摘要:

AbstractThe organization of sensory and motor regions of the cerebral cortex has been studied in the platypus (Ornithorhynchus anatinus), of the order Monotremata. Comparisons were made with the organization found in the other representative of this order, the echidna, and with primitive species of eutherian and metatherian mammals. Evoked potential and single neuron studies revealed a large single area of somatosensory representation in the posterior region of the hemisphere, extending from an approximately mid‐sagittal position around to the region of the rhinal sulcus on the ventrolateral surface of the hemisphere. The mediolateral representation of contralateral body parts was consistent with the pattern in the primary somatosensory area of other mammalian species. No evidence of a second somatosensory area was found. Neurons with similar receptive fields were grouped in columns normal to the cortical surface and a highly ordered pattern of somatotopic representation was found. Within the large area of bill representation individual neurons had receptive fields which were often punctate and no more than 1 mm in diameter. They responded to dynamic components of tactile stimuli delivered to their receptive fields on the bill.Movements on the contralateral side of the body could be elicited by bipolar electrical stimulation over an area on the dorsal surface of the hemisphere which largely overlapped the somatosensory area, but extended further anteriorly towards the frontal pole of the hemisphere. Visual and auditory projection regions were found overlapping the somatosensory area in the posterior part of the hemisphere. The auditory area overlapped the visual area and appeared to be displaced posteromedially in relation to its position in other species, a displacement which may be a consequence of the large expanse of cortical area associated with the bill.The observation that a large proportion of cortical area is devoted to specific sensory and motor function in platypus corresponds with earlier findings in primitive eutherian and metatherian species. The platypus neocortex appears to represent a more primitive stage of cortical development than that found in the other member of the order Monotremata, the echidn

ISSN:0092-7317    

DOI:10.1002/cne.901740102

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

年代:1977

数据来源: WILEY

摘要:

AbstractIn Midwestern Siamese cats each cerebral hemisphere receives visual inputs from both temporal retinae, and the conflicting signals that arise from these two disparate afferent sources appear to prevent the establishment of some normal functional connections for the whole temporal retina. As a result, these cats show no behaviorally demonstrable visual orientation for the temporal retina, although they respond normally for the nasal retina. The visual capacities of Midwestern cats can be changed by modifying early visual experience, and some of the rules that govern the formation of central visual pathways can thus be defined.The apparent blindness of the temporal retina of a Midwestern cat can be modified by monocular rearing. When such a cat is raised with one eye sutured or removed, the other eye develops a field of view that is normal in terms of visual orientation. Cortical lesions show that the vision acquired by the temporal retina depends upon areas 17 and 18 of occipital cortex. The modification of vision in the open eye can be produced by deprivation starting between the 8th and 80th day of life; later stages remain to be tested. In contrast, modifications produced in the deprived eye show a different relation to the time of the suture: if the lid suture is done at eight to ten weeks, the deprived eye develops vision for only the nasal retina and thus demonstrates the visual connections that developed while both eyes were open: if the suture is done at about the age of eye opening, the sutured eye develops no demonstrable vision at all. This is in striking contrast to the effect seen in non‐Siamese cats in which the sutured eye shows vision for the monocular crescent (Sherman, 1973).Experiments using alternate deprivation (one eye closed on the tenth day and then opened when the other is closed or removed at the eighth to fourteenth week) show that if one eye has sole access to the geniculo‐cortical system during the first eight or more weeks of life, functional connections demonstrable by behavioral testing of visual orientation are established permanently for the temporal retina of this eye. Thereafter the other eye cannot also establish functional connections for its temporal retina, even when the “successful” eye is sutured or removed surgically. In contrast, opening a previously sutured eye at the eighth or tenth week will allow visual development for the pathways from the temporal retina of the opened eye, provided that both eyes had been kept closed initially. Thus, after the eighth week, vision for the temporal retina can still be established, but we have been unable to make both temporal retinae share the pathways available in one hemisphere.Some segments of the geniculo‐cortical system are essentially non‐functional in Midwestern cats and other segments are made non‐functional by monocular deprivation. However, since all parts show about the same degree of retrograde reaction after cortical lesions, it appears that all parts send geniculo‐cortical axons to the visual cortex. The monocular suture itself affects geniculate cell growth in the normal segments of lamina A1 more than in the rest of the nucleus. The large monocular segments of lamina A, which are characeristic of the Siamese nucleus, do not show the sparing effect that is seen for geniculate cell growth in normal cats (Guillery and Stelzner, 1970), all parts of lamina A showing approximately the same cell size after mo

ISSN:0092-7317    

DOI:10.1002/cne.901740103

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

年代:1977

数据来源: WILEY

摘要:

