The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
David A. Lewis - One of the best experts on this subject based on the ideXlab platform.
-
altered parvalbumin Basket Cell terminals in the cortical visuospatial working memory network in schizophrenia
Biological Psychiatry, 2021Co-Authors: Kenneth N. Fish, Brad R Rocco, Adam M Dedionisio, Samuel J Dienel, Robert A Sweet, David A. LewisAbstract:Abstract Background Visuospatial working memory (vsWM), which is commonly impaired in schizophrenia, involves information processing across primary visual (V1), association visual (V2), posterior parietal (PPC), and dorsolateral prefrontal (DLPFC) cortices. Within these regions, vsWM requires inhibition from parvalbumin (PV)-expressing Basket Cells (PVBCs). Here, we analyzed indices of PVBC axon terminals across regions of the vsWM network in schizophrenia. Methods For 20 matched pairs of schizophrenia and unaffected comparison subjects, tissue sections from V1, V2, PPC, and DLPFC were immunolabeled for PV, the two isoforms of glutamic acid decarboxylase (GAD65 and GAD67) that synthesize GABA, and the vesicular GABA transporter (vGAT). The density of PVBC terminals and of protein levels per terminal was quantified in layer 3 of each cortical region using fluorescence confocal microscopy. Results : In comparison subjects, all measures, except for GAD65 levels, exhibited a caudal-to-rostral decline across the vsWM network. In schizophrenia, the density of detectable PVBC terminals was significantly lower in all regions except DLPFC, whereas PVBC terminal levels of PV, GAD67 and GAD65 proteins were lower in all regions. A composite measure of inhibitory strength was lower in schizophrenia subjects, although the magnitude of the diagnosis effect was greater in V1, V2 and PPC than in DLPFC. Conclusions In schizophrenia, alterations in PVBC terminals across the vsWM network suggest the presence of a shared substrate for cortical dysfunction during vsWM tasks. However, regional differences in the magnitude of the disease effect on an index of PVBC inhibitory strength suggest region-specific alterations in information processing during vsWM tasks.
-
Altered parvalbumin Basket Cell inputs in the dorsolateral prefrontal cortex of schizophrenia subjects
Molecular psychiatry, 2013Co-Authors: Jill R. Glausier, Kenneth N. Fish, David A. LewisAbstract:Altered parvalbumin Basket Cell inputs in the dorsolateral prefrontal cortex of schizophrenia subjects
-
parvalbumin containing chandelier and Basket Cell boutons have distinctive modes of maturation in monkey prefrontal cortex
The Journal of Neuroscience, 2013Co-Authors: Kenneth N. Fish, Gil D Hoftman, Wasiq Sheikh, Michael Kitchens, David A. LewisAbstract:Parvalbumin (PV)-containing cortical GABA neurons include chandelier Cells (PVChCs) and Basket Cells (PVBCs), which innervate the axon initial segment (AIS) and soma/proximal dendrites of pyramidal Cells, respectively. In monkey prefrontal cortex (PFC), the density of PVChC axon cartridges detectable by PV immunoreactivity peaks prior to the onset of puberty before declining markedly to adult levels, whereas the density of PV-immunoreactive (IR) puncta (presumed PVBC boutons) increases during adolescence. These inverse developmental changes in bouton density could explain why an electron microscopy study found no change in the density of symmetric, presumably GABAergic, synapses between infancy and adulthood in monkey PFC. Alternatively, the inverse developmental trajectories of PVChC and PVBC boutons could represent Cell type-specific differences in the maturation of PV protein levels. To differentiate between these two alternatives, multilabel confocal microscopy was used to quantify the number of PVChC and PVBC boutons per pyramidal neuron in the PFC of 3-month-old and adult monkeys. The mean number of PVChC boutons per pyramidal neuron AIS was, significantly, 32% lower in adult compared with 3-month-old monkeys, whereas the density of PVBC boutons per pyramidal neuron did not differ between age groups. In contrast, relative levels of PV protein were approximately twofold higher in PVBC boutons in adult animals, whereas PV levels in PVChC boutons did not differ between age groups. These findings suggest Cell type-specific mechanisms of maturation of PV-containing GABAergic boutons in monkey PFC.
-
Cortical Basket Cell dysfunction in schizophrenia.
