bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitatory transmitter amino acid‐containing neurons in the rat visual cortex: A light and electron microscopic immunocytochemical study
Authors: Dori Ioanna , Petrou Mario , Parnavelas John G.
Published: January 2005

The distribution and morphology of neurons labelled with antisera to glutamate or aspartate were examined, at the light and electron microscope levels, in the rat visual cortex. Using widely accepted light microscopic features as well as well‐established nuclear, cytoplasmic, and synaptic criteria, we noted that glutamate‐immunoreactive neurons were pyramidal cells distributed in layers II‐VI, with an increased concentration in layers II and III. Aspartate immunoreactivity was localized chiefly to pyramidal neurons in layers II‐VI. However, approximately 10% of immunolabelled cells were nonpyramidal neurons scattered throughout the cortex. Cell‐body measurements revealed that, for both groups of neurons, layer V contained the largest labelled neurons, whereas layers IV and VI contained the smallest. Furthermore, in every layer, aspartate‐stained neurons were larger than glutamate‐positive cells. Finally, glutamate‐ and aspartate‐labelled axon terminals formed asymmetrical synapses, which are presumably excitatory in nature, primarily with dendritic spines. These findings, together with recent detailed studies of the projections of glutamate‐ and aspartate‐labelled cortical neurons, may provide essential background information for studies aimed to elucidate the function(s) of excitatory amino acids in the cortex and their role in pathological conditions.
Ultrastructural analysis of the development and maturation of synapses and subsynaptic structures in the ectostriatum of the zebra finch
Authors: Nixdorf Barbara E.
Published: January 2005

The development of synapses and subsynaptic features in the neuropil of the ectostriatum, a visual projection area in birds, was examined ultrastructurally at 5, 10, 20, and 100 days posthatching. The maturation of the synaptic complex is accompanied by a variety of different dynamic processes. The number of synapses in ectostriatum and the number of specific synaptic types vary with age as does the constellation of subsynaptic structures. At day 5, before eye opening, the total number of synapses is 16% of the adult value. These synapses, unlike synapses seen at maturity, have indistinct synaptic contact zones and generally are associated with few synaptic vesicles. Synapse number increases continuously until 20 days of age, paralleled by a steady increase of the observed brain volume. The largest increase in synapse number takes place during the time of eye opening (i.e., between 5 and 10 days). This increase is mainly due to an increase of asymmetric synapses, the most common type in the neuropil of ectostriatum (90% of the synapse population). At day 20 the number of synapses has reached its maximum and remains high in adulthood. Synapses on spines are more prominent in younger animals than in adults. The percentage of presynaptic terminals involved in synaptic contact with more than one postsynaptic element (multiple synapses) shows a significant reduction from 12% to 4% early in development (between days 10 and 20). Presynaptic terminal size and postsynaptic density (PSD) length increase until 20 days of age. From day 20 to adulthood the PSD shows a 10% reduction in contact length, and the presynaptic terminal further increases in size by 27%. Therefore, the pre‐ and postsynaptic structures described above continue to develop after the number of synapses remains constant.
Morphology of neuropeptide y‐immunoreactive neurons in the cat olfactory bulb and olfactory peduncle: Postnatal development and species comparison
Authors: Sanides‐Kohlrausch Claudia , Wahle Petra
Published: January 2005

The distribution and morphology of Neuropeptide Y ‐immunoreactive (NPY‐ir) neurons in the olfactory bulb and the olfactory peduncle was studied in the adult cat and rat, and the common marmoset Callithrix jacchus. Significant species differences were not observed. In all three species, the population of NPY‐ir neurons is localized in the white matter extending from the main olfactory bulb to the border of the striatum. The neurons are characterized by a conspicuously looping axonal ramification pattern with some major collaterals running toward the olfactory bulb and others running toward the internal olfactory tract. The former, ipsilateral projection terminates in the granule cell layer of the main and accessory olfactory bulb and in layer II/III of the anterior olfactory nucleus. Reconstruction of the latter projection has revealed that the fibers are continuous with the olfactory limb of the anterior commissure and the anterior commissure proper suggesting a commissural contralateral projection. The analysis of the postnatal development of the cat NPY neuron system supports this assumption in a very clear‐cut way. In young animals growing fibers are observed to cross the brachium of the commissure.

The NPY neuron system develops postnatally. The maximum cell number is reached during the third postnatal week. The appearance of more and more NPY‐ir neurons slightly precedes the formation of the terminal fields and of the fiber projection in the internal olfactory tract. The density of this early fiber projection by far exceeds the fiber density observed in the adult. Later in development the fiber density in the olfactory limb and the anterior commissure becomes considerably reduced. In contrast, the plexus density in the anterior olfactory nucleus and the granule cell layer of the main and accessory olfactory bulb undergoes only a slight reduction, and the NPY‐ir cell number remains roughly constant. These observations suggest that the ipsilateral NPY‐ir projection remains largely unchanged, in contrast to the contralateral projection, which exists to a large extent only for the first four postnatal months.

