Visual discrimination in sharks without optic tectum

After complete removal of the optic tectum, nurse sharks can learn to discriminate black versus white and horizontal versus vertical stripes. This finding is contrary to the traditional belief of exclusive tectal control over visuomotor behavior in lower vertebrates and suggests a role for the telencephalon in the vision of these primitive animals.     

Merging of modalities in the optic tectum: infrared and visual integration in rattlesnakes

The optic tectum of pit vipers (Crotalinae) contains a layer of infrared-sensitive neurons subjacent to the visual layer; these indirectly receive input from the facial pit organs. They respond transiently to the appearance or motion of warm objects within their 25 degrees to 70 degrees excitatory receptive fields (some have inhibitory regions) and presumably allow the snake to orient or strike toward prey. The infrared and visual spatiotopic tectal maps have similar but not identical axes; the infrared magnification is greater than that for vision. Bimodal neurons have receptive fields for each modality that reflect the disparity of the two maps. This finding suggests that (i) during development the infrared and visual fibers spread out independently to fill available tectal sites and (ii) bimodal neurons form local connections without regard to establishing spatial correspondence between the two modalities.     

雏鸡中脑视顶盖I层细胞构筑研究

为进一步阐明鸟类视觉通路的结构特征,试验采用Golgi-Cox法,灌流固定后尼氏体(Nissl bodies)染色和羰花青荧光染料DiI(1,1-’dioctadecyl-3,3,3’,3-t’etramethylindocarbo-cyanine perchlorate)逆向神经标记技术,对雏鸡视顶盖I层的厚度和该层的细胞形态、大小进行了观察研究和数理统计。结果表明,I层细胞多数呈梭形,还有少数呈圆形、椭圆形、锥形、三角形和不规则形状等。I层外侧部较背侧部和腹侧部厚。按照胞体面积大小将细胞分为4类:巨细胞、大细胞、中细胞和小细胞,I层背侧、腹侧和外侧以巨细胞最少,其中背侧、腹侧以小细胞为主,外侧以中细胞数量最多。I细胞具有2~6个主树突,其中有2个主树突的细胞最多(60.7%,n=128)。     

雏鸡中脑视顶盖Ⅰ层细胞构筑研究

为进一步阐明鸟类视觉通路的结构特征, 试验采用Golgi-Cox法, 灌流固定后尼氏体(Nissl bodies)染色和羰花青荧光染料DiⅠ(1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbo-cyanine perchlorate)逆向神经标记技术,对雏鸡视顶盖Ⅰ层的厚度和该层的细胞形态、大小进行了观察研究和数理统计.结果表明,Ⅰ层细胞多数呈梭形,还有少数呈圆形、椭圆形、锥形、三角形和不规则形状等.Ⅰ层外侧部较背侧部和腹侧部厚.按照胞体面积大小将细胞分为4类:巨细胞、大细胞、中细胞和小细胞,Ⅰ层背侧、腹侧和外侧以巨细胞最少,其中背侧、腹侧以小细胞为主,外侧以中细胞数量最多.Ⅰ细胞具有2～6个主树突,其中有2个主树突的细胞最多(60.7%, n=128).     

Corresponding spatial gradients of TOP molecules in the developing retina and optic tectum

The topographic map of cell position in the avian retina is inverted in its projection to the optic tectum. Dorsal retinal ganglion cell axons project to ventral tectum, and ventral retinal ganglion cells project to dorsal tectum. Topographic gradients of toponymic (TOP) cell surface molecules along the dorsoventral axes of retina and tectum also are inverted. TOP molecules are most abundant in dorsal retina and ventral tectum and least abundant in ventral retina and dorsal tectum during the period of initial retinal-tectal interaction. Thus, TOP molecules may be involved in orienting the retinotectal map.     

Visual instruction of the neural map of auditory space in the developing optic tectum

Neural maps of visual and auditory space are aligned in the adult optic tectum. In barn owls, this alignment of sensory maps was found to be controlled during ontogeny by visual instruction of the auditory spatial tuning of neurons. Large adaptive changes in auditory spatial tuning were induced by raising owls with displacing prisms mounted in spectacle frames in front of the eyes; neurons became tuned to sound source locations corresponding to their optically displaced, rather than their normal, visual receptive field locations. The results demonstrate that visual experience during development calibrates the tectal auditory space map in a site-specific manner, dictating its topography and alignment with the visual space map.     

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.     

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.     

Transport of protein by goldfish optic nerve fibers

After tritiated leucine was injected into the eye of goldfish, radio-active protein synthesized by the ganglion cell bodies moved down the optic axons at an average rate of 0.4 mm per day. Radioautograms of the optic tectum in which these axons end show that, as early as 24 hours after the injection, before the radioactivity in the tectal layer containing the optic axons had risen above background level, the layer containing the axon terminals was already heavily labeled. The radioactivity in the terminals reached a maximum about 48 hours after the injection and remained approximately constant for at least 23 days thereafter, whereas the radioactivity in the fiber layer increased significantly during the same interval, as the slowly moving protein component entered it. Thus there appears to be a special mechanism for rapid transport of protein from the cell body to the synaptic terminals, as well as a slower movement of protein down the axon.     

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.     

三日龄雏鸡中脑视顶盖H层神经元形态研究

为深入了解禽类中脑视顶盖的内部构造,用羰花青荧光染料DiI(1,1-’dioctadecyl-3,3,3’3-’tetramethyl-indocarbo-cyanine perchlorate)神经标记技术,对雏鸡视顶盖H层神经元形态进行了观察。结果显示,DiI标记H层神经元可分为2种类型,Ⅰ型神经元数量较多,胞体为多边形,树突野大,树突的数量和分支多,伸展较远,树突末端最远可达视顶盖A层;Ⅱ型神经元较少,胞体呈梨形、梭形、三角形等多种形态,树突野小,树突数量与分支少,伸展较近,最远只达视顶盖E层。     

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.     

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.     

Activation of single lateral geniculate cells by stimulation of either optic nerve

The lateral geniculate nucleus is organized in such a way that, initially at least, information from the one eye is almost exclusively segregated from that from the other eye. Single-unit recording, however, confirms the histological evidence that bilateral integration does take place. A small number of cells (< 8.5 percent) receive afferents directly from both optic nerves and are discharged by stimulating either nerve (direct interaction). More common is delayed interaction, where the cells are discharged independently by either optic nerve but only after a relatively long latency. Indirect interaction effects also occur.     

Receptive fields of directionally selective units in the optic nerve of the ground squirrel

These units responded vigorously to stimuli moving entirely across their receptive field centers in one direction (preferred) and not at all when the direction of motion was reversed (null). The directional selectivity was the result of an inhibitory mechanism which prevented responses to null movements. Surrounding each field center was a concentric antagonistic region produced by a second inhibitory mechanism.     

Receptive fields of opponent color units in the optic nerve of the ground squirrel

When mapped with white light, each receptive field consisted either of an excitatory ("on") center and a concentric inhibitory ("off") surround, or of the reverse arrangement. Monochromatic stimuli revealed that each receptive field was composed of two mutually antagonistic components (one excitatory, one inhibitory) which had different spectral sensitivities and different spatial distributions. For some units the two chromatic components had identical spatial distributions.     

Electrical responses of the retinal nerve and optic ganglion of the squid

Recordings were obtained from the retinal nerves and optic ganglia of intact squid, which were maintained in good condition by perfusing their mantles with sea water. Only "on" discharges were found in the nerves, whereas "on" and "off" discharges as well as spontaneous activity and tactile responses were obtained from the ganglia.