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T J Ebner

Publications and source records attributed to T J Ebner.

At least 73 records · Page 4Linked to original sources
PubMed1987

Changes in the responses of cerebellar nuclear neurons associated with the climbing fiber response of Purkinje cells.

Previous studies demonstrated that climbing fiber activity produces a short-term increase in the responsiveness of Purkinje cells to mossy fiber inputs. This led to the hypothesis that there are concomitant alterations in the discharge of cerebellar nuclear neurons. This series of experiments was initiated to test this hypothesis in simultaneously recorded Purkinje cell-nuclear cell pairs in related regions of the cerebellar cortex and nuclei. In decerebrate cats 50 pairs of Purkinje cells and nuclear neurons were identified and simultaneously recorded during spontaneous activity and during peripheral inputs. Auto-correlograms of nuclear cell activity and cross-correlograms of the simple spike and nuclear cell activity triggered on the occurrence of spontaneous complex spikes demonstrated little correlation between these events and the discharge of nuclear neurons. To examine the effect of evoked climbing fiber inputs on the Purkinje cell simple spike and nuclear cell responses, square wave mechanical stimuli which modulated the discharge of both cells of a pair were applied to the forepaw. A separation technique was used to construct one histogram illustrating the responses of the nuclear neuron and Purkinje cell in trials in which the peripheral stimulus evoked a climbing fiber input to the Purkinje cell and another histogram showing their responses in trials in which no climbing fiber input was activated. Using this separation technique it was shown that the amplitude of most Purkinje cell responses increased by 120-1200% in trials in which climbing fiber inputs were activated. The response amplitude of 68% of the nuclear cells was modified for these pairs. Most changes in nuclear cell responses were increases ranging from 120-220%. These changes were felt to reflect the action of many Purkinje cells converging on the isolated nuclear neuron. The modulation of the nuclear neuron was not due only to the effect of the related Purkinje cell, since the gain change of the Purkinje cell and nuclear cell of each pair was not correlated (r = 0.01). The discussion of these findings emphasizes that the increased responses of the nuclear cell are most likely produced by the intracortical action of the climbing fiber system on the responsiveness of Purkinje cells to mossy fiber inputs. Climbing fiber collateral input to nuclear neurons also may contribute to the changes in the nuclear cell responses observed in these experiments.

Afferent Pathways↗
PubMed1987

Evaluations of combined premotor and supplementary motor cortex lesions on a visually guided arm movement.

The kinematics of a visually guided, multi-joint arm movement were examined before and after combined bilateral premotor and supplementary motor cortex lesions. Two rhesus monkeys were trained to move a manipulandum from a start zone to one of three equally spaced target zones and then return to the initial start zone. Various features of the movement trajectory including space error, time error, peak velocity and turnaround time were quantified and analyzed before and after the premotor and supplementary motor cortex ablations. Statistical analysis showed no major differences in the trajectories toward or away from the target between the pre- and postlesion state. The major difference following the ablation was an increase in the time spent in the target zone, reflecting an increase in time spent in redirecting the trajectory. Normalization of the movement duration revealed a slight delay in the initial part of the movement. These results suggest the premotor and supplementary motor cortex are involved in redirecting the trajectory and/or obtaining the target zone during the execution of a complex movement.

Animals↗
PubMed1987

Climbing fiber afferent modulation during a visually guided, multi-joint arm movement in the monkey.

During a visually guided, multi-joint voluntary arm movement Purkinje cell simple and complex spike activity was recorded from the ipsilateral hemisphere and intermediate zone of the cerebellum in the rhesus monkey. The task consisted of moving a manipulandum over a horizontal video screen. Manipulandum (hand position) was represented by a cursor on the screen, the animal required to place the manipulandum within displayed start and target boxes. Purkinje cell complex spike discharge was examined using two paradigms. In the first the animal moved the manipulandum from a start box to a target box. In the second the animal was required to modify an ongoing movement and place the cursor within a repositioned target box. A majority of the cells (44/74) exhibited a statistically significant increase in the probability of complex spike discharge at various times during the movement. The increase was observed when the movement trajectory was redirected (36/44) and/or during the initial portion of the movement (27/44). These results suggest the climbing fiber afferent system is routinely involved in the execution of multi-joint movements especially when the movement is redirected. Possibilities include that climbing fiber afferent input is required when the motor state changes and/or during errors in motor performance.