The observation that the NPY neuron system gives rise to a contralateral projection does not support a classification of NPY neurons as short axon cells.
Effects of protein deprivation on pyramidal cells of the visual cortex in rats of three age groups
Authors: Díaz‐Cintra S. , Cintra L. , Ortega A. , Kemper T. , Morgane P. J.
Published: January 2005

The effect of protein deprivation on rapid Golgi impregnated pyramidal neurons in layers II/III and V of the rat visual cortex was studied at 30, 90, and 220 days of age using morphometric methods. In order to mimic human undernutrition female rats were adapted to either an 8% or control 25% casein diet 5 weeks prior to conception and maintained on these diets during gestation and lactation. The pups were then weaned and maintained on their respective diets. The undernourished rats showed a significant decrease in brain weight only at 90 days, indicating that the protein deprivation had a mild effect on brain development. Crrespondingly, the number of significant histological differences between the two diet groups were least at 30 and 220 days of age. The effect of the diet was greater on layer V than on layer II/III pyramids. At 30 days of age the effect of the diet was different on the pyramids of these two cell layers, at 90 days there was a mixture of similar and dissimilar effects, and at 220 days the pyramids of these two cell layers showed only minor differences between the two diet groups. Analysis of age‐related changes indicated that the effect of the diet was different on layer II/III pyramids compared to layer V pyramidal cells. These different effects apparently accounted for the progression from a dossimilar effect of the diet at 30 days on the pyramids of the two cell layers to only minor differences between them at 220 days. Further analysis of these age‐related changes shows that two prominent effects of protein deprivation are for age‐related changes to occur in undernourished rats but not in controls and for age‐related changes to be out‐of‐phase with each other in the two diet groups. From these findings, and a review of similar studies in the literature, we propose that these mechanisms are a prominent effect of undernutrition in the post‐weaning period and help account for the unexpected increases in morphometric measurements noted in undernourished rats in this and other studies.
Organization and actions of the noradrenergic input to the hamster's superior colliculus
Authors: Mooney Richard D. , Bennett‐Clarke Carol , Chiaia Nicolas L. , Sahibzada Niaz , Rhoades Robert W.
Published: January 2005

Immunocytochemistry using antisera directed against dopamine‐hydroxylase (DBH) was used to determine the organization of the noradrenergic (NE) input to the hamster's superior colliculus (SC). Immunocytochemistry for DBH was combined with retrograde transport of fluorogold (FG) to determine the sources of NE input to SC. Microiontophoretic techniques were used together with extracellular single unit recording and receptive field mapping techniques to determine the manner in which NE influenced the responses of individual SC neurons. The hamster's SC contained numerous DBH‐positive fibers but no immunopositive cells. These fibers formed a plexus that was most dense in the lower stratum griseum superficiale SCS. The density of DBH‐positive fibers was very low in the stratum opticum SO and increased in density in the stratum griseum intermediale SGI and the other deep layers. When FG injections into the SC were combined with immunocytochemical detection of DBH, double‐labeled cells were observed in the contralateral locus ceruleus. DBH‐positive neurons were observed in several other portions of the mesencephalon and pons, but none of these were labelled with FG. The effects of NE iontophoresis were assessed for a total of 135 SC neurons. In 74% N = 100, NE reduced spontaneous and/or stimulus evoked activity. In 3% (N = 4 cells), NE increased activity, and in 23%; N = 31 cells it had no effect. These percentages were essentially the same for superficial layer visual cells and somatosensory neurons in the deep laminae. The effect of NE iontophoresis upon signal to noise ratios was assessed for 46 visual and 56 somatosensory neurons. For 54% (N = 25) of the visual cells and 16% N = 9 of the somatosensory cells, NE iontophoresis decreased signal to noise ratios. For 13% N = 6 of the visual cells and 21% N = 12 of the somatosensory cells, NE iontophoresis increased signal to noise ratios. The effects of NE on the responsivity of SC neurons were antagonized by propranolol 86% of the 21 cells tested, sotalol 67% of the six cells tested, and atenolol effective in the single cell tested. All these agents are β‐adrenergic antagonists. The single β‐adrenergic antagonist that we evaluated, corynanthine, potentiated the effects of NE on the responsivity of the two SC neurons that we tested.
Ultrastructural study of synapses at the time of neuronal migration and early differentiation in the tangential vestibular nucleus of the chick embryo in vivo
Authors: Petralia R. S. , Peusner K. D.
Published: January 2005

The chick tangential nucleus is a primary vestibular nucleus whose two main neuron types migrate and begin to differentiate between 5 and 8 days in the embryo (gestation takes 20‐21 days). Based on rapid Golgi impregnations of developing tangential neurons and growing fibers, we have identified ultrastructural counterparts and characterized interactions in the nucleus from 5 to 8 days.

Developing tangential neurons received the earliest synapses at 5 days on their primitive processes and subsequently on their cell bodies by longitudinal fibers of unknown origins. In contrast, the primary vestibular afferents did not form identified synapses on the developing tangential neurons until 7½ days.

In conclusion, the earliest synapses in the tangential nucleus are formed by longitudinal fibers, which are probably not primary vestihular afferents. Since a specific class of fibers forms particular synapses on the tangential neuron precursors at predictable times prior to and during neuronal migration and also at the onset of differentiation, the role of these synapses in developmental events should be explored.
Bulbospinal serotoninergic pathways in the frog rana pipiens
Authors: Tan Hongjing , Miletic Vjekoslav
Published: January 2005

We combined retrograde fluorescent tracing with rhodamine immunofluorescence to identify the origin of serotoninergic neurons with descending projections to the spinal cord of frogs. After injections of Fluoro‐gold into the spinal cord, retrogradely labeled immunoreactive serotoninergic neurons were detected in the caudal part of the brainstem from the level of the obex through the level of the VIII nerve. These doubly labeled cells were distributed along the midline throughout the rostrocaudal extent of the dorsal portion of the raphe nuclear region. Doubly labeled neurons were more numerous in the rostral than in the caudal part of the raphe area.

The fluorescent tracer 1,1′‐dioctadecyl‐‐3,3,3′3′‐tetramethylindocarbocyanine perchlorate (DiI) was then placed in and around the middle and rostral raphe nuclear region. Anterogradely labeled fibers could be traced bilaterally in the lateral portion of the dorsal funiculus and the lateral and ventral funiculi. These fibers were seen terminating in the dorsal and ventral horns, as well as in the intermediate grey matter. After placement of DiI in the caudal raphe area, labeled fibers were found only in the intermediate grey and ventral horn.

These findings suggest that the organization of bulbospinal serotoninergic pathways in the frog is similar to that of mammals, and that an isolated amphibian spinal cord preparation could be a useful model for pharmacological and physiological studies of the action of serotonin (5HT) in the spinal cord.
Analysis of taste bud innervation based on glycoconjugate and peptide neuronal markers
Authors: Silverman James D. , Kruger Lawrence
Published: January 2005

Primary gustatory neurons and their peripheral and central processes were evaluated histochemically in the geniculate and petrosal cranial nerve ganglia, lingual fungiform taste buds, and the nucleus of the solitary tract (NST) using (1) the plant lectin Griffonia simplicifolia I‐B4, which binds specifically to D‐galactose residues and selectively labels primarily nonpeptidecontaining peripheral somatosensory neurons, and (2) calcitonin gene‐related peptide immunoreactivity (CGRP‐IR), which labels most peptidergic somatosensory neurons.

Lectin reactivity was expressed by the vast majority of geniculate and petrosal ganglion cells, while CGRP‐IR labeled very few cells. Peripherally, gustatory intragemmal axons penetrating fungiform taste buds were labeled only by the lectin and were depleted following chorda tympani transection. However, both lectin‐labeled and CGRP‐IR subpopulations of somatosensory perigemmal axons surrounding the taste buds were observed and were eliminated by section of the lingual nerve. The differing brainstem projection patterns of lectin‐reactive vs. CGRP‐IR central axons reflected their distinct ganglionic origins and the differential distributions of lectin reactivity and CGRP‐IR among taste buds. Central lectin‐reactive terminals were found throughout the entire rostrocaudal extent of the NST, including its rostral lateral “gustatory” zone; the extensive lectin‐reactive visceral afferent projection can be presumed to have originated mainly from the large proportion of lectinlabeled neurons in the nodose ganglion. The lectin also prominently and selectively labeled the area postrema. CGRP‐IR central terminals, however, was relatively sparse and restricted primarily to the caudal and medial “visceral” divisions of the NST.

The results are discussed with respect to the possible functional implications of cell surface glycoconjugate expression by gustatory axons innervating taste bud receptor cells of the tongue.
Immunohistochemical subpopulations of retinopetal neurons in the nucleus olfactoretinalis in a teleost, the whitespotted greenling (Hexagrammos stelleri)
Authors: Uchiyama Hiroyuki
Published: January 2005

Two subpopulations of retinopetal neurons in the nucleus olfactoretinalis (NOR) were revealed by means of general histological, tract tracing, and immunohistochemical methods in a marine teleost, the whitespotted greenling (Hexagrammos stelleri). Two types of cells in the NOR (M cell, L cell) were morphologically distinguishable from one another. The cell bodies of M cells were medium‐size and fusiform, while those of L cells were large and ellipsoidal or irregular. M cells were located at the ventralmost region of the junction between the olfactory bulb and telencephalon, while L cells were scattered more rostrally along the ventromedial surface of the olfactory bulb. Following applications of HRP or Fluoro‐Gold to the optic nerve, almost all M cells and about half of the L cells were labeled in the contralateral NOR. L cells showed strong immunoreactivities to gonadotropin releasing hormone (GnRH) and Phe‐Met‐Arg‐Phe‐NH2 (FMRFamide), whereas M cells showed only weak GnRH‐immunoreactivity and no FMRFamide‐immunoreactivity. Axons of L cells were detected in the optic nerve by means of GnRH‐ and FMRFamide‐immunohistochemistry. The axons were concentrated in the myelinated edge (the oldest area) of the “ribbon” optic nerve. GnRH‐ and FMRFamideimmunoreactive fibers constituted a plexus at the junction between the inner nuclear layer and inner plexiform layer. The existence of two structurally separate classes of NOR cells suggests two functionally separate channels from the NOR to the retina.
Somatostatin‐immunoreactive cells in the adult cat retina
Authors: White C. A. , Chalupa L. M. , Johnson D. , Brecha N. C.
Published: January 2005

Peptides have been found in the retinas of all mammalian species studied to date, but little is known about their localization and function in the cat. Using two mouse monoclonal antibodies directed to somatostatin 14, we have observed two sparse groups of somatostatin‐immunoreactive neurons in the cat, both distributed preferentially in the inferior retina. The more numerous cell type is characterized by a small‐ to medium‐sized soma (mean diameter = 16.3 =9.0 μm; n = 186) with sparsely branching, far‐reaching varicose processes that ramify mainly in the inner plexiform layer. The majority of these cells are located in the ganglion cell layer, with the remainder in the proximal inner nuclear layer and the inner plexiform layer. They are in especially high density at the retinal margin. In morphology and soma size, these cells resemble wide‐field amacrine cells. The second cell type has a large, granular‐staining soma (mean diameter = 29.7 ± 14.8 μm; n = 145) with poorly stained primary processes and is found only in the ganglion cell layer. Cells of this type are most similar in their size and morphology to alpha ganglion cells.

In contrast to the location of somatostatin‐immunoreactive somata, a dense meshwork of immunoreactive processes was observed at all eccentricities within the inner plexiform layer, adjacent to the inner nuclear layer and to the ganglion cell layer. Labeled processes arising from the inner plexiform layer were also occasionally detected in the outer plexiform layer and the nerve fiber layer. Additional processes of unknown origin were observed in the nerve fiber layer and the optic nerve head. The extensive distribution of immunoreactive processes suggests that somatcstatin‐immunoreactive somata located preferentially in the inferior half of the retina have a widespread influence on neural activity.
Brainstem projection of the vestibular nerve in the guinea pig: An HRP (horseradish peroxidase) and WGA‐HRP (wheat germ agglutinin‐HRP) study
Authors: Burian M. , Gstoettner W. , Mayr R.
Published: January 2005

We explored the course and termination of primary vestibular afferent fibers within the brainstem of the guinea pig by means of anterograde axonal transport of horseradish peroxidase (WGA‐HRP). Primary vestibular afferent fibers distribute within the entire vestibular nuclear complex, with the exception of the dorsal part of the lateral vestibular nucleus. The superior vestibular nucleus is characterized by the concentration of terminals within its central part. Although terminal labeling is weaker within the periphery, no area completely lacks primary input. The lateral vestibular nucleus can be divided into a ventral and a dorsal part; within the ventral part small and giant cells receive primary afferent fibers, whereas no significant terminal labeling occurs in the dorsal part. The medial vestibular nucleus shows the most uniform labeling, although the lateral part of its rostral third has a few more terminals than the medial half. Primary projection to the descending vestibular nucleus is widespread, although in its rostrodorsal part it is less impressive. Of the small cell groups commonly associated with the vestibular nuclear complex, only group y receives abundant primary input. Whereas group z completely lacks labeled fibers as well as terminals, single primary axons can be observed passing groups x and f. However, no terminals can be found within the borders of these two cell groups. Scanty projections can be detected within the prepositus hypoglossi nucleus, as well as within the external cuneate nucleus, the cochlear nucleus, the abducent nucleus, and parts of the reticular formation.
Morphological variability is a characteristic feature of granule cells in the primate fascia dentata: A combined Golgi/electron microscope study
Authors: Seress Laszlo , Frotscher Michael
Published: January 2005

This study analyzes the structural variability of granule cells in the monkey fascia dentata. The hippocampi of three adult rhesus monkeys (Macaca mulatta) and two 1‐year‐old female baboons (Papio anubis) were used for a combined Golgi/electron microscope (EM) study. The results were compared with other Golgi/EM studies on dentate granule cells in small laboratory animals.

Whereas the granule cells in small rodents form a relatively uniform population of neurons, we observed a much greater variability of granule cell morphology in monkeys. This variability concerned the size of the cell body, the length and thickness of apical dendrites, the spine density, and the occasional occurrence of basal dendrites. The dendritic length of individual granule cells largely depended on their position in the highly convoluted granular layer. These convolutions caused significant variations in the thickness of the molecular layer and consequently in the length of individual granule cell dendrites. Granule cells with thick dendrites densely covered with spines could be differentiated from those exhibiting much thinner dendritic processes and moderate spine numbers. About 10% of granule cells in the monkey fascia dentata exhibited basal dendrites. Occasionally in the hilus ectopic granule cells were observed that gave rise to long apical dendrites traversing the granular layer. The axons of granule cells, the mossy fibers, entered the hilus, where they gave off several collaterals.

In contrast to the light microscopic variability, subtypes of granule cells revealed similar fine structural characteristics, i. e., a round nucleus lacking indentations, a thin rim of cytoplasm, and characteristic spine formations. Large complex spines and smaller, “stubby” spines were observed on apical as well as basal dendrites. This suggests that characteristic spine formations were not induced by specific afferent fibers. All synaptic contacts on spines were of the asymmetric type, whereas both symmetric and asymmetric synapses occured on cell bodies and dendritic shafts.

Unlike in rodents, we found a large variability of granule cells in the primate fascia dentata. This variability has to be considered in neropathological studies of this cell type.
Morphology and cellular interactions of growth cones in the developing corpus callosum
Authors: Norris Carolyn R. , Kalil Katherine
Published: January 2005

Previous studies of growth cones in invertebrates have shown that they become larger and more complex when changing direction in response to cellspecific contacts (Bentley and Caudy, '83; Raper et al., '83b; Caudy and Bentley, '86). In pathways of the vertebrate nervous system, analogous regions, termed “decision regions,” have been identified in which axons change direction and their growth cones become more elaborate than when tracking along straight trajectories (Tosney and Landmesser, '85a; Bovolenta and Mason, '87). In order to assess the generality of these principles to the mammalian CNS, we studied the morphology of growth cones and their interactions with the environment in the developing corpus callosum. Given the straight pathway that callosal axons could use to navigate across the callosum, one might predict that later arriving axons would extend on those growing out earlier and that therefore, by analogy with previous studies, many growth cones would have simple tapered morphologies. Surprisingly, however, virtually all growth cones in the callosal white matter, regardless of age or position, were complex with broad lamellipodial veils and/or numerous, often lengthy filopodia. Only growth cones entering the cortical target were consistently smaller. As seen in the EM, the predominant elements in the callosal pathway are other axons and growth cones; we found no evidence for specialized contacts. These results suggest that there is no specific decision region for the fiber population as a whole; rather it is possible that in this mammalian CNS pathway individual growth cones respond independently to molecular cues broadly distributed in the callosum.
Candidate cell populations for respiratory chemosensitive fields in the human infant medulla
Authors: Filiano James J. , Choi John C. , Kinney Hannah C.
Published: January 2005

The histology and location of human respiratory chemosensitive fields are not known. In contrast, the physiology of respiratory chemosensory areas in the ventral medulla of cats has been studied extensively, and their anatomy has been partially described. Using basic principles of comparative cytoarchitecture and computer‐aided reconstructions of serial‐sectioned medullae, we describe the histology and three‐dimensional distribution of putative respiratory chemosensors in the feline and human infant medulla. We found that ventrolateral neurons of the human nucleus conterminalis are homologous to neurons identified in the feline L chemosensitive field by Trouth and others, and that ventrolaterally situated neurons in the human arcuate nucleus correspond to neurons predominating in the feline S and M fields. In addition, there are foci of thickened marginal glia along the feline ventral medullary surface that colocalize with chemosensitive fields identified by physiologic studies reported by others; we identify similar foci in the infant medulla. Thickened marginal glia are intermixed with neuronal fibers, often adjacent to neurons of the feline chemosensitive fields and their human counterparts, suggesting that they constitute a chemosensory neuropil at the medullary surface. Computer‐aided reconstructions provide insight into the three‐dimensional topography of putative respiratory chemosensors and their relationships to other brainstem structures in ways not obvious in single or even multiple sections. This delineation of candidate human respiratory chemosensors is a first step toward their postmortem analysis in patients with central ventilatory control disorders where finding histological abnormalities in these sites would support their role in human ventilation.
Interspecific variation in the projection of primary afferents onto the electrosensory lateral line lobe of weakly electric teleosts: Different solutions to the same mapping problem
Authors: Lannoo Michael J. , Maler Leonard
Published: January 2005

We demonstrate that preterminal axons composing the primary afferent projection onto the four somatotopically organized electrosensory lateral line lobe (ELL) segments in weakly electric gymnotiform teleosts course in fundamentally different directions in the most commonly studied species. Afferents enter the deep fiber layer (dfl) of the ELL and course in variable, but speciesspecific, directions within a horizontal plane before turning dorsally to terminate within the deep neuropil layer of the ELL (dnl). Among the species considered here, apteronotids exhibit the tightest projection pattern. Afferents enter the rostral ELL from the anterior lateral line nerve ganglion (ALLNG) in a nonsomatotopic fashion. As they course horizontally, these fibers undergo a rostrocaudal somatotopic sorting along the ventrolateral border of the dfl, then turn within a horizontal plane to course medially across the ELL segments. These medially coursing horizontal fibers are sorted: they form sublaminae according to the nerve branch containing their peripheral axon. Horizontal axons then turn dorsally, form fascicles, and terminate within the dnl. Within the dorsal fascicles, axons run directly into the dnl with little deviation, and their terminal fields exhibit no appreciable spread.

In sternopygids, dfl horizontal fibers course in directions orthogonal to those in apteronotids. Fibers enter the rostral ELL and course medially across segments before turning caudally within segments. Unlike apteronotids, sternopygid horizontal fibers do not sort tightly by nerve branch. As horizontal axons turn dorsally they also form tight fascicles. But rather than terminating directly and without spreading, as in apteronotids, sternopgid fibers disperse from these fascicles and become sorted horizontally a second time prior to terminating in the dnl. Gymnotids show a third pattern: their primary afferents course into the rostral ELL without an obvious organization, they form no tight laminae of horizontal fibers and no fascicles of dorsal fibers. Unlike the other gymnotiforms examined, afferents coursing to the gymnotid MS can take one of two routes, ventrally through the dfl in the manner of all other gymnotiforms, or, uniquely, dorsally through the plexiform layer of the ELL (pl), which is typically the location of ELL efferents. These afferents then turn ventrally to terminate.

