摘要:

AbstractA cobaltic lysine complex was injected separately into the right and left fasciculi retroflexes of the frog. This tracing technique labeled, in a Golgi‐like manner, the neurons which initiate the fasciculi retroflexes and revealed details of their morphological pattern.The fasciculi retroflexes originate from various neurons distributed in the diencephalon and mesencephalon, but their main source is the habenular nuclei. In the frog there are dorsal and ventral habenulae which are homologous to the medial and lateral habenulae, respectively, of mammals. In the frog the dorsal habenulae are strikingly asymmetric.Our study shows that the fasciculus retroflexus is composed of several compact separated bundles of fibers and that the fibers originating from the dorsal habenular nuclei project to the interpeduncular nucleus, while those originating from the ventral habenular nuclei project beyond the interpeduncular nucleus, but so far we have not been able to show the exact site of their termination.The labeling of cells within the interpeduncular nucleus raises the possibility that the habenulo‐interpeduncular tract is reciprocal in function.The finds support our previously reported hypothesis on the theoretical interpretation of the functional circuitry of the frog habenulo‐interpeduncular s

ISSN:0092-7317    

DOI:10.1002/cne.902330102

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe cellular architecture of theDaphniacompound eye visual system was studied by using computer‐aided techniques. All the neurons in one half of the bilaterally symmetric optic ganglion (OG) were reconstructed in three dimensions from serial electron micrographs. The techniques employed were those developed by Levinthal and collaborators (Macagno, Levinthal, and Sobel, Ann. Rev. Biophys. Bioeng.8:323–351, 1979). The approximately 200 neurons reconstructed were classified according to where they branch in the OG (the lamina and/or the medulla) and whether they send processes to the supraesophageal ganglion and/or across the midplane. Within each class, neurons were further characterized according to cell body location and size and location of their branching fields. Centrifugal processes from neurons with cell bodies not in the OG were also identified. These results provide the bases for a detailed examination of the synaptic connectivity of the identified neurons and for hypotheses concerning their functional roles in visually evoked behavi

ISSN:0092-7317    

DOI:10.1002/cne.902330103

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe interhemispheric pathways originating in the hippocampal formation, presubiculum, and entorhinal and posterior parahippocampal cortices and coursing through the fornix system were investigated by autoradiographic tracing in 29 rhesus monkeys (Macaca mulatta). The results revealed that crossing fibers are segregated into three contiguous systems. Aventral hippocampal commissurelies at the transition between the body and anterior columns of the fornix in the vicinity of the subfornical organ and the interventricular foramina of Monro; it is formed by axons arising in the most anterior (uncal and genual) subdivisions of the hippocampal formation. Adorsal hippocampal commissurelies inferior to the posterior end of the body of the corpus callosum; it is formed by axons arising in the presubiculum and entorhinal cortex of the anterior parahippocampal gyrus and the proisocortical and neocortical subdivisions of the posterior parahippocampal gyrus but not in the hippocampal formation. Ahippocampal decussationlies between the ventral hippocampal commissure and dorsal hippocampal commissure; it is formed by axons arising in the body of the hippocampal formation. In contrast to the fibers of the ventral hippocampal commissure and dorsal hippocampal commissure, which terminate in contralateral cortical areas, thesedecussatingfibers terminate in the contralateral septum. Thus, the ventral hippocampal commissure and dorsal hippocampal commissure of the rhesus monkey appear to be homologous to similarly designated structures in other mammals. To the extent that these observations also apply to the interhemispheric fibers of the human hippocampal formation and parahippocampal areas, their possible preservation must be considered when interpreting the effect of callosal transection on seizures and the results of “split‐brain” studies, since callosal transection may fail to sever the hippocampal commissures in their ent

ISSN:0092-7317    

DOI:10.1002/cne.902330104

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

年代:1985

数据来源: WILEY

摘要:

AbstractTectoreticular projections in turtles were examined by reconstructing from serial sections axons that were anterogradely filled with horseradish peroxidase after tectal injections. Three tectoreticular pathways each contain extensively collateralized axons. The crosseddorsal pathway(TBd) contains large and small caliber axons. After leaving the tectum, TBd axons emit collaterals into the ipsilateral profundus mesencephali rostralis and then give off a main rostral branch that bears secondary collaterals in the ipsilateral interstitial nucleus, of the medial longitudinal fasciculus and the suprapeduncular nucleus. The main trunks cross the midline and descend in the predorsal bundle, generating collaterals at regular intervals. These terminate mostly in the medial half of the reticular core from the midbrain to the caudal medulla. Axons in the uncrossedintermediate pathwayalso emit collaterals into a midbrain reticular nucleus (profundus mesencephali caudalis) and often have a thick rostral branch. The main caudal trunks, however, remain ipsilateral and travel in a diffuse, laterally placed tract, where each emits a long series of collaterals into the lateral half of the reticular core. The uncrossedventral pathway(TBv) contains medium and small caliber axons. TBv axons often have collateralswithinthe tectum and apparently lack main rostral branches. Their caudal trunks run in the tegmental neuropile below the TBi where they collateralize less exuberantly than do TBd and TBi axons.The morphology of axons in all three pathways suggests that projections from disjunct tectal loci converge at many rostrocaudal levels within the reticular formation. This point was examined explicitly in experiments in which two disjunct injections were placed in one tectal lobe. Intermediate pathway axons traced from the two loci initially formed two distinct bundles but then intermingled in the reticular formation.

