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| 2. |
- Hellgren Kotaleski, Jeanette, et al.
(författare)
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Sensitivity to interstimulus interval due to calcium interactions in the Purkinje cell spines
- 2002
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 44, s. 13-18
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Tidskriftsartikel (refereegranskat)abstract
- Pairing specific LTD (PSD) is produced by paired parallel fiber (PF) and climbing fiber (CF) stimulation and requires Ca2+ elevation. CF or PF activation cause Ca2+ increase through voltage dependent channels and IP3 induced Ca2+ release, respectively. We developed a model of Ca2+ dynamics in Purkinje cell spines to investigate why paired PF-CF activation is necessary for PSD. Simulations show a supralinear increase of the Ca2+ signal if the CF input occurs in a restricted time interval following the PF input. Ca2- buffers significantly contribute to this phenomenon. This mechanism may be involved in the requirement of temporal specificity in classical conditioning.
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| 3. |
- Hellgren Kotaleski, Jeanette, et al.
(författare)
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Simulation of metabotropic glutamate receptor induced effects in the lamprey CPG
- 2000
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- Metabotropic glutamate receptor (mGluR) activation modulates the lamprey spinal locomotor network. Potentiation of the NMDA receptor current is observed suggesting that one possible mechanism for mGluR to regulate locomotion is through such an interaction. The present study investigates this possibility. The behavior of NMDA induced oscillations are explored when potentiation is achieved of different contributing factors of the NMDA receptor current. The effects on the duration of the depolarized phase as well as hyperpolarized interval depend on both level of activation and holding potential of the cells. From these effects on the cell level the network effects are predicted.
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| 4. |
- Hellgren Kotaleski, Jeanette, et al.
(författare)
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Subcellular interactions between parallel fibre and climbing fibre signals in Purkinje cells predict sensitivity of classical conditioning to interstimulus interval
- 2002
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Ingår i: Integrative Physiological & Behavioral Science. - 1053-881X .- 2168-7846. ; 37:4, s. 265-292
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Tidskriftsartikel (refereegranskat)abstract
- Classical conditioning of the nictitating membrane response requires a specific temporal interval between conditioned stimulus and unconditioned stimulus, and produces an increase in Protein Kinase C (PKC) activation in Purkinje cells. To evaluate whether biochemical interactions within the Purkinje cell may explain the temporal sensitivity, a model of PKC activation by Ca2+, diacylglycerol (DAG), and arachidonic acid (AA) is developed. Ca2+ elevation is due to CF stimulation and IP3 induced Ca2+ release (IICR). DAG and IP3 result from PF stimulation, while AA results from phospholipase A2 (PLA(2)). Simulations predict increased PKC activation when PF stimulation precedes CF stimulation by 0.1 to 3 s. The sensitivity of IICR to the temporal relation between PF and CF stimulation, together with the buffering system of Purkinje cells, significantly contribute to the temporal sensitivity.
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| 5. |
- Huss, Mikael, et al.
(författare)
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Role of A-current in lamprey locomotor network neurons
- 2003
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Ingår i: Neurocomputing. - : Elsevier BV. - 0925-2312 .- 1872-8286. ; 52-54, s. 295-300
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Tidskriftsartikel (refereegranskat)abstract
- A compartmental model of lamprey central pattern generator neurons was built in order to examine the effects of a fast, transient, high-voltage-activated potassium current (A-current) found experimentally. The model consisted of a soma, a compartment corresponding to the axon initial segment, and a dendritic tree. The simulation showed that the A-current was necessary for repetitive spiking in the single neuron following current injection. The functional role of adding an A-current was also examined in a network model. In this model, the A-current stabilizes the swimming rhythm by making the burst cycle duration and the number of spikes per burst less variable. All these effects are also seen experimentally.
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| 6. |
- Kozlov, Alexander, et al.
(författare)
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Detailed reduced models excitatory hemi-cord locomotor network lamprey
- 2003
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Rhythmic locomotor-related activity can be induced in the isolated hemi-spinal cord of lamprey during bath application of D-glutamate or NMDA (Cangiano and Grillner, 2003). This bursting activity is not dependent on glycinergic inhibition but relies on mutual glutamatergic excitation among network interneurons. The possibility of such oscillatory activity was suggested by earlier simulations (Hellgren-Kotaleski et al. 1999). Here the underlying mechanisms are further examined using both detailed and reduced mathematical models. The detailed network model comprises a population of compartmental excitatory interneurones with Na+, K+, Ca2+, KCa channels as well as two Ca-pools. The synaptic interactions are mediated by AMPA receptors and voltage-dependent NMDA receptors, as established experimentally. This model reproduces the main experimental observations on both cell and network level, including the slow (NMDA/Mg2+ dependent) and the fast rhythm. Burst frequency can be modulated by changing the AMPA and/or NMDA drive, the latter providing only a narrow dynamic range. Further, the distributed network of the entire hemi-cord has been simulated. A weakly asymmetric rostro-caudal connectivity (stronger descending) could support a uniform intersegmental phase lag along most of the spinal cord, whereas a symmetric connectivity could not. The intersegmental phase lag is effectively controlled (forward and backward direction) by adding excitation or inhibition to the most rostral segments. The detailed model was progressively reduced until only the most important (slow) currents remained. The dynamics of the reduced model followed that of the detailed model. Ca influx and activation of KCa currents was shown to play a key role in the burst generation.