AbstractIn five adult cats and three adult monkeys the dorsal rootlets at cervical and various lumbar levels were examined by both light and electron microscopy. In both species, the rootlets could be divided into three anatomically distinct parts: a peripheral, a transitional, and a central zone. The anatomy of the peripheral and transitional parts of the cat were identical with those of the monkey. The peripheral part of the rootlet in both these species had many of the ultrastructural characteristics of a peripheral nerve: and, as in the peripheral nerve, the small caliber axons were randomly distributed throughout the rootlet. In the transitional part of the rootlet, where the anatomical characteristics change to those typifying the tracts of the central nervous system, the unmyelinated axons and small caliber myelinated axons become organized into bundles at the periphery of the fascicles of large myelinated axons. In the central part there were differences between the two species in the distribution of the unmyelinated axons. In the cat no reorganization of the fibers of the central part of the rootlet could be found: the rootlets entered the cord and passed through the dorsal part of Lissauer's tract, and the bundles of unmyelinated axons simply merged with the tract as they came into contact with it. In the monkey, however, the dorsal root enters dorsal to Lissauer's tract and as each part of the rootlet passed from transitional to central, the small caliber axons took a ventrolateral course within the rootlet. As the rootlet merged with the dorsal columns, these axons formed a single bundle on the ventral and lateral surface of the rootlet which then merged with Lissauer's tract. These results indicate that a “lateral division” of the dorsal root is present in the monkey, but not the

ISSN:0092-7317    

DOI:10.1002/cne.901740104

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

年代:1977

数据来源: WILEY

摘要:

AbstractOrganization of the neocortical second somatic sensory area (SmII) of anesthetized Virginia opossums has been examined utilizing microelectrode recording techniques. SmII is situated between the first somatic sensory area (SmI) medially, and the rhinal fissure laterally. The head representation is located anteromedially within SmII, and the hindlimb representation posterolaterally, with the forelimb representation in between. Approximately 49% of SmII is devoted to representation of the head, 36% to forelimb representation, and 15% to trunk and hindlimb representation. All peripheral receptive fields (RF's) were either contralateral or bilateral. Approximately 63% of head RF's, 25% of forelimb RF's and 100% of hindlimb RF's were bilateral. For a given body locus, SmII RF's are larger than those for SmI. SmII is contained entirely within an area yielding evoked potentials responses to auditory click stimuli.

ISSN:0092-7317    

DOI:10.1002/cne.901740105

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

年代:1977

数据来源: WILEY

摘要:

AbstractFourteen cats were trained on three visual discrimination tasks: light vs. dark, horizontal vs. vertical stripes, and upright vs. inverted triangles. Four of the cats then underwent large, bilateral occipito‐temporal cortex ablations; postoperatively, they demonstrated little or no visually guided orienting behavior and could solve only the brightness task and not the preoperatively learned pattern discriminations. Six other cats underwent the same cortical ablations plus a transection of the commissure of the superior colliculus; postoperatively, they demonstrated good visually guided orienting behavior (i.e., the Sprague effect) but still could solve only the brightness task. The final four cats were controls and underwent no surgery; they demonstrated good retention of the pattern task despite an extensive idle period corresponding to the postoperative period before retesting in the above ten cats. These data indicate that, while a transection of the collicular commissure after visual decortication dramatically improves visual orienting, it does not obviously improve visual discrimination abilitie

ISSN:0092-7317    

DOI:10.1002/cne.901740106

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

年代:1977

数据来源: WILEY

摘要:

AbstractFour cats were raised with binocular eyelid suture and, after their eyes were opened, were trained on a series of discrimination tasks. They performed at normal rates on the brightness task but indicated some difficulty with the pattern tasks. They then received large, bilateral occipito‐temporal cortex ablations. Postoperatively, this in no observable way affected their visually guided orienting behavior, but it did destroy their capacity to perform the preoperatively learned pattern tasks. Postoperative performance on the brightness task remained good. These data indicate that, in these deprived cats, there is little or no cortical development for visual orienting, but cortex is necessary for visual discrimination learnin

ISSN:0092-7317    

DOI:10.1002/cne.901740107

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe first optic ganglion (FOG) of the principal eyes of jumping spider has been studied by both light and electron microscopy. Each FOG receives projections from the ipsilateral principal eye in a compact optic nerve. Some of the retinal axons, as they pass to the ganglion, cross in a chiasm within the optic nerve. The FOG is composed of a rind of nerve cell bodies which are unipolar cells giving rise anteriorly to second order nerve fibers in the central neuropile of the ganglion and posteriorly to processes which pass into the second optic ganglion. The neuropil is composed of neural and glial processes and of scattered glial cell bodies and it can be divided into a terminal zone and a fibrous zone. The terminal zone is the site of termination for all of the retinal axons. A unique feature of the retinal axon terminals is the presence of numerous fine post‐terminal processes extending away from the main portion of the retinal terminal. The fibrous zone is composed of second order nerve fibers with terminals in the terminal zone and it is continuous with a connective between the FOG and the second optic ganglion called the chiasm where the majority of the second order fibers cross.All of the synapses in the FOG are modified ribbon synapses and occur in the terminal zone within ensheathed synaptic glomeruli as dyads or triads. Large retinal terminals containing pleomorphic vesicles are presynaptic to smaller second order terminals containing spherical vesicles. Second order terminals are also presynaptic to retinal terminals in addition to forming serial‐like synapses with each ot

