bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructural study of remodeled rubral afferents following neonatal lesions in the rat
Authors: Naus C. G. , Flumerfelt B. A. , Hrycyshyn A. W. 
Published: January 2005

AbstractFollowing neonatal hemicerebellectomy, an aberrant ipsilateral cerebellorubral projection develops that maintains the topographic specificity of the normal contralateral projection. Similarly, neonatal lesions of the sensorimotor cortex lead to the appearance of an aberrant contralateral corticorubral projection that mirrors the topographic specificity of the normal ipsilateral input. The specificity of synaptic localization in these aberrant projections was studied by use of ultrastructural visualization of anterogradely transported HRP‐WGA. Following neonatal ablations, adults received HRP‐WGA injections in the unablated deep cerebellar nuclei or sensorimotor cortex. After 48 hours, animals were sacrificed and processed for ultrastructural localization of anterogradely transported HRP‐WGA. In hemicerebellectomized animals, both the contralateral and ipsilateral interpositorubral projections terminated on the somatic and proximal dendritic membrane of magnocellular neurons. Some of these labeled synaptic terminals were located on somatic and dendritic spines. Following HRP‐WGA injection in the unablated nucleus lateralis, anterogradely labeled synaptic terminals were located bilaterally on small‐ to medium‐sized dendrites of parvicellular neurons. Injection of HRP‐WGA in the remaining sensorimotor cortex of animals that had undergone neonatal unilateral ablation of the sensorimotor cortex resulted in labeled corticorubral synaptic terminals that contacted distal dendrites of ipsilateral and contralateral parvicellular neurons. These results demonstrate that, following neonatal deafferentation of the rat red nucleus, the topographic specificity of the aberrant rubral afferents is accompanied by a specificity of synaptic localization on discrete membrane areas of rubral neurons.
Serotonin‐containing structures in the nucleus raphe dorsalis of the cat: An ultrastructural analysis of dendrites, presynaptic dendrites, and axon terminals
Authors: Chazal G. , Ralston H. J. 
Published: January 2005

AbstractIn the nucleus raphe dorsalis of the cat, an electron microscopic immunocytochemistry method was used to identify the fine structure of serotoninergic dendritic profiles and axon terminals analyzed in serial sections. Two classes of serotoninergic dendrites were distinguished in the nucleus. The first class was constituted by conventional serotonin (5‐HT) dendrites that were contacted by unlabeled axon terminals containing differing populations of synaptic vesicles. The second class consisted of serotoninergic dendrites that contained vesicles in their dendritic shafts. Such 5‐HT dendrites were further subdivided into two groups according to their synaptic contacts. In some 5‐HT vesicle‐containing dendrites, the vesicles were densely packed in small clusters and were associated with a well‐defined synaptic specialization. These dendrites were classified as serotoninergic presynaptic dendrites and established synaptic contacts with unlabeled and labeled dendrites and were contacted by unlabeled axon terminals. In other 5‐HT vesicle‐containing dendrites, extensive serial section examination showed that the vesicles could be observed near the membrane but were never found to be associated with any synaptic membrane specialization. Serotoninergic axon terminals that were presumed to be recurrent collaterals of 5‐HT neurons were present in the nucleus. Some of them were observed in synaptic contact with dendrites or dendritic protrusions whereas others did not exhibit synaptic specializations. The existence of serotoninergic dendrodendritic synaptic contacts and axon terminals suggests direct local interactions between serotoninergic neurons within the nucleus raphe dorsalis.
An ultrastructural analysis of afferent terminals to the anterior pretectal nucleus in the cat
Authors: Kitao Yasuko , Nakamura Yasuhisa 
Published: January 2005

AbstractThe synaptic organization of three kinds of afferent projections in the feline anterior pretectal nucleus (PTA) was analyzed by a combination of the degeneration and retrograde transport of horseradish peroxidase (HRP) techniques, along with that of the degeneration and anterograde transport of HRP techniques. Retrograde labeling of PTA neurons was performed by injections of HRP in the dorsal accessory olivary nucleus (DAO). Three kinds of afferent sources of the PTA–the cerebral motor cortex, the anterior interpositus nucleus of the cerebellum, and the gracile nucleus‐were subjected to electrolysis, suction, or injection of kainic acid or HRP for identification of axon terminals of each system. Axon terminals of these different afferent sources identified by degeneration or anterograde HRP transport techniques showed similar morphological features: They were relatively large (1–6.5 μm in diameter), contained round or ovoid synaptic vesicles, and made asymmetrical synaptic contacts. When the degeneration study was combined with the retrograde HRP transport technique, some degenerating terminals from the motor cortex, anterior interpositus, or gracile nuclei were found to synapse directly with HRP‐labeled dendrites or somata of the PTA neurons projecting to the DAO. Each combination of the degeneration and anterograde HRP transport techniques revealed the fact that neither degenerating nor HRP‐labeled terminals were found to synapse with the same neuronal structure.These observations indicate (1) that the PTA neurons relay afferent inputs from three different sources directly to the DAO, and (2) that there is a possibility of parallel processing rather than convergence of three different afferent systems via the PTA to the DAO.
Evidence for interlaminar inhibitory circuits in the striate cortex of the cat
Authors: Kisvarday Z. F. , Martin K. A. C. , Somogyi P. , Friedlander M. J. 
Published: January 2005

AbstractAn interlaminar, ascending, and GABAergic projection is demonstrated in the striate cortex of the cat. We have examined a basket cell, with soma and smooth dendrites in layers V and VI, that was injected intracellularly with HRP in the kitten. Three‐dimensional reconstruction of its axon revealed (1) a horizontal plexus in layer V and upper VI, extending about 1.8 mm anteroposteriorly and 0.8 mm mediolaterally; (2) a dense termination in the vicinity of the soma in layers V and VI; and (3) an ascending tuft terminating in layers II and III in register above the soma and about 250 μm in diameter. Many boutons of this cell contacted neuronal somata and apical dendrites of pyramidal cells and subsequent electron microscopy snowed that these boutons formed type II synaptic contacts with these structures. A random sample of postsynaptic targets (n=199) in layers III, V, and VI showed that somata (20.1%), dendritic shafts (38.2%), and dendritic spines (41.2%) were contacted. The fine structural characteristics of postsynaptic elements indicated that the majority originated from pyramidal cells. Direct identification of postsynaptic neurons was achieved by Golgi impregnation of four large pyramidal cells in layer V, which were contacted on their somata and apical dendrites by between three and 34 boutons of the HRP‐filled basket cell. Layer IV neurons were not contacted. Golgi‐impregnated neurons similar to the HRP‐filled basket cell were also found in the deep layers. The axonal boutons of one of them were studied; it also formed type II synapses with somata and apical dendrites of pyramidal cells.Boutons of the HRP‐filled neuron were shown to be GABA‐immunoreactive by the immunogold method. This is direct evidence in favour of the GABAergic nature of deep layer basket cells with ascending projections. The existence of an ascending GABAergic pathway was also demonstrated by injecting [3H]GABA into layers II and III. The labelled amino acid was transported retrogradely by a subpopulation of GABA‐immunoreactive cells in layers V and VI, in addition to cells around the injection site.The axonal pattern and mode of termination of deep basket cells make them a candidate for producing or enhancing directional selectivity, a characteristic of layer V cells. The results together with our previous data on basket cells terminating mainly either in layer IV or layers II and III demonstrate great specificity in the origin and laminar distribution of axosomatic, GABAergic, and presumably inhibitory synaptic terminals. The laminar specificity suggests that those functional properties that are brought about by basket cells have to be generated and/or reinforced at each level of cortical processing.
Development of substance P‐like immunoreactivity in Xenopus embryos
Authors: Gallagher Betty C. , Moody Sally A. 
Published: January 2005

AbstractThe development of substance P‐like immunoreactivity (SPLI) was studied in the Xenopus embryonic nervous system in order to determine in which neuronal populations and at what developmental times SPLI is expressed. Although Rohon‐Beard neurons initially were thought to be the only substance P‐immunoreactive cells in the embryonic frog spinal cord, we have demonstrated that several neuronal phenotypes are immunoreactive. The earliest evidence of SPLI was seen at stage 28 (Nieuwkoop and Faber, '67), at which time only some trigeminal ganglion cells, their axons in the ophthalmic nerve, and axons in the lateral tracts of the hindbrain showed SPLI. In the embryonic brain at stages 29/30, 37/38, and 42, SPLI was seen in the hypothalamus, trigeminal ganglion cells and their peripheral axons, the sensory roots of cranial nerve IX/X, and axons in the hindbrain lateral tracts. At premetamorphic stages, SPLI was found in several populations that are immunoreactive in adult amphibia.In the embryonic spinal cord, Rohon‐Beard neurons were labeled consistently with reaction product; there was a rostrocaudal time gradient of immunoreactivity with increasing development. The Rohon‐Beard neurons were not immunoreactive at developmental stages in which axonal outgrowth was beginning (stage 21), but were strongly immunoreactive at stages in which target cells had been contacted (stage 29). Several types of interneurons in the spinal cord (as classified by Roberts and Clarke, '82) showed SPLI during embryonic stages. At premetamorphic stages the Rohon‐Beard neurons began to disappear and the immunoreactive interneurons were distributed similarly to those reported in the adult. Dorsal root ganglia differentiated during these stages, and at this time some of the neurons belonging to these ganglia exhibited substance P‐like immunoreactivity.
Subset of neurons characterized by the presence of NADPH‐diaphorase in human substantia innominata
Authors: Ellison David W. , Kowall Neil W. , Martin Joseph B. 
Published: January 2005

AbstractThe substantia innominata encompasses an area of the basal forebrain that is ventral to the lenticular nucleus and anterior commissure, medial to the claustrum and external capsule, and lateral to the hypothalamus. The nucleus basalis of Meynert consists primarily of large acetylcholinesterase (AchE)‐positive neurons embedded within the substantia innominata. Damage to these neurons may be important in the pathogenesis of cortical dysfunction in Alzheimer's disease. In order to characterize other neuronal elements in the substantia innominata and their relationship to the nucleus basalis, we chose to study a biochemically distinct neuronal subset containing the enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH‐d).The substantia innominata was blocked from six normal brains obtained postmortem and fixed in neutral‐buffered formalin at 4°C for 48 hours. Free‐floating 50‐μm sections from several levels were stained for NADPH‐d or AchE activities. Selected sections were double stained for NADPH‐d and AchE.NADPH‐d activity was present in a network of pleomorphic neurons that extended through all levels of the substantia innominata and into the striatum and amygdala. NADPH‐d neurons were particularly numerous at the level of the anterior commisure and were closely associated with the cholinergic neurons of the nucleus basalis. They were not seen in the ventral pallidum, or the vertical limb of the diagonal band of Broca or in the islands of Calleja. The cell bodies of NADPH‐d neurons were quite varied in shape, ranging from ovoid to fusiform, and about half the cells were bipolar. Where neuronal density was high, their dendrites formed an interlacing pattern. NADPH‐d‐positive fibres were seen coursing through the external capsule, hypothalamus, and amygdala.This novel set of neurons in the substantia innominata may be part of a more extensive network that interacts with the magnocellular basal fore‐brain system at the level of the nucleus basalis. Whether other neurotransmitters are present within these neurons and whether NADPH‐d neurons are involved in Alzheimer's disease remain to be elucidated.
Redirected growth of pyramidal tract axons following neonatal pyramidotomy in cats
Authors: Tolbert D. L. , Der T. 
Published: January 2005

AbstractAfter the pyramidal tract at the pontomedullary junction in neonatal cats had been cut and the ipsilateral frontoparietal cortex injected with intra‐axonal markers at 40 to 74 days of age, cortical axons were labeled in aberrant pathways that descended into the caudal medulla and spinal cord. Some labeled axons from the damaged pyramidal tract crossed the midline, descended with fibers in the intact pyramidal tract through the pyramidal decussation, and entered the lateral corticospinal tract. Another group of aberrant projections descended bilaterally along the ventrolateral edge of the medulla and either ended in the lateral reticular nuclei or continued into the spinal cord. Finally, some axons descended individually through the central medullary tegmentum and ended bilaterally in the spinal trigeminal, dorsal column, and lateral reticular nuclei. Although these findings suggest that pyramidal tract axons regenerate after injury, the findings from a second series of experiments refute this conclusion. In 2‐to 5‐day‐old cats, the fluorescent dye Fast Blue was injected into the spinal cord, and 7 to 8 days later the contralateral pyramidal tract was cut. In these animals, there were never any cortical neurons retrogradely labeled with Fast Blue in the frontoparietal cortex ipsilateral to the pyramidotomy, although numerous neurons were labeled contralaterally. Control experiments confirmed that the interval between the Fast Blue injections and the pyramidotomies was long enough for retrogradely labeling cortical neurons, that the spinal cord injections did not adversely affect the retrogradely labeled cortical neurons, and following axotomy dying cortical neurons could be demonstrated directly using silver impregnation techniques. We conclude that neonatal pyramidotomy causes the death of all axotomized cortical neurons in kittens, and, therefore, the aberrant cortical projections seen caudal to the lesion must be redirected, late‐developing, and undamaged cortical axons, and not regenerated axons.
Development of myelinated nerve fibers in the sixth cranial nerve of the rat: A quantitative electron microscope study
Authors: Hahn Angelika F. , Chang Yoong , deF. Webster Henry 
Published: January 2005

AbstractMyelination was studied quantitatively in the sixth cranial nerves of rats by counting and measuring all myelinated fibers during the first three postnatal weeks. In transverse semithin and thin sections cut serially at a well‐defined anatomical site in the midsphenoid region, only a few axons (mean 12) were myelinated at birth. On days 2, 4, and 8, counts of myelinated fibers were respectively 5 times (mean 57), 20 times (mean 230), and 24 times (mean 273) the number seen at birth. During the second postnatal week, the number of myelinated fibers remained constant, whereas growth of axons and their myelin sheaths continued. By 15 days these fibers were large and relatively uniform in size; they had compact, circular myelin sheaths. During the third postnatal week, myelination of previously unmyelinated, smaller axons began. The number of myelinated fibers increased again and the size distribution of myelinated fibers became bimodal. Axon diameters, fiber diameters, and myelin sheath dimensions for all fibers were calculated from measurements made on electron micrographs. The transverse length of the myelin membrane increased exponentially with time. The growth increased rapidly during the formation of the first 20 spiral layers and remained relatively constant during the subsequent enlargement of the compact sheath. The association of axon diameter and myelin sheath thickness was poor at young ages, but it improved progressively with maturation of the sheath. The results show that myelination begins around axons that have a wide range of diameters. Also, the first axons to be myelinated become the large myelinated fibers of the sixth nerve. The small myelinated fibers originate from axons that do not become myelinated until the third postnatal week. Myelination, though differing in onset by 2 weeks, appeared to be similar in both populations as judged by similarity of sheath morphology and growth rates. It is of interest that at the level studied, the sixth nerve also contains a fascicle of unmyelinated cranial sympathetic fibers.
Postnatal development of the feline lateral cervical nucleus: I. A quantitative light and electron microscopic study
Authors: Broman Jonas , Flink Roland , Westman Jan 
Published: January 2005

AbstractWith the aim of obtaining some basic information for future developmental studies, the lateral cervical nucleus (LCN) was investigated in 32 kittens of different ages by electron microscopic and stereologic methods. Corresponding light microscopic measurements of neuronal and nuclear profiles and of the total LCN volume were also performed. The total LCN volume increased sixfold between the ages of 12 hours and 120 days, the most rapid increase occurring during the first month. The neuronal size was fairly constant up to the age of 9 days, whereafter it showed greater variation. The mean profile area increased rapidly during the second week and then more slowly. The relative volume of boutons increased significantly between birth and the age of 34 days and then decreased slightly up to 120 days postnatally. The total bouton volume showed a steady increase, which was most pronounced between the ages of 9 and 34 days. The relative dendritic volume decreased during the 120 days of observation, whereas the total volume of dendrites increased up to the age of 92 days and then decreased. The total volume of glial cells increased during the 120‐day observation period, as did both the relative and total volumes of myelinated axons. The changes in the relative volumes of mitochondria in boutons and dendrites were very similar, with increases that were most marked between the ages of 9 and 34 days and between 92 and 120 days.
Localization of immunoreactive tyrosine hydroxylase in the goldfish brain
Authors: Hornby P. J. , Piekut D. T. , Demski L. S. 
Published: January 2005

