摘要:

AbstractThe central projections of the retina in the nurse shark were studied by anterograde transport of horseradish peroxidase and tritiated proline. With regard to efferent retinal fibres, both techniques gave completely identical results. Projections were found to pretectal area, dorsal thalamus, basal optic nucleus, and optic tectum, all at the contralateral side. The retinal target cells in the dorsal thalamus are restricted to the ventrolateral optic nucleus and the posterior optic nucleus. No evidence was found for an earlier‐reported projection to the lateral geniculate nucleus. The present findings show that the ventrolateral optic nucleus exhibits homological features of the dorsal lateral geniculate nucleus in other vertebrate groups, whereas the lateral geniculate nucleus of the nurse shark is much more comparable to the nucleus rotundus of teleosts and birds and would be more appropriately so named. The application of the HRP technique also allowed us to study afferents to the retina by retrograde transport of tracer. Retrogradely labeled cells were observed in the contralateral optic tectum and are apparently similar to those reported for teleosts and bird

ISSN:0092-7317    

DOI:10.1002/cne.901960402

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAs part of a study on retino‐telecephalic pathways the ascending connections to the telencephalic central nucleus were investigated by retrograde transport of horseradish peroxidase. The central nucleus of the telencephalon, which is the main recipient for input from the brainstem, grossly can be divided into three rostrocaudal parts according to their afferent connections. The rostral third receives input mainly from the contralateral central thalamic nucleus and to a lesser degree from the lateral geniculate nucleus, periventricular gray, and a nucleus called the ventral mesencephalic tegmentum. The middle third of the central nucleus maintains an afferent connection with contralateral lateral geniculate, ventrolateral optic, and central thalamic nucleus, with the ventral mesencephalic tegmentum and periventricular gray bilaterally, and with a group of cells in the superior raphé nucleus. Caudal central nucleus injections of HRP resulted in labeling of cells in the contralateral lateral geniculate nucleus, ventral mesencephalic tegmentum, and central thalamic bilaterally, and in the superior raphé nucleus preoptic area and periventricular gray. From these results it can be concluded that visual information may reach the central telencephalic nucleus by two separate pathways: one pathway from retina via ventrolateral optic nucleus to the middle third of the central nucleus, and a second pathway from retina to optic tectum, which reportedly projects to the lateral geniculate nucleus, which in turn provides afferents to the caudal two‐thirds of the central nucleus. As such the nurse shark's visual system posesses structural features that are homologous to the two visual systems of higher vertebrate g

ISSN:0092-7317    

DOI:10.1002/cne.901960403

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractIntraventricular injections of kainic acid were used to create a model of selective cell death in order to study the fate of afferent projections that are deprived of their postsynaptic targets. This treatment rapidly destroyed hipocampal CA3 pyramidal cells, but not those neurons that give rise to their mossy fiber and entorhinal afferents. Light microscopic studies with the Timm's sulfide silver stain indicated that half or more of the mossy fiber boutons in area CA3b were lost within the first 1–3 days after kainic acid administration. This finding was confirmed by electron microscopy. Electron‐dense, usually vacuolated mossy fiber boutons accounted for about 10–20% of the total population present at a 4‐hour survival time, but were not encountered in control rats nor at survival times longer than 1 day. Other mossy fiber boutons remained electron lucent, but enlarged became more rounded in shape, and suffered and apparent loss of synaptic vesicles. It is suggested that degeneration of some mossy fiber boutons and resorption of others into the axon may have accounted for the precipitous decline in their number. The dendritic excrescences contacted by these boutons were nearly all undergoing electron‐dense degeneration 4 hours after kainic acid administration. In rats that survived 6–8 weeks mossy fiber boutons remained somewhat scarce, individual boutons appeared relatively small, and only one‐third the normal percentage were observed to be engaged in more than one synaptic contact within a single cross section. A qualitative electron microscopic study of the entorhinal projection to area CA3 suggested a response to kainic acid treatment similar to that of the mossy fiber projection, except that no entorhinal boutons were seen to become electron dense.These findings suggest that presynaptic fibers in the mature hippocampus adjust the size of their terminal arborizations and number of synaptic contacts to accommodate a reduction in the target cell population. The rapid loss of mossy fiber boutons may be attributable to an unsual fragility of these structures when they are deprived of the mechanical support normally provided by the pyramidal cell. Finally, the ability of kainic acid administration to alter the number and distribution of presynaptic elements must be taken into account whenever this toxin is used to make selective lesions of posts