The Journal of physiology, 2012Co-Authors: Allison A. Curley, David A. LewisAbstract:Schizophrenia, a debilitating illness affecting 0.5-1% of the world's population, is characterized by positive, negative and cognitive symptoms. The latter are the best predictor of functional outcome, though largely untreated by current pharmacotherapy; thus a better understanding of the mechanisms underlying cognitive deficits in schizophrenia is crucial. Higher order cognitive processes, such as working memory, are associated with θ (4-7 Hz) and γ (30-80 Hz) oscillations in the prefrontal cortex (PFC), and subjects with schizophrenia exhibit working memory impairments and reduced cortical θ and γ band power. Cortical θ and γ oscillations are dependent on perisomatic inhibition of pyramidal neurons from Basket Cells expressing cholecystokinin (CCK(b) Cells) and parvalbumin (PV(b) Cells), respectively. Thus, alterations in Basket Cells may underlie the cortical oscillation deficits and working memory impairments in schizophrenia. Recent findings from postmortem studies suggest that schizophrenia is associated with multiple molecular alterations that regulate signalling from CCK(b) and PV(b) Cells. These alterations include lower CCK and cannabinoid 1 receptor (CB1R) in CCK(b) Cells, and lower glutamic acid decarboxylase 67 (GAD67) and increased μ opioid receptor (μOR) in PV(b) Cells, as well as lower GABA(A) receptor α1 subunit in pyramidal neurons postsynaptic to PV(b) Cells. These changes are thought to lead to increased and decreased strength, respectively, of CCK(b) and PV(b) Cell-mediated inhibition of postsynaptic pyramidal Cells. Therefore, a convergence of evidence suggests a substantial shift in the relative strengths of PFC pyramidal Cell inhibition from CCK(b) and PV(b) Cells that may underlie cortical oscillation deficits and working memory impairments in schizophrenia.
Robert S. Sloviter - One of the best experts on this subject based on the ideXlab platform.
-
"Dormant Basket Cell" hypothesis revisited: relative vulnerabilities of dentate gyrus mossy Cells and inhibitory interneurons after hippocampal status epilepticus in the rat.
The Journal of comparative neurology, 2003Co-Authors: Robert S. Sloviter, Colin A. Zappone, Brian D. Harvey, Argyle V. Bumanglag, Roland A. Bender, Michael FrotscherAbstract:The "dormant Basket Cell" hypothesis suggests that postinjury hippocampal network hyperexcitability results from the loss of vulnerable neurons that normally excite insult-resistant inhibitory Basket Cells. We have reexamined the experimental basis of this hypothesis in light of reports that excitatory hilar mossy Cells are not consistently vulnerable and inhibitory Basket Cells are not consistently seizure resistant. Prolonged afferent stimulation that reliably evoked granule Cell discharges always produced extensive hilar neuron degeneration and immediate granule Cell disinhibition. Conversely, kainic acid-induced status epilepticus in chronically implanted animals produced similarly extensive hilar Cell loss and immediate granule Cell disinhibition, but only when granule Cells discharged continuously during status epilepticus. In both preparations, electron microscopy revealed degeneration of presynaptic terminals forming asymmetrical synapses in the mossy Cell target zone, including some terminating on gamma-aminobutyric acid-immunoreactive elements, but no evidence of axosomatic or axoaxonic degeneration in the adjacent granule Cell layer. Although parvalbumin immunocytochemistry and in situ hybridization revealed decreased staining, this apparently was due to altered parvalbumin expression rather than Basket Cell death, because substance P receptor-positive interneurons, some of which contained residual parvalbumin immunoreactivity, survived. These results confirm the inherent vulnerability of dendritically projecting hilar mossy Cells and interneurons and the relative resistance of dentate inhibitory Basket and chandelier Cells that target granule Cell somata. The variability of hippocampal Cell loss after status epilepticus suggests that altered hippocampal structure and function cannot be assumed to cause the spontaneous seizures that develop in these animals and highlights the importance of confirming hippocampal pathology and pathophysiology in vivo in each case.
-
Permanently altered hippocampal structure, excitability, and inhibition after experimental status epilepticus in the rat: The “dormant Basket Cell” hypothesis and its possible relevance to temporal lobe epilepsy
Hippocampus, 1991Co-Authors: Robert S. SloviterAbstract:The relationship between an episode of status epilepticus, the resulting hippocampal pathology, and the subsequent development of pathophysiological changes possibly relevant to human cpilepsy was explored using the experimental epilepsy model of perforant path stimulation in the rat. Granule Cell hyperexcitability and decreased feedforward and feedback inhibition were evident immediately after 24 hours of intermittent perforant path stimulation and persisted relatively unchanged for more than 1 year. All of the pathophysiological changes induced by perforant path stimulation were replicated in normal animals by a subconvulsive dose of bicuculline, suggesting that the permanent “epileptiform” abnormalities produced by sustained perforant path stimulation may be due to decreased GABA-mediated inhibition. Granule Cell pathophysiology was seen only in animals that exhibited a loss of adjacent dentate hilar mossy Cells and hilar somatostatin/neuropeptide Y-immunoreactive neurons. GABA-immunoreactive dentate Basket Cells survived despite the extensive loss of adjacent hilar neurons. However, Parvalbumin immunoreactivity, present normally in a subpopulation of GABA-immunoreactive dentate Basket Cells, was absent on the stimulated side. Whether this represents decreased parvalbumin synthesis in surviving Basket Cells or a loss of a specific subset of inhibitory Cells is unclear. Hyperexcitability and decreased paired-pulse inhibition in response to ipsilateral perforant path stimulation were also present in the CA1 pyramidal Cell layer on the previously stimulated side, despite minimal damage to CA1 pyramidal Cells or interneurons. The possibility that CA1 inhibitory neurons were hypofunctional or “dormant” due to a loss of excitatory input to inhibitory Cells from damaged CA3 pyramidal Cells was tested by stimulating the contralateral perforant path in order to activate the same CA1 Basket Cells via different inputs. Contralateral stimulation evoked CA1 pyramidal Cell paired-pulse inhibition immediately in the previously stimulated hippocampus. Thus, we propose the “dormant Basket Cell” hypothesis, which implies that despite malfunction, inhibitory systems remain intact in “epileptic” tissue and are capable of functioning if appropriately activated.
Alex M. Thomson - One of the best experts on this subject based on the ideXlab platform.
-
The 3D reconstructions of CA1 Cells in rat hippocampus used in this study.
2018Co-Authors: Rosanna Migliore, Alex M. Thomson, Carmen A. Lupascu, Luca L. Bologna, Armando Romani, Jean-denis Courcol, Stefano Antonel, Werner A. H. Van Geit, Audrey Mercer, Sigrun LangeAbstract:(Top) Pyramidal Cells; dendrites are shown in black, axons in red; Cell identifier, from left: 990803, oh140807_A0_idJ, oh140807_A0_idH, oh140807_A0_idG, oh140807_A0_idF, 050921AM2, oh140807_A0_idC, oh140807_A0_idB, oh140807_A0_idA; (Bottom) Interneurons, from left to right: Basket Cell (dendrites in black, axon in pink [Cell number 990111HP2]); bistratified Cell (dendrites in black, axon in blue [Cell number 980513B]); axo-axonic Cell (dendrites in black, axon in purple [Cell number 970911C]); OLM Cell (dendrites in black, axon in dark blue [Cell number 011017HP2]); Ivy Cell (dendrites in black; axon in light pink [Cell number 010710HP2]); perforant path associated Cell (dendrites in black, axon in red [Cell number 011127HP1]); Schaffer collateral-associated Cell (dendrites in black, axon in green [Cell number 990827IN5HP3]). Reconstructions by Joanne Falck and Sigrun Lange. SO Stratum Oriens, SP Stratum Pyramidale, SR Stratum Radiatum, SLM Stratum Lacunosum-Moleculare. 3D reconstructions of the PPA, OLM, axo-axonic Cells and of other examples of different types of Cells are available in S1 Fig of Mercer and Thomson [17].
-
IPSPs elicited in CA1 pyramidal Cells by putative Basket Cells in slices of adult rat hippocampus.
The European journal of neuroscience, 1999Co-Authors: Alex M. ThomsonAbstract:CA1 Basket Cells are identifiable by an axonal arbour largely confined to, and spanning, the entire depth of stratum pyramidale where they innervate pyramidal somata and proximal dendrites. Basket Cells display a range of electrophysiological properties and the inhibitory postsynaptic potentials (IPSPs) they elicit in pyramidal Cells vary widely in duration. To determine whether these parameters are correlated, we used paired intraCellular recordings, with biocytin filling, in pyramidal Cells of adult hippocampal slices, and studied gamma-aminobutyric acid (GABAA) IPSPs (n = 43) elicited by putative Basket Cells (n = 35) with axons largely confined to stratum pyramidale in simultaneously recorded pyramidal Cells. Fast-spiking interneurons elicited relatively brief IPSPs, while IPSPs elicited by burst-firing Cells were amongst the slowest. Regular spiking interneurons elicited fast and slow GABAA IPSPs, but any one interneuron elicited IPSPs with remarkably similar durations in two to four pyramidal targets. However, with different types of target for a single putative Basket Cell, IPSPs elicited in postsynaptic interneurons were briefer than in pyramidal Cells. Vertical oriens Cells with somata in stratum oriens and a narrow, sparse axonal arbour in stratum pyramidale in transverse hippocampal slices, elicited IPSPs whose rise times and half widths clustered around intermediate values. Durations of IPSPs in pyramidal Cells thus correlate, to a degree, with the physiological properties of presynaptic Basket Cells. The seven-fold range of durations observed (10-70 ms half widths) may underlie contributions made by different Basket Cells to hippocampal rhythms of different frequencies.
-
Modulation of bistratified Cell IPSPs and Basket Cell IPSPs by pentobarbitone sodium, diazepam and Zn2+: dual recordings in slices of adult rat hippocampus.
The European journal of neuroscience, 1999Co-Authors: Hannelore Pawelzik, Jim Deuchars, Ilia M, Alex M. ThomsonAbstract:Simultaneous intraCellular recordings from presynaptic Stratum pyramidale interneurons and postsynaptic pyramidal Cells in adult rat hippocampal slices were performed to investigate the strength of the modulation of single-axon inhibitory postsynaptic potentials (IPSPs) by the GABAA receptor modulators pentobarbitone, diazepam and zinc. The processing of biocytin-filled interneurons for light microscopy revealed that these single-axon IPSPs were generated by Basket Cells (n = 33), bistratified Cells (n = 18) and axo-axonic Cells (n = 2). The IPSPs generated by these three groups of interneurons had amplitudes and widths at half amplitude with similar ranges, but when bistratified Cell IPSPs were compared with Basket Cell IPSPs with similar half widths their rise times were slower. Pentobarbitone sodium (250 microM) powerfully enhanced 13 tested IPSPs generated by all three Cell types. Amplitudes were enhanced by 82 +/- 56%, 10-90% rise times by 150 +/- 101% and the widths at half amplitude by 71 +/- 29%. Diazepam (1-2 microM) also increased all IPSPs tested, although the changes were more moderate in Basket Cell IPSPs (amplitudes increased by 19 +/- 11%, n = 8) than in bistratified Cell IPSPs (amplitudes increased by 66 +/- 48%, n = 5). Basket Cell IPSP 10-90% rise times and widths at half amplitude were not significantly increased. Bistratified Cell IPSP 10-90% rise times were increased by 44 +/- 24% and the widths at half amplitude by 32 +/- 35%. The one tested IPSP generated by an axo-axonic Cell was also diazepam-sensitive. Zinc, 250 microM, decreased four out of 10 IPSPs generated by Basket Cells and four out of five IPSPs generated by bistratified Cells. The one tested axo-axonic Cell IPSP was zinc-insensitive. These data suggest that IPSPs generated in CA1 pyramidal Cells by Basket and bistratified Cells display different pharmacologies and may be mediated by different receptors or receptor combinations.
Andrew P. Southan - One of the best experts on this subject based on the ideXlab platform.
-
electrophysiological characterization of voltage gated k currents in cerebellar Basket and purkinje Cells kv1 and kv3 channel subfamilies are present in Basket Cell nerve terminals
The Journal of Neuroscience, 2000Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:To understand the processes underlying fast synaptic transmission in the mammalian CNS, we must have detailed knowledge of the identity, location, and physiology of the ion channels in the neuronal membrane. From labeling studies we can get clues regarding the distribution of ion channels, but electrophysiological methods are required to determine the importance of each ion channel in CNS transmission. Dendrotoxin-sensitive potassium channel subunits are highly concentrated in cerebellar Basket Cell nerve terminals, and we have previously shown that they are responsible for a significant fraction of the voltage-gated potassium current in this region. Here, we further investigate the characteristics and pharmacology of the voltage-dependent potassium currents in these inhibitory nerve terminals and compare these observations with those obtained from somatic recordings in Basket and Purkinje Cell soma regions. We find that α-DTX blocks Basket Cell nerve terminal currents and not somatic currents, and the IC50 for α-DTX in Basket Cell terminals is 3.2 nm. There are at least two distinct types of potassium currents in the nerve terminal, a DTX-sensitive low-threshold component, and a second component that activates at much more positive voltages. Pharmacological experiments also reveal that nerve terminal potassium currents are also markedly reduced by 4-AP and TEA, with both high-sensitivity (micromolar) and low-sensitivity (millimolar) components present. We suggest that Basket Cell nerve terminals have potassium channels from both the Kv1 and Kv3 subfamilies, whereas somatic currents in Basket Cell and Purkinje Cell bodies are more homogeneous.
