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1.

001-es BibID:BIBFORM020247
Első szerző:Li, Wen-Chang
Cím:Persistent responses to brief stimuli : feedback excitation among brainstem neurons / Wen-Chang Li, Stephen R. Soffe, Ervin Wolf, Alan Roberts
Dátum:2006
ISSN:0270-6474
Megjegyzések:The ability of brief stimuli to trigger prolonged neuronal activity is a fundamental requirement in nervous systems, common to motor responses and short-term memory. Bistable membrane properties and network feedback excitation have both been proposed as suitable mechanisms to sustain such persistent responses. There is now good experimental evidence for membrane bistability. In contrast, the long-standing hypotheses based on positive feedback excitation have yet to be supported by direct evidence for mutual excitatory connections between appropriate neurons. In young frog tadpoles (Xenopus), we show that a small region of caudal hindbrain and rostral spinal cord is sufficient to generate prolonged swimming in response to a brief stimulus. We used paired whole-cell patch recordings to identify hindbrain neurons in this region that actively excite spinal neurons to drive sustained swimming. We show directly that some of these hindbrain neurons make reciprocal excitatory connections with each other. We use a population model of the hindbrain network to illustrate how feedback excitation can provide a robust mechanism to generate persistent responses. Our recordings provide direct evidence for feedback excitation among neurons within a network that drives a prolonged response. Its presence in a lower brain region early in development suggests that it is a basic feature of neuronal network design.
Tárgyszavak:Orvostudományok Természettudományok Klinikai orvostudományok Biológiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
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Megjelenés:The Journal of Neuroscience. - 26 : 15 (2006), p. 4026-4035. -
További szerzők:Wolf Ervin (1961-) (fizikus, neurobiológus) Soffe, Stephen R. Roberts, Alan
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2.

001-es BibID:BIBFORM029494
Első szerző:Roberts, Alan
Cím:Properties of networks controlling locomotion and significance of voltage dependency of NMDA channels : simulation study of rhythm generation sustained by positive feedback / Roberts A., Tunstall M. J., Wolf E.
Dátum:1995
ISSN:0022-3077
Megjegyzések:We have built a realistic 24-neuron model based on data from the spinal pattern generator for swimming in Xenopus embryos with the use of the SWIM programs. The neurons have dendrite, soma, and axon compartments with voltage-gated Na+ and K+ channels. Dendritic synapses were modeled as modulated ionic conductances with currents that have different reversal levels. One of these conductances was voltage dependent to model N-methyl-D-aspartate ("NMDA") synapses in the presence of Mg2+. 2. In this model, rhythm generation is initiated by a brief excitation, depends on rebound from reciprocal inhibition, and is sustained by long-duration "NMDA-dependent" feedback excitation. 3. Without NMDA voltage dependency, rhythmic activity is stable over a wide range of synaptic conductances. Its frequency decreases with more inhibition and increases with more excitation. The introduction of normally distributed variation in soma size or excitatory synaptic conductance extends the lower stable frequency range. Without such variation the frequency of the 24-neuron model is the same as a 4-neuron model provided that the synaptic conductances for each neuron are the same. 4. The effect of introducing NMDA voltage dependency on rebound after negative current injections or synaptic inhibition was investigated in single depolarized model neurons. With NMDA voltage dependency, hyperpolarizations and rebound spike responses were increased. 5. Network activity with NMDA voltage dependency was similar to that without it, but inhibitory postsynaptic potentials (IPSPs) and spikes were larger, and frequencies were lower and more sensitive to changes in excitatory and inhibitory conductance. 6. We conclude that in the model, mutual reexcitation among excitatory spinal interneurons can sustain rhythm generation by positive feedback and that NMDA voltage dependency can enhance postinhibitory rebound, stabilize swimming activity and extend its lower frequency range, and steepen the dependency of frequency on synaptic drive.
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
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Megjelenés:Journal Of Neurophysiology. - 73 : 2 (1995), p. 485-495. -
További szerzők:Tunstall, Mark J. Wolf Ervin (1961-) (fizikus, neurobiológus)
Internet cím:Intézményi repozitóriumban (DEA) tárolt változat
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3.

001-es BibID:BIBFORM029490
Első szerző:Roberts, Alan
Cím:Central circuits controlling locomotion in young frog tadpoles / Roberts A., Soffe S. R., Wolf E. S., Yoshida M., Zhao F. Y.
Dátum:1998
Megjegyzések:The young Xenopus tadpole is a very simple vertebrate that can swim. We have examined its behavior and neuroanatomy, and used immobilized tadpoles to study the initiation, production, coordination, and termination of the swimming motor pattern. We will outline the sensory pathways that control swimming behavior and the mainly spinal circuits that produce the underlying motor output. Our recent work has analyzed the glycinergic, glutamatergic, cholinergic, and electrotonic synaptic input to spinal neurons during swimming. This has led us to study the nonlinear summation of excitatory synaptic inputs to small neurons. We then analyzed the different components of excitation during swimming to ask which components control frequency, and to map the longitudinal distribution of the components along the spinal cord. The central axonal projection patterns of spinal interneurons and motoneurons have been defined in order to try to account for the longitudinal distribution of synaptic drive during swimming.
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
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Megjelenés:Annals of the New York Academy of Sciences. - 860 (1998), p. 19-34. -
További szerzők:Soffe, Stephen R. Wolf Ervin (1961-) (fizikus, neurobiológus) Yoshida, Manabu Zhao, Fey-Yue
Internet cím:Intézményi repozitóriumban (DEA) tárolt változat
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4.

001-es BibID:BIBFORM004109
Első szerző:Roberts, Alan
Cím:Origin of excitatory drive to a spinal locomotor network / Alan Roberts, W.-C. Li, S. R. Soffe, Ervin Wolf
Dátum:2008
Tárgyszavak:Orvostudományok Elméleti orvostudományok Természettudományok Biológiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
egyetemen (Magyarországon) készült közlemény
Megjelenés:Brain Research Reviews. - 57 : 1 (2008), p. 22-28. -
További szerzők:Li, Wen-Chang Soffe, Stephen R. Wolf Ervin (1961-) (fizikus, neurobiológus)
Internet cím:elektronikus változat
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5.

001-es BibID:BIBFORM029493
Első szerző:Wolf Ervin (fizikus, neurobiológus)
Cím:Non-linear summation of excitatory synaptic inputs to small neurons : a case study in spinal motoneurones of the young Xenopus tadpole / Wolf E., Zhao F. Y., Roberts A.
Dátum:1998
ISSN:0022-3751
Megjegyzések:We examined the steady-state summation of postsynaptic potentials (PSPs) in small, electrotonically compact neurones with short dendrites, using a one-compartment electrical equivalent model of the passive membrane with conductances to represent chemical synapses and electrotonic junctional connections to neighbouring neurones. 2. Our model shows that PSP summation is non-linear and for small depolarizations is mainly determined by the increase in total neurone conductance due to the opening of synaptic channels. At bigger depolarizations the change in synaptic driving force becomes an equally important cause of non-linearity. 3. Non-linear summation of AMPA-mediated PSPs was measured experimentally when two monosynaptic pathways to motoneurones were stimulated. The conductances underlying these PSPs were calculated relative to the resting neurone conductance using our model. These conductance ratios were hardly affected by the size of electrotonic coupling conductances. The non-linearity in PSP summation could be predicted by the model provided that the depolarizations remained negative to potentials at which voltage-dependent channels open. 4. The model was used to estimate the relative contributions of glutamatergic, cholinergic and electrotonic excitation to EPSPs measured in Xenopus tadpole spinal motoneurones during swimming. Estimates of synaptic conductances and electrotonic coupling to other motoneurones suggest that ligand-gated conductance mediated by glutamate may be twice that due to acetylcholine. 5. We conclude that in small electrotonically compact motoneurones of the Xenopus tadpole, our simple model can predict the non-linearity in PSP summation and may allow the conductances of different synaptic inputs to be compared. Furthermore, excitatory synaptic conductances can increase the resting neurone conductance significantly and limit depolarization. Our general model may also be applicable to other small neurones.
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
egyetemen (Magyarországon) készült közlemény
Megjelenés:Journal Of Physiology (London). - 511 : (Pt3) (1998), p. 871-886. -
További szerzők:Zhao, Fey-Yue Roberts, Alan
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6.

001-es BibID:BIBFORM029498
Első szerző:Wolf Ervin (fizikus, neurobiológus)
Cím:The influence of premotor interneurone populations on the frequency of the spinal pattern generator for swimming in Xenopus embryo: a simulation study / Wolf E., Roberts A.
Dátum:1995
ISSN:0953-816X
Megjegyzések:Our aim was to test the hypothesis that the frequency of neuronal rhythm-generating networks is partly controlled by the size of the active premotor interneuron population. We have tested possible mechanisms for frequency changes in a population model of the Xenopus laevis embryo spinal rhythm-generating networks for swimming. After initiation by a brief sensory excitation, the frequency of swimming activity decreases to a steady level determined by the properties of the 24 interneurons and their connections. The initial frequency decrease was dependent on the time-course of initiating sensory synaptic excitation. When some premotor excitatory interneurons were given weaker synaptic connections to reflect the variability in the spinal cord, they could drop out and stop firing during the initial frequency decrease while swimming activity continued. If the synaptic input of such weak excitatory interneurons was graded finely, they could drop out consecutively. This led to further decreases in the level of tonic excitation and in network frequency which depended on the number, type and distribution of excitatory interneurons that stopped firing. Silent weak excitatory interneurons could be recruited by a second sensory excitation and cause an increase in tonic depolarization and frequency which outlasted the sensory input. Such recruitment could occur on both sides after local sensory stimulation to only one region or one side of the model. We conclude that these computer simulations support the hypothesis that premotor interneuron drop-out and recruitment is one mechanism which can control frequency in a locomotor central pattern generator.
Tárgyszavak:Természettudományok Biológiai tudományok idegen nyelvű folyóiratközlemény külföldi lapban
egyetemen (Magyarországon) készült közlemény
Megjelenés:European Journal Of Neuroscience. - 7 : 4 (1995), p. 671-678. -
További szerzők:Roberts, Alan
Internet cím:Intézményi repozitóriumban (DEA) tárolt változat
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7.

001-es BibID:BIBFORM008786
Első szerző:Wolf Ervin (fizikus, neurobiológus)
Cím:Longitudinal neuronal organization and coordination in a simple vertebrate : a continuous, semi-quantitative computer model of the central pattern generator for swimming in young frog tadpoles / Ervin Wolf, S. R. Soffe, Alan Roberts
Dátum:2009
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
egyetemen (Magyarországon) készült közlemény
Megjelenés:Journal of Computational Neuroscience. - 27 : 2 (2009), p. 291-308. -
További szerzők:Soffe, Stephen R. Roberts, Alan
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8.

001-es BibID:BIBFORM029491
Első szerző:Zhao, Fey-Yue
Cím:Longitudinal disribution of components of excitatory input to motoneurones during swimming in young Xenopus tadpoles : experiments with antagonists / Zhao F. Y., Wolf E., Roberts A.
Dátum:1998
ISSN:0022-3751
Megjegyzések:Recent studies have revealed that the excitatory synaptic input to spinal motoneurones during fictive swimming in Xenopus tadpoles has three main components: glutamatergic (Glu) from premotor excitatory interneurones, nicotinic cholinergic (nACh) from more rostral motoneurones, and electrotonic coupling from neighbouring motoneurones. During swimming, these components sum to produce two kinds of excitation: phasic excitation (EPSPs) underlying spikes, and tonic depolarization. 2. We have investigated the longitudinal distribution of these excitatory synaptic inputs to presumed motoneurones at different positions along the spinal cord using intracellular recording techniques. Different antagonists (10 microM dihydro-beta-erythroidine (DHbetaE) for nicotinic ACh receptors (nAChRs), 2 mM kynurenate (Kyn) for glutamate receptors (GluRs), and 100 microM Cd2+ for all chemical synapses) were microperfused very locally to unmask the relative contributions of these components to the total excitatory drive, and their distribution along the spinal cord during swimming. 3. If the potentials remaining when all chemical components were blocked by Cd2+ were subtracted from potentials recorded after blocking nAChRs and GluRs with DHbetaE plus Kyn, a small unidentified component was observed. This component was blocked by the specific AMPA antagonist 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (NBQX, 5 microM), so is glutamate mediated. 4. We used the potential measurements to calculate the relative synaptic conductances of the different synaptic inputs, and conclude that: (a) there is a rostral-caudal gradient in input during EPSPs and tonic depolarization; (b) the glutamatergic component accounts for most of the excitation, and decreases caudally; (c) cholinergic and electrotonic components are relatively constant in different positions along the spinal cord; and (d) these two components provide an increasing proportion of the input in more caudal neurones. 5. We propose that the glutamate components of excitation are fundamental to rhythm generation in the brainstem and rostral cord, while the electrotonic and cholinergic components ensure that the central pattern generator activates motoneurones effectively in all parts of the spinal cord.
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
külföldön készült közlemény
Megjelenés:Journal Of Physiology (London). - 511 : (Pt3) (1998), p. 887-901. -
További szerzők:Wolf Ervin (1961-) (fizikus, neurobiológus) Roberts, Alan
Internet cím:Intézményi repozitóriumban (DEA) tárolt változat
DOI
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9.

001-es BibID:BIBFORM029489
Első szerző:Zhao, Fey-Yue
Cím:Asymmetries in sensory pathways from skin motoneurons on each side of the body determine the direction of an avoidance response in hatchling Xenopus tadpoles / Zhao F. Y., Burton G. B., Wolf E., Roberts A.
Dátum:1998
ISSN:0022-3751
Megjegyzések:When swimming is initiated by tail stimulation in hatchling Xenopus tadpoles, the first trunk contraction is usually on the opposite side and directs the animal away from the stimulus. We have investigated how asymmetries in the skin sensory pathways mediate this response. 2. In alpha-bungarotoxin-immobilized tadpoles, intracellular recordings were made of responses to ipsilateral (ISS) and contralateral skin stimulation (CSS) in thirty-two presumed motoneurons. ISS evokes an inhibitory postsynaptic potential (IPSP) followed by an excitatory postsynaptic potential (EPSP) whereas CSS only evokes an EPSP. Blocking the short latency IPSP evoked by ISS with strychnine reduced the difference in spike latency on the two sides but spikes still occurred first to CSS. 3. Motoneuron EPSPs evoked by ISS and CSS were therefore recorded during microperfusion of strychnine to block the short latency IPSP. We found: (a) the CSS-EPSPs have lower threshold, larger amplitude at a given intensity of stimulus, faster rising phase, and shorter latencies than those of ISS-EPSPs; (b) the ISS-EPSP onset latencies were longer than CSS-EPSPs and became shorter as the stimulus intensity increased while those of CSS-EPSPs remained little changed. At high stimulus intensities, EPSPs caused by CSS and ISS became similar; and (c) onset latencies of ISS-EPSPs had higher variance than those of CSS-EPSPs. However, this difference was reduced as the stimulus intensity was increased. 4. Since motoneuron EPSP onset latencies varied with stimulus intensity, we proposed that the pathway from the opposite side had stronger synapses from afferents to sensory interneurons. To test this proposal we built a neuronal population model of the spinal pathway from skin afferents, via sensory interneurons to ipsilateral and contralateral motoneurons incorporating this asymmetry. Inhibition was omitted from the model. 5. Simulated motoneuron EPSPs in response to skin stimulation on each side of the body showed the major asymmetries found experimentally. If the distribution and axonal projections of the interneurons in the two sensory pathways were made the same these differences remained. However, if the synaptic strength from sensory afferents onto interneurons projecting to the two sides were made equal, the difference between the two sides were lost. 6. We propose that the sensory pathway to contralateral motoneurons has more effective excitation from afferents to sensory interneurons which leads to these motoneurons firing first. At higher stimulus strengths, when population recruitment can blur these subtle differences in excitation between the two sides, inhibition normally plays a significant role to ensure that most first responses are still contralateral.
Tárgyszavak:Orvostudományok Természettudományok Biológiai tudományok Elméleti orvostudományok idegen nyelvű folyóiratközlemény külföldi lapban
külföldön készült közlemény
Megjelenés:Journal Of Physiology (London). - 506 : (Pt2) (1998), p. 471-487. -
További szerzők:Burton, G. Brian Wolf Ervin (1961-) (fizikus, neurobiológus) Roberts, Alan
Internet cím:Intézményi repozitóriumban (DEA) tárolt változat
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