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Biomedical subjects

S Gilman

Publications and source records attributed to S Gilman.

At least 181 records · Page 10Linked to original sources
PubMed1976

Kinematic effects of deafferentation and cerebellar ablation.

Trajectories of hand movements directed visually toward a stationary target were compared by kinematic methods in control monkeys, those with bilateral upper limb deafferentation, those with cerebellar ablation and those with both these lesions. The purpose of the investigation was to determine whether: (1) deafferented animals display kinematic abnormalities similar to those of decerebellate animals, and (2) a combination of these two lesions results in cumulative motor disorders. The decerebellate preparation had significant increases of the ratio of path length to target distance, mean deviation from a straight line path, segment angle (average change in direction between successive segments of the trajectory), target angle (average angle between the path taken by the hand and a straight line path to the target), peak velocity, average acceleration and peak acceleration. The deafferented preparation had increases of these parameters significantly greater than the decerebellate preparation. Neither preparation showed abnormalities of average linear velocity. The deafferented preparation rendered decerebellate had significant additional increases in all parameters except average segment angle, an index of angular velocity. Scatter plots of acceleration versus velocity and of segment angle versus target angle revealed increasing dispersion in the sequence: control, decerebellate, deafferented, deafferented with subsequent cerebellar ablation. The quantitative demonstration of cumulative worsening of motor performance when the deafferented animal is rendered decerebellate indicates that there are mechanisms of cerebellar dysmetria independent of the fusimotor efferent-spindle afferent reflex arc.

Afferent Pathways↗
PubMed1975

Alpha motoneuron responses to natural stimuli in decerebellate cats.

The responses of single alpha motoneurons to various "natural' stimuli were recorded from dissected ventral root filaments in lightly anesthetized control and recently decerebellate cats. The identity of the motoneurons was established by recording the unitary responses to orthodromic stimulation of nerves innervating the triceps surae muscles in the hindlimb. We recorded only the activity of units which responded to electrical stimulation of the medial or lateral gastrocnemius nerves, though some units responded to stimulation of both these nerves, and some also responded to stimulation of the posterior tibial nerve. The distributions of unit latencies and amplitudes did not differ between the two groups of animals. Baseline firing rates were also similar. However, unit firing rates in response to neck extension, ipsilateral hindfoot dorsi- or ventral-flexion were significantly higher in decerebellate than in control cats. The discharge rates in response to other stimuli, including neck flexion, pinna stimulation, and noxious stimulation in the hindlimb, were not significantly different between the two groups. Since the alpha motoneurons showed an increase in responsiveness only to some stimuli, specific mechanisms probably explain this release. The most important mechanism seems to be a loss of inhibition normally exerted by the cerebellum on vestibular and joint proprioceptive reflexes. The pathways to the ventral horn cells are thought to involve the vestibulo-spinal and reticulo-spinal tracts.

Animals↗
PubMed1975

A direct input from amygdaloid complex to caudate nucleus of the rat.

Spontaneous unit activity was recorded from the caudate nucleus in rats anesthetized with urethane. Amygdaloid nucleus stimulation altered the spontaneous activity of 51 units (65% of the population tested); 23 units (29%) showed an increase and 28 (36%) a decrease of discharge rate. Moreover, 25 units (32%) responded to stimulation with stimulus-locked spikes. Post-stimulus time histograms revealed 7 patterns of response to amygdaloid stimulation. In 4 groups of cells, stimulus-locked spikes occurred followed by alteration of spontaneous discharge rate. In another 2 groups there was a change of spontaneous discharge without stimulus-locked spikes and in the final group no effect occurred. The possibility of mono-, oligo-, and polysynaptic connections from amygdaloid nuclear complex to caudate nucleus was discussed. It was suggested that an amygdalofugal connection to basal ganglia may provide a pathway whereby activity of the limbic system may exert a modulatory influence on somatic motor mechanisms.