AbstractThis report describes the distribution of tyrosine hydroxylase immunoreactive (TH‐ir) structures in the brain of the goldfish (Carassius auratus). The localization of TH‐ir cell groups revealed by immunocytochemical techniques is largely in accordance with catecholamine distribution previously reported in teleosts by using monoamine fluorescence; however, in the telencephalon and diencephalon, several new cell groups are elucidated. In the telencephalon, TH‐ir cell bodies are observed in the olfactory bulb, area ventralis telencephali, and the central zone of the area dorsalis telencephali. TH‐ir fibers and terminals are moderately dense throughout the telencephalon except for a sparse innervation of the area dorsalis, pars medialis. Immunostained cells are present in the suprachiasmatic nucleus and magnocellular and parvicellular components of the preoptic nucleus. Immunoreactive fibers from preoptic cells can be traced caudally in two main tracts to the infundibulum. Dense immunoreactivity around cells in the pituitary provides anatomical support for catecholamine involvement in the neuroendocrine axis probably via preopticohypophysial connections. At middiencephalic levels, immunoreactive cells are present in the ventral thalamus, nucleus pretectalis periventricularis, pars ventralis, and paraventricular organ pars anterioris. In the caudal diencephalon, TH‐ir cells are seen within the posterior tuberal nuclei and dorsal to posterior recess. No immunostained cells are observed in the midbrain. In the hindbrain, tyrosine hydroxylase containing cells comprise three groups similar to that described using Falck‐Hillarp histofluorescence (Parent et al., ′78), i.e., isthmal, central medullary, and medullospinal groups. Tyrosine hydroxylase immunoreactivity is interpreted as evidence for the presence of catecholamines and not only provides an anatomical basis for the functional significance of catechol amines in teleosts, but may be useful in elucidating homologous structures in tetrapod vertebrates, although certain sites of immunoreactivity may prove to be unique to teleosts.
Ultracytochemical distribution of ouabain‐sensitive, K+‐dependent, p‐nitrophenylphosphatase in the synaptic layers of goldfish retina
Authors: Yazulla Stephen , Studholme Keith M. 
Published: January 2005

AbstractOuabain‐sensitive, K+‐dependent p‐nitrophenylphosphatase (K+‐pNPPase) activity, which represents the second dephosphorylation step of Na+, K+‐ATPase, was localized histochemically at the light and electron microscopical levels in the goldfish retina. K+‐pNPPase staining was most intense in the outer and inner plexiform layers and less intense over the photoreceptor inner segments. K+‐pNPPase staining was observed on the membranes of horizontal cell dendrites and presynaptic membrane of all cone pedicles but only rarely over rod spherules. Bipolar cell dendrites in the outer plexiform layer were not stained for K+‐pNPPase. In the inner plexiform layer (IPL), K+‐pNPPase staining was observed at 90% of the bipolar cell ribbon synapses but only at 40% of amacrine cell synapses. The proportion of K+‐pNPPase staining at amacrine cell synapses increased from 26 to 49% as one progressed from the outer to inner layers of the IPL, while staining at bipolar cell synapses showed no such trend. Only 16% of the amacrine synapses onto mixed, rod‐cone (mb) bipolar cell synaptic terminals were positive for K+‐pNPPase. We suggest that the differential distribution of K+‐pNPPase staining at retinal synapses can be explained, in part, by the ionic conductances gated at the postsynaptic sites. In addition, the presence of K+‐pNPPase on lateral horizontal cell dendrites in cone pedicles is consistent with the hypothesis that the sodium pump is involved in the release of GABA at feedback synapses from horizontal cells to cone photo‐receptors.