Variations in axonal trajectories do not appear to reflect major functional differences in the processing of electrosensory information, but instead may reflect the phylogenetic relationships of the developmental processes involved in guiding axons. We propose a simple model for the development of these different trajectories based on the assumption that among species similar guidance cues are expressed at different times as the projection develops.
Substance P‐, FMRFamide‐, and gastrin/cholecystokinin‐like immunoreactive neurons in the thoraco‐abdominal ganglia of the flies Drosophila and Calliphora
Authors: Lundquist Tomas , Nässel Dick R.
Published: January 2005

Immunocytochemical analysis of the thoraco‐abdominal ganglia of the flies Drosophila melanogaster and Calliphora vomitoria revealed neurons displaying substance P‐ (SPLI), FMRFamide‐(FLI), and cholecystokinin‐like (CCKLI) immunoreactivity. It could be demonstrated that a number of neurons contain peptides reacting with antisera against all the three types of substances, others were either FLI or CCKLI alone. No neurons displayed only SPLI. Instead, the total number (about 30) of SPLI neurons constitute a subpopulation of the FLI/CCKLI neurons. Many of the identifiable immunoreactive neurons seem to be homologous in the two fly species. One set of six large neurons, termed ventral thoracic neurosecretory neurons (VTNCs), are among those that are SPLI, FLI, and CCKLI in both Drosophila and Calliphora. With the present immunocytochemical technique, the detailed morphology of the VTNCs could be resolved. These neurosecretory neurons supply the entire dorsal neural sheath of the thoraco‐abdominal ganglia with terminals, thus forming an extensive neurohaemal area. The VTNCs also have processes connecting the thoracic neuromeres to the cephalic suboesophageal ganglion, as well as extensive arborizations in the thoracic ganglia, suggesting an important role in integrating and/or regulating large portions of the central nervous system, in addition to their neurosecretory function. Most of the other SPLI, FLI, and CCKLI neurons in the thoraco‐abdominal ganglia seem to be interneurons. However, there are four FLI neurons that appear to be efferents innervating the hindgut and a few abdominal FLI and CCKLI neurons may be additional neurosecretory cells. From the present study it appears as if neuropeptides related to substance P, FMRFamide and CCK have roles as neurotransmitters/neuromodulators and circulating neurohormones in Drosophila and Calliphora.
Dendritic bundling in layer I of granular retrosplenial cortex: Intracellular labeling and selectivity of innervation
Authors: Michael J. Wyss , Van Groen Thomas , Sripanidkulchai Kittisak
Published: January 2005

The extrinsic projections to and from the retrosplenial cortex have been studied in detail, but the intrinsic circuitry within this region has been characterized less completely. To further define the internal connections, small injections of the retrograde, fluorescent tracer Fluorogold were made into the retrosplenial cortex of the rat. These injections label neurons in layers II‐V of the contralateral homotopic cortex. In layers III‐V, the labeled neurons are present over an area much larger than the injection site, but in layer II neurons are labeled in a very precise homotopic pattern. Following these injections, only the neurons in layer II display heavily labeled apical dendrites, and these labeled dendrites form tight bundles in layer Ic and Ib of the cortex and spread out in layer Ia. An examination of Golgi‐stained material demonstrates that most of the neurons in layer II are small pyramidal cells with 2–3 small basal dendrites and a single, large apical dendrite that arborizes extensively in layer Ia. To verify the structure of the layer II neurons, they were intracellularly filled with Lucifer yellow. Examination of these labeled cells confirms the observations from the Golgi‐stained material and demonstrates that many apical dendrites of the layer II cells angle acutely, apparently to join a bundle and/or avoid an interbundle space. Tract tracing experiments demonstrate that the anteroventral nucleus of the thalamus appears to project selectively to the region containing the dendritic bundles, whereas intracortical projections appear to terminate in layers Ib and Ic in the 30–200 μm spaces between the bundles. Furthermore, the areas containing the bundles display dense AChE staining, but the interbundle spaces are almost free of AChE staining. These findings demonstrate a form of dendritic bundling that is input and output specific and may play an important role in the regulation of thalamic inputs to the cingulate cortex.
Immunolocalization and quantitation of a novel nerve terminal protein in spinal cord development
Authors: Cabalka L. M. , Ritchie T. C. , Coulter J. D.
Published: January 2005

In the adult spinal cord, the neuron‐specific protein NT75 is located in nerve terminals synapsing in the superficial laminae of the dorsal horn. The present study examines the occurrence of NT75 in the developing rat spinal cord. NT75 immunoreactivity is detectable in primary afferent axons at the dorsal root entry zone on embryonic day 15. Subsequently, staining of presumptive nerve terminals appears in the deeper laminae of the dorsal horn, expanding into the superficial laminae during the first postnatal week. NT75 staining also appears in developing corticospinal tract axons in the brainstem at birth, and at lumbosacral levels by postnatal day 5. As NT75‐positive nerve terminals approach the adult distribution, staining of primary afferent and corticospinal axons decreases, becoming undetectable by postnatal day 30. Dense transient staining of presumed nerve terminals in the ventral horn is also apparent during early postnatal development. Quantitative analysis of developing spinal cord shows a low level of NT75 immunoreactivity at birth. NT75 activity then increases substantially, reaching values by the third and fourth postnatal weeks up to 2.5 times that seen in adults. The occurrence of NT75 immunoreactivity correlates with the reported time course of synaptic development in the spinal cord. In addition, the results suggest that NT75 immunoreactivity is maintained at high levels in the nerve terminals of certain neural pathways into adulthood, whereas in other systems NT75 immunoreactivity may be detectable only during development.
Central projections of cochlear nerve fibers in the alligator lizard
Authors: Szpir M. R. , Sento S. , Ryugo D. K.
Published: January 2005

The auditory (cochlear) ganglion cells of the alligator lizard (Gerrhonotus multicarinatus) give rise to two types of peripheral fibers: tectorial fibers, which contact hair cells covered by a tectoria membrane, and free‐standing fibers, which contact hair cells without a tectorial membrane. To determine the central projections of these fibers, we applied intracellular and extracellular injections of horseradish peroxidase (HRP) to the peripheral component of the cochlear nerve. After histological processing with diaminobenzidine, individual cochlear nerve fibers could be traced through serial sections with the aid of a light microscope and drawing tube. The projection patterns formed two morphologically distinct groups. Neurons whose peripheral processes contacted tectorial hair cells in the cochlea projected to three divisions of the cochlear nucleus: nucleus magnocellularis lateralis (NML), nucleus magnocellularis medialis (NMM), and nucleus angularis lateralis (NAL). Neurons whose peripheral processes contacted freestanding hair cells projected primarily to the nucleus angularis medialis (NAM), although some also sent a single, thin branch to the NML; these neurons never projected to NAL or NMM. Morphometric comparisons of tectorial and free‐standing fibers demonstrate that tectorial fibers have a larger axonal diameter, form a greater number of terminal swellings, and make proportionally more somatic contacts. By correlating the morphologically defined groups with previously reported physiologically defined groups, we conclude that different divisions of the cochlear nucleus are associated with separate frequency ranges and that stimuli in the different frequency ranges may be orocessed separately in the brain.
Radial glia and astrocytes in developing and adult telencephalon of the lizard Gallotia galloti as revealed by immunohistochemistry with anti‐GFAP and anti‐vimentin antibodies
Authors: Yanes C. , Monzon‐Mayor M. , Ghandour M. S. , De Barry J. , Gombos G.
Published: January 2005

The development of radial glia and astrocytes in the telencephalon of the lizard Gallotia galloti was studied by immunohistochemistry with anti‐vimentin and anti‐GFAP antibodies.

Vimentin appears at embryonic stage 32 (E32) in the proliferative zone of the lateral ventricle and subpial end‐feet in the marginal zone. At E34‐35 the staining intensity for vimentin in all radial glia is maximal. It then decreases and disappears in most structures in adult animals.

GFAP appears at E35 in the end‐feet in the marginal zone and its intensity increases until adulthood, particularly in radial and sinuous fibers and in fibers that originate from the sulci and invade the ventral striatum and the septum. In contrast, the reaction is weak in the cortex, in the anterior dorso‐ventricular ridge, and in the amygdala nuclei.

Radial glia is still present in the adult, and the composition of its intermediate filaments changes during development from vimentin to GFAP.

No GFA‐positive cell bodies except those of ependymal glia were deceted in telencephalon.
Neonatal capsaicin treatment induces invasion of the substantia gelatinosa by the terminal arborizations of hair follicle afferents in the rat dorsal horn
Authors: Shortland Peter , Molander Carl , Woolf Clifford J. , Fitzgerald Maria
Published: January 2005

Capsaicin, administered on the day of birth, was found to alter laminar distribution, but not the receptive field properties or the morphology of the collateral arborizations of hair follicle afferents (HFAs) intra‐axonally injected with horseradish peroxidase (HRP). Of the 65 HFA terminal arbors in capsaicin treated rats, 46 (71 %) were found to enter the substantia gelatinosa (in control rats, 44/165, 27%). All of the collaterals projected to somatotopically normal areas of cord. Dorsal horn shrinkage (21%), as estimated by planimetric measurements of Nissl and acetylcholinesterase‐stained material, was only a partial explanation of this result. This idea was supported by the statistically significant increase (27%, P < 0.05) in the absolute dorsoventral length of collaterals.

