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B. Torres - One of the best experts on this subject based on the ideXlab platform.
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modulation of the input output function by gabaa receptor mediated currents in rat Oculomotor Nucleus motoneurons
The Journal of Physiology, 2014Co-Authors: Julio Torrestorrelo, B. Torres, Livia CarrascalAbstract:The neuronal input-output function depends on recruitment threshold and gain of the firing frequency-current (f-I) relationship. These two parameters are positively correlated in ocular motoneurons (MNs) recorded in alert preparation and inhibitory inputs could contribute to this correlation. Phasic inhibition mediated by γ-amino butyric acid (GABA) occurs when a high concentration of GABA at the synaptic cleft activates postsynaptic GABAA receptors, allowing neuronal information transfer. In some neuronal populations, low concentrations of GABA activate non-synaptic GABAA receptors and generate a tonic inhibition, which modulates cell excitability. This study determined how ambient GABA concentrations modulate the input-output relationship of rat Oculomotor Nucleus MNs. Superfusion of brain slices with GABA (100 μm) produced a GABAA receptor-mediated current that reduced the input resistance, increased the recruitment threshold and shifted the f-I relationship rightward without any change in gain. These modifications did not depend on MN size. In absence of exogenous GABA, gabazine (20 μm; antagonist of GABAA receptors) abolished spontaneous inhibitory postsynaptic currents and revealed a tonic current in MNs. Gabazine increased input resistance and decreased recruitment threshold mainly in larger MNs. The f-I relationship shifted to the left, without any change in gain. Gabazine effects were chiefly due to MN tonic inhibition because tonic current amplitude was five-fold greater than phasic. This study demonstrates a tonic inhibition in ocular MNs that modulates cell excitability depending on cell size. We suggest that GABAA tonic inhibition acting concurrently with glutamate receptors activation could reproduce the positive covariation between threshold and gain reported in alert preparation.
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Modulation of the input–output function by GABAA receptor‐mediated currents in rat Oculomotor Nucleus motoneurons
The Journal of physiology, 2014Co-Authors: Julio Torres-torrelo, B. Torres, Livia CarrascalAbstract:The neuronal input-output function depends on recruitment threshold and gain of the firing frequency-current (f-I) relationship. These two parameters are positively correlated in ocular motoneurons (MNs) recorded in alert preparation and inhibitory inputs could contribute to this correlation. Phasic inhibition mediated by γ-amino butyric acid (GABA) occurs when a high concentration of GABA at the synaptic cleft activates postsynaptic GABAA receptors, allowing neuronal information transfer. In some neuronal populations, low concentrations of GABA activate non-synaptic GABAA receptors and generate a tonic inhibition, which modulates cell excitability. This study determined how ambient GABA concentrations modulate the input-output relationship of rat Oculomotor Nucleus MNs. Superfusion of brain slices with GABA (100 μm) produced a GABAA receptor-mediated current that reduced the input resistance, increased the recruitment threshold and shifted the f-I relationship rightward without any change in gain. These modifications did not depend on MN size. In absence of exogenous GABA, gabazine (20 μm; antagonist of GABAA receptors) abolished spontaneous inhibitory postsynaptic currents and revealed a tonic current in MNs. Gabazine increased input resistance and decreased recruitment threshold mainly in larger MNs. The f-I relationship shifted to the left, without any change in gain. Gabazine effects were chiefly due to MN tonic inhibition because tonic current amplitude was five-fold greater than phasic. This study demonstrates a tonic inhibition in ocular MNs that modulates cell excitability depending on cell size. We suggest that GABAA tonic inhibition acting concurrently with glutamate receptors activation could reproduce the positive covariation between threshold and gain reported in alert preparation.
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Glutamate modulates the firing rate in Oculomotor Nucleus motoneurons as a function of the recruitment threshold current.
The Journal of physiology, 2012Co-Authors: Julio Torres-torrelo, Livia Carrascal, Pedro Nunez-abades, David Rodríguez-rosell, B. TorresAbstract:Studies in alert preparations have demonstrated that ocular motoneurons exhibit a phasic-tonic firing rate related to eye velocity and position, respectively. The slopes of these relationships are higher in motoneurons with higher recruitment threshold and have been proposed to depend upon synaptic input. To investigate this hypothesis, motoneurons of the rat Oculomotor Nucleus were recorded in a brain slice preparation in control conditions and during glutamate (5 μM) application to the bath. Glutamate did not affect membrane potential or input resistance, but produced a decrease in rheobase and depolarization voltage as a function of the current needed for generating a maintained repetitive discharge (recruitment threshold current). In addition, glutamate compressed the range of recruitment threshold current (0.1-0.4 nA) as compared to the control (0.15-0.7nA). Glutamate exposed motoneurons showed an increase in the tonic frequency gain and the peak frequency. Such increments depended on the recruitment threshold current and the last recruited motoneurons almost doubled the tonic frequency gain (35.2 vs. 57.9 spikess −1 nA −1 ) and the peak frequency (52.4 vs. 102.6 spikess −1 ). Finally, glutamate increased the spike frequency adaptation due to a significant increase in the phasic firing component as compared to the tonic one. In conclusion, glutamate modulates tonic and phasic discharge properties as a function of the recruitment threshold current and, presumably, motoneuron size. These findings contribute to understand the link between cellular functions and motoneuron discharge during Oculomotor behaviour.
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Diminution of Voltage Threshold Plays a Key Role in Determining Recruitment of Oculomotor Nucleus Motoneurons during Postnatal Development
PLOS ONE, 2011Co-Authors: Livia Carrascal, Jose Luis Nieto-gonzalez, B. Torres, Pedro Nunez-abadesAbstract:The size principle dictates the orderly recruitment of motoneurons (Mns). This principle assumes that Mns of different sizes have a similar voltage threshold, cell size being the crucial property in determining neuronal recruitment. Thus, smaller neurons have higher membrane resistance and require a lower depolarizing current to reach spike threshold. However, the cell size contribution to recruitment in Mns during postnatal development remains unknown. To investigate this subject, rat Oculomotor Nucleus Mns were intracellularly labeled and their electrophysiological properties recorded in a brain slice preparation. Mns were divided into 2 age groups: neonatal (1–7 postnatal days, n = 14) and adult (20–30 postnatal days, n = 10). The increase in size of Mns led to a decrease in input resistance with a strong linear relationship in both age groups. A well-fitted inverse correlation was also found between input resistance and rheobase in both age groups. However, input resistance versus rheobase did not correlate when data from neonatal and adult Mns were combined in a single group. This lack of correlation is due to the fact that decrease in input resistance of developing Mns did not lead to an increase in rheobase. Indeed, a diminution in rheobase was found, and it was accompanied by an unexpected decrease in voltage threshold. Additionally, the decrease in rheobase co-varied with decrease in voltage threshold in developing Mns. These data support that the size principle governs the recruitment order in neonatal Mns and is maintained in adult Mns of the Oculomotor Nucleus; but during postnatal development the crucial property in determining recruitment order in these Mns was not the modifications of cell size-input resistance but of voltage threshold.
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GABAergic Projections to the Oculomotor Nucleus in the Goldfish (carassius Auratus).
Frontiers in neuroanatomy, 2011Co-Authors: M. Angeles Luque, Livia Carrascal, B. Torres, Julio Torres-torrelo, L. HerreroAbstract:The mammalian Oculomotor Nucleus receives a strong -aminobutyric acid (GABA)ergic synaptic input, whereas such projections have rarely been reported in fish. In order to determine whether this synaptic organization is preserved across vertebrates, we investigated the GABAergic projections to the Oculomotor Nucleus in the goldfish by combining retrograde transport of biotin dextran amine, injected into the antidromically identified Oculomotor Nucleus, and GABA immunohistochemistry. The main source of GABAergic afferents to the Oculomotor Nucleus was the ipsilateral anterior octaval Nucleus, with only a few, if any, GABAergic neurons being located in the contralateral tangential and descending nuclei of the octaval column. In mammals there is a nearly exclusive ipsilateral projection from vestibular neurons to the Oculomotor Nucleus via GABAergic inhibitory inputs; thus, the vestibuloOculomotor GABAergic circuitry follows a plan that appears to be shared throughout the vertebrate phylogeny. The second major source of GABAergic projections was the rhombencephalic reticular formation, primarily from the medial area but, to a lesser extent, from the inferior area. A few GABAergic Oculomotor projecting neurons were also observed in the ipsilateral Nucleus of the medial longitudinal fasciculus. The GABAergic projections from neurons located in both the reticular formation surrounding the abducens Nucleus and the Nucleus of the medial reticular formation have primarily been related to the control of saccadic eye movements. Finally, all retrogradely labeled internuclear neurons of the abducens Nucleus, and neurons in the cerebellum (close to the caudal lobe), were negative for GABA. These data suggest that the vestibuloocular and saccadic inhibitory GABAergic systems appear early in vertebrate phylogeny to modulate the firing properties of the Oculomotor Nucleus motoneurons.
Livia Carrascal - One of the best experts on this subject based on the ideXlab platform.
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modulation of the input output function by gabaa receptor mediated currents in rat Oculomotor Nucleus motoneurons
The Journal of Physiology, 2014Co-Authors: Julio Torrestorrelo, B. Torres, Livia CarrascalAbstract:The neuronal input-output function depends on recruitment threshold and gain of the firing frequency-current (f-I) relationship. These two parameters are positively correlated in ocular motoneurons (MNs) recorded in alert preparation and inhibitory inputs could contribute to this correlation. Phasic inhibition mediated by γ-amino butyric acid (GABA) occurs when a high concentration of GABA at the synaptic cleft activates postsynaptic GABAA receptors, allowing neuronal information transfer. In some neuronal populations, low concentrations of GABA activate non-synaptic GABAA receptors and generate a tonic inhibition, which modulates cell excitability. This study determined how ambient GABA concentrations modulate the input-output relationship of rat Oculomotor Nucleus MNs. Superfusion of brain slices with GABA (100 μm) produced a GABAA receptor-mediated current that reduced the input resistance, increased the recruitment threshold and shifted the f-I relationship rightward without any change in gain. These modifications did not depend on MN size. In absence of exogenous GABA, gabazine (20 μm; antagonist of GABAA receptors) abolished spontaneous inhibitory postsynaptic currents and revealed a tonic current in MNs. Gabazine increased input resistance and decreased recruitment threshold mainly in larger MNs. The f-I relationship shifted to the left, without any change in gain. Gabazine effects were chiefly due to MN tonic inhibition because tonic current amplitude was five-fold greater than phasic. This study demonstrates a tonic inhibition in ocular MNs that modulates cell excitability depending on cell size. We suggest that GABAA tonic inhibition acting concurrently with glutamate receptors activation could reproduce the positive covariation between threshold and gain reported in alert preparation.
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Modulation of the input–output function by GABAA receptor‐mediated currents in rat Oculomotor Nucleus motoneurons
The Journal of physiology, 2014Co-Authors: Julio Torres-torrelo, B. Torres, Livia CarrascalAbstract:The neuronal input-output function depends on recruitment threshold and gain of the firing frequency-current (f-I) relationship. These two parameters are positively correlated in ocular motoneurons (MNs) recorded in alert preparation and inhibitory inputs could contribute to this correlation. Phasic inhibition mediated by γ-amino butyric acid (GABA) occurs when a high concentration of GABA at the synaptic cleft activates postsynaptic GABAA receptors, allowing neuronal information transfer. In some neuronal populations, low concentrations of GABA activate non-synaptic GABAA receptors and generate a tonic inhibition, which modulates cell excitability. This study determined how ambient GABA concentrations modulate the input-output relationship of rat Oculomotor Nucleus MNs. Superfusion of brain slices with GABA (100 μm) produced a GABAA receptor-mediated current that reduced the input resistance, increased the recruitment threshold and shifted the f-I relationship rightward without any change in gain. These modifications did not depend on MN size. In absence of exogenous GABA, gabazine (20 μm; antagonist of GABAA receptors) abolished spontaneous inhibitory postsynaptic currents and revealed a tonic current in MNs. Gabazine increased input resistance and decreased recruitment threshold mainly in larger MNs. The f-I relationship shifted to the left, without any change in gain. Gabazine effects were chiefly due to MN tonic inhibition because tonic current amplitude was five-fold greater than phasic. This study demonstrates a tonic inhibition in ocular MNs that modulates cell excitability depending on cell size. We suggest that GABAA tonic inhibition acting concurrently with glutamate receptors activation could reproduce the positive covariation between threshold and gain reported in alert preparation.
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Glutamate modulates the firing rate in Oculomotor Nucleus motoneurons as a function of the recruitment threshold current.
