The electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisti... more The electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisting of four bilaterally arranged electrocyte rows; and an anterior portion composed of only two. The lateral row (LR) of the anterior portion contains doubly innervated electrocytes with axon terminals from different nerves on their rostral and caudal faces. The LR is continuous with the most dorsal row of the caudal region. This row also contains doubly innervated electrocytes. The medial row (MR) electrocytes of the anterior region and ventral rows of the caudal region are exclusively caudally innervated. All caudal faces of the anterior or abdominal region are supplied by two nerves which originate from spinal roots VIII to XXI. Roots I to VII give origin to pure rostral nerves whose electromotor axons terminate on the rostral surfaces of the first seven LR electrocytes. A given doubly innervated electrocyte is supplied on its caudal face by a nerve originating several segments (usually seven) posterior to the spinal root supplying its rostral face. Transections of the spinal cord at the level of root VIII isolate the activity of the rostral surfaces of the first electrocytes. The EO discharge (EOD) then appears as a head negative deflection which arises from abdominally located electrocytes. Its monophasic character reveals that the activity remains restricted to the rostral electrocyte surfaces. Damage of the abdominal portion of the EO abolishes the first negative deflection of the normal pulse. Transections of the spinal cord at the level of root XXI isolate the activity of the whole abdominal portion of the EO.(ABSTRACT TRUNCATED AT 250 WORDS)
ABSTRACT Static and dynamic measurements of the righting reflex were performed in intact toads (B... more ABSTRACT Static and dynamic measurements of the righting reflex were performed in intact toads (Bufo arenarum platensis) and at different stages of recovery from hemilabyrinthectomy. Reflex activity was evaluated by the toad's capacity to maintain a horizontal head position while rolled sideways. Static data were obtained from frontal photographs. In dynamic experiments platform position (stimulus) was measured through a potentiometer, while a linear accelerometer glued to the cranium was used to record head tilts. The dynamic study included a linear systems analysis using sinusoids of 0.5-3 Hz with rolls of up to 30° to each side. Hemilabyrinthectomy produced a head tilt towards the lesioned side, and gain decay and phase lag increase in the dynamic response. All postural defects recovered progressively within 30-60 days as already described in other species. Nevertheless, the tonic head deviation produced by dynamic stimuli of frequencies above 1 Hz did not recover. This remnant defect has not been observed in previous studies in which only static observations were performed. The involvement of a frequency-dependent rectifying mechanism in postural compensation is discussed.
The subthalamic nucleus participates in the control of movement and is considered a surgical targ... more The subthalamic nucleus participates in the control of movement and is considered a surgical target in the treatment of parkinsonian symptoms. Using the rat brain in vitro slice technique we show that sustained high-frequency (>100 Hz) electrical stimulation (i.e., ‘tetanic stimulation’) of the nucleus, as used in humans to treat Parkinson’s disease, silenced subthalamic neurons. Two main cell types were
The subthalamic nucleus participates in the control of movement and is considered a surgical targ... more The subthalamic nucleus participates in the control of movement and is considered a surgical target in the treatment of parkinsonian symptoms. Using the rat brain in vitro slice technique we show that sustained high-frequency (>100 Hz) electrical stimulation (i.e., 'tetanic stimulation') of the nucleus, as used in humans to treat Parkinson's disease, silenced subthalamic neurons. Two main cell types were identified. 'Tonic cells' (68%) showed delayed inward rectification, fired continuously, switched to bursting and stopped firing when strongly depolarized with injected current. Tetanic stimulation of the nucleus induced a steady depolarization (approximately 18 mV) that triggered action potentials at a high rate followed by bursts and finally (approximately 25 s) totally silenced tonic cells. The control tonic activity was recovered rapidly (<10 s) after ending stimulation. 'Phasic cells' (25%) discharged a single initial brief burst of action pote...
Neuronal synchronization is a basic feature in the generation of epileptiform discharges. Spontan... more Neuronal synchronization is a basic feature in the generation of epileptiform discharges. Spontaneous large sharp waves (LSWs) can be recorded in the turtle brain in vitro, indicating the synchronous activation of large neuronal populations. The aim of this study was to analyze the spatial and temporal distribution of LSWs within the brain; the participation of glutamate in LSWs generation was also investigated. Extracellular field potentials were recorded in vivo (n = 4) and in vitro (n = 36). LSWs were recorded from cerebral cortex, optic tectum, and thalamus. LSWs were recorded from cerebral cortex, optic tectum and thalamus. No LSWs were observed in cerebellum and brain stem. In some experiments, LSWs could be recorded only from medial cortex. Latency studies demonstrated that, within each hemisphere, medial cortex led the generation of LSWs; in addition, isolated medial cortex could sustain LSWs. Intracortical laminar field potentials in medial cortex indicated that LSWs generate mainly in the molecular layer, probably at pyramidal cell dendrites. Pharmacological experiments demonstrated that NMDA and non-NMDA glutamate receptors are involved in LWSs generation. These results suggest that turtle medial cortex is the pacemaker area for LSWs generation and it can be a useful model to study cellular and circuital mechanisms of neuronal synchronization.
Vestibular habituation was studied in normal subjects and in patients with cerebellar disease usi... more Vestibular habituation was studied in normal subjects and in patients with cerebellar disease using a stimulation paradigm proposed in this paper. Six caloric stimuli were repeated daily in the same ear during six days and electronystagmographic responses at the beginning and the end of that period were compared. The normal behaviour was a clear reduction of the response across time. Two groups of cerebellar patients were identified by their ability to recover from positional imbalance after treatment. Compensated patients responded to repeated caloric stimulation in the same way as normal subjects. Conversely, uncompensated patients increased their response after the stimulation paradigm. The role played by the cerebellum in vestibular plasticity is discussed together with the observed correlation between vestibular habituation and the ability for postural recovery to occur.
1. We classified the utricular afferents on the basis of their spontaneous acitivity and response... more 1. We classified the utricular afferents on the basis of their spontaneous acitivity and responses to tilts and vibrations. 2. Type I afferents fire spontaneously in a regular pattern; their responses to tilts consist of a phasic-tonic change in firing rate. They may respond to vibrations by increasing or decreasing their rate and show no adaptation. 3. The spontaneous activity and the responses to tilts of type II are similar to those observed in type I afferents. The differences become apparent when the preparation is subjected to a vibrational stimulus, since type II neurons increase their firing rate regardless of the stimulus frequency and show adaptation. 4. Type III neurons have no spontaneous activity. They respond to tilts by firing during the transition from one position to the other. They respond to a vibrational stimulus with maintained firing and show no adaptation. 5. We studied the dynamic responses of each type of neuron. We used sensitivity curves for the study of t...
The electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisti... more The electrogenic organ (EO) of Gymnotus carapo has two main portions: a posterior region consisting of four bilaterally arranged electrocyte rows; and an anterior portion composed of only two. The lateral row (LR) of the anterior portion contains doubly innervated electrocytes with axon terminals from different nerves on their rostral and caudal faces. The LR is continuous with the most dorsal row of the caudal region. This row also contains doubly innervated electrocytes. The medial row (MR) electrocytes of the anterior region and ventral rows of the caudal region are exclusively caudally innervated. All caudal faces of the anterior or abdominal region are supplied by two nerves which originate from spinal roots VIII to XXI. Roots I to VII give origin to pure rostral nerves whose electromotor axons terminate on the rostral surfaces of the first seven LR electrocytes. A given doubly innervated electrocyte is supplied on its caudal face by a nerve originating several segments (usually seven) posterior to the spinal root supplying its rostral face. Transections of the spinal cord at the level of root VIII isolate the activity of the rostral surfaces of the first electrocytes. The EO discharge (EOD) then appears as a head negative deflection which arises from abdominally located electrocytes. Its monophasic character reveals that the activity remains restricted to the rostral electrocyte surfaces. Damage of the abdominal portion of the EO abolishes the first negative deflection of the normal pulse. Transections of the spinal cord at the level of root XXI isolate the activity of the whole abdominal portion of the EO.(ABSTRACT TRUNCATED AT 250 WORDS)
ABSTRACT Static and dynamic measurements of the righting reflex were performed in intact toads (B... more ABSTRACT Static and dynamic measurements of the righting reflex were performed in intact toads (Bufo arenarum platensis) and at different stages of recovery from hemilabyrinthectomy. Reflex activity was evaluated by the toad&#39;s capacity to maintain a horizontal head position while rolled sideways. Static data were obtained from frontal photographs. In dynamic experiments platform position (stimulus) was measured through a potentiometer, while a linear accelerometer glued to the cranium was used to record head tilts. The dynamic study included a linear systems analysis using sinusoids of 0.5-3 Hz with rolls of up to 30° to each side. Hemilabyrinthectomy produced a head tilt towards the lesioned side, and gain decay and phase lag increase in the dynamic response. All postural defects recovered progressively within 30-60 days as already described in other species. Nevertheless, the tonic head deviation produced by dynamic stimuli of frequencies above 1 Hz did not recover. This remnant defect has not been observed in previous studies in which only static observations were performed. The involvement of a frequency-dependent rectifying mechanism in postural compensation is discussed.
The subthalamic nucleus participates in the control of movement and is considered a surgical targ... more The subthalamic nucleus participates in the control of movement and is considered a surgical target in the treatment of parkinsonian symptoms. Using the rat brain in vitro slice technique we show that sustained high-frequency (>100 Hz) electrical stimulation (i.e., ‘tetanic stimulation’) of the nucleus, as used in humans to treat Parkinson’s disease, silenced subthalamic neurons. Two main cell types were
The subthalamic nucleus participates in the control of movement and is considered a surgical targ... more The subthalamic nucleus participates in the control of movement and is considered a surgical target in the treatment of parkinsonian symptoms. Using the rat brain in vitro slice technique we show that sustained high-frequency (>100 Hz) electrical stimulation (i.e., 'tetanic stimulation') of the nucleus, as used in humans to treat Parkinson's disease, silenced subthalamic neurons. Two main cell types were identified. 'Tonic cells' (68%) showed delayed inward rectification, fired continuously, switched to bursting and stopped firing when strongly depolarized with injected current. Tetanic stimulation of the nucleus induced a steady depolarization (approximately 18 mV) that triggered action potentials at a high rate followed by bursts and finally (approximately 25 s) totally silenced tonic cells. The control tonic activity was recovered rapidly (<10 s) after ending stimulation. 'Phasic cells' (25%) discharged a single initial brief burst of action pote...
Neuronal synchronization is a basic feature in the generation of epileptiform discharges. Spontan... more Neuronal synchronization is a basic feature in the generation of epileptiform discharges. Spontaneous large sharp waves (LSWs) can be recorded in the turtle brain in vitro, indicating the synchronous activation of large neuronal populations. The aim of this study was to analyze the spatial and temporal distribution of LSWs within the brain; the participation of glutamate in LSWs generation was also investigated. Extracellular field potentials were recorded in vivo (n = 4) and in vitro (n = 36). LSWs were recorded from cerebral cortex, optic tectum, and thalamus. LSWs were recorded from cerebral cortex, optic tectum and thalamus. No LSWs were observed in cerebellum and brain stem. In some experiments, LSWs could be recorded only from medial cortex. Latency studies demonstrated that, within each hemisphere, medial cortex led the generation of LSWs; in addition, isolated medial cortex could sustain LSWs. Intracortical laminar field potentials in medial cortex indicated that LSWs generate mainly in the molecular layer, probably at pyramidal cell dendrites. Pharmacological experiments demonstrated that NMDA and non-NMDA glutamate receptors are involved in LWSs generation. These results suggest that turtle medial cortex is the pacemaker area for LSWs generation and it can be a useful model to study cellular and circuital mechanisms of neuronal synchronization.
Vestibular habituation was studied in normal subjects and in patients with cerebellar disease usi... more Vestibular habituation was studied in normal subjects and in patients with cerebellar disease using a stimulation paradigm proposed in this paper. Six caloric stimuli were repeated daily in the same ear during six days and electronystagmographic responses at the beginning and the end of that period were compared. The normal behaviour was a clear reduction of the response across time. Two groups of cerebellar patients were identified by their ability to recover from positional imbalance after treatment. Compensated patients responded to repeated caloric stimulation in the same way as normal subjects. Conversely, uncompensated patients increased their response after the stimulation paradigm. The role played by the cerebellum in vestibular plasticity is discussed together with the observed correlation between vestibular habituation and the ability for postural recovery to occur.
1. We classified the utricular afferents on the basis of their spontaneous acitivity and response... more 1. We classified the utricular afferents on the basis of their spontaneous acitivity and responses to tilts and vibrations. 2. Type I afferents fire spontaneously in a regular pattern; their responses to tilts consist of a phasic-tonic change in firing rate. They may respond to vibrations by increasing or decreasing their rate and show no adaptation. 3. The spontaneous activity and the responses to tilts of type II are similar to those observed in type I afferents. The differences become apparent when the preparation is subjected to a vibrational stimulus, since type II neurons increase their firing rate regardless of the stimulus frequency and show adaptation. 4. Type III neurons have no spontaneous activity. They respond to tilts by firing during the transition from one position to the other. They respond to a vibrational stimulus with maintained firing and show no adaptation. 5. We studied the dynamic responses of each type of neuron. We used sensitivity curves for the study of t...
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