摘要:

AbstractRe‐innervation of skin and muscle by identified sensory and motor neurons in segmental ganglia of the leech was studied using physiological techniques. After lesions of peripheral nerves, sensory axons which re‐innervated the skin always regained sensitivity to their original stimulus modality (touch, pressure or noxious stimuli). Motor neurons invariably re‐innervated the appropriate type of body wall muscle, such as longitudinal or circular muscle layers. Both sensory and motor axons usually returned to the appropriate region of the body wall (dorsal, lateral, or ventral) when regenerating after a nerve crush or cut. This capacity was lost, however, when growth along old nerve branches was prevented by evulsing long segments of the nerve. Re‐innervation usually occurred by way of growth of new axons all the way the periphery, but in a few cases reconnection with the surviving distal segment of the original axon had taken place. The specificity of reinnervation can be accounted for by a combination of selective growth along appropriate nerve branches and specific interactions with target

ISSN:0092-7317    

DOI:10.1002/cne.901710402

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe projections of the retina inNecturus maculosuswere studied by injecting radioactive proline into one eye. Labeling was seen in both the contralateral and ipsilateral diencephalon and tectum. The contralateral fibers are divided into three major tracts: the marginal, axial, and basal. The ipsilateral fibers separate into a marginal and an axial optic tract.The contralateral and ipsilateral axial optic tracts have a similar distribution. The contralateral and ipsilateral marginal optic tracts projecting to the diencephalon also have a similar distribution. However, in the tectum the ipsilateral marginal optic tract ends in the anterior third while the contralateral extends almost the entire length of the tectum. The retinotectal ipsilateral projection ends in clumps as has been described in other vertebrates. A direct ipsilateral retinotectal projection has not been described in any other amphibian.

ISSN:0092-7317    

DOI:10.1002/cne.901710403

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractUnilateral enucleations were performed on larval, transforming and adult sea lampreys. Following 5 to 11 days survival, the animals were sacrificed and the brains were processed using a modified Fink‐Heimer technique. In larvae, contralateral optic projections were found to the posterior one‐third of the dorsal thalamus, the pretectum, and the optic tectum. No ipsilateral projections were present in the larvae. In enucleated transforming and adult lampreys, degenerating axons were observed in the optic chiasm and bilaterally in the optic tracts. Retinal efferents projected bilaterally to a lateral neuropil region (“tractus opticus”) in the posterior one‐half of the dorsal thalamus. Contralaterally, a conspicuous dorsomedial cell group (lateral geniculate nucleus) also received a projection. Contralateral projections to the superficial layers of the pretectum and optic tectum were observed. Ipsilateral retinal projections to the pretectum and optic tectum in transforming and adult lampreys were restricted to a small zone at the ventrolateral margins of the pretectum and tectum. The changes in distribution of retinofugal projections during transformation appear to be occurring at the same time that the eye differentiates into its a

ISSN:0092-7317    

DOI:10.1002/cne.901710404

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe postnatal differentiation of neurons in the dorsal lateral geniculate nucleus of the albino rat was studied using the Golgi‐Cox technique. At least four animals were used at postnatal ages 12 hours, 2, 4, 6, 8, 10, 11, 12, 13, 14, 15, 16, 18, 20, 24, 28, 35 days and adult.Presumptive thalamo‐cortical projection cells (Class A cells of Grossman et al., '73) and non‐projection, intrinsic neurons (Class B cells), are distinguishable at 12 hours after birth. At this stage both types of neuron are immature, with prominent growth cones at their dendritic extremities. Dendritic growth and differentiation appear to be complete by 18 days.Relay cells display two apparent “growth spurts” characterized by noticeable enlargement of the perikaryon and a marked increase in dendritic length and complexity. One occurs between days 4 and 6 and coincides with a period of enhanced synaptogenesis and gliogenesis: the second occurs between days 14 and 15, around the time of eye opening (day 14) and may be related to a further phase of increased synaptogenesis and gliogenesis (Karlsson, '67; Biesold et al., '76).Class B cells appear to “lag” behind class A cells in their initial postnatal differentiation, but also reach their mature condit

