摘要:

AbstractPostembryonic development of the dorsal ocellus of the cockroachPeriplaneta americanawas examined. Small ocelli (20 μm in diameter) with less than 100 cells in the newly hatched nymph become adult ocelli (more than 500 μm in diameter) with more than 10,000 retinular cells, through ten to 11 nymphal stages. Thus, sequential steps of morphogenesis of rhabdomeres from loose interdigitations of apposed cell membranes to regularly arranged microvilli can be seen in the nymphal ocelli. Some retinular axons appear to extend into the brain as a bundle in the first‐instar nymph. Retinular axons differentiated later also extend toward the brain, but there is no evidence that they enter it. The ultrastructure of the ocellus and component analysis of the ocellar electroretinogram suggest that functional connections between retinular axons and ocellar interneurons do not occur in the ocellar capsule until mid (the fifth or sixth)‐instar nymphs. The ocellar diameter increases linearly with increase in body length during the nymphal stages, but it increases by a factor of 1.5–2.0 during the final molting: the body length of the adult is almost the same as that of the last‐instar nymph. These data suggest that the function of the dorsal ocelli may be closely related to specific adult behavior such

ISSN:0092-7317    

DOI:10.1002/cne.902690202

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe early postnatal development of interstitial cells (IC) in the white matter of the temporal cortex in kittens was studied. Counts in Nissl‐stained preparations show that the number of 1C diminishes by about 60% during the second postnatal week. In Golgi preparations, IC are bipolar or bitufted with long, beaded dendrites coursing in the white matter toward the ventricular surface. Ascending, shorter dendrites are thinner, often branch in a short bush, and possess long spines resembling filopodia. The majority of their axons descend in the white matter, emitting numerous recurrent collaterals that become ascending fibers reaching various cortical layers. Most 1C resemble inverted pyramidal cells. They appear well developed at the time of birth and continue to develop elaborate axonal complexes in the white matter of older animals. Electron microscopic observations of degenerating 1C were detected in all cases studied and their presence was related to the existence of cell death responsible for elimination of a fraction of 1C. They were recognized by their dark aspect and by dilations of the endoplasmic reticulum. Synapses contacting degenerating profiles were also observed. It is concluded that 1C belong to the population of early generated subplate cells which may have a transient function involved in certain morphogenetic events during the development of the cortical plate. Some persist in the adult where they can be recognized as IC of the white matte

ISSN:0092-7317    

DOI:10.1002/cne.902690203

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractUsing a variety of neuroanatomical and histological techniques, we compare the spinal cord and peripheral nerve distribution in the tails of larvae fromXenopus laevisand three species ofRana.The relatively large, postsacral spinal, cord ofXenopuscontains abundant motoneurons and their axons. Spinal nerves exit from the spinal cord in a regular array, one nerve per myotome, from the cervical region to near the end of the tail. Somata of motoneurons innervating caudal myotomes are found along the entire length of the tail. In contrast, the caudal cord ofRanais reduced to a filum terminate consisting of little more than an ependymal tube; spinal nerves to all caudal myotomes leave the cord in the sacral region and reach their motor targets via a cauda equina and caudal plexus. Motoneuron cell bodies innervating caudal myotomes are found only in the sacral region.TheRanalarval pattern is similar to that of adult frogs and mammals, whereas theXenopuslarval pattern is more like that of salamanders and reptiles. These gross neuroanatomical differences are not due to differences in the size or developmental stage of the tadpoles, but instead are associated with differences in the swimming behavior of the larvae.The presence of motoneurons in the caudal spinal cord ofXenopusmay provide local intermyotomal control within the tail; the elongated topography of the cord appears to permit finer, rostral‐to‐caudal regulation of neuromuscular activity. TheRanaspinal cord, on the other hand‐with motoneurons clustered anteriorly‐may produce concurrent firing of adjacent ipsilateral myotomes, but at the expense of fine intermyotomal regulation. The fact that nerves in the tail ofXenopusenter and exit from the spinal cord locally, as opposed to far anteriorly as inRana, means that for tadpoles of the same size, reflex arc lengths are many times shorter in

ISSN:0092-7317    

DOI:10.1002/cne.902690204

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractCalibers and microtubules of sural nerve axons were studied in young (6‐week‐old), mature (14‐week‐old), and aging (2‐year‐old) rats. The mean cross‐sectional area of nonmedullated fibers was about 0.50 μm2(range: 0.47–0.52) in the three age groups. Their caliber spectra were also similar. In contrast, myelinated axons grew from 6.6 to 16.7 μm2between the sixth and 14th week of age. The increase of cross‐sectional area was greater, the greater the initial caliber of axon (range 44–154%). No further change of caliber was observed in the aging rat. The cross‐sectional area of nerve allotted per myelinated fiber was 42, 66, and 97 μm2in young, mature, and aging rats, respectively. The fraction of nerve tissue occupied by the axoplasm, though, did not change substantially; it was 20, 28, and 21%, respectively. The microtubules density of 3‐μm3myelinated axons had a general average of 21 microtubules μm2. Differences between groups were not significant. In nonmedullated fibers, the microtubular density decreased as the size of the axon increased. No differences were observed between age groups. We conclude that nonmedullated fibers of the sural nerve stop growing before the sixth week whereas myelinated fibers keep growing until the 14th week of age. The correlation between microtubular content and axonal caliber is

ISSN:0092-7317    

DOI:10.1002/cne.902690205

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractDisplaced retinal ganglion cells (DRGCs) were retrogradely labelled by injections of the fluorescent dye Fast Blue into the superior colliculi of pigmented rats. Following fixation these cells were intracellularly injected with Lucifer Yellow to determine their dendritic morphology and distribution.Graphic reconstruction of Lucifer Yellow‐filled prelabelled neurones revealed a heterogeneous population of DRGCs. Their stratification within the inner plexiform layer was diverse and cells were classified according to their dendritic morphology.The present sample consists largely of unistratifying neurones, the dendrites of which arborized within a narrow sublamina of the inner plexiform layer. They were characterized by a centrally located soma and densely branched dendritic network with little overlap within the branching pattern. In contrast, bistratifying DRGCs possessed a loose and sparsely branched dendritic structure, while diffusely stratifying neurones contained a high degree of dendritic crossing, culminating in a complex network, in which the soma position was biased toward the periphery.One type of DRGC bore a striking resemblance to type 1 neurones (Perry, 1979; Proc. R. Soc. Lond. [Biol.]204:363–375) in the ganglion cell layer. They were characterized by a large soma (15.8 μm ± 2.2 μm s.d.) and a dendritic field diameter averaging 288 μm (s.d. ± 62 μm) and were on average larger than the rest of the displaced population but smaller than type 1 cells in the ganglion cell layer. Since the stratification patterns of the displaced and nondisplaced type 1 neurones were indistinguishable, it is reasonable to assume that the Lucifer Yellow‐filled cells in the present study represent the displaced counterpart of regular type 1 ganglion cells. Therefore, it appears that despite the aberrant location of the soma within the inner nuclear layer, the dendritic morphology of the cell develops unimpeded into a normal stratification pattern, although both soma and dendritic field size are reduced. If displacement is a developmental aberration, this size decrease may arise from overcrowding within the inner nuclear layer where the soma becomes lodged erroneously during its migration to the ganglion cell layer. This would also account for the heterogeneity of displaced cells found in the present study, since the randomness of a developmental error would ensure that a variety of ganglion cell types was included in the displaced

ISSN:0092-7317    

DOI:10.1002/cne.902690206

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe postsynaptic targets of cholinergic boutons in the rat neostriatum were assessed by examination in the electron microscope of boutons that were immunoreactive for choline acetyltransferase, the synthetic enzyme for acetylcholine. These boutons formed symmetrical synaptic specializations with neostriatal neurons. Of 209 immunoreactive synaptic boutons observed in random searches of the neostriatum, 45% made contact with dendritic shafts, 34% with dendritic spines, and 20% with neuronal perikarya. Many of the postsynaptic structures had ultrastructural characteristics of the most common type of striatal neuron, the medium‐size densely spiny neuron. This was confirmed by the examination in the electron microscope of Golgi‐impregnated medium‐size spiny neurons from sections that had also been immunostained for choline acetyltransferase. Immunoreactive boutons formed symmetrical synaptic specializations with all parts of the neurons examined, i.e., perikarya, proximal and distal dendritic shafts, and dendritic spines. Two of the Golgi‐impregnated medium‐size spiny neurons that received input from the cholinergic boutons were also retrogradely labelled with horseradish peroxidase that had been injected into the substantia nigra, they were thus further characterized as striatonigral neurons. Similarly, seven retrogradely labelled perikarya of striatonigral neurons were found to receive input from the cholinergic boutons.It is concluded that cholinergic boutons in the neostriatum form synaptic specializations and that one of their major targets is the medium‐size densely spiny neuron that projects to the substantia nigra. The topography of the cholinergic afferents of these cells is distinctly different from that of other boutons derived from local neurons and from boutons that form asymmetrical synaptic specializations, but it is similar to that of the dopaminergic boutons originating from neurons in the subst

ISSN:0092-7317    

DOI:10.1002/cne.902690207

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe afferent and efferent connections of the primary auditory cortex (AI) of common marmosets were traced following small injections of wheat germ agglutinin conjugated with horseradish peroxidase (WGA‐HRP) made at best frequency (BF)‐defined sites in the AI. After the injections the animals remained anesthetized for 15–23 hours; they were then perfused transcardially with fixative and the brains were processed for WGA‐HRP reaction product.Examination of the disposition of labelled material revealed the following results. First, patches of terminal labelling, and to a lesser extent retrograde labelling, were found outside the injection site in the ipsilateral cortex rostral and caudal to the AI. Second, the region of the contralateral cortex corresponding to the injection site contained labelled terminals throughout the depth of the cortex; labelled neurons were found in the middle layers. Third, in each experiment a discrete region of the medial geniculate body (MG) contained retrogradely labelled neurons interspersed with anterogradely labelled terminals. These regions had a banded appearance, were found in the dorsal and rostral half of the MG, and shifted in location progressively dorsal and as the injection site BF increased.The presence of projection zones rostral and caudal to the AI of marmosets, and the disposition of the MG sources of projection in relation to BF, are similar to observations made on other New World monkeys. The ipsilateral corticocortical projections confirm electrophysiological evidence suggesting the existence of auditory fields rostral and caudal to the AI. The thalamocortical auditory system of the marmoset appears relatively simple, with a comparatively undifferentiated MG projecting to a cortical auditory system dominated by a l

ISSN:0092-7317    

DOI:10.1002/cne.902690208

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractAngiotensin II receptor and angiotensin converting enzyme distributions in the human medulla oblongata were localised by quantitativein vitroautoradiography. Angiotensin II receptors were labelled with the antagonist analogue125I‐[Sar1, Ile8] All while angiotensin converting enzyme was labelled with125I‐351A, a derivative of the specific converting enzyme inhibitor, lisinopril.Angiotensin II receptor binding and angiotensin converting enzyme are present in high concentrations in the nucleus of the solitary tract, the dorsal motor nucleus of vagus, the rostral and caudal ventrolateral reticular nucleus, and in a band connecting the dorsal and ventral regions.In the rostral and caudal ventrolateral reticular nucleus, angiotensin II receptors are distributed in a punctate pattern that registers with neuronal cell bodies. The distribution and density of these cell bodies closely resemble those of catecholamine‐containing neurones mapped by others. In view of the known interactions of angiotensin II with both central and peripheral catecholamine‐containing neurons of laboratory animals, the current anatomical findings suggest similar interactions between these neuroactive compounds in the human central nervous system.The presence of angiotensin II receptors and angiotensin converting enzyme in the nucleus of the solitary tract, dorsal motor nucleus of vagus, and rostral and caudal ventrolateral reticular nucleus demonstrates sites for central angiotensin II to exert its known actions on vasopressin release and autonomic functions including blood pressure control. These data also suggest a possible interaction between angiotensin II and central catechol‐eminergi

ISSN:0092-7317    

DOI:10.1002/cne.902690209

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractSmall injections of peroxidase‐labeled wheat germ agglutinin into cat area 18 gave rise to patches of labeled cells and axon terminals around the injection site. In EM sections it was found that the labeled cells had a pattern of synaptic inputs characteristic of spiny‐dendrite neurons (pyramidal or spiny stellate cells). The labeled axon terminals formed type 1 (asymmetric) synapses, most of which were made onto dendritic spines. In other experiments injections of fluorescent beads were made into area 18, giving rise to a similar patchy distribution of labeled cells. The sections were then processed for immunocytochemical demonstration of γ‐aminobutyric acid (GABA). The bead‐labeled cells in the patches were GABA negative. The findings suggest that the patchy projections mediate mutual excitation between groups of spiny‐dendri

ISSN:0092-7317    

DOI:10.1002/cne.902690210

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractIntracellular injection of HRP combined with immunocytochemistry for [Leu]enkephalin was used to demonstrate striatal spiny neuron dendritic and local axonal arborizations in the same section as enkephalin‐rich patches (striosomes). Cobalt intensification of the first DAB reaction prior to the immunoperoxidase steps resulted in good contrast between the black reaction product in the intracellularly labeled cells and the brown staining for [Leu]enkephalin. Serial reconstructions of the labeled cells and nearby boundaries between the enkephalin‐rich striosomes and enkephalin‐poor matrix allowed the relationship between the arborizations of the labeled cells and these boundaries to be established. It was also possible to examine the relationship to compartmental boundaries of a second neuronal class consisting of large, pallidallike neurons whose somatodendritic morphology was outlined by immunoperoxidase‐labeled terminals.We found that spiny projection neurons in both compartments have dendritic arbors and local axonal collaterals that are confined by compartmental boundaries. The termination or recurvature of dendrites at such boundaries suggests that the cellular basis of striatal compartmental organization is provided by this class of striatal neuron. On the other hand, large pallidumlike striatal neurons were found to have dendrites that extend across compartmental boundaries. These results support previous reports that striatal spiny projection neurons preserve the compartmental segregation of parallel striatal input‐output systems, whereas other classes of striatal neurons may serve to provide limited integration between com

ISSN:0092-7317    

DOI:10.1002/cne.902690211

出版商:Alan R. Liss, Inc.    

年代:1988

数据来源: WILEY