The Experts below are selected from a list of 42 Experts worldwide ranked by ideXlab platform
Alan Roberts - One of the best experts on this subject based on the ideXlab platform.
-
Functional projection distances of spinal Interneurons mediating reciprocal inhibition during swimming in Xenopus tadpoles
The European journal of neuroscience, 2001Co-Authors: Stephen R Soffe, F-y Zhao, Alan RobertsAbstract:The basis for longitudinal coordination among spinal neurons during locomotion is still poorly understood. We have now examined the functional projection distances for the longitudinal axons of reciprocal inhibitory 'Commissural Interneurons' in the spinal cord of young Xenopus tadpoles. In quiescent animals, glycinergic inhibitory postsynaptic potentials (IPSPs) were evoked in ventral spinal neurons by stimulating small rostral and caudal groups of Commissural Interneuron somata at different distances on the opposite side of the hindbrain and spinal cord. Unitary IPSPs, produced by single synaptic contacts, could be distinguished from background noise. Local cord stimulation at different distances revealed maximum functional projection distances up to approximately 0.5 mm for both descending and ascending axons, but with the probability of recording connections falling steeply over this distance. These maximum longitudinal projection distances are smaller than predicted by axonal anatomy (approximately 1.2 mm). We then measured functional projection distances during swimming by examining the synaptic output of a surgically isolated group of rostral Commissural Interneurons, mapping the occurrence of the mid-cycle, reciprocal IPSPs they produced in more caudal neurons. IPSPs occurred with high probability up to 0.9 mm away, nearly twice the projection distance found in quiescent tadpoles. These results show that synaptic contacts from Commissural Interneurons could influence longitudinal coupling during swimming at distances of up to 0.9 mm (approximately 4-5 myotome segments or approximately 25% of the spinal cord). They provide direct evidence for functional projection distances of a characterized class of Interneurons belonging to a spinal locomotor pattern generator.
-
Early functional organization of spinal neurons in developing lower vertebrates.
Brain research bulletin, 2000Co-Authors: Alan RobertsAbstract:The spinal neurons in the embryos and young larvae of two amphibians (Xenopus and Triturus) and two fish (Oryzias and Brachydanio) are described and compared. They can be placed into a limited number of common neuron classes: Rohon-Beard sensory, dorsolateral and dorsolateral Commissural sensory Interneurons, inhibitory ascending Interneurons, two classes of inhibitory Commissural Interneuron, excitatory descending Interneurons, motoneurons and possible sensory Kolmer-Agdhur neurons. In Triturus and other urodeles, there are also giant dorsolateral Commissural sensory Interneurons. The functions of the spinal neurons in simple flexion responses and swimming are considered in relation to evidence mainly from the Xenopus tadpole.
-
Axon projections of reciprocal inhibitory Interneurons in the spinal cord of young Xenopus tadpoles and implications for the pattern of inhibition during swimming and struggling
The Journal of comparative neurology, 1998Co-Authors: Masayuki Yoshida, Alan Roberts, Stephen R SoffeAbstract:We have examined the morphology and longitudinal axon projections of a population of spinal Commissural Interneurons in young Xenopus tadpoles. We aimed to define how the distribution of axons of the whole population constrains the longitudinal distribution of the inhibition they mediate. Forty-three neurons at different positions were filled intracellularly with biocytin and processed with avidin-conjugated horseradish peroxidase. Soma size did not vary longitudinally and only one ipsilateral axon was found. Contralateral axons ascended, descended, or usually branched to do both. Total axon length and the extent of dendritic arborisation decreased caudally. The distributions of ascending and descending axon lengths were different; there were more long ascending (mean 737 ± standard deviation 365 μm) than long descending (447 ± 431 μm) axons. We used the axon length distribution data with existing data on the distribution of Commissural Interneuron somata to calculate the overall longitudinal density of these inhibitory axons. Axon numbers showed a clear rostrocaudal gradient. Axon length distributions were then incorporated into a simple spatiotemporal model of the forms of inhibition during swimming and struggling motor patterns. The model predicts that the peak of inhibition on each cycle will decrease from head to tail in both motor patterns, a feature already confirmed physiologically for swimming. It also supports a previous proposal that ascending inhibition during struggling shortens cycle period by shortening rostral motor bursts, whereas descending inhibition could delay subsequent burst onset. J. Comp. Neurol. 400:504–518, 1998. © 1998 Wiley-Liss, Inc.
Stephen R Soffe - One of the best experts on this subject based on the ideXlab platform.
-
Functional projection distances of spinal Interneurons mediating reciprocal inhibition during swimming in Xenopus tadpoles
The European journal of neuroscience, 2001Co-Authors: Stephen R Soffe, F-y Zhao, Alan RobertsAbstract:The basis for longitudinal coordination among spinal neurons during locomotion is still poorly understood. We have now examined the functional projection distances for the longitudinal axons of reciprocal inhibitory 'Commissural Interneurons' in the spinal cord of young Xenopus tadpoles. In quiescent animals, glycinergic inhibitory postsynaptic potentials (IPSPs) were evoked in ventral spinal neurons by stimulating small rostral and caudal groups of Commissural Interneuron somata at different distances on the opposite side of the hindbrain and spinal cord. Unitary IPSPs, produced by single synaptic contacts, could be distinguished from background noise. Local cord stimulation at different distances revealed maximum functional projection distances up to approximately 0.5 mm for both descending and ascending axons, but with the probability of recording connections falling steeply over this distance. These maximum longitudinal projection distances are smaller than predicted by axonal anatomy (approximately 1.2 mm). We then measured functional projection distances during swimming by examining the synaptic output of a surgically isolated group of rostral Commissural Interneurons, mapping the occurrence of the mid-cycle, reciprocal IPSPs they produced in more caudal neurons. IPSPs occurred with high probability up to 0.9 mm away, nearly twice the projection distance found in quiescent tadpoles. These results show that synaptic contacts from Commissural Interneurons could influence longitudinal coupling during swimming at distances of up to 0.9 mm (approximately 4-5 myotome segments or approximately 25% of the spinal cord). They provide direct evidence for functional projection distances of a characterized class of Interneurons belonging to a spinal locomotor pattern generator.
-
Axon projections of reciprocal inhibitory Interneurons in the spinal cord of young Xenopus tadpoles and implications for the pattern of inhibition during swimming and struggling
The Journal of comparative neurology, 1998Co-Authors: Masayuki Yoshida, Alan Roberts, Stephen R SoffeAbstract:We have examined the morphology and longitudinal axon projections of a population of spinal Commissural Interneurons in young Xenopus tadpoles. We aimed to define how the distribution of axons of the whole population constrains the longitudinal distribution of the inhibition they mediate. Forty-three neurons at different positions were filled intracellularly with biocytin and processed with avidin-conjugated horseradish peroxidase. Soma size did not vary longitudinally and only one ipsilateral axon was found. Contralateral axons ascended, descended, or usually branched to do both. Total axon length and the extent of dendritic arborisation decreased caudally. The distributions of ascending and descending axon lengths were different; there were more long ascending (mean 737 ± standard deviation 365 μm) than long descending (447 ± 431 μm) axons. We used the axon length distribution data with existing data on the distribution of Commissural Interneuron somata to calculate the overall longitudinal density of these inhibitory axons. Axon numbers showed a clear rostrocaudal gradient. Axon length distributions were then incorporated into a simple spatiotemporal model of the forms of inhibition during swimming and struggling motor patterns. The model predicts that the peak of inhibition on each cycle will decrease from head to tail in both motor patterns, a feature already confirmed physiologically for swimming. It also supports a previous proposal that ascending inhibition during struggling shortens cycle period by shortening rostral motor bursts, whereas descending inhibition could delay subsequent burst onset. J. Comp. Neurol. 400:504–518, 1998. © 1998 Wiley-Liss, Inc.
Timothy M. Gomez - One of the best experts on this subject based on the ideXlab platform.
-
Adjacent pioneer Commissural Interneuron growth cones switch from contact avoidance to axon fasciculation after midline crossing.
Developmental biology, 2005Co-Authors: Myung-soon Moon, Timothy M. GomezAbstract:Abstract Commissural Interneurons (CI) of the vertebrate spinal cord are guided ventrally toward the floor plate, but subsequently cross the midline and select a longitudinal fascicle at specific dorsal–ventral (D–V) positions. We examined at high resolution the detailed behaviors of individual pathfinding CI growth cones on the ipsilateral and contralateral sides of the spinal cord of living Xenopus embryos. We find that pre-crossing CI growth cones exhibit distinct pathfinding behaviors compared to post-crossing axons and that the behavioral switch occurs immediately upon crossing to the contralateral side. Groups of pioneer Commissural axons typically extend simultaneously toward the ventral midline following discrete paths with separation between adjacent Commissurals apparently maintained through contact inhibition. In contrast, shortly after crossing the midline, Commissural axons turn longitudinally and begin to fasciculate with other crossed CIs. However, growth cones of crossed Commissurals often select their final D–V longitudinal track through a series of rapid step-like dorsal adjustments that may be due to differential fasciculation with longitudinal axons. Together, our results suggest that guidance of Commissural axons is controlled in part through interactions among CIs that switch rapidly from avoidance to fasciculation after midline crossing.
Masayuki Yoshida - One of the best experts on this subject based on the ideXlab platform.
-
Axon projections of reciprocal inhibitory Interneurons in the spinal cord of young Xenopus tadpoles and implications for the pattern of inhibition during swimming and struggling
The Journal of comparative neurology, 1998Co-Authors: Masayuki Yoshida, Alan Roberts, Stephen R SoffeAbstract:We have examined the morphology and longitudinal axon projections of a population of spinal Commissural Interneurons in young Xenopus tadpoles. We aimed to define how the distribution of axons of the whole population constrains the longitudinal distribution of the inhibition they mediate. Forty-three neurons at different positions were filled intracellularly with biocytin and processed with avidin-conjugated horseradish peroxidase. Soma size did not vary longitudinally and only one ipsilateral axon was found. Contralateral axons ascended, descended, or usually branched to do both. Total axon length and the extent of dendritic arborisation decreased caudally. The distributions of ascending and descending axon lengths were different; there were more long ascending (mean 737 ± standard deviation 365 μm) than long descending (447 ± 431 μm) axons. We used the axon length distribution data with existing data on the distribution of Commissural Interneuron somata to calculate the overall longitudinal density of these inhibitory axons. Axon numbers showed a clear rostrocaudal gradient. Axon length distributions were then incorporated into a simple spatiotemporal model of the forms of inhibition during swimming and struggling motor patterns. The model predicts that the peak of inhibition on each cycle will decrease from head to tail in both motor patterns, a feature already confirmed physiologically for swimming. It also supports a previous proposal that ascending inhibition during struggling shortens cycle period by shortening rostral motor bursts, whereas descending inhibition could delay subsequent burst onset. J. Comp. Neurol. 400:504–518, 1998. © 1998 Wiley-Liss, Inc.
Marlene Bartos - One of the best experts on this subject based on the ideXlab platform.
-
Somatostatin-Expressing Interneurons Form Axonal Projections to the Contralateral Hippocampus.
Frontiers in neural circuits, 2019Co-Authors: Mark D. Eyre, Marlene BartosAbstract:Conscious memories are critically dependent upon the bilateral hippocampal formation, and interhemispheric Commissural projections made by mossy cells and CA3 pyramidal cells. GABAergic Interneurons also make long-range axonal projections, but little is known regarding their Commissural, inter-hippocampal connections. We used retrograde and adeno-associated viral tracing, immunofluorescent and electron microscopy, and in vitro optogenetics to assess contralateral projections of neurochemically defined Interneuron classes. We found that contralateral-projecting Interneurons were 24-fold less common compared to hilar mossy cells, and mostly consisted of somatostatin- and parvalbumin-expressing types. Somatostatin-expressing cells made denser contralateral axonal projections than parvalbumin-expressing cells, although this was typically 10-fold less than the ipsilateral projection density. Somatostatin-expressing cells displayed a topographic-like innervation according to the location of their somata, whereas parvalbumin-expressing cells mostly innervated CA1. In the dentate gyrus molecular layer, Commissural Interneuron post-synaptic targets were predominantly putative granule cell apical dendrites. In the hilus, varicosities in close vicinity to various Interneuron subtypes, as well as mossy cells, were observed, but most contralateral axon varicosities had no adjacent immunolabelled structure. Due to the relative sparsity of the connection and the likely distal dendritic location of their synapses, Commissural projections made by Interneurons were found to be weak. We postulate that these projections may become functionally active upon intense network activity during tasks requiring increased memory processing.