ISSN:0092-7317    

DOI:10.1002/cne.901710405

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe basal dendritic trees of layer V pyramidal cells in the rat auditory cortex were examined quantitatively in a group of 3‐month‐old and a group of 34‐ and 36‐month‐old rats. Two forms of analysis were used on the Golgi preparations: (1) the number of intersections between the basal dendrites and a series of concentric circles whose common center lies over the perikaryon center, and (2) the number of dendritic branches, by order, per neuron. The data indicate that in the old animals the density of the dendritic tree has decreased significantly within a radius of about 150 μ of the perikaryon, yet the extent of the dendritic domain has not changed appreciably. Analysis of the dendritic branching suggests that there has been a deterioration not only in the peripheral branches of the dendritic tree, but also that entire dendrites have been lost. This loss of primary branches was confirmed through the reconstruction of layer V neuronal perikarya and their proximal dendrites from 1‐μ plastic serial sections of auditory cortex. Concomitant with the loss of dendrites which accompanies advancing age is a tendency for the perikaryon to be smaller, but not distorted, in th

ISSN:0092-7317    

DOI:10.1002/cne.901710406

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractReceptoneural junctions and synapses in the organ of Corti of the chinchilla have been examined with the freeze‐fracture technique. The presynaptic membranes at the receptoneural junctions of inner and outer hair cells have many structural features in common with membranes found at chemical synapses outside the organ of Corti. However, the membranes of the postsynaptic afferent terminals are quite different depending on whether they are part of an inner or outer hair cell synapse. These differences in the distribution of intramembrane particles suggest that the transmitters, or transmitter actions, may be different at these two synapses. The distribution of particles in the postsynaptic membrane at efferent synapses with outer hair cell differs from that in the postsynaptic membrane at efferent synapses with afferent terminals or fibers, suggesting that transmitter actions at these locations could also diffe

ISSN:0092-7317    

DOI:10.1002/cne.901710407

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractBarrels of the PMBSF of the mouse somatosensory cortex become apparent in Nissl‐stained tangential sections simultaneously, on the fourth postnatal day. At this time they are miniatures of those in the adult and are situated in the deepest sublamina of the trilaminar cortical plate. An early barrel appears as a patch of decreased cell density: the prospective hollow of the barrel. Septa become noticeable during the sixth postnatal day. From that period to adulthood, the relative contribution of the PMBSF to the total cortical surface area increases — an increase that goes against one's expectation: the barrel related periphery matures very early and so does the central, lateral region of the cortex. Barrel growth parallel to the pial surface is greater along the major axes than along the minor axes. By using the barrels to identify prospective layer IV in immature cortex, we could determine that layers V and VI attain their adult height during the sixth postnatal day — an age when prospective layers I‐IV are only half their adult height. The onset of barrel formation coincides with the moment after which injury to the pertinent somatosensory periphery (the vibrissal papillae) no longer causes profound alterations in barrel mor

ISSN:0092-7317    

DOI:10.1002/cne.901710408

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe entorhinal cortex of rats was removed at various times during development, and the reaction of the cholinergic septohippocampal input to the dentate gyrus was examined by use of acetylcholinesterase histochemistry. When the ipsilateral entorhinal cortex is completely removed, the outer 70‐75% of the molecular layer of the dentate gyrus is almost completely denervated. After such a lesion at 5 to 33 days of age, the acetylcholinesterase staining initially intensified throughout the denervated area, indicating that the septohippocampal fibers branched or elongated. This reaction could be detected within one day after a lesion at 11 days of age and within three or five days after lesions at earlier or later times. Whereas the initial response of the septohippocampal fibers was independent of the age at which the lesion was made, their final localization depended on the developmental state of the animal. After lesions at the age of 5 or 11 days, the reactive septohippocampal fibers became restrictd to the outer one‐sixth to one‐third of the molecular layer within two days after appearance of their initial reaction. A similar concentration of reactive fibers was demonstrable after lesions at 16, 18 or 21 days of age, but some reaction persisted in the middle third of the molecular layer. Finally, after lesions at 26 or 33 days of age the proliferating cholinergic fibers ultimately were uniformly distributed throughout the outer 60% of the molecular layer.These results suggest that septohippocampal fibers initially extend or sprout throughout the denervated area to replace the lost perforant path fibers. However, the reactive fiber population becomes restricted to the outer edge of the molecular layer if the entorhinal lesion is made before the period of cholinergic synaptogenesis and concentrates in this same zone if it is made while cholinergic synapses are forming. We suggest that either the proliferative reaction continues in the outer part of the molecular layer and subsides in other parts of the denervated area or septohippocampal fibers move outward through the molecular layer to assume a more superficial location.After entorhinal lesions at 16 days of age or later the pale‐staining zone (containing fibers that originate in hippocampus regio inferior) immediately deep to the denervated area widened. If the lesion was made earlier, this zone never developed at most septotemporal levels of the dentate gyrus. These results are probably related to the extension of regio inferior fibers into the denervat

