bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experience‐independent development of dendritic organization in the avian nucleus laminaris
Authors: Parks Thomas N. , Gill Sarvjit S. , Jackson Hunter 
Published: January 2005

AbstractThe third‐order auditory neurons of the avian nucleus laminaris (NL) have distinct dorsal and ventral dendritic tufts that receive their predominant synaptic input from, respectively, the ipsilateral and contralateral cochlear nucleus. Beginning about embryonic day (E) 14 in the chick and continuing for some weeks after hatching, NL neurons undergo a complex series of morphological transformations that result in the formation of a steep anteromedial‐to‐posterolateral gradient of increasing total dendritic length across the nucleus. This gradient perfectly parallels the tonotopic axis of NL. It has been proposed that acoustically evoked activity in the auditory pathway contributes importantly to formation of the gradient of dendritic length in NL and to several other features of dendritic development. The present experiment tested this hypothesis by surgically removing both otocysts (embryonic precursors of the inner ear) and studying the developing NL in the absence of peripheral input. The results of a quantitative study of Golgi‐impregnated material show that at E17 both the steepness and predictability of the spatial gradient of dendritic length in operated animals are indistinguishable from normal. Similarly, the correlation of dorsal and ventral dendritic lengths on individual cells in operated animals is not significantly different from normal. The absolute length of both dendritic fields is reduced below normal, although only dorsal dendrites show a statistically reliable (14%) decrease. This is a significantly smaller effect than the 44% length reduction seen previously in animals with unilateral otocyst removal (T.N. Parks: J. Comp. Neurol. 202:47–57, '81); symmetrical afferent input appears more important to the regulation of NL dendritic length than the absolute level of this input. The only other significant effect of otocyst removal is to retard or prevent the alignment of the gradients of dorsal and ventral dendritic length that occurs normally between E15 and E17; the immature dorsal gradient has a much less prominent lateral‐to‐medial component than the ventral gradient at the same age. Thus, whereas the absolute size of NL dendrites depends upon a normal inner ear, most of the highly specialized dendritic organization of NL can develop normally in the complete absence of peripheral influences. The results suggest that each brainstem auditory nucleus is organized along an intrinsically determined axis that specifies how incoming auditory afferent axons will be organized into tonotopic arrays.
Initial junctions between developing parallel fibers and Purkinje cells are different from mature synaptic junctions
Authors: Landis Dennis M. D. 
Published: January 2005

AbstractDuring postnatal development of cerebellar cortex, junctions are formed between parallel fiber axons and the shafts of Purkinje cell dendrites. These shaft junctions resemble synaptic junctions on spines in thin sections, in that the axon contains a cluster of synaptic vesicles, and the pre‐ and postjunctional membranes are lined by electron‐dense material. The shaft junctions do not have the aggregate of particles arrayed on the extracellular half of the postjunctional membrane that is characteristic of mature spine synaptic junctions in freeze‐fractured preparations, however, and so presumably have a different protein composition. Shaft junctions are transient specializations, present only in developing tissue, but do not appear simply to be intermediates in the formation of mature spine synaptic junctions. In normal development, spines are formed by the Purkinje cell dendrite at sites not occupied by shaft junctions. Moreover, in certain neurological mutant mice, shaft junctions form in the absence of spine synapses, and in other systems spines develop in the absence of shaft junctions. We suggest that shaft junctions are a class of synapse formed during development which is distinguished by its capacity to dissociate, and that only some fraction of the parallel fibers forming shaft synapses with a developing Purkinje cell will have established spine synapses in the adult.
Several morphological types of terminal arborizations of primary afferents in laminae I‐II of the rat spinal cord, as shown after HRP labeling and golgi impregnation
Authors: Cruz F. , Lima D. , Coimbra A. 
Published: January 2005

AbstractThe morphology of the terminal arborizations in laminae I‐II of primary afferent fibers was studied in sections stained by the heavy metal (nickel and cobalt) intensification of diaminobenzidine (DAB) after crushing one dorsal root with horseradish peroxidase (HRP) crystals, and with the mixed Golgi method which duplicated the staining provided by the first method. Besides the flame‐shaped arbors located in deep lamina IIi as an extension of the arbors of lamina III, which were derived from 1.7‐μm thick stem fibers (probably Aαβ fibers), six types of terminal arbors, all rostrocaudally oriented, arising from fine stem fibers and having preferential locations, were disclosed. The lateral third of laminae I‐II contained a longitudinal plexus of parallel 0.8‐μm thick stem fibers (C fibers) with longitudinal side branches generating many boutons en passant. Laminae I and IIo, in their middle third, contained dichotomizing longitudinal fibers with elongated boutons, arising from 1‐μm thick stem fibers (C or Aδ), and, in the medial third, a dense plexus with terminal networks carrying large boutons, which arose from 1.3‐μm thick stem fibers (Aδ). Fibers ending in terminal bouquets and issuing from 1‐μm thick stem fibers (C or Aδ) occupied the dorsal part of middle and medial lamina IIi, while the intermediate part contained clusters (swarms) of ultrafine boutons arising from extremely fine fibers. The whole medial lamina Hi also contained fine undulating fibers arising from 0.3 μm‐thick stem fibers (C fibers) with large boutons near their ends. The functional meaning of this multiplicity of morphological types and locations is still unclear. It may be clarified when single unit analysis of HRP‐injected fine fibers is made possible, or immunocytochemical stainings disclose the neurotransmitters utilized by each fiber type.
Wheat germ agglutinin‐apoHRP gold: A new retrograde tracer for light‐ and electron‐microscopic single‐ and double‐label studies
Authors: Basbaum A. I. , Menetrey D. 
Published: January 2005

