Information processing through a neuronal microcircuit depends essentially on three major feature... more Information processing through a neuronal microcircuit depends essentially on three major features:(1) the anatomical organization and the function of its synaptic connections;(2) the biophysical or intrinsic properties of its neuronal elements; and (3) how the synaptic and ...
Adenosine A1 and A2A receptors are expressed in striatal projection neurons (SPNs). A1 receptors ... more Adenosine A1 and A2A receptors are expressed in striatal projection neurons (SPNs). A1 receptors are located in direct (dSPN) and indirect SPNs (iSNP). A2A receptors are only present in iSPNs. Dopamine D2 receptors are also expressed in iSPNs and interactions between D2 and A2A receptors have received attention. iSPNs activity increases during parkinsonism (PD) and A2A receptors may be responsible by enhancing Ca2+ currents (iCa2+). Therefore, A2A receptors blockade is a therapeutic approach. We asked whether A2A receptors need the interaction with D2 receptors (D2R) to exert their actions. By using isolated and identified iSPNs to avoid indirect influences, we show that D2R action habilitates A2A receptors (A2AR) modulation. iCa2+ through voltage gated Ca2+ channels (CaV) was used as a signal to observe this interaction. Voltage-clamp recordings in acutely dissociated iSPNs, current-clamp recordings in slices and calcium imaging in transgenic A2A-Cre mice, showed that D2R reduction...
Amantadine and clozapine have proved to reduce abnormal involuntary movements (AIMs) in preclinic... more Amantadine and clozapine have proved to reduce abnormal involuntary movements (AIMs) in preclinical and clinical studies of L-DOPA-Induced Dyskinesias (LID). Even though both drugs decrease AIMs, they may have different action mechanisms by using different receptors and signaling profiles. Here we asked whether there are differences in how they modulate neuronal activity of multiple striatal neurons within the striatal microcircuit at histological level during the dose-peak of L-DOPA in ex-vivo brain slices obtained from dyskinetic mice. To answer this question, we used calcium imaging to record the activity of dozens of neurons of the dorsolateral striatum before and after drugs administration in vitro. We also developed an analysis framework to extract encoding insights from calcium imaging data by quantifying neuronal activity, identifying neuronal ensembles by linking neurons that coactivate using hierarchical cluster analysis and extracting network parameters using Graph Theory. The results show that while both drugs reduce LIDs scores behaviorally in a similar way, they have several different and specific actions on modulating the dyskinetic striatal microcircuit. The extracted features were highly accurate in separating amantadine and clozapine effects by means of principal components analysis (PCA) and support vector machine (SVM) algorithms. These results predict possible synergistic actions of amantadine and clozapine on the dyskinetic striatal microcircuit establishing a framework for a bioassay to test novel antidyskinetic drugs or treatments in vitro.
Synaptic inputs from cortex and thalamus were compared in electrophysiologically defined striatal... more Synaptic inputs from cortex and thalamus were compared in electrophysiologically defined striatal cell classes: direct and indirect pathways' striatal projection neurons (dSPNs and iSPNs), fast-spiking interneurons (FS), cholinergic interneurons (ChINs), and low-threshold spiking-like (LTS-like) interneurons. Our purpose was to observe whether stimulus from cortex or thalamus had equivalent synaptic strength to evoke prolonged suprathreshold synaptic responses in these neuron classes. Subthreshold responses showed that inputs from either source functionally mix up in their dendrites at similar electrotonic distances from their somata. Passive and active properties of striatal neuron classes were consistent with the previous studies. Cre-dependent adeno-associated viruses containing Td-Tomato or eYFP fluorescent proteins were used to identify target cells. Transfections with ChR2-eYFP driven by the promoters CamKII or EF1.DIO in intralaminar thalamic nuclei using Vglut-2-Cre mice, or CAMKII in the motor cortex were used to stimulate cortical or thalamic afferents optogenetically. Both field stimuli in the cortex or photostimulation of ChR2-YFP cortical fibers evoked similar prolonged suprathreshold responses in SPNs. Photostimulation of ChR2-YFP thalamic afferents also evoked suprathreshold responses. Differences previously described between responses of dSPNs and iSPNs were observed in both cases. Prolonged suprathreshold responses could also be evoked from both sources onto all other neuron classes studied. However, to evoke thalamostriatal suprathreshold responses, afferents from more than one thalamic nucleus had to be stimulated. In conclusion, both thalamus and cortex are capable to generate suprathreshold responses converging on diverse striatal cell classes. Postsynaptic properties appear to shape these responses.
