摘要:

AbstractFollowing dark incubation of isolated retinas ofXenopus laevisin Ringer solution supplemented with3H‐2 Deoxy‐D‐glucose (2DG), virtually all of the uptake of the label was by the inner segments and synaptic bases of the photoreceptor cells. Autoradiographs prepared from conventionally fixed tissue showed the same cellular distribution of label as those prepared from identically incubated, unfixed, freeze‐dried retinas. However, fixation removed about 77% of the total counts. This fixation‐labile, soluble fraction was identified as being primarily 2DG‐6 phosphate by thin‐layer chromatography. The remaining insoluble fraction corresponded in distribution to glycogen grains. In cones, glycogen is stored primarily in the paraboloid, whereas in rods it is distributed throughout the inner segment and synaptic base. EM autoradiographs illustrated that these were the sites over which fixationresistant 2DG label was localized. Measurements of radioactivity associated with extracts of retinal glycogen following 2DG incubation demonstrated that a disproportionately high fraction of total counts were associated with the glycogen fraction. We conclude that in the amphibian retina 2DG may be incorporated

ISSN:0092-7317    

DOI:10.1002/cne.902040202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe perikaryal sizes and retinal distribution of ganglion cells labeled after small iontophoretic injections of horseradish peroxidase (HRP) into the medial interlaminar nucleus (MIN) were studied. Injections were also made into the LGNv and the C‐laminae of the dorsal lateral geniculate nucleus (LGNd) for comparison. The results are consistent with suggestions that the MIN contains three approximately vertically oriented laminae which, from medial to lateral, receive their retinal input from, respectively, contralateral nasal, ipsilateral temporal, and contralateral temporal retina.Each MIN lamina receives afferents from two distinct groups of retinal ganglion cells: (1) cells with large somas (over 25 μm), coarse primary dendrites, large dendritic trees (500–900 μm in diameter), and coarse axons; (2) cells with medium‐sized somas (14–20 μm), medium‐caliber primary dendrites, large dendritic trees (350–700 μm), and fine axons. The large cells are clearly Y‐cells or alpha cells, and they provide approximately 50% of the retinal input to all layers of the MIN. The medium‐sized cells, which provide the remaining 50% of the retinal input to the MIN, are, we argue, W‐cells, since they do not differ in soma size, dendritic morphology, axon caliber, or receptive field properties from medium‐sized W‐cells which project to other thalamic or midbrain structures. These results suggest two phylogenetic trends within the W‐cell group: (1) the differentiation of thalamic and midbrain components; and (2) the further differentiation of ipsilateral and contralateral projections within the midbrain component. This latter division corresponds to the distinction between W1 and W2 cells described previously

ISSN:0092-7317    

DOI:10.1002/cne.902040203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractAfferent projections to the deep mesencephalic nucleus (DMN) of the rat were demonstrated with axonal transport techniques. Potential sources for projections to the DMN were first identified by injecting the nucleus with HRP and examining the cervical spinal cord, brain stem, and cortex for retrogradely labeled neurons. Areas consistently labeled were then injected with a tritiated radioisotope, the tissue processed for autoradiography, and the DMN examined for anterograde labeling. Afferent projections to the medial and/or lateral parts of the DMN were found to originate from a number of spinal, bulbar, and cortical centers.Rostral brain centers projecting to both medial and lateral parts of the DMN include the ipsilateral motor and somatosensory cortex, the entopeduncular nucleus, and zona incerta. At the level of the midbrain, the ipsilateral substantia nigra and contralateral DMN likewise project to the DMN. Furthermore, the ipsilateral superior colliculus projects to the DMN, involving mainly the lateral part of the nucleus.Afferents from caudal centers include bilateral projections from the sensory nuclei of the trigeminal complex and the nucleus medulla oblongata centralis, as well as from the contralateral dentate nucleus. The projections from the trigeminal complex and nucleus medullae oblongatae centralis terminate in the intermediate and medial parts of the DMN, whereas projections from the contralateral dentate nucleus terminate mainly in its lateral part.In general, the afferent connections of the DMN arise from diverse areas of the brain. Although most of these projections distribute throughout the entire extent of the DMN, some of them project mainly to either medial or lateral parts of the nucleus, thus suggesting that the organization of the DMN is comparable, at least in part, to that of the reticular formation of the pons and medulla, a region in which hodological differences between medial and lateral subdivisions are known to exist.

ISSN:0092-7317    

DOI:10.1002/cne.902040204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractA conscious rabbit which crouches in the ‘freeze’ position has an unequivocal 24° wide binocular field formed by the overlap of the two 12° sectors of uniocular optical field which extend nasal of its midline. Although this investigation reveals that the horizontal representation of the uniocular visual field in cortical visual area I extends more nasal than in earlier reports, it is found to terminate at the midline when the eyes are set in the standard freeze position. The 12° sectors of uniocular field nasal of the midline were not represented in spite of being served by retina. The binocular field of the rabbit in the freeze posture thus appears to have no binocular representation in visual area I.Nevertheless, the presence of a binocular region was confirmed in rabbit visual area I but the projections to it, via the contralateral and ipsilateral eyes, deal with the nonoverlapping sectors of monocular field when the eyes are in the freeze position. The maps of the visual field obtained in one hemisphere via the contralateral and ipsilateral projections were subject to a horizontal divergent disparity of some 18°. The presence of binocular single units in these regions was also confirmed but their two receptive fields were necessarily located in different visual hemispheres and again subject to an 18° mean horizontal divergent disparity. They could not be simultaneously stimulated by any localized feature of an object and are thus precluded from involvement in binocular single vision during the freeze position.The systematic, rather than reportedly random, topography of the ipsilateral projection to visual area I ensured that it could be well fused with the similarly organized contralateral projection by means of an 18° vergence of the eyes from the freeze position. The horizontal receptive field disparity of binocular single units is then brought to a zero mean value which enables their receptive fields through each eye to be simultaneously stimulated by the same part of an image. Tested units then evinced response summation; a minimum requirement for binocular vision. In thisequivalent primary positionof the eyes, the entire binocular visual field is completely represented in visual area one of both hemispheres.The rabbit thus appears to employ a two‐state cortical system for forward vision. In the freeze position the visual field attains a cyclopean extent of 360° but the receptive fields of cortical binocular units are widely divergent. The classic binocular optical fieldmaythen project to some other region of brain which subserves binocular vision. Upon examination of a frontal object the animal must verge its eyes in order to obtain binocular single vision in visual area I; it then temporarily surrenders part of its rear visual field. An explanation in terms of ocular image quality

ISSN:0092-7317    

DOI:10.1002/cne.902040205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe horseradish peroxidase (HRP) technique was used to investigate the laminar distribution of the cell bodies of origin of the two major descending pathways from the avian tectum to the hindbrain, the crossed tectobulbar pathway (CTB) and the ipsilateral tectopontine‐tectoreticular pathway (ITP). The CTB, which projects to the contralateral paramedian reticular formation of the hindbrain, was found to arise mainly (80–95%) from the large multipolar neurons characteristic of layer 13 of the tectum. In addition, multipolar neurons of layers 14 and 15 of the dorsal tectum contribute to rostrally terminating portions of the CTB. Neurons of layers 11–12, particularly at rostroventral tectal levels, were also found to contribute to the CTB. The ITP, which projects to the ipsilateral lateral pontine nucleus and the overlying reticular formation, was found to arise chiefly from neurons of layers 9–10, 13, and 14–15, with some slight contributions from neurons of tectal layers 8, 11, and 12. Cells of layers 8–10 that contributed to the ITP tended to be of two general types: (1) small‐mediumsized fusiform neurons with vertically disposed processes, and (2) medium‐large‐sized multipolar neurons whose processes showed no consistent orientation from neuron to neuron. The lateral pontine nucleus apparently receives input from tectal layers 8–15 inclusive, while the reticular formation overlying the lateral pontine nucleus appears to receive input only from tectal layers 13–15. Injections of HRP into the CTB and ITP also resulted in labeled cells in subtectal sites within the optic lobe (nucleus intercollicularis and the lateral mesencephalic reticular formation).The present results indicate that the major descending projections of the avian tectum arise from neurons located in tectal layers 8–15. Previous studies have shown that neurons of tectal layers 10 and 13–14 also give rise to the ascending projections of the avian tectum to the ventral lateral geniculate nucleus and to the nucleus rotundus, respectively (Benowitz and Karten, '76; Hunt and Kunzle, '76b). Thus, the major ascending and descending tectofugal pathways in birds share the same layers of origin. The present results in birds are in contrast to those in mammals, in which the ascending projections of the midbrain roof to diencephalic “visual” structures arise from superficial layers of the superior colliculus (layers I–III) while the major descending projections arise largely from the deeper layers of the superior colliculus (Harting et al., '73; Holcombe and Hall, '81). The decending pathways of the midbrain roof are presumed to be involved in motor functions while the ascending pathways of the midbrain roof are thought to be more involved in the sensory processing of visual information. The similarity in the laminar sources of the ascending and descending tectofugal pathways in birds, as reflected by the present study, indicates that the asending and desending tectofugal pathways of birds may convey simi

ISSN:0092-7317    

DOI:10.1002/cne.902040206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractThe localization of nicotinic‐cholinergic receptors in the inner plexiform layer (IPL) of goldfish retina was studied by electron microscopic analysis of the binding pattern of a conjugate of horseradish peroxidase and αbungarotoxin (HRP‐αBTx). Specific HRP reaction product (blockable by 1mm curare) was found at both synaptic and nonsynaptic sites. Synaptic binding sites for HRP‐αBTx, which accounted for only 16% of the total specific reaction product sites, always involved an amacrine process as the presynaptic element, whereas amacrine, ganglion, and bipolar cells could be postsynaptic elements at labeled synapses. Only 17.5% of the total number of amacrine synapses were labeled by HRP‐αBTx. Labeled synapses showed the same distribution in the IPL as unlabeled synapses: bimodal for amacrine‐to‐bipolar synapses with peak concentrations at the 20% and 80% layers and unimodal for amacrine‐to‐nonbipolar synapses with a peak concentration at the 60% layer. Nonsynaptic binding sites for HRP‐αBTx (84% of total) were seen on the dendrites of ganglion, amacrine, and bipolar cells. The distribution of the nonsynaptic sites in the IPL largely accounts for the trilaminar binding pattern of125I‐αBTx as observed in light microscopic autoradiographs. If, as appears likely, the distribution of synapses is the relevant variable in determining the sites of neuronal interaction for a given transmitter system, then this study further illustrates the importance of distinguishing synaptic from nonsynaptic binding when using receptorligand probes to localize sites of chemi

ISSN:0092-7317    

DOI:10.1002/cne.902040207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

摘要:

AbstractBy means of autoradiographic and ablation‐degeneration techniques, the intrinsic cortical connections of the posterior parietal cortex in the rhesus monkey were traced and correlated with a reappraisal of cerebral architectonics. Two major rostral‐to‐caudal connectional sequences exist. One begins in the dorsal postcentral gyrus (area 2) and proceeds, through architectnic divisions of the superior parietal lobule (areas PE and PEc), to a cortical region on the medial surface of the parietal lobe (area PGm). This area has architectonic features similar to those of the caudal inferior parietal lobule (area PG). The second sequence begins in the ventral post/ central gyrus (area 2) and passes through the rostral inferior parietal lobule (areas PF and PFG) to reach the caudal inferior parietal lobule (area PG). Both the superior parietal lobule and therostralinferior parietal lobule also send projections to various other zones located in the parietal opercular region, the intraparietal sulcus, and the caudalmost portion of the cingulate sulcus. Areas PGm and PG, on the other hand, project to each other, to the cingulate region, to the caudalmost portion of the superior temporal gyrus, and to the upper bank of the superior temporal sulcus. Finally, a reciprocal sequence of connections, directed from caudal to rostral, links together many of the above‐mentioned parietal zones. With regard to the laminar pattern of termination, the rostral‐to‐caudal connections are primarily distributed in the form of cortical “columns” while the caudal‐to‐rostral connections are found mainly over the first

ISSN:0092-7317    

DOI:10.1002/cne.902040208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902040201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1982

数据来源: WILEY