bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative study of the tectally projecting retinal ganglion cells in the adult frog: I. The size of the contralateral and ipsilateral projections
Authors: Singman Eric L. , Scalia Frank 
Published: January 2005

AbstractThe proportion of ganglion cells connected to the several central targets of the retinal projection varies in different species. In the frog, the retinotectal projection is clearly the largest branch of the optic pathway and the relative size of the tectally projecting population can be expected to be correspondingly great. However, there have been no studies aimed at quantifying the size of this population and at partitioning its contralateral and ipsilateral components. We injected the tectum with horseradish peroxidase (HRP) dried onto fine needles to count the numbers of retinal ganglion cells labeled by retrograde transport. The retinas were prepared as flat‐mounts to facilitate the cell counting. The tecta were injected either unilaterally or bilaterally in mirror‐symmetric loci. Specimens included completely normal frogs and frogs which had undergone unilateral optic nerve regeneration, although only normal retinas are presented in the current study. The retrograde transport interval was varied progressively (from 3 to 5 days), and single or multiple injection's of HRP were placed singly or as clusters, in order to increment the cell counts toward a level of saturation. Approximately 70.9% of the neurons in the ganglion cell layer could be labeled by this method. Correcting for the presence of displaced amacrine cells, estimated to comprise approximately 16% of the neurons in the ganglion cell layer (Scalia et al., '85, Brain Res. 344:267–280), we calculate that approximately 84.4% of the retinal ganglion cells project contralaterally to the optic tectum.Flat‐mounted retinas ipsilateral to unilaterally injected tecta of completely normal frogs were also examined for labeled cells. The results of injections in the rostrolateral, caudomedial, and caudolateral tectum were studied. We found that ipsilaterally labeled cells comprised no more than 2.3% of the overall population of ganglion cells in the ganglion cell layer. The ipsilaterally projecting cells were found in loci which were approximately mirror‐symmetric to the regions of maximal cell labeling in the contralateral retinas from the same animals. The ipsilateral population was always displaced toward the periphery of the retina with respect to the contralateral population, regardless of whether the contralateral locus was centered in the temporal, ventronasal, or dorsonasal sector of the retina. Because the ipsilaterally projecting ganglion cells form such a minor population, and because they exist in the monocular as well as the binocular parts of the retina, it seems likely that they may not play a significant role in visual function in the frog.
Organization of local axon collaterals of efferent projection neurons in rat visual cortex
Authors: Burkhalter Andreas , Charles Vinod 
Published: January 2005

AbstractWe have studied the laminar origins of local long‐range connections within rat primary visual cortex (area 17), by using retrograde tracing of nerve cell bodies with fluorescent markers. Injections throughout the thickness of cortex produce distinct laminar labeling patterns which indicate that a substantial number of cells in layers 2/3, 5, and 6 have wide local axon collateral arbors, while the local arbors of layer 4 cells are much narrower. Double labeling experiments which combined area 17 injections with injections into different projection targets of area 17 (opposite area 17, area 18a, and area 18b) show that many cortico‐cortically projecting cells make widespread projections within area 17. In contrast, the overwhelming majority of subcortically projecting cells have narrow collateral arbors within area 17.Anterograde tracing of local projections within areas 17 with the lectin Phaseolus vulgaris leucoagglutinin shows an extensive system of horizontally running fibers which terminate in distinct 0.15–0.25 mm wide clusters up to 1.8 mm from the injection site. On horizontal sections the termination pattern resembles a closely spaced lattice.The results indicate that cortico‐cortically projecting cells provide for long‐range interactions between distant points of the visuotopic map, while subcortically projecting cells mediate information within a cortical column. Interestingly, subcortically projecting cells differ functionally from cortico‐cortically projecting cells in that they are not orientation selective (Klein et al., Neurosci. 17:57–78, '86; Mangini and Pearlman, J. Comp. Neurol 193:203–222, '80; Simmons and Pearlman, J. Neurophysiol. 50:838–848, '83). We therefore suggest that cortico‐cortically projecting cells with wide collateral arbors are orientation selective and that clustered long‐range projections within area 17 connect columns with similar functional specificity.
Preproenkephalin upregulation in nucleus caudalis: High and low intensity afferent stimulation differentially modulate early and late responses
Authors: Nishimori Toshikazu , Buzzi M. Gabriella , Chudler Eric H. , Poletti Charles E. , Moskowitz Michael A. , Uhl George R. 
Published: January 2005

AbstractNucleus caudalis expression of preproenkephalin mRNA changes following lesions depleting small‐caliber primary afferent fibers and after stimulation of trigeminal afferents at different intensities.Animals treated neonatally with capsaicin display reduced preproenkephalin gene expression in nucleus caudalis neurons.Stimulation of normal animals at low intensities enhances preproenkephalin expression in a bimodal temporal pattern. High intensity stimulation is effective only at later time points in normal animals, but it causes both early and late effects on preproenkephalin expression when applied to animals neonatally lesioned with capsaicin.Transsynaptic regulation of preproenkephalin expression in pain‐modulating areas of the nucleus caudalis of the trigeminal nerve thus depends on the specific type of primary afferent input. The rapid responses noted after selective large fiber stimulation appear to be suppressed by coactivation of small caliber fibers. Later responses appear less influenced by the quality of the eliciting afferent stimulus.
Stability of dendritic mass during aestivation
Authors: Chase Ronald , Tidd Caroline 
Published: January 2005

AbstractIn hot and dry weather, terrestrial snails withdraw into their shells and remain inactive for long periods of time. This phenomenon, known as aestivation, is the basis for our investigation of the effects of behavioral inactivity on neuronal structure. Several recent studies have shown that the level of afferent electrical activity is an important modifier of structure, even in adult animals. During aestivation, sensory stimulation (and therefore presumably afferent activity) is greatly reduced. We have tested the hypothesis that long‐term behavioral inactivity causes a regression of dendrites. Two identified neurons of Achatina fulica were selected for study, the giant cerebral neuron (GCN) and RPall. The cells were viewed on 10‐μm‐thick sections after intracellular injection of hexamminecobalt chloride. They were reconstructed by using a video camera attached to a light microscope and a digitizing board resident in a microcomputer. Snails in the aestivated group were completely inactive for 8 weeks beginning at age 23 weeks. A quantitative analysis showed that there were no significant differences in either cell, in either the total mass of material or its distribution, comparing cells from the Aestivated snails and cells from the Younger snails (age 23 weeks) and the Older snails (age 33 weeks). These results suggest limits to the modifiability of neuronal structure.
Coexistence of GABA and glutamate in mossy fiber terminals of the primate hippocampus: An ultrastructural study
Authors: Sandler Robert , Smith A. David 
Published: January 2005

AbstractOne of the links in the trisynaptic circuit of the hippocampus is the synapse between the mossy fibre terminals of dentate granule cells and CA3 pyramidal cells of Ammon's horn. This synapse has been physiologically characterized as excitatory, and there is pharmacological and immunohistochemical evidence that mossy fibre terminals utilize glutamate as a neurotransmitter. This study demonstrates the presence of GABA‐immunoreactivity in mossy fibre axons and terminals of the monkey at the electron microscopic level. We combined Golgi impregnation to identify CA3 pyramidal neurones, with postembedding immunocytochemistry to characterize the inputs to the identified cells. GABA immunoreactivity was present in mossy fibre terminals that made synaptic contact with complex embedded spines of identified Golgi‐impregnated CA3 pyramidal neurones. GABA immunoreactivity could be demonstrated in serial sections of the same mossy fibre terminals by using 3 different, antisera raised against GABA. In serial sections, the mossy fibre terminals were shown to be immunoreactive for both glutamate and GABA. In contrast, glutamate immunoreactivity but not GABA immunoreactivity was found in other terminals that did not have the morphological characteristics of mossy fibre terminals. GABA immunoreactivity in mossy fibre terminals was also demonstrated in a human surgical specimen of hippocampus.The coexistence of an “excitatory” amino acid and of an “inhibitory” amino acid in the same “excitatory” nerve terminal raises the possibility of corelease of the two transmitters, suggesting that the control of hippocampal neural activity is more complex than hitherto suspected.
Thalamo‐cortical processing of vibrissal information in the rat. I. Intracortical origins of surround but not centre‐receptive fields of layer IV neurones in the rat S1 barrel field cortex
Authors: Armstrong‐James Michael , Callahan Christopher A. , Friedman Michael A. 
Published: January 2005

