bluuebunny/crossref_metadata_2025 huggingface dataset:
Further study of the outward displacement of retinal ganglion cells during optic nerve regeneration, with a note on the normal cells of dogiel in the adult frog
Authors: Singman Eric L. , Scalia Frank
Published: January 2005

In a previous study we observed massive retinal ganglion cell death in adult Rana pipiens after periods of optic nerve regeneration, and reported that large numbers of the surviving cells had become displaced bodily into the inner plexiform layer of the affected eye (Scalia et al.: Brain Research 344:267–280, 1985). The outwardly displaced cells could be identified as retinal ganglion cells because they could be back‐filled with horseradish peroxidase (HRP) injected into the regenerated optic nerve. Quantitative observations on the abnormal outward displacement of ganglion cells are reported here. Parallel observations on normally displaced ganglion cells (cells of Dogiel) are also reported to clarify the distinctions between these two classes of cells.

For the present work, injections of HRP of varying size were placed in the optic tectum bilaterally in 3 normal frogs and 9 frogs sustaining unilateral optic nerve regeneration. Most injections were centered at loci mapping the middle region of the nasal retina. The retinas were examined as flat‐mounts and in‐section. In 8 other frogs sustaining optic nerve regeneration, the HRP was administered bilaterally directly to the optic nerves in the orbit. Ganglion cells were labeled by retrograde transport of the HRP in the retinal ganglion cell layer in both the normal and affected eyes in areas topographically isomorphic with the tectal areas subtended by the injections. In the normal eyes, the orthotopic ganglion cells formed a strict monolayer, and virtually no cells existed in the inner plexiform layer. In the retinas sustaining optic nerve regeneration, the retinal ganglion cells abnormally displaced into the inner plexiform layer were also labeled topographically in correspondance with the injection sites.

The abnormally displaced cells comprised 5.5% of the total population of surviving neurons in the retinal ganglion cell and inner plexiform layers. The mean outward dislocation of the displaced cells, as measured in one frog surviving optic nerve crush for 8 weeks, was 69.9 ± 2.4% of the distance across the inner plexiform layer, which itself was uniformly 14.3 ± 0.39 μm thick.

Cells of Dogiel, which were embedded within the inner nuclear layer, were also labeled when the injections of HRP spread to include the area of representation of the optic disc. The labeled cells were restricted to a dorsal, peripapillary locus capping the optic disc. Therefore, some cells of Dogiel project to the tectum normally, but only from the central retina.

Some possible mechanisms behind the abnormal postoperative displacement of the ganglion cells are discussed.
Cytoarchitecture of the human dorsal raphe nucleus
Authors: Baker Kerry G. , Halliday Glenda M. , Törk Istvan
Published: January 2005

Serial 50 μm Nissl‐stained sections through the midbrain and pontine central gray of four adult humans (mean age 56 years, mean postmortem delay 3 hours) were analysed and the subnuclei of the dorsal raphe nucleus (DR) delineated on the basis of neuronal morphology and density. Five subnuclei were apparent: the interfascicular, ventral, ventrolateral, dorsal, and caudal. The area of each subnucleus was measured in sections selected at regular intervals throughout the length of the DR. The number of neurons was counted and their density within each subnucleus calculated. The dorsal subnucleus was the largest and contained the majority of neurons but had the lowest neuronal density. The ventrolateral subnucleus had the highest density of neurons. A total of 235,000 ± 15,000 neurons (average of 1,200 ± 200 neurons per section) were found within a volume of 71.3 ± 4.5 mm3 of DR with a mean neuronal density of 3,300 ± 200 neurons/mm3. Morphometric and morphological analysis of DR neurons revealed four distinct neuron types: round, ovoid, fusiform, and triangular. These types of neurons characterized particular subnuclei. The location and boundaries of the subnuclei of the human dorsal raphe are presented in the form of an atlas. The subdivisions described are similar to that described in other mammals. On the basis of this information the location of particular projection neurons within the human dorsal raphe can be predicted and the effects of disease on this nucleus may be forecast.
Type‐specific localization of monoamine oxidase in the enteric nervous system: Relationship to 5‐hydroxytryptamine, neuropeptides, and sympathetic nerves
Authors: Gershon M. D. , Sherman D. L. , Pintar J. E.
Published: January 2005

