摘要:

AbstractSeveral monkey retinae were stained, by using the reduced silver technique, in order to analyse long‐distance intraretinal connections. Long, bifurcating processes covering very large areas were identified. Morphological investigation of these processes suggests that they are members of two different systems of branching axons.The first population of these processes originates as axon collaterals from cells in the ganglion cell layer. These cells have a relatively large, elongated soma and straight, sparsely branching dendrites, stratified in the vitreal half of the inner plexiform layer. The main axon (0.6 μm average diameter) passes along the optic fibre bundles, disappearing into the optic disk, whilst its collaterals run mainly in the inner plexiform layer. A cell showing similar morphology has also been found in the ganglion cell layer of a cat retina.The second population of processes consists of very thick fibres (2.1 μm average diameter) apparently originating from the optic disk. The main branches run in the space between the optic fibre layer and the ganglion cell layer, with short, secondary processes crossing the ganglion cell layer orthogonally. Many higher‐order processes originate from the second‐order branches; these run almost horizontally in the inner plexiform layer.The ganglion cells generating axon collaterals may constitute an intraretinal firing synchronization system, or they may be a residual feature of retinal development. The centrifugal fibres may be related to the sensitivity control during retinal dark ada

ISSN:0092-7317    

DOI:10.1002/cne.903080202

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

年代:1991

数据来源: WILEY

摘要:

AbstractPurkinje cell nucleoli are used as counting units in order to obtain unbiased (fractionator)estimates of the number, N, of Purkinje neurons in adult mammalian cerebella of known weight, W. Regression analysis is then employed to establish the nature of the relationship between logN and logW. The linear regression equation defines an allometric relation that is employed to predict number in cerebella of known weight from other mammals. Predicted numbers are tested against empirical estimates.For 19 cerebella ranging in weight from 0.2 g (rat) to 113 g (human), the allometric relation between Purkinje cell number and organ weight was determined. By using this relation, the mean complement in three rabbit cerebella (average weight, 0.87 g) is predicted to be 0.63 million. This figure is confirmed by fractionator estimates made on the same three brains. The cat cerebellum should contain about 1.5–2.0 million Purkinje cells. An estimate of 1.2–1.3 million cells is to be found in the literature.Including rabbit cerebella in a refined equation yields the following relation:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm N = 686000W}^{{\rm 0}{\rm .695}}. $$\end{document}With this refined equation, further predictions are made about the numbers likely to be found in the cerebella of the dog, goat, pig, ox, and horse. The numbers predicted for these animals must await experimental verification, but they are entirely consistent with previous suggestions that neuronal packing densities decrease with increasing brain s

ISSN:0092-7317    

DOI:10.1002/cne.903080203

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe morphology of neonatal rat phrenic motoneurons was studied following retrograde labeling with horseradish peroxidase, which resulted in Golgi‐like fills of phrenic motoneuron somata and dendrites. At birth, these neurons have well‐developed dendritic trees with many characteristics described for phrenic motoneurons in the adult rat. The dendrites form tightly fasciculated bundles that emerge from the phrenic nucleus primarily along four axes: ventromedial, ventrolateral, dorsolateral, and rostral/caudal, with smaller and more variable projections directly lateral and ventral. Although sparse, some dendritic appendages were also present, and in a few animals, somata clustering was apparent. The most significant difference between adult and neonatal rat phrenic motoneurons is in the extent to which medially and laterally projecting dendrites extend beyond the borders of the ipsilateral gray matter. In the neonate, unlike the adult, these dendrites project extensively past the gray/white border to the edge of the hemicord. Ventromedial dendrites occasionally cross to the contralateral ventral horn in the ventral white commissure and laterally projecting dendrites could be seen reaching the edge of the cord, turning and traveling rostrally or caudally for up to 100 μm. Phrenic motoneurons are not unique in having long dendrites at birth. A brief comparative study showed that neonatal cervical, thoracic, and lumbar motoneurons also have long dendrites that project to the medial and lateral borders of the hemi

ISSN:0092-7317    

DOI:10.1002/cne.903080204

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo compare nerve regeneration in young adult and aging mice, the right sciatic nerves of 6‐ and 24‐month‐old mice were crushed at the sciatic notch. Two weeks later, both groups of mice were perfused with an aldehyde solution, and, after additional fixation, the sciatic nerves were processed so that the transverse sections of each, nerve subsequently studied by light and electron microscopy included the entire posterior tibial fascicle 5 mm distal to the crush site. The same level was sectioned in unoperated contralateral nerves; these nerves served as controls. Electron micrographs and the Bioquant Image Analysis System IV were used to measure areas of posterior tibial fascicles and count the number of myelinated axons, the number of unmyelinated axons, and their frequency in Schwann cell units. In aging mice, the total number of regenerating myelinated axons was significantly reduced, but totals of regenerating unmyelinated axons in aging and young adults did not differ significantly. In aging mice, the frequency of Schwann cells that contained a single unmyelinated axon was greater, suggesting that before myelination began, Schwann cell ensheathment of axons also was slowed. After axotomy by a crush injury, the area of the posterior tibial fascicle was less than that in young adults and the distal disintegration of myelin sheath remnants also appeared to be retarded. The results indicate that responses of neurons, axons, and Schwann cells could be important in slowing the regeneration of myelinated fibers found in sciatic nerves from aging

ISSN:0092-7317    

DOI:10.1002/cne.903080205

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

年代:1991

数据来源: WILEY

摘要:

AbstractNeurons within the precursor of the adult leg, the imaginal disc, innervate a larval sense organ, Keilin's organ. Electron microscopical investigations of first instar larvae show that five dendrites end at the organ: three insert at the bases of the three hairs of the organ and two end against the cuticle, without any apparent cuticular specialization. In third instar larvae, the imaginal leg discs invaginate into the body cavity, and only four of the dendrites (the outer segments of which become greatly elongated) remain in contact with Keilin's organ. The axons of the neurons that supply Keilin's organ project into a ventral neuropile region of the central nervous system, with a pattern that resembles the projections of other larval sensilla. Electrical activity can be recorded from neurons of the imaginal disc in response to mechanical stimulation.

ISSN:0092-7317    

DOI:10.1002/cne.903080206

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe imaginal leg disc ofPhormia reginacontains eight neurons that arise during embryogenesis. Five of the neurons are associated with Keilin's organ, and of these five, two persist to the adult fly. Two new neurons arise at about the time of pupariation and flank each of these persisting neurons, forming two triplets of cells. Both triplets can be followed throughout metamorphosis; in the late pupa they are situated anteriorly and posteriorly at the tip of the fifth tarsomere. Two triplets of cuticular specializations are found at corresponding positions in the adult fly, each consisting of two campaniform sensilla and a trichoid hair. The central member of each set of sensilla, a campaniform sensillum, is associated with the persisting cell.

ISSN:0092-7317    

DOI:10.1002/cne.903080207

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes some central terminations of type II spiral ganglion neurons as labeled by extracellular injections of horseradish peroxidase (HRP) into the auditory nerve of cats. After histological processing with diaminobenzidine, both thick (2–4 μm) and thin (0.5 μm) fibers of the auditory nerve were stained. Whenever traced, thick fibers always originated from type I spiral ganglion neurons and thin fibers always from type II ganglion neurons. Because the labeling of type II axons faded as fibers projected into the cochlear nucleus, this report is limited to regions of the ventral cochlear nucleus near the auditory nerve root. The central axons of type II neurons are unmyelinated, have simple yet variable branching patterns in the cochlear nucleus, and form both en passant and terminal swellings. Under the light microscope, most swellings are located in the neuropil but they are also found in the vicinity of cell bodies, nodes of Ranvier of type I axons, and blood vessels. Eighteen en passant swellings in the neuropil were located by light microscopy and resectioned for electron microscopy; two of these swellings exhibited ultrastructural features characteristic of chemical synapses. The data indicate that inputs from outer hair cells might be able to influence auditory processing in the cochlear nucleus through type II primary neur

ISSN:0092-7317    

DOI:10.1002/cne.903080208

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe present investigation was designed to determine the origins in the temporal lobe, and terminations in the pons, of the temporopontine pathway. Injections of tritiated amino acids were placed in multimodal regions in the upper bank of the superior temporal sulcus (STS), and in unimodal visual, somatosensory, and auditory areas in different sectors of the lower bank of the STS, the superior temporal gyrus (STG), and the supratemporal plane (STP). The distribution of terminal label in the nuclei of the basis pontis was studied using the autoradiographic technique.Following injections of isotope into the multimodal areas (TPO and PGa) in the upper bank of the STS, intense aggregations of label were observed in the extreme dorsolateral, dorsolateral, and lateral nuclei of the pons, and modest amounts of label were seen in the peripeduncular nucleus. The caudalmost area TPO projected in addition to the ventral and intrapeduncular pontine nuclei. The second auditory area, AII, and the adjacent auditory association areas of the STG and STP contributed modest projections to the dorsolateral, lateral, and peripeduncular nuclei, but generally spared the extreme dorsolateral nucleus. The lower bank of the STS, which subserves central vision, the somatosensory associated region at the fundus of the rostral STS, and the primary auditory area did not project to the pons.The higher order, multimodal STS contribution to the corticopontocerebellar circuit may provide a partial anatomical substrate for the hypothesis that the cerebellum contributes to the modulation of nonmotor functions.

ISSN:0092-7317    

DOI:10.1002/cne.903080209

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

年代:1991

数据来源: WILEY

摘要:

AbstractOn the basis of stimulation studies, it has been proposed that the infralimbic cortex (ILC), Brodmann area 25, may serve as an autonomic motor cortex. To explore this hypothesis, we have combined anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA‐L) and retrograde tracing with wheat germ aggutinin conjugated to horseradish peroxidase (WGA‐HRP) to determine the efferent projections from the ILC.Axons exit the ILC in one of three efferent pathways. The dorsal pathway ascends through layers III and V to innervate the prelimbic and anterior cingulate cortices. The lateral pathway courses through the nucleus accumbens to innervate the insular cortex, the perirhinal cortex, and parts of the piriform cortex. In addition, some fibers from the lateral pathway enter the corticospinal tract. The ventral pathway is by far the largest and innervates the thalamus (including the paraventricular nucleus of the thalamus, the border zone between the paraventricular and medial dorsal nuclei, and the paratenial, reuniens, ventromedial, parafasicular, and subparafasicular nuclei), the hypothalamus (including the lateral hypothalamic and medial preoptic areas, and the suprachiasmatic, dorsomedial, and supramammillary nuclei), the amygdala (including the central, medial, and basomedial nuclei, and the periamygdaloid cortex) and the bed nucleus of the stria terminalis. The ventral efferent pathway also provides descending projections to autonomic cell groups of the brainstem and spinal cord including the periaqueductal gray matter, the parabrachial nucleus, the nucleus of the solitary tract, the dorsal motor vagal nucleus, the nucleus ambiguus, and the ventrolateral medulla, as well as lamina I and the intermediolateral column of the spinal cord.The ILC has extensive projections to central autonomic nuclei that may subserve a role in modulating visceral responses to emotional stimuli, such as str

ISSN:0092-7317    

DOI:10.1002/cne.903080210

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn previous studies on reptiles and elasmobranchs, we determined that some reticular groups are either absent or may be displaced compared to their locations in mammals. For example, nucleus raphe dorsalis, the largest serotoninergic cell group in mammals, is not present in rays, skates, or guitarfish. In the present study, we chose heterodontid sharks, a sister group to these batoids, for an out‐group comparison of this and other characters. We identified cells in the brainstem ofHeterodontus francisciby use of antibodies against tyrosine hydroxylase, serotonin, or leu‐enkephalin and compared the distribution of these nuclei to descriptions in mammals and other elasmobranchs. The majority of tyrosine hydroxylase‐positive cells were found in the midbrain tegmentum (A8–A10) and the hypothalamus. In addition, putative A1, A2, A5, A7 (noradrenergic) groups were found in the metencephalon and myelencephalon. Serotonin‐positive cells were found in raphe nuclei and scattered lateral to the raphe. We identified probable homologues to raphe pallidus, raphe obscurus, raphe magnus, and raphe centralis superior (B8) cell groups, which have been described in mammals. A cluster of cells dorsomedial to the medial longitudinal fasciculus was identified as raphe dorsalis. The distributions of leu‐enkephalin and serotonin immunoreactive cells were similar to each other, but the tyrosine‐hydroxylase immunoreactive cells rarely intermingle with the former two immunoreactive cell types. Other reticular groups that contained both serotonin‐and leu‐enkephalin‐positive cells included reticularis (r.) ventralis, r. magnocellularis, r. paragigantocellularis lateralis, r. pontis caudalis, and r. pontis oralis medialis and lateralis. Thus, this shark contains many of the major brainstem raphe and catecholaminergic cell groups described for rats, but the relative distribution of the immunopositive cell groups differs in mammals and

ISSN:0092-7317    

DOI:10.1002/cne.903080211

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

年代:1991

数据来源: WILEY