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Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.
Rats with geniculate laminae that run perpendicular to the lines of projection are described. Earlier reports of laminae parallel to the lines of projection were based on mammalian mutants that may be relatively common. In these mutants, the chiasmatic course of axons arising in a patch of retinal ganglion cells is wrongly specified.
We have studied the onset of expression of glial filament protein (GFP) in astrocytes along a single axon trajectory, the mouse retinal axon pathway, and the relationship of GFP expression to maturation of astroglial morphology. In fetal optic nerve from embryonic day (E) 12 to E16, primitive glia (neuroepithelial cells) lack GFP, but express vimentin and contain intermediate filaments. GFP is expressed at E17 in two gradients: cells in the optic nerve become GFP-positive first in the borders of the nerve, then in the central nerve by postnatal day (P)0. The second gradient is a distoproximal one, with GFP appearing in the optic nerve at E17, in the optic chiasm by PO, and in the optic tract by P3. The expression of GFP in the optic nerve marks the transformation of radial neuroepithelial cells to multipolar astroglia, accomplished by outgrowth of filament-rich glial processes tipped by a growth cone. Several days after the onset of GFP expression in each portion of the pathway astrocytes exhibit a transient increase in staining, and resemble reactive astrocytes after injury. During this period, filaments are arranged in densely packed bundles, and appear coalesced at points. Thus, primitive glial cells in optic nerve express vimentin. In the retinofugal pathway, GFP is expressed in a distinct spatiotemporal sequence from optic nerve to optic tract. Finally, in contrast to neurons, the extension of astroglial processes is accompanied by the increased expression and assembly of intermediate filaments.
Young chickens and rats were injected intravitreally with [3H]proline and sacrificed at short intervals thereafter. Regression lines calculated for the plotted points (survival time, transport distance) revealed a transport rate of 329 mm/day in the chick and 350 mm/day in the rat. Both rates are close to those reported for peripheral axons (410 +/- 50 mm/day).
The isthmo-optic nucleus (NIO) at the origin of the retinopetal pathway was examined in 12 birds of prey (strigiforms and falconiforms) using cytoarchitectonic methods and after the intraocular injection of the regrograde tracers Rhodamine beta-isothiocyanate and Fast blue. The NIO was found to be poorly differentiated and reticular in appearance and depending on the species contained between 900 and 1400 neurons. These values are approximately 10 times less than those recorded in the pigeon and chicken. As in the latter species, the experimental data obtained in the strigiform Tyto alba showed the presence of retinopetal ectopic neurons bilaterally. However the ipsilateral contingent was proportionally larger in the nocturnal raptor. The functional significance of the poorly developed centrifugal visual system in birds of prey is discussed.
1. The high affinity uptake of GABA in optic tectum was found to be about 40% higher in frogs kept in complete darkness for 3 weeks, than in frogs in the normal condition. 2. No effects were obtained in uptake of glutamate and activity of GAD in the optic tectum. 3. The isoenzyme composition of cholinesterases in frog optic tectum and retina was not affected by dark adaptation either.
The authors examined five young children with monocular vision loss who developed monocular nystagmus. The nystagmus was of fast frequency and small amplitude in all fields of gaze. In four children, successful treatment of the cause of the vision loss resulted in cessation of the nystagmus. No child showed signs of spasmus nutans, or of optic nerve or chiasmal tumor. The evaluation of the young child with unilateral nystagmus should begin with a careful eye examination.
Hemorrhage confined to the optic pathways is rare. We describe a patient with diffuse hemorrhage of the intracranial optic nerves, optic chiasm, and optic tracts, attributed to alcohol-induced coagulopathy. The hemorrhage resolved completely as the patient's vision improved, and subsequent neuroimaging studies showed atrophy of the affected structures.
The flash ERG and VEP have conspicuous immature features during the first 4 months following birth. The most marked maturational changes occur in ERG amplitude and VEP latency. Concurrent recording of the skin ERG and VEP provides information which is very useful in helping to arrive at a diagnosis in the young infant with nystagmus who appears to be blind and has a fundus of normal appearance. ERG and VEP features associated with Leber's Amaurosis, congenital cone dysfunction, albinism, optic nerve hypoplasia and unilateral hemisphere dysfunction are described.