AbstractThe receptive fields of cells restricted to the D1 cortical barrel territory in the S1 cortex of the rat were examined before and after substantial lesions of the D2 barrel. We tested 131 cells (N = 62, unlesioned controls; N = 69, lesioned animals) for modal latency and response magnitude to standard vibrissal deflections of 1.14 degrees.Lesions ranged in size to encompass 22–95% of the volume of the D2 barrel hollow and 5–75% of its neighbouring septal region, as calculated from cytochrome oxidase and Nissl staining of alternate sections. Negligible loss (mean 1.1%) of other barrel hollows and their septal regions (6.3%) occurred. A mean loss of 58% of the D2 barrel hollow and 27% of its accompanying septa was paralleled by a highly significant deficit in response magnitude (57.3%) p< 0.0051 of D1 barrel cells to D2 vibrissal stimulation, when compared with controls. The best‐fit relationship between deficit and volumetric loss of the D2 barrel hollow was linear (regression coefficient −0.91). In the extreme case where 95% loss of D2 barrel hollow occurred, there was a 92% deficit in response of D1 barrel cells to the D2 input. No significant loss in response magnitude to other vibrissae, including the principal D1 input, occurred. Postlesioned animals exhibited some increase in excitability to the D1 vibrissa, and to vibrissae whose principal barrel territories were undamaged (δ, γ, C1). Lesioning of the D2 barrel caused a highly significant mean increase (60%) in latency of residual responses to stimulation of the D2 vibrissal input (15.2 ms controls; 24.3 ms experimentals). No significant changes in response latency to other vibrissae compared to controls occurred. These results suggest that an intact D2 barrel is essential for the generation of responses of D1 barrel cells by the D2 vibrissa, and further imply that surround receptive fields of layer IV barrel cells are largely generated intracortically by barrel‐to‐barrel relay. The implications of these findings to cortical processing of tactile information and plasticity in the somatosensory system are discussed.
First step of selective motoneuron axonal growth: Selective outgrowth at discrete sites in the spinal cord
Authors: Tanaka Hideaki 
Published: January 2005

AbstractSelective axonal growth at a series of choice points along pathways is essential for the establishment of precise motoneuron projections. To reveal some of the molecules responsible for this selective growth of motoneuron axons, this study investigates the phenomenon of why motoneurons extend axons outside the spinal cord, whereas interneurons do not. Axonal growth in the chick embryonic spinal cord at early stages of development was examined immunohistochemically. MAb SC1 staining of serial sections selectively revealed the entire distribution of motoneuron axons in the embryo. In the cervical segments, some motoneurons, called dorsal motoneurons, extended axons outside the cord via the dorsal root entry zone. The axons of both dorsal and ventral motoneurons were distributed only in the anterior half of the sclerotome; inside the cord motoneuron cell bodies and axons were distributed evenly along the anterior‐posterior axis. Motoneurons and interneurons extended axons during the same period, and although the growth cones of both were intermixed in the same locations, only motoneuron axons grew out from the cord. The outgrowth of all st 19 motoneurons from the cord through either the dorsal or ventral exit zone strongly suggests that extension of their axons outside the cord is a selective rather than random process.
The effect of TTX‐activity blockade and total darkness on the formation of retinotopy in the goldfish retinotectal projection
Authors: Olson Michael D. , Meyer Ronald L. 
Published: January 2005

