摘要:

AbstractHorseradish peroxidase techniques were employed to trace the central projections of afferents from the individual endorgans of the membranous labyrinth and to delineate the efferent projections from the primary octaval nuclei to the spinal cord and midbrain octavolateralis area in the clearnose skate,Raja eglanteria.First‐order octaval afferents project ipsilaterally to five primary octaval nuclei, namely: magnocellular, descending, posterior, anterior, and periventricular. Octaval afferents also terminate in the reticular formation, nucleus intermedius (primary mechanoreceptive lateral‐line nucleus), and vestibulolateral lobe of the cerebellum. Each primary octaval nucleus receives afferent input from each labyrinthine endorgan, with the possible exception of macula neglecta input to the magnacellular nucleus. Within the anterior, descending, and to a lesser extent posterior and magnocellular nuclei, this input is largely nonoverlapping. Semicircular canal cristae afferents terminate ventrally, saccular and lagenar afferents dorsally, utricular afferents laterally, and macula neglecta afferents course ventrally but terminate largely dorsally within these nuclei. In the vestibulolateral lobe of the cerebellum, cristae afferents project primarily to the pars medialis, whereas macular endorgan afferents terminate in the pars lateralis. Primary afferent input to the reticular formation is predominantly from the horizontal canal crista. The densest projections to nucleus intermedius are from the utriculus and sacculus. Vestibulospinal projections originate primarily from the magnocellular and descending nuclei. Secondorder auditory neurons are most likely located in dorsomedial parts of the descending and anterior nuclei. Cells in these nuclei project directly to the auditory area of the midbrain octavolateralis complex, but projections to this area originate predominantly from nuclei C1 and C2, which are possible superior olivary homolog

ISSN:0092-7317    

DOI:10.1002/cne.902660403

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn a recent study of the cat visual cortex, it was shown that there are interindividual differences in the numerical density (Nv) of symmetrical synapses associated with flat vesicles (FS synapses) but not of asymmetrical synapses associated with round vesicles (RA synapses). Since many of the environment‐sensitive properties of visual cortex neurons are GABA‐dependent, it was suggested that the interindividual differences in FS synapses might be duo to environmental factors. To verify this possibility we estimated the Nvof both types of synapses in two groups of six cats, paired by litter and by sex, and raised either in isolation or in a colony from the time of weaning to the age of 8 months. We also measured the Nvof neurons and the thickness of the cortex and made some gross anatomical measurements.The brains of animals raised in the enriched environment are 7% heavier, and their total body weight is 10% greater: The brain‐to‐body‐weight ratio remains unchanged. The total length of the brain is not affected, but the length and width of the cerebral hemispheres are each 5% greater in the enriched cats. As in comparable rat studies, the thickness of the cortex is 4% greater, but in the present study this difference is not significant. The numerical density of neurons is diminished by 17% in enriched animals. This is probably due to a wider separation of neuronal cell bodies in a larger cortical volume, rather than to a loss of neurons.There are no significant changes in the numerical density of RA synapses between the two milieux, but there are nearly twice as many FS synapses per mm3of tissue in the impoverished cortex. The coefficient of variation of FS synapses, which in the previous study was on the order of 30%, has been reduced to 10% and 7% in enriched and impoverished cats, respectively. We conclude that environmental conditions can lead to selective interindividual differences in the Nvof FS synapses, as seen in our previous study of animals whose rearing conditions were not controlled.The average diameter of RA synaptic profiles is not affected by the environment but FS synapses are 25% wider in the enriched animals. Because of the smaller neuronal Nvin enriched animals, there are, in fact, 18% more RA synapses and 34% fewer FS synapses per neuron in the enriched condition. As a consequence the total area of RA contacts per neuron is 16% greater in enriched animals, hut changes in size of FS contacts compensate perfectly for the change in number so fiat the total area of contact per neuron is not affected.Changes in the number of neurons and synapses are similar in all individual laminae. Modifications in the number of FS synapses occur on both dendritic spines and on dendritic trunks. It is not clear whether axosomatic synapses are also affected.Changes in the number of neurons and synapses are similar in all individual laminae. Modifications in the number of FS synapses occur on both dendritic spines and on dendritic trunks. It is not clear whether axosomatic synapses are also affected.We conclude that the richness of the environment modifies the excitatory‐inhibitory equilibrium on the neurons of the visual cortex through a restructuring of inhibitory circuits. We predict that this will have a profound effect on the receptive field properties of the cortical neurons. The dramatic differences in the reaction of the two types of synapses to the environment suggest that different mechanisms subserve the adaptation of excitatory and inhibitory circuits to environmen

ISSN:0092-7317    

DOI:10.1002/cne.902660404

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractAbdominal ganglia of crayfish contain identifiable neuropils, commissures, longitudinal tracts, and vertical tracts. To determine the functional significance of this ganglionic framework, we backfilled the following types of neurons with cobalt chloride: sensory hair afferents, slow and fast extensor motor neurons, the segmental stretch receptor neurons, and their inhibitory accessory cells. After the cobalt ions were precipitated and intensified, we studied the central projections of the filled neurons within the ganglionic structures. All of the axons of these neurons exit or enter each of the first five abdominal ganglia through the second pair of nerves.Our description of the central projections of the hair afferents is the first in the literature. These afferents innervate the large ventral horseshoe neuropil (HN) in the core of each ganglion. This neuropil is homologous to the insect ventral association centers, which also process sensory information. Furthermore, we discovered that some of the crayfish afferents innervate glomeruli within the HN.The slow and fast extensor motor neurons, the stretch receptor neurons, and the accessory cells branch mostly in the dorsal part of the ganglion. We reinterpret previous identifications of the extensor neurons that were based largely on soma position. Together with our previous descriptions of the flexor motor neurons, these results allow us to relate both rapid tail‐flips and slower postural movements to the structure of the segmental gangli

ISSN:0092-7317    

DOI:10.1002/cne.902660405

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn this study the organization of the projection from the lateral superior olivary nucleus (LSO) to the inferior colliculus was investigated in the cat by using anterograde tract‐tracing techniques. The findings indicated that LSO projected bilaterally to the central nucleus of the inferior colliculus as well as to the ventrolateral and rostral pole nuclei. In the central nucleus a larger medial component of the projection ended in pars medialis and centralis. A smaller lateral component ended in the region of the pars lateralis. Both components of the projection appeared to be topographically organized, but in the lateral component the low‐frequency part of LSO appeared to have greater representation.The uncrossed and crossed LSO projections to the inferior colliculus exhibited several important differences in their distribution. First, periodic bands of dense labeling were more prominent in the distribution of the uncrossed projection. The bands measured 150–200 μ in thickness and in some cases interruptions or gaps were present along the length of the bands. The distribution of the crossed projection was more diffuse, but some banding was also apparent. Second, the positions of the bands of dense labeling on the two sides were not homotopic as determined by labeling projections from the ipsilateral and contralateral LSO in the same tissue. The dense bands labeled with WGA‐HRP from an injection in LSO on one side and bands labeled with3H‐leucine from an injection in LSO on the other side either were interdigitating or were only partially overlapping. Finally, the area over which the uncrossed projection distributed endings varied in size with respect to that of the crossed projection. The variation in size of the area of the projections was a function of the frequency representation. A model based on the three‐dimensional reconstruction of bands as projection sheets is proposed as a substrate for selective integration of afferents in the inferio

ISSN:0092-7317    

DOI:10.1002/cne.902660406

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have used physiological and anatomical techniques to address three general issues concerning the topographic organization of the middle temporal visual area (MT) of the macaque monkey. First, we carried out a quantitative analysis of irregularities and asymmetries in the visual representation in MT. This analysis revealed a striking overemphasis on a restricted portion of the visual field that runs obliquely through the inferior contralateral quadrant and largely avoids both the horizontal meridian and the inferior vertical meridian. This corresponds to the portion of the visual field that would be maximally stimulated during visually guided hand movements. Second, the physiologically determined topographic organization of MT was compared to the pattern of callosal inputs in the same hemisphere, which are known to be distributed irregularly within MT. Callosal inputs tended to be densest near the representation of the vertical meridian, but there were numerous exceptions to this trend. Thus, topographic irregularities account for only part of the irregularities in callosal inputs to MT. Finally, comparison of these data with previous reports shows a strong correlation between body weight and the average size of MT. The representation in myeloarchitectonically defined MT was found to include much of the visual periphery, although it is unclear from our data whether this representation is invariably complete.

ISSN:0092-7317    

DOI:10.1002/cne.902660407

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn larval frogs the retina and tectum grow in topologically dissimilar patterns: new cells are added as peripheral annuli in the retina and as caudal crescents in the tectum. Retinotopy is maintained by the continual caudalward shifting of the terminals of the optic axons. After metamorphosis the pattern of growth changes. The retina continues to add new ganglion cells peripherally, but there is no neurogenesis in the tectum. To maintain retinotopy in postmetamorphic frogs, the terminals of the optic axons must continually shift toward the central tectum.We tested the proposal of centripetally shifting axons by making punctate injections of horseradish peroxidase (HRP) in the tectum of adultRana pipiensand observing the patterns of filled cells in the contralateral retina, as was done in the goldfish (Easter and Stuermer, '84). Punctate applications of HRP in the tectum should be taken up: (1) by fascicles, and label a partial anulus of cells, (2) by terminals, and label a cluster of cells in the corresponding retinotopic site, and (3) by the extrafascicular axonal segments, and label a band of cells connecting the partial annulus to the cluster. If the terminals have shifted centripetally, the band of cells labeled through their extrafascicular segments should have a spoke‐like orientation, with the center of the retina as the hub. As the tectal site moves from rostral to caudal, this band of cells should move, pendulum‐like, from temporal to nasal retina.In general, the patterns of HRP‐filled retinal cells we observed were consistent with our predictions. In addition, HRP taken up by the oldest (rostral) tectal axons produced more complex patterns of filled cells that indicated that these axons had shifted both caudally before metamorphosis and centripetally

ISSN:0092-7317    

DOI:10.1002/cne.902660408

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902660402

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY