摘要:

AbstractThe peripheral retina of rabbits aged 0 to 60 days was studied by electron microscopy. Ribbon and conventional synaptogenesis was studied with serial sections, and the density of synapses of the inner plexiform layer was measured on large (1,500μm2) montages.Photoreceptor and bipolar ribbon synapses seem to develop similarly in that processes of the prospective dyad or triad contact the presynaptic ribbon‐containing terminal one at a time. No statistically significant difference in the lengths of ribbon lamellae was found at 11 and 30 days. Conventional synapses appear to result from the aggregation of synaptic vesicles on one side of junctions that first existed as symmetrical membrane densities without vesicles. The length of the synaptic membrane specialization remains constant between 0 and 30 days.The density of inner plexiform layer conventional synapses remains at a low and roughly constant level from 0 to 9 days, after which there is an abrupt increase to a plateau at about 20 days. After nine days the density of ribbon synapses also increases, with an initially steep time course similar to that of conventional synapses. All subcategories of synapse studied (amacrine‐to‐amacrine, amacrine‐to‐bipolar, serial, and reciprocal) participate in the general increase between 9 and 20 days. Functional circuits of the inner plexiform layer thus seem to be assembled primarily during the second and third wee

ISSN:0092-7317    

DOI:10.1002/cne.901750302

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractRetinas isolated from rabbits aged less than eight hours to adult were maintained in a flowing physiological medium. The electroretinogram or activity of single ganglion cells were recorded, and receptive fields were studied using stimulation of the retina with focused light. Retinal activity was stable for at least eight hours of incubation.Retinal ganglion cells are electrophysiologically active on the first day of life. They generate spontaneous bursts of action potentials at rates of 10 to 30 spikes/ sec, separated by silent intervals of one to six minutes. Maintained trains of action potentials follow elevation of the concentration of K+in the incubating medium to 10 mM. Ganglion cells are also stimulated by acetylcholine, with apparent threshols equal to or lower than those of ganglion cells in adult retinas.The first response of the retina to light is a small cornea‐negative transretinal potential at day 6, presumably PIII of the electroretinogram. Responses of the ganglion cells are seen at eight days, but the responses are weak and adapt quickly to repeated stimulation. Many unresponsive cells are present. By ten days 60% of ganglion cells respond to light, and examples of mature receptive fields are present. Immature receptive fields at ten days fall into two rough classes, one characterized by a large responsive area with no antagonistic surround, and a second in which the surround can suppress the response to illumination of the center but can not itself cause a discharge. Immature fields are progressively replaced by mature ones, and by 20 days the qualitative organization of receptive fields is indistinguishable from adul

ISSN:0092-7317    

DOI:10.1002/cne.901750303

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe cytoarchitecture of the tectum mesencephali in the siluroid teleostsBagrusandIctaluruswas studied by means of the Golgi method. These animals are known to have a restricted visual system and it seemed important to study whether this fact would affect the existence or the shape of the main neuron types which have been described for highly visual teleosts. It had been shown for a variety of teleosts that the retinotectal axons and terminals occupy almost exclusively the stratum opticum and the stratum fibrosum et griseum superficiale. The thickness of these strata inBagrusandIctaluruswas found to be reduced. However, the main types of especially the vertically oriented neurons, such as the pyramidal, fusiform, large pyriform and periventricular neurons which have been described for highly visual species of teleosts, were also found inBagrusandIctalurus. Although their shape was somewhat distorted, these neurons, nevertheless, showed processes distributed to the same tectal layers as in highly visual teleosts and are accessible to horizontally distributed fiber systems such as marginal, telencephalotectal and commissural tectal fibers, as well as the retinotectal fibers. Nonvisual inputs appear to be considerably involved in the maintenance of the main neuron types in the siluroid tectum. For example, the pyramidal neuron's apical dendritic tree, which receives the excitatory input from the marginal fibers, is as well developed in siluroids as in highly visual teleosts.