AbstractIn the normal goldfish, neighboring retinal ganglion cells terminate in one small tectal locus to produce the precise retinotopy characteristic of this projection. This can be directly demonstrated by labeling neighboring ganglion cells with small “spot” injections of WGA‐HRP, which yield a single small patch of product at the retinotopically appropriate part of the tectum. When the optic nerve is crushed, label from these spot injections was previously found to be widely dispersed during the early phase of regeneration. With time, label subsequently condensed, typically into several discrete patches reminiscent of ocular dominance columns.In this study, we tested whether the formation of these patches required impulse activity by injecting tetrodotoxin (TTX) into the eye during regeneration. We found that impulse blockade completely inhibited the formation of discrete patches while permitting considerable condensation of the label. This implies that these patches are generated by activity but that some map “refinement” utilized cellular processes that are activity independent. This activity‐independent condensation progressed at a noticeably slower rate than the equivalent condensation seen with activity, thus suggesting that activity normally participates as a “helper factor,” even though it is not strictly required.Since the formation of discrete patches during regeneration provides a sensitive measure of activity‐dependent refinement, this was used to further address two controversial questions concerning the role of impulse activity. One is whether there is a chronologically defined critical period for activity‐dependent refinement. This was tested by blocking impulse activity for 2 to 4 months, much longer than the activity‐dependent refinement is thought to last, and then permitting activity to resume. We found that multiple patches were formed following this period of late activity, thus indicating that synaptic plasticity extends for several months beyond the supposed critical period.The other question was whether spontaneous retinal activity was sufficient for activity‐dependent ordering. To test this, fish were kept in constant darkness during optic nerve crush and labelled with retinal spot injections at various times during regeneration. Condensation of label with the final formation of multiple patches formed at about the same time as fish with normal visual experience. This implies that the amount and extent of correlation of spontaneous activity in retina is adequate for driving activity‐dependent refinement.
Striatonigral projection neurons: A retrograde labeling study of the percentages that contain substance P or enkephalin in pigeons
Authors: Anderson Keith D. , Reiner Anton 
Published: January 2005

AbstractTwo largely separate populations of neuropeptide‐containing striatonigral projection neurons have been distinguished in pigeons, one population whose neurons contain substance P (SP) and dynorphin (DYN) and a second population whose neurons contain enkephalin (ENK) (Reiner, '86a; Anderson and Reiner, 90a). In the present study, we investigated the abundance of these two types of neurons relative to all striatonigral projection neurons by combining retrograde labeling by the fluorescent dye fluorogold with immunofluorescence labeling for SP and ENK.Pigeons received large intranigral injections of fluorogold to retrogradely label the striatonigral projection neurons, and several days later they were treated with colchicine (32 hours before transcardial perfusion). Adjacent series of sections through the basal ganglia were labeled for SP and ENK using immunofluorescence techniques. The tissue was examined using fluorescence microscopy and the percentages of retrogradely labeled neurons containing either SP or ENK were quantified. We found that 85–95% of the fluorogold‐labeled striatonigral neurons were SP+, whereas only 1–4% were ENK+.Thus the majority of striatonigral projection neurons in pigeons appear to contain SP, whereas a small percentage contain ENK. Only a small percentage of striatonigral neurons did not contain either. Since striatal projection neurons also contain GABA (Reiner, '86b), the present results suggest that a high percentage of striatonigral projection neurons coexpress SP, DYN and GABA, whereas a small fraction coexpress ENK and GABA. The available data are consistent with the conclusion that this is true in reptilian and mammalian species as well.
Early development and innervation of taste bud‐bearing papillae on the rat tongue
Authors: Farbman Albert I. , Mbiene Joseph‐Pascal 
Published: January 2005