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| 7. |
- Kozlov, A. K., et al.
(författare)
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Modeling control of roll-plane body orientation in lamprey
- 2000
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 871-877
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Tidskriftsartikel (refereegranskat)abstract
- A phenomenological model of the mechanism of stabilization of the dorsal-side-up orientation in the lamprey is suggested. Mathematical modeling is based on the experimental results on investigation of postural control in lampreys using combined in vivo and robotics approaches. Dynamics of the model agrees qualitatively with the experiment. It is shown by computer simulations that postural correction commands from one or several reticulospinal neurons provide information which may be sufficient for stabilization of body orientation in the lamprey.
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| 8. |
- Kozlov, A. K., et al.
(författare)
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Modeling postural control in the lamprey
- 2001
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Ingår i: Biological Cybernetics. - : Springer Nature. - 0340-1200 .- 1432-0770. ; 84:5, s. 323-330
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Tidskriftsartikel (refereegranskat)abstract
- A phenomenological model of the mechanism of stabilization of the body orientation during locomotion (dorsal side up) in the lamprey is presented. The mathematical modeling is based on experimental results obtained during investigations of postural control in lampreys using a combined in vivo and robotics approach. The dynamics of the model agree qualitatively with the experimental data. It is shown by computer simulations that postural correction commands from reticulospinal neurons provide information sufficient to stabilize body orientation in the lamprey. The model is based on differences between the effects exerted by the vestibular apparatus on the left and the right side.
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| 9. |
- Kozlov, Alexander, et al.
(författare)
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Modeling of plasticity of the synaptic connections in the lamprey spinal CPG - consequences for network behavior
- 2000
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 441-446
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Tidskriftsartikel (refereegranskat)abstract
- Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed. This is motivated by the experimentally found effects substance P and 5-hydroxytryptamin (5-HT) have on the inhibitory and excitatory synaptic transmission. The effects can be a change of the amplitude of the postsynaptic potentials as well as induction of an activity-dependent facilitation or depression during repetitive activation. Simulations show that network level effects (i.e. swimming frequency) of substance P and 5-HT can to a substantial part be explained based on their effects on the plasticity of the synaptic transmission.
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| 10. |
- Kozlov, Alexander, et al.
(författare)
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Modeling of substance P and 5-HT induced synaptic plasticity in the lamprey spinal CPG : Consequences for network pattern generation
- 2001
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Ingår i: Journal of Computational Neuroscience. - 0929-5313 .- 1573-6873. ; 11:2, s. 183-200
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Tidskriftsartikel (refereegranskat)abstract
- Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed by means of simulations. This is motivated by the effects substance P (a tachykinin) and serotonin (5-hydroxytryptamin; 5-HT) have on synaptic transmission in the locomotor network. Activity-dependent synaptic depression and potentiation have recently been shown experimentally using paired intracellular recordings. Although normally activity-dependent plasticity presumably does not contribute to the patterning of network activity, this changes in the presence of the neuromodulators substance P and 5-HT, which evoke significant plasticity. Substance P can induce a faster and larger depression of inhibitory connections but potentiation of excitatory inputs, whereas 5-HT induces facilitation of both inhibitory and excitatory inputs. Changes in the amplitude of the first postsynaptic potential are also seen. These changes could thus be a potential mechanism underlying the modulatory role these substances have on the rhythmic network activity. The aim of the present study has been to implement the activity dependent synaptic depression and facilitation induced by substance P and 5-HT into two alternative models of the lamprey spinal locomotor network, one relying on reciprocal inhibition for bursting and one in which each hemicord is capable of oscillations. The consequences of the plasticity of inhibitory and excitatory connections are then explored on the network level. In the intact spinal cord, tachykinins and 5-HT, which can be endogenously released, increase and decrease the frequency of the alternating left-right burst pattern, respectively. The frequency decreasing effect of 5-HT has previously been explained based on its conductance decreasing effect on K underlying the postspike afterhyperpolarization (AHP). The present simulations show that short-term synaptic plasticity may have strong effects on frequency regulation in the lamprey spinal CPG. In the network model relying on reciprocal inhibition, the observed effects substance P and 5-HT have on network behavior (i.e., a frequency increase and decrease respectively) can to a substantial part be explained by their effects on the total extent and time dynamics of synaptic depression and facilitation. The cellular effects of these substances will in the 5-HT case further contribute to its network effect.
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