Activation Analysis↗
PubMed1975

Chronic cerebellar stimulation in the monkey. Preliminary observations.

In a single monkey, the surface of the cerebellum was stimulated electrically for 205 hours with electrodes and parameter values similar to those currently used in humans for treatment of epilepsy. Im pedance of stimulating and nonstimulating control electrodes remained unchanged throughout an observation period of six months. Potentials evoked by cerebellar stimulation could be recorded from the cranium, providing a noninvasive technique of determining the level of current delivered to cerebellum. Examination of the implantation site showed marked meningeal thickening surrounding the stimulating electrodes. Such thickening was not observed surrounding a control set. Light and electron microscopical examination revealed severe loss of Purkinje cells in tissue near the stimulating electrodes. There was also a moderate loss in other parts of cerebellar cortex down to a depth of about 1 mm from the exposed surface. Biochemical analysis revealed metabolic abnormalities consistent with the morphologic evidence of widespread tissue damage.

Animals↗
PubMed1975

Technique for vestibular neurotomy in the rat.

A technique for vestibular neurotomy in the rat has been developed. Removal of the tympanic membrane and ossicles through the external auditory meatus permits access to the auditory bulla. After the pterygopalatine artery has been cauterized, and the electrode may be introduced through the oval widow. The vestibular branch of the VIII nerve can then be cauterized with the electrode without direct visualization.

Animals↗
PubMed1975

Chronic cerebellar stimulation in the monkey. Electron microscopic and biochemical observations.

The effects of chronic electrical stimulation to the surface of cerebellum in the Macaca mulatta monkey were studied with morphologic and biochemical techniques. There was considerable damage and loss of Purkinje cells in all specimens examined, including an area without electrodes, but the greatest changes appeared in tissue beneath the cathode and anode. Despite the damage, normal appearing synapses persisted in the molecular layer of all specimens. Fibrous glial processes were more numerous beneath the cathode. There were abnormalities in gamma-amino butyric acid (GABA) and polyamine concentrations in virtually all specimens, consistent with the morphologic evidence of widespread tissue damage.

Animals↗
PubMed1975

Primate models of postural disorders.

Dorsal column lesions in the high cervical region of the monkey result in severe defects of movements projected into space and contactual orienting reactions of the forelimbs. The hindlimbs are less affected provided a pathway through the lateral columns, Morin's tract, remains intact. Interruption of this pathway results in a defect of hindlimb function similar to that of the forelimbs. Cerebellar ablations in monkeys result in postural and movement disorders, including hypotonia of limb extensor muscles. An important mechanism underlying the hypotonia is a depression of the responses to muscle extension of spindle primary afferents owing to a decrease of fusimotor activity. In the decerebellate animal abnormalities of limb trajectory during active movements projected into space (cerebellar "dysmetria") appear to result principally from dysfunction of systems separate from the peripheral fusimotor efferent-spindle afferent reflex arc. Precentral cortical ablation results initially in a contralateral hypotonic hemiparesis, later in a hypertonic hemiparesis. A depression of the responses of muscle spindle afferents occurs during the hypotonic phase, but during the hypertonic phase spindle function returns to normal levels. Accordingly a depression of fusimotor function appears to be important in the hypotonic phase of hemiplegia; however, there is no evidence that an enhancement of fusimotor function underlies the hypertonic phase. Bilateral section of the medullary pyramids results in an enduring hypotonic paresis. Abnormalities of contactual orienting responses of limbs are similar to those following dorsal column lesions. Responses of spindle primary afferents are depressed during the initial stages after acute pyramidotomy, then approach but do not reach normal levels. It is concluded that the dorsal columns constitute an afferent, and the pyramidal tracts an efferent, pathway important in oriented contactual reactions of the limbs. The hypotonia resulting from cerebellar lesions, precentral ablation, and pyramidal tract section stems, at least in part, from a depression of the fusimotor innervation of muscle spindle afferent activity.

Animals↗