The localization in the guinea pig enteric nervous system (ENS) of monoamine oxidase (MAO) types A and B was investigated at the light and electron microscopic levels. Immunocytochemistry was used to visualize the enzyme protein and histochemistry was employed to study catalytic activity. Type specificity was achieved in histochemical studies by using deprenyl (0.5 μM) to inhibit MAO‐B or clorgyline (0.1 μM) to inhibit MAO‐A. The distribution of MAO‐B immunoreactivity in the ENS corresponded to that of the sites of MAO activity found histochemically to be inhibited by deprenyl, but not clorgyline. MAO‐B was observed to be the primary type of MAO found in the intrinsic elements of the ENS and was located in subsets of neurons in both submucosal and myenteric plexuses. MAO‐B was not demonstrated immunocytochemically or histochemically in enteric glia, nor, at the light microscopic level, was there significant MAO‐B activity or immunoreactivity in serotonin (5‐HT)‐immunoreactive neuronal cell bodies. In the submucosal plexus about 50% of the neurons expressed MAO‐B; these neurons also contained neuropeptide Y (NPY) and/or calcitonin gene related peptide (CGRP), but not substance P or vasoactive intestinal polypeptide (VIP). About 10% of myenteric neurons were intensely reactive for MAO‐B; again MAO‐B was co‐localized with NPY and/or CGRP. In contrast to intrinsic neurons, extrinsic CGRP‐immunoreactive nerve fibers contained no demonstrable MAO activity or immunoreactivity. Moreover, the sympathetic innervation, identified as varicose axons that degenerated after administration of 6‐hydroxydopamine, contained abundant MAO‐A, but no MAO‐B activity or immunoreactivity. It is concluded that MAO‐B is characteristic of a subset of intrinsic enteric neurons, while MAO‐A is confined to the sympathetic innervation, which is extrinsic. At the electron microscopic level individual cells varied greatly in their degree of immuno‐ or cytochemically demonstrable MAO‐B, which was most concentrated on the outer membranes of mitochondria. MAO‐B immunoreactivity (but not cytochemical activity) was found on mitochondria in some serotoninergic perikarya identified by the simultaneous radioautographic detection of the uptake of 3H‐5‐HT. Mitochondria in most serotoninergic axon terminals displayed both MAO‐B activity and immunoreactivity. Neurons receiving serotoninergic synapses often, but not invariably, contained MAO‐B. Inhibition of neither MAO‐B nor MAO‐A appeared to slow the disappearance of 3H‐5‐HT loaded into enteric neurons significantly, even when intraneuronal storage of 5‐HT was inhibited with tetrabenazine. Alternative pathways for 5‐HT catabolism, such as glucuronidation, which do not occur in the brain, may be available to enteric serotoninergic neurons. The role of MAO‐B in enteric neurons that are not monoaminergic but peptidergic remains to be determined.
Morphology of retinal ganglion cells in the flying fox (Pteropus scapulatus): A lucifer yellow investigation
Authors: Dann J. F. , Buhl E. H.
Published: January 2005

The morphology of retinal ganglion cells was determined in megachiroptera, commonly known as flying foxes. Retinal ganglion cells were intracellularly injected with the fluorescent dye Lucifer yellow in fixed retinae from adult little red flying foxes (Pteropus scapulatus) captured in their natural habitat. Ganglion cells closely resembled the three main classes of cat retinal ganglion cells, and therefore were classified into alpha‐, beta‐, and gamma‐type cells. The size of the alpha‐ and beta‐type somas and dendritic fields increased with increasing distance from the area centralis. However, this eccentricity dependence was not as pronounced as in the cat. The gamma‐type cells were sub‐divided into mono‐, bi‐, and diffusely stratified, in accordance with the ramification of their dendrites within the inner plexiform layer. The alpha‐and beta‐type cells were uni‐stratified in either the sublamina of the inner plexiform layer closest to the ganglion cell layer or in that closest to the inner nuclear layer. These laminae correspond to those in the cat retina which contain the dendritic ramifications of ganglion cells whose central receptive fields respond best to onset of light (the “on‐centre” cells), or to ganglion cells whose centres respond optimally to light being extinguished (the “off‐centre” cells). Thus the flying fox retina contains a morphological correlate of the “on”/“off” dichotomy of alpha and beta cells in the cat retina. In general the flying fox retinal ganglion cells exhibit a degree of morphological complexity reminiscent of cat retinal cells and this may reflect similar functional properties.
Multiplicity of vestibulospinal projections to the upper cervical spinal cord of the cat: A study with the anterograde tracer Phaseolus vulgaris leucoagglutinin
Authors: Donevan A. H. , Neuber‐Hess M. , Rose P. K.
Published: January 2005

The distribution and frequency of vestibulospinal axons and boutons in the upper cervical spinal cord of the cat were investigated. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA‐L) was injected into discrete regions of the vestibular nuclei, including the medial and descending nuclei, as well as small regions of the lateral vestibular nucleus along its medial border with the medial vestibular nucleus. In contrast to previous reports, labelled vestibulospinal axons were not found to be restricted to the ventromedial and ventrolateral funiculi, but were also observed bilaterally in the lateral funiculi, the dorsolateral funiculi and the dorsal columns. The diameter of these axons ranged from 0.5 to 7.4 μm. Labelled boutons were found bilaterally from lamina IV to IX as well as in lamina X. Contralateral to the injection site, boutons were frequently found as far dorsal as lamina II. Ipsilaterally, boutons were found this far dorsal in only one experiment. There was a dense projection to the contralateral central cervical nucleus, while very few, if any, boutons were observed in the ipsilateral central cervical nucleus. In each experiment, the density of boutons was greater in the rostral cervical segments than in more caudal segments. The “new” vestibulospinal projections to the dorsal horn and central cervical nucleus were confirmed in separate experiments using retrograde transport of horseradish peroxidase.

These results show that vestibulospinal axons project to the upper cervical spinal cord via multiple funicular paths. The rich terminations of these axons outside of the ventral horn, as well as in the neck motoneuron nuclei, indicate that vestibulospinal projections must play a wide variety of functions in addition to their well‐documented role in the direct control of head movement.
Quantitative nissl study of the neuronal types, and recognition of cytoarchitectural subdivisions, within the rabbit periaqueductal gray
Authors: Meller S. T. , Dennis B. J.
Published: January 2005

A quantitative analysis of 4,621 Nissl‐stained neurons within the periaqueductal gray of the rabbit found that there were four main cell types (stellate/round, ovoid, spindle, and triangular) distributed throughout this complex. Further statistical analysis on these neurons confirmed that there were morphological grounds to subdivide the periaqueductal gray into four cytologically distinct regions: ventral, lateral, dorsal, and medial.

Neurons in the narrow medial zone, which completely surrounds the aqueduct, were orientated essentially parallel to the aqueduct. The majority of these neurons were small, ovoid, or spindle in shape, and highly basophilic. The cells in this region had the lowest packing density of those in any periaqueductal gray subdivision. The dorsal subdivision, a small midline region, contains the largest cells of any division and the highest packing density of glial cells. The neurons in this region show no preference for orientation, tend to be round, and are moderately basophilic. Cells in the lateral zone are also quite large and demonstrate a preferred orientation either parallel or perpendicular to the aqueduct. The average cell density within lateral PAG is considerably higher than in other regions. Most of these neurons are round or ovoid, and moderately basophilic. Neurons in the ventral zone are mainly ovoid, of medium size, highly basophilic, and lie fairly sparsely arrayed and are orientated essentially parallel to the aqueductal surface.
Transcallosal non‐pyramidal cell projections from visual cortex in the cat
Authors: Peters Alan , Payne Bertram R. , Josephson Karen
Published: January 2005