-
Electrophysiological characterization of voltage-gated K(+) currents in cerebellar Basket and purkinje Cells: Kv1 and Kv3 channel subfamilies are present in Basket Cell nerve terminals.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:To understand the processes underlying fast synaptic transmission in the mammalian CNS, we must have detailed knowledge of the identity, location, and physiology of the ion channels in the neuronal membrane. From labeling studies we can get clues regarding the distribution of ion channels, but electrophysiological methods are required to determine the importance of each ion channel in CNS transmission. Dendrotoxin-sensitive potassium channel subunits are highly concentrated in cerebellar Basket Cell nerve terminals, and we have previously shown that they are responsible for a significant fraction of the voltage-gated potassium current in this region. Here, we further investigate the characteristics and pharmacology of the voltage-dependent potassium currents in these inhibitory nerve terminals and compare these observations with those obtained from somatic recordings in Basket and Purkinje Cell soma regions. We find that α-DTX blocks Basket Cell nerve terminal currents and not somatic currents, and the IC50 for α-DTX in Basket Cell terminals is 3.2 nm. There are at least two distinct types of potassium currents in the nerve terminal, a DTX-sensitive low-threshold component, and a second component that activates at much more positive voltages. Pharmacological experiments also reveal that nerve terminal potassium currents are also markedly reduced by 4-AP and TEA, with both high-sensitivity (micromolar) and low-sensitivity (millimolar) components present. We suggest that Basket Cell nerve terminals have potassium channels from both the Kv1 and Kv3 subfamilies, whereas somatic currents in Basket Cell and Purkinje Cell bodies are more homogeneous.
-
K+ channel blockers and Ca2+ signals in Basket Cell terminals.
The Journal of Physiology, 1999Co-Authors: Brian D. Robertson, Andrew P. SouthanAbstract:A key issue in neurophysiology is understanding the mechanisms of fast synaptic transmission between neurones. Progress is being made on many fronts, using powerful techniques to describe such physiological processes in terms of their molecular components. For instance, we are now beginning to define the molecular identity of several key ion channels at synapses between Basket Cells and Purkinje Cells in the cerebellar cortex. The cerebellum has long been a happy and profitable hunting ground for physiologists and anatomists. Indeed, some of the most significant advances in understanding how neurones communicate have come from studies of the cerebellar cortex, and it is still an incredibly useful in vitro preparation today, as the article by Tan & Llano (1999) in this issue of The Journal of Physiology shows. In 1888, Santiago Ramon y Cajal published his first papers on the structure of the cerebellar cortex in birds and mammals. Using the Golgi staining method, Cajal discovered the beautiful geometry and unique Cells of the cerebellum (Ramon y Cajal, 1911). Figure 1 shows Cajal's depiction of a Basket Cell, whose axon collaterals make contact with several successive Purkinje Cells. These collaterals form both the ‘periCellular Basket’ around the Purkinje soma and, below this, a highly unusual specialization (the ‘pinceau’) around the axon initial segment. These terminals are therefore strategically located to control the ultimate output of Purkinje Cells (the sole efferent output of the cerebellar cortex), as the axon initial segment is the region of action potential generation. Figure 1 The Basket Cell and its terminals on Purkinje Cells in the cerebellum (after Ramon y Cajal, 1911) Basket Cells inhibit Purkinje Cells primarily through conventional GABAA receptor-mediated synaptic mechanisms, and study of the Basket Cell-Purkinje Cell synapse has revealed many interesting features. Antibody labelling experiments revealed that Basket Cell terminals expressed extremely high densities (perhaps the richest in the brain) of the voltage-gated K+ channel proteins Kv1.2 and 1.1 (e.g. Wang et al. 1994). This high density of known Kv channels in a clearly identifiable nerve terminal invites us to speculate on the roles that such channels play in synaptic transmission, and the favourable anatomy of the Basket-Purkinje Cell contacts has allowed two alternative experimental approaches to deciphering the part played by Kv channels here. Isabel Llano and colleagues (Llano et al. 1997) had already shown (using whole-Cell recordings combined with fluorescence measurements of intraCellular Ca2+) that depolarization of Basket Cells leads to high local increases in [Ca2+]i in synaptic terminals and axonal branch points. These changes were greater when intraCellular Cs+ was used to dialyse the Cells rather than K+, presumably due to block of K+ channels. In their present paper, Tan & Llano (1999) use the extremely powerful technique of two-photon laser excitation scanning microscopy (2PLSM) to measure changes in [Ca2+]i caused by ‘action potentials’ in Basket Cells, and have examined the effects of a variety of selective and non-selective Kv channel blockers on [Ca2+]i rises. By filling the Basket Cell with the Ca2+-sensitive probe Oregon Green-1 during whole-Cell patch clamp, and scanning small sections of the Basket Cell terminals and axon close to, or around, Purkinje Cell bodies, the authors are able to peek inside the terminals and measure tiny changes in [Ca2+]i elicited by action potential-like pulses in the Cell soma. 2PLSM allows enormously improved spatial