theoretical approach to the study of electricallycoupled networks. .
Cerebellar inhibitory interneurons respond to parallel fiber input with a characteristic train of... more Cerebellar inhibitory interneurons respond to parallel fiber input with a characteristic train of action potentials. Here we show that the characteristics of these trains reflect the intrinsic properties of the interneurons. In in vitro cerebellar slices, the response of these neurons to synaptic-like current resembles their in vivo response to parallel fiber input-a train of action potentials characterized by a gradual increase in interspike interval and spike amplitude. A large variability in spike timing, or jitter, was observed, the last action potential emerging from a slow depolarizing wave that lasted beyond the synaptic current and was prevented by either TTX or membrane hyperpolarization. While response duration was weakly dependent on current intensity, the variability of the overall duration was closely related to the variability of the timing of the last action potential. Blocking the Ca 2ϩ currents or partial blockade of the delayed rectifier (TEA 2 mM) decreased the excitability, leading to a decrease in the duration and variability of the response and increasing its dependence on stimulus intensity. Increased duration and variability was observed in the presence of Cs ϩ ions (5 mM) that blocked an h-like current. We conclude that a persistent Na ϩ current governs the duration of the response, whereas the synaptic current and the spiking mechanism shape its pattern. The large variability between trials is due to the stochastic nature of the persistent Na ϩ current. Thus unless precise timing is achieved by a network of interconnected neurons, these results vote against temporal coding as a player in the cerebellar computational processing.
Proceedings of the National Academy of Sciences of the United States of America, Mar 3, 2009
Complex movements require accurate temporal coordination between their components. The temporal a... more Complex movements require accurate temporal coordination between their components. The temporal acuity of such coordination has been attributed to an internal clock signal provided by inferior olivary oscillations. However, a clock signal can produce only time intervals that are multiples of the cycle duration. Because olivary oscillations are in the range of 5-10 Hz, they can support intervals of Ϸ100-200 ms, significantly longer than intervals suggested by behavioral studies. Here, we provide evidence that by generating nonzero-phase differences, olivary oscillations can support intervals shorter than the cycle period. Chronically implanted multielectrode arrays were used to monitor the activity of the cerebellar cortex in freely moving rats. Harmaline was administered to accentuate the oscillatory properties of the inferior olive. Olivaryinduced oscillations were observed on most electrodes with a similar frequency. Most importantly, oscillations in different recording sites retained a constant phase difference that assumed a variety of values in the range of 0-180°, and were maintained across large global changes in the oscillation frequency. The inferior olive may thus underlie not only rhythmic activity and synchronization, but also temporal patterns that require intervals shorter than the cycle duration. The maintenance of phase differences across frequency changes enables the olivo-cerebellar system to replay temporal patterns at different rates without distortion, allowing the execution of tasks at different speeds.
Neurons in the mammalian CNS receive 104-105 synaptic inputs onto their dendritic tree. Each of t... more Neurons in the mammalian CNS receive 104-105 synaptic inputs onto their dendritic tree. Each of these inputs may fire spontaneously at a rate of a few spikes per second. Consequently, the cell is bombarded by several hundred synapses in each and every millisecond. An extreme example is the cerebellar Purkinje cell (PC) receiving approximately 100,000 excitatory synapses from the parallel fibers (p.f.s) onto dendritic spines covering the thin dendritic branchlets. What is the effect of the p.f.s activity on the integrative capabilities of the PC? This question is explored theoretically using analytical cable models as well as compartmental models of a morphologically and physiologically characterized PC from the guinea pig cerebellum. The input of individual p.f.s was moaeled as a transient conductance change, peaking at 0.4 nS with a rise time of 0.3 msec and a reversal potential of f60 mV relative to rest. We found that already at a firing frequency of a few spikes per second the membrane conductance is several times larger than the membrane conductance in the absence of synaptic activity. As a result, the cable properties of the PC significantly change; the most sensitive parameters are the system time constant (70) and the steady-state attenuation factor from dendritic terminal to soma. The implication is that the cable properties of central neurons in freely behaving animals are different from those measured in slice preparation or in anesthetized animals, where most of the synaptic inputs are inactive. We conclude that, because of the large conductance increase produced by the background activity of the p.f.s, the activity of the PC will be altered from this background level either when the p.f.s change their firing frequency for a period of several tens of milliseconds or when a large population of the p.f.s fires during a narrow time window.
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Papers by Yosef Yarom