Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0028738 (nystagmus)
 7,431 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Monocular enucleation reduces the asymmetry of horizontal optokinetic nystagmus (H-OKN) in afoveate mammals by increasing responses to naso-temporal visual stimulation. The origin of these larger responses was investigated in adult pigmented rats monocularly enucleated as neonates or as adults by analyzing retinal and commissural projections to the deafferented nucleus of the optic tract (NOT) and the functional role of this nucleus before and after section of the posterior commissure. Anatomically, monocular enucleation reduces the volume of the contralateral deafferented NOT. Anterograde tracers injected in the intact eye reveal a crossed projection of the retina to the NOT and to the dorsal (DTN) and medial (MTN) terminal nuclei of the accessory optic system as in normal rats. In addition, there is an uncrossed projection to the MTN in the rats enucleated as neonates. Retrograde tracer injected in the deafferented NOT confirms the absence of an uncrossed retinal projection but reveals connections between both NOT via the posterior commissure as in normal rats. Electrophysiologically, the larger naso-temporal optokinetic responses in monocularly enucleated rats return to normal after posterior commissurotomy. This study demonstrates that no anatomical remodelling takes place to increase naso-temporal responses in monocularly enucleated rats. The larger responses must then result from functional changes. The role of exclusive contralateral projections of the retina to the NOT and of the commissural connections in mediating the asymmetry of the optokinetic nystagmus in afoveate mammals is discussed.
 ...
PMID:Horizontal optokinetic nystagmus in unilaterally enucleated pigmented rats: role of the pretectal commissural fibers. 178 84

1. The role of the pretectal NOT and the DTN in producing horizontal OKN and OKAN were studied using electrical stimulation and lesions. Positive stimulation sites lay in NOT, DTN, and in a fiber bundle in the pulvinar that is presumably a cortical input to NOT. 2. When the region of NOT was electrically stimulated in darkness, horizontal nystagmus was evoked with ipsilateral slow phases. Eye velocity rose slowly to a steady-state level and was followed by afternystagmus at the end of stimulation. The time constant of rise of stimulus-induced nystagmus was similar to the slow rise of slow-phase eye velocity during OKN. The saturation velocity of the induced nystagmus and the falling time constant of the stimulus afternystagmus were the same as those of OKAN. This suggests that electrical stimulation of NOT and DTN had elicited the slow component of OKN, i.e., that component produced by the velocity storage mechanism in the vestibular system. 3. Consistent with this postulate, activity induced by NOT stimulation could enhance, prolong, or block the slow component of OKN and OKAN depending on whether slow phases were to the same or opposite side. Stimulus-induced activity also interacted with vestibular nystagmus as would OKN and OKAN. 4. Unilateral lesions of NOT and DTN caused a loss of OKAN and the slow rise in OKN to the ipsilateral side. Steady-state velocities of OKN were reduced. The initial jump of OKN slow-phase velocity was the same or somewhat less after lesions but was not lost. 5. Partial lesions of a fiber bundle in the lateral pulvinar caused a transient change in OKN and OKAN, consistent with the idea that it carries activity for the slow component from the cortex to NOT. A lesion of the MRF, just rostral to the superior colliculus, caused a transient loss of the rapid component of OKN. This region appears to carry activity responsible for the initial jump in slow-phase velocity at the onset of stimulation. 6. We conclude that: (a) NOT and probably DTN lie in the indirect pathway that produces the slow component of horizontal OKN and OKAN to the ipsilateral side in the rhesus monkey. This pathway activates the velocity storage mechanism in the vestibular nuclei. (b) At the level of NOT, the pathway responsible for the slow component of OKN and OKAN is anatomically distinct from the pathway responsible for rapid changes in eye velocity at the onset of OKN.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Contribution of the nucleus of the optic tract to optokinetic nystagmus and optokinetic afternystagmus in the monkey: clinical implications. 210 53

Large numbers of neurons were retrogradely labeled in both the dorsal and ventral medial terminal nucleus (MTN) after fluoro-gold injections into the rat pretectal nucleus of the optic tract/dorsal terminal nucleus (NOT/DTN). Fluorescence immunocytochemistry for GABA in the same brains revealed GABA-positive neurons distributed mainly in the dorsal MTN. Approximately half of all the GABAergic neurons in the MTN were double-labeled. Therefore, GABAergic neurons comprise a significant component of the MTN-NOT/DTN projection which most likely inhibits the pretectal pathway mediating horizontal optokinetic nystagmus.
 ...
PMID:The projection of GABA-ergic neurons of the medial terminal accessory optic nucleus to the pretectum in the rat. 213 69

The visual responses of single units in the lateral and dorsal terminal nuclei (LTN and DTN) of the accessory optic system (AOS) were studied in adult cats reared in total darkness. In the LTN of the normal cat equal numbers of cells prefer upward and downward vertical stimulus motion (previous results). While direction selectively continued to be a characteristic property of LTN and DTN units in dark-reared animals, the distribution of preferred and non-preferred directions of LTN cells was radically altered such that almost every LTN cell examined in the dark-reared cat preferred downward stimulus motion. In contrast, the distribution of preferred directions among DTN cells was largely unaffected by dark rearing. Both normal and dark-reared cat DTN cells responded best to stimuli moving horizontally toward the recorded hemisphere. The velocity preferences of DTN units of the dark-reared cat were, however, much slower than those of normal DTN units. LTN units responding to downward motion in dark-reared cats showed similar velocity preferences to those downward direction-selective LTN units in normal animals. Unlike the highly binocular responses of AOS cells encountered in the normal cat, the ocular dominance distribution obtained from units in the LTN and DTN of the dark-reared cat is completely monocular, favoring the contralateral eye. Thus, dark rearing renders the distribution of preferred directions most affected in the LTN, velocity preference most affected in the DTN and ocular dominance strongly affected in both nuclei. The physiological response properties of the dark-reared cat presented in this report bear a close resemblance to those we have described in the AOS of acutely decorticated animals (previous results). Data obtained from the dark-reared cat support our earlier suggestion that the visual cortex is a major source of upward direction selectively, high-velocity tuning and ipsilateral eye input for AOS cells. Some of the functional consequences of these findings are discussed in relation to frontal eye placement and optokinetic nystagmus.
 ...
PMID:Response properties of single units in the accessory optic system of the dark-reared cat. 370 78

Several studies have demonstrated the importance of the pretectal Nucleus of the Optic Tract (NOT) and the Dorsal Terminal Nucleus of the accessory optic system (DTN) for the generation of horizontal optokinetic nystagmus (OKN). Although single unit data from trained rhesus monkey NOT/DTN cells are available it is still unclear if there is a link between the pursuit and the optokinetic system at this level of motion analysis. In order to address the question whether the NOT/DTN is important for the optokinetic as well as the pursuit system an electrolytic lesion was placed where NOT/DTN activity was recorded previously. The monkey was tested on optokinetic and pursuit paradigms. Immediately following the lesion the monkey performed a spontaneous nystagmus with slow phases directed away from the lesioned side. This spontaneous nystagmus persisted even during optokinetic stimulation in the opposite direction. During the first week postlesion the spontaneous nystagmus disappeared and the monkey regained the ability to perform optokinetic nystagmus toward the lesioned side. The gain of the mean slow phase eye velocity was, however, largely reduced for this stimulus direction. The onset of OKN following the onset of optokinetic stimulation was not affected by the lesion. During smooth pursuit the mean eye velocity was more reduced for pursuit towards the lesioned side. The resulting position error was compensated by an increase in the number of catch-up saccades. In addition to the confirmation of the well-known directional deficits of the optokinetic system caused by a lesion of the pretectum, a directional deficit in the pursuit system was demonstrated.
 ...
PMID:Optokinetic and pursuit system: a case report. 829 51

It has been previously assumed that the asymmetry of the monocular optokinetic nystagmus (OKN) of lateral-eyed mammals is caused by an absence of visual cortex projections to directional selective neurons in the pretectal nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN). In contrast to this generally accepted hypothesis, we present multiple evidence that OKN-related neurons in the rat NOT-DTN in fact do receive input from the visual cortex. We studied the corticofugal projection to NOT-DTN physiologically, with extracellular single unit recording and electrical stimulation of the optic chiasma and the visual cortex, and anatomically, using retrograde and anterograde tracing techniques. In particular we focussed our attention on the NOT-DTN neurons, which control eye movements during OKN. All OKN-related NOT-DTN cells were activated after optic chiasma stimulation. Forty-five percent of these neurons were also activated after stimulation of the visual cortex (VC). The majority of neurons activated from VC (80%) also responded to monocular stimulation of either eye. On the contrary, most of the neurons that responded to stimulation of the contralateral eye only were not activated from VC. After injection of fluorescent latex microspheres into the NOT-DTN, retrogradely labeled neurons were found in areas 17, 18, and 18A of the visual cortex. Phaseolus vulgaris leucoagglutinin injected into the visual cortex anterogradely labeled fibres and terminals throughout the NOT-DTN complex. Labeled boutons were found in close proximity to OKN-related NOT-DTN cells, selectively stained after horseradish peroxidase (HRP) injections into the inferior olive. Our results demonstrate that NOT-DTN cells in the rat, which are involved in the generation of horizontal OKN, receive a direct input from the ipsilateral visual cortex.
 ...
PMID:OKN-related neurons in the rat nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system receive a direct cortical input. 849 67

The nucleus of the optic tract (NOT) and the dorsal terminal nucleus of the accessory optic tract (DTN) are essential nuclei for the generation of slow-phase eye movements during horizontal optokinetic nystagmus. We recorded from 101 neurons (all directionally selective) in four NOT/DTN of three trained and behaving rhesus monkeys. Neuronal activity increased when stimuli moved ipsiversively with respect to the recording site and decreased below spontaneous activity when stimuli moved contraversively. While the monkey fixated a small spot, some NOT/DTN neurons did not respond at all to the retinal image slip of a whole-field random dot pattern; others showed a monotonic increase of activity to increasing velocities of that stimulus. The velocity range tested was up to 100 degrees/s. During the execution of optokinetic nystagmus, 39 of 73 cells tested showed a velocity-tuned response with an average optimum at 21 degrees/s retinal image slip. Following saccades during optokinetic nystagmus (quick phases), the NOT/DTN neuronal activity briefly attained the level of spontaneous activity, as predicted from the velocity selectivity during optokinetic nystagmus. Immediately upon cessation of optokinetic stimulation in the preferred direction, NOT/DTN activity returned to the spontaneous level and did not reflect the ongoing optokinetic afternystagmus in darkness. Most NOT/DTN neurons displayed direction selectivity also during smooth pursuit. Twenty-one of 50 cells tested (42%) always responded to the retinal slip of the target (target velocity cells), 16 cells (32%) responded to the retinal slip of the background (background velocity cells), and 13 cells (26%) did not respond at all during smooth pursuit. We conclude from our results that the NOT/DTN is an essential structure for the processing of the direction and speed of retinal image slip. This information is then used for the generation and maintenance of slow eye movements, preferentially during horizontal optokinetic nystagmus but also during pursuit eye movements.
 ...
PMID:Responses of neurons of the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic tract in the awake monkey. 871 53

Horizontal optokinetic nystagmus (OKN) as well as neuronal response properties in the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system (NOT-DTN) were investigated in three monocularly deprived squirrel monkeys. In two monkeys occlusion of one eye was performed at birth (early) and in the third after 7 weeks (late). In adulthood, in early deprived monkeys monocular horizontal OKN tested through the non-deprived eye was symmetrical and in no way different from normal, i.e. stimulation in the temporonasal and nasotemporal direction elicited equal and robust responses. OKN through the early occluded eye, however, was grossly abnormal with low gain and great variability in the consistency of nasotemporal and temporonasal slow phase eye movements. When in the late deprived monkey the non-deprived eye was occluded a strong spontaneous nystagmus developed despite the deprived eye viewing a stationary pattern. The slow phases were directed from nasal to temporal for the deprived eye. When tested through the non-deprived eye all neuronal responses of the NOT-DTN were normal. The deprived eye's influence on NOT-DTN neurons was extremely weak. No neuron with a moderate or even dominant input from the deprived eye was found after early deprivation. In the late deprived case the deficit was not as severe but still the non-deprived eye was clearly dominating the responses in all neurons tested. Velocity tuning of neurons tested through the non-deprived eye was normal and qualitatively corresponded well to slow phase eye velocity in response to equivalent retinal slip during OKN. Through the early deprived eye, however, velocity tuning was extremely poor. It was somewhat better through the late deprived eye. We suggest that the dramatic deterioration in the optokinetic reflex found after long-term monocular deprivation for the amblyopic eye is probably caused by the almost complete loss of retinal and cortical input driven by that eye to the NOT-DTN. These results are discussed in relation to our previous results in cats and reports in the literature for humans with occlusion amblyopia.
 ...
PMID:Optokinetic reflex in squirrel monkeys after long-term monocular deprivation. 975 82

Using classical neuroanatomical retrograde tracing methods we investigated the retinal ganglion cells projecting to the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) in macaque monkeys. Our main aim was to quantify the strength of the projection from the ipsilateral retina to the NOT-DTN. We therefore examined the number, distribution, and soma size of retinal ganglion cells involved in this projection. Electrophysiologically controlled small injections into the NOT-DTN revealed a clearly bilateral retinal projection originating mainly from the central retina but also involving peripheral retinal regions. Labelled cells were found nasally in the contralateral retina and temporally in the ipsilateral retina with some overlap in the fovea. The projection from the ipsilateral retina was 36-43% of that from the contralateral retina. On average, only 1-6% of the local population of ganglion cells projected to the NOT-DTN. Small soma size and large dendritic fields imply that in monkey rarely encountered, 'specialized' ganglion cells provide the direct retinal input to the accessory optic system (AOS). These results are discussed with respect to the symmetry of monocular horizontal optokinetic nystagmus (OKN) in primates.
 ...
PMID:Retinal ganglion cells projecting to the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system in macaque monkeys. 1094 15

The goal of the present investigation was to elucidate the role of the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system (NOT-DTN) for slow eye movements other than horizontal. Retinal slip neurons in the NOT-DTN in the awake behaving cat respond direction selectively to the ipsiversive component of horizontal and oblique image motion. They are, however, influenced neither by pure vertical stimulus movement nor by eye movements in the dark. Electrical stimulation of the NOT-DTN leads to pure horizontal optokinetic nystagmus with ipsiversive slow phases and does not influence vertical eye position. In addition, unilateral reversible inactivation of the NOT-DTN with muscimol elicits spontaneous contraversive horizontal nystagmus without vertical component. During oblique optokinetic stimulation, the ipsiversive OKN component is significantly decreased in all directions. After bilateral NOT-DTN inactivation, OKN can only be elicited in a narrow range of upward directions. These data indicate that the NOT-DTN is the only source to drive the horizontal component of OKN.
 ...
PMID:Directional effect of inactivation of the nucleus of the optic tract on optokinetic nystagmus in the cat. 1171 81


1 2 Next >>