摘要:

AbstractStudies of the rat basilar pontine gray in Nissl‐stained frozen sections revealed the presence of four major subdivisions referred to as medial, ventral, lateral, and peduncular nuclei with respect to their position relative to the cerebral peduncle. Neurons located adjacent to the surface of, or within the cerebral peduncle were considered collectively as the peduncular nucleus. It should be emphasized that the above subdivisions are useful only for descriptive purposes and do not necessarily reflect distinct cytological similarities or differences within the identified cell groups. The dorsal peduncular (pontine) region was continuous around the lateral and medial boundaries of the peduncle with more ventral pontine areas. A distinct cluster of neurons was consistently observed near the ventromedial surface of the basilar pons, seemingly walled‐off by fascicles of pontocerebellar axons. In addition, in most animals, a cleft appeared in the peduncle and allowed direct communication between dorsal and ventral peduncular regions, while the medial lemniscus formed a partial boundary separating dorsal pontine neurons from the nucleus reticularis tegmenti pontis.Golgi studies indicated that four general varieties of pontine neurons could be distinguished, and in order of relative frequency were described as spine‐laden, pauci‐spined, pauci‐spined with long, thin dendrites, and small bipolar or unipolar cells whose axon sometimes collateralized within the pons. A wide variety of spinous processes and finger‐like dendritic protrusions, some of which formed a terminal tuft‐like arrangement, characterized pontine neuron dendrites. In addition, some dendrites of small neurons gave rise to rather long, thin, beaded processes which in certain instances emanated from an unusual triangulated branch point enlargement. Dendritic orientation (neuron shape) was sometimes determined by location, with cells in the peduncular nucleus oriented parallel to the nearest peduncular surface, while cells near the ventral pontine surface were arranged parallel to transversely directed pontocerebellar axons. Cells of medial pontine regions did not project dendrites across the midline, while neurons near the peduncular cleft sent dendrites into that space. Based on the locations of various pontine afferent termination zones as determined in previous as well as ongoing studies, it appears that some pontine neurons exhibit dendritic systems reaching into more than one afferent projection area, thereby affording them an opportunity to receive inputs from several aff

ISSN:0092-7317    

DOI:10.1002/cne.901950202

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe basilar pontine gray in adult rats was subjected to electron microscopic examination in order to characterize: (1) certain general cytologic features, (2) the principle categories of presynaptic profiles, and (3) the postysnaptic targets of the various categories of presynaptic boutons. General cytologic features included the presence of neuronal somata exhibiting either a smooth contoured nucleus and central nucleous or an irregularly contoured nucleus with numerous invaginations and an eccentric nucleolus. In addition, dendritic protrusions with variable morphology were apparent as well as a class of dendrites and somata with a curious dense, granular matrix. Four general types of presynaptic profiles were distinguished and were classified as: round vesicle boutons, elongate vesicle, pleomorphic vesicle, and dense core vesicle boutons. The category ofround vesicle boutonsformed asymmetric synaptic contacts and included three subtypes. One group contained vesicles with diameters of 25–35 nm, a second group contained larger (40–60 nm) round vesicles, and a third group of much larger boutons (2.5–6.8 μm) exhibited the smaller round vesicles. Another general category of presynaptic profile contained distinctlyelongated synaptic vesicles, formed symmetrical active sites, and ranged in size from 0.4–1.7 μm. A third category of synaptic end‐strucutures was distinguished by the presence ofpleomorphic synaptic vesiclesand microtubules and exhibited a distinctive pale or lucent matrix, while the fourth type was characterized by a mixed population of clear anddense core vesicles. Analysis of the distribution of such bouton types over the surface of pontine neurons revealed that: somata and proximal dendrites were contacted by round, elongate, and dense core vesicle boutons; intermediate and distal dendrites received synapses from all categories of boutons including the large endings with smaller round vesicles, while dendritic spines were contacted by round vesicle boutons (large and small), the large boutons, and elongate vesicle boutons. Synapses were also observed to occur between two vesicle‐containing profiles. In such situations, pleomorphic vesicle boutons were found to be postsynaptic to either elongate vesicle boutons or small boutons with round vesicles and at the same time were presynaptic to a dend

ISSN:0092-7317    

DOI:10.1002/cne.901950203

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

年代:1981

数据来源: WILEY

摘要:

AbstractEvidence from horseradish peroxidase (HRP) and electron microscopic (EM) studies was interpreted to suggest that both the corticopontine and cerebellopontine systems each arise from two separate populations of neurons within their respective sites of origin. Following injection of HRP into the pontine nuclei using a ventral approach, labeled neurons insensorimotor cortexincluded the large pyramidal cells deep in layer Vb and small‐to‐intermediate‐sized neurons located more superficially in Vb. Previous studies (Wise and Jones, '77) have shown that these same large pyramidal neurons give rise to fibers of the corticospinal system while smaller more superficial cells project either to various brainstem locations or also to the spinal cord. In these same cases, HRP‐positive neurons were also observed invisual corticalareas where they were again restricted to layer Vb, which has been shown to be the source of cells projecting to the superior colliculus and pulvinar (Gilbert and Kelley, '75; Lund et al., 75). These findings suggest that the corticopontine projection consists of collateral terminations of the corticospinal system as well as branches of a corticofugal system which arises from neurons in sensorimotor and visual cortices and projects primarily to certain brainstem locations. In support of this notion, EM studies revealed that following sensorimotor or visual cortex lesions both filamentous and dark degenerating boutons were evident in the pons. The small dark boutons terminated distally on pontine neurons and predominated after sensorimotor lesions while the larger filamentous endings contacted more proximal parts of pontine neurons and predominated after visual cortex lesions.Similar results were obtained in studies of the cerebellopontine system. Basilar pontine HRP injections resulted in the labeling of cells in each of the cerebellar nuclei, the majority of which were classified as medium‐to‐large multipolar neurons while a lesser number appeared to be smaller fusiform or spindle‐shaped cells. After interruption of cerebellopontine axons in the brachium conjuctivum, many large filamentous degenerating boutons were observed in contact with a characteristic cluster of dendritic spines as well as somata and dendritic shafts. In addition, a lesser number of small boutons undergoing the typical dark type of degeneration were found in apposition to singular, small dendritic shafts. Thus, the combination of HRP and EM observations has been interpreted to suggest that the cerebellopontine system, like the corticopontine system, consists of two neuronal elements: (1) larger multipolar neurons giving rise to the large boutons which form the central element in a characteristic synaptic complex and undergo filamentous degeneration, and (2) smaller neurons whose axons terminate as the small boutons which contact only small dendritic profiles and do not participate in the synap

ISSN:0092-7317    

DOI:10.1002/cne.901950204

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

年代:1981

数据来源: WILEY

摘要:

AbstractTwo techniques have been used to examine the organization of spinothalamic tract axons within the spinal cord of the rat. In the initial experiments, the thalamus was filled on one side with horseradish peroxidase (HRP) using a series of small injections. The injections were preceded by lesions of various areas of the ventral quadrant. These studies indicated that the cells of origin of STT axons ascending within the ventral funiculus (VF) are located primarily in the ventral‐most areas of the dorsal horn and the intermediate gray zone. The cells of origin of STT axons projecting within the ventrolateral funiculus (VLF) are located not only deep within the gray matter but in addition within the dorsal‐most two thirds of the dorsal horn, the area of the spinal cord gray matter shown in previous studies to contain the vast majority of cells with cutaneous tactile and nociceptive input. To examine these projections directly, rats received either a series of HRP injections that filled the thalamus on one side or a small injection into either medial or lateral thalamus. Examination of the labeled axons in horizontal sections through the cervical cord indicated that STT axons ascending to lateral thalamus do so in the VLF. In contrast, axons terminating in medial thalamus ascend in the VF. Additional experiments have shown that axons ascending to the lateral thalamus are distributed throughout the VLF at lumbar levels. Within the thoracic cord, lateral projecting STT axons are distributed throughout much of the VLF but are not found in close proximity to the ventral horn. At cervical levels all lateral‐projecting STT axons have assumed a position on the lateral rim of the VLF. These and previously published data have demonstrated that the rat spinothalamic tract is composed of two components that differ in the distribution of their cells of origin, the area of the cord in which they ascend, and the thalamic nuclei in which they term

ISSN:0092-7317    

DOI:10.1002/cne.901950205

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

年代:1981

数据来源: WILEY

摘要:

AbstractSynapses involving thalamocortical afferents and hitherto unexamined neuron types of the posteromedial barrel subfield (PMBSF) of the mouse have been identified using a combined degeneration and Golgi/EM technique (Peters et al., '77). Degeneration of thalamocortical axon terminals was produced with electrolytic lesions of the nucleus ventralis posterior, pars lateralis thalami, and the nucleus posterior thalami. Four days after receiving lesions, the animals were perfused, and blocks of cortex containing the PMBSF were processed by the Golgi method. The blocks were tissue‐chopped at 125 μm and examined with the light microscope. Sections containing neurons of interest were gold‐toned and deimpregnated in preparation for electron microscopy (Fairén et al., '77). Portions of selected neurons contained in layers III‐V were serially thin‐sectioned and examined with an electron microscope to determine if they were involved in synapses with degenerating thalamocortical axon terminals. Results showed thalamocortical synapses on the apical dendrites of five different sized pyramidal cells whose somata occurred in layers V and VI, and on dendrites of one spiny bitufted neuron and one non‐spiny multipolar neuron with somata in layer V. A non‐spiny bitufted neuron of layer IV which was not impregnated also received thalamocortical synapses.Although every neuron examined formed at least one thalamocortical synapse, some formed very few, whereas others formed many. Of the pyramidal cells, small layer V and VI pyramidal cells and a large deep layer V pyramidal cell were involved in small numbers of thalamocortical synapses, while a medium superficial layer V pyramidal cell and a large layer VI pyramidal cell each formed many. The spiny bitufted neuron formed a small number of thalamocortical synapses, while the non‐spiny bitufted neuron formed very many. The non‐spiny multipolar neuron was involved in a moderate number of thalamocortical synapses. The findings suggest that, whereas any type of neuron with a dendrite in layer IV likely receives some synaptic input from the thalamus, individual neurons were involved in very different quantities of thalamo

ISSN:0092-7317    

DOI:10.1002/cne.901950206

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

年代:1981

数据来源: WILEY

摘要:

AbstractA Golgi impregnated, non‐spiny multipolar cell whose soma occurred in layer V of the region of mouse SmI cortex containing the posteromedial barrel subfield (PMBSF) (Woolsey and Van der Loos, '70) was gold‐toned and deimpregnated (Fairen et al., '77). Two of its dendrites, contained within a single PMBSF barrel, were serial thin‐sectioned and then reconstructed in three dimensions. Dendrites of an unimpregnated, non‐spiny layer IV bitufted cell, present within the same barrel, were also reconstructed in three dimensions from the series of thin sections. This approach permitted a comparison of the distribution of synapses along dendrites of the two non‐spiny neurons. Results showed dendrites of the layer IV bitufted cell formed about twice as many synapses per unit lenght as those of the multipolar cell. Particularly striking was the contrast between the large number of synapses made by degenerating thalamocortical axon terminals with the dendrites of the bitufted cell and the rarity with which such synapses occur on dendrites of the multipolar cell. Furthermore, the proportion of the total number of synapses made by thalamocortical axon terminals onto dendrites of the bitufted cell was six times greater than the proportion of the thalamocortical synapses onto the multipolar cell

ISSN:0092-7317    

DOI:10.1002/cne.901950207

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe central projection and retinal distribution of displaced ganglion cells (DGC's) are described for the pigeon. Discrete, localized injections of horseradish peroxidase (HRP) into the nucleus of the basal optic root (nBOR) complex labeled as many as 4,800 DGC's in the contralateral retina. The greatest densities of DGC's were observed in the more peripheral regions of the middle and inferior temporal regions of the retina, with lowest densities occurring in the inferior nasal, red field, and foveal areas. Large HRP injections of the tectal lobes, which did not include the pretectal, accessory optic (nBOR), hypothalamic, or thalamic visual nuclei, labeled only ganglion cells within the ganglion cell layer. An HRP injection centered within the nucleus lentiformis mesencephali, also including portions of the optic tectum and optic tract, labeled only ganglion cells within the ganglion cell layer of the contralateral retina. DGC's thus appear to be the primary, if not exclusive, source of retinal afferents to the nBOR complex in pigeon. The observed retinal distribution of DGC's indicates that the areas of retina with the greatest density of cells in the receptor layer, inner nuclear layer, and ganglion cell layer are relatively devoid of DGC's. Since the nBOR complex projects directly upon the vestibulocerebellum and oculomotor nuclei, DGC's would thus appear to be involved in neural circuits that mediate oculomotor reflexes and visuomotor behavior.

