摘要:

AbstractIn the gray squirrel (Sciurus carolinensis), the prairie dog (Cynomys ludovicianus), and the Mexican and 13‐line ground squirrels (Citellus mexicanusandC. tridecemlineatus) there exist two distinct classes of photoreceptors that have cone‐like and rod‐like anatomical features respectively. These two receptor classes were previously known to exist in the gray squirrel, but only the cone‐like (C) receptor had been observed in the other species. We have now found small numbers of rod‐like (R) receptors in the other species. as well. R‐receptors comprise about 40% of the receptors in the gray squirrel, 10% of the receptors in the prairie dog, and 4–5% of the receptors in the two species of ground squirrel.This paper describes certain light and electron microscopic features of these two receptor classes including their synaptic connections with second‐order cells and with each other. We find that the C‐receptor has a morphology and synaptic organization characteristic of other mammalian cones. However. the R‐receptor differs from other mammalian rods in certain morphological respects, and its synaptic organization has both cone and rod characteristics as well as so

ISSN:0092-7317    

DOI:10.1002/cne.901590402

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractSpectral sensitivities of the gray squirrel, Mexican and 13‐line ground squirrel and prairie dog were determined by electroretinography under both dark‐ and light‐adapted conditions. The dark‐adapted spectral sensitivity function obtained from intact eyes of these species peaks between 515—525 nm; however, when corrected for lens absorption or recorded from the lensless eye, it peaks near 500 nm and closely matches in shape a rhodopsin nomogram curve (λmax= 502 nm). Upon light adaptation all these retinas become relatively more sensitive to long‐wave stimuli (i.e., they show a small Purkinje shift). The light‐adapted spectral sensitivity function is broader than that obtained from the dark‐adapted eye, especially toward the longer wavelengths. We conclude that in all these species the dark‐adapted spectral sensitivity is mediated by a single, rhodopsin‐like photopigment and that light‐adapted sensitivity is mediated by two (

ISSN:0092-7317    

DOI:10.1002/cne.901590403

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractIn Golgi preparations of goldfish retina we have observed three types of horizontal cell which receive exclusively from cones and one which receives exclusively from rods. The cone horizontal cells were designatedH1,H2andH3, in order of increasing dendritic spread, increasing separation from the outer synaptic layer, decreasing size of perikaryon, and decreasing density of cone contacts. Slender appendages with knobby terminal enlargements project horizontally from the perikarya and larger dendrites of both rod and cone horizontal cells.We determined patterns of cone inputs to Golgi‐impregnated horizontal cells by analyzing serial 1 μm sections with the light microscope. The probable inputs, in terms of visual pigments in the cones which contact them, are:H1, red + green + blue;H2, green + blue;H3, blue. Analysis of previously published work suggests (1) thatH1cells generate monophasic or L‐type responses,H2cells generate biphasic or C1‐type responses, andH3cells generate triphasic or C2‐type responses; (2) thatH1cells receive direct functional input at least from red‐sensitive cones,H2cells from green‐sensitive cones, andH3cells from blue‐sensitive cones; and (3) thatH1cells constitute pathways from cones toH2cells, andH2cells constitute pathways from cones andH1cells toH3cells. The precise location and route of the transfers, fromH1toH2and fromH2toH3, are

ISSN:0092-7317    

DOI:10.1002/cne.901590404

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractRetinas of ordinary and black moor varieties of goldfish (Carassius auratus) were prepared by the Golgi method, mounted flat or sectioned vertically, and studied in the light microscope. Three types of horizontal cells whose dendrites contact only cones, and one type whose dendrites contact only rods, were observed. The cone horizontal cells (Cajal's “external horizontal cells”) all have slender axons which descend gradually to the inner nuclear layer and terminate there in long, fusiform expansions (Cajal's “internal horizontal cells”). The thin and thick portions of the axons, as well as the perikarya of the horizontal cells, bear small numbers of straight, horizontally‐directed, knobby filamentous appendages which may be sites of synaptic contact. The cone horizontal cell axons in goldfish, unlike those in higher vertebrates, do not terminate in contact with synaptic endings of photoreceptor cells, but in proximity to cells and processes deep in the inner nuclear layer. Axons have not yet been demonstrated on rod horizontal cells in

