摘要:

AbstractExtracellular recordings were obtained of 177 neurons throughout the lumbar spinal dorsal horn of urethane‐ or halothane‐anesthetized rats. These neurons all responded to Iontophoretically applied L‐glutamate and their responses to natural stimulation of the ipsilateral hindlimb were characterized. Iontophoretically applied norepinephrine was tested on 94 of these neurons. Fifty‐one neurons were inhibited and 22 were excited. Norepinephrine produced a biphasic inhibitory/excitatory effect on nine neurons. Norepinephrine was exclusively inhibitory on superficial dorsal horn neurons that responded only to innocuous brush and touch and on neurons in the nucleus proprius that responded to brush, touch, and noxious skin pinch. Norepinephrine excited some superficial brush/touch/pinch neurons and produced short inhibitions that were followed by prolonged excitations of some nucleus proprius neurons that responded only to noxious skin pinch. Neurons in the base of the dorsal horn that responded to low‐threshold proprioceptive stimulation were excited by norepinephrine. Both the inhibitory and excitatory effects of norepinephrine were stereoselective, but they were not blocked by receptor subtype‐selective antagonists. Desensitization to norepinephrine occurred for 30% of the neurons.This study demonstrates that the inhibitory effects of norepinephrine on rat dorsal horn neurons are not restricted to neurons that are responsive to noxious stimuli and that some of these neurons are primarily excited by norepinephrine. The excitatory effects of norepinephrine on low‐threshold proprioceptive neurons may contribute to norepinephrine's known enhancement of spinal flexor re

ISSN:0092-7317    

DOI:10.1002/cne.902550102

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractA minor population of cone photoreceptors (called B‐cones) can be distinguished from the major population (called R‐cones) on morphological criteria as seen by light microscopy in foveal and peripheral human retina. The B‐cones are characterized by (1) a longer inner segment projecting into subretinal space, (2) a larger‐diameter inner segment, (3) an increased staining intensity of the inner segment, and (4) a different distribution relative to the R‐cones in the cone mosaic. B‐cones occur even in the foveolar center (3–5%) and rise to a maximum (15%) in the foveolar slope. They can also be identified in peripheral retina where they form 7–10% of the total cone population. The B‐cone population follows the distribution profile postulated for the blue‐sensitive system from histochemical studies on monkeys and from psychophysical studies on humans. The B‐cones also share many of the same morphological features of the putative blue cones of the ground squirrel and monkey retinas. For these reasons we suggest that our B‐cone group is the blue cone populat

ISSN:0092-7317    

DOI:10.1002/cne.902550103

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have studied the distribution of astrocytes in the ganglion cell and nerve fibre layers of the retina in cat, rat, rabbit, and possum using antiserum and a monoclonal antibody against glial fibrillary acidic protein (GFAP) and our own monoclonal antibody against glial filaments. The distribution of retinal astrocytes appears to be strongly determined by the vasculature of the retina; astrocytes are absent from almost all the retina of the possum and from the avascular regions of the rabbit retina. In the cat and rabbit, retinal astrocytes also show a strong affinity for the bundles of ganglion cell axons found at the inner surface of the retina.Retinal astrocytes do not invest the somas of ganglion cells, and even in areas of retina in which they are numerous, they are sharply confined to the layer of ganglion cell axons. It is suggested that retinal astrocytes are “immigrant” fibrous astrocytes that enter the retina with its vasculat

ISSN:0092-7317    

DOI:10.1002/cne.902550104

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractPrevious studies have shown that after embryonic day 50 (E50) the kitten retina undergoes a relatively rapid period of maturation that begins at the area centralis and spreads toward the retinal periphery. The mechanism controlling this pattern is unknown. One possibility is that the area centralis is the most developmentally advanced region of retina from the earliest stages of eyecup formation. The present study tests this hypothesis.Retinae from ten kittens aged between E21 and E54 were sectioned horizontally at 10 μm and stained with haematoxylin and eosin. During the earliest stages of development in other vertebrate species, the oldest part of the retina is at the posterior pole of the eyecup, just dorsal to the optic fissure. At E21 in the kitten retina, this site appeared to be developmentally advanced by several criteria. A developmentally advanced region (DAR) was recognized at each subsequent age. It gradually became displaced temporally toward the site of the area centralis in the adult. Developmental events beginning here include the formation of cell‐free channels at the vitreal margin; the appearance of the first ganglion cells and their axons; the formation of continuous inner and outer plexiform layers; the differentiation of cells in the ganglion cell, inner, and outer nuclear layers; and the cessation of cytogenesis at the outer limiting membrane. By E54 the DAR could be recognized as the area centralis by the criteria used in the adult.Between E25 and E37 cell density in the ganglion cell layer is higher in the DAR than at other retinal eccentricities. During the E40s cell density becomes uniform across the retina because more cells migrate into the ganglion cell layer in peripheral retina than in the DAR. Several observations suggest that cells added to the ganglion cell layer from E37 onward are not ganglion cells.The proportion of retinal area occupied by the DAR decreases geometrically between E21 and E54, indicating that this region grows at a slower rate than the rest of the retina. It is suggested that this differential growth combined with differential cell addition may be the principal mechanism responsible for generating centroperipheral cell gradients in the reti

ISSN:0092-7317    

DOI:10.1002/cne.902550105

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe size and branching structure of the dendritic tree were studied in nine type‐identified triceps surae α‐motoneurons that were labeled intracellularly with horseradish peroxidase and reconstructed from serial sections in the light microscope. The average total membrane area (AN) for motoneurons of type S (slow‐twitch) motor units was about 22% smaller than ANfor cells of type F units (including both FF and FR motor unit types in this category) (480.1 × 103μml;m2vs. 617.7 ×103μm2, respectively). Systematic correlations were found between stem dendrite diameter and three measures of dendritic size: dendrite membrane area, combined dendritic length, and number of terminations. All of these correlations were significantly different for the dendrites of F and S montoneurons. Power‐function relations between stem diameter and dendritic membrane area were used to estimate ANfor a sample of 79 type‐identified motoneurons. Mean estimated ANvalues were significantly different for the F and S motoneuron groups, despite a large overlap in ANvalues between these groups.The branching structure of dendrites of F and S motoneurons also showed clear differences. Type S motoneuron dendrites showed less‐profuse branching and a more‐even radial distribution of branch points than found in type F cells. Examination of two forms of the “3/2 power rule” for the relation between the diameters of parent and daughter dendritic branches at branch points showed that the dendrites of type S motoneurons conform less well with the anatomical constraints necessary to represent binary branching trees as equivalent cylinders than do dendrites of type F cells. There was no systematic difference between F and S motoneuron dendrites in the degree of asymmetry of first‐order daughter trees. The results overall indicate that the dendrites of F and S motoneuron groups are structurally different, giving rise to a systematic difference in ANbetween these groups. Such structural differences suggest that the F and S groups of α‐motoneurons can be viewed as intrinsically distinct cell types and not just large vs. small varian

ISSN:0092-7317    

DOI:10.1002/cne.902550106

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have studied the spatial distribution of dendrites of type‐identified triceps surae α‐motoneurons, labeled intracellularly with HRP, using a variety of analytical approaches that were designed to quantify the ways in which dendrites occupy three‐dimensional space. All of the methods indicated a strong tendency for motoneuron dendrites to project radially. However, regions dorsal and ventral to the somata contained fewer dendritic elements, and less membrane area, than expected for complete radial symmetry. Individual dendrites projecting into these regions tended to be smaller than those projecting rostrocaudally or mediolaterally. Nevertheless, the center of mass of membrane area for five of six fully analyzed cells was within 100 μm of the soma and, in all six cells, was located in the same dorsoventral plane as the cell soma. Maps of the projection of dendritic branches onto concentric shells at various radial distances from the soma showed that some regions have high concentrations of branches, sometimes with considerable overlap between branches arising from different stem dendrites, while other regions have relatively few branches, or none at all. Each motoneuron exhibited a different pattern of projection and there were no systematic differences between fast‐twitch (type F, including both types FF and FR units) and slow‐twitch (type S) motoneurons evident in the patterns of dendritic concentration. Assessment of the three‐dimensional territories of individual dendrites showed that dendrites with larger numbers of terminal branches tended to have larger spatial territories. Despite considerable scatter, the results suggest that the density of branches tends to be approximately the same in large and small dendrites, and in F and S cell groups. The results are discussed in relation to the spatial location of synaptic input t

ISSN:0092-7317    

DOI:10.1002/cne.902550107

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIn mammals binocular vision is made possible by the existence in the temporal retina of ipsilaterally projecting ganglion cells (IGCs) (with axons that do not cross the brain midline and join optic fibers from the opposite eye). To learn whether early interactions between fibers of each eye play a role in generating a mixed ipsi + contralateral projection pattern, we studied with horseradish peroxidase the origin of uncrossed retinal projections in mice that developed after one eye was destroyed at very early embryonic ages. One eye was removed on embryonic day 16 (E16; when optic fibers have grown past the chiasm bilaterally, but very few have grown into the visual centers) or onE13orE12(when few or no optic fibers have passed the presumptive chiasm region).Normal adult mice have a mean of 946 IGCs (range: 784–1,073) within the temporal sector of the retina, and less than 25 in the rest of the retina. In adult mice enucleated atE16, an average of 1,354 (1,215–1,484) IGCs are present within a clearly demarcated temporal sector of the remaining retina and 265 (152–312) are present throughout the rest of the retina. In both the temporal and nasal retina the excess IGCs in these mice have, generally, very small somas. In some of these mice the most peripheral part of the temporal sector contains fewer IGCs. InE12orE13enucleates, IGCs are also generally located in a narrow (often narrower than normal) region along the temporo‐inferior retinal border, but their number is less than in normal or E16‐enucleated mice: E13 enucleates have a mean of 639 cells (range: 361–875) in the temporal sector and 109 (8–275) in the rest of the retina. Following enucleation of one mouse at E12, the respective values are 349 and 31 cells. The reduction in numbers of IGCs in these mice is especially pronounced for ganglion cells with small cell bodies.These findings suggest that the development of uncrossed projections in mice depends on selective guidance mechanisms of axons from temporal retina through the chiasm. These may consist of interactions of optic axons with guidance cues distributed in the presumptive chiasm (possibly at early stages) and also of fiber‐fiber guidance mechanisms, in particular between fiber

ISSN:0092-7317    

DOI:10.1002/cne.902550108

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe fine structure of neurons containing human growth‐hormone‐releasing factor (hGRF) immunoreactivity located in the arcuate nucleus of the guinea pig was studied by means of the preembedding immunohistochemical technique.The perikaryon of labeled neurons was fusiform or ovoid; the nucleus was regular in shape and contained a prominent nucleolus. The main ultrastructural features of the hGRF‐immunoreactive neurons were (1) the presence of numerous labeled secretory granules (100–120 nm in diameter) and (2) the abundance and the enlargement, of the organelles involved in the synthesis of the peptides: a well‐developed rough endoplasmic reticulum and a conspicuous Golgi apparatus. Synaptic inputs were observed on immunoreactive perikarya but, above all, on the labeled dendrites. The unstained presynaptic nerve endings most often contained only small clear vesicles and formed symmetrical contacts. In rare cases, the presynaptic terminals exhibited both small clear and large dense vesicles and constituted asymmetrical contacts. Immunoreactive nerve endings were also observed in this area: the synaptic boutons contained large, stained vesicles and small, unlabeled, clear vesicles. These axon terminals made synaptic contacts with unstained dendritic processes; the contacts were symmetrical.The results indicate that hGRF‐immunoreactive neurons of the guinea pig arcuate nucleus present morphological features of neuroendocrine cells. Moreover, the presence of hGRF‐labeled nerve endings in the arcuate nucleus itself suggests that a substance related to hGRF might be a neuromodulator, at least

ISSN:0092-7317    

DOI:10.1002/cne.902550109

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe hypothalamic distribution of cholecystokinin‐immunoreactive (CCKI) cell bodies in colchicine‐treated male and female rats was studied. Immunoreactive neurons were visualized along the anterior two‐thirds of the third ventricle but were especially numerous in the preoptic periventricular nucleus. Dense aggregations of CCKI cells were found in the anterior magnocellular, posterior magnocellular, medial parvicellular, and posterior parvicellular divisions of the paraventricular nucleus. Both the supraoptic nucleus and the central, cell‐dense part of the dorsomedial nucleus contained large numbers of CCKI cells.CCKI cells in the preoptic periventricular nucleus were more numerous in the female, as was a population of labeled cells in the dorsal medial preoptic area. However, CCKI cell bodies in this part of the medial preoptic area were larger in males than in females. Males had more CCKI cells in the central part, of the medial preoptic nucleus and in the posterior magnocellular subdivision of the paraventricular nucleus. Both males and females had similar numbers of immunoreactive cells in the anterior magnocellular and the parvicellular divisions of the paraventricular nucleus as well as in the anterior hypothalamus, dorsal areas, dorsomedial nucleus, and supramammillary region. These data provide morphological evidence for a sexually differentiated hypothalamic CCKI

ISSN:0092-7317    

DOI:10.1002/cne.902550110

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractCytochrome oxidase (CO) activity was examined in the neostriatum of normal adult rats at the tight and electron microscopic level. At the light microscopic level a heterogeneous distribution of CO activity was observed and was characterized by patches of high activity ranging in size from 200 to 800 μm surrounded or adjacent to regions of lower activity. The most dorsomedial and ventromedial regions of the caudate nucleus appeared to be consistently high in activity in all animals. At the ultrastructural level CO reaction product was localized to the membranes and intracristal spaces of mitochondria. The most reactive mitochondria (those containing the densest precipitates of reaction product) were found within the dendrites of spiny neurons in all caudate regions. In areas of high CO activity the mitochondria within bundles of myelinated fibers and in many axon terminals were also highly reactive whereas those in neuronal somata, primary dendrites, and glial cells and processes exhibited relatively little activity.Quantitative study showed that mitochondria within dendrites accounted for most of the CO activity in caudate neuropil. The mitochondria within dendrites and axon terminals were more reactive in regions of high CO activity than in regions of low CO activity. No differences in the density of synapses or in the proportions of axospinous and axodendritic synapses were observed between CO‐rich and CO‐poor areas.Heterogeneity in the distribution of CO activity in the caudate nucleus may be related to the “patchy” pattern of localization previously observed for some neostriatal afferents, enzymes, transmitters, peptides, and receptor ligands. Also the present results suggest that differences in metabolic activity between regions of the caudate nucleus may depend more on the relative frequency of neuronal discharge at individual synaptic sites than on the density of synapses present within a given area. The high metabolic demands of spiny dendrites as compared to other neuronal profiles in the neostriatum may reflect their level of synaptic activity, since spines are known to participate in the majority of synapses in the caudate

ISSN:0092-7317    

DOI:10.1002/cne.902550111

出版商:Alan R. Liss, Inc.    

年代:1987

数据来源: WILEY