ISSN:0092-7317    

DOI:10.1002/cne.901950208

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe fine structure and norepinephrine content of small granular vesicle‐containing profiles were studied in normal and norepinephrine‐depleted cerebral cortex of the turtle,Pseudemys. The cortex was fixed for electron microscopy with the KMnO4procedure of Koda and Bloom ('77), while the norepinephrine content was assayed with the radioenzymatic method of Coyle and Henry ('73). Green fluorescent fibers have been described by Parent and Poitras ('74) as located almost exclusively in the outer half of the molecular layer in turtle cortex. Small granular vesicle‐containing profiles are found down to 100 μm below the pial surface, but over 50% lie within 20 μm of the surface. Within the outer 100 μm of cortex, the frequency of labeled varicosities is 1.39/1,000 μm2. The average area of the norepinephrine‐containing varicosities is 0.61 μm2, and there is a mean of 18.4 vesicles per single section. The average number of large plus small vesicles in an entire varicosity was estimated to be 72. Synaptic membranes are not well‐preserved with KMnO4fixation, but good examples were found of small granular vesicle‐containing profiles forming both symmetrical and asymmetrical membrane differentations. Only a small percentage of the small granular vesicle profiles were associated with a synaptic membrane differentiation in single sections. When norepinephrine‐fiber synapses are seen, they usually share a postsynaptic element with another unlabeled vesicle‐containing profile. Normal turtle cortex contains an average norepinephrine concentration of 1.95 μg/gr, which is about eight times higher than in rat cortex. The ratio of norepinephrine to dopamine is about 18 to one, suggesting that dopamine is present predominantly in a precursor pool for norepinephrine. Small granular vesicle‐containing profiles were eliminated after tratment with reserpine and 6‐hydroxydopamine in concentrations that were shown to reducenorepinephrine concentration by 94% and 86%, respectively. The labeled varicosities were partially depleted by midbrain hemisection and by an inhibitor of dopamine‐beta‐hydroxylase (FLA‐63). The norepinephrine‐containing varicosities are remarkably coextensive with the distribution of thalamic fibers, both in the total extent of cortex where they are found and in the depth of cortex where they terminate. The results support the idea that there is a close structural and functional association between locus coeruleus and thalamic fibers in cerebral cortex, and the apparent difference in frequency of synapses suggests that each fiber system exerts its influence on

ISSN:0092-7317    

DOI:10.1002/cne.901950209

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe peroxidase‐anti‐peroxidase method was used on paraffin‐embedded material to demonstrate the distribution of glial fibrillary acidic (GFA) protein, an astrocyte‐specific protein, in the developing retina of the albino rat. At birth activity was scant and was confined to scattered, poorly differentiated cells in the inner retinal layers near the optic disc. At 3 days primitive astrocytes which displayed GFA protein activity were confined to the stratum opticum near the optic disc. With increasing age these cells were found at greater distances from the optic disc and began to assume the appearance of typical fibrous astrocytes. By 30 days the perikarya of these cells were confined almost exclusively to the region between the nerve fiber layer and the inner limiting membrane. The processes of these cells terminated either in suckerlike end‐feet upon blood vessels or, to a lesser extent, ended in relation to axon fascicles of the nerve fiber layer.A second population of GFA protein‐active cells existed as perivascular glia which were found upon vessels in the inner portion of the stratum opticum in young animals. In the mature retina perivascular glia were found on vessels throughout the stratum opticum and in the inner portion of the inner plexiform layer.Unequivocal staining of Müller cells or their processes was not obtained.The best staining was obtained with fixatives containing minimal concentrations of aldehydes, especially in tissue from younger animals. The fixative which gave the best preservation of cellular structure along with preservation of GFA protein antigenicity was Perfix (Fischer Scienti

ISSN:0092-7317    

DOI:10.1002/cne.901950210

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

年代:1981

数据来源: WILEY

摘要:

AbstractNewly formed neurons in the adult mammalian neocortex have been reported by several investigators using light microscopic radioautography, but these reports have not been confirmed by electron microscopy—probably because their rarity precludes any reasonable chance of observing these cells with electron microscopic radioautography. To overcome this problem I have used a recently developed method that allows serial thin sectioning and subsequent electron microscopic examination of plastic‐embedded sections previously prepared for light microscopic radioautography. Ninety‐day‐old rats were injected with 4.3 μCi per gm body weight of [H3] thymidine and allowed to survive for 30 days. In the light radioautographs, labeled cells were found in layer IV of the visual cortex, and analysis of electron micrographs of selected examples of these labeled cells clearly demonstrated their neuronal nature with synapses along their cell bodies and dendrites. In order to quantify the relative frequency of labeled neurons, the number of labeled cells seen in the light microscopic sections was expressed as a percentage of the total number of neurons found in sections through the entire thickness of the visual cortex; the percentage was 0.011%, or about 1 in 10,000. The results of this study are in agreement with evidence of neurogenesis of granular neurons in the adult rat olfactory bulb and dentate gyrus (Kaplan and Hinds, '77). Thus, it has now been confirmed that relatively small labeled neurons and their synapses are found in at least 3 brain regions (olfactory bulb, dentate gyrus, and visual cortex) in a normal adul

ISSN:0092-7317    

DOI:10.1002/cne.901950211

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

年代:1981

数据来源: WILEY