ISSN:0092-7317    

DOI:10.1002/cne.901740108

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

年代:1977

数据来源: WILEY

摘要:

AbstractWhen viewed in Nissl preparations, the lateral reticular nucleus (LRN) of the opossum can be divided into three subgroups: a medial internal portion, a lateral external portion and a rostral trigeminal division. Neurons within the internal division measure 13‐45 μ in their greatest dimension whereas those within the external and trigeminal portions measure 11‐32 μ and 14‐27 μ respectively.Golgi impregnations reveal that many neurons in all three subdivisions display a radial dendritic pattern although some of the nerve cells within the external division have dendrites which orient mainly in a ventromedial to dorsolateral direction. The cell bodies of LRN neurons are relatively spine‐free. However, a small percentage of neurons exhibit clusters of sessile spines on proximal and more distal dendritic segments. No locally ramifying axons or axon collaterals were found within the LRN.Synaptic terminals within the LRN were divided into four categories: (1) small terminals measuring 2.5 μ or less containing agranular spherical vesicles; (2) small terminals (2.5 μ or less) with agranular pleomorphic synaptic vesicles, i.e., a mixture of spherical and elliptical synaptic vesicles; (3) small terminals (2.5 μ or less) containing agranular spherical or pleomorphic vesicles with a variable number (4‐27) of dense core vesicles; and (4) large terminals (greater than 2.5 μ) which contain agranular spherical synaptic vesicles and a variable number of dense core vesicles (1‐17).Dendritic diameters were measured from Golgi impregnations and correlated with cross‐sectioned profiles in electron micrographs to help determine the post‐synaptic distribution of synaptic endings. Small terminals containing agranular spherical or pleomorphic synaptic vesicles contact the soma and entire dendritic tree in each portion of the nucleus, whereas the small terminals containing dense core vesicles are usually located on distal dendrites or spines. Some large terminals make multiple synaptic contacts with a cluster of spines, others contact groups of small (distal) dendrites.In order to identify two of the major afferent systems to the LRN, 15 adult opossums were subjected to either a cervical spinal cord hemisection or a stereotaxic lesion of the red nucleus. Two days subsequent to spinal hemisection, large terminals in the caudal part of the ipsilateral LRN exhibit either an electron dense or filamentous reaction. Their postsynaptic loci are spines and shafts of proximal dendrites or a number of distal dendrites and spines. In addition, small terminals containing spherical agranular synaptic vesicles undergo an electron dense reaction in the same areas. Their postsynaptic loci are proximal or distal dendrites. Two days subsequent to rubral lesions, small terminals containing agranular spherical synaptic vesicles undergo a dark reaction in rostral portions of the contralateral nucleus. They contact intermediate or distal dendrites a

ISSN:0092-7317    

DOI:10.1002/cne.901740109

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

年代:1977

数据来源: WILEY

摘要:

AbstractConformational, histochemical and histofluorescent studies reveal that the entire lateral reticular nucleus (LRN) of the Virginia opossum is positive for cholinesterase activity and that its rostral portion is rich in fluorescent varicosities of the catecholamine type. Although neocortical‐LRN connections are relatively meagre, projections to the LRN from the red nucleus are extensive and topographically organized. Rubral‐LRN fibers arise from large‐medium sized neurons and distribute to the trigeminal division of the LRN as well as to specific portions of its external and internal divisions. Certain areas of the midbrain and pontine reticular formation, as well as the vestibular nuclei, project to the LRN and there is some evidence that reticular neurons adjacent to the LRN provide additional input. Although a relatively small fastigial‐LRN projection exists, no evidence was found for a contribution from any of the other deep cerebellar nuclei. Spinal‐LRN connections are extensive and topographically organized. Each of the inputs to the LRN have specific terminal targets, but there are varying degrees of overlap.Most of the LRN projects in an organized fashion to the anterior lobe of the spinal cerebellum, whereas only relatively restricted areas relay to the paramedian lobule and the pyramis. Lateral reticular axons distribute to specific longitudinal zones in such areas and the available material suggests that both convergence and divergence exist. The LRN also relays to the lobus simplex, and perhaps to crus I, as well as to visual‐auditory areas of the cerebellar vermis. The distribution of the various afferent connections of the LRN is interpreted in light of LRN‐cerebellar connections. Although we have described details that have not been elucidated in other species, where comparisons can be made it appears that the connectivity of the opossum LRN is comparable in most respects to that of plac

ISSN:0092-7317    

DOI:10.1002/cne.901740110

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

年代:1977

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901740101

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

年代:1977

数据来源: WILEY