Unit responses from commissural fibers of optic lobes of fish

The paired optic lobes of teleost fish are connected by two commissures. One of these, the tectal commissure, was studied with metal microelectrodes. Fibers are rhythmically active for prolonged periods in the dark and respond to light by a decrease in the rate of discharge. There is a rebound acceleration when the light is turned of. Each fiber is influenced by light in one eye only, and there is no response when light is projected into the opposite eye. This behavior resembles the "off" response recorded from the optic lobes and the optic nerve of fish. Unlike most units from the visual pathways of lower animals, single commissural fibers do not seem to give any recognizable response to patterned input such as small light or dark objects or small light sources stationary or moving anywhere in the visual field, nor do they respond to a vertical black bar moved over a white background.     

Neuronal correlates of eye movements in the visual cortex of the cat

About 10 percent of the cells in the visual cortex of awake cats do not respond to stationary parallel stripes in any orientation or to stripes moving across the visual field in any direction at a moderate speed (up to 132 degrees per second), but these cells are either excited or inhibited during saccadic eye movements when the animal faces a patterned visual environment. Of nineteen such cells tested in total darkness, seven discharged in association with eye movements. For saccade-related discharges, the latency during retinal stimulation is typically shorter than the latencey in total darkness.     

Enhancement of flicker by lateral inhibition

Sinusoidal modulation of illumination on the compound eye of the horseshoe crab, Limulus, produces a corresponding variation in the rate of discharge of optic nerve impulses. Increasing the area of illumination decreases the variation at low frequencies of modulation, but unexpectedly enhances-or "amplifies"-the variation at the intermediate frequencies to which the eye is most sensitive. Both effects must result from inhibition since it is the only significant lateral influence in this eye.     

Axonal transport of gangliosides in the goldfish optic nerve

Radioactive glucosamine and N-acetylmannosamine injected into the goldfish eye are incorporated into gangliosides that undergo rapid axonal transport to the optic nerve terminals. All ganglioside fractions are labeled. These data provide the first evidence that axonal transport has a role in neuronal ganglioside function and metabolism.     

Synaptic adjustment after deafferentation of the superior colliculus of the rat

Eyes were removed from rats shortly after birth, when there are few formed synapses in the colliculus. It was found that synaptogenesis continues to give a near-normal ratio of terminals containing either spheroidal or flattened vesicles. After eye removal in adult rats, however, reinvasion of synaptic sites vacated by degenerate optic terminals occurs, with an incomplete return toward a normal proportion of synaptic types.     

Glial cell diversification in the rat optic nerve

A central challenge in developmental neurobiology is to understand how an apparently homogeneous population of neuroepithelial cells in the early mammalian embryo gives rise to the great diversity of nerve cells (neurons) and supporting cells (glial cells) in the mature central nervous system. Because the optic nerve is one of the several types of glial cells but no intrinsic neurons, it is an attractive place to investigate how neuroepithelial cells diversify. Studies of developing rat optic nerve cells in culture suggest that both cell-cell interactions and intrinsic cellular programs play important parts in glial cell diversification.     

Order in the optic nerve of goldfish

A small amount of horseradish peroxidase, injected into the goldfish optic nerve and transported into the retina, filled an annulus of ganglion cells. Since the retina grew by annular addition of cells, this result shows that axons from cells of similar age clustered together in the nerve.     

Uncoupling of a nerve cell membrane junction by calcium-ion removal

Calcium ion participates in maintaining electrical connections between the nerve cells of Retzius (Hirudo medicinalis). The conductance across the junction between these cells decreases with decreasing concentration of free, extracellular Ca(++) At a certain level of Ca(++) withdrawal from the cell system, junctional conductance reaches a critical low point at which the cells become functionally disconnected: the nerve impulses which are normally discharged in synchrony by the cells become asynchronous. These effects of Ca(++) on junctional connection are irreversible, in contrast to those on nonjunctional surface membrane permeability.     

Electrophysiologic responses in hamster superior colliculus evoked by regenerating retinal axons

Autologous peripheral nerve grafts were used to permit and direct the regrowth of retinal ganglion cell axons from the eye to the ipsilateral superior colliculus of adult hamsters in which the optic nerves had been transected within the orbit. Extracellular recordings in the superior colliculus 15 to 18 weeks after graft insertion revealed excitatory and inhibitory postsynaptic responses to visual stimulation. The finding of light-induced responses in neurons in the superficial layers of the superior colliculus close to the graft indicates that axons regenerating from axotomized retinal ganglion cells can establish electrophysiologically functional synapses with neurons in the superior colliculus of these adult mammals.     

Radioautography of the optic tectum of the goldfish after intraocular injection of ( 3 H)proline

Radioautography of the optic tectum of the goldfish, performed after injection of [(3)H]proline into the contralateral eye, effectively resolves several distinct layers of retinal synapses. Silver grains are found unilaterally over nerve tracts containing efferent fibers from the tectum, a result that suggests intercellular migration of labeled molecules. The low background and high specific grain density obtained with [(3)H]proline radioautography indicate the usefulness of this technique for the elucidation of neuroanatomical connections in the visual system.     

Central role for the lens in cave fish eye degeneration

Astyanax mexicanus is a teleost with eyed surface-dwelling and eyeless cave-dwelling forms. Eye formation is initiated in cave fish embryos, but the eye subsequently arrests and degenerates. The surface fish lens stimulates growth and development after transplantation into the cave fish optic cup, restoring optic tissues lost during cave fish evolution. Conversely, eye growth and development are retarded following transplantation of a surface fish lens into a cave fish optic cup or lens extirpation. These results show that evolutionary changes in an inductive signal from the lens are involved in cave fish eye degeneration.     

Acetylcholine receptor synthesis in retina and transport to optic tectum in goldfish

Previous studies have suggested that the retinotectal system of the goldfish contains a nicotinic acetylcholine receptor (nAChR) that is sensitive to alpha-bungarotoxin. Extracellularly recorded field potentials elicited in response to visual stimulation can be blocked by alpha-bungarotoxin, and alpha-bungarotoxin can interfere with the maintenance of retinotectal synaptic connections. Whether the transmission between the retinal ganglion cells and the tectal cells is mediated by acetylcholine and whether nAChR's exist on the dendrites of tectal cells are questions that remain. The experiments described in this report were designed to determine the site of synthesis of the nAChR's associated with the goldfish retinotectal projection. Radioactive (35S-labeled) methionine was injected into either the eye or the tectal ventricle, and the incorporation of radioactivity into the nAChR was measured by immunoprecipitation. The use of this technique provides evidence that an nAChR associated with the goldfish retinotectal projection is synthesized in the retina and transported to the optic tectum, which suggests a presynaptic site of acetylcholine action on retinal terminals.     

Regenerating fish optic nerves and a regeneration-like response in injured optic nerves of adult rabbits

Regeneration of fish optic nerve (representing regenerative central nervous system) was accompanied by increased activity of regeneration-triggering factors produced by nonneuronal cells. A graft of regenerating fish optic nerve, or a "wrap-around" implant containing medium conditioned by it, induced a response associated with regeneration in injured optic nerves of adult rabbits (representing a nonregenerative central nervous system). This response was manifested by an increase of general protein synthesis and of selective polypeptides in the retinas and by the ability of the retina to sprout in culture.     

Superior colliculus cell responses related to eye movements in awake monkeys

Single cell responses were recorded from the superior colliculus of awake monkeys trained to move their eyes. A class of cells that discharged before eye movements was found in the intermediate and deep layers of the colliculus. The response of the cells was most vigorous before saccadic eye movements within a particular range of directions. These cells had no visual receptive fields, and visually guided eye movements were not necessary for their discharge, since they responded in total darkness before spontaneous eye movements and vestibular nystagmus.     

Binocularly driven neurons in visual cortex of split-chiasm cats

In cats with midsagittal section of the optic chiasm, some visual cortex neurons can be driven not only by the ipsilateral eye, through the direct geniculocortical pathways, but also by the contralateral eye, through the opposite visual cortex and corpus callosum. The receptive fields and the response characteristics observed upon stimulation of the contralateral eye are very similar to those observed upon stimulation of the ipsilateral eye; the two monocular receptive fields of a given cell lie in corresponding points of heteronymous halves of the visual field in close contact with the vertical meridian, thus adding in visual space and forming a binocular receptive area which crosses the vertical meridian and extends equally on either side of it.     

Synchronous bursts of action potentials in ganglion cells of the developing mammalian retina

The development of orderly connections in the mammalian visual system depends on action potentials in the optic nerve fibers, even before the retina receives visual input. In particular, it has been suggested that correlated firing of retinal ganglion cells in the same eye directs the segregation of their synaptic terminals into eye-specific layers within the lateral geniculate nucleus. Such correlations in electrical activity were found by simultaneous recording of the extracellular action potentials of up to 100 ganglion cells in the isolated retina of the newborn ferret and the fetal cat. These neurons fired spikes in nearly synchronous bursts lasting a few seconds and separated by 1 to 2 minutes of silence. Individual bursts consisted of a wave of excitation, several hundred micrometers wide, sweeping across the retina at about 100 micrometers per second. These concerted firing patterns have the appropriate spatial and temporal properties to guide the refinement of connections between the retina and the lateral geniculate nucleus.     

Neuronal activity in narcolepsy: identification of cataplexy-related cells in the medial medulla

Narcolepsy is a neurological disorder characterized by sleepiness and episodes of cataplexy. Cataplexy is an abrupt loss of muscle tone, most often triggered by sudden, strong emotions. A subset of cells in the medial medulla of the narcoleptic dog discharged at high rates only in cataplexy and rapid eye movement (REM) sleep. These cells were noncholinergic and were localized to ventromedial and caudal portions of the nucleus magnocellularis. The localization and discharge pattern of these cells indicate that cataplexy results from a triggering in waking of the neurons responsible for the suppression of muscle tone in REM sleep. However, most medullary cells were inactive during cataplexy but were active during REM sleep. These data demonstrate that cataplexy is a distinct behavioral state, differing from other sleep and waking states in its pattern of brainstem neuronal activity.     

Protein modification by amino acid addition is increased in crushed sciatic but not optic nerves

Rat optic and sciatic nerves were crushed, and 10 minutes to 3 days later nerve segments between the crushed site and the cell body were removed and assayed for posttranslational protein modification by amino acid addition. Protein modification was comparable in intact optic and sciatic nerves, but in sciatic nerves increased to 1.6 times control levels 10 minutes after crushing and reached a maximum of ten times control levels by 2 hours. In optic nerves activity was decreased throughout the time course studied. The results indicate that, in a nerve which is capable of regeneration (sciatic), protein modification by the addition of amino acids increases immediately after injury, but a nerve incapable of regeneration (optic) is incapable of activating the modification reaction. These findings may be important in understanding the reasons for the lack of a regenerative response after injury to central mammalian nerves.     

astray, a zebrafish roundabout homolog required for retinal axon guidance

As growing retinotectal axons navigate from the eye to the tectum, they sense guidance molecules distributed along the optic pathway. Mutations in the zebrafish astray gene severely disrupt retinal axon guidance, causing anterior-posterior pathfinding defects, excessive midline crossing, and defasciculation of the retinal projection. Eye transplantation experiments show that astray function is required in the eye. We identify astray as zebrafish robo2, a member of the Roundabout family of axon guidance receptors. Retinal ganglion cells express robo2 as they extend axons. Thus, robo2 is required for multiple axon guidance decisions during establishment of the vertebrate visual projection.