Action Potentials↗
PubMed1987

Responses of interposed and dentate neurons to perturbations of the locomotor cycle.

This study examined the relationship of antidromically identified neurons in the dentate and interposed nuclei to perturbed and unperturbed locomotion in the pre-collicular, mid-mamillary, decerebrate cat. During treadmill locomotion two methods were used to perturb the step cycle. In the first, the treadmill was braked in different phases of the step cycle, the "treadmill" perturbation. In the second, the motion of the ipsilateral forelimb was interrupted by a rod placed transiently in the limb's path, the "single limb" perturbation. Most interposed cells were modulated during locomotion, their discharge being highly correlated with the EMG of the ipsilateral biceps or triceps. When the locomotion was perturbed, the modulation ceased for the duration of the perturbation. A few interposed cells displayed activity patterns unrelated to the EMG but were responsive to perturbations of a single limb. These responses may be explained by the putative activation of peripheral afferents produced by the perturbation. Most dentate cells were not modulated during unperturbed locomotion but did respond to features of the treadmill perturbation. Usually the response was coupled to the resumption of treadmill motion. A minority of dentate neurons was modulated slightly during unperturbed locomotion. Their modulation was less dramatic than that of interposed cells and was only weakly related to limb movement or EMG activity. Like the interposed neurons, these dentate cells responded to the treadmill perturbation with a cessation of modulation. All dentate cells were unresponsive to single limb perturbations. In a preparation lacking cerebral cortical input, the findings show that neurons of the interposed and dentate nuclei are modulated differently during perturbed and unperturbed treadmill walking in the decerebrate cat. The activity of interposed neurons is related to specific features of EMG activity recorded from muscles in the ipsilateral forelimb. Although some dentate cells were weakly modulated during unperturbed locomotion, the majority of these neurons responded most dramatically to the occurrence of a perturbation which completely stopped the walking behavior.

Animals↗
PubMed1987

Climbing fiber afferent modulation during treadmill locomotion in the cat.

The relationship of the climbing fiber afferent discharge to the unperturbed and perturbed step cycle was evaluated in the cat. Following a precollicular-premamillary decerebration, cats walked spontaneously on a motorized treadmill. Purkinje cells were recorded extracellularly and simple and complex spikes were discriminated. Right forelimb displacement, biceps and triceps EMG activity, as well as treadmill velocity, were also monitored. In some animals pressure measurements of the contact of the footpad with the treadmill were obtained. Cells were studied during both "normal" and perturbed locomotion. The perturbation consisted of a braking of the treadmill at different phases in the step cycle. Histograms of the simple and complex spike activity, and averages of the right forelimb displacement, biceps, and triceps EMG activity and treadmill velocity were constructed. The complex spike activity of 163 Purkinje cells was averaged through a minimum of 50 sweeps in either normal and/or perturbed locomotion. Statistical analysis revealed that the probability of the climbing fiber afferent discharge in 54% of the cells (36/67) studied during normal locomotion was significantly modulated with the step cycle. For most Purkinje cells the onset of the increase in climbing fiber afferent discharge was coupled to triceps activity and the onset of stance phase. A group of cells exhibited complex spike discharge in association with biceps onset and swing. These observations suggest that complex spike discharge occurs preferentially at the phase transition periods in the step cycle when the trajectory of the forelimb changes from swing to stance or stance to swing. During treadmill braking 51% of the cells exhibited complex spike modulation (70/137). A number of different patterns of climbing fiber afferent modulation occurred. The most common pattern was an increase in complex spike discharge with the resumption of the treadmill movement and locomotion. Analysis of the time of these periods of increased climbing fiber activity suggests that, although in some cells the response is coupled to the treadmill onset, in other cells the modulation occurs at longer latencies. Subsequent analysis aligning the EMG, displacement, and treadmill velocity signals with the times of the climbing fiber afferent discharge suggested some responses were coupled to the reinitiation of the locomotor cycle. The second most common pattern was an increase in climbing fiber afferent discharge at the onset of the perturbation. Also, in some cells, complex spike discharge decreased during the period in which the step cycle was arrested.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Reduction of cerebellar norepinephrine alters climbing fiber enhancement of mossy fiber input to the Purkinje cell.