AbstractEarly development of fungiform papillae on the fetal rat tongue was examined: (1) to determine whether morphogenesis of the taste bud‐bearing fungiform papillae is induced by nerve and (2) to study the growth pattern of the two sensory nerves that innervate the papilla. The papillae first appear on the 15th day of gestation (E15; E1 is the day when the dam is sperm positive) in rows parallel to the midline sulcus. There appears to be a medial‐lateral and an anterior‐posterior gradient in the sequence of papilla differentiation. The epithelium of the early papilla resembles a multilayered placode topped by a flattened surface periderm. Close examination of the peridermal cells at the apex of the papillae reveals that the cells have fewer surface microvilli and their cytoplasm is more electron opaque than that of similar cells in interpapillary regions. The basal cells in the placode‐like epithelium differ from those in interpapillary regions in that they are postmitotic and have more mitochondria. At later stages, the papilla acquires a mesenchymal core and nerves grow into the core. Results from organ culture experiments of tongue fragments taken from E14 fetuses indicate that morphogenesis of fungiform papillae is initiated in the absence of sensory nerve influence, but the nerve exerts a trophic effect on their maintenance. The two sensory nerves of the tongue, the chorda tympani and the lingual branch of the trigeminal nerve, enter the tongue mesenchyme at E14 and grow toward the epithelium. By E15 the chorda tympani branches have reached the developing fungiform papillae, by E16 many have entered the papilla, and by E17 they have penetrated the epithelium at the papilla apex. Their fibers are associated exclusively with the cells at the papilla apex, where the taste bud will develop. The trigeminal nerve ramifies beneath the surface of the entire epithelium by E15. Later, it, too, sends branches into fungiform papillae; these ascend along the trunk of the chorda tympani and at E17 terminate in the connective tissue core around the chorda tympani field. The results are compatible with the notion that the tongue epithelium exerts a general tropic effect on growing axons of both sensory nerves, and the epithelial cells of the fungiform papilla apex exert a similar effect to which only the chorda tympani axons are responsive.
Representation of the cecum in the lateral dorsal motor nucleus of the vagus nerve and commissural subnucleus of the nucleus tractus solitarii in rat
Authors: Altschuler Steven M. , Ferenci David A. , Lynn Richard B. , Miselis Richard R. 
Published: January 2005

AbstractMotor fibers of the accessory celiac and celiac vagal branches are derived from the lateral columns of the dorsal motor nucleus of the vagus nerve. These branches also contain sensory fibers that terminate within the nucleus of the tractus solitarii. This study traces the innervation of the intestines by using the tracer cholera toxin‐horseradish peroxidase. In 53 rats, the tracer was injected into either the stomach, duodenum, jejunum, terminal ileum, cecum, or ascending colon.With all cecal injections, prominent retrograde labeling of cell bodies occurred bilaterally in the lateral columns of the dorsal motor nucleus of the vagus nerve above, at, and below the level of the area postrema. Dendrites of laterally positioned neurons projected medially and rostrocaudally within the dorsal motor nucleus of the vagus nerve and dorsomedially into both the medial subnucleus and parts of the commissural subnucleus of the nucleus of the tractus solitarii. Sensory terminal labeling occurred in the dorsolateral commissural subnucleus at the level of the rostral area postrema and the medial commissural subnucleus caudal to the area postrema. Additionally, there was sensory terminal labeling within a small confined area of the dorsomedial zone of the nucleus of the tractus solitarii immediately adjacent to the fourth ventricle at a level just anterior to the area postrema. Stomach injections labeled motoneurons of the medial column of the entire rostrocaudal extent of the dorsal motor nucleus of the vagus nerve and a sensory terminal field primarily in the subnucleus gelatinosus, with less intense labeling extending caudally into the medial and ventral commissural subnuclei. Dendrites of gastric motoneurons project rostrocaudally and mediolaterally within the dorsal motor nucleus of the vagus nerve and dorsolaterally within the nucleus of the tractus solitarii. They are most pronounced at the level of the rostral area postrema where many dendrites course dorsolaterally terminating primarily within the subnucleus gelatinosus.Injections of the duodenum labeled a small number of the cells within the medial aspects of the dorsal motor nucleus of the vagus nerve. Jejunal, ileal, and ascending colon injections labeled cells sparsely within the lateral aspects of the dorsal motor nucleus of the vagus nerve bilaterally. No afferent terminal labeling was evident after injection of these areas of the bowel.The dorsal vagal complex has a prominent viscerotopography: the dorsal motor nucleus of the vagus nerve has a mediolateral organization corresponding to end‐organ innervation; the nucleus of the tractus solitarii has a rostrocaudal axis of visceral representation with some overlap corresponding to rostrocaudal positioning along the alimentary canal and mediolateral separation of terminals within the nucleus.