ISSN:0092-7317    

DOI:10.1002/cne.901750304

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractBy utilizing a horizontal dissection technique the entire floor of the third ventricle has been examined. When viewedin totothe ventricular floor was seen to have an hourglass shape with the supraoptic and infundibular recesses equalling the widened portions. Consistent regional differences were also noted. The rostral half of the floor was densely ciliated while the caudal portion, containing ependymal elements of the underlying median eminence, possessed few cilia. The ciliated cells ended in an abrupt transition zone located about halfway along the floor. The rostral portion of the infundibular recess had many more apical blebs and microvilli than did the caudal areas. Supraependymal cells of both the phagocyte‐like and neuron‐like variety were observed in all of the animals examined. In some animals, complex, branching, interconnecting networks of fine calibered fibers interconnected neuron‐like cells that occurred singly and occasionally in clusters. Female rats examined at all phases of the estrus cycle demonstrated no cyclic alterations of the ependymal su

ISSN:0092-7317    

DOI:10.1002/cne.901750305

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe organization of thalamic afferents to the rat's visual cortex was investigated autoradiographically and through the retrograde transport of horseradish peroxidase (HRP) following injections into striate and peristriate cortex. The results revealed that Nucleus lateralis posterior (NLP) projects to a large peristriate cortical field that includes areas 18A, 7, and the anterior portion of area 18, and to a circumscribed temporal area corresponding to Krieg's ('46a,b) area 20. The dorsal lateral geniculate nucleus (LGNd) was shown to project to two spatially discontinuous cortical areas. The largest geniculate receiving area is partially coextensive with Krieg's area 17, but an extension of this projection posterior and medial to the striate cortex was found. In addition, a geniculate projection to a restricted field located in the lateral peristriate cortex was identified.Concurrent investigations were designed to assess the pattern discrimination abilities of rats prepared with striate cortical ablations, lesions in NLP and combined striate‐cortical and thalamic ablations. Comparison of these animals with normal control subjects revealed that the striate cortex in the rat (as in the cat [Doty, '71; Sprague et al., '77] and the tree shrew [Killackey and Diamond, '71; Ware et al., '74]) is not necessary for successful pattern discrimination, and that the geniculo‐striate and NLP‐extra‐striate projection systems are both involved in mediating the visual discriminative abilities of the rat.The results add species generality to the concept that the central connections to the visual cortex are characterized by parallel‐conducting thalamic channels and contribute to the growing number of demonstrations that the extra‐striate cortex and associated thalamic cell groups contribute significantly to the process of visual‐patter

ISSN:0092-7317    

DOI:10.1002/cne.901750306

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe orientation of the visual streak of the cat's retina was compared to that of the long axis of the slit pupil in the same eye. In five paralyzed, anesthetized cats, the retinal projection to the superior colliculus was mapped with electrophysiological techniques. The orientation of the visual streak was estimated from the projection in visual space of the collicular region of high magnification which corresponds to the central projection of the streak. The angle by which the streak was tilted from absolute horizontal was always within one or two degrees of the angle by which the pupil axis was tilted from absolute vertical. This relationship was confirmed in three of the animals in which small retinal lesions were placed a known distance from the histologically determined axis of the streak. From the visual coordinated of these lesions, an independent estimate of the streak's orientation was obtained. In each case, the tilt of streak axis from horizontal differed by no more than 0.5° from the tilt of the pupil axis from vertical. The results support the hypothesis that planes containing the long axis of the cat's slit pupil are perpendicular to planes containing the long axis of the visual streak of the same eye

ISSN:0092-7317    

DOI:10.1002/cne.901750307

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe nucleus of the pontobulbar body (PBu) in the North American opossum is located, for the most part, adjacent to the motor root of the trigeminal nerve. Material prepared by degeneration and autoradiographic methods shows that the PBu receives projections from the facial motor‐sensory cortex, red nucleus, spinal cord and cerebellum. The latter fibers probably take origin within the fastigial nucleus. Each of the afferent connections ends in a restricted part of the PBu, but there is considerable overlap. Use of the horseradish peroxidase technique reveals that the PBu projects to the spinal cerebellum (anterior lobe, pyramis and paramedian lobules), to visual‐auditory areas of the vermis and to the lobus simplex as well as to crus I and II of the hemispheres. Although there is some topography to such projections, it is not sharply defined and many regions of the PBu contain labelled neurons after injections of horseradish peroxidase into widely separate areas of the cerebellar cortex.Because of its embryogenesis and position, the PBu is often considered part of the dorsolateral basilar pons. It appears from our material, however, that the organization of PBu afferent and efferent connections is different from that of the adjacent basilar pons, and arguments for considering the PBu a separate precerebellar nucleus are presen

ISSN:0092-7317    

DOI:10.1002/cne.901750308

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901750301

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY