bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographical organization of the projections from the reticular thalamic nucleus to the intralaminar and medial thalamic nuclei in the cat
Authors: Velayos J. L. , Jiménez‐Castellanos J. , Reinoso‐Suárez F.
Published: January 2005

The topography of the projections from the reticular nucleus of the thalamus (RT) to the intralaminar and medial thalamic nuclei were studied in the cat by the method of retrograde transport of horseradish peroxidase (HRP). Single small injections of the enzyme were made in the different intralaminar nuclei‐mediodorsal, ventromedial, midline, and habenular‐and in anterior group nuclei. The location and density of the neuronal labeling in the different parts of the RT were studied in each case.

Our results show that 1) after injections located in all the nuclei here studied, a consistent number of labeled neurons were found in the RT, except for the injections in the lateral habenula and the anterior thalamic nuclear complex, both of which did not label neurons in the RT. 2) Among the other thalamic nuclei here studied, the most medially situated receive less numerous RT projections than those most laterally located. 3) Injections in all the nuclei studied gave rise to a cellular labeling in the anterior sectors of the RT, except for the anterior nuclear group and the lateral habenula. The projections from the rostral pole of the RT were topographically mediolaterally organized. 4) The anterodorsal part of the pregeniculate sector of the RT projects upon the large‐called part of the lateral central nucleus and to a lesser extent upon the paracentral, centromedian, and ventromedial nuclei, the anterior part of the lateral central nucleus, and the lateral band of the mediodorsal nucleus. The posterodorsal part of the RT pregeniculate sector only projects to the large‐celled part of the lateral central nucleus. The dorsal portion of the posteroventral part of the RT pregeniculate sector also projects upon the large‐celled part of the lateral central nucleus; its ventral portion projects to the ventromedial nucleus, the posterior part of the paracentral nucleus, the lateral band of the mediodorsal nucleus, and the centromedian nucleus. 5) The infrageniculate sector of the RT projects to the posterior part of the ventromedial nucleus. A weaker projection to the large‐celled part of the lateral central nucleus, the centromedian nucleus, and the lateral band of the mediodorsal nucleus was also observed. 6) The ventral lateral geniculate nucleus projects upon the large‐celled part of the lateral central nucleus, the lateral band of the mediodorsal nucleus, and the ventromedial nucleus.

All these findings suggest an important modulatory action of the RT on the activity of the thalamic nuclei considered here.
Organization of the GABAergic system in the rat hippocampal formation: A quantitative immunocytochemical study
Authors: Woodson Walter , Nitecka Liliana , Ben‐Ari Yehezkel
Published: January 2005

Specific antibodies against gamma aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD) were used to study the organization of the GABAergic system in the rat hippocampal formation. Both the number of GABA‐like‐immunoreactive (Li) somata and neuropil density were assessed in semithin sections. Cell counts revealed that approximately 11% of the hippocampal neuronal population showed GABA‐Li within the various planes of section.

Each layer in the hippocampal formation had a characteristic organization of GABA‐Li elements. In Ammon's horn, 80–95% of the neuronal somata within the apical and basal dendritic regions were GABA‐Li positive. Within the pyramidal cell layer 5–8% of the cells were GABA‐Li in the CA1 to CA3 subfields of Ammon's horn and only 3% were GABA‐Li within that portion of the pyramidal cell layer that inserts into the hilus. Only slight differences in the density of the GABA‐Li neuropil were observed within the CA1‐CA3 dendritic regions. Restricted to the stratum lucidum was a dense band of GABA‐Li label. Counts of immunoreactive grains localized on the perimeter of pyramidal (CA1‐CA3) and granule somata revealed more terminal boutons on the CA3 cells than on CA1 and granule neuronal somata.

A topographical distribution of GABA‐Li somata and neuropil was found in the fascia dentata: There the label particularly concerned its suprapyramidal and rostrolateral portions. Approximately 40% of neurons in the molecular layer, 60% in the polymorph layer, and 18% within the hilar region were GABA‐Li. Within the granule cell layer only 2% of the neurons were GABA‐Li positive. Distinct differences in the density of the GABA‐Li neuropil were present in the molecular, pericellular granular, and hilar regions of the fascia dentata.

While the morphology of GABA‐Li neuronal somata varied according to their hippocampal layer, the most heterogeneous cell types were found in the regio inferior of the hippocampus. There we have identified neurons that are reminiscent of the inferior region interneuron described in Golgi material by Amaral and Woodward (Brain Res. 124:225–236, '77). Moreover, particularly in the sagittal plane, we have identified oval, triangular, and round cells and that have processes oriented in a parallel arrangement, appearing to be aligned along the granule cell mossy fibers.
Comparative quantitative study of the hippocampal region of two closely related species of wild mice: Interspecific and intraspecific variations in volumes of hippocampal components
Authors: Slomianka L. , West M. J.
Published: January 2005

To investigate the structural changes in the hippocampal region (subiculum, Ammon's horn, and area dentata) associated with speciation, the volumes of homologous components of this region of the forebrain were compared in the two closely related murine rodent species, Apodemus flavicollis (yellow‐necked wood mice) and A. sylvaticus (long‐tailed field mice), and in two geographically separated groups of A. sylvaticus.

With the exception of the mossy fiber zone, no significant differences were found in the relative sizes of the components of Ammon's horn. Significant interspecific differences were found in the deep subiculum, in the intermediate (medial perforant path) and deep (commissural‐associational) zones of the molecular layer of the area dentata, and in the hilus. A significant intraspecific difference was found in the combined intermediate and superficial (medial and lateral perforant path) zone of the dentate molecular layer.

Differences found in the relative size of the hilus and the mossy fiber zone of Ammon's horn were complementary in that the combined volumes of these zones, which are both terminal fields of dentate granule cells, did not differ in the two species. This finding provides evidence that the distribution of the terminal field of a projection system can be altered while the size of the terminal field is maintained.

Within the hippocampal region, components of Ammon's horn appear well suited for quantitative comparative studies that span taxonomic units beyond the species level. In agreement with previous quantitative studies, differences in the volumes of components of Ammon's horn found in species of different orders are more likely to reflect phylogenetic trends rather than changes resulting from specializations of the particular species used. This is not true for the subiculum and the components of the area dentata.

Experimentally induced changes in the connectivity of the hippocampal region are discussed in terms of the structural changes which may be responsible for the quantitative differences observed between the two species studied here.
Distribution of radioactive leucine following uptake by olfactory sensory neurons in normal and heteromorphic crayfish antennules
Authors: Mellon DeForest , Tuten H. Robert , Redick Jan
Published: January 2005

Surgical excision of one of the compound eyes from juvenile crayfish leads to the regeneration of a heteromorphic antennule in 30% of the cases. Most of the heteromorphic antennules generated this way are bifurcate appendages possessing morphologically distinct medial and lateral branches. These structures are identical to the internal and external flagella of the normal antennules, and the homolog of the external flagellum bears aesthetascs supplied by olfactory sensory neurons. Autoradiographic analysis of the brain following exposure of heteromorphic antennules to tritiated leucine indicates that the supernumerary sensory axons transport the labeled amino acid into their central terminals at appropriate target locations within the ipsilateral olfactory lobe. The data suggest that olfactory input from heteromorphic antennules is incorporated into the organized central projection of olfactory afferents from the normal antennule.
Modification of left‐right pairing during the development of individual crest synapses in the rat interpeduncular nucleus
Authors: Lenn Nicholas J. , Whitmore Leanna
Published: January 2005

The synaptic organization of the rat interpeduncular nucleus is highly ordered in the normal adult. By 90 days of age, 90% of crest synapses in its intermediate subnuclei are formed by two cholinergic endings, one from each medial habenula. Stereological calculation of the number of crest synapses per intermediate subnucleus, based on total samples of crest synapses in 3–4 sections through the subnucleus, allows comparisons of afferent pairing among ages without interference by other developmental changes. Between 21 and 90 days of age, the total number of crest synapses per intermediate subnucleus increases tenfold (p ≤ 10−8), from 90,000 at 21 days of age, through 130,000 at 28 days, 440,000 at 45 days, to 1,000,000 at 90 days. The volume of the intermediate subnucleus increases fivefold during the same interval.

Electron microscopic degeneration was used to estimate the pairing of left and right habenula afferents at crest synapses at the same ages. Through 21 days of age, only one‐third of crest synapses are formed with pairing of one left and one right medial habenula afferent, whereas two‐third have both afferent endings arising from the same medial habenula. At 28 days of age left‐right pairing has increased to 43%, and at 45 days of age 53%, or 240,000, are so paired. The number of same‐side paired crest synapses at 45 days, 210,000, is 3.5 times the number so paired at 21 days (p = .003). This indicates continued formation of considerable numbers of crest synapses with this transient mode of pairing as late as 45 days of age. Since the number with same‐side pairing in the adult, 100,000, is half the number at 45 days (p ≤ 10 −8), remodeling of afferent pairing must continue to be an important process in the development of interpeduncular nucleus throughout the period of synaptogenesis. Conversely, the data are inconsistent with the principal alternative, a marked change in synapse formation after 21 days of age such that newly forming crest synapses are initially left‐right paired.

The remodeling may involve any of several modes of synapse elimination and/or altered pairing. It appears to be similar to remodeling observed in a number of other systems, although these have rarely addressed connectivity at the level of individual synapses. Since the cellular and molecular mechanisms of remodeling in general remain to be discovered, a system where these processes can be experimentally approached in terms of their level of action at individual synaptic sites may facilitate analysis.
Topography and morphology of retinal ganglion cells in the coral trout Plectropoma leopardus (Serranidae): A retrograde cobaltous‐lysine study
Authors: Collin Shaun P.
Published: January 2005

The retinal topography of the adult coral trout Plectropoma leopardus (Serranidae, Perciformes) is examined in Nissl‐stained material and confirmed by means of retrograde labelling with cobalt‐lysine from the optic nerve. Concentric isodensity contours surround a temporoventral area centralis of over 1.5 × 104 cells per mm2 which lies ventral of the elongated optic nerve head. Peripheral densities of ganglion cells fall to less than 0.25 × 104 cells per mm2. A total of 1.17 × 105 ganglion cells is found over the entire retina. Silver intensifications of cobalt‐lysine‐stained cells allow a detailed analysis of ganglion cell morphology. Soma and dendritic field size increase with eccentricity, and within the confines of the area centralis only the smallest cell size is found. Dendritic arbors of peripheral ganglion cells are all oriented parallel to the retinal margin with an axon lying close to the vitreous humor. Nine classes of cells are characterized on the criteria of soma size, dendritic field size, primary and secondary branching patterns, soma position, and dendritic termination areas. Possible morphological homologies with ganglion cells of other teleosts are also discussed.
Bouton ultrastructure and synaptic growth in a frog autonomic ganglion
Authors: Streichert Laura C. , Sargent Peter B.
Published: January 2005

Postmetamorphic growth in the frog, Xenopus laevis, is accompanied by an increase both in the size of autonomic neurons in the heart and in the number of synaptic boutons that contact their surface. To determine whether the properties of individual boutons change as their number increases, serial‐section electron microscopy was used to examine bouton ultrastructure at the end of metamorphosis and in the adult. The area of bouton contact, number of active zones per bouton, active zone size, percent of bouton area occupied by active zone, and vesicle density were examined. No differences were found between the two bouton populations for any of the parameters examined. These results support the hypothesis that boutons are structural units of synaptic growth, whereby the total area of synaptic contact increases through the addition of boutons without a change in their morphological properties.
Topographic organization of the central projections of the spiral ganglion in cats
Authors: Leake Patricia A. , Snyder Russell L.
Published: January 2005

The morphological organization of inputs from restricted sectors of the cat cochlear spiral ganglion into the cochlear nucleus was studied by making focal extracellular injections of horseradish peroxidase (HRP) into the spiral ganglion. Injections resulted in Golgi‐like labeling of a small cluster of spiral ganglion cells and their peripheral and central axons.

Large injections involved most of the cells within Rosenthal's canal in sectors of the spiral ganglion innervating ≥;1 mm of the basilar membrane and resulted in narrow, complete laminae of labeled axons and preterminal fields within each cochlear nucleus subdivision. The positions of these bands were consistent with the “isofrequency laminae” appropriate for the frequencies represented at the injection sites, with high frequency laminae situated more dorsally, and lower frequencies progressively more ventral. A discrete projection to the small cell cap area was observed that was discontinuous with the main projection laminae in the ventral cochlear nuclei (VCN). In the dorsal cochlear nucleus, projecting fibers and terminals were excluded from the molecular cell layer. No labeled fibers entered the granule cell areas.

In contrast to larger injections, very small HRP deposits labeled only part of an isofrequency lamina. Specifically, injections restricted to the scala tympani aspect of the spiral ganglion labeled only the lateral part of VCN isofrequency laminae, whereas injections limited to the scala vestibuli aspect of the ganglion labeled the medial aspect of the isofrequency planes. Thus these data indicate a previously unrecognized topographic representation of the vertical dimension of the spiral ganglion across VCN isofrequency laminae. Some posible functional implications of this projection organization are discussed.
Thalamic connections of the cortex of the superior temporal sulcus in the rhesus monkey
Authors: Yeterian Edward H. , Pandya Deepak N.
Published: January 2005

The thalamocortical connections of the superior temporal sulcus (STS) were studied by means of the WGA‐HRP retrograde tracing technique. The results indicate that the distribution of thalamic projections varies along the rostral‐caudal dimension of the STS. Thus the rostral portion of the upper bank receives input primarily from the medialmost portion of the medial pulvinar (PM) nucleus. The middle region of the upper bank receives projections from medial and central portions of the PM nucleus, and also from the oral pulvinar, limitans, suprageniculate, medial geniculate, and dorsomedial nuclei. The cortex of the caudal portion of the upper bank has basically similar thalamic input; however, the projections from the PM nucleus originate in central and lateral portions. Additionally, there are projections from the lateral pulvinar (PL), ventroposterolateral, central lateral, parafascicular, and paracentral nuclei. In contrast to the dorsal bank, the cortex of the ventral bank of the STS receives somewhat different and less extensive thalamic input. The rostral portion of the lower bank receives projections only from the ventromedial sector of the PM nucleus whereas the middle portion of the lower bank receives projections from the PL and the inferior pulvinar nuclei as well as from the PM nucleus.

The upper bank of the STS, on the basis of physiological and anatomical studies (Jones and Powell, '70; Seltzer and Pandya, '78; Gross et al., '81; Baylis et al., '87), has been shown to contain multimodal areas. The present data indicate that the multimodal region of the STS has a preferential relationship with the central sector of the PM nucleus.
Enzyme‐histochemical demonstration of microglial cells in the adult and postnatal rabbit retina
Authors: Schnitzer Jutta
Published: January 2005

Enzyme‐histochemical methods for thiamine pyrophosphatase (TPPase) and nucleoside diphosphatase (NDPase) were applied to wholemounted rabbit retinae to demonstrate the shape and distribution of microglial cells in early postnatal and adult animals. At birth, microglial cells were already present in the entire retina. They acquired their adult “resting shape” during the first 3 postnatal weeks. Early postnatally labeled microglial cells were scattered throughout the nerve fiber layer, the inner plexiform layer, and the outer plexiform layer (OPL); at adulthood, they were not detected in the OPL. Nissl‐stained retinae revealed that the number of microglial cells continuously increased during postnatal development. The same Nissl‐stained preparations were used to evaluate the topography of degenerating cells in the developing postnatal retina of the rabbit. Large numbers of degenerating pyknotic cells were observed throughout the entire retinal ganglion cell layer during the first postnatal week. Later their number decreased, and from the third postnatal week onward degenerating cells were rare. Also discussed is that the emergence of microglial cells during development may be related to cell death, whereas at adulthood the function(s) of microglial cells remains obscure.

Evidence for the blood‐derived origin of microglia was not obtained in this study. It is argued here that if this mode of development, which has been demonstrated for other species, is also applied to the rabbit retina, then microglia would have to migrate over considerable distances, since, postnatally, the rabbit retina is avascular for more than 1 week.
Noradrenergic innervation of monkey prefrontal cortex: A dopamine‐β‐hydroxylase immunohistochemical study
Authors: Lewis David A. , Morrison John H.
Published: January 2005

Norepinephrine has been implicated in the regulation of a number of cortical functions, yet relatively little is known about the anatomical organization of noradrenergic axons in the expanded and highly differentiated prefrontal cortex of primates. In this study, the distribution of fibers containing dopamine‐ß‐hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, was characterized immunohistochemically in the prefrontal cortical regions of Old World cynomolgus monkeys (Macaca fascicularis) and New World squirrel monkeys (Saimiri sciureus). In both species, differences in the density of DBH‐labeled fibers were detected both across and within many prefrontal cytoarchitectonic regions. In cynomolgus monkeys, area 8B had the greatest density of DBH‐immunoreactive fibers; within this region, the medial surface had a greater density of labeled processes than the dorsal surface. Areas 9 and 24 also had a high density of DBH‐labeled fibers, areas 11, 12, 13 and 25 were of intermediate density, and portions of areas 10 and 46 had the lowest density of immunoreactive fibers. Regional differences in the density of DBH‐immunoreactive fibers were also present in squirrel monkey prefrontal cortex.

Despite the regional variations in the density of DBH‐immunoreactive fibers, the laminar distribution of these fibers was very similar across cytoarchitectonic areas of cynomolgus prefrontal cortex. Layer I contained a low density of labeled fibers which were primarily tangential in orientation. The predominantly radially oriented fibers in layers II‐IV were slightly higher in density. The density of both radially and tangentially oriented immunoreactive fibers increased substantially in layer V. Fiber density decreased in layer VI; a band of tangentially oriented fibers was present in the deep portion of this layer. With a few exceptions, the laminar distribution of DBH‐immunoreactive fibers in the prefrontal regions of squirrel monkey cortex was similar to that of cynomolgus monkey.

Since other data suggest that anti‐DBH selectively labels noradrenergic axons in monkey neocortex, the distinctive innervation patterns exhibited by DBH‐immunoreactive fibers reveal the regions and layers that may be the principal sites of action of norepinephrine in exerting its effects on prefrontal cortical function.
Extension of the critical period for developmental plasticity of the corticospinal pathway
Authors: Bregman Barbara S. , Kunkel‐Bagden Ellen , McAtee Marietta , O'Neill Andrea
Published: January 2005

The corticospinal tract (CST) of the rat undergoes a prolonged period of postnatal development. Lesions of the presumptive CST pathway at birth are followed by the aberrant rerouting of the developing corticospinal axons around the lesion site through adjacent undamaged CNS tissue. This developmental plasticity becomes severely restricted by 5‐6 days of age, so the axons are no longer capable of growth around the site of injury. The aim of the current study was to determine whether altering the environment at the site of injury by filling the lesion with transplanted fetal spinal cord tissue could prolong the critical period for developmental plasticity of the corticospinal pathway. The spinal cord was damaged (overhemisection) at three stages in the development of the corticospinal (CS) pathway: 1) prior to the arrival of CS axons, 2) after the axons elongated through the cord but prior to synaptogenesis, and 3) after both axonal elongation and synaptogenesis were completed. One to 9 months later, anterograde neuronal tracing with horseradish peroxidase was used to assess the growth of the corticospinal pathway with or without a fetal transplant at the site of injury, and the pattern of labeling was compared with that observed in adult nonlesioned control animals. Our results indicate that the presence of a transplant prolongs the critical period for developmental plasticity of the CST. Transplants elicited growth of CST axons throughout the postnatal period examined. CST axons damaged prior to synaptogenesis exhibited more robust growth than those lesioned after synaptogenesis had been completed. These results suggest that both environmental and neuronal factors interact to regulate the response of immature CS neurons to injury.
Neurogenesis and cell death in the isthmic nuclei of the frog Limnodynastes dorsalis
Authors: Dann J. F. , Beazley L. D.
Published: January 2005

In Limnodynastes dorsalis, neurogenesis of the isthmic nuclei was determined by 3H‐thymidine autoradiography. The nuclei developed in a rostroventral to caudodorsal direction. Peak neurogenesis occurred in midlarval life, resulting in the formation of a substantial protion of each nucleus. Cell death was evidenced by the presence of pyknotic cells within the nucleus in all except the earliest stages. Peak cell death occurred around metamorphic climax. It was during this period that a rim neuropil appeared that segregates within the nucleus the contralateral and ipsilateral components of the tecto‐isthmo‐tectal pathways underlying binocular vision. It is also a time just prior to the onset of electrophysiologically detectable ipsilateral visual responses. However, no systematic cell death was found. Therefore the role of cell death in the formation of the isthmic nuclei remains obscure, although it may be involved in the establishment of tecto‐isthmo‐tectal connections.
Morphology and distribution of synapses onto a type of large field ganglion cell in the retina of the goldfish
Authors: Hitchcock Peter F.
Published: January 2005

The morphology and dendritic distribution of terminals that synapse onto a type of large‐field ganglion cell in the retina of the goldfish are described. Electron microscopy was combined with retrograde labelling of cells with horseradish peroxidase (HRP). Synapses from both amacrine (four types) and bipolar cells contacted the dendrites (all orders) of these cells. In contrast to a recent report describing the synaptic organization of large‐field ganglion cells in the catfish (Sakai et al., '86), the synapses were relatively evenly distributed throughout the dendritic arbor, not clustered at discrete sites, and no presynaptic specializations were seen in the dendrites of the ganglion cells.
Morphology and physiology of cells in slice preparations of the dorsal cochlear nucleus of mice
Authors: Oertel Donata , Wu Shu Hui
Published: January 2005

Horseradish peroxidase (HRP) was injected into cells from which intracellular recordings were made in slices of the dorsal cochlear nucleus (DCN) in order to correlate physiology with morphology. In general, the morphology of cells labeled intracellularly with HRP corresponded to those made with Golgi impregnations in mice and other mammals. The following cells were labeled: one granule cell, four cartwheel cells, eight fusiform cells, two other cells in the fusiform cell layer, and two tuberculoventral association cells in the deep layers of the DCN The axon of the granule cell runs parallel to isofrequency laminae with collaterals branching perpendicularly and running along the tonotopic axis. The cartwheel cells have dendrites in the molecular layer that are densely covered with spines. The axon of one cell terminates just dorsally to the cell body. Fusiform cells have the characteristic spiny, apical and smooth, basal dendrites. The basal dendrites are conspicuously oriented parallel to isofrequency laminae. Axons of the fusiform cells exit through the dorsal acoustic stria without branching. The two tuberculoventral association cells in the deep DCN have axons that terminate both in the deep DCN, within the same isofrequency lamina that contains the cell body, and in the ventral cochlear nucleus (VCN).

Intracellular recordings from 11 of these cells show that they cannot be distinguished on the basis of their responses to intracellularly injected current. All cell types fired large action potentials that were followed by a fast and a slower undershoot, distinguishing them from cells of the VCN but not from one another. Most cells responded to shocks of the auditory nerve root with early EPSPs and later IPSPs. The latencies of EPSPs show that some were monosynaptic and others polysynaptic. That there was no systematic relationship between the latencies of EPSPs and the cell types from which they were recorded shows that shocks to the nerve root may have activated more than just the large, myelinated, auditory nerve fibers.
Distribution of sympathetic preganglionic neurons and monoaminergic nerve terminals in the spinal cord of the rat
Authors: Anderson C. R. , McLachlan Elspeth M. , Srb‐Christie Olga
Published: January 2005

A study was made of the distribution of sympathetic preganglionic neurons identified by retrograde labeling with horseradish peroxidase from various peripheral nerve trunks and of the distributions of monoaminergic terminals in the spinal cord of the rat. Nerve terminals were stained immunohistochemically by using antisera raised against tyrosine hydroxylase, phenylethanolamine‐N‐methyl‐transferase, neuropeptide Y, and 5‐hydroxytryptamine and by using formaldehyde‐induced fluorescence. The three‐dimensional distribution of sympathetic preganglionic neurons was described by using computer reconstruction and compared with the arrangement of each population of immunohistochemically stained terminals in the intermediate zone. Although monoaminergic terminals are associated with most sympathetic neurons, particularly in the intermediolateral column, the relationship of many terminals to sympathetic neuron somata in other parts of the intermediate zone is tenuous. Some of the descending innervation may terminate on interneurons. The data are consistent with the coexistence of phenylethanolamine‐N‐methyl‐transferase and neuropeptide Y in terminals arising from cell bodies in the C1 region in the ventrolateral medulla and with the presence of at least two populations of catecholaminergic terminals as well as the adrenergic one. Serotoninergic terminals are denser and have a different arrangement from those of catecholaminergic terminals in the intermediate zone.
Rapid changes in cochlear nucleus cell size following blockade of auditory nerve electrical activity in gerbils
Authors: Pasic Thomas R. , Rubel Edwin W.
Published: January 2005

