摘要:

AbstractThe dentate gyrus of the rat contains about 600,000 granule cells. These small neurons are generated over a prolonged period from the 14th day of gestation until sime time after the second postnatal week. The majority of the cells pass through their last phase of DNA synthesis in the postnatal period, and during the peak period of cell generation, between the fifth and seventh days after birth, up to 50,000 granule cells are formed each day. Contrary to earlier reports, most of the cells pass through their last mitotic division either within thestratum granulosumitself, or within the hilar region of the developing gyrus. The precursor population of cells in the hilar region must therefore constitute a pool of true neuroblasts. The origin of this pool of cells has not been definitely established but it seems probable that its cells are derived from the neuroepithelium lining the lateral ventricle adjacent to the region from which the hippocampal pyramidal cells are generated. Examination of the final location of granule cells labeled at different stages reveals three distinct morphogenetic gradients in the gyrus. The cells in the dorsal blade tend to be formed earlier than those in the ventral blade; cells in the more caudal (or temporal) portions of the gyrus are generated earlier than those in more rostral (or septal) regions; and in all regions the more superficial neurons in thestratum granulosumare formed earlier than the deeper granule cells. The bearing of some of these findings on the development and organization of the connections of the dentate gyrus is discussed.

ISSN:0092-7317    

DOI:10.1002/cne.901590202

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractIn our Golgi collection of adult monkey brains the striatal efferents, i.e., the radial fibers in the globus pallidus and the “comb” bundle fibers in the internal capsule and in the cerebral peduncle, are well impregnated in the horizontally sectioned brain and in a sagittal sectioned brain. Since collaterals emerging from radial fibers are seen only in the horizontal series and not in the sagittal series, the interpretation is that they proceed anteriorly and posteriorly only, following the curvature of the pallidal segments, and do not run superiorly or inferiorly as they emerge.Although radial fibers emitting collaterals in the lateral segment and in the medial segment of the globus pallidus have been observed, it has not been possible to observe the same radial fiber emitting collaterals in both pallidal segments and the prospects of ever doing so are not good. The radial fibers converging in the globus pallidus pursue many radii and there is little coincidence between the plane of section and the planes in which they travel. At most only severed radial fiber segments 100–150 microns in length can be found in the horizontal sections needed to observe the collaterals. Moreover, sagittal sections show that radial fibers are deflected in their course, either dorsoventrally or ventrodorsally, as they pass through the internal medullary lamina to enter the medial segment of the globus pallidus.The radial fibers in the medial segment of the globus pallidus are continuous with the “comb” bundle fibers and appear to be thinner than the radial fibers in the lateral segment of the globus pallidus. It is not proved; nonetheless, the view expressed here is that the radial fibers are thinner in the medial segment of the globus pallidus because they may be the same fibers that gave off collaterals in the lateral segment of the globus pallidus. This is discussed in the light of the electrophysiological disclosure of Yoshida et al. ('71, '72) that caudatopallidal fibers are collaterals off caudatonigral fibers.The afferent plexuses of fine, “bouton en passage” fibers, which completely ensheath the long radiating dendrites in the globus pallidus (Fox et al., '66) are well impregnated in the horizontal series. Obviously, they are formed by a number of ultimate branches converging from the collateral branches of a number of different radial fibers. The divergence, too, in this system must be considerable; however, its true extent can only be surmised from the severed radial fibers and radial fiber collaterals seen in the incompletely impregnated Golgi section. One severed segment of a radial fiber displays three collaterals and one of these collaterals has five branches, one of which can be traced to a point where it gives off an ultimate branch in an afferent, dendrite‐ens

ISSN:0092-7317    

DOI:10.1002/cne.901590203

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractIn electron micrographs of the squirrel monkey (Saimiri sciureus) brain the striatal efferents were observed at two different levels in their course: (1) in cross‐sectioned radial fiber bundles just before they enter the globus pallidus; (2) in cross‐sectioned “comb” bundle fibers just before they enter the substantia nigra. In the radial bundles nearly all of the fibers are myelinated; in the “comb” bundle most are unmyelinated. The polarity of all the “comb” bundle fibers is descending. None of them degenerate following a large lesion in the substantia nigra but they do degenerate following a large lesion in the striatum. Also following this latter lesion the endings with large synaptic vesicles, which make up most of the endings in the globus pallidus and the substantia nigra, degenerate.For computer measurements, electron micrographs of the radial bundle were enlarged photographically to a final magnification of 20,000; those of the “comb” bundle to × 50,000. Measurements of 1309 radial fibers revealed a mean axis‐cylinder diameter of 0.68 microns, and measurements of 749 unmyelinated “comb” bundle fibers gave a mean axis‐cylinder diameter of 0.21 microns. Myelinated fibers were not included in the “comb” bundle measurements because it contains myelinated fibers of pallidal origin in addition to myelinated fibers of striatal origin.The results here indicate that the striatal efferents undergo a decided decrease in axis‐cylinder diameter during their transit through the globus pallidus. It is suggested that the large non‐spine bearing neurons in the striatum are the source of the striatal efferents and that they send their axons into the substantia nigra and enroute spend a great quantity of their axoplasm by extending extensive collaterals in both segments of the globus pallidus. This could account for the decreased caliber of the striatal efferents in the “comb” bundle and other findings in the striat

ISSN:0092-7317    

DOI:10.1002/cne.901590204

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractAn attempt has been made to establish, so far as possible, the specific types of synaptic bulbs on motoneurons which arise from extrinsic (descending and dorsal root) and intrinsic sources (interneurons). This has involved the laborious analysis of thousands of electron micrographs of material from normal motoneuron neuropil, and motoneuron neuropil of animals with lesions of spinal tracts, spinal roots, and motor cortex.Our studies have established that the large synaptic bulbs on dendrites, which are the only type in the spinal cord to possess pre‐synaptic synapses (serial synapses), are derived from monosynaptic dorsal root fibers (R bulbs). The presynaptic component of the serial synapse appeared to degenerate at levels below spinal cord transections (P bulbs). By means of transections of spinal cord we have found that descending fibers in the spinal cord terminate as one of at least two distinct classes of synaptic bulbs, one with spheroid synaptic vesicles (S) and one with flattened vesicles (F). There is evidence from several sources that the first type may often be excitatory in function and the second type inhibitory. Only synaptic bulbs with spheroid vesicles show definite signs of degeneration after lesions of the opposite motor cortex. The large (L) synaptic bulbs on motoneuron somata, associated with subsynaptic cisterns, are clearly not derived from the descending systems, or from posterior root fiber

ISSN:0092-7317    

DOI:10.1002/cne.901590205

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractThe innervation of the nasal septum and around the olfactory bulb has been investigated in rats by means of whole‐mount preparations and histological sections. Silver staining, OsO4staining, PAS staining, cholinesterase reaction and fluorescence for catecholamine‐containing nerves were used. The nervus terminalis forms on the medial side of the olfactory bulb a ganglionated plexus, from which branches are given off which course peripherally with the vomeronasal nerves. From a dorsal part of the terminalis nerve plexus an anterior branch is given off which runs along the anterior ethmoidal nerve to the nasal vestibule where it connects with a group of ganglia. The peripheral branches of the nerve run from here along two epithelial cristae formed histologically like dermal papillae. Ventrally in the respiratory region at the junction of the nasal cavity and the nasopharynx is a 1 × 2 mm area with olfactory epithelium, glands of Bowman and an independent innervation from the olfactory bulb. This is the so‐called septal olfactory organ. Trigeminal nerves form a plexus in the respiratory region and in the vestibule, but do not supply the olfactory region. Catecholamine‐containing and cholinesterase‐positive nerves run along the meningeal arteries on the cribriform plate and accompany their branches to the vascular plexus in the olfactory and respiratory regions. Double innervation is found not only of this vascular plexus but of the venous sinuses in the swell bodies of the vestibule. The glands of the nose are not surrounded by catecholamine‐conta

ISSN:0092-7317    

DOI:10.1002/cne.901590206

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

摘要:

AbstractThe scanning electron microscope (SEM) was used to investigate the morphology of the neuroepithelial regions of the vestibular ampullary structures in 47 White King pigeons. The specific neural surfaces studied were (1) the cristae ampullares of the vertical and lateral membranous ampullae, (2) the hair cells lining the cristae, (3) the ampullary nerve fibers, and (4) the bipolar cells of the vestibular (Scarpa's) ganglion. Additionally, some observations of the gross anatomical structures of the bony labyrinth are given. Arguments are advanced which show that if the surface area of a given semicircular canal can be projected onto one of the three normal head planes, then that canal can be made to respond to motion in the appropriate plane, provided that the projected area is sufficiently large to achieve a threshold pressure as determined by a generalized form of Groen's equation ('57). With regard to the cristae ampullares, it is hypothesized that their surface areas can be described by means of a revolved catenary, i.e., a catenoid of revolution. (The catenary is found in nature as the approximate shape taken by a flexible cable when it is suspended at two points). The surface area of a catenoid provides a minimum surface of revolution. In the context of a crista, this implies that the given number of hair cells could not be fitted onto a smaller surface area. One advantage of this is that nature is able to utilize a thinner cupula than would be possible with other configurations and therefore an increased sensitivity to cupular motion can be realized. A second important factor is that all hair cells must revolve (by way of cupular motion) about the same centre of rotation in response to angular acceleration. Thus, all of the orthogonally‐positioned hair cell tufts on the cristae surface may be stimulated simultaneously by way of a tangential shear. Other arguments show that the classical “swinging door” type of cupular motion is not consistent with SEM and other recent observations. Two alternate modes of cupular motion are presented, each of which requires far less energy expenditure than does the “swinging door” cupula. The suggestion is then made that, during normal head movements, the cupula behaves as a drum much like the tympanic membrane and that only for large, non‐physiological motions does the “swinging door” mode of cupular motion take place. It must be remembered, however, that cupular motions during normal physiological head movements are infinitesimally small (Oman

ISSN:0092-7317    

DOI:10.1002/cne.901590207

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901590201

出版商:The Wistar Institute of Anatomy and Biology    

年代:1975

数据来源: WILEY