| 1. |
- Lebedev, Alexander, 2000-, et al.
(författare)
-
A study of thick 3C-SiC epitaxial layers grown on 6H-SiC substrates by sublimation epitaxy in vacuum
- 2007
-
Ingår i: Semiconductors (Woodbury, N.Y.). - 1063-7826 .- 1090-6479. ; 41:3, s. 263-265
-
Tidskriftsartikel (refereegranskat)abstract
- 3C-SiC epitaxial layers with a thickness of up to 100 μm were grown on 6H-SiC hexagonal substrates by sublimation epitaxy in vacuum. The n-type epitaxial layers with the area in the range 0.3-0.5 cm2 and uncompensated donor concentration N d - N a ∼ (10 17-1018) cm-3 were produced at maximum growth rates of up to 200 μm/h. An X-ray analysis demonstrated that the epitaxial layers are composed of the 3C-SiC polytype, without inclusions of other polytypes. The photoluminescence (PL) spectrum of the layers was found to be dominated by the donor-acceptor (Al-N) recombination band peaked at hv ≈ 2.12 eV. The PL spectrum measured at 6 K was analyzed in detail. It is concluded that the epitaxial layers obtained can serve as substrates for 3C-SiC-based electronic devices. © Nauka/Interperiodica 2007.
|
|
| 2. |
|
|
| 3. |
- Wang, YQ, et al.
(författare)
-
Muscle-selective RUNX3 dependence of sensorimotor circuit development
- 2019
-
Ingår i: Development (Cambridge, England). - : The Company of Biologists. - 1477-9129 .- 0950-1991. ; 146:20
-
Tidskriftsartikel (refereegranskat)abstract
- The control of all our motor outputs requires constant monitoring by proprioceptive sensory neurons (PSNs) that convey continuous muscle sensory inputs to the spinal motor network. Yet, the molecular programs that control the establishment of this sensorimotor circuit remain largely unknown. The transcription factor RUNX3 is essential for the early steps of PSNs differentiation, making it difficult to study its role during later aspects of PSNs specification. Here, we conditionally inactivate Runx3 in PSNs after peripheral innervation and identify that RUNX3 is necessary for maintenance of cell identity of only a subgroup of PSNs, without discernable cell death. RUNX3 controls also the sensorimotor connection between PSNs and motor neurons at limb level, with muscle-by-muscle variable sensitivities to the loss of Runx3 that correlate with levels of RUNX3 in PSNs. Finally, we find that muscles and neurotrophin-3 signaling are necessary for maintenance of RUNX3 expression in PSNs. Hence, a transcriptional regulator critical for specifying a generic PSN type identity after neurogenesis, is later regulated by target muscle-derived signal to contribute to the specialized aspects of the sensorimotor connection selectivity.
|
|
| 4. |
|
|
| 5. |
- Agren, J, et al.
(författare)
-
Aquaporin-1 and -3 in perinatal skin
- 1999
-
Ingår i: PEDIATRIC RESEARCH. - : Springer Science and Business Media LLC. - 0031-3998 .- 1530-0447. ; 45:4, s. 47A-47A
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
- Beloozerova, IN, et al.
(författare)
-
Postural control in the rabbit maintaining balance on the tilting platform
- 2003
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:6, s. 3783-3793
-
Tidskriftsartikel (refereegranskat)abstract
- A deviation from the dorsal-side-up body posture in quadrupeds activates the mechanisms for postural corrections. Operation of these mechanisms was studied in the rabbit maintaining balance on a platform periodically tilted in the frontal plane. First, we characterized the kinematics and electromyographic (EMG) patterns of postural responses to tilts. It was found that a reaction to tilt includes an extension of the limbs on the side moving down and flexion on the opposite side. These limb movements are primarily due to a modulation of the activity of extensor muscles. Second, it was found that rabbits can effectively maintain the dorsal-side-up body posture when complex postural stimuli are applied, i.e., asynchronous tilts of the platforms supporting the anterior and posterior parts of the body. These data suggest that the nervous mechanisms controlling positions of these parts of the body can operate independently of each other. Third, we found that normally the somatosensory input plays a predominant role for the generation of postural responses. However, when the postural response appears insufficient to maintain balance, the vestibular input contributes considerably to activation of postural mechanisms. We also found that an asymmetry in the tonic vestibular input, caused by galvanic stimulation of the labyrinths, can affect the stabilized body orientation while the magnitude of postural responses to tilts remains unchanged. Fourth, we found that the mechanisms for postural corrections respond only to tilts that exceed a certain (threshold) value.
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Deliagina, TG, et al.
(författare)
-
Activity of reticulospinal neurons during locomotion in the freely behaving lamprey
- 2000
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 83:2, s. 853-863
-
Tidskriftsartikel (refereegranskat)abstract
- The reticulospinal (RS) system is the main descending system transmitting commands from the brain to the spinal cord in the lamprey. It is responsible for initiation of locomotion, steering, and equilibrium control. In the present study, we characterize the commands that are sent by the brain to the spinal cord in intact animals via the reticulospinal pathways during locomotion. We have developed a method for recording the activity of larger RS axons in the spinal cord in freely behaving lampreys by means of chronically implanted macroelectrodes. In this paper, the mass activity in the right and left RS pathways is described and the correlations of this activity with different aspects of locomotion are discussed. In quiescent animals, the RS neurons had a low level of activity. A mild activation of RS neurons occurred in response to different sensory stimuli. Unilateral eye illumination evoked activation of the ipsilateral RS neurons. Unilateral illumination of the tail dermal photoreceptors evoked bilateral activation of RS neurons. Water vibration also evoked bilateral activation of RS neurons. Roll tilt evoked activation of the contralateral RS neurons. With longer or more intense sensory stimulation of any modality and laterality, a sharp, massive bilateral activation of the RS system occurred, and the animal started to swim. This high activity of RS neurons and swimming could last for many seconds after termination of the stimulus. There was a positive correlation between the level of activity of RS system and the intensity of locomotion. An asymmetry in the mass activity on the left and right sides occurred during lateral turns with a 30% prevalence (on average) for the ipsilateral side. Rhythmic modulation of the activity in RS pathways, related to the locomotor cycle, often was observed, with its peak coinciding with the electromyographic (EMG) burst in the ipsilateral rostral myotomes. The pattern of vestibular response of RS neurons observed in the quiescent state, that is, activation with contralateral roll tilt, was preserved during locomotion. In addition, an inhibition of their activity with ipsilateral tilt was clearly seen. In the cases when the activity of individual neurons could be traced during swimming, it was found that rhythmic modulation of their firing rate was superimposed on their tonic firing or on their vestibular responses. In conclusion, different aspects of locomotor activity—initiation and termination, vigor of locomotion, steering and equilibrium control—are well reflected in the mass activity of the larger RS neurons.
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Gunnarson, E., et al.
(författare)
-
Lead induces increased water permeability in astrocytes expressing aquaporin 4
- 2005
-
Ingår i: Neuroscience. - : Elsevier BV. - 0306-4522 .- 1873-7544. ; 136:1, s. 105-114
-
Tidskriftsartikel (refereegranskat)abstract
- The water channel aquaporin 4 (AQP4) is abundantly expressed in astrocytes. There is now compelling evidence that AQP4 may contribute to an unfavorable course in brain edema. Acute lead intoxication is a condition that causes brain damage preceded by brain edema. Here we report that lead increases AQP4 water permeability (P-f) in astrocytes. A rat astrocyte cell line that does not express aquaporin 4 was transiently transfected with aquaporin 4 tagged with green fluorescent protein (GFP). Using confocal laser scanning microscopy we measured water permeability in these cells and in AQP4-negative cells located on the same plate. AQP4-expressing astrocytes had a three-fold higher water permeability than astrocytes not expressing AQP4. Lead exposure induced a significant, 40%, increase in water permeability in astrocytes expressing AQP4, but had no effect on Pf in astrocytes not expressing AQP4. The increase in water permeability persisted after lead washout, while treatment with a lead chelator, meso-2,3-dimercaptosuccinic acid, abolished the lead-induced increase in Pf. The effect of lead was attenuated in the presence of a calcium (Ca2+)/ calmodulin-dependent protein kinase 11 (CaMKII) inhibitor, but not in the presence of a protein kinase C inhibitor. In cells expressing AQP4 where the consensus site for CaMKII phosphorylation was mutated, lead failed to increase water permeability. Lead exposure also increased Pf in rat astroglial cells in primary culture, which express endogenous AQP4. Lead had no effect on Pf in astrocytes transfected with aquaporin 3. In situ hybridization studies on rat brain after oral lead intake for three days showed no change in distribution of AQP4 mRNA. It is suggested that lead-triggered stimulation of water transport in AQP4-expressing astrocytes may contribute to the pathology of acute lead intoxication.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
- Illarionova, N. B., et al.
(författare)
-
FUNCTIONAL AND MOLECULAR INTERACTIONS BETWEEN AQUAPORINS AND Na,K-ATPase
- 2010
-
Ingår i: Neuroscience. - : Elsevier BV. - 0306-4522 .- 1873-7544. ; 168:4, s. 915-925
-
Tidskriftsartikel (refereegranskat)abstract
- The water channel aquaporin 4 (AQP4) is abundantly expressed in astrocytes and provides a mechanism by which water permeability of the plasma membrane can be regulated. Astrocytes play a key role in the clearance of both potassium (K+) and glutamate released during neuronal activity. Emerging evidence suggests that AQP4 facilitates K+ clearance by astrocytes and contributes to recovery of neuronal excitability. Here we report that AQP4 can assemble with its regulator metabotropic glutamate receptor 5 (mGluR5) and with Na,K-ATPase; the enzyme responsible for active K+ transport and for establishing the electrochemical gradient across the cell plasma membrane. We have, by use of pull down assays in rat brain tissue, identified the segment in the AQP4 NH2-terminus containing the amino acid residues 23-32 as the site for interaction with Na,K-ATPase catalytic subunit and with mGluR5. Mutagenesis studies revealed that the AQP4 amino acids K27 and W30 are of key importance for interaction with both Na,K-ATPase and mGluR5. To confirm that interaction also occurs within intact cells, we have performed fluorescence resonance energy transfer (FRET) studies in primary astrocytes derived from rat striatum. The results indicate close proximity of wild type AQP4 and Na,K-ATPase in the plasma membrane of rat astrocytes. FRET efficiencies observed with the mutants AQP4 K27A and AQP4 W30A were significantly lower, highlighting the importance of these residues for the interaction between AQP4 and Na,K-ATPase. We conclude that AQP4/Na,K-ATPase/mGluR5 can form a macromolecular complex/transporting microdomain in astrocytes. This complex may be of functional importance for the regulation of water and K+ homeostasis in the brain, as well as for neuron-astrocyte metabolic crosstalk. (C) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.
|
|
| 27. |
- Islam, SS, et al.
(författare)
-
Pattern of motor coordination underlying backward swimming in the lamprey
- 2006
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 96:1, s. 451-460
-
Tidskriftsartikel (refereegranskat)abstract
- The main form of locomotion in the lamprey (a lower vertebrate, cyclostome) is forward swimming (FS) based on periodical waves of lateral body flexion propagating from head to tail. The lamprey is also capable of backward swimming (BS). Here we describe the kinematical and electromyographic (EMG) pattern of BS, as well as the effects on this pattern exerted by different lesions of the spinal cord. The BS was evoked by tactile stimulation of a large area in the anterior part of the body. Swimming was attributed to the waves of lateral body undulations propagating from tail to head. The EMG bursts on the two sides alternated, and the EMG in more caudal segments led in phase the EMG in more rostral segments. Main kinematical characteristics of BS strongly differed from those of FS: the amplitude of undulations was much larger and their frequency lower. Also, the maintenance of the dorsal-side-up body orientation ascribed to vestibular postural reflexes (typical for FS) was not observed during BS. A complete transection of the spinal cord did not abolish the generation of forward-propagating waves rostral to the lesion. After a lateral hemisection of the spinal cord, the BS pattern persisted on both sides rostral to the lesion; caudal to the lesion, it was present on the intact side and reduced or abolished on the lesioned side. The role of the spinal cord in generation of different forms of undulatory locomotion (FS and BS) is discussed.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
|
|
| 31. |
|
|
| 32. |
- Khan, F, et al.