resolution over conventional Ca2+ imaging (by reduction of scattering, and focusing on the true area of excitation), minimizing photodamage of the Cell, and allowing one to look at Cells deep in the brain slice. Figure 1 also shows the tiny, but now resolvable, changes in Ca2+ fluorescence in terminals evoked by a train of eight action potentials. Work from our own laboratory showed that α-dendrodotoxin (α-DTX), a potent and selective blocker of just three Kv subtypes (Kv1.1, 1.2 and 1.6), caused a marked enhancement of both the frequency and amplitude of spontaneous GABA-ergic synaptic currents in Purkinje Cells. Kv1.1/1.2 subunits are highly concentrated in the Basket Cell terminals, and we have shown, using direct patch clamp recordings, that α-DTX blocks about 40 % of the Kv current here, whilst leaving somatic currents unscathed (Southan & Robertson, 1998). We were still in the dark as to the roles of DTX-sensitive subunits in the terminal, however; block of these might simply be increasing excitability, or decreasing the likelihood of ‘failures’ of transmission to the synaptic zones. Alternatively, block of the ‘delayed-rectifier’ type current encoded by Kv1.1/1.2 subunits may broaden action potentials, increasing Ca2+ entry and hence transmitter release. The direct, and beautiful measurements of action potential-evokedCai2+ rises reported here by Tan & Llano show that α-DTX does not increase Ca2+ entry during the spike, suggesting that Kv1.1/1.2-containing channels are not involved in repolarizing the action potential in the Basket Cell terminals. Tan & Llano further show that only 4-aminopyridine strongly increased action potential-evoked [Ca2+]i, and suggest another Kv channel subtype is involved in action potential repolarization here. This leaves us with the possibility that the α-DTX-sensitive Kv channels might be involved in the resting K+ conductance of the terminal, or perhaps in determining propagation/failures of transmission along the axon. There are now several types of K+ channel known to be localized in Basket Cell nerve terminals, and we need multidisciplinary approaches to dissect out the precise physiological roles of these channels in synaptic transmission; the powerful technique applied by Tan & Llano is a warmly welcomed addition.
-
Patch-Clamp Recordings from Cerebellar Basket Cell Bodies and Their Presynaptic Terminals Reveal an Asymmetric Distribution of Voltage-Gated Potassium Channels
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:Cerebellar Basket Cells form highly specialized inhibitory synaptic contacts with Purkinje Cells, namely the periCellular Basket and pinceau nerve terminal structures, wrapping around the Purkinje Cell somatic and axon hillock regions. These inhibitory synaptic contacts are ideally located to control the ultimate output of the cerebellar cortex. Previous immunohistochemical studies have shown that these synaptic structures possess a very high density of the dendrotoxin (DTX)-sensitive potassium channel subunit, Kv1.2. We have taken advantage of this unique anatomical arrangement offering a high concentration of identified Kv channel subunits by combining whole-Cell patch-clamp recording and fluorescence microscopy to establish a novel preparation and perform the first recordings from unambiguously identified mammalian CNS inhibitory presynaptic terminals. We report that DTX-sensitive potassium channels are present in Basket Cell terminals but not in the Basket Cell soma. This selective Cellular distribution suggests that these channels play an important role in modulating cerebellar inhibitory synaptic transmission.
Brian D. Robertson - One of the best experts on this subject based on the ideXlab platform.
-
electrophysiological characterization of voltage gated k currents in cerebellar Basket and purkinje Cells kv1 and kv3 channel subfamilies are present in Basket Cell nerve terminals
The Journal of Neuroscience, 2000Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:To understand the processes underlying fast synaptic transmission in the mammalian CNS, we must have detailed knowledge of the identity, location, and physiology of the ion channels in the neuronal membrane. From labeling studies we can get clues regarding the distribution of ion channels, but electrophysiological methods are required to determine the importance of each ion channel in CNS transmission. Dendrotoxin-sensitive potassium channel subunits are highly concentrated in cerebellar Basket Cell nerve terminals, and we have previously shown that they are responsible for a significant fraction of the voltage-gated potassium current in this region. Here, we further investigate the characteristics and pharmacology of the voltage-dependent potassium currents in these inhibitory nerve terminals and compare these observations with those obtained from somatic recordings in Basket and Purkinje Cell soma regions. We find that α-DTX blocks Basket Cell nerve terminal currents and not somatic currents, and the IC50 for α-DTX in Basket Cell terminals is 3.2 nm. There are at least two distinct types of potassium currents in the nerve terminal, a DTX-sensitive low-threshold component, and a second component that activates at much more positive voltages. Pharmacological experiments also reveal that nerve terminal potassium currents are also markedly reduced by 4-AP and TEA, with both high-sensitivity (micromolar) and low-sensitivity (millimolar) components present. We suggest that Basket Cell nerve terminals have potassium channels from both the Kv1 and Kv3 subfamilies, whereas somatic currents in Basket Cell and Purkinje Cell bodies are more homogeneous.
-
Electrophysiological characterization of voltage-gated K(+) currents in cerebellar Basket and purkinje Cells: Kv1 and Kv3 channel subfamilies are present in Basket Cell nerve terminals.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:To understand the processes underlying fast synaptic transmission in the mammalian CNS, we must have detailed knowledge of the identity, location, and physiology of the ion channels in the neuronal membrane. From labeling studies we can get clues regarding the distribution of ion channels, but electrophysiological methods are required to determine the importance of each ion channel in CNS transmission. Dendrotoxin-sensitive potassium channel subunits are highly concentrated in cerebellar Basket Cell nerve terminals, and we have previously shown that they are responsible for a significant fraction of the voltage-gated potassium current in this region. Here, we further investigate the characteristics and pharmacology of the voltage-dependent potassium currents in these inhibitory nerve terminals and compare these observations with those obtained from somatic recordings in Basket and Purkinje Cell soma regions. We find that α-DTX blocks Basket Cell nerve terminal currents and not somatic currents, and the IC50 for α-DTX in Basket Cell terminals is 3.2 nm. There are at least two distinct types of potassium currents in the nerve terminal, a DTX-sensitive low-threshold component, and a second component that activates at much more positive voltages. Pharmacological experiments also reveal that nerve terminal potassium currents are also markedly reduced by 4-AP and TEA, with both high-sensitivity (micromolar) and low-sensitivity (millimolar) components present. We suggest that Basket Cell nerve terminals have potassium channels from both the Kv1 and Kv3 subfamilies, whereas somatic currents in Basket Cell and Purkinje Cell bodies are more homogeneous.
-
K+ channel blockers and Ca2+ signals in Basket Cell terminals.
The Journal of Physiology, 1999Co-Authors: Brian D. Robertson, Andrew P. SouthanAbstract:A key issue in neurophysiology is understanding the mechanisms of fast synaptic transmission between neurones. Progress is being made on many fronts, using powerful techniques to describe such physiological processes in terms of their molecular components. For instance, we are now beginning to define the molecular identity of several key ion channels at synapses between Basket Cells and Purkinje Cells in the cerebellar cortex. The cerebellum has long been a happy and profitable hunting ground for physiologists and anatomists. Indeed, some of the most significant advances in understanding how neurones communicate have come from studies of the cerebellar cortex, and it is still an incredibly useful in vitro preparation today, as the article by Tan & Llano (1999) in this issue of The Journal of Physiology shows. In 1888, Santiago Ramon y Cajal published his first papers on the structure of the cerebellar cortex in birds and mammals. Using the Golgi staining method, Cajal discovered the beautiful geometry and unique Cells of the cerebellum (Ramon y Cajal, 1911). Figure 1 shows Cajal's depiction of a Basket Cell, whose axon collaterals make contact with several successive Purkinje Cells. These collaterals form both the ‘periCellular Basket’ around the Purkinje soma and, below this, a highly unusual specialization (the ‘pinceau’) around the axon initial segment. These terminals are therefore strategically located to control the ultimate output of Purkinje Cells (the sole efferent output of the cerebellar cortex), as the axon initial segment is the region of action potential generation. Figure 1 The Basket Cell and its terminals on Purkinje Cells in the cerebellum (after Ramon y Cajal, 1911) Basket Cells inhibit Purkinje Cells primarily through conventional GABAA receptor-mediated synaptic mechanisms, and study of the Basket Cell-Purkinje Cell synapse has revealed many interesting features. Antibody labelling experiments revealed that Basket Cell terminals expressed extremely high densities (perhaps the richest in the brain) of the voltage-gated K+ channel proteins Kv1.2 and 1.1 (e.g. Wang et al. 1994). This high density of known Kv channels in a clearly identifiable nerve terminal invites us to speculate on the roles that such channels play in synaptic transmission, and the favourable anatomy of the Basket-Purkinje Cell contacts has allowed two alternative experimental approaches to deciphering the part played by Kv channels here. Isabel Llano and colleagues (Llano et al. 1997) had already shown (using whole-Cell recordings combined with fluorescence measurements of intraCellular Ca2+) that depolarization of Basket Cells leads to high local increases in [Ca2+]i in synaptic terminals and axonal branch points. These changes were greater when intraCellular Cs+ was used to dialyse the Cells rather than K+, presumably due to block of K+ channels. In their present paper, Tan & Llano (1999) use the extremely powerful technique of two-photon laser excitation scanning microscopy (2PLSM) to measure changes in [Ca2+]i caused by ‘action potentials’ in Basket Cells, and have examined the effects of a variety of selective and non-selective Kv channel blockers on [Ca2+]i rises. By filling the Basket Cell with the Ca2+-sensitive probe Oregon Green-1 during whole-Cell patch clamp, and scanning small sections of the Basket Cell terminals and axon close to, or around, Purkinje Cell bodies, the authors are able to peek inside the terminals and measure tiny changes in [Ca2+]i elicited by action potential-like pulses in the Cell soma. 2PLSM allows enormously improved spatial resolution over conventional Ca2+ imaging (by reduction of scattering, and focusing on the true area of excitation), minimizing photodamage of the Cell, and allowing one to look at Cells deep in the brain slice. Figure 1 also shows the tiny, but now resolvable, changes in Ca2+ fluorescence in terminals evoked by a train of eight action potentials. Work from our own laboratory showed that α-dendrodotoxin (α-DTX), a potent and selective blocker of just three Kv subtypes (Kv1.1, 1.2 and 1.6), caused a marked enhancement of both the frequency and amplitude of spontaneous GABA-ergic synaptic currents in Purkinje Cells. Kv1.1/1.2 subunits are highly concentrated in the Basket Cell terminals, and we have shown, using direct patch clamp recordings, that α-DTX blocks about 40 % of the Kv current here, whilst leaving somatic currents unscathed (Southan & Robertson, 1998). We were still in the dark as to the roles of DTX-sensitive subunits in the terminal, however; block of these might simply be increasing excitability, or decreasing the likelihood of ‘failures’ of transmission to the synaptic zones. Alternatively, block of the ‘delayed-rectifier’ type current encoded by Kv1.1/1.2 subunits may broaden action potentials, increasing Ca2+ entry and hence transmitter release. The direct, and beautiful measurements of action potential-evokedCai2+ rises reported here by Tan & Llano show that α-DTX does not increase Ca2+ entry during the spike, suggesting that Kv1.1/1.2-containing channels are not involved in repolarizing the action potential in the Basket Cell terminals. Tan & Llano further show that only 4-aminopyridine strongly increased action potential-evoked [Ca2+]i, and suggest another Kv channel subtype is involved in action potential repolarization here. This leaves us with the possibility that the α-DTX-sensitive Kv channels might be involved in the resting K+ conductance of the terminal, or perhaps in determining propagation/failures of transmission along the axon. There are now several types of K+ channel known to be localized in Basket Cell nerve terminals, and we need multidisciplinary approaches to dissect out the precise physiological roles of these channels in synaptic transmission; the powerful technique applied by Tan & Llano is a warmly welcomed addition.
-
Patch-Clamp Recordings from Cerebellar Basket Cell Bodies and Their Presynaptic Terminals Reveal an Asymmetric Distribution of Voltage-Gated Potassium Channels
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998Co-Authors: Andrew P. Southan, Brian D. RobertsonAbstract:Cerebellar Basket Cells form highly specialized inhibitory synaptic contacts with Purkinje Cells, namely the periCellular Basket and pinceau nerve terminal structures, wrapping around the Purkinje Cell somatic and axon hillock regions. These inhibitory synaptic contacts are ideally located to control the ultimate output of the cerebellar cortex. Previous immunohistochemical studies have shown that these synaptic structures possess a very high density of the dendrotoxin (DTX)-sensitive potassium channel subunit, Kv1.2. We have taken advantage of this unique anatomical arrangement offering a high concentration of identified Kv channel subunits by combining whole-Cell patch-clamp recording and fluorescence microscopy to establish a novel preparation and perform the first recordings from unambiguously identified mammalian CNS inhibitory presynaptic terminals. We report that DTX-sensitive potassium channels are present in Basket Cell terminals but not in the Basket Cell soma. This selective Cellular distribution suggests that these channels play an important role in modulating cerebellar inhibitory synaptic transmission.