摘要:

AbstractThe postnatal development of myelin in the optic nerve and tract of normal and dark reared cats has been studied quantitatively with light and electron microscopy. In the newborn cat few myelinated fibers (3% of the population) are seen in the optic tract. Until the end of the second postnatal week, the total number of myelinated axons in the tract remains low (23%). At this time, however, there is an explosive increase in the rate of myelination and by the end of the fourth postnatal week 80% of the optic tract axons have acquired a myelin sheath. Thereafter, the number of myelinated axons increases gradually, reaching adult levels (100%) at 12 weeks. During the initial period of myelination, the average axon diameter is 0.6 μ for unmyelinated fibers and 1.2 μ for myelinated fibers. Both of these means remain substantially unchanged until myelination is completed, suggesting that initial myelination of an axon is not a continuous process but rather proceeds in a step‐wise manner. Dark rearing appears to have no effect on the initiation of myelinat

ISSN:0092-7317    

DOI:10.1002/cne.901650202

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe initial phase of synaptogenesis in the molecular layer of the albino rat cerebellum has been studied quantitatively and qualitatively with the electron microscope. Using both aldehyde‐osmium (AL‐OS) and ethanolic phosphotungstic acid (E‐PTA) preparations, synapses were observed as early as embryonic day 19 throughout the entire rostro‐caudal extent of the vermal molecular layer. The undeveloped nature of the elements participating in the formation of these synapses precluded their identification, for at this stage of cerebellar development, the Purkinje cells have not developed characteristic dendrites and both the massive production of cells within the external granule layer and the migration of neuroblasts through the molecular layer are in their initial phases. Evidence of synapse formation at this early stage of molecular layer development indicates that the rudiments of neuronal systems are present before the bulk of the molecular layer has come into existence and before most of the constituent elements of the cerebellum have differentiated. From embryonic day 19 to embryonic day 22, the number of E‐PTA synaptic contacts was always less than the number of AL‐OS synapses. This discrepancy and the variations observed in the morphology of the presynaptic components of E‐PTA stained synaptic contacts, indicate that E‐PTA morphology, and particularly the development of presynaptic dense projections, represents a late stage of sy

ISSN:0092-7317    

DOI:10.1002/cne.901650203

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe efferent pathways of the optic tectum have been investigated in the percomorphEugerresand the berycomorphHolocentrus. A portion of the dorsal‐dorsolateral region of the optic tectum was unilaterally resected by suction. The animals were perfused 6–30 days thereafter, and the brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink‐Heimer ('67) technique for the selective silver impregnation of degenerating axons and terminals.Three groups of fibers emerge from the lesioned region: (a) a medial group, which runs towards the midline and terminates in the ipsilateral torus longitudinalis and the contralateral tectum; (b) an ascending group, which enters the dorsocaudal region of the diencephalon and terminates in pretectal cell groups, in the dorsomedial optic thalamic nucleus, and in the nucleus rotundus or prethalamicus; and (c) a descending group, which funnels down into the midbrain tegmentum. Here abundant terminals are given to dorsolateral cell groups and to the nucleus isthmi. A recurrent fascicle leaves the mainstream and ascends to terminate in scattered diencephalic cell groups, in the nucleus geniculatus posterior pars ventralis, and in the nucleus rotundus or prethalamicus. The bulk of descending fibers then forms an ipsilateral bundle, which gives terminals to the lateral reticular formation of mesencephalon and rhombencephalon, and a contralateral (i.e., the predorsal) bundle, which terminates in the medial reticular formation of mesencephalon and rhombencep

ISSN:0092-7317    

DOI:10.1002/cne.901650204

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe efferent pathways of the telencephalon were investigated in the percomorphEugerresand the berycomorphHolocentrus. One telencephalic hemisphere was resected by suction and the animals were perfused 7–35 days thereafter. The brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink‐Heimer ('67) technique for selective silver impregnation of degenerating axons and terminals.Some fibers emerging from the lesioned telencephalic hemisphere terminate upon the contralateral hemisphere. The large bulk of efferent fibers, however, descends into the ipsilateral diencephalon and gives off the so‐called strio‐tectal bundle (STB) as well as the medial forebrain bundle (MFB). The remaining contingent eventually splits into the so‐called strio‐lobar bundle (SLB) and the lateral forebrain bundle (LFB), but, previous to splitting, it contributes most of the telencephalic projection to the optic tectum inEugerres, and gives abundant terminals to the ipsilateral nucleus rotundus or prethalamicus in bothEugerresandHolocentrus. The STB conveys all telencephalo‐tectal fibers inHolocentrus, and some of them inEugerres. Telencephalic efferents terminate ipsilaterally in the middle level of the tectum's stratum griseum centrale; inHolocentrusthere is also a small projection to the stratum opticum.The MFB terminates at the caudal hypothalamus and gives terminals all along its course. The LFB also gives terminals all along its course and terminates upon a nucleus located between the midline and the corpus glomerulosum. The SLB spreads out and terminates in the inferior lobe of the