ISSN:0092-7317    

DOI:10.1002/cne.901710409

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractIt has been concluded previously that the septohippocampal fibers which project to the rat dentate gyrus extend or branch in the denervated area of the molecular layer following a complete ipsilateral entorhinal lesion. The septohippocampal fibers thus appear to replace some of the perforant fibers which degenerate as a result of the lesion. The reactive fibers eventually become localized to a much smaller and more superficial area after lesions of immature rats than after lesions made in adulthood. To determine whether this difference in the response results from a selective reaction to loss of the lateral perforant path in the immature rat, various portions of the entorhinal cortex were removed at the age of 11 days, and the cholinergic septohippocampal fibers were visualized by acetylcholinesterase histochemistry. An alternative possibility, that the difference between immature and adult rats is attributable to an interaction with other reactive afferents, was tested by removing other sources of input (the contralateral entorhinal cortex, contralateral hippocampal formation or both) along with the ipsilateral entorhinal cortex at the age of 11 days and then demonstrating the septohippocampal fibers histochemically.Lesions of the lateral part of the ipsilateral entorhinal cortex (source of the lateral perforant path) at 11 days of age evoked a septohippocampal reaction along the outer edge of the molecular layer, where the lateral perforant path fibers normally terminate. This result matched that produced by a complete entorhinal lesion. Lesions of the medial entorhinal cortex evoked no obvious reaction. In contrast, the septohippocampal fibers in adult rats proliferated in the denervated area of the molecular layer after lesions of either part of the entorhinal cortex.Combining lesions of other sources of innervation to the dentate gyrus with an ipsilateral entorhinal lesion at 11 days of age did not alter the response of septohippocampal fibers, as determined histochemically. Neither did the septohippocampal fibers react to removal of commissural afferents alone. The response at any age was unaffected by prior or subsequent removal of the contralateral entorhinal cortex.These results indicate that in immature rats the septohippocampal fibers respond only to loss of the lateral perforant path, but these same fibers can later react to loss of any part of the perforant path. They are regarded as support for the hypothesis that the reactive septohippocampal fibers preferentially interact with dendritic growth cones. Our results do not support explanations based on a hypothetical attraction between septohippocampal and crossed perforant path fibers (which react in the same area) or on competition with commissural fibers (which reinnervate an adjacent area). We suggest further that proximity to the degenerating elements does not in itself determine the pattern of reinnervation after lesions of the central nervous system.

ISSN:0092-7317    

DOI:10.1002/cne.901710410

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY

摘要:

AbstractThe ultrastructure of axons in the preganglionic cervical sympathetic trunk of the mouse is described with emphasis on the number, distribution and stability of fibrous elements in the axoplasm. Neurofilaments outnumbered microtubules in myelinated and non‐myelinated axons of all sizes, and the ratio of neurofilaments to microtubules in non‐myelinated axons at each point studied was fairly consistent and independent of axonal diameter. The density of neurofilaments and microtubules, however, was greater in axons of progressively smaller dismeter. In non‐myelinated axons and small myelinated axons neurofilaments were uniformly distributed throughout the axoplams resulting in minimum and maximum interfilament distances of 300 Å and 500 Å respectively; the spacing of fibrous elements within any one axon was dependent upon its diameter and position with respect to the superior cervical ganglion in the preganglionic trunk. The maximum interfilament distance was also found in large myelinated axons where neurofilaments, occurring in fascicles, were separated by distances of approximately 500 Å. Cytochemical staining of axons with lanthanum hydroxide, ruthenium red or alkaline bismuth delineated the delicate filamentous matrix interconnecting microtubules, neurofilaments and other organelles in the axoplasm. Alkaline bismuth stain was most intense in myelinated axons where heaviest deposition of reaction product was associated with neurofilaments. Treatment in vitro of the cervical sympathetic trunk with 5 × 10−5M vinblastine sulfate dissociated microtubules and induced formation of crystalline arrays of “tubular” elements. A uniform center to center spacing of 250–300 Å was found for crystalloids in nonmyelinated axons; however, in myelinated axons the center to center spacing was not uniform and varied in the range 300–600 Å. Neurofilaments and their surface projections were unaffected by vinblastine. Fixation in the presence of lanthanum enhanced delineation of crystalloid elements. Exposure of 0–4°C for up to three hours had no consistent effect on microtubules or neurofilaments. In contrast, cold treatment disrupted the delicate axonal matrix and resulted in the formation of aggregates of coarse flocculent

ISSN:0092-7317    

DOI:10.1002/cne.901710411

出版商:The Wistar Institute of Anatomy and Biology    

年代:1977

数据来源: WILEY