A pipeline is proposed here to describe different features to study brain microcircuits on a hist... more A pipeline is proposed here to describe different features to study brain microcircuits on a histological scale using multi-scale analyses, including the uniform manifold approximation and projection (UMAP) dimensional reduction technique and modularity algorithm to identify neuronal ensembles, Runs tests to show significant ensembles activation, graph theory to show trajectories between ensembles, and recurrence analyses to describe how regular or chaotic ensembles dynamics are. The data set includesex-vivoNMDA-activated striatal tissue in control conditions as well as experimental models of disease states: decorticated, dopamine depleted, and L-DOPA-induced dyskinetic rodent samples. The goal was to separate neuronal ensembles that have correlated activity patterns. The pipeline allows for the demonstration of differences between disease states in a brain slice. First, the ensembles were projected in distinctive locations in the UMAP space. Second, graphs revealed functional conne...
The activity of midbrain dopamine neurons is strikingly similar to the reward prediction error of... more The activity of midbrain dopamine neurons is strikingly similar to the reward prediction error of TD reinforcement learning models. Experimental evidence and simulation studies suggest that dopamine neuron activity serves as an effective reinforcement signal for learning of sensorimotor associations in striatal matrisomes. In the current study, we simulate dopamine neuron activity with the Extended TD model (Suri and Schultz, submitted) and examine the influence of this signal on medium spiny neurons in striatal matrisomes. This model includes transient membrane effects of dopamine, dopamine-dependent longterm adaptations of corticostriatal transmission, and rhythmic fluctuations of the membrane potential between an elevated "up-state" and a hyperpolarized "down-state." The most dominant activity in the striatal matrisomes elicits behaviors via projections from the basal ganglia to the thalamus and the cortex. This "standard model" performs successfully when tested for sensorimotor learning and goaldirected behavior (planning). To investigate the contributions of these model assumptions to learning and planning, we test the performance of several model variants that lack one of these mechanisms. These simulations show that the adaptation of the dopamine-like signal is necessary for planning and for sensorimotor learning. Lack of dopamine-like novelty responses decreases the number of exploratory acts, which deteriorates planning capabilities. Sensorimotor learning requires dopamine-dependent long-term adaptation of corticostriatal transmission. The model loses its planning capabilities if the dopamine-like signal is simulated with the original TD model. The capability for planning is improved by transient dopamine membrane effects, dopamine-dependent long-term effects on corticostriatal transmission, dopamine-and input-dependent influences on the durations of membrane potential fluctuations, and manipulations that prolong the reaction time of the model. These simulation results suggest that striatal dopamine is important for sensorimotor learning, exploration, and planning.
Human embryonic stem cells (hESCs) differentiate into specialized cells, including midbrain dopam... more Human embryonic stem cells (hESCs) differentiate into specialized cells, including midbrain dopaminergic neurons (DAN). Non-human primates (NHPs) injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine develop some alterations observed in Parkinson’s disease (PD) patients. We obtained DAN from hESCs and confirmed that they express dopaminergic markers, generate action potentials, and release dopamine (DA) in vitro. DAN were transplanted bilaterally in the putamen of parkinsonian NHPs. After grafting, animals improved motor behavior, evaluated by the HALLWAY task, and in agreement with this recovery, DA release was detected by microdialysis. Imaging techniques revealed changes in fractional anisotropy and mean diffusivity in magnetic resonance imaging and higher 11C-DTBZ binding in positron-emission tomography scans, associated with grafts. Postmortem analysis showed that transplanted DAN survived over ten months in the putamen, without developing tumors, in the immunosuppressed N...