ISSN:0092-7317    

DOI:10.1002/cne.901960404

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe morphology of the nucleus of the lateral descending tract of V has been studied in species of two genera of pit vipers, cottonmouth moccasin(Agkistrodon piscivorus piscivours), and rattlesnake(Crotalus ruberandCrotalus horridus horridus). The nucleus is the site of termination of primary afferent neurons forming the infrared receptors in the facial pits. It is located on the external surface of the common descending tract of V and contains somata that range in size from 7 to 22 μm in A.A. p. piscivorusand 7 to 27 μm inC. ruber.Electron microscopy reveals that the lateral descending tract contains both Aδ and C fibers. Degeneration experiments indicate that the Aδ fibers are primary afferents. The source of the C fibers is unknown.The lateral descending nucleus in both the cottonmouth and rattlesnake is fundamentally similar in organization. Afferent terminals containing clear spherical vesicles make synaptic contact with dendritic processes within the main neuropil. These axon terminals are also postsynaptic to boutons containing pleomorphic vesicles and some large dense‐core vesicles.The C fibers terminate in a neuropil at the margin of the lateral descending tract on small dendritic processes that appear to come from neurons within the nucleus. This neuropil is found external to the tract in the cottonmouth and internal to the tract in the rattlesnake. The terminals contain clear spherical vesicles and large dense‐core vesicles.The singularity of input to this nucleus is apparently reflected in the morphology. This is discussed in relation to the subnucleus caudalis of the mammalian br

ISSN:0092-7317    

DOI:10.1002/cne.901960405

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractMaps of ganglion‐cell distribution have been constructed from whole‐mounted retinas of five Australian marsupial species. The pademelon wallaby(Thylogale billiardieri), the scrub wallaby or tammar(Macropus eugenii), and the carnivorous Tasmanian devil(Sarcophilus harissi)have both a visual streak and an area centralis. The retina of the brown bandicoot(Isoodon obesulus)also shows both these features but they are less prominent than in the former three species, whereas the burrow‐dwelling, hairy‐nosed wombat(Lasiorhinus latifrons)possesses a well‐developed visual streak but seems to lack an area centralis.A study of ganglion‐cell sizes comparing nasal and temporal retina, the visual streak, and/or the area centralis was undertaken in each species. Results show that as in the cat, small ganglion cells tend to concentrate in the visual streak. However, the temporal‐nasal differences in cell sizes described in the cat (Stone et al., '80) could be detected only in those marsupials in which an area centralis was clearly

ISSN:0092-7317    

DOI:10.1002/cne.901960406

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractWe have reported previously that during optic nerve regeneration inRana pipiens, axons are misrouted into the opposite nerve and retina. In the present investigation we have examined the time course of formation of these “misrouted” axons and their cells of origin. The right eye of 31 frogs was injected with3H‐proline at various times after right optic nerve crush. In every frog examined 2 weeks and later after nerve crush, the distribution of autoradiographic label indicated that axons from the right eye had grown into the left optic nerve at the chiasm. The amount of label increased from 2 weeks to reach a maximum at 6 weeks where the entire left nerve was filled with silver grains. At 5 to 6 weeks after crush, laboled axons were found within the ganglion cell fiber layer (GCFL) of the retina of the opposite eye for a maximum distance of 2.3 mm from the optic disc. In frogs examined at intervals later than 6 weeks after crush, the amount of label within the left eye and nerve progressively decreased, indicating a gradual disappearance of the misrouted axons. Studies using anterograde transport of horseradish peroxidase (HRP) after nerve injection confirmed these autoradiographic findings. The position of ganglion cells in the right eye whose axons were misrouted to the left eye was determined by retrograde transport of HRP. Five or 6 weeks after crushing therightoptic nerve, thelefteye was injected with HRP and labled ganglion cells were found throughout the right eye retina. The largest percentage of labeled cells was found within the ventral half of the retina, particularly within the temporal quadrant, and nearly all of the labeled cells were found in more peripheral portions of the retina. Since few retino‐retinal axons are found during normal development, the present results show that the factors guiding regenerating axons in the adult frog differ substantially from those present during deve

ISSN:0092-7317    

DOI:10.1002/cne.901960407

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractPrevious experiments have shown that a substantial number of regenerating optic axons in adult frogs (Rana pipiens) are misrouted into the opposite optic nerve and retina during early stages of regeneration. This projection is maximal at 5 and 6 weeks after optic nerve crush. To further characterize this anomalous projection, small quantities of horseradish peroxidase (HRP) were injected into the right eye or right optic nerve 5 or 6 weeks after right optic nerve crush. Twenty‐four hours later the animals were killed and regenerating axons anterogradely filled with HRP were reacted with the tetramethyl‐benzidine method or a diaminobenzidine‐CoCl2method. Serial reconstruction tracing the course of individual axons through the optic chiasm showed that few of the axons projecting into the opposite optic nerve were collaterals of axons projecting centrally. Instead, the majority of labeled axons misdirected into the opposite nerve or contributing to an expanded projection into the ipsilateral optic tract turned out of the chiasm without branching. Many of the labeled regenerating axons had unusual trajectories within the chiasm, making abrupt turns or changing their direction of growth. Most of the axons misrouted into the opposite nerve came from portions of the chiasm nearest to the nerve of the other eye. In three of eight frogs with an intact optic nerve, a small number of HRP‐labeled axons were found in the left nerve after right nerve injection, but there was no indication that these axons reached the left eye. The results from this investigation suggest that the most parsimonious explanation for the chiasmal misrouting of regenerating frog optic axons is that axons are mechanically deflected into inappropriate p

ISSN:0092-7317    

DOI:10.1002/cne.901960408

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractPrevious reports from this laboratory have shown that a substantial number of optic axons are misrouted after optic nerve regeneration in the adult frog,Rana pipiens. Regenerating axons from a crushed optic nerve are distributed throughout the opposite nerve. In this study, we report the effect of crushing both optic nerves (double crush) on the pattern and degree of axonal misrouting. In 28 frogs both optic nerves were crushed at the same time (simultaneous double crush) and animals survived for varying periods before the right eye was injected with3H‐proline and the brain processed for autoradiography 24 hours later. In every frog with postoperative survivals longer than 2 weeks, labeled axons from the right eye were found in the left optic nerve. However, when compared to the amount of label seen in frogs in which only the right optic nerve was crushed (single crush) there was substantially less label within the left nerve of frogs after crushing both nerves. Label was also found only at the edge of the left nerve in material from double crush frogs, unlike that found after single crush. In four of six frogs where the left nerve was crushed 1 week after the right nerve (delayed double crush), the proximal end of the left nerve was completely filled with label, but more distally, label was found only along the edge of this nerve. Although fewer optic axons were labeled in the opposite optic nerve of double crush frogs, label did extend to the optic disc of that eye. However, label was not apparent in the ganglion cell fiber layer of the opposite eye. Instead, it was confined to the edge of the optic disc in a space apparently associated with papilledema resulting from crushing the optic nerve of that eye. In six frogs the retina of the left eye was removed at the same time the right optic nerve was crushed. Labeled axons of the right eye filled the left optic nerve to the retina‐less shell of the left eye. Thus, these data show that the amount and distribution of axonal misrouting into the opposite optic nerve during optic nerve regeneration is affected by intact or regenerating optic axons from the other

ISSN:0092-7317    

DOI:10.1002/cne.901960409

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractRana pipienswere raised through metamorphosis after extirpation of both eye primordia at Shumway embryonic stage 17 (Shumway '40). The visual connections between the isthmic nuclei and the optic tectum were examined in these animals using horseradish peroxidase (HRP) histochemistry. Isthmo‐tectal projections are normally aligned with the primary retinotectal map. We asked whether these connections would develop normal topographic organization in the absence of normal retinal input.HRP was formed into a solid pellet (≃ 200–500 μm diameter) and inserted into one tectal lobe on the tip of a fine metal probe. The procedure produced relatively restricted retrograde label in somas and dendrites in both isthmi nuclei. In the nucleus isthmus ipsilateral to the tectal lobe receiving the HRP pellet, processes of tecto‐isthmi neurons were labeled by anterograde transport.The topography of the isthmo‐tectal and tecto‐isthmic projections were identical in the developmentally enucleated animals and in normal frogs, even though eye removal severely reduced the volume of the optic tecta and the isthmi nuclei. Thus our analyses indicate that retinal contacts do not play an active role in the development of the positional or polarity cues that are involved in “mapping” projections between central visual nuclei. These results are discussed in the context of peripheral specification of central connections and in terms of models that have recently been proposed to explain the development of the ret

ISSN:0092-7317    

DOI:10.1002/cne.901960410

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractRetrograde and orthograde transport techniques show that the nucleus reticularis gigantocellularis pars ventralis and the nucleus reticularis gigantocellularis project the entire length of the spinal cord. Double‐labelling methods show that some of the neurons in each area innervate both cervical and lumbar levels. There is evidence, however, that neurons in the lateral part of the nucleus reticularis gigantocellularis pars ventralis and the dorsal extreme of the nucleus reticularis gigantocellularis project mainly to cervical and thoracic levels. The autoradiographic method shows that the above nuclei supply direct innervation to somatic and autonomic motor columns as well as to laminae V–VIII and X. The nucleus reticularis gigantocellularis pars ventralis provides additional projections to lamina I and the outer part of lamina II.Several areas of the medullary reticular formation project mainly, and in some cases exclusively, to cervical and thoracic levels. These areas include the nucleus reticularis parvocellularis, the nucleus reticularis lateralis, the nucleus retrofacialis, the nucleus ambiguus, the nucleus lateralis reticularis, caudal parts of the nuclei reticularis medullae oblongatee dorsalis and ventralis, and the nucleus supraspinalis. Autoradiographic experiments reveal that neurons in the ventrolateral medulla, particularly rostrally (the nucleus reticularis lateralis and neurons related to the nucleus lateralis reticularis), innervate sympathetic nuclei.Our results indicate that spinal projections from bulbar areas of the reticular formation are more complicated than previously supposed. Axons from separate areas project to different spinal levels and in some cases to different nuclear targets. These data are in conformity with the evolving concept of reticular heterogene

ISSN:0092-7317    

DOI:10.1002/cne.901960411

出版商:Alan R. Liss, Inc.    

年代:1981

数据来源: WILEY