Non‐pyramidal cells with transcallosal projections were identified in the area 17/18 border region of the cat by retrograde transport of horseradish peroxidase injected into border region of the opposite hemisphere. From several hundred neurons filled with a Golgi‐like diaminobenzidine (DAB) reaction product, seven cells were identified by their radially oriented smooth dendrites as possible non‐pyramidal cells. Following thin‐sectioning and examination with the electron microscope, four of the neurons proved to be layer IV spiny stellate cells with incompletely filled dendritic spines, and two proved to be layer III pyramidal cells with an incompletely labelled apical dendrite and dendritic spines. The remaining neuron was a non‐pyramidal cell whose essentially smooth dendrites were covered with synapses, and whose cell body formed both symmetric and asymmetric synapses with presynaptic terminals. To better assess how many non‐pyramidal cells might be labelled, thin sections of the area 17/18 border were surveyed using material processed with tetramethylbenzidine (TMB), and another five labelled non‐pyramidal cells with transcallosal projections were identified by the needle‐like crystals of TMB reaction product they contained. During the study it became evident that both the DAB and TMB reaction products in the lightly labelled neurons tended to be associated with granules that are 0.5 μm or larger in diameter and that had the characteristics of lysosomes. These granules are also visible in the light microscope as dark puncta. The numbers of puncta in profiles of pyramidal and of non‐pyramidal cells in layers II/III and IVa of the area 17/18 border region and in the control acallosal region of area 17 were counted and compared. These comparisons revealed that labelled transcallosally projecting non‐pyramidal cells may constitute 10–32% of the non‐pyramidal cell population at the area 17/18 border region. Similar values were also obtained for pyramidal cells in this region. Consequently, it is concluded that significant numbers of non‐pyramidal cells have axons that project through the corpus callosum to the contralateral hemisphere.
Reorganization of persistent motoneurons in a metamorphosing insect (Tenebrio molitor L., coleoptera)
Authors: Breidbach Olaf
Published: January 2005

The present analysis outlines how the shape of motoneurons which persist through metamorphosis in the beetle Tenebrio molitor is regulated by cellular interactions. This study focused on the structural changes of prothoracic leg motoneurons. The fate of these neurons is described in normal metamorphic development, so as to provide a basis for experimental analysis. In a first experiment the prothoracic leg imaginal discs or part of these were extirpated in the prepupa or early pupa. In a second experiment the leg imaginal discs were rotated by 180° in early larval instars of Tenebrio; the procedure caused a threefold leg anlage. Thereafter, the treated individuals continued to develop. In both experiments the effect of the operation on the structure of the dendritic trees of the persisting motoneurons was analyzed at the imaginal stage. In the first experiment the dendritic tree of the motoneurons is locally deleted. In the second experiment the branching index (quantitative description of dendritic arborization pattern) of the dendritic tree of the persisting motoneurons increased. Both experiments provided evidence that the shape of persistent leg motoneurons is stabilized and even regulated by cellular interactions during metamorphosis. Evidence is presented that sensory neurons are effective both in stabilization and regulation of the shape of persistent motoneurons.
Ontological study of calbindin‐D28k‐like and parvalbumin‐like immunoreactivities in rat spinal cord and dorsal root ganglia
Authors: Zhang Jian‐Hua , Morita Yasuhiro , Hironaka Takashi , Emson P. C. , Tohyama Masaya
Published: January 2005

The calcium ion plays an important role in some critical developmental events in the nervous system, such as neurulation and neurite elongation. Therefore, as the intracellular calcium‐binding proteins calbindin‐D28k (CaB) and parvalbumin (PV) may be expressed in these developmental events. Accordingly, the ontological expression of CaB and PV was examined immunocytochemically in the spinal cord and dorsal root ganglia (DRG) of the rat, in order to evaluate the relationship between CaB and PV expression, and other important developmental events.

During the ontogenesis of the spinal cord, the CaB‐like immunoreactivity was mainly observed in the cell somata. The immunoreactive cells in the ventral horn of the cervical and thoracic, lumbar, and sacral segments first appeared at embryonic day (E)‐12, E‐13, and E‐14, respectively. However, these cells were not detected in the intermediate gray matter of the same segments at E‐14, E‐15, and E‐16, respectively, and in the dorsal horn at E‐14‐E‐15, E‐16, and E‐17, respectively. The peak of immunoreactive cells, both as to number and intensity, occurred in the perinatal period. However, from postnatal day (P)‐14 on, the number and intensity of the positive cells decreased, the adult levels being reached at P‐35.