ISSN:0092-7317    

DOI:10.1002/cne.902330105

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe morphology of tectoreticular neurons in turtles was examined with serial section reconstructions of neurons retrogradely filled with HRP. Six classes of tectal neurons project into the three tectobulbar pathways characterized in the preceding paper (Sereno, '85). (1) Large multipolar neurons with somata in the central gray layers, and with moderately branched dendrites sometimes spanning over a millimeter, project into the dorsal tectobulbar pathway, TBd. Their dendrites are covered with fine spicules and tend to arborize in the lower third of the superficial gray layers. (2) Medium‐sized neurons with multiple radial dendrites and somata in the central white and upper periventricular layers probably project into the ipsilateral intermediate tectobulbar pathway, TBi. Their dendrites also bear fine spicules and usually reach the tectal surface. (3) Small radial cells in the periventricular layers, and (4) small bitufted radial cells in the superficial gray project into the small caliber component of the ipsilateral ventral tectobulbar pathway, TBv(sm). (5) Medium‐sized central gray neurons with stratified dendrites, and (6) medium‐sized central gray neurons with horizontal dendrites probably project into the medium caliber component of the ventral tectobulbar pathway, TBv(med). In contrast to TBd and TBi neurons, these last four classes emit a spray of long, filamentous dendritic appendages in the central gray and have dendritic arbors near the top of the superficial gray.The morphology of the neurons described in this and the preceding paper is briefly discussed in light of current ideas about tectally mediated sensorimotor transforma

ISSN:0092-7317    

DOI:10.1002/cne.902330106

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

年代:1985

数据来源: WILEY

摘要:

AbstractGolgi‐impregnated ganglion cells were studied in two flat‐mounted human retinas. A number of different morphologic forms were observed, and those showing a thickly branching dendritic field with terminals that stratified within a narrow zone of the inner plexiform layer were selected for further investigation. When the dendritic field diameter of these cells was plotted against distance from the fovea, the scatter diagram showed two distinct clusters. At any given eccentricity, there was no overlap between the cell group with large dendritic fields and the group with small dendritic fields. Those with the larger dendritic fields also tended to have larger somas and thicker axons than the group with the smaller dendritic fields.The dendritic fields of both groups tended to be elongated, and the orientation and degree of this elongation were quantified by determining the best‐fitting ellipse for each dendritic field. The degree of elongation was independent of eccentricity. The orientation of the dendritic field (major axis of the ellipse) of a cell did not appear to be independent of its position on the retina. To test whether the major axes tended to be directed toward any particular point on the retina, the positions of the cells on the retinal flat mount were transformed to relative positions on the retinal hemisphere, and the orientations of the dendritic fields were expressed in a spherical coordinate system for this hemisphere. A search was made for the position on the hemisphere which minimized the mean square deviation of the orientations from this point. The group with the large dendritic fields showed a significant tendency to be radially oriented toward a specific location on the retinal hemisphere, and that location lay within a few degrees of the fovea. Leventhal and Schall ('83) have reported a similar finding for ganglion cells of the cat retina. For the group with small dendritic fields, the retinal location that minimized the mean square deviation was also near the fovea; however, the set of orientations showed no greater tendency for mutual alignment than did a randomized set.The cell group with the large dendritic fields appears to correspond to Dogiel's (1891) type II cells, to Polyak's ('41) parasol cells, to theAcells of the monkey retina described by Leventhal et al. ('81), observed following HRP injection to the magnocellular layer of the LGN, and to the Pα cells of the monkey retina, observed by Perry and Cowey ('81), following HRP uptake by cut axons of the optic nerve.The cell group with the smaller dendritic fields appears to correspond to Dogiel's type III cells, to Polyak's midget ganglion cells, and in the monkey retina to theBcells of Leventhal et al., observed following HRP injection to the parvocellular laminae of the monkey LGN, and to the Pβ cells of Perry an

ISSN:0092-7317    

DOI:10.1002/cne.902330107

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe G, B1, and B2 neurons are three prominent interneurons located in adjacent segmental ganglia in the central nervous system of locusts. Previous studies on the adult nervous system have shown that each of these cells has its own distinctive morphology and responsiveness to auditory input. Previous studies on the embryonic nervous system have described the lineage and development of one of these cells, the G neuron, in the mesothoracic (T2) segment. In this paper it is shown that the G, B1, and B2 neurons are segmental homologues in that they arise from equivalent lineages during embryogenesis in the T2, T3, and A1 segments, respectively. Each cell arises (along with its identified sibling neuron) from the division of the second ganglion mother cell of neuroblast 7–4. The segment‐specific morphology of the G homologues was determined in the T3 and A1 segments between 60–70% of embryonic development, and their identity was established as the adult B1 and B2 neurons by comparing the distinctive cell‐specific features of their morphology between embryo and adult. Although all three neurons display striking morphological differences, they all share certain structural features in common, including the location of their primary axons and neurites in specific tracts in the neuropil.By recording intracellularly from the main neurites of the G, B1, and B2 neurons, clear differences were found in the synaptic inputs each of the neurons receives and the synaptic outputs each makes. For example, G and B2, but not B1, receive direct monosynaptic input from the descending contralateral movement detector (DCMD) interneurons and from auditory afferents; B1, but not B2, connects directly to G; and B2, but not B1 or G, connects directly to flight motoneurons. The main conclusion from these observations is that lineally equivalent neurons in different segments can develop similar primary structures but quite different secondary morphologies and synaptic connections. How these segment‐specific differences arise during embryogenesis remain

ISSN:0092-7317    

DOI:10.1002/cne.902330108

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

年代:1985

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902330101

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

年代:1985

数据来源: WILEY