i n Neostriatal Neurons similar morphology. In this restricted population, Ca2+ currents were fou... more i n Neostriatal Neurons similar morphology. In this restricted population, Ca2+ currents were found to be of the HVA type, in agreement with previous slice studies. To provide structural information about the channel types underlying these currents, single-cell mRNA expression profiling was performed to determine whether mRNA from one or more of the cloned HVA gene families could be detected in individual neurons subjected biophysical analysis. Materials and Methods Acute-dissociationprocedure. Neostriatal neurons from adult (> 4 weeks) rats were acutely dissociated using procedures similar to those we have previously described (Surmeier et al., 1991, 1992). In brief, rats were anesthetized with methoxyflurane and decapitated; brains were quickly removed, iced and then blocked for slicing. The blocked tissue was cut in 400 pm slices with a Vibroslice (Campden Instruments, London, England) while bathed in a low-Ca*+ (100 WM), N-[2-hydroxyethyllpiperazine-N-[2-ethanesulfonic acid] (HEPES)-buffered salt solution (in mM: 140 Na isethionate, 2 KCl, 4 MgCl,, 0.1 CaCl,, 23 glucose, 15 HEPES, pH = 7.4,300-305 mOsm/liter). Slices were then incubated for l-6 hr at room temperature (20-22°C
Current-clamp studies have shown that voltage-dependent Ca currents are present in rat neostriata... more Current-clamp studies have shown that voltage-dependent Ca currents are present in rat neostriatal neurons. Although these studies have provided evidence for the presence of high-voltage activated Ca channels, it has been unclear whether low-voltage activated channels are also present. Using the whole-cell variant of the patch-clamp technique, we have studied isolated Ca currents in an attempt to answer this question. We have found that both high-and low-voltage activated calcium currents are expressed by neostriatal neurons cultured from embryonic rat brain. These currents are similar in voltage-dependence and pharmacology to those found in other brain neurons.
Transient potassium currents of the A type are thought to be important in a number of physiologic... more Transient potassium currents of the A type are thought to be important in a number of physiological processes of excitable cells, including spike repolarization and synaptic integration. This functional diversity may reflect the contribution of distinct subtypes of A channel to cellular behavior. Using the whole-cell variant of the patch clamp technique, we have found that two types of A-current are expressed in rat neostriatal neurons, one that is similar to previous descriptions in mammals and a second that is activated at considerably more depolarized potentials.
Whole cell voltage-clamp recordings were made from cultured rat neostriatal neurons. Depolarizing... more Whole cell voltage-clamp recordings were made from cultured rat neostriatal neurons. Depolarizing voltage commands evoked transient and sustained outward K-currents. The transient K-current was activated by depolarizing commands beyond-50 mV; peak current was dependent upon holding potential. Bath application of 4-aminopyridine, but not inorganic calcium channel blockers (Cd, Co, Mn), attenuated the transient current. Reversal was near the K-equilibrium potential. These properties suggest that this transient K-current is similar to the A-current described in a number of other neurons.
American Journal of Physiology-cell Physiology, Apr 1, 2004
We studied the K ϩ-selective conductances in primary cultures of rat renal inner medullary collec... more We studied the K ϩ-selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above Ϫ20 mV induced a time-dependent outward K ϩ current (Ivto) similar to a delayed rectifier. Ivto showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K ϩ /Na ϩ selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba 2ϩ and was not Ca 2ϩ dependent. The delayed rectifying characteristics of Ivto prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv ␣-subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv ␣-subunit antibodies for Kv1.1 and Kv1.3 showed labeling of ϳ70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na ϩ-K ϩ-ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells.
Neuronal synchronization in basal ganglia circuits plays a key role in the encoding of movement, ... more Neuronal synchronization in basal ganglia circuits plays a key role in the encoding of movement, procedural memory storage and habit formation. Striatal dopamine (DA) depletion during Parkinsonism causes abnormal synchronization in corticobasal ganglia loops resulting in motor dysfunction. However, the dynamics of the striatal microcircuit underlying abnormal synchronization in Parkinsonism is poorly understood. Here we used targeted whole-cell recordings, calcium imaging allowing the recording from dozens of cells simultaneously and analytical approaches, to describe the striking alterations in network dynamics that the striatal microcircuit undergoes following DA depletion in a rat model of Parkinson disease (PD): In addition to a significant enhancement of basal neuronal activity frequent periods of spontaneous synchronization were observed. Multidimensional reduction techniques of vectorized network dynamics revealed that increased synchronization resulted from a dominant network state that absorbed most spontaneously active cells. Abnormal synchronous activity can be virtually abolished by glutamatergic antagonists, while blockade of GABAergic transmission facilitates the engagement of striatal cell assemblies in the dominant state. Finally, a dopaminergic receptor agonist was capable of uncoupling neurons from the dominant state. Abnormal synchronization and "locking" into a dominant state may represent the basic neuronal mechanism that underlies movement disorders at the microcircuit level.