Extra-cellular simple and complex spike activity from 58 Purkinje cells were recorded in cats that previously received an intracisternal injection of 6-OHDA which depletes brain catecholamines. The severest catecholamine depletion was noted for cerebellar norepinephrine (21.1% of controls). Less depletion occurred in the brainstem and the visual cortex. Past studies have shown that in normal non-depleted cats, somatosensory stimuli (forepaw tap) evoke both complex and simple spike responses. On those trials where complex spike or climbing fiber responses are evoked, there is an enhancement or increase in responsiveness in the majority of excitatory and inhibitory simple spike responses. In the norepinephrine depleted animal, there is a significant decrease in this climbing fiber enhancement only for the excitatory response components. Furthermore, on those trials where no complex spikes are evoked, there is a significant decrease in the excitatory but not in the inhibitory response amplitude. A slight but non-significant increase in Purkinje cell background firing rate is also observed in the depleted animals. Thus, depletion of norepinephrine is associated with a reduction of both response amplitude and climbing fiber induced enhancement of excitatory simple spike responses. The inhibitory responses in these same cells are unchanged when compared to those recorded in the normal non-depleted animals.

Animals↗
PubMed1986

Comparison of response properties of dorsal and ventral spinocerebellar tract neurons to a physiological stimulus.

The response characteristics of dorsal spinocerebellar tract (DSCT) neurons and ventral spinocerebellar tract (VSCT) neurons to the cutaneous inputs applied to footpads were studied in the cat. Three different wave forms were used: step displacement of varying amplitudes (0.1-3.5 mm); constant amplitude ramps with different slopes (5-120 mm/s); and constant amplitude sinusoidal displacements of varying frequencies (1-20 Hz). Both DSCT and VSCT neurons responded phasically to cutaneous stimuli of different wave forms. The phasic responses were related to both the amplitude and velocity of the peripheral stimulus. However, the responses of DSCT neurons were graded over only a very narrow, low range of stimulus intensities, whereas the responses of VSCT neurons were graded over a larger range of skin indentation up to 3 mm. Only the DSCT neurons exhibited some length sensitivity to ramp stimuli, and only DSCT neurons were activated repetitively by periodic stimuli. These results suggest both DSCT and VSCT can transmit exteroceptive information but respond selectively to different features of these stimuli.

Afferent Pathways↗
PubMed1985

Electrophysiological study of the corticonuclear projection in the cat cerebellum.

Experiments were designed to examine the relationship between the responses of Purkinje cells to natural peripheral stimuli and the location of these neurons within identified zones of the corticonuclear projection in lobule V of the cat cerebellar cortex. It was hypothesized that the corticonuclear zones are sharply demarcated and that the responses of Purkinje cells to a restricted natural stimulus is not localized to only one zone but rather is present and varies in character across these 3 zones. Initially the spatial distribution of the antidromic field potential evoked by stimulating in the fastigial (FN), lateral vestibular (LVN), and anterior interposed nuclei (AIN) was determined in sublobules Va-Vc in unanesthetized decerebrate cats. In some animals the corticonuclear projection was further examined by evaluating the location of Purkinje cells responding antidromically to stimuli in the FN, LVN and AIN, or FN, AIN and the posterior interposed nuclei (PIN). Once a Purkinje cell was identified, its simple and complex spike responses to a step-like flexion-extension passive movement of the ipsilateral forepaw were determined. The boundary based on the antidromic activation of Purkinje cells between the fastigial zone (FZ) and the anterior interposed zone (AIZ) in sublobules Va-Vc of the cerebellar cortex was highly reproducible from cat to cat, although there was a slight overlap between these zones based on the antidromic field potential. The FZ-AIZ border was located at 2.1 +/- 0.12 mm lateral and parallel to the midline. The FZ also contained a few cells projecting to the LVN. However, the AIZ only contained neurons projecting to the AIN. The boundary between AIZ and PIZ in lobule Va-Vc was between 3.3 and 3.8 mm from the midline and ran parallel to it. The peristimulus time histograms (PSTHs) of the simple and complex spike activity to a passive forepaw displacement revealed extensive modulation of neurons located across the mediolateral extent of the AI and PIZ. Both the simple and complex spike discharge of Purkinje cells projecting to the FN also were modulated, but to a lesser degree than cells in AIZ or PIZ. The spatial distribution of simple and complex spike responses recorded from Purkinje cells overlapped extensively. The data support previous findings that the corticonuclear projection is organized into longitudinally oriented sagittal zones. Electrophysiologically the boundaries were remarkably reproducible from animal to animal. The results also show that information processing involving the modulation of Purkinje cell activity in response to the forepaw stimulus occurs in all 3 zones examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Climbing fiber action on the responsiveness of Purkinje cells to parallel fiber inputs.