The results show that the destruction of unmyelinated fibres during the early postnatal period by capsaicin induces HFA invasion into the area that C fibres normally occupy. This invasion suggests that the laminar termination sites for different primary afferent fibres are not altogether specified and that intact neonatal primary afferents have the capacity to sprout into denervated regions of spinal cord.
GABA and tyrosine hydroxylase immunocytochemistry reveal different patterns of colocalization in retinal neurons of various vertebrates
Authors: Wulle I. , Wagner H.‐J.
Published: January 2005

Colocalization of GABA‐ and tyrosine hydroxylase‐like immunoreactivity was studied in the retinae of various vertebrate species in order to ascertain whether the presumed coexistence of GABA and dopamine, reported earlier for mammals (Kosaka et al.: Exp. Brain Res. 66:191–210, '87; Wässle and Chun: J. Neurosci. 8:3383–3394, '88) is a common phenomenon. GABA‐immunopositive cells constituted a separate population from tyrosine hydroxylase‐positive cells in fish and amphibians, whilst in higher–i.e., amniote–vertebrates, such as reptiles, birds, and mammals, all dopaminergic cells contained GABA‐like immunoreactivity. No clear correlation was found between the type of dopaminergic cell (amacrine/interplexiform) and the presence or absence of colocalization.
Expression of C‐fos‐like protein as a marker for neuronal activity following noxious stimulation in the rat
Authors: Bullitt Elizabeth
Published: January 2005

C‐fos is a proto‐oncogene that is expressed within some neurons following depolarization. The protein product, c‐fos protein, can be identified by immunohistochemical techniques. Therefore, c‐fos expression might be used as a marker for neuronal activity throughout the neuraxis following peripheral stimulation. This study has analyzed patterns of c‐fos expression in both control and anesthetized animals and in anesthetized rats subjected to various forms of peripheral stimulation. Labeled cells were counted in the spinal cord, brainstem, hypothalamus, and thalamus. Little c‐fos immunoreactivity was found in control animals. Prolonged inhalational anesthesia increased the number of labeled cells at several brainstem sites. Noxious stimulation of anesthetized rats induced c‐fos within the neuraxis in patterns consistent with data obtained from electrophysiological studies and in additional locations for which few direct electrophysiological data are available, such as the ventrolateral medulla, the posterior hypothalamic nucleus, and the reuniens and paraventricular thalamic nuclei. Gentle mechanical stimulation was ineffective in inducing c‐fos‐like protein. The data suggest that c‐fos can be used as a transynaptic marker for neuronal activity following noxious stimulation. However, c‐fos is expressed only in some kinds of neurons following peripheral stimulation, and it therefore may be an incomplete marker for nociresponsive activity. In addition, at least a few neurons express c‐fos protein in the absence of noxious stimulation. Experiments analyzing c‐fos expression must be designed with care, as both extraneous stimuli and anesthetic depth influence the results.
Migration of neuroblasts by perikaryal translocation: Role of cellular elongation and axonal outgrowth in the acoustic nuclei of the chick embryo medulla
Authors: Book Kathryn J. , Morest D. Kent
Published: January 2005

The neuroblasts forming nucleus magnocellularis, the avian homologue of the mammalian ventral cochlear nucleus, migrate by growth and elongation of their leading processes and by perikaryal translocation through these processes from the matrix zone of the rhombic lip to the acoustico‐vestibular anlage. Golgi methods were used on staged chick embryos to reconstruct the morphogenetic phases of migration and early differentiation in situ. Fluorescence labeling of the living cells in vitro elucidated the role of axonal growth in the migratory process.

In situ, branching cochlear nerve fibers, tipped with growth cones, enter the acoustico‐vestibular anlage at E4.5–5.5 before migration of the magnocellularis neuroblasts at E.5.5–6.5. The premigratory neuroblasts in the matrix zone of the rhombic lip resemble primitive epithelial cells, which extend branched, curving processes into a characteristic formation, the rhombic whorl. The leading process of the migrating magnocellularis neuroblasts gives rise to a bifurcating axon at the interface between the matrix and mantle zones. The lateral branch becomes the recurrent ipsilateral collateral; the medial branch crosses the midline, heading toward the contralateral target site in the region of the presumptive nucleus laminaris. The cell bodies of the migratory neuroblasts appear in intermediate locations along the migration route as they translocate radially through their leading processes past the axonal bifurcation and then tangentially and obliquely into the mantle zone. Neuroblasts destined for nucleus laminaris migrate coincidentally with magnocellularis neuroblasts. Nucleus angularis neuroblasts migrate later in development, after E6.5.

In vitro, injections of a nontoxic fluorescent dye (diI) were made into explants of the medulla in the region of the contralateral target area at the time of neuroblast migration. DiI retrogradely labeled the cell bodies of premigratory magnocellularis neuroblasts in the matrix zone and of migratory neuroblasts in the mantle zone through their medial, crossing axonal branches. The morphology of the living neuroblasts in the explants resembled that in the Golgi impregnations at the corresponding stages of migration. Anterograde axonal transport also occurred.

These results demonstrate migration by perikaryal translocation and early axon extension of a specific group of neuroblasts in the central nervous system. The morphology of the migrating neuroblasts is such that a simple radial arrangement of cellular guides, glial or otherwise, would not account for their configurations. The available evidence supports the proposition that cellular elongation and perikaryal translocation constitute the general mode of neuronal migration in the central nervous system. The early extension of axons into their target sites may play a critical role in migration and early development of specific types of neurons.