(författare)
-
Negative reciprocity between angiotensin II type 1 and dopamine D1 receptors in rat renal proximal tubule cells
- 2008
-
Ingår i: American journal of physiology. Renal physiology. - : American Physiological Society. - 1931-857X .- 1522-1466. ; 295:4, s. F1110-F1116
-
Tidskriftsartikel (refereegranskat)abstract
- Sodium excretion is bidirectionally regulated by dopamine, acting on D1-like receptors (D1R) and angiotensin II, acting on AT1 receptors (AT1R). Since sodium excretion has to be regulated with great precision within a short frame of time, we tested the short-term effects of agonist binding on the function of the reciprocal receptor within the D1R-AT1R complex in renal proximal tubule cells. Exposure of rat renal proximal tubule cells to a D1 agonist was found to result in a rapid partial internalization of AT1R and complete abolishment of AT1R signaling. Similarly, exposure of rat proximal tubule cells and renal tissue to angiotensin II resulted in a rapid partial internalization of D1R and abolishment of D1R signaling. D1R and AT1R were, by use of coimmunoprecipitation studies and glutathione- S-transferase pull-down assays, shown to be partners in a multiprotein complex. Na+-K+-ATPase, the target for both receptors, was included in this complex, and a region in the COOH-terminal tail of D1R (residues 397-416) was found to interact with both AT1R and Na+-K+-ATPase. Results indicate that AT1R and D1R function as a unit of opposites, which should provide a highly versatile and sensitive system for short-term regulation of sodium excretion.
|
|
| 33. |
- Kozlov, A. K., et al.
(författare)
-
Modeling control of roll-plane body orientation in lamprey
- 2000
-
Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 871-877
-
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.
|
|
| 34. |
- Kozlov, A. K., et al.
(författare)
-
Modeling postural control in the lamprey
- 2001
-
Ingår i: Biological Cybernetics. - : Springer Nature. - 0340-1200 .- 1432-0770. ; 84:5, s. 323-330
-
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.
|
|
| 35. |
- Lal, MA, et al.
(författare)
-
Combined antioxidant and COMT inhibitor treatment reverses renal abnormalities in diabetic rats
- 2000
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 49:8, s. 1381-1389
-
Tidskriftsartikel (refereegranskat)abstract
- The development and progression of diabetic nephropathy is dependent on glucose homeostasis and many other contributing factors. In the present study, we examined the effect of nitecapone, an inhibitor of the dopamine-metabolizing enzyme catechol-O-methyl transferase (COMT) and a potent antioxidant, on functional and cellular determinants of renal function in rats with streptozotocin-induced diabetes. Administration of nitecapone to diabetic rats normalized urinary sodium excretion in a manner consistent with the dopamine-dependent inhibition of proximal tubule Na,K-ATPase activity. Hyperfiltration, focal glomerulosclerosis, and albuminuria were also reversed by nitecapone, but in a manner that is more readily attributed to the antioxidant potential of the agent. A pattern of elevated oxidative stress, measured as CuZn superoxide dismutase gene expression and thiobarbituric acid-reactive substance content, was noted in diabetic rats, and both parameters were normalized by nitecapone treatment. In diabetic rats, activation of glomerular protein kinase C (PKC) was confirmed by isoform-specific translocation and Ser23 phosphorylation of the PKC substrate Na,K-ATPase. PKC-dependent changes in Na,K-ATPase phosphorylation were associated with decreased glomerular Na,K-ATPase activity. Nitecapone-treated diabetic rats were protected from these intracellular modifications. The combined results suggest that the COMT-inhibitory and antioxidant properties of nitecapone provide a protective therapy against the development of diabetic nephropathy.
|
|
| 36. |
- Lebedev, A.A., et al.
(författare)
-
Studying 3C-SiC epilayers grown on the (0001)C face of 6H-SiC substrates
- 2007
-
Ingår i: Technical physics letters. - 1063-7850 .- 1090-6533. ; 33:6, s. 524-526
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial 3C-SiC films grown on the (0001)C face of 6H-SiC substrates by sublimation epitaxy in vacuum have been studied. The results of x-ray diffraction measurements show evidence of a rather high structural perfection of silicon carbide epilayers. The Raman spectroscopy data confirm that the 3C-SiC layer grows immediately on the 6H-SiC substrate without any transition layers. It is concluded that the structures under consideration are well suited for the investigation of a two-dimensional electron gas at the 3C-SiC/6C-SiC heterojunction. © Nauka/Interperiodica 2007.
|
|
| 37. |
|
|
| 38. |
|
|
| 39. |
- Lyalka, VF, et al.
(författare)
-
Impairment and recovery of postural control in rabbits with spinal cord lesions
- 2005
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 94:6, s. 3677-3690
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to characterize impairment and subsequent recovery of postural control after spinal cord injuries. Experiments were carried out on rabbits with three types of lesion—a dorsal (D), lateral (L), or ventral (V) hemisection (HS) at T12 level. The animals were maintaining equilibrium on a platform periodically tilted in the frontal plane. We assessed the postural limb/trunk configuration from video recordings and postural reflexes in the hindquarters from kinematical and electromyographic (EMG) recordings. We found that for a few days after DHS or LHS, the animals were not able to maintain the dorsal-side-up position of their hindquarters. This ability was then gradually restored, and the dynamic postural reflexes reached the prelesion value within 2–3 wk. By contrast, a VHS almost completely abolished postural reflexes, and they did not recover for ≥7 wk. The DHS, LHS, and VHS caused immediate and slowly compensated changes in the postural limb/trunk configuration as well as gradually developing changes. After DHS, both hind limbs were placed in an abnormal rostral and medial position. After LHS, the limb on the undamaged side was turned inward and occurred at the abnormal medial position; LHS also caused a gradually developing twisting of the caudal trunk. VHS caused gradually developing extension of the ankle and knee joints. These findings show that ventral spinal pathways are of crucial importance for postural control. When a part of these pathways is spared, postural reflexes can be restored rapidly, but not the postural limb/trunk configuration. Spinal and supraspinal mechanisms responsible for postural deficits and their compensation are discussed.
|
|
| 40. |
- Miyakawa-Naito, A., et al.
(författare)
-
Cell signaling Microdomain with Na,K-ATPase and inositol 1,4,5-trisphosphate receptor generates calcium oscillations
- 2003
-
Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 17:4, s. A43-A43
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies indicate novel roles for the ubiquitous ion pump, Na,K-ATPase, in addition to its function as a key regulator of intracellular sodium and potassium concentration. We have previously demonstrated that ouabain, the endogenous ligand of Na, K-ATPase, can trigger intracellular Ca2+ oscillations, a versatile intracellular signal controlling a diverse range of cellular processes. Here we report that Na, K-ATPase and inositol 1,4,5-trisphosphate (InsP(3)) receptor (InsP(3)R) form a cell signaling microdomain that, in the presence of ouabain, generates slow Ca2+ oscillations in renal cells. Using fluorescent resonance energy transfer ( FRET) measurements, we detected a close spatial proximity between Na, K-ATPase and InsP(3)R. Ouabain significantly enhanced FRET between Na, K-ATPase and InsP(3)R. The FRET effect and ouabain-induced Ca2+ oscillations were not observed following disruption of the actin cytoskeleton. Partial truncation of the NH2 terminus of Na, K-ATPase catalytic alpha1-subunit abolished Ca2+ oscillations and downstream activation of NF-kappaB. Ouabain-induced Ca2+ oscillations occurred in cells expressing an InsP3 sponge and were hence independent of InsP3 generation. Thus, we present a novel principle for a cell signaling microdomain where an ion pump serves as a receptor.
|
|
| 41. |
|
|
| 42. |
|
|
| 43. |
- Sourial-Bassillious, N, et al.
(författare)
-
Expression of class I MHC in postnatal rat hippocampus
- 2004
-
Ingår i: PEDIATRIC RESEARCH. - : Springer Science and Business Media LLC. - 0031-3998 .- 1530-0447. ; 56:3, s. 505-505
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 44. |
|
|
| 45. |
- Zelenin, PV, et al.
(författare)
-
Comparison of the motor effects of individual vestibulo- and reticulospinal neurons on dorsal and ventral myotomes in lamprey
- 2003
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 90:5, s. 3161-3167
-
Tidskriftsartikel (refereegranskat)abstract
- In the lamprey (a lower vertebrate), motor commands from the brain to the spinal cord are transmitted through the reticulospinal (RS) and vestibulospinal (VS) pathways. The axons of larger RS neurons reach the most caudal of approximately 100 spinal segments, whereas the VS pathway does not descend below the 15th segment. This study was carried out to compare functional projections of RS and VS neurons in the rostral spinal segments that the neurons innervate together. To reveal these projections, individual RS or VS neurons were stimulated, and the responses of different groups of spinal motoneurons were recorded in ventral root branches to dorsal and ventral parts of myotomes. The responses were detected using a spike-triggered averaging technique on the background of ongoing motoneuronal activity. Individual RS and VS neurons exerted uniform effects on segmental motor output within this rostral part of the spinal cord. The effects of VS neurons on different groups of motoneurons were weaker and less diverse than those of RS neurons. The results indicate that VS neurons are able to elicit a flexion of the rostral part of the body and to turn the head in different planes without affecting more caudal parts. By contrast, larger RS neurons can elicit head movement only together with movement of a considerable part of the body and thus seem to be responsible for formation of gross motor synergies.