Recent work in our laboratory has demonstrated that spontaneous or evoked climbing fiber inputs are associated with an increased responsiveness of Purkinje cells to mossy fiber inputs activated by natural peripheral stimuli. These experiments were designed to test the hypothesis that this increased responsiveness occurs in the cerebellar cortex. In decerebrate, unanesthetized cats Purkinje cells in the surface folium were isolated and their simple and complex spikes discriminated. A bipolar concentric stimulating electrode was placed on the surface of the folium to activate the parallel fiber volley and modulate the Purkinje cell's simple spike discharge. The cell's simple spike discharge was evaluated when the surface stimulus was presented randomly and when this stimulus was timed to occur at a fixed interval after the spontaneous complex spike activity. When the surface stimulus was timed to occur at short intervals after the spontaneous complex spike, the response to the surface stimulus was accentuated. This increase in simple spike modulation occurred independent of whether the simple spike discharge increased or decreased in response to the surface stimulus. These results support the hypothesis that the climbing fiber input changes the gain of Purkinje cells' simple spike responses to mossy fiber inputs due to interactions occurring in the cerebellar cortex.

Afferent Pathways↗
PubMed1984

Effects of periaqueductal gray and raphe magnus stimulation on the responses of spinocervical and other ascending projection neurons to non-noxious inputs.

Experiments were performed in cats anesthetized with alpha-chloralose to examine the effects of stimulating in the periaqueductal gray (PAG) and nucleus raphe magnus (NRM) on the responses of spinocervical cells and unidentified ascending projection neurons to non-noxious peripheral stimuli. Peripheral stimuli consisted of low amplitude sinusoidal displacements applied to either the glabrous skin or the hairy skin of the neuron's receptive field. Stimulating in either the periaqueductal gray or nucleus raphe magnus reduced the impulse activity of most neurons in both groups. By applying brainstem stimuli at various phases of the sinusoidal peripheral stimulus, it was demonstrated that the effects of stimulating either the PAG or NRM on the responses of both types of neurons was dependent on the timing of the electrical stimuli relative to the peripheral input. The effects of stimulating in the PAG and NRM on the responses of these cells to non-noxious stimuli were reversibly blocked by naloxone. It was concluded that stimulating in the nucleus raphe magnus and in the periaqueductal gray can produce dramatic modifications in the responses of spinocervical cells and unidentified ascending projection neurons to non-noxious peripheral stimuli, suggesting a role for these descending systems in non-noxious information processing.

Afferent Pathways↗
PubMed1984

Rhythmic discharge of climbing fibre afferents in response to natural peripheral stimuli in the cat.

The rhythmicity of inferior olivary neurones evoked by natural ipsilateral forepaw inputs was evaluated in the climbing fibre afferent discharge of Purkinje cells recorded in the cerebellar cortex of the decerebrate, unanaesthetized cat. Almost 50% of all Purkinje cells responding to the forepaw stimulus with an increase in complex spike activity exhibited periodic discharge, with the dominant periodicity being between 100 and 160 ms. In ten of twenty-five neighbouring, simultaneously recorded Purkinje cells the forepaw stimulus evoked similar periodicity in their complex spike discharge. For some cells two peaks of complex spike activity were evoked by a forepaw stimulus without an obvious third peak. By altering the stimulus duration the second peak of the response was shown to be temporally uncoupled to the 'off' phase of the displacement for many cells. The interdependence of the trials contributing to the periodic peaks in the peristimulus time histogram (p.s.t.h.) was examined by a 'separation technique'. This analysis indicated that the complex spikes contributing to a specific peak in the p.s.t.h. were generated with a high degree of independence (i.e. in different trials) from the complex spikes contributing to any other peak. It was hypothesized that the independence of the rhythmic complex spike peaks is due to the long relative refractoriness following a complex spike in a single cell. Therefore, the probability of a complex spike occurring at the next one or two cycles is decreased significantly. As a consequence, an inferior olivary neurone fires usually at only one of the various peaks in response to a single presentation of the forepaw stimulus. This hypothesis predicts that stimuli evoking a complex spike at the initial peak in a high percentage of trials should give rise to less periodicity. This prediction was tested by comparing the presence or absence of evoked oscillation with the probability of evoking a complex spike in the first peak of the p.s.t.h. Cells exhibiting a probability for complex spike discharge of over 50% in the first peak showed much less periodicity than cells with a complex spike occurring in less than 50% of the trials in the first peak. These results are discussed in the context of the inferior olive being viewed as a population of coupled elements with a tendency to oscillate. The natural forepaw stimulus is hypothesized as synchronizing the phases of spontaneously oscillating climbing fibre afferents, resulting in the observed periodicity in the complex spike p.s.t.h.

Action Potentials↗
PubMed1983

Increase in Purkinje cell gain associated with naturally activated climbing fiber input.

These experiments were designed to test the hypothesis that climbing fiber inputs evoked by a peripheral stimulus increase the responsiveness of Purkinje cells to mossy fiber inputs. This hypothesis was based on a previous series of observations demonstrating that spontaneous climbing fiber inputs are associated with an accentuation of the Purkinje cell responses to subsequent mossy fiber inputs (10, 12). Furthermore, short-term nonpersistent interactions between climbing and mossy fiber inputs have been an important aspect of many theories of cerebellar function (5, 7, 8, 12, 36). Extracellular unitary recordings were made from Purkinje cells in lobule V of decerebrate, unanesthetized cats. To activate mossy and climbing fiber inputs, the forepaw was passively flexed by a Ling vibrator system. A data analysis was developed to sort the simple spike trials into two groups, based on the presence or absence of complex spikes activated by the stimulus. In addition, during those trials in which complex spikes were activated, the simple spike train was aligned on the occurrence of the complex spike. For each simple spike response to the forepaw input, the average firing rate during the response was compared to background both in those trials in which complex spikes were activated and in those in which they were not. The ratio of the response amplitudes in the histograms constructed from these two groups of trials permitted a quantification of the change in responsiveness when climbing fiber inputs were activated. The results show that both excitatory and inhibitory simple spike responses are accentuated when associated with the activation of a complex spike. Using an arbitrary level of a gain change ratio of 120% as indicating a significant modification, 64% of the response components analyzed increased their amplitude when climbing fiber input was present. Simple spike response components occurring prior to complex spike activation were usually not accentuated, although in a few cells the amplitude of this component of the response increased. In addition, in a small number of cells the occurrence of complex spikes was associated with a new simple spike component. For excitatory responses, the magnitude of the gain change ratio was shown to be inversely related to the amplitude of the simple spike response evoked by the mossy fiber inputs. The data obtained is consistent with the hypothesis that the climbing fiber input is associated with an increase in the responsiveness of Purkinje cells to mossy fiber inputs. The increased responsiveness occurs whether the simple spike modulation evoked by the peripheral stimulus is excitatory or inhibitory. The change in responsiveness is short term and nonpersistent. It is argued that the activation of climbing fiber inputs to the cerebellar cortex is associated with an increase in the gain of Purkinje cells to mossy fiber inputs activated by natural peripheral stimuli.

Afferent Pathways↗
PubMed1982

The changes in Purkinje cell simple spike activity following spontaneous climbing fiber inputs.