AbstractIn this report, we describe a new colloidal‐gold‐labelled retrograde tracer, wheat germ agglutinin (WGA) conjugated to enzymatically inactive horseradish peroxidase (apoHRP). This protein gold complex (WGAapoHRP‐Au) is a sensitive marker for retrograde tracing of the projections of CNS neurons at the light‐microscopic (LM) level when a silver‐enhancement procedure is used to detect the gold in the tracer. For electron‐microscopic (EM) analysis, the silver‐enhanced sections undergo a further gold‐toning step. This protects against rapid oxidation and dissolution of the silver precipitate during the osmication procedure.A major advantage of WGAapoHRP‐Au is that it can be used in a variety of multiple‐labelling studies. When the retrograde transport of the new tracer is combined with that of the fluorescent dye, True Blue, neurons that have bifurcating axons can be readily demonstrated. Simultaneous immunofluorescent detection of the cytochemistry of the double‐retrogradely labelled neurons is also possible. In contrast to a WGA‐HRP gold complex, the new complex has no enzymatic activity. Thus HRP‐based techniques (e.g., anterograde transport of WGA‐HRP or peroxidase‐antiperoxidase immunocytochemistry) can be performed on tissue that contains retrogradely labelled neurons marked with WGAapoHRP‐Au without having to pretreat tissue so as to destroy endogenous HRP enzyme activity. At the EM level, the gold is readily distinguished from DAB immunoreaction product. This makes both LM and EM double‐labelling studies possible.The great sensitivity of the new tracer, its compatibility with a variety of aldehyde fixatives, its ease of detection, and the fact that it can be simultaneously used with several fluorescent and HRP‐based immunocytochemical and tracing techniques make WGAapoHRP‐Au a valuable tool for LM and EM characterization of CNS cytochemistry and connectivity.
Development of the brachial lateral motor column in the wingless mutant chick embryo: Motoneuron survival under varying degrees of peripheral load
Authors: Lanser Mark E. , Fallon John F. 
Published: January 2005

AbstractSurvival of motoneurons in the lateral motor column (LMC) of the chick embryo is known to depend on the periphery. How this dependence relates to the normally occurring death of motoneurons is unknown. Analysis of the time course of LMC cell loss in the absence of varying amounts of limb musculature could help bring about an understanding of this relationship. We undertook this analysis by studying LMC development in wingless chick embryos. Grossly these embryos lack wings, but we have reported that some of them possess more than 40% of the normal volume of wing bud‐derived muscles (M.E. Lanser and J.F. Fallon, Anat. Rec. 217:61–78, 1987). In the present work we compared the time course of LMC development in wingless embryos that possessed varying amounts of wing bud‐derived musculature with that in normal embryos. In normal embryos little cell loss occurs from the brachial LMC prior to day 8 (15% of the: total cell loss). Most of the normal cell loss occurs between 8 and 10 days (62% of the total cell loss). In the wingless LMC, anywhere from 55% to 70% of the total cell loss occurs before day 8. The death of motoneurons prior to day 8 is proportional to the amount of wing bud musculature eliminated by the mutation. Cell loss after day Bis proportional to the amount of wing bud musculature spared by the mutation. Therefore, when the limb is missing, most motoneurons die before the major period of cell loss even begins in the normal LMC. Counts of dead cells in the LMC also support this conclusion. In addition, curves plotting the rates at which cells are lost from the brachial LMC provide a suggestion that normal cell loss is biphasic and that limb removal enhances primarily the first phase of cell loss. These data suggest that the majority of motoneurons may die for different reasons in the normal and the limb‐deprived LMCs. Overall, the number of motoneurons surviving in the brachial LMC is proportional to the volume of wing bud‐derived muscle present. However, as the muscle volume approaches zero, motoneuron number does not. This suggests that most, but not all, motoneurons depend on limb bud‐derived muscles for survival. Finally, the decreased motoneuron number in the wingless LMC, when compared to normal after the cell death period, cannot be totally accounted for by the additional loss of cells that occurred during the cell death period in the wingless LMC. This raises the possibility that limb absence influences the initial formation of the LMC, a possibility that deserves further investigation.
Corneal sensory pathway in the rat: A horseradish peroxidase tracing study
Authors: Marfurt Carl F. , Del Toro David R. 
Published: January 2005

AbstractThe methods of transganglionic transport of horseradish peroxidase (HRP) and horseradish peroxidase–wheat germ agglutinin (HRP‐WGA) were used to determine the location within the trigeminal ganglion of the primary afferent neurons that innervate the rat central cornea, and the brainstem and spinal cord termination sites of these cells. In each of 18 animals, solutions of HRP or HRP‐WGA were applied to the scarified corneal surface and allowed to infiltrate into the corneal epithelium and stroma for 15 minutes. Postmortem examination of the corneal whole mounts from the experimental animals, and of corneas and neural tissues from several control animals, showed that the HRP/HRP‐WGA remained confined to the central cornea with no spread into adjacent intra‐ or extraorbital tissues.HRP‐labeled corneal afferent somata were located in the dorsal part of the ophthalmic region of the ipsilateral trigeminal ganglion. The central fibers of the corneal afferent neurons projected very heavily to interstitial nuclei of Cajal in the spinal tract of V at the level of caudal pars interpolaris and rostral pars caudalis, lightly to the pars caudalis/C1 transition zone, and sparsely to the dorsal horn of spinal cord segments C1‐C3. The trigeminal main sensory nucleus, pars oralis, the rostral three‐fourths of pars interpolaris, and an extensive midregion of pars caudalis were totally devoid of reaction product. Terminal fields in Caudal pars caudalis and in the spinal cord dorsal horn were concentrated largely in the outer half of lamina II, with lesser accumulations in lamina I, the deeper half of lamina II, and in lamina III.The present study demonstrates for the first time by means of an anatomical tracing procedure the brainstem termination sites of corneal afferent neurons in the rat. The patchy, discontinuous nature of the corneal afferent projection to the caudal trigeminal brainstem nuclear complex (TBNC), and the total lack of corneal projections to rostral subdivisions of the TBNC, provide an exception to the general rule of trigeminal organization in which most areas of the head and face are represented as continuous columns throughout the rostrocaudal extent of the ipsilateral TBNC.
Transneuronally transported wheat germ agglutinin labels glia as well as neurons in the rat visual system
Authors: Rhodes C. Harker , Stieber Anna , Gonatas Nicholas K. 
Published: January 2005

AbstractFollowing intraocular injection in adult rats of 125I‐labeled wheat germ agglutinin (I‐WGA), the ultrastructural distribution of label in the superior colliculus and lateral geniculate was examined by electron microscope auto‐radiography. Three days after injection, 5.4% of the label in the lateral geniculate was associated with neuronal perikarya, and 3.6% was associated with glial perikarya. The corresponding figures for the superior colliculus were 5.1% and 0.8%. When the data were expressed as number of grains per μm2 cytoplasm, there was no statistically significant difference between the grain density over neuronal or glial cytoplasm in either the lateral geniculate or the superior colliculus, A statistical analysis of the distance between the silver grains and the cell membranes showed that in both neurons and glia, the observed labeling was the product of internalized I‐WGA and not the result of scatter from the neuropil or from label bound to the surface of the cells. These results indicate that much of the WGA released from axons and axon terminals is not confined to a specific “transsynaptic” pathway, but produces a generalized labeling of nearby cells, much like a microinjection of WGA into the region.
Distribution of external cuneate nucleus afferents to the cerebellum: I. Notes on the projections from the main cuneate and other adjacent nuclei. An experimental study with radioactive tracers in the cat
Authors: Jasmin L. , Courville J. 
Published: January 2005

AbstractTransport of radioactive leucine was used to demonstrate cerebellar projections from the external cuneate nucleus (NCE) and from adjacent portions of the main cuneate nucleus (NC), of the spinal trigemmal nucleus (N.tr.sp.V) and of the vestibular nuclei. Projections from NCE and NC in part terminate over exclusive regions and in part overlap. After injections limited to NCE, labeling is found in all regions of the anterior lobe and lobule VI, in vermal lobules VII, VIII, and IX, and in medial regions of central folia of the paramedian lobule. Afferents from NC are observed in intermediate and lateral regions of lobules IV‐VI, in lobules VIII and IX, in medial portions of crura I and II, and in lateral parts of central folia of the paramedian lobule as well as in its rostral folia. Afferents from N.tr.sp.V are distributed in lateral regions of lobules II‐VI, in the rostral folium of lobule IX, in medial parts of crura I and II, and in rostral folia of the paramedian lobule. Afferents from the vestibular nuclei are present in vermal lobules VII, IX, and X and in the paramedian lobule. Projections from NCE are bilateral with ipsilateral predominance, whereas those from NC and N.tr.sp.V are ipsilateral. Projections from NCE are generally much denser than those from the other nuclei. Throughout the projection area, afferents from NCE are distributed in greater amounts in folia close to the medullary core and are much less dense near the surface. Afferents from the other nuclei do not show surface‐to‐depth density differences.
Organization of amygdaloid projections to the mediodorsal thalamus and prefrontal cortex: A fluorescence retrograde transport study in the rat
Authors: McDonald Alexander J. 
Published: January 2005