Differences in the intrinsic properties of intralaminar thalamo-striatal neurons such as expressi... more Differences in the intrinsic properties of intralaminar thalamo-striatal neurons such as expressing low-threshold-spikes (LTS) or after hyperpolarizing potentials (AHPs) of different duration have been attributed to different maturation stages. However, two morphological types: "diffuse" and "bushy" have been described. Therefore, we explored whether electrophysiological differences persist in adult mice using whole cell recordings. Some recorded neurons were identified by intracellular labeling with biocytin and double labeling with retrograde or anterograde tracings using Cre-mice. We classified these neurons by their AHPs during spontaneous firing. Neurons with long duration AHPs, with fast and slow components, were mostly found in the parafascicular (Pf) nucleus. Neurons with brief AHPs were mainly found in the central lateral (CL) nucleus. However, neurons with both AHPs were found in both nuclei in different proportions. Firing frequency adaptation differed between these neuron classes: those with prolonged AHPs exhibited firing frequency adaptation with fast and slow time constants whereas those with brief AHPs were slow adapters. Neurons with more prolonged AHPs had significant higher input resistances than neurons with brief AHPs. Both cell classes could fire in two modes: trains of single action potentials at depolarized potentials or high frequency bursts on top of LTS at more hyperpolarized potentials. LTS were probably generated by Cav3 calcium channels since they were blocked by the selective antagonist TTA-P2. About 11% of neurons with brief AHPs and 55% of neurons with prolonged AHPs do not show LTS and bursts, even when potassium currents are blocked.
In recent years, there has been a great deal of progress toward understanding the role of the str... more In recent years, there has been a great deal of progress toward understanding the role of the striatum and dopamine in action selection. The advent of new animal models and the development of optical techniques for imaging and stimulating select neuronal populations has provided the means by which identified synapses, cells and circuits can be reliably studied. This review attempts to summarize some of the key advances in this broad area, focusing on dopaminergic modulation of intrinsic excitability and synaptic plasticity in canonical microcircuits in the striatum as well as recent work suggesting that there are neuronal assemblies within the striatum devoted to particular types of computation and possibly action selection.
Information processing through a neuronal microcircuit depends essentially on three major feature... more Information processing through a neuronal microcircuit depends essentially on three major features:(1) the anatomical organization and the function of its synaptic connections;(2) the biophysical or intrinsic properties of its neuronal elements; and (3) how the synaptic and ...
Adenosine A1 and A2A receptors are expressed in striatal projection neurons (SPNs). A1 receptors ... more Adenosine A1 and A2A receptors are expressed in striatal projection neurons (SPNs). A1 receptors are located in direct (dSPN) and indirect SPNs (iSNP). A2A receptors are only present in iSPNs. Dopamine D2 receptors are also expressed in iSPNs and interactions between D2 and A2A receptors have received attention. iSPNs activity increases during parkinsonism (PD) and A2A receptors may be responsible by enhancing Ca2+ currents (iCa2+). Therefore, A2A receptors blockade is a therapeutic approach. We asked whether A2A receptors need the interaction with D2 receptors (D2R) to exert their actions. By using isolated and identified iSPNs to avoid indirect influences, we show that D2R action habilitates A2A receptors (A2AR) modulation. iCa2+ through voltage gated Ca2+ channels (CaV) was used as a signal to observe this interaction. Voltage-clamp recordings in acutely dissociated iSPNs, current-clamp recordings in slices and calcium imaging in transgenic A2A-Cre mice, showed that D2R reduction...
Amantadine and clozapine have proved to reduce abnormal involuntary movements (AIMs) in preclinic... more Amantadine and clozapine have proved to reduce abnormal involuntary movements (AIMs) in preclinical and clinical studies of L-DOPA-Induced Dyskinesias (LID). Even though both drugs decrease AIMs, they may have different action mechanisms by using different receptors and signaling profiles. Here we asked whether there are differences in how they modulate neuronal activity of multiple striatal neurons within the striatal microcircuit at histological level during the dose-peak of L-DOPA in ex-vivo brain slices obtained from dyskinetic mice. To answer this question, we used calcium imaging to record the activity of dozens of neurons of the dorsolateral striatum before and after drugs administration in vitro. We also developed an analysis framework to extract encoding insights from calcium imaging data by quantifying neuronal activity, identifying neuronal ensembles by linking neurons that coactivate using hierarchical cluster analysis and extracting network parameters using Graph Theory. The results show that while both drugs reduce LIDs scores behaviorally in a similar way, they have several different and specific actions on modulating the dyskinetic striatal microcircuit. The extracted features were highly accurate in separating amantadine and clozapine effects by means of principal components analysis (PCA) and support vector machine (SVM) algorithms. These results predict possible synergistic actions of amantadine and clozapine on the dyskinetic striatal microcircuit establishing a framework for a bioassay to test novel antidyskinetic drugs or treatments in vitro.