The Journal of physiology, 2012Co-Authors: Julio Torres-torrelo, Livia Carrascal, Pedro Nunez-abades, David Rodríguez-rosell, B. TorresAbstract:Studies in alert preparations have demonstrated that ocular motoneurons exhibit a phasic-tonic firing rate related to eye velocity and position, respectively. The slopes of these relationships are higher in motoneurons with higher recruitment threshold and have been proposed to depend upon synaptic input. To investigate this hypothesis, motoneurons of the rat Oculomotor Nucleus were recorded in a brain slice preparation in control conditions and during glutamate (5 μM) application to the bath. Glutamate did not affect membrane potential or input resistance, but produced a decrease in rheobase and depolarization voltage as a function of the current needed for generating a maintained repetitive discharge (recruitment threshold current). In addition, glutamate compressed the range of recruitment threshold current (0.1-0.4 nA) as compared to the control (0.15-0.7nA). Glutamate exposed motoneurons showed an increase in the tonic frequency gain and the peak frequency. Such increments depended on the recruitment threshold current and the last recruited motoneurons almost doubled the tonic frequency gain (35.2 vs. 57.9 spikess −1 nA −1 ) and the peak frequency (52.4 vs. 102.6 spikess −1 ). Finally, glutamate increased the spike frequency adaptation due to a significant increase in the phasic firing component as compared to the tonic one. In conclusion, glutamate modulates tonic and phasic discharge properties as a function of the recruitment threshold current and, presumably, motoneuron size. These findings contribute to understand the link between cellular functions and motoneuron discharge during Oculomotor behaviour.
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Diminution of Voltage Threshold Plays a Key Role in Determining Recruitment of Oculomotor Nucleus Motoneurons during Postnatal Development
PLOS ONE, 2011Co-Authors: Livia Carrascal, Jose Luis Nieto-gonzalez, B. Torres, Pedro Nunez-abadesAbstract:The size principle dictates the orderly recruitment of motoneurons (Mns). This principle assumes that Mns of different sizes have a similar voltage threshold, cell size being the crucial property in determining neuronal recruitment. Thus, smaller neurons have higher membrane resistance and require a lower depolarizing current to reach spike threshold. However, the cell size contribution to recruitment in Mns during postnatal development remains unknown. To investigate this subject, rat Oculomotor Nucleus Mns were intracellularly labeled and their electrophysiological properties recorded in a brain slice preparation. Mns were divided into 2 age groups: neonatal (1–7 postnatal days, n = 14) and adult (20–30 postnatal days, n = 10). The increase in size of Mns led to a decrease in input resistance with a strong linear relationship in both age groups. A well-fitted inverse correlation was also found between input resistance and rheobase in both age groups. However, input resistance versus rheobase did not correlate when data from neonatal and adult Mns were combined in a single group. This lack of correlation is due to the fact that decrease in input resistance of developing Mns did not lead to an increase in rheobase. Indeed, a diminution in rheobase was found, and it was accompanied by an unexpected decrease in voltage threshold. Additionally, the decrease in rheobase co-varied with decrease in voltage threshold in developing Mns. These data support that the size principle governs the recruitment order in neonatal Mns and is maintained in adult Mns of the Oculomotor Nucleus; but during postnatal development the crucial property in determining recruitment order in these Mns was not the modifications of cell size-input resistance but of voltage threshold.
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GABAergic Projections to the Oculomotor Nucleus in the Goldfish (carassius Auratus).
Frontiers in neuroanatomy, 2011Co-Authors: M. Angeles Luque, Livia Carrascal, B. Torres, Julio Torres-torrelo, L. HerreroAbstract:The mammalian Oculomotor Nucleus receives a strong -aminobutyric acid (GABA)ergic synaptic input, whereas such projections have rarely been reported in fish. In order to determine whether this synaptic organization is preserved across vertebrates, we investigated the GABAergic projections to the Oculomotor Nucleus in the goldfish by combining retrograde transport of biotin dextran amine, injected into the antidromically identified Oculomotor Nucleus, and GABA immunohistochemistry. The main source of GABAergic afferents to the Oculomotor Nucleus was the ipsilateral anterior octaval Nucleus, with only a few, if any, GABAergic neurons being located in the contralateral tangential and descending nuclei of the octaval column. In mammals there is a nearly exclusive ipsilateral projection from vestibular neurons to the Oculomotor Nucleus via GABAergic inhibitory inputs; thus, the vestibuloOculomotor GABAergic circuitry follows a plan that appears to be shared throughout the vertebrate phylogeny. The second major source of GABAergic projections was the rhombencephalic reticular formation, primarily from the medial area but, to a lesser extent, from the inferior area. A few GABAergic Oculomotor projecting neurons were also observed in the ipsilateral Nucleus of the medial longitudinal fasciculus. The GABAergic projections from neurons located in both the reticular formation surrounding the abducens Nucleus and the Nucleus of the medial reticular formation have primarily been related to the control of saccadic eye movements. Finally, all retrogradely labeled internuclear neurons of the abducens Nucleus, and neurons in the cerebellum (close to the caudal lobe), were negative for GABA. These data suggest that the vestibuloocular and saccadic inhibitory GABAergic systems appear early in vertebrate phylogeny to modulate the firing properties of the Oculomotor Nucleus motoneurons.
N. M. Gerrits - One of the best experts on this subject based on the ideXlab platform.
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GABAergic and glycinergic inputs to the rabbit Oculomotor Nucleus with special emphasis on the medial rectus subdivision
Brain research, 1996Co-Authors: P.r. Wentzel, N. M. Gerrits, C. I. De ZeeuwAbstract:Contradictory results have been reported about the inhibitory input to the medial rectus subdivision of the Oculomotor Nucleus of the cat. In the present ultrastructural study, we quantified the GABAergic and glycinergic terminals in the various subdivisions of the rabbit Oculomotor Nucleus with the use of post-embedding immunocytochemistry combined with retrograde tracing of horseradish peroxidase. The density of the GABAergic input to the medial rectus subdivision was as substantial as that to the other subdivisions and the postsynaptic distribution of the GABAergic and glycinergic innervation did not differ among the different Oculomotor subdivisions.
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INHIBITORY SYNAPTIC INPUTS TO THE Oculomotor Nucleus FROM VESTIBULO-OCULAR -REFLEX-RELATED NUCLEI IN THE RABBIT
Neuroscience, 1995Co-Authors: P.r. Wentzel, C. I. De Zeeuw, J.c. Holstege, N. M. GerritsAbstract:Abstract Studies of the pathways involved in the vestibulo-ocular reflex have suggested that the projection from the superior vestibular Nucleus to the ipsilateral Oculomotor Nucleus is inhibitory, whereas the medial vestibular Nucleus, the abducens Nucleus and the contralateral superior vestivular Nucleus most likely exert excitatory effects on Oculomotor neurons. In order to determine directly the termination pattern and the neurotransmitter of these afferents, we studied their input to the Oculomotor Nucleus in the rabbit at the light microscopic level with the use of anterograde tracing of Phaseolus vulgaris -leucoagglutinin combined with retrograde tracing of horseradish peroxidase from the extraocular muscles, and at the ultrastructural level with the use of anterograde tracing of wheatgerm-agglutinated horseradish peroxidase combined with GABA and glycine postembedding immunocytochemistry. The general ultrastructural characteristics of the neuropil and the types of boutons observed in the rabbit Oculomotor nuclei are in general agreement with the descriptions for the Oculomotor complex of other mammals. The superior vestibular Nucleus projected bilaterally to the superior rectus and inferior oblique subdivisions, and ipsilaterally to the inferior rectus and medial rectus subdivision; the medial vestibular Nucleus projected bilaterally to the medial rectus, inferior oblique, inferior rectus and superior rectus subdivisions with a strong contralateral predominance. The abducens Nucleus projected contralaterally to the medial rectus subdivision. More than 90% of all the anterogradely labled terminals from the ipsilateral superior vestibular Nucleus were GABAergic. These terminals were characterized by flattened vesicles and symmetric synapses, and they contacted somata, as well as proximal and distal dendrites of motoneurons. All terminals derived from the medial vestibular Nucleus the abducens Nucleus and the contralateral superior vestibular Nucleus were non-GABAergic. These non-GABAergic terminals showed spherical vesicles and asymmetric synapses, and they contacted predominantly distal dendrites. None of the anterogradely labeled terminals from the studied vestibular nuclei or abducens Nucleus were glycinergic. The present study provides the first direct anatomical evidence that most, if not all, of the synaptic input from the superior vestibular Nucleus to the ipsilateral Oculomotor Nucleus is GABAergic, and that the medial rectus subdivision is included in the termination area. Furthermore, it confirms that the projections from the medial vestibular Nucleus, the abducens Nucleus and the contralateral superior vestibular Nucleus are exclusively non-GABAergic.
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Colocalization of GABA and glycine in the rabbit Oculomotor Nucleus.
Neuroscience Letters, 1993Co-Authors: P.r. Wentzel, C. I. De Zeeuw, J.c. Holstege, N. M. GerritsAbstract:In the present study we examined the possible colocalization of the inhibitory neurotransmitters glycine and GABA in the Oculomotor Nucleus of the rabbit. Serial sections were processed alternately for glycine and GABA postembedding immuno-cytochemistry. Ultrastructural analysis revealed that all terminals that showed glycine-positive immunoreactivity were also GABA positive; up to 5% of the GABA-positive terminals were also glycine positive.
Pedro Nunez-abades - One of the best experts on this subject based on the ideXlab platform.
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Glutamate modulates the firing rate in Oculomotor Nucleus motoneurons as a function of the recruitment threshold current.