ISSN:0092-7317    

DOI:10.1002/cne.901650205

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe cytological and topographical distribution of S‐100 and glial fibrillary acidic (GFA) proteins in the adult rat brain has been compared using the horseradish peroxidase‐labelled antibody technique. Both proteins are present in astrocytes and structures composed of astrocytic processes, namely the glial limitans and the perivascular membranes, but the cytological localization varies between the two proteins. S‐100 is found in the nucleus and cytoplasm whereas GFA protein is confined to the cytoplasm. Neither is found in neurons, but S‐100 is present in some oligodendroglia, suggesting a general regulatory role in glia. Although GFA protein is present in both protoplasmic and fibrous astrocytes, it is more prominent in the latter, confirming its association with astrocytic fi

ISSN:0092-7317    

DOI:10.1002/cne.901650206

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe California ground squirrel is a highly diurnal species previously thought to have an all‐cone retina. This issue was re‐examined in physiological and anatomical experiments. The electroretinogram (ERG) was used to measure the spectral sensitivity of the eye under different conditions of adaptation. The occurrence of a Purkinje shift could be demonstrated, although there was some indication that not all members of this species show such a shift. Spectral sensitivity of the dark‐adapted eye of this squirrel is close to that predicted by a typical mammalian rhodopsin. Light adaptation produces a shift in spectral sensitivity to a peak location of about 525 nm. It was shown that two mechanisms having different spectral sensitivities contribute to the photopically recorded ERG. The degree to which these two mechanisms contribute to the ERG was found to be strikingly different from the degree to which the two contribute to visual behavior.Our anatomical results indicate that the retina of the California ground squirrel has two structurally distinct photoreceptors which, on the basis of various criteria, can be classified as cone and rod‐like. The rod‐like receptors comprise about 6–7% of the total. The two photoreceptor types differ in placement of their inner segments, size of their outer segments, outer segment ultrastructure, and terminal structure and o

ISSN:0092-7317    

DOI:10.1002/cne.901650207

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

年代:1976

数据来源: WILEY

摘要:

AbstractOrganization of opossum somatic sensory cortex has been investigated utilizing closely spaced microelectrode penetrations (0.25–0.5 mm apart) and delicate mechanical stimulation of body surfaces including the facial vibrissae. Results may be summarized as follows: (1) the general organization of somatic sensory cortex, as originally defined by Lende ('63a) has been confirmed; (2) a double representation of the contralateral mystacial vibrissae and rhinarium, implicit in Lende's original data, was revealed in detail, the two representations being orderly, adjacent, mirror‐images of each other; (3) units at a given cortical locus responded to deflection of between one and five mystacial vibrissae, about half responding to movement of a single vibrissa only; (4) about 40% of mystacial vibrissa units showed a directional specificity to the extent that they responded to deflections in only one or two cardinal directions; (5) units located in the medial vibrissa area showed a greater directional specificity than did units located in the lateral vibrissa area; (6) the surface area of rhinarial receptive fields was about ten times the area of first‐order rhinarial unit receptive fields (B. Pubols et al., '73); (7) representation of the contralateral forelimb, especially the ventral surface of the forepaw, is extensive, orderly, and precise; (8) representation of the contralateral hindlimb, foot, and tail is minimal, and is confined to the midline convexity; (9) the presence of a small region of bilateral representation, lateral to the regions of contralateral representation, was confirmed. It is suggested that the region of contralateral postcranial representation plus the medial rhinarium and mystacial vibrissa areas are the homologue of SmII in placental mammals, and the region of bilateral representation is homologous to SmII of placental mammals, but that the lateral vibrissa and rhinarium areas are a specialization of somatic sensory cortex unique to the Virginia op

ISSN:0092-7317    

DOI:10.1002/cne.901650208

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe development of the central optic projections in albino rat fetuses has been studied using light and electron microscopic degeneration techniques and the horseradish peroxidase method for demonstrating axonal projections of neurons. The first optic axons to reach the region of the optic chiasm arrive at day 15. By day 16, a substantial optic chiasm is seen and the optic tract can be traced into the epithalamus, having first passed through the ventral lateral geniculate nucleus and a thin lamina of cells which is thought to correspond to part of the future dorsal lateral geniculate nucleus. A growth rate of 80–100 μm per hour is estimated for the fastest growing axons. By day 16‐1/3 the first axons have entered the anterior border of the superior colliculus and in the next day have grown across the entire rostrocaudal extent with the exception of the medial and lateral edges. The optic axons are recognized at day 17 as bundles lying just below the surface, but in older animals they come to lie deeper, as the whole layer of optic innervation broadens. The first synapses to be formed in the superior colliculus (some of them of optic origin) appear on day 17. Subsequently, there is a gradual increase in the number of contacts, the great majority being formed by optic axons.Compared with previous studies onXenopusand chick, one of the most striking features of the development of the central visual connections in the rat is the relatively long time before the first optic axons reach the brain and the speed with which they innervate the central structures once they have arr

ISSN:0092-7317    

DOI:10.1002/cne.901650209

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

年代:1976

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901650201

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

年代:1976

数据来源: WILEY