Electroretinogram (ERG) responses to alternating gratings have been recorded in patients with temporary occlusion of the retinal artery, retrobulbar optic neuritis, and other ganglion cell diseases. The ERG responses to alternating gratings were absent in first case and dramatically depressed in the others, whereas the ERG responses to light flashes or to homogeneous flickering light were normal. These findings corroborate recent evidence from studies on the cat, showing that the ERG in response to alternating gratings is correlated with ganglion cell activity.
Positive- and negative-contrast stimuli yield the perceptions of brightness and darkness, respectively, and are processed separately by ON and OFF neural pathways. The properties of these morphologically and pharmacologically distinct subsystems were measured in humans by recording visual evoked potentials (VEPs). These electrical responses from the visual cortex were elicited by novel positive- and negative-contrast stimuli, designed to emphasize, selectively, contributions from ON and OFF pathways. Results revealed differential processing of the two types of contrast information, suggesting asymmetries in ON and OFF subsystems; OFF subsystems have finer spatial tuning and greater contrast gain than ON subsystems. These VEPs may be useful in diagnosing neurological disorders that involve primarily one subsystem.
We have examined the cellular and subcellular distribution and the patterns of expression of brain-derived neurotrophic factor (BDNF), and of its high affinity receptor, tyrosine kinase B (TrkB), in retinorecipient regions of the brain, including the superior colliculus, the lateral geniculate nucleus and the olivary pretectal nucleus. In the retinorecipient layers of the superior colliculus, BDNF protein and mRNA were present in the cell bodies of a subpopulation of neurons, and BDNF protein was present in the neuropil as punctate or fiber-like structures. In the lateral geniculate nucleus, however, BDNF mRNA was not detected, and BDNF protein was restricted to punctate and fiber-like structures in the neuropil, especially in the most superficial part of the dorsal lateral geniculate nucleus, just below the optic tract. At the ultrastructural level, BDNF protein was localized predominantly to axon terminals containing round synaptic vesicles and pale mitochondria with irregular cristae, which made asymmetric (Gray type I) synaptic specializations (R-boutons). Enucleation of one eye was followed by loss of BDNF immunoreactivity and disappearance of BDNF-positive R-boutons in the contralateral visual centers, confirming the retinal origin of at least most of these terminals. TrkB was present in postsynaptic densities apposed to immunoreactive R-boutons in the superior colliculus and lateral geniculate nucleus, and was also associated with axonal and dendritic microtubules. These findings suggest that BDNF is synthesized by a subpopulation of retinal ganglion cells and axonally transported to visual centers where this neurotrophin is assumed to play important roles in visual system maintenance and/or in modulating the excitatory retinal input to neurons in these centers.
Horizontal and vertical components of optokinetic nystagmus (OKN) were measured using the magnetic search coil technique in normal human adults during presentation of simple and complex moving patterns. Simple patterns were gratings moving horizontally and obliquely. Complex moving patterns consisted of plaids formed by superimposed oblique motion of two sets of gratings or of illusory contours formed by offset discontinuities in gratings. Slow-phase OKN gains (eye velocity divided by stimulus velocity) induced by high-contrast type I and type II plaids were comparable with those generated by one-dimensional moving gratings. The axis of OKN for high-contrast plaids was along the resultant direction determined by the intersection-of-constraints rule and not along any component. With low-contrast presentations, OKN induced by type I patterns remained in the resultant direction, but the OKN direction induced by type II patterns was biased toward the components' directions. The OKN generated by texture boundaries embedded in real pattern motion was measured for motion of illusory contours having systematically varying directions. The gain of OKN induced by real motion was independent of the direction of illusory contour motion, but the gain to illusory contour motion decreased with increasing contour angles. All these results suggest that input signals for driving the optokinetic system come from visual areas extracting higher order two-dimensional motion information.