The Journal of physiology, 2012Co-Authors: Julio Torres-torrelo, Livia Carrascal, Pedro Nunez-abades, David Rodríguez-rosell, B. TorresAbstract:Studies in alert preparations have demonstrated that ocular motoneurons exhibit a phasic-tonic firing rate related to eye velocity and position, respectively. The slopes of these relationships are higher in motoneurons with higher recruitment threshold and have been proposed to depend upon synaptic input. To investigate this hypothesis, motoneurons of the rat Oculomotor Nucleus were recorded in a brain slice preparation in control conditions and during glutamate (5 μM) application to the bath. Glutamate did not affect membrane potential or input resistance, but produced a decrease in rheobase and depolarization voltage as a function of the current needed for generating a maintained repetitive discharge (recruitment threshold current). In addition, glutamate compressed the range of recruitment threshold current (0.1-0.4 nA) as compared to the control (0.15-0.7nA). Glutamate exposed motoneurons showed an increase in the tonic frequency gain and the peak frequency. Such increments depended on the recruitment threshold current and the last recruited motoneurons almost doubled the tonic frequency gain (35.2 vs. 57.9 spikess −1 nA −1 ) and the peak frequency (52.4 vs. 102.6 spikess −1 ). Finally, glutamate increased the spike frequency adaptation due to a significant increase in the phasic firing component as compared to the tonic one. In conclusion, glutamate modulates tonic and phasic discharge properties as a function of the recruitment threshold current and, presumably, motoneuron size. These findings contribute to understand the link between cellular functions and motoneuron discharge during Oculomotor behaviour.
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Diminution of Voltage Threshold Plays a Key Role in Determining Recruitment of Oculomotor Nucleus Motoneurons during Postnatal Development
PLOS ONE, 2011Co-Authors: Livia Carrascal, Jose Luis Nieto-gonzalez, B. Torres, Pedro Nunez-abadesAbstract:The size principle dictates the orderly recruitment of motoneurons (Mns). This principle assumes that Mns of different sizes have a similar voltage threshold, cell size being the crucial property in determining neuronal recruitment. Thus, smaller neurons have higher membrane resistance and require a lower depolarizing current to reach spike threshold. However, the cell size contribution to recruitment in Mns during postnatal development remains unknown. To investigate this subject, rat Oculomotor Nucleus Mns were intracellularly labeled and their electrophysiological properties recorded in a brain slice preparation. Mns were divided into 2 age groups: neonatal (1–7 postnatal days, n = 14) and adult (20–30 postnatal days, n = 10). The increase in size of Mns led to a decrease in input resistance with a strong linear relationship in both age groups. A well-fitted inverse correlation was also found between input resistance and rheobase in both age groups. However, input resistance versus rheobase did not correlate when data from neonatal and adult Mns were combined in a single group. This lack of correlation is due to the fact that decrease in input resistance of developing Mns did not lead to an increase in rheobase. Indeed, a diminution in rheobase was found, and it was accompanied by an unexpected decrease in voltage threshold. Additionally, the decrease in rheobase co-varied with decrease in voltage threshold in developing Mns. These data support that the size principle governs the recruitment order in neonatal Mns and is maintained in adult Mns of the Oculomotor Nucleus; but during postnatal development the crucial property in determining recruitment order in these Mns was not the modifications of cell size-input resistance but of voltage threshold.
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Postnatal development enhances the effects of cholinergic inputs on recruitment threshold and firing rate of rat Oculomotor Nucleus motoneurons.
Neuroscience, 2010Co-Authors: Livia Carrascal, B. Torres, M.a. Luque, V. Sobrino, Pedro Nunez-abadesAbstract:Changes in the electrophysiological and morphological characteristics of motoneurons (Mns) of the Oculomotor Nucleus during postnatal development have been reported, however synaptic modifications that take place concurrently with postnatal development in these Mns are yet to be elucidated. We investigated whether cholinergic inputs exert different effects on the recruitment threshold and firing rate of Mns during postnatal development. Rat Oculomotor Nucleus Mns were intracellularly recorded in brain slice preparations and separated in neonatal (4-7 postnatal days) and adult (20-30 postnatal days) age groups. Stimulation of the medial longitudinal fasciculus evoked a monosynaptic excitatory potential in Mns that was attenuated with atropine (1.5 μM, a muscarinic antagonist). Mns were silent at their resting membrane potential, and bath application of carbachol (10 μM, a cholinergic agonist) induced depolarization of the membrane potential and a sustained firing rate that were more pronounced in adult Mns. Pharmacological and immunohistochemical assays showed that these responses were attributable to muscarinic receptors located in the membrane of Mns. In addition, compared to control Mns, carbachol-exposed Mns exhibited a higher firing rate in response to the injection of the same amount of current, and a decrease in the current threshold required to achieve sustained firing. These latter effects were more pronounced in adult than in neonatal Mns. In conclusion, our findings suggest that cholinergic synaptic inputs are already present in neonatal Mns, and that the electrophysiological effects of such inputs on recruitment threshold and firing rate are enhanced with the postnatal development in Oculomotor Nucleus Mns. We propose that cholinergic input maturation could provide a greater dynamic range in adult Mns to encode the output necessary for graded muscle contraction.