Large spherical cells of the mammalian anteroventral cochlear nucleus (AVCN) receive direct excitatory input from auditory nerve axons. Trans‐synaptic regulation of neuronal cell size and cell number after cochlear ablation has been previously demonstrated in neonates of several vertebrate species, including the gerbil. Such changes may be related to loss of spontaneous or evoked auditory nerve electrical activity or to loss of activity‐independent factors. We have developed a method to chronically, yet reversibly, block auditory nerve electrical activity without violating the integrity of the inner ear. Tetrodotoxin (TTX) was embedded in an ethylene‐vinyl acetate copolymer resin (Elvax). A small piece of Elvax containing TTX was placed next to the round window membrane, which allowed TTX to diffuse into the inner ear. As a measure of the effectiveness of manipulation, the onset, duration, and magnitude of the auditory threshold shift were measured by the auditory brainstem response. The sound‐evoked response was abolished within 10 minutes of placement of TTX on the round window membrane. The duration of threshold shift was dose‐dependent and lasted 24–46 hours. Implants of Elvax without TTX did not produce a significant threshold shift. TTX, which blocks voltage‐gated sodium channels, did not abolish the potassium‐based cochlear microphonic response.

The consequence of blocking afferent electrical activity on gerbil AVCN large spherical cells was examined by measuring their cross‐sectional area after each of four manipulations: unilateral auditory nerve action potential blockade with TTX; unilateral surgical cochlear ablation; ipsilateral TTX exposure/contralateral cochlear ablation; and unilateral sham operation (Elvax without TTX). Large spherical cells ipsilateral to cochlea TTX exposure were 21% smaller than contralateral large spherical cells. Cells ipsilateral to cochlear ablation were 25% smaller than contralateral cells. There was not a significant difference between the effect of cochlear ablation and TTX exposure on AVCN cell size and there was not a reliable effect of sham operation. These findings are consistent with previous work in the avian auditory system and support the hypothesis that electrical activity or the sequelae of electrical activity is a major factor in transneuronal regulation of cell size.
Changes in dorsal horn synaptic disc numbers following unilateral dorsal rhizotomy
Authors: Chung K. , McNeill D. L. , Hulsebosch C. E. , Coggeshall R. E.
Published: January 2005

The present study estimates the numbers of synaptic discs and numbers of degenerating synaptic terminals in laminae I–IV of the rat S2 dorsal horn ipsi‐ and contralateral to unilateral dorsal rhizotomy. These data allow us to estimate the loss of synapses of primary afferents and to correlate this loss with the rate of axon disappearance in the proximal stump of a transected S2 dorsal root. Our first findings are that 47% of the ipsilateral synapses and 27% of the contralateral synapses disappear within a day following unilateral rhizotomy. Conclusions are that the predominant synaptic population in this part of the rat spinal cord is of primary afferent origin and that there is an extensive bilateral projection of the dorsal root fibers. The contralateral projection is confirmed by the appearance of numerous degenerating terminals on the contralateral side. We also find that synaptic loss and appearance of degenerating terminals occur relatively synchronously in laminae I–IV. Finally we find that the time course of the synaptic loss correlates primarily with the disappearance of unmyelinated fibers in the proximal stump of the transected dorsal root.
Human reticular formation: Cholinergic neurons of the pedunculopontine and laterodorsal tegmental nuclei and some cytochemical comparisons to forebrain cholinergic neurons
Authors: Mesulam M. ‐Marsel , Geula Changiz , Bothwell Mark A. , Hersh Louis B.
Published: January 2005

Choline acetyltransferase immunohistochemistry showed that the human rostra1 brainstem contained cholinergic neurons in the oculomotor, trochlear, and parabigeminal nuclei as well as within the reticular formation. The cholinergic neurons of the reticular formation were the most numerous and formed two intersecting constellations. One of these, designated Ch5, reached its peak density within the compact pedunculopontine nucleus but also extended into the regions through which the superior cerebellar peduncle and central tegmental tract course. The second constellation, designated Ch6, was centered around the laterodorsal tegmental nucleus and spread into the central gray and medial longitudinal fasciculus. There was considerable transmitterrelated heterogeneity within the regions containing Ch5 and Ch6. In particular, Ch6 neurons were intermingled with catecholaminergic neurons belonging to the locus coeruleus complex. The lack of confinement within specifiable cytoarchitectonic boundaries and the transmitter heterogeneity justified the transmitter‐specific Ch5 and Ch6 nomenclature for these two groups of cholinergic neurons.

The cholinergic neurons in the nucleus basalis (Ch4) and those of the Ch5‐Ch6 complex were both characterized by perikaryal heteromorphism and isodendritic arborizations. In addition to choline acetyltransferase, the cell bodies in both complexes also had high levels of acetylcholinesterase activity and nonphosphorylated neurofilament protein. However, there were also marked differences in cytochemical signature. For example, the Ch5‐Ch6 neurons had high levels of NADPHd activity, whereas Ch4 neurons did not. On the other hand, the Ch4 neurons had high levels of NGF receptor protein, whereas those of Ch5‐Ch6 did not.