The PV‐like immunoreactivity was mainly detected in the fibers and punctata during the ontogenesis of the spinal cord. The immunoreactive fibers first appeared on the surface of the dorsal horn in the cervical and thoracic segments at E‐14, then entered the dorsal horn at E‐15, and reached the intermediate gray matter and ventral horn at E‐16. The first appearance of these fibers in the same areas of the lumbar and sacral segments occurred 1 day later than in the cervical and thoracic segments. During the perinatal period, the maximum content of PV‐like immunoreactive fibers, together with many punctata, was seen in the gray matter. However, between P‐14 and P‐17, most of them lost immunoreactivity rapidly, with the exception of the medial region of the intermediate gray matter, where the PV‐immunoreactive punctata remained up to the adult stage.

In DRG neurons, both CaB and PV was expressed, but in different neurons. Neurons labeled with anti‐CaB and anti‐PV sera were first detected at E‐16 and E‐14, respectively. These neurons were large or medium‐sized in the prenatal period. Small neurons were also labeled with these sera after birth. Positive neurons of different sizes in DRG increased in number in the postnatal period. Up to P‐35, the expression of CaB and PV in DRG reached the adult levels.

The appearance of and developmental changes in CaB‐like and PV‐like immunoreactivities in the spinal cord and DRG may be maintained during the neurogenesis of the immunoreactive regions, suggesting the possible developmental roles of CaB and PV.
Variability in tactile projection patterns to cerebellar folia crus IIa of the norway rat
Authors: Bower James M. , Kassel Jeffrey
Published: January 2005

Tactile responses in the granule cell layers of the cerebellar hemispheres of rats are topographically arranged as a series of patches each representing a different region of the body surface. Previous observations had suggested that patches representing specific body parts recur in similar folial positions in different individuals; however, these relationships were not quantified. In this study we make inter‐animal comparisons of the detailed distribution of receptive fields in the granule cell layer of the crown of crus IIa by using physiological mapping techniques. The results suggest that maps from different individuals do, in fact, share several topological features. These include the regions of the body surface represented, the general proportions of these representations, the relative positions of patches representing the same body parts, and the organization of receptive fields within patches located in similar positions. The principal variability seen in these comparisons was in the detailed neighborhood relations between different patches. As a result of the analysis of the consistent and variable features of these maps, we propose and discuss a new role for these cerebellar regions in coordinating the acquisition of tactile sensory information.
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

The 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

We 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

Nucleus 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

In 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

One 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

The 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

Selective 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

In 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

Two 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

Early 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

Motor 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.
Plasticity of spinal systems after unilateral lumbosacral dorsal rhizotomy in the adult rat
Authors: Wang Shwun‐De , Goldberger Michael E. , Murray Marion
Published: January 2005

Plasticity of spinal systems in response to lumbosacral deafferentation has previously been described for the cat, by using immunocytochemistry to demonstrate plasticity of tachykinin systems and degeneration methods to demonstrate plasticity of descending systems. In this study, we describe the response to lumbosacral deafferentation in the adult rat. Application of immunocytochemical methods to visualize tachykinins (predominantly substance P [SP]), serotonin (5‐HT), and dopamine B‐hydroxylase (DBH), the synthesizing enzyme for norepinephrine, permits us to compare the response of SP systems in rat and cat spinal cord and to examine the response of two descending systems, serotoninergic and noradrenergic, to deafferentation. We used image analysis of light microscopic preparations to quantify the immunoreaction product in the spinal cord in order to estimate the magnitude, time course and localization of changes induced by the lesion. The distribution of SP, serotoninergic (5‐HT), and noradrenergic staining in the spinal cord of rat is very similar to that of the cat. Unilateral lumbosacral rhizotomy elicits a partial depletion, followed by a partial replacement of tachykinin immunoreactivity in laminae I and II. This response was similar to that described for the cat, although characterized by a longer time course, and, as in the cat, is likely due to plasticity of tachykinin containing interneurons. The same lesion elicits no depletion but a marked and permanent increase in 5‐HT immunoreactivity in laminae I and II, which develops more rapidly than the response by the SP system. These results indicate sprouting or increased production of SP and 5‐HT in response to deafferentation. No change was seen in DBH immunoreactivity, indicating that the noradrenergic system does not show plasticity in response to deafferentation. Our results demonstrate that dorsal rhizotomy evokes different effects in different systems in the adult spinal cord of the rat and thus suggests that the response of undamaged pathways to partial denervation of their target is regulated rather than random.