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Changes in Somatodendritic Morphometry of Rat Oculomotor Nucleus Motoneurons During Postnatal Development
The Journal of comparative neurology, 2009Co-Authors: Livia Carrascal, Jose Luis Nieto-gonzalez, B. Torres, Pedro Nunez-abadesAbstract:This work investigates the somatodendritic shaping of rat Oculomotor Nucleus motoneurons (Mns) during postnatal development. The Mns were functionally identified in slice preparation, intracellularly injected with neurobiotin, and three-dimensionally reconstructed. Most of the Mns (85%) were multipolar and the rest (15%) bipolar. Forty multipolar Mns were studied and grouped as follows: 1–5, 6 –10, 11–15, and 21–30 postnatal days. Two phases were distinguished during postnatal development (P1–P10 and P11– P30). During the first phase, there was a progressive increase in the dendritic complexity; e.g., the number of terminals per neuron increased from 26.3 (P1–P5) to 47.7 (P6 –P10) and membrane somatodendritic area from 11,289.9 m 2 (P1–P5) to 19,235.8 m 2 (P6 –P10). In addition, a few cases of tracer coupling were observed. During the second phase, dendritic elongation took place; e.g., the maximum dendritic length increased from 486.7 m (P6 – P10) to 729.5 m in adult Mns, with a simplification of dendritic complexity to values near those for the newborn, and a slow, progressive increase in membrane area from 19,235.8 m 2 (P6 –P10) to 24,700.3 m 2 (P21–P30), while the somatic area remained constant. In conclusion, the electrophysiological changes reported in these Mns with maturation (Carrascal et al. [2006] Neuroscience 140:1223–1237) cannot be fully explained by morphometric variations; the dendritic elongation and increase in dendritic area are features shared with other pools of Mns, whereas changes in dendritic complexity depend on each population; the first phase paralleled the establishment of vestibular circuitry and the second paralleled eyelid opening. J. Comp. Neurol.
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Phasic and tonic firing properties in rat Oculomotor Nucleus motoneurons, studied in vitro.
The European journal of neuroscience, 2007Co-Authors: Jose Luis Nieto-gonzalez, Livia Carrascal, Pedro Nunez-abades, B. TorresAbstract:Alert-chronic studies show that ocular motoneurons (Mns) exhibit a phasic and tonic firing correlated with eye saccade-velocity and position (fixation), respectively. Differences in the phasic and tonic firing among Mns depend on synaptic inputs and ⁄or the intrinsic membrane properties. We have used in vitro slice preparation to investigate the contribution of membrane properties to firing properties of Wistar rat Oculomotor Nucleus Mns. We recorded different discharge patterns and focused on Mns with sustained discharge (type I) because they were the most abundant, and their firing pattern resembles that reported in alert preparations. Various differences divided these Mns into types IA and IB; the afterhyperpolarization (AHP) phase of the spike was monophasic in IA and biphasic in IB ;I A Mns showed tonic or phasic-tonic firing depending on the current intensity, while IB Mns showed phasic-tonic discharge; the phasic firing was higher in IB than in IA Mns; IA Mns fired in a narrower range than did IB Mns; and IA Mns showed lower maximum frequency than did IB Mns. In conclusion, IA and IB Mns show different phasic firing properties and dynamic range, supported by intrinsic membrane properties. We suggest that IA and IB Mns innervate fast-twitch muscle fibres with different contraction speeds, and could contribute to generating a fine phasic signal for a graded muscle contraction. Finally, we have demonstrated an inverse relationship between Mn thresholds and tonic firing gain, concluding that intrinsic membrane properties could not support the covariation between tonic firing gain and recruitment thresholds reported in alert studies.
Jean A. Büttner-ennever - One of the best experts on this subject based on the ideXlab platform.
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INTERNAL ORGANIZATION OF MEDIAL RECTUS AND INFERIOR RECTUS MUSCLE NEURONS IN THE C-GROUP OF THE Oculomotor Nucleus IN MONKEY
The Journal of comparative neurology, 2015Co-Authors: Xiaofang Tang, Jean A. Büttner-ennever, Michael J. Mustari, Anja K. E. HornAbstract:Mammalian extraocular muscles contain singly innervated twitch muscle fibers (SIF) and multiply innervated nontwitch muscle fibers (MIF). In monkey, MIF motoneurons lie around the periphery of Oculomotor nuclei and have premotor inputs different from those of the motoneurons inside the nuclei. The most prominent MIF motoneuron group is the C group, which innervates the medial rectus (MR) and inferior rectus (IR) muscle. To explore the organization of both cell groups within the C group, we performed small injections of choleratoxin subunit B into the myotendinous junction of MR or IR in monkeys. In three animals the IR and MR myotendinous junction of one eye was injected simultaneously with different tracers (choleratoxin subunit B and wheat germ agglutinin). This revealed that both muscles were supplied by two different, nonoverlapping populations in the C group. The IR neurons lie adjacent to the dorsomedial border of the Oculomotor Nucleus, whereas MR neurons are located farther medially. A striking feature was the differing pattern of dendrite distribution of both cell groups. Whereas the dendrites of IR neurons spread into the supraOculomotor area bilaterally, those of the MR neurons were restricted to the ipsilateral side and sent a focused bundle dorsally to the preganglionic neurons of the Edinger-Westphal Nucleus, which are involved in the "near response." In conclusion, MR and IR are innervated by independent neuron populations from the C group. Their dendritic branching pattern within the supraOculomotor area indicates a participation in the near response providing vergence but also reflects their differing functional roles.
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Delineation of motoneuron subgroups supplying individual eye muscles in the human Oculomotor Nucleus.
Frontiers in neuroanatomy, 2014Co-Authors: Emmanuel Che Ngwa, Jean A. Büttner-ennever, Christina Zeeh, Ahmed Messoudi, Anja K. E. HornAbstract:The Oculomotor Nucleus (nIII) contains the motoneurons of medial, inferior and superior recti (MR, IR, SR), inferior oblique (IO) and levator palpebrae (LP) muscles. The delineation of motoneuron subgroups for each muscle is well-known in monkey, but not in human. We studied the transmitter inputs to human nIII and the trochlear Nucleus (nIV), which innervates the superior oblique muscle (SO), to outline individual motoneuron subgroups. Parallel series of sections from human brainstems were immunostained for different markers: acetylcholine transferase (ChAT) combined with glutamate decarboxylase (GAD), calretinin (CR) or glycine receptor (GlyR). The cytoarchitecture was visualized with Cresyl violet, Gallyas staining and expression of non-phosphorylated neurofilaments (NP-NF). Apart from nIV, seven subgroups were delineated in nIII: the central caudal Nucleus (CCN), a dorsolateral (DL), dorsomedial (DM), central (CEN), and ventral group (VEN), the Nucleus of Perlia (NP) and the non-preganglionic centrally projecting Edinger-Westphal Nucleus (EWcp). DL, VEN, NP and EWcp were characterized by a strong supply of GAD-positive terminals, in contrast to DM, CEN and nIV. CR-positive terminals and fibres were confined to CCN, CEN and NP. Based on location and histochemistry of the motoneuron subgroups in monkey, CEN is considered as the SR and IO motoneurons, DL and VEN as the B- and A-group of MR motoneurons, respectively, and DM as IR motoneurons. A good correlation between monkey and man is seen for the CR input, which labels only motoneurons of eye muscles participating in upgaze (SR, IO and LP). The CCN contained LP motoneurons, and nIV those of SO. This study provides a map of the individual subgroups of motoneurons in human nIII for the first time, and suggests that NP may contain upgaze motoneurons. Surprisingly, a strong GABAergic input to human MR motoneurons was discovered, which is not seen in monkey and may indicate a functional Oculomotor specialization.
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Twitch and nontwitch motoneuron subgroups in the Oculomotor Nucleus of monkeys receive different afferent projections.
The Journal of comparative neurology, 2004Co-Authors: Richard Wasicky, Anja K. E. Horn, Jean A. Büttner-enneverAbstract:Motoneurons in the primate Oculomotor Nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical Oculomotor Nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens Nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular Nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular Nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the Nucleus of the optic tract (NOT), and the olivary pretectal Nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system. J. Comp. Neurol. 479:117–129, 2004. © 2004 Wiley-Liss, Inc.