AbstractPrevious studies have shown that the amygdala projects to both the mediodorsal thalamic nucleus (MD) and its cortical projection area, the prefrontal cortex (PFC). In this investigation rats received injections of different fluorescent retrograde tracers (true blue and diamidino yellow) into MD and either the lateral, polar, or medial PFC in order to examine the relationship of amygdaloid neurons with cortical and/or thalamic projections. PFC injections labeled neurons in the basolateral (BL), basomedial (BM), ventral endopiriform (Env), and rostral lateral nuclei as well as the periamygdaloid cortex (PAC) and the medial part of the amygdalohippocampal area (AHA). In BL, which contained the great majority of neurons projecting to PFC, most labeled cells were concentrated in particular parts of the nucleus and were topographically organized. The overwhelming majority of labeled neurons in BL were large pyramidal or piriform cells that correspond to class I neurons described in Golgi studies. Occasional small neurons with thin dendrites were also observed; these cells may be class II neurons.MD injections labeled numerous cells in the anterior division of the cortical nucleus, medial nucleus, and caudomedial part of the central nucleus. Moderate numbers of labeled cells were found in caudal portions of BM and PAC, whereas scattered cells were observed throughout the rest of the amygdala with the exception of the lateral nucleus. In BL and AHA many MD‐projecting neurons were observed along nuclear boundaries and in the adjacent white matter. Neurons in BL, BM, and AHA usually had large elongated or irregular somata and two to four primary dendrites that branched sparingly. Other cells had smaller ovoid somata. The morphology and distribution of MD‐projection cells in the basolateral amygdala indicate that they are primarily large class II neurons.Double‐labeled amygdaloid neurons, labeled by both cortical and thalamic injections, were observed only in a small number of animals. Control experiments suggest that most of the double‐labeled cells in these cases were artifacts caused by spread of the thalamic injectate into the third ventricle with subsequent uptake by fibers in the anterior commissure. Thus the findings of this study suggest that different neuronal populations in the amygdala project to the two poles of the MD‐PFC system. In the basolateral amygdala class I neurons are the predominant cell type involved in PFC projections, whereas a subpopulation of class II neurons, hitherto thought to be primarily local‐circuit neurons, project to MD.
Development of the rhesus monkey retina: II. A three‐dimensional analysis of the sequences o synaptic combinations in the inner plexiform layer
Authors: Nishimura Yozo , Rakic Pasko 
Published: January 2005

AbstractThe inner plexiform layer (IPL) of the retina provides a useful model for ultrastructural analysis of synaptic development. In primates, the IPL consists of numerous combinations of neuronal contacts that assume the morphological configuration of either conventional or ribbon synapses. We have determined the sequential development of these combinations by analyzing serial electron microscopic sections from fetal rhesus monkeys. Our analysis reveals an orderly emergence of various pre‐ and postsynaptic elements: (1) patches of dense filamentous membrane first appear on the dendrites of ganglion (G) cells; (2) membrane densities on ganglion cell dendrites then become apposed to amacrine (A) cell processes still lacking their own membrane densities and synaptic vesicles; (3) amacrine cell processes acquire membrane specializations associated with vesicles at the sites apposing ganglion cell dendrites, thereby establishing the first morphologically complete, A → G subtype of conventional synapse; (4) pairs of amacrine cell processes form A → A subtypes of conventional synapses; (5) next, monad ribbon synapses are established between bipolar (B) and ganglion or amacrine cell processes (B → G; B → A); (6) the three subclasses of dyad ribbon synapses (B → GG; B → GA; B → AA) are subsequently formed by the introduction of additional amacrine or ganglion cell processes in the dyad synapse; (7) concurrently, processes of some amacrine and interplexiform (I) cells form a feedback circuit with bipolar cell axons (A → B; I → B), thereby completing the synaptic microcircuitry of the IPL.Present findings provide evidence that the sequence of synaptic differentiation in the IPL proceeds from the postsynaptic to the presynaptic site. Furthermore, lateral interactions (A → G and A → A) are established prior to the formation of the “straight signal” pathway from photoreceptors (P) via bipolar cells to ganglion cells (P → B → G). Observed developmental events provide new insight into the order of establishment of local neuronal circuits in the primate retina.