The purpose of these experiments was to systematically examine the characteristics of the excitability change occurring after the inactivation period evoked by the climbing fiber input to Purkinje cells. Ninety-eight Purkinje cells were isolated extracellularly in unanesthetized decerebrate cats. Simple spikes and complex spikes were discriminated separately. Post-stimulus time histograms were constructed from 100 consecutive trials triggered by the occurrence of spontaneous complex spikes. Seventeen Purkinje cells exhibited a reduction of simple spike discharge rate following the inactivation period. However, 14 cells showed no change in simple spike activity, and in 67 cells the discharge rate increased. These changes in excitability following a spontaneous complex spike were independent of the tonic simple spike activity of the Purkinje cell. Single traces of spike train data from Purkinje cells showed that the change in discharge rate was variable, some complex spikes being followed by an increase and others by a decrease in activity. The basis for these observations and the differences between these data and those from studies in which the climbing fiber input was evoked by electrical olivary stimulation are discussed.

Afferent Pathways↗
PubMed1982

The effects of cerebellar stimulation on the stretch reflex in the spastic monkey.

The effects of stimulating the cerebellar surface on abnormal segmental reflexes were examined in monkeys rendered spastic by either bilateral or unilateral decortication of areas 1, 2, 3, 4 and 6. Rectified, integrated electromyographic (EMG) activity from the biceps and triceps as well as the torque were recorded and averaged during successive flexion-extension movements of the arm produced by a displacement controlled torque motor. Two movement paradigms were employed. The first consisted of a ramp and hold paradigm with an initial rapid flexion of the forearm, a subsequent two second period during which the arm position was held constant, and a rapid extension returning the limb to the initial position. In the second paradigm, the forearm was modulated sinusoidally at several different frequencies. Cerebellar stimulating electrodes were placed over the paravermal region bilaterally. Different frequencies (10 to 300 HZ) and different charge densities (1.5 to 10 microC/cm2) were used in each animal. In each experimental trial short periods of cerebellar stimulation (10 to 30 minutes) were interspersed between control periods. As observed in some types of clinical spasticity, flexion or extension of the extremity was capable of evoking coactivation of the biceps and triceps. Cerebellar surface stimulation reduced the amplitude of the phasic and tonic stretch reflexes recorded from the triceps during flexion and decreased the abnormal triceps response during passive shortening. The biceps response to stretch was increased by cerebellar stimulation and its abnormal response to flexion was decreased. These combined effects modified the organization of the segmental reflexes, producing a more normal reciprocal relationships of the EMG activity in the biceps and triceps. Evaluation of many different combinations of stimulus parameters revealed that not only the magnitude of the passive reflex but also the nature of the effect was dependent on stimulus parameters. Although these studies demonstrate an improvement in the abnormal reflexes present in spastic primates, they emphasize the complexities of the response evoked by cerebellar stimulation and the importance of stimulus parameters in the modifications produced by this technique.

Animals↗
PubMed1982

The early involvement of subcortical structures during the development of a cortical seizure focus.

Cortical surface electrodes and bipolar depth electrodes were implanted stereotaxically in the ventral posterolateral and paracentral thalamic nuclei, amygdala, hippocampus, and putamen in adult cats to determine the progressive involvement of these structures in the generalization of an experimentally induced seizure disorder. Prior to (45-65 days) and following (50-70 days) subpial injection of 0.04 ml of aluminum hydroxide in the sensorimotor cortex, 30 min EEG records were obtained regularly in each animal. At the time of aluminum hydroxide injection, there was no persistent abnormal EEG activity resulting from electrode implantation. In all animals, intermittent slow waves and epileptiform activity appeared in subcortical or extrafocal structures prior to the development of epileptiform activity in the primary focus. These abnormalities were frequently associated with brief clinical seizures and were clearly independent of abnormal activity in the primary focus. Only later in the development of the seizure disorder was activity in the secondary foci observed to be dependent on frequent epileptiform activity in the primary focus. These results demonstrate that multiple, independent foci develop in subcortical structures before the occurrence of a well developed, fully "mature" cortical primary focus.

Aluminum Hydroxide↗