摘要:

AbstractMorphogenesis of photoreceptor outer segment disks appears to occur by an evagination of the ciliary plasma membrane (Steinberg et al., J Comp Neurol190: 501–519, 80). We tested if polymerized actin (F‐actin) was necessary for the regulation of this postulated process by incubatingXenopuseyecups with 5 or 25 μM cytochalasin D for 6–28 hours. During the second hour, the incubation medium contained3H‐leucine. Both concentrations of cytochalasin resulted in: (1) dissolution of the rhodamine‐phalloidin labeling pattern of photoreceptors, and (2) collapse of the calycal processes (which are normally filled with actin filaments) and disappearance of the inner segment microfilaments. In addition, the few most basal rod and cone outer segment disks appeared several times their normal diameter. These oversized disks had incorporated3H‐leucine and extended along the margin of the outer or inner segment. The nature of the overgrown disks is consistent only with a morphogenetic process involving evaginations of the ciliary plasma membrane. Deregulation by cytochalasin D was manifest by excessive growth of a few nascent disks rather than normal growth of many. Therefore, the normal network of actin filaments is apparently not necessary for continued evagination of the membrane, but it does seem to be an essential part of the mechanism that initiates the evagination of the ciliary plasma membrane and\or the mechanism that controls how far nascen

ISSN:0092-7317    

DOI:10.1002/cne.902720202

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

年代:1988

数据来源: WILEY

摘要:

AbstractWhat are the mechanisms acting during development at points of intersection of central nervous system fiber tracts which influence the direction taken by a population of growing axons? In order to address this question, the ontogeny of the intersecting rostral corpus callosum and its perforating fiber pathway (PF), and the microenvironment through which these fiber systems grow, were examined in a series of mouse embryos and early postnates.Our results show that the perforating fibers are identifiable in silverstained sections between embryonic days (E) 15 and 16, at least 1 day prior to the initial appearance of the callosal projection. Soon after the PF can be identified, a dense accumulation of subventricular cells surrounds the PF at a point just ventral to the location where the callosum and PF will intersect (i.e., at the corticoseptal boundary). Callosal axons, which are present at the point of intersection beginning on E17, do not join the perforating fibers, nor do they appear to penetrate the underlying population of subventricular cells. Instead, the callosal fibers turn across the PF and enter the contralateral cerebral hemisphere.Thus, the intersection of the callosal and perforating fiber systems during development may be related both to the sequential development of each pathway and to the altered nonneuronal environment at the point of intersection.

ISSN:0092-7317    

DOI:10.1002/cne.902720203

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

年代:1988

数据来源: WILEY

摘要:

AbstractIn this study we have examined the developmental fate of a population of cells that is located beneath the rostral corpus callosum during the perinatal period. These cells form a distinct slinglike structure along the geographically defined corticoseptal boundary (CSB) and may play a role in guiding callosal axons across the midline. The sling is a transient structure present in fetal and neonatal animals but not in adults.Here we show that the CSB cells die and that this debris is removed by macrophages. The sequence of cell degeneration in the CSB is highly stereotyped and follows a spatiotemporal pattern that is correlated with fusion of the cerebral hemispheres and subsequent growth across the midline of the callosal axons. The subcallosal location of the resorbing CSB is found in the exact place in which a fluid‐filled cavity (the cavum septi pellucidi) is transiently found during the perinatal period.The tight temporal and spatial correlation between callosal axon decussation, degeneration of the CSB, and cavum septi formation suggests that these three phenomena may be causally relate

ISSN:0092-7317    

DOI:10.1002/cne.902720204

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe aim of the experiments reported here was to identify cortical and subcortical forebrain structures from which anterior cingulate cortex (CGa) receives input in the cat. Deposits of retrograde tracers were placed at nine sites spanning the anterior cingulate area and patterns of retrograde transport were analyzed.Thalamic projections to CGa, in descending order of strength, originate in the anteromedial nucleus, lateroposterior nucleus, ventroanterior nucleus, rostral intralaminar complex, reuniens nucleus, mediodorsal nucleus, and laterodorsal nucleus. Minor and inconsistent ascending pathways arise in the paraventricular, parataenial, parafascicular, and subparafascicular thalamic nuclei. The basolateral nucleus of the amygdala, the hypothalamus, the nucleus of the diagonal band, and the claustrum are additional sources of ascending input.Cortical projections to CGa, in descending order of strength, derive from posterior cingulate cortex, prefrontal cortex, motor cortex (areas 4 and 6), parahippocampal cortex (entorhinal, perirhinal, postsubicular, parasubicular, and subicular areas), insular cortex, somesthetic cortex (areas 5 and SIV), and visual cortex (areas 7p, 20b, AMLS, PS and EPp).In general, the limbic, sensory, and motor afferents of CGa are weak. The dominant sources of input to CGa are other cortical areas with highorder functions. This finding calls into question the traditional characterization of cingulate cortex as a bridge between neocortical association areas and the limbic system.

ISSN:0092-7317    

DOI:10.1002/cne.902720205

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

年代:1988

数据来源: WILEY

摘要:

AbstractWe have analyzed the cortical and subcortical afferent connections of the medial prefrontal cortex (MPF) in the cat with the specific aim of characterizing subregional variations of afferent connectivity. Thirteen tracer deposits were placed at restricted loci within a cortical district extending from the proreal to the subgenual gyrus. The distribution throughout the forebrain of retrogradely labeled neurons was then analyzed.Within the thalamus, retrogradely labeled neurons were most numerous in the mediodorsal nucleus and in the ventral complex. The projection from each region exhibited continuous topography such that more medial thalamic neurons were labeled by tracer from more ventral and posterior cortical deposits. Marked retrograde labeling without any sign of topographic order occurred in a narrow medioventral sector of the lateroposterior nucleus. Several additional thalamic nuclei contained small numbers of labeled neurons. In a subset of nuclei closely affiliated with the limbic system (the parataenial, paraventricular, reuniens, and basal ventromedial nuclei), retrograde labeling occurred exclusively after deposits at extremely ventral and posterior cortical sites.Within the amygdala, retrogradely labeled neurons occupied the anterior basomedial nucleus, the posterior basolateral nucleus, and a narrow strip of the lateral nucleus immediately adjoining the basolateral nucleus. The number of labeled neurons was greater after more ventral deposits. Very ventral deposits resulted in extensive labeling of the cortical amygdala.Within the cerebral cortex, the distribution of labeled neurons depended on the location of the tracer deposit. Comparatively dorsal deposits produced prominent retrograde transport to the anterior and posterior cingulate areas, to the agranular insula, and to lateral prefrontal cortex. Comparatively ventral deposits gave rise to prominent labeling of the hippocampal subiculum, various parahippocampal areas, and prepiriform cortex.On the basis of afferent connections, it is possible to divide the cat's medial prefrontal cortex into an infralimbic component, MPFil, marked by strong afferents from prepiriform cortex and the cortical amygdala, and a dorsal component, MPFd, without afferents from these structures. Further, within MPFd, it is possible to define an axis, running from ventral and posterior to dorsal and anterior levels, along which limbic afferents gradually become weaker and projections from cortical association areas gradually become stronger.

ISSN:0092-7317    

DOI:10.1002/cne.902720206

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

年代:1988

数据来源: WILEY

摘要:

AbstractIn newborn kittens, cortical auditory areas (including AI and AII) send transitory projections to ipsi‐ and contralateral visual areas 17 and 18. These projections originate mainly from neurons in supragranular layers but also from a few in infragranular layers (Innocenti and Clarke:Dev. Brain Res. 14:143–148, 84; Clarke and Innocenti:J. Comp. Neurol. 251:1–22, 86). The postnatal development of these projections was studied with injections of anterograde tracers (wheat germ agglutinin‐horseradish peroxidase [WGA‐HRP]) in AI and AII and of retrograde tracers (WGA‐HRP, fast blue, diamidino yellow, rhodamine‐labeled latex beads) in areas 17 and 18. It was found that the projections are nearly completely eliminated in development, this, by the end of the first postnatal month. Unitl then, most of the transitory axons seem to remain confined to the white matter and the depth of layer VI; a few enter it further but do not appear to form terminal arbors. As for other transitory cortical projections the disappearance of the transitory axons seems not to involve death of their neurons of origin. In kittens older than 1 month and in normal adult cats, retrograde tracer injections restricted to, or including, areas 17 and 18 label only a few neurons in areas AI and AII. Unlike the situation in the kitten, nearly all of these are restricted to layers V and VI. A similar distribution of neurons projecting from auditory to visual areas is found in adult cats bilaterally enucleated at birth, which suggests that the postnatal elimination of the auditory‐to‐visual projection is independent of visual experience and more generally of information comin

ISSN:0092-7317    

DOI:10.1002/cne.902720207

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

年代:1988

数据来源: WILEY

摘要:

AbstractBy employing a combination of the immunohistochemistry for rat corticotropin‐releasing factor (rCRF) and retrograde tracing with biotinylated wheat germ agglutinin (b‐WGA) injected into the posterior pituitary (group 1) or into the middle portion of the median eminence (group 2), functionally different populations of CRF neurons were identified in the rat hypothalamus. In the group 1 animals, WGA‐labeling was seen not only in the posterior lobe but also in the intermediate lobe, in which CRF fibers exist. In these animals, WGA‐labeling occurred for almost all large neurons in the anterior commissural, paraventricular (PV), and supraoptic (SO) nuclei, some of the neurons showing a slight immunoreactivity for anti‐rCRF. Conversely, CRF positive neurons appeared in large numbers, some being labeled with WGA, in the caudal periventricular region (CPR), and in the dorsomedial to lateral hypothalamic area (DLH), especially in the latter. In the group 2 animals, WGA was disparsed throughout the subependymal, internal, and external layers of the medial portion of the median eminence, and was taken up by many small cells in the PV, almost half of the cells being immunoreactive for CRF. Slight WGA‐labeling further occurred in some large neurons of the PV and SO, and in some cells of the DLH. It is concluded that hypophysiotropic CRF existing in the external layer of the median eminence originates from small neurons located in the PV, whereas CRF distributed in the posterior and intermediate pituitary originates from the magnocellular PV and SO, and from some neurons in the

ISSN:0092-7317    

DOI:10.1002/cne.902720208

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

年代:1988

数据来源: WILEY

摘要:

AbstractNeurotensin is widely distributed in the central and peripheral nervous systems. Extensive radioimmunoassay and immunohistochemical studies in rats show that the neurotensin immunoreactive perikarya and fibers are most prominent in the hypothalamus. Radioimmunoassay studies have suggested that the levels of neurotensin in the hypothalamus of cats may be six times higher than that of rats. We studied the distribution pattern of neurotensin immunoreactivity within the hypothalamus of the cat by avidinbiotin modification immunohistochemical methods: (1) to define its distribution pattern within the hypothalamus, and (2) to compare our findings with the patterns that have been described in rats. Results show that neurotensin immunoreactive cell bodies and fibers are most prominent in the rostral and intermediate regions of the cat hypothalamus. Cell bodies with neurotensinlike immunoreactivity are seen maximally in the medial preoptic region, the infundibular nucleus, and the lateral hypothalamus. The neurotensin positive fibers are dense in the periventricular regions of the entire rostrocaudal extent of the hypothalamus. This pattern of distribution of neurotensin immunoreactivity is similar to that described in rats. The suprachiasmatic nuclei of the cat hypothalamus, however, contained a significant number of neurotensin immunoreactive cell bodies, an observation not noted in the rat hypothalamus. The neurotensin immunoreactive neurons were more numerous in the lateral hypothalamus than has been reported in rats, but the paraventricular nucleus of the hypothalamus in cats contained fewer neurotensin immunoreactive perikarya. The presence of neurotensin immunoreactive perikarya in the suprachiasmatic nucleus and the apparent increase in the number of neurotensin immunoreactive neurons in the lateral hypothalamus may account for the increased levels of neurotensin reported in cats. Neurotensin has been speculated to play a role in nociception, thermoregulation, and control of arterial pressure by acting as a hormone or a neurotransmitter. Details of the pattern of colocalization of neurotensin with that of other neuropeptides and neurotransmitters will aid in our understanding of its role in these functions.

ISSN:0092-7317    

DOI:10.1002/cne.902720209

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

年代:1988

数据来源: WILEY

摘要:

AbstractWe have performed a serial‐section electron microscopic study of the inner plexiform layer (IPL) of the retina of the turtlePseudemys scripta elegans.A qualitative and quantitative assessment of the neuropil of the IPL has been done from photomontages taken from the linear visual streak area and peripheral retina.Counts of conventional, ribbon, serial, and reciprocal synapses, of ganglion cell dendrites, and of profiles containing large, dense‐cored vesicles were made in five equal‐thickness strata in each montage. Averages of these different features were plotted for each stratum in the linear visual streak and compared with peripheral retina. The trend was for stratum 2 to have the highest overall absolute number of amacrine and bipolar interactions, and also of serial synapses, both in the linear visual streak and in peripheral regions. Stratum 4 tended to have the second‐highest number of synapses. The total number of synapses for the entire thickness of the IPL, regardless of stratification, is higher in the streak than in the periphery. The total amacrine‐to‐bipolar‐synapse ratio in the IPL is the highest of any vertebrate studied to date (11.0 in the streak and 14.5 in the periphery) but the number of synapses\μm2was found to be similar to that reported for other vertebrates. Amacrine‐to‐amacrine synaptic contacts greatly outnumber other types of synapses; amacrines constitute the principal input to ganglion cells, whereas bipolar output is mainly onto amacrines.The trend for higher numbers of synaptic interactions in strata 2 and 4 of the streak region of the turtle IPL can be correlated with the branching of small‐field amacrine and ganglion cells described in Golgi studies (Kolb:Philos. Trans. R. Soc. Lond. B 298:355–393, 82). In peripheral retina, branching of large‐field amacrines and a lower number of bipolar pathways may account for the trend for larger numbers of amacrine synapses in strata 2 and 4. Profiles having large, dense‐cored vesicles tend to occur most frequently in strata 1 and 5, which correlates well with the stratification in the IPL of the processes of immunoreactive amacrine cells

ISSN:0092-7317    

DOI:10.1002/cne.902720210

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

年代:1988

数据来源: WILEY

摘要:

AbstractPhysiological studies suggest that the function of the visual cortical gamma‐aminobutyric acid (GABA) system is abnormal in cats reared in total darkness. The present study asked whether visual input is necessary for the normal postnatal anatomical development of the GABA system by comparing GABA neurons and receptors in the visual cortex of normal and dark‐reared cats. Immunohistochemical techniques (anti‐GABA) were used to localize GABA neurons. In both rearing conditions, GABA neurons were stained rather uniformly in all cortical layers. Counts of GABA cells indicated a marked increase in density in dark‐reared compared to normal cats. Counts of total cellular density in cresyl‐stained sections, however, indicated a comparable increase in dark‐reared cats. When corrected for total cellular density, there were no differences between dark‐reared and normal cats in the density of GABA cells per layer, or the relative proportion of GABA cells across cortical layers.In vitro receptor binding of3H‐muscimol was used to compare GABAAreceptors in the two rearing conditions. When corrected for total cellular density, saturation kinetics indicated no difference in the total number or affinity of receptors. Similarly, autoradiographic histology indicated no difference in the laminar distribution of receptors across cortical layers between dark‐reared and normal cats.These results indicate that the postnatal development of GABA neurons and receptors occurs normally in the absenc

ISSN:0092-7317    

DOI:10.1002/cne.902720211

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

年代:1988

数据来源: WILEY