Synaptic inputs from cortex and thalamus were compared in electrophysiologically defined striatal... more Synaptic inputs from cortex and thalamus were compared in electrophysiologically defined striatal cell classes: direct and indirect pathways' striatal projection neurons (dSPNs and iSPNs), fast-spiking interneurons (FS), cholinergic interneurons (ChINs), and low-threshold spiking-like (LTS-like) interneurons. Our purpose was to observe whether stimulus from cortex or thalamus had equivalent synaptic strength to evoke prolonged suprathreshold synaptic responses in these neuron classes. Subthreshold responses showed that inputs from either source functionally mix up in their dendrites at similar electrotonic distances from their somata. Passive and active properties of striatal neuron classes were consistent with the previous studies. Cre-dependent adeno-associated viruses containing Td-Tomato or eYFP fluorescent proteins were used to identify target cells. Transfections with ChR2-eYFP driven by the promoters CamKII or EF1.DIO in intralaminar thalamic nuclei using Vglut-2-Cre mice, or CAMKII in the motor cortex were used to stimulate cortical or thalamic afferents optogenetically. Both field stimuli in the cortex or photostimulation of ChR2-YFP cortical fibers evoked similar prolonged suprathreshold responses in SPNs. Photostimulation of ChR2-YFP thalamic afferents also evoked suprathreshold responses. Differences previously described between responses of dSPNs and iSPNs were observed in both cases. Prolonged suprathreshold responses could also be evoked from both sources onto all other neuron classes studied. However, to evoke thalamostriatal suprathreshold responses, afferents from more than one thalamic nucleus had to be stimulated. In conclusion, both thalamus and cortex are capable to generate suprathreshold responses converging on diverse striatal cell classes. Postsynaptic properties appear to shape these responses.
A pipeline is proposed here to describe different features to study brain microcircuits on a hist... more A pipeline is proposed here to describe different features to study brain microcircuits on a histological scale using multi-scale analyses, including the uniform manifold approximation and projection (UMAP) dimensional reduction technique and modularity algorithm to identify neuronal ensembles, Runs tests to show significant ensembles activation, graph theory to show trajectories between ensembles, and recurrence analyses to describe how regular or chaotic ensembles dynamics are. The data set includesex-vivoNMDA-activated striatal tissue in control conditions as well as experimental models of disease states: decorticated, dopamine depleted, and L-DOPA-induced dyskinetic rodent samples. The goal was to separate neuronal ensembles that have correlated activity patterns. The pipeline allows for the demonstration of differences between disease states in a brain slice. First, the ensembles were projected in distinctive locations in the UMAP space. Second, graphs revealed functional conne...
The activity of midbrain dopamine neurons is strikingly similar to the reward prediction error of... more The activity of midbrain dopamine neurons is strikingly similar to the reward prediction error of TD reinforcement learning models. Experimental evidence and simulation studies suggest that dopamine neuron activity serves as an effective reinforcement signal for learning of sensorimotor associations in striatal matrisomes. In the current study, we simulate dopamine neuron activity with the Extended TD model (Suri and Schultz, submitted) and examine the influence of this signal on medium spiny neurons in striatal matrisomes. This model includes transient membrane effects of dopamine, dopamine-dependent longterm adaptations of corticostriatal transmission, and rhythmic fluctuations of the membrane potential between an elevated "up-state" and a hyperpolarized "down-state." The most dominant activity in the striatal matrisomes elicits behaviors via projections from the basal ganglia to the thalamus and the cortex. This "standard model" performs successfully when tested for sensorimotor learning and goaldirected behavior (planning). To investigate the contributions of these model assumptions to learning and planning, we test the performance of several model variants that lack one of these mechanisms. These simulations show that the adaptation of the dopamine-like signal is necessary for planning and for sensorimotor learning. Lack of dopamine-like novelty responses decreases the number of exploratory acts, which deteriorates planning capabilities. Sensorimotor learning requires dopamine-dependent long-term adaptation of corticostriatal transmission. The model loses its planning capabilities if the dopamine-like signal is simulated with the original TD model. The capability for planning is improved by transient dopamine membrane effects, dopamine-dependent long-term effects on corticostriatal transmission, dopamine-and input-dependent influences on the durations of membrane potential fluctuations, and manipulations that prolong the reaction time of the model. These simulation results suggest that striatal dopamine is important for sensorimotor learning, exploration, and planning.
Human embryonic stem cells (hESCs) differentiate into specialized cells, including midbrain dopam... more Human embryonic stem cells (hESCs) differentiate into specialized cells, including midbrain dopaminergic neurons (DAN). Non-human primates (NHPs) injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine develop some alterations observed in Parkinson’s disease (PD) patients. We obtained DAN from hESCs and confirmed that they express dopaminergic markers, generate action potentials, and release dopamine (DA) in vitro. DAN were transplanted bilaterally in the putamen of parkinsonian NHPs. After grafting, animals improved motor behavior, evaluated by the HALLWAY task, and in agreement with this recovery, DA release was detected by microdialysis. Imaging techniques revealed changes in fractional anisotropy and mean diffusivity in magnetic resonance imaging and higher 11C-DTBZ binding in positron-emission tomography scans, associated with grafts. Postmortem analysis showed that transplanted DAN survived over ten months in the putamen, without developing tumors, in the immunosuppressed N...
i n Neostriatal Neurons similar morphology. In this restricted population, Ca2+ currents were fou... more i n Neostriatal Neurons similar morphology. In this restricted population, Ca2+ currents were found to be of the HVA type, in agreement with previous slice studies. To provide structural information about the channel types underlying these currents, single-cell mRNA expression profiling was performed to determine whether mRNA from one or more of the cloned HVA gene families could be detected in individual neurons subjected biophysical analysis. Materials and Methods Acute-dissociationprocedure. Neostriatal neurons from adult (> 4 weeks) rats were acutely dissociated using procedures similar to those we have previously described (Surmeier et al., 1991, 1992). In brief, rats were anesthetized with methoxyflurane and decapitated; brains were quickly removed, iced and then blocked for slicing. The blocked tissue was cut in 400 pm slices with a Vibroslice (Campden Instruments, London, England) while bathed in a low-Ca*+ (100 WM), N-[2-hydroxyethyllpiperazine-N-[2-ethanesulfonic acid] (HEPES)-buffered salt solution (in mM: 140 Na isethionate, 2 KCl, 4 MgCl,, 0.1 CaCl,, 23 glucose, 15 HEPES, pH = 7.4,300-305 mOsm/liter). Slices were then incubated for l-6 hr at room temperature (20-22°C
Current-clamp studies have shown that voltage-dependent Ca currents are present in rat neostriata... more Current-clamp studies have shown that voltage-dependent Ca currents are present in rat neostriatal neurons. Although these studies have provided evidence for the presence of high-voltage activated Ca channels, it has been unclear whether low-voltage activated channels are also present. Using the whole-cell variant of the patch-clamp technique, we have studied isolated Ca currents in an attempt to answer this question. We have found that both high-and low-voltage activated calcium currents are expressed by neostriatal neurons cultured from embryonic rat brain. These currents are similar in voltage-dependence and pharmacology to those found in other brain neurons.
Transient potassium currents of the A type are thought to be important in a number of physiologic... more Transient potassium currents of the A type are thought to be important in a number of physiological processes of excitable cells, including spike repolarization and synaptic integration. This functional diversity may reflect the contribution of distinct subtypes of A channel to cellular behavior. Using the whole-cell variant of the patch clamp technique, we have found that two types of A-current are expressed in rat neostriatal neurons, one that is similar to previous descriptions in mammals and a second that is activated at considerably more depolarized potentials.
Whole cell voltage-clamp recordings were made from cultured rat neostriatal neurons. Depolarizing... more Whole cell voltage-clamp recordings were made from cultured rat neostriatal neurons. Depolarizing voltage commands evoked transient and sustained outward K-currents. The transient K-current was activated by depolarizing commands beyond-50 mV; peak current was dependent upon holding potential. Bath application of 4-aminopyridine, but not inorganic calcium channel blockers (Cd, Co, Mn), attenuated the transient current. Reversal was near the K-equilibrium potential. These properties suggest that this transient K-current is similar to the A-current described in a number of other neurons.
American Journal of Physiology-cell Physiology, Apr 1, 2004
We studied the K ϩ-selective conductances in primary cultures of rat renal inner medullary collec... more We studied the K ϩ-selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above Ϫ20 mV induced a time-dependent outward K ϩ current (Ivto) similar to a delayed rectifier. Ivto showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K ϩ /Na ϩ selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba 2ϩ and was not Ca 2ϩ dependent. The delayed rectifying characteristics of Ivto prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv ␣-subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv ␣-subunit antibodies for Kv1.1 and Kv1.3 showed labeling of ϳ70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na ϩ-K ϩ-ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells.
Neuronal synchronization in basal ganglia circuits plays a key role in the encoding of movement, ... more Neuronal synchronization in basal ganglia circuits plays a key role in the encoding of movement, procedural memory storage and habit formation. Striatal dopamine (DA) depletion during Parkinsonism causes abnormal synchronization in corticobasal ganglia loops resulting in motor dysfunction. However, the dynamics of the striatal microcircuit underlying abnormal synchronization in Parkinsonism is poorly understood. Here we used targeted whole-cell recordings, calcium imaging allowing the recording from dozens of cells simultaneously and analytical approaches, to describe the striking alterations in network dynamics that the striatal microcircuit undergoes following DA depletion in a rat model of Parkinson disease (PD): In addition to a significant enhancement of basal neuronal activity frequent periods of spontaneous synchronization were observed. Multidimensional reduction techniques of vectorized network dynamics revealed that increased synchronization resulted from a dominant network state that absorbed most spontaneously active cells. Abnormal synchronous activity can be virtually abolished by glutamatergic antagonists, while blockade of GABAergic transmission facilitates the engagement of striatal cell assemblies in the dominant state. Finally, a dopaminergic receptor agonist was capable of uncoupling neurons from the dominant state. Abnormal synchronization and "locking" into a dominant state may represent the basic neuronal mechanism that underlies movement disorders at the microcircuit level.
Differences in the intrinsic properties of intralaminar thalamo-striatal neurons such as expressi... more Differences in the intrinsic properties of intralaminar thalamo-striatal neurons such as expressing low-threshold-spikes (LTS) or after hyperpolarizing potentials (AHPs) of different duration have been attributed to different maturation stages. However, two morphological types: "diffuse" and "bushy" have been described. Therefore, we explored whether electrophysiological differences persist in adult mice using whole cell recordings. Some recorded neurons were identified by intracellular labeling with biocytin and double labeling with retrograde or anterograde tracings using Cre-mice. We classified these neurons by their AHPs during spontaneous firing. Neurons with long duration AHPs, with fast and slow components, were mostly found in the parafascicular (Pf) nucleus. Neurons with brief AHPs were mainly found in the central lateral (CL) nucleus. However, neurons with both AHPs were found in both nuclei in different proportions. Firing frequency adaptation differed between these neuron classes: those with prolonged AHPs exhibited firing frequency adaptation with fast and slow time constants whereas those with brief AHPs were slow adapters. Neurons with more prolonged AHPs had significant higher input resistances than neurons with brief AHPs. Both cell classes could fire in two modes: trains of single action potentials at depolarized potentials or high frequency bursts on top of LTS at more hyperpolarized potentials. LTS were probably generated by Cav3 calcium channels since they were blocked by the selective antagonist TTA-P2. About 11% of neurons with brief AHPs and 55% of neurons with prolonged AHPs do not show LTS and bursts, even when potassium currents are blocked.
In recent years, there has been a great deal of progress toward understanding the role of the str... more In recent years, there has been a great deal of progress toward understanding the role of the striatum and dopamine in action selection. The advent of new animal models and the development of optical techniques for imaging and stimulating select neuronal populations has provided the means by which identified synapses, cells and circuits can be reliably studied. This review attempts to summarize some of the key advances in this broad area, focusing on dopaminergic modulation of intrinsic excitability and synaptic plasticity in canonical microcircuits in the striatum as well as recent work suggesting that there are neuronal assemblies within the striatum devoted to particular types of computation and possibly action selection.
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Papers by José Bargas