On the basis of animal experiments, it can he assumed that the Ch5 and Ch6 neurons provide the major cholinergic innervation of the human thalamus and that they participate in the neural circuitry of the reticular activating, limbic, and perhaps also extrapyramidal systems.
Axonal branching of the olivocerebellar projection in the rat: A double‐labeling study
Authors: Hrycyshyn A. W. , Ghazi H. , Flumerfelt B. A.
Published: January 2005

Collateralization of olivocerebellar (climbing) fibers was studied in the rat by means of the fluorochrome double‐labeling technique. Most of the olivocerebellar projection is crossed except for a minimal ipsilateral component which arises from the most rostral part of the inferior olivary nucleus (ION). ION neurons in the caudolateral part of the medial accessory olive (MAO) and the dorsal accessory olive (DAO) give off axons that branch to supply both hindlimb areas of the contralateral cerebellar cortex, i.e., the rostral anterior lobe and the caudal paramedian lobule. In addition, neurons in the middle one‐third of the contralateral MAO and DAO send axons that divide to terminate in both the caudal part of the anterior lobe and the rostral part of the paramedian lobule (forelimb receiving areas). Neurons within the caudal part of the MAO, the lateral part of the DAO, the ventral lamella of the principal olive (PO), and the dorsomedial cell column (DMCC) send axonal branches that terminate within at least two different areas of the same sagittal zones throughout the contralateral cerebellar cortex. Thus, the ION contains specialized cells that provide a divergence of integrated information from the ION to at least two cerebellar regions.
HRP labeling and ultrastructural localization of prepacemaker terminals within the medullary pacemaker nucleus of the weakly electric gymnotiform fish Apteronotus leptorhynchus
Authors: Szabo T. , Heiligenberg W. , Ravaille‐Veron M.
Published: January 2005

The prepacemaker nucleus (PPN) in the midbrain of gymnotiform electric fish projects to the pacemaker nucleus (PN) in the medulla and modulates its rhythmic discharges in the context of social electric communication. Anterograde labeling of PPN axons with HRP and ultrastructural studies of their terminations in the PN have shown that PPN neurons form synaptic contacts with both types of neurons in the PN, pacemaker cells, and relay cells.
Retrovesicular ganglion of the nematode Ascaris
Authors: Angstadt James D. , Donmoyer Judith E. , Stretton Antony O.W.
Published: January 2005

The nematode nervous system is distinguished by the small number and morphological simplicity of its neurons. Recently, the shapes and synaptic interactions of each of the 302 neurons in the small free‐living nematode, Caenorhabditis elegans, have been determined from reconstructions of serial sections by electron microscopy. Comparable anatomical studies of the large parasitic nematode Ascaris have concentrated on the dorsal and ventral nerve cords where reconstructions of motor neurons by light microscopy led to the identification of seven distinct types of motor neurons, each corresponding to a homologous cell type in C. elegans.

In this study the shapes of the 13 neurons with cell bodies in the retrovesicular ganglion (RVG) of Ascaris suum were reconstructed from light micrographs of serial sections. In other preparations the morphology of RVG neurons was observed in whole mounts after the cells were impaled with microelectrodes and injected with the fluorescent dye Lucifer yellow. The intracellular electrodes also permitted electrical recordings and revealed that one type of cell, the AVF‐like interneuron, expresses spontaneous repetitive plateau potentials.

Comparisons of neuronal morphologies in the retrovesicular ganglia of Ascaris and C. elegans suggest that each neuron in Ascaris can be assigned a corresponding homolog in C. elegans. These data provide further evidence for a remarkable conservation of neuronal morphology in nematodes despite large differences in size and habitat.
Nonspiking interneurons in the ventilatory central pattern generator of the shore crab, Carcinus maenas
Authors: Dicaprio R. A.
Published: January 2005

Eight nonspiking interneurons were identified that are elements of the central pattern generator controlling ventilation in the shore crab, Carcinus maenas. Intracellular recordings from these neurons in an isolated ganglion preparation revealed that these cells exhibit large amplitude oscillations in their membrane potentials, which are in‐phase with the ventilatory motor pattern. These oscillations are present during the expression of the two distinct ventilatory motor output patterns corresponding to forward and reversed ventilation, and the oscillations stopped during pauses in the ventilatory rhythm. Injection of intracellular current pulses into these interneurons caused a resetting of the ongoing ventilatory rhythm, indicating that these cells are part of the ventilatory central pattern generator. The structure of each interneuron was determined by the intracellular injection of Lucifer Yellow dye. These neurons have a large diameter main neurite ranging from 10 to 20 μm in diameter with very restricted primary and secondary branching from the main neurite. All of the interneurons are restricted to a single hemiganglion and perturbation of these cells with intracellular current pulses only affect the motor output of the hemiganglion containing the interneuron. These eight nonspiking interneurons appear to be the primary components of the central pattern generator underlying ventilation in the crab.
Distribution and morphometric characteristics of oxytocin‐ and vasopressin‐immunoreactive neurons in the rabbit hypothalamus
Authors: Schimchowitsch Sarah , Moreau Catherine , Laurent Francoise , Stoeckel Marie‐Elisabeth
Published: January 2005

The distribution, morphological features, and morphometric characteristics of cell bodies producing oxytocin (OT) and vasopressin (AVP) were studied in the rabbit hypothalamus by means of a conventional immunoperoxidase method. The aim of the present study was to determine the existence or not of a species‐specific OT‐cell group that might be involved in the dense OT innervation of the intermediate lobe in the leporidae.

No OT‐cell group clearly distinct from the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei was found, even in colchicine‐treated animals. Most immunoreactive perikarya were found within these nuclei. In addition, small AVP neurons occurred in the suprachiasmatic nucleus.

In the SON, the predominant, tightly packed AVP cells occupied the ventral part of the nucleus, whereas OT neurons were dorsolaterally located. The PVN presented a loose organization without any obvious subdivision. OT cells, which predominated, occupied the medial part of the nucleus. The PVN had a prominent rostral anterobasal extension composed mainly of OT cells. Laterally to the nucleus, numerous large AVP neurons, with few and smaller OT cells, dispersed along the neurosecretory tract without forming definite cell clusters. AVP cell bodies had a rough granular aspect contrasting with the smooth and fine one of OT cells. Spinelike processes were rarely observed on the perikarya, except on large scattered AVP neurons, but frequently covered the proximal dendrites of both types of neurons. Throughout the hypothalamus, OT neurons had definitely smaller mean somal areas and were more homogeneous in size than AVP cells.
Somatotopic organization of inputs from the hand to the spinal gray and cuneate nucleus of monkeys with observations on the cuneate nucleus of humans
Authors: Florence S. L. , Wall J. T. , Kaas J. H.
Published: January 2005

Central termination patterns of primary afferents from the hand and forelimb were studied following subdermal injections of HRP conjugates in macaque monkeys. In the middle layers of the dorsal horn of the spinal cord, afferents from digits 1–5 terminated in a rostrocaudal sequence in separate, elongated columns at cervical levels 5–7. Afferents from teh glabrous digits extended to the medial margin of the dorsal gray, while afferents from the dorsal skin of the digits terminated more laterally. Afferents from the dorsal hand and palm terminated lateral to those from the digits, while inputs from the forearm occupied tissue rostral and caudal to the representation of the hand. In the cuneate nucleus, terminations from each digit formed an elongated column that was densely labelled in the central pars rotunda and sparsely labelled in both the rostral and caudal reticular poles. Within the pars rotunda, digits 1–5 were represented in order from lateral to medial. Inputs from the digit tips terminated ventral to inputs from the proximal digits. Afferents from the dorsal skin of the digits terminated in an even more dorsal position, while the most dorsal portion of the pars rotunda related to the glabrous and dorsal hand. Within the pars rotunda, terminations from specific parts of the hand overlapped parcellated clusters of neurons. These clusters were densely reactive for cytochrome oxidase (CO) and were surrounded by myelinated fibers. Much sparser label in the reticular poles was found consistently only after injections in the glabrous digits. Inputs to the poles appeared diffuse and overlapping while preserving some somatotopic order. When treated for CO or stained for Nissl substance or myelin, the pars rotunda of humans showed parcellation patterns that closely resembled the patterns seen in monkeys. From the relationship of inputs to the CO dense cell clusters in monkeys, it was possible to postulate in detail the somatotopic organization of inputs to pars rotunda of humans.

The present results provide a comprehensive description of the somatotopic patterns of termination of afferents from the skin of the hand and forearm in the spinal cord and cuneate nucleus of macaque monkeys. A direct relationship of afferent somatotopy and identifiable cell clusters in the pars rotunda of the cuneate nucleus is further demonstrated. Finally, the patterns of cell clusters in the pars rotunda of macaque monkeys and humans suggest that the somatotopic organization of the cuneate nucleus may be very similar in human and nonhuman primates.
Histochemistry of acetylcholinesterase and immunocytochemistry of an acetylcholine receptor‐like antigen in the brain of the honeybee
Authors: Kreissl Sabine , Bicker Gerd
Published: January 2005

A histochemical staining method for acetylcholinesterase (AChE) and an antiserum raised against nicotinic acetylcholine receptors (AChR) of locust nervous tissue were applied in order to reveal certain candidates of cholinergic pathways in the brain of the honeybee. The AChE staining marked layers in the optic lobes, fibers connecting the two brain hemispheres, and fiber tracts as well as soma clusters within the protocerebrum. The calycal input regions of the mushroom bodies were labelled, whereas the intrinsic Kenyon cells showed no staining. Although the antennal afferents projecting into the dorsal lobe showed strong AChE activity, projections into the antennal lobe showed rather weak staining.

Application of the antiserum against the AChR showed immunoreactivity in neuropiles, tracts, somata, and the antennal nerve. The immunoreactivity of the optic lobes coincided with the banding pattern of the AChE staining. A particularly striking overlap of AChR immunoreactivity and AChE staining was found in the lip neuropile of the mushroom bodies, which would suggest a cholinergic input into this neuropile via fibers of the median antennoglomerular tract. Because the antiserum against locust AChR binds in neuropiles displaying AChE activity, we conclude that this antiserum also cross‐reacts with the bee's receptor. This interpretation is supported by experiments showing α‐bungarotoxin (α‐BTX) binding sites in some areas of strong immunoreactivity.