摘要:

AbstractThe maturation of the stato‐acoustic nerve in the cat was studied by light and electron microscopy from the fetal stage to the adult. Measurement of the outer diameter of the fibers and the study of the myelination process revealed that myelination begins earlier for the vestibular nerve than for the cochlear nerve: by the fifty‐third day of gestation 64% of the vestibular fibers have already passed the promyelin stage whereas for the cochlear nerve this promyelin stage begins for the majority of fibers on the fifty‐seventh gestation day. Afterward, maturation proceeds more rapidly for the cochlear nerve. In the case of both nerves, maturation is still incomplete at two months of age.Concerning the relationship between the thickness of the myelin sheath and the axoplasmic diameter, there is already a good correlation by the fifty‐seventh day of gestation in the vestibular nerve, whereas it appears several days after birth in the cochlea

ISSN:0092-7317    

DOI:10.1002/cne.901700102

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractRight or left eye primordia of Shumway stage 16–18Rana pipiensembryos were transplanted to the position normally occupied by the ear, where they developed into externally normal eyes.Ganglion cell density in the retina of the transplanted eye was significantly lower than the ganglion cell density in the animal's normal eyes. No significant difference was observed between normal and transplanted inner and outer nuclear layers.In several preparations a large piece of embryonic forebrain was included in the initial eye graft. Optic nerves from the transplanted eyes penetrated this transplanted forebrain and established a dorsocaudal growth trajectory relative to the ectopic tissue's original anterior‐posterior and dorsal‐ventral axes. After traversing the forebrain, the transplanted optic nerve fibers penetrated the medulla where they invariably grew dorsocaudally to take up and maintain a dorsolateral position in the white matter of the spinal cord.The consistent dorsocaudal trajectory established by the translocated optic tract in the ectopic forebrain and in the hindbrain and spinal cord is very similar to the growth trajectory in the normal diencephalon, suggesting that dorsocaudal growth relative to the three major axes of the neural tube is an inherent property of optic nerve fibers. These results also suggest that the polarity cues which guide normal optic tract growth are not unique to the diencephalic regions of the neural

ISSN:0092-7317    

DOI:10.1002/cne.901700103

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractWhen a primordial eye was transplanted to the ear position inRana pipiensembryos, the optic nerve from the ectopic eye penetrated the medulla and invariably established a tract in the dorsolateral white matter of the ipsilateral spinal cord. In response to visual stimulation of the transplanted eye, extracellular recordings with metal microelectrodes were conducted within the spinal cords of post‐metamorphic animals.Visual activity in the spinal cord couldonlybe recorded in those experimental animals in which the transplanted optic nerve succeeded in penetrating the medulla. This activity was frequently encountered in the gray matter of the cord well below the dorsolateral position of the transplanted optic tract. The discharge characteristics and adaptation properties of the visual activity were often similar to that of optic nerve fibers from normal eyes suggesting that axons or their collaterals branch off from the transplanted optic tract and arborize within the spinal cord. However, occassionally stimulation of the transplanted eye evoked activity with adaptation and/or response characteristics unlike that of normal optic nerve fibers.Visual activity in the spinal cords of our experimental animals could be driven by moving small dark objects within circumscribed regions in the visual field of the transplanted eye. However we were unable to find any evidence of a systematic mapping of the transplanted retina within these abnormally penetrated spinal cord

ISSN:0092-7317    

DOI:10.1002/cne.901700104

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe normal cytoarchitectonic pattern of barrels in layer IV of mouse SmI face cortex is altered by early damage to the mystacial vibrissae (Van der Loos and Woolsey, '73). In the present study, the middle row of vibrissae (row‐C) on one side of the face in groups of Swiss mice was cauterized on the day of birth (postnatal day [PND] – 1) or on PND's – 2, 3, 4, 5, 7, 10, 12, 15, 20 and 30; littermates in each group served as controls. All animals were perfused on PND‐60 and the brains sectioned parallel to SmI layer IV. For each specimen, the posteromedialbarrel subfields (PMBSF) of the two hemispheres were reconstructed with a camera lucida and the cross‐sectional areas of individual barrels measured using a small computer.The findings are: (1) The hemispheres ipsilateral to the vibrissal damage are quantitatively indistinguishable from the littermate controls indicating that the ipsilateral hemispheres in lesioned animals can serve as controls for observations of the type reported in this paper. (2) There are no consistent differences in the cross‐sectional areas of the PMBSF's as a whole in the hemispheres ipsi‐ and contralateral to the peripheral damage, suggesting that there is no net loss of cortex as a result of the lesions. (3) The contralateral row‐C barrels are reduced in size. Expressed as a percentage of normal values; row‐C is reduced to 17% for animals lesioned on PND‐1, 16% on PND‐2, 38% on PND‐3, 52% on PND‐4, and 79% on PND‐5; on PND‐7 and later the cross‐sectional areas of row‐C barrels are normal. This implies that the barrel field of the SmI face cortex becomes progressively refractory to the effects of peripheral damage during the first postnatal week and in the period prior to PND‐6, an intact periphery isnecessaryfor normal cortical development. (4) In every case, thedecreasedcross‐sectional area of row‐C is accompanied by preciselyincreasedcross‐sectional areas of the barrels in adjacent rows‐B and D. In the case of the restricted peripheral damage which we produced, there is a “compensation” in the contralateral hemisphere, which can be correlated with patte

ISSN:0092-7317    

DOI:10.1002/cne.901700105

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractEfferent projections of the anterior vermis were studied in a prosimian primate (Galago senegalensis). Cerebellar corticonuclear and corticovestibular fibers of the anterior lobe vermis are, in toto, ipsilateral. Two additional main points emerge. First, evidence is given which suggests that the cortical area defined as vermis converges, in a rostral direction (from lobules V to I + II), as the hemispheres of these lobules become latero‐medially foreshortened. The anterior vermis is a cortical region reflected by its efferent projections and not an arbitrary median strip of cortex which is either constant in width or morphologically separated from adjacent paravermal areas. Secondly, two patterns of organization emerge concerning cortical efferents, one suggestive of longitudinal zones and a second which shows that individual lobules project mainly to specific areas of the ipsilateral NM and into portions of the vestibular complex. Three zones are recognized. A very narrow midline area which appears to project bilaterally to the NM, a wider intermediate area (homologous to zone A) related to the ipsilateral NM, and a lateral area (homologous to zone B) related mainly to the ipsilateral vestibular complex, primarily its lateral nucleus. Within this overall zonal organization individual lobules project to specific areas of the NM and vestibular complex. Lobules V and IV project to rostrodorsal and rostrocentral NM respectively and into the dorsal LVN. Lobules III and II + I project to rostroventral‐medial and rostroventral‐lateral NM respectively, throughout the LVN and minimally into the SVN and SpVN. The specificity of corticonuclear terminations in the NM from the anterior vermis, heretofore not described for any primate, are similar, in terms of a general pattern, to that recently reported for the cat (Courville and Diakiw,

ISSN:0092-7317    

DOI:10.1002/cne.901700106

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractStudies were made of the fiber composition and of single unit discharge characteristics in the dorsal and intermediate acoustic striae. Counts of fibers and cells revealed more than twice as many fibers as cochlear nucleus cells of the types known to contribute axons to these tracts. Recordings were made in the striae to confirm the classes of discharge patterns which are transmitted from the posterior cochlear nucleus to more central structures and to seek evidence for descending activity entering the cochlear nucleus through the striae. Discharge patterns of the majority of units resembled those seen in previous studies when recordings were made from regions of the cochlear nucleus which are known to contribute fibers to the striae. Some patterns, however, were unlike any which have been reported in the cochlear nucleus on the same side as the recording site, but resembled activity of other auditory structures, suggesting that these were descending inputs. To confirm the presence of descending activity, recordings were made in the dorsal acoustic stria at a point medial to where the stria had been completely severed. Recordings made under these conditions demonstrated the presence of descending activity. The physiological findings help explain the disparity between the counts of fibers and cells, and point out a need for more detailed descriptions of the origins of descending inputs through the striae.

ISSN:0092-7317    

DOI:10.1002/cne.901700107

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractOrigins and terminations of fibers of the dorsal and intermediate acoustic striae were studied by surgically severing these tracts and injecting HRP into the incision. This procedure results in filling the severed axons with HRP. Filled axons were traced to cell groups of origin and to some terminations of the acoustic striae. HRP‐labeled terminals were found in the cochlear nuclei as well as in periolivary cell groups. Filling of cells with HRP ranged from being complete, resulting in Golgi‐like images, to being barely detectable. Labeled cells were abundant in the dorsal and posteroventral cochlear nucleus adjacent to the injection as well as scatered throughout the periolivary cell groups of both sides, being highest in concentration around the ipsilateral lateral superior olive. On the side contralateral to the injection, labeled cells were found along the medial border of the dorsal cochlear nucleus, in the interstitial nucleus of the stria of Held, and sparsely throughout the ventral cochlear nucleus. The distribution of labeled cells was similar following HRP injections of the dorsal cochlear nucleus, except that these injections revealed additional descending projections from the inferior colliculi and from the ventral nucleus of the trapezoid body of both sides. These additional projections were interpreted as entering the CN by a ventral route. Findings of this study are in accord with physiological recordings made from fibers of the acoustic str

ISSN:0092-7317    

DOI:10.1002/cne.901700108

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

摘要:

AbstractThe paper sets out to determine whether the spinal motoneurons that die during the normal development ofXenopustadpoles have been peripherally connected before death. The numbers of cells in the control ventral horns were compared with the numbers remaining after early (stage 50 or 52/53) amputation of the limb bud. Up to stage 52, there was no difference between the two sides, but thereafter the numbers on the amputated side fell away until at stage 57 none were left. Thus, as neurons mature, they become dependent for survival on contacting the limb. During this time, there was no difference between amputees and controls in the numbers of mitoses in that part of the ventricular layer that gives rise to ventral horn cells, indicating no change in proliferation. Thus, the numbers of ventral horn cells remaining after early amputation is a measure of the numbers of cells in the normal animal that are still independent of the limb (Phase I cells) and hence by subtraction, the other cells (post‐Phase I cells) are those that only survive by virtue of having contacted the limb. A graph of numbers of post‐Phase I cells shows a peak at stage 54 and thereafter declines as metamorphosis approaches. This is interpreted to indicate that a number of cells that survive at stage 54 by reason of peripheral contacts or connections in the limb subsequently themselves die, that is, that at least some of the cells that die during normal development have previously made contacts within the l

ISSN:0092-7317    

DOI:10.1002/cne.901700109

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901700101

出版商:The Wistar Institute of Anatomy and Biology    

年代:1976

数据来源: WILEY