The projection from the superior and inferior colliculi to the basilar pons in the rat was studied with the technique of orthograde transport of labeled amino acids and autoradiography. Injections restricted to the medial or lateral regions of the superior colliculus gave rise to grain labeling representing terminal fields over the ipsilateral peduncular, dorsolateral, and ventrolateral regions of the caudal basilar pons and over the dorsomedial area of the contralateral nucleus reticularis tegmenti pontis (NRTP). The pontine projection from the superior colliculus to the lateral basilar pons is topographically organized; the medial superior colliculus projects primarily to the peduncular region, whereas the lateral superior colliculus terminates chiefly in ventrolateral pontine areas. A projection from the superior colliculus to the contralateral dorsomedial pontine and medial peduncular pontine regions, a previously undescribed finding, has also been shown. Descending fibers from the inferior colliculus do not appear to terminate extensively within the basilar pons but rather course adjacent to pontine cells of the dorsolateral region in the caudal pons. Pretectal nuclei project ipsilaterally to medial and lateral nuclei in the rostral and middle basilar pons, respectively. A rostrocaudal topography exists in the tectopontine projection; the pretectum projects to rostromiddle basilar pons, the superior colliculus to more caudal pontine regions, and the inferior colliculus (although sparsely) to further caudal areas. The pontine projection pattern from the colliculi and pretectum differs from the pontine afferents from the visual cortices. The findings of this study, when compared to our results from previous investigations on the pontocerebellar projection system, suggest that the tectal inputs to certain lateral cerebellar lobules are relayed primarily through NRTP rather than the basilar pons. The collicular projection to midvermal lobules of the cerebellum appear to be mediated in part by both NRTP and lateral pontine nuclei.
The dorsal lateral geniculate nucleus, suprachiasmatic nucleus and superior colliculus of the hamster were examined autoradiographically after administration of [3H]thymidine for the presence of spatiotemporal gradients of neuron production and for the relationship between neuron cell body size and birthdate. The dorsal lateral geniculate nucleus had a dorsolateral-to-ventromedial (superficial-to-deep) gradient of neuron production, the suprachiasmatic nucleus had a caudoventral to rostrodorsal gradient, and the superior colliculus had a complex laminar gradient. In the lateral geniculate nucleus and in the superior colliculus, labeled neurons were typically larger than unlabeled neurons at early stages and unlabeled neurons were typically larger than labeled neurons at late stages; however, variation in neuron size does not account for the neurogenetic gradients in hamsters.
Retinal axons are led out of the eye by netrin-1, an attractive guidance cue which is secreted at the optic nerve head. In the optic pathway, however, netrin-1 is expressed in areas that exclude retinal axon growth. This suggests that axons may change in their responsiveness to netrin-1 as they advance along the pathway. Indeed, in our 'whole-pathway' preparation in Xenopus, a gradual change from attraction to repulsion occurred as retinal axons emerged from progressively distal points along the pathway. We also found that axons that were aged in culture without pathway experience underwent a similar change, which correlated with a decline in cyclic AMP (cAMP) and netrin-1 receptor expression. Cyclic AMP elevators and adenosine A2b receptor agonists rejuvenated the behavior of old growth cones, causing them to regain attraction to netrin-1, whereas antagonists caused young growth cones to be repelled. These findings show that netrin-1 responsiveness is developmentally regulated and suggest that intrinsic changes that lower cAMP levels underlie this regulation.
Successive presentations of Glass patterns (randomly positioned pairs of dots oriented in a coherent pattern) create a strong sense of global motion along the orientation of the pattern, but ambiguous in direction. Here we report that dynamic "anti-Glass" patterns, created by successive pairs of globally structured pairs of opposite polarity, create an even more powerful motion illusion that is unambiguous in direction: the dark dots always move toward the light. The motion can be cancelled and reversed by introducing a real delay in the presentation of the light dots, suggesting that the effective stimulation of the light is about 3 ms faster than the dark dots. The most plausible explanation for this is that human on channels are faster than off channels, as has been shown in the macaque.
Potentials of single cells of the dorsal lateral geniculate nucleus (dLGN) were recorded extracellularly in albino rats by means of micropipettes filled with trypan blue for iontophoretic marking of tip localization. The cells were grouped concerning their response latencies to photic stimuli, their response patterns, and their localization within the dLGN. It could be shown in a conditioning paradigm that combination of light with electrical tail stimulation resulted in temporary response changes of "fast" OFF-cells which are mainly localized in the rostroventromedial part of dLGN. "Fast" ON-cells had mainly stable response patterns to light. Changes which persisted after the end of tail stimulation trials occurred in "slow" oN- and oFF-cells located in the dorsolateral and caudal part of dLGN.