|
|
| 46. |
|
|
| 47. |
|
|
| 48. |
- Zelenin, PV, et al.
(författare)
-
Postural control in the lamprey: A study with a neuro-mechanical model
- 2000
-
Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 84:6, s. 2880-2887
-
Tidskriftsartikel (refereegranskat)abstract
- The swimming lamprey normally maintains the dorsal-side-up orientation due to activity of the postural control system driven by vestibular organs. Commands for postural corrections are transmitted from the brain stem to the spinal cord mainly by the reticulospinal (RS) pathways. As shown in previous studies, RS neurons are activated by contralateral roll tilt, they exhibit a strong dynamic response, but much weaker static response. Here we test a hypothesis that decoding of these commands in the spinal cord is based on the subtraction of signals in the left and right RS pathways. In this study, we used a neuro-mechanical model. An intact lamprey was mounted on a platform that restrained its postural activity but allowed lateral locomotor undulations to occur. The activity in the left and right RS pathways was recorded by implanted electrodes. These natural biological signals were then used to control an electrical motor rotating the animal around its longitudinal axis toward the stronger signal. It was found that this “hybrid” system automatically stabilized a normal orientation of the lamprey in the gravitational field. The system compensated for large postural disturbances (lateral tilt up to ±180°) due to wide angular zones of the gravitational sensitivity of RS neurons. In the nonswimming lamprey, activity of RS neurons and their vestibular responses were considerably reduced, and the system was not able to stabilize the normal orientation. However, the balance could be restored by imposing small oscillations on the lamprey, which elicited additional activation of the vestibular organs. This finding indicates that head oscillations caused by locomotor movements may contribute to postural stabilization. In addition to postural stabilization, the neuro-mechanical model reproduced a number of postural effects characteristic of the lamprey: 1) unilateral eye illumination elicited a lateral tilt (“dorsal light response”) due to a shift of the equilibrium point in the vestibular-driven postural network; 2) removal of one labyrinth resulted in a loss of postural control due to an induced left-right asymmetry in the vestibulo-reticulospinal reflexes, which 3) could be compensated for by asymmetrical visual input. The main conclusion of the present study is that natural supraspinal commands for postural corrections in the roll plane can be effectively decoded on the basis of subtraction of the effects of signals delivered by the left and right RS pathways. Possible mechanisms for this transformation are discussed.
|
|
| 49. |
- Zelenin, PV, et al.
(författare)
-
The pattern of motor coordination underlying the roll in the lamprey
- 2003
-
Ingår i: The Journal of experimental biology. - : The Company of Biologists. - 0022-0949 .- 1477-9145. ; 206:15Pt 15, s. 2557-2566
-
Tidskriftsartikel (refereegranskat)abstract
- The lamprey swims by caudally directed lateral undulations of its body. During swimming the animal is oriented with its dorsal side up, and any deviation from this posture (roll tilt) elicits a corrective motor response aimed at restoring the normal orientation. Video recording was used to study the kinematic pattern of the response to a 90° roll tilt imposed in the intact lamprey. The corrective responses were associated with specific modifications of the swimming movements. The plane of locomotor undulations deviated from the normal, i.e. frontal plane in one direction at the beginning of the rotation and in the opposite direction at its end. A similar motor pattern was also observed in the anterior part of the body of lampreys in which the spinal cord had been transected in the mid-body area, when performing postural corrections. It could also be observed during roll turns performed by lampreys after a rostral hemisection of the spinal cord. We argue that these modifications of the locomotor pattern generate the moments of force necessary for initiation and termination of the corrective roll turn. Possible neuronal mechanisms causing the corrective movements are discussed.
|
|
| 50. |
|
|