ISSN:0092-7317    

DOI:10.1002/cne.901590405

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractNeurons within the basilar pontine gray (BPG) of the American opossum can be subdivided into four major nuclei which are named medial, lateral, ventral and peripeduncular in accordance with previous studies. In addition, several smaller subnuclei, such as the median and dorsolateral cell groups, are present, as well as two longitudinal columns of neurons within the ventral nucleus. Neurons in the BPG range in size from 9 to 35 μ and appear randomly distributed so that none of the subdivisions contains exclusively nerve cells of the same perikaryal dimension. Projection neurons as shown in Golgi impregnations have a variable dendritic pattern; those in peripeduncular zones exhibit dendrites closely applied to the surface of the cerebral peduncle, whereas those in other regions generally have a radial type of arrangement. Certain projection neurons can be distinguished on the basis of their dendritic surface, which bears either claw‐like protrusions or stalked appendages. Smaller nerve cells measuring less than 18 μ may be intrinsic neurons, since axon‐like processes arise from their dendrites and course for some distance near the parent cell before becoming thin and beaded. Ultrastructural observations show profiles of neurons comparable in size to those seen in Golgi impregnations and suggest at least four classes of presynaptic profiles. One category ranges in size from 2 to 8 μ, contains round vesicles (average diameter 450 Å) and characteristically forms multiple asymmetric syaptic contacts with several small postsyaptic profiles, some of which appear to be the dendritic claws mentioned above. The other three types of axon terminals measure less that 2 μ in their greatest dimension and are distinguished by their synaptic vesicles; one group containing round vesicles with an average diameter of 380 Å, a second group exhibiting larger round vesicles with an average diameter of 500 Å and a third group containing flattened or eliptical vesicles. Transection of the superior cerebellar peduncle produces early filamentous and later electron dense degenerative chages in some, but not all, of the larger types of presynaptic profiles. Subsequent to large motor‐sensory cortex ablations both filamentous and dark degenerating profiles are simultaneously observed at all survival times. In one case with a cortical lesion restricted to the motor‐sensory cortex, mainly dark degenerating terminals are apparent in the ipsilateral pontine gray, whereas in a lesion confined to the visual cortex only filamentous degeneration was observed. It is suggested, therefore, that some of the dark degenerating profiles represent the terminals of collaterals of corticospinal axons and the filamentous boutons are terminal expansions of direct cortico

ISSN:0092-7317    

DOI:10.1002/cne.901590406

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractThree‐month‐old male C57BL/10 mice were exercised by voluntary running activity in vertically revolving wheels for two hours each day until 24 months of age. Activity scores were recorded each day and the animals were regularly weighed and inspected for abnormalities. Control animals were similarly treated except that the acitvity wheels were immobilized.At the end of the exercise period, survival was 84% for the exercise group and 64% for the controls. Light microscopic examination of the posterior tibial nerve of the surviving animals showed a significant fiber hypertrophy in response to the exercise. The number of myelinated fibers in nerves from exercised animals did not differ from those of the controls.On the basis of these data, it is suggested that prolonged exercise does not prevent the loss of peripheral nerve fibers associated with age but rather, may exert an effect on the nervous system by modifying the surviving ce

ISSN:0092-7317    

DOI:10.1002/cne.901590407

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractA pattern of alternative dark and pale bands was observed in the straite cortex of the macaque monkey. The bands, which ran parallel to the surface, were seen in tangential sections stained with a reduced silver method for normal fibers and were most clear in layer 4C α, immediately deep to the line of Gennari. The dark bands were about 300 μ wide and showed blind endings and bifurcations. The light bands were about 50 μ wide and did not branch or terminate within area 17.Because the dark bands were similar in width to the bands of terminal degeneration which have been shown to result from single‐layer lesions of the lateral geniculate body, it seemed possible that they corresponded to ocular dominance columns. To test this idea, the boundaries of ocular dominance columns were marked in a physiological experiment: tangential electrode penetrations were made in an anesthetized monkey and, as the electrode was advanced horizontally in the fourth layer, the eye preference of single units and of the background activity was monitored. Small electrolytic lesions were placed at the points where a change in eye preference occurred. The brain was subsequently fixed, sectioned tangentially and stained with the silver method. All the lesions — a total of 12 — fell directly on the pale bands. Moreover, the electrode had not passed over any pale bands without a lesion being placed. It was concluded that the dark bands do correspond to single ocular dominance columns and the pale bands to the boundaries between columns.The banding appearance is due to a greater density of tangential fibers within columns than at the borders of columns. These tangential fibers are in part the preterminal arborizations of geniculocortical axons, since some of them have been shown to degenerate after geniculate lesion.The ocular dominance columns were mapped for most of the striate cortex, using serial tengential sections stained with the silver method. The overall pattern was similar in several monkeys, though the details of the branching arrangements vaired from animal to animal. The columns met the 17–18 border at rigtht angles. On the outer surface of the hemisphere the columns converged from the 17–18 border, turned medially with repeated fusions of columns, and streamed over the lip of the calcarine fissure. In the roof of the fissure they met a second system of columns oriented parasagittally. In terms of the visual field, the columns ran roughly horizontally for the central 10° of the field, and circumferentially beyond that. The columns were not mapped in the stem of the fissure, the area corresponding to the far periphery of the field.The constancy of column width across the cortex probably allows a functional matching between ocular‐dominance and orie

ISSN:0092-7317    

DOI:10.1002/cne.901590408

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901590409

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901590401

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY