摘要:

AbstractThe differentiation of serotonin‐immunoreactive (5‐HTi) neurons in the optic lobes of fleshflies was studied during in situ development and in in vivo cultures. All 5‐HTi neurons with cell bodies in the imaginal optic lobes differentiate during postembryonic (pupal) development. These are local anaxonal neurons. In addition there are two large 5‐HTi bilateral neurons that connect all optic lobe neuropil regions on both sides of the brain and have their cell bodies in the midbrain proper.Deafferentation of optic lobes cultured in vivo leads to drastic reduction in optic lobe volume and increased cell death. All the 5‐HTi neurons differentiate after deafferentation but their morphology changes. The neuropil receiving the photoreceptor inputs, the lamina, degenerates but a disorganized “pseudolamina” is formed by the processes of the two large 5‐HTi neurons. The layering of the optic lobe neuropils cannot be distinguished and 5‐HTi processes form novel projectional patterns. Hence, the 5‐HTi neurons do not require afferent inputs from the retina for their differentiation and survival, but the effect on other optic lobe interneurons is reflected in the morphological plasticity o

ISSN:0092-7317    

DOI:10.1002/cne.902550302

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractNeuronal and synaptic reorganization in the lateral geniculate nucleus (dLGN) of adult cats following chronic visual deafferentation has been investigated with the aid of GABA immunocytochemistry and quantitative electron microscopy. The main purpose of this study was to establish the morphological counterpart of the functional plasticity of dLGN relay cells after total visual deafferentation (Eysel:Brain Res. 166:259–271, '79). The results provide evidence that the regained excitability of relay cells is not the result of disinhibition (caused hypothetically by the selective loss of GABAergic cells) since the proportion of GABA‐positive and GABA‐negative cells as well as the inhibitory synaptic density did not change. The alternative suggestion that the enhanced excitability could be the result of compensatory axonal sprouting by corticothalamic fibers had also to be dropped: the absolute number of corticothalamic axons to the deafferented dLGN remains unchanged. Because of shrinkage of the dendritic trees of dLGN neurons, however, the density of cortical synaptic input at dLGN cells becomes elevated by almost 60%. It is suggested that the regained excitability of relay neurons is the consequence of the combined effects of (1) adaptive (structural) reduction in size (“atrophy”) of retinally denervated nerve cells, and, as a consequence, (2) increase of input resistance, (3) reduced shunting effects, and (4) relative increase in density of the excitatory cortical input p

ISSN:0092-7317    

DOI:10.1002/cne.902550303

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn this paper we characterize the architecture and segmental innervation, histochemical composition, muscle spindle populations, and motor pool organization of rat spinal accessory (SA) muscles: sternomastoid (SM), cleidomastoid (CM), cleidotrapezius (CT), and acromiotrapezius (AT). We also consider (1) whether individual rat neck muscles are supplied by more than one population of motor neurons as they are in turtles and cats and (2) whether in SA muscles motor neuron size scales with target muscle fiber type.SM, CM, and CT are ventral, parallel strap muscles. Each can be divided into grossly visible white and red compartments. AT is a dorsolateral sheetlike muscle that shows no gross compartmentalization. All four muscles are dominated by fast‐twitch glycolytic (FG) and fast oxidative glycolytic (FOG) fibers, and FG fibers are significantly more numerous than the FOG type in three out of four muscles. Thus SA muscles in rats appear to be specialized for rapid, phasic head movements. Topographical analyses revealed that there is a striking compartmentalization of fiber types in the ventral muscles that corresponds to the red and white segments seen grossly. Spindles are found only in regions containing slow‐twitch oxidative (SO) fibers. Cross‐muscle comparisons indicate that there are significant differences between SA muscles in their fiber type composition.The motor pools of SA muscles form a single column from lower medulla to C5. Rostral cells lie dorsomedially in the ventral horn and, at the C1/C2 junction, the column shifts ventrolaterally. Within this column, each motor pool occupies a characteristic rostrocaudal position in the order SM:CM:CT:AT. Thus SM and (in part) CM motor neurons lie more medially than cells supplying the trapezius complex, suggesting that they may be under different patterns of synaptic drive. We saw no evidence that rat SA muscles are supplied by more than one population of motor neurons. Direct comparisons between the soma sizes of motor neurons that supply muscles or parts of muscles with significantly different histochemical compositions indicate that these size differences are in the direction predicted from their histochemical profiles, thus suggesting that in these muscles motor neuron soma size may scale with muscle fiber

ISSN:0092-7317    

DOI:10.1002/cne.902550304

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn this paper we characterize the architecture, histochemistry, spindle composition, and motor pool organization of rat dorsal neck muscles: splenius (SP), biventer cervicis (BC) and complexus (COM). We also consider (1) whether individual rat neck muscles are innervated by more than one population of motor neurons as they are in turtles and cats and (2) whether in these muscles motor neuron size scales with muscle fiber type.Dorsal neck muscles are divided by tendinous inscriptions into quasiserially arranged compartments. Each compartment is supplied by a separate peripheral nerve branch from C1–C5 dorsal rami; thus each dorsal neck muscle is innervated from multiple segments. Our histochemical data indicate that slow‐twitch oxidative (SO) fibers are always the least numerous group, and fast fibers are split almost equally between fast oxidative glycolytic (FOG) and fast glycolytic (FG) types. There are significant cross‐muscle differences in the relative frequency of each fiber type. Topographic analyses reveal a mosaic pattern of fiber types with no clear compartmentalization, and muscle spindle distribution is essentially homogeneous.Motor neurons supplying rat dorsal neck muscles are restricted to the ventral third of the ipsilateral ventral horn from lower medulla to C4. The SP motor pool is located dorsally in the ventral horn, and BC and COM motor pools form overlapping columns in the tip. There is little evidence that these muscles are supplied by more than one population of motor neurons, as reported in turtles and cats. To help assess these differing results, in two cats we infiltrated the C2 nerve to BC and COM; our results were similar to those previously reported in cats including the presence of contralateral motor neurons. Thus disparate results between rat and cat experiments may represent species differences in neck muscle innervation. In five experiments we made direct comparisons between the sizes of motor neurons that supply muscles with significantly different histochemical compositions. In each case there was a difference in mean soma size in the direction predicted by the muscles' histochemical profiles, thus suggesting that in these muscles motor neuron size may scale with muscle fiber

ISSN:0092-7317    

DOI:10.1002/cne.902550305

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn this study we have examined the trajectories taken by populations of ganglion cell axons and the spatial gradients of terminal arbor maturity within the lateral geniculate nucleus (LGN) during the prenatal development of the cat's visual system. To do so, anin vitromethod of labeling optic tract axons from fetal brains between embryonic day 37 (E37) and postnatal day 2 (P2) with horseradish peroxidose (HRP) was used.At the earliest ages studied (E37–E53), optic axons leave the optic tract to run across the LGN toward their sites of termination in straight trajectories parallel to each other. At later ages (E57–P2), however, axons with abrupt changes in their course across the nucleus can be clearly identified. When the detailed terminal arbor morphology of the set of retinogeniculate axons filled with HRP at a given age was examined, two different spatial gradients of maturation could be detected. The terminal arbors of axons within LGN layer A are always more mature than those ending in layer A1, an observation consistent with previous findings that axons from the contralateral eye arrive within the LGN several days before those from the ipsilateral eye. Moreover, the terminal arbors of axons projecting to the medial portions of each layer are always more mature than their more lateral counterparts. These gradients are likely to be a direct reflection of the central‐first, peripheral‐last gradient associated with the neurogenesis of the retinal ganglion cells themselves.In the oldest animals studied (E58–P2), a remarkable periodic pattern of terminal arbor labeling was seen following a localized HRP injection into the optic tract. Within the labeled portions of the LGN, densely filled axon terminal arbors are separated by unlabeled gaps of similar width. This pattern of labeling could reflect local topographic disorder within the optic tract or could arise if axons of different classes of retinal ganglion cells run in separate portions of the optic tract.Taken together, all of these observations suggest that there may be a fair degree of topographic order in the retinogeniculate projection within the cat's LGN early on in development. However, when topographic errors are present, some can be corrected by minor readjustments in axonal tra

ISSN:0092-7317    

DOI:10.1002/cne.902550306

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe developed a flat‐mount technique in order to visualize, without additional reconstruction, the system of orientation columns in the cat visual cortex by using 2‐deoxyglucose‐autoradiography.Experimental animals were injected with 2‐deoxyglucose and then stimulated for 45–60 minutes either with vertical or horizontal or oblique gratings alone or with vertical and horizontal gratings presented in alternation.In both areas 17 and 18 stimulation with either vertical or horizontal or oblique stripes produced similar and highly ordered patterns of parallel bands of increased 2‐deoxyglucose uptake that were perpendicular to the boundaries of the areas. In area 17 they occasionally extended without interruption from the 17/18 border on the top of the lateral gyrus to the monocular segment in the splenial sulcus. Superposition of serial sections revealed that these bands were present in all cortical layers and in precise register along lines orthogonal to the lamination. The center‐to‐center spacing of the bands was 1.0–1.1 mm in area 17 and 1.2–1.4 mm in area 18. Stimulation with alternating vertical and horizontal contours led to a pattern the general organization of which resembled that induced by a single orientation but the spacing of which was reduced by a factor of 0.5. This strongly supports the concept that orientation is mapped in a system of parallel bands and argues against a recently formulated hypothesis that iso‐orientation bands extend like spokes from centers that lack orientation selectivity (Braitenberg and Braitenberg,Biol. Cybern, 33:179–186, '79).Another characteristic feature, revealed by the flat‐mount technique, was a periodic variation of 2‐deoxyglucose uptake along the bands that gave them a beaded appearance. The mean center‐to‐center distance between adjacent beads on the same band was in the range of 0.9–1.2 mm and remained unchanged when horizontal and vertical gratings were presented in alternation. We propose that these beads reflect another columnar system whose f

ISSN:0092-7317    

DOI:10.1002/cne.902550307

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWhen a kitten is reared with one eyelid sutured closed, there are profound changes in the developing visual system. In the lateral geniculate nucleus, the neurons in the laminae innervated by the deprived eye are smaller than normal, and some of these neurons may lose connections with the visual cortex. In the present study a variety of double label retrograde transport methods were used to define the effects of monocular deprivation on cortical projections of geniculate neurons. One marker was injected into area 17 and the other was injected into area 18. Neurons projecting to area 17 are on average 16.4% smaller than those in the nondeprived laminae. The neurons that normally would project to both areas 17 and 18 by an axon that branches are the most severely affected by monocular deprivation. These cells are nearly 40% smaller than their counterparts in the nondeprived laminae, and many of the neurons appear to lose their projection to one of the cortical areas. These neurons may be at a distinct disadvantage, since they must compete with neurons from the nondeprived laminae for a considerable amount of cortical territory in two different cortical areas. This competition may be so severe that some of the neurons are no longer capable of maintaining connections with both cortical areas.

ISSN:0092-7317    

DOI:10.1002/cne.902550308

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe enteric system is formed by cells that migrate to the bowel from the neural crest. In order to gain insight into intraenteric factors that influence this migration, the colonization of the bowel of thels/lsmouse was investigated. The terminal 2 mm ofls/lsintestine fails to become colonized by crest cells and thus remains aganglionic. The entire bowel of control mice andls/lsmice was explanted before the appearance in situ of recognizable neurons and grown in organotypic tissue culture. Neurons, detected by the histochemical demonstration of acetylcholinesterase activity, developed throughout the length of the control gut, but, even in vitro, were excluded from the terminal segment of thels/lsintestine. Co‐culture experiments were done, in which primary and secondary sources of crest cells were combined with recipient segments of bowel, to test the ability of the recipient tissue to become colonized by neural precursors. The primary source was murine crest cells migrating away from an explant of the neuraxis. Secondary sources included avian and murine foregut (control andls/ls) containing migratory crest cells as well as the quail ganglion of Remak. Recipient segments of bowel included control avian and murine hindgut, explanted before the tissue had become colonized by crest cells in situ, as well as the presumptive aganglionic bowel ofls/lsmice. Both primary and secondary sources of crest cells proved to be able to contribute neurons to the control segments of recipient hindgut. Species differences were no barrier to the colonization of the bowel in vitro. Moreover, thels/lsforegut was as good a source of neural precursors for a normal recipient bowel, as was control avian or murine foregut. In contrast, none of the sources of crest cells that were utilized contributed neurons to the presumptive aganglionic gut ofls/lsmice. Both cells and processes of enteric neurons developing in vitro (detected by demonstrating neurofilament immunoreactivity) tended to be excluded from the presumptive aganglionic tissue. On the other hand, neurites, but not cell bodies, of dorsal root ganglia co‐cultured with presumptive aganglionicls/lsbowel did enter the abnormal zone. These data are consistent with the hypothesis that nonneuronal elements of the wall of the presumptive aganglionic region of thels/lsgut are abnormal and prevent the colonization of this segment of the gut with viable neural precursors from the neural crest. This defect in thels/lsintestine is restricted to intrinsic elements and does not prevent it from becoming innervated by ingrowingextrinsicnerve fibers, such as those from dorsal root ganglia. Sincels/lscrest cells can colonize the proximalls/lsbowel as well as explants of hindgut from control mice or birds, thels/lscrest cells themselves are probably not abnor

ISSN:0092-7317    

DOI:10.1002/cne.902550309

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThis study used the retrograde transport of a protein‐gold complex to examine the distribution of spinal cord and trigeminal nucleus caudalis neurons that project to the nucleus of the solitary tract (NST) in the rat.In the spinal grey matter, retrogradely labeled cells were common in the marginal zone (lamina I), in the lateral spinal nucleus of the dorsolateral funiculus, in the reticular part of the neck of the dorsal horn (lamina V), around the central canal (lamina X), and in the region of the thoracic and sacral autonomic cell columns. The pattern of labeling closely resembled that seen for the cells at the origin of the spinomesencephalic tract and shared some features with that of the spinoreticular and spinothalamic tracts. Labeled cells in lamina IV of the dorsal horn were only observed when injections spread dorsally, into the dorsal column nuclei, and are thus not considered to be at the origin of the spinosolitary tract. They are probably neurons of the postsynaptic fibers of the dorsal column.Retrogradely labeled cells were also numerous in the superficial laminae of the trigeminal nucleus caudalis, through its rostrocaudal extent. The pattern of marginal cell labeling appeared to be continuous with that of labeled neurons in the paratrigeminal nucleus, located in the descending tract of trigeminal nerve.Since the NST is an important relay for visceral afferents from both the glossopharyngeal and vagus nerves, we suggest that the spinal and trigeminal neurons that project to the NST may be part of a larger system that integrates somatic and visceral afferent inputs from wide areas of the body. The projections may underlie somatovisceral and/or viscerovisceral reflexes, perhaps with a significant afferent nociceptive componen

ISSN:0092-7317    

DOI:10.1002/cne.902550310

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIntracellular recording and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional characteristics of the superior collicular cells in the hamster, which could be antidromically activated from the first cervical segment of the spinal cord. Thirty‐one such neurons were characterized, filled with HRP, and recovered. Complete physiological data were obtained from another 21 tectospinal cells for which anatomical data were sufficient only to define the laminar location of the cell body from which recordings were made. Of the total sample of 52 cells, 7.7% had their somata in thestratum griseum intermediale(SGI), 50% were in thestratum album intermedium(SAI), 36.5% were in thestratum griseum profundum(SGP), and 5.8% were in thestratum album profundum(SAP). The tectospinal cells were fairly uniform morphologically. They had large (27.7 ± 5.5 μm diameter) cell bodies, which gave rise to an average of 6.7 ± 1.2 primary dendrites. These were generally smooth and extended up to 500 μm away from the cell body. In many cases, they ascended out of the deep laminae into thestratum opticum(SO) and/orstratum griseum superficiale(SGS). The axons of TS cells averaged 3.4 ± 0.8 μm in diameter, and they generally coursed radially to the SAP where they curved around the periaqueductal gray and entered the predorsal bundle. These axons often gave rise to collaterals that arborized in the deep laminae of the ipsilateral superior colliculus and subjacent reticular formation.The tectospinal cells were also fairly uniform physiologically. Their average conduction latency was 2.0 ± 2.3 ms, and this variable had a strong negative correlation (−.81) with axon diameter for the recovered cells. Most (63.5%) of the TS cells were exclusively somatosensory and gave rapidly adapting responses to deflection of vibrissae and/or guard hairs; 7.7% were bimodal (visual‐somatosensory); 11.5% had complex (Rhoades et al., '83) somatosensory receptive fields; 1.9% were discharged only by a noxious pinch, and 15.4% were unresponsive. A common feature of all bimodal tectospinal neurons was dendrites that extended at least as far dorsally as the SO. Whereas there were no other clear‐cut correlations between the structural and functional characteristics of these tectal neurons, we did note thatallof the cells with complex somatosensory receptive fields received inhibitory input from axons that either originated from, or passed through, the contralateral super

ISSN:0092-7317    

DOI:10.1002/cne.902550311

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY