bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunocytochemical demonstration of early appearing astroglial structures that form boundaries and pathways along axon tracts in the fetal brain
Authors: Silver Jerry , Edwards Michael A. , Levitt Pat
Published: January 2005

During normal development of the mammalian forebrain, the paired cerebral hemispheres are initially separated midsagittally by the connective tissue‐filled longitudinal fissure. During subsequent stages, the hemispheres fuse as basal lamina is remodeled and fibroblasts are eliminated from the fissure to create new central nervous system (CNS) territory in the midline. Two axon pathways, the corpus callosum and dorsal callosal stria, eventually use this region as part of their pathway. In order to assess the possible role of glial cells in the fusion process and in the guidance of axons in this and several other areas of the forebrain, we have analyzed the developing brain in timed cat and mouse embryos with immunohistochemical and morphological techniques. With the use of astroglial‐specific antibodies and electron microscopy, we have visualized two distinct, primitive astroglial structures associated with the cerebral midline, and seven more associated with other specific brain regions. The way in which one of these structures moves as a column along the hemispheric midline in synchrony with seam formation suggests the possibility that during morphogenesis of the telencephalon, astrocytes may aid in the fusion process. In addition, the compact assemblage, early appearance and location of this and the other glial structures in relation to well defined neuroanatomical landmarks or axon pathways suggest that they may transiently compartmentalize relatively large regions of the CNS and organize certain developing fiber systems by acting as guides or barriers at critical stages of ontogeny. © 1993 Wiley‐Liss, Inc.
Distributions of mRNAs for alpha‐2 adrenergic receptor subtypes in rat brain: An in situ hybridization study
Authors: Nicholas Anthony P. , Pieribone Vincent , Hökfelt Tomas
Published: January 2005

Selective 35S‐labeled oligonucleotide probes were designed to sequences of the rat alpha‐2A (RG20), alpha‐2B (RNG), and alpha‐2C (RG10) adrenoreceptor mRNAs for use in in situ hybridization experiments on sections of unfixed rat brain, spinal cord and kidney. After hybridized sections were exposed to film or dipped in autoradiographic emulsion, specific and selective labeling patterns characteristic for each probe and region of the central nervous system were observed. Alpha‐2A mRNA labeling was most pronounced in neurons in layer six of the cerebral cortex, hypothalamic paraventricular nucleus, reticular thalamic nucleus, pontine nuclei, locus coeruleus, vestibular nuclei, trapezoid nuclei, deep cerebellar nuclei, nucleus tractus solitarii, ventrolateral medullary reticular formation, and the intermediolateral cell column of the thoracic spinal cord. In some of these locations, the receptor mRNA, in all probability, is present in noradrenaline and perhaps adrenaline neurons. The alpha‐2B probe, which primarily labels the kidney, gave only a very light signal in the thalamus in the central nervous system after extended exposure times. Alpha‐2C mRNA labeling was primarily observed in the olfactory bulb, cerebral cortex, islands of Calleja, striatum, hippocampal formation, cerebellar cortex, and dorsal root ganglia. Labeling patterns disappeared when excess unlabeled probes were added to their respective radiolabeled probes, or when sense probes were employed. When a hybrid antisense probe homologous to all three alpha‐2 probes was used, labeling patterns also disappeared. The present study therefore justifies the pharmacological subclassification of alpha‐2 receptors by providing anatomical evidence for specific and selective cell groups in the rat central nervous system containing mRNA for three alpha‐2 receptor subtypes. © 1993 Wiley‐Liss, Inc.
Histochemical localization of synaptic zinc in the developing cat visual cortex
Authors: Dyck Richard , Beaulieu Clermont , Cynader Max
Published: January 2005

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle‐bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc‐positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 μm in diameter, with a centre‐to‐centre spacing of approximately 900 μm. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex. © 1993 Wiley‐Liss, Inc.
The organization of the efferent projections from the pontine parabrachial area to the amygdaloid complex: Aphaseolus vulgarisleucoagglutinin (PHA‐L) study in the rat
Authors: Bernard Jean‐Françlois , Alden Marie , Besson Jean‐Marie
Published: January 2005

The organization of the efferent projections from the pontine parabrachial (pPB) area to the amygdala has been studied in the rat by using microinjections ofPhaseolus vulgarisleucoagglutinin (PHA‐L), a sensitive and selective anterograde axonal marker, into restricted subregions of the pPB area.

The results confirmed that the pPB area primarily projected onto the ipsilateral nucleus centralis of the amygdala (Ce), and to a lesser extent onto the ipsilateral posterior basolateral (BLP), anterior basomedial (BMA), and amygdaloid cortical (ACo) nuclei of the amygdala. Substantial projections were also found in the substantia innominata dorsal/ventral portion of the globus pallidus (SId/GPv), substriatal (SStr), and fondus striatal (FStr) regions which continue the amygdala rostrally.

The results demonstrated that the projections of the pPB area onto the Ce were topically organized: (1) The region of the pPB area mainly including the medial subnucleus (pPBm), the waist area (pPBwa), and a thin rostral lamina of the ventral lateral subnucleus (pPBvl) projects primarily to the medial portion of the Ce (CeM). Dense projections were also found in the BLP, BMA, and ACo nuclei of the amygdala, and in the SId/GPv, SStr, and FStr rostral areas. (2) The region of the pPB mainly including the rostral portion of the central lateral subnucleus (pPBcl) and the outer‐rostral protion of the external lateral subnucleus (pPBel) projects primarily to the lateral portion of the Ce (CeL). (3) The region of the pPB mainly including the dorsolateral subnucleus (pPBdl), the remaining pPBel, and the external medial (pPBem) subnuclei projects primarily to the lateral capsular protion of the Ce (CeLC) and bilaterally to its rostral portion. Dense projections were also found in the regions which extend the CeLC rostrally and in the SId/GPv, SStr, and FStr rostral areas.

The possible role of each of the three parabrachio‐amygdaloid pathways described is discussed. It was suggested that the pPB‐CeM pathway is mainly implicated in gustatory processes; the pPB‐CeL pathway is mainly implicated in visceral and chemosensitive processes; and the pPB‐CeLC pathway is mainly implicated in respiratory, cardiovascular, and nociceptive processes. © 1993 Wiley‐Liss, Inc.
Coincidence of Schwann cell‐derived basal lamina development and loss of regenerative specificity of spinal motoneurons
Authors: Meeker Marianne L. , Farel Paul B.
Published: January 2005

The Schwann cell‐derived basal lamina forms a tube around single peripheral axons or small groups of axons that is continuous from the spinal cord to the target. In bullfrog tadpoles (Rana catesbeiana), motor axons transected at early developmental stages regenerate to the appropriate hindlimb region. In the present paper, we found that at these stages Schwann tubes are absent by morphological criteria, and individual axons are separated only by occasinal extensions of support cells. At stages when axons no longer regenerate to the correct hindlimb region, every axon is encased in a basal lamina tube. Schwann tubes persist in the distal stump after nerve transection, and regenerating axons grow within these tubes. These findings are consistent with previous results showing that the errors regenerating axons make in older animals are not random, but depend upon the course of the denervated Schwann tubes to which they ahve acces. In order to determine whether formation of the Schwann tube itself or interaction of its molecular constituents with growing axons was associated with loss of regenerative specificity, the expression during development of two major constituents of the basal lamina, laminin and heparan sulfate proteoglycan, was investigated. Immunoreactivity to both constituents was present both before and after the transition from specific to nonspecific regeneration, indicating that their expression per se was not sufficient to limit regnerative specificity. These data support the hypothesis that the physical constraint imposed by the Schwann cell‐derived basal lamina prevents regenerative specificity. © 1993 Wiley‐Liss, Inc.
Dendritic remodelling of retinal ganglion cells during development of the rat
Authors: Yamasaki Edna N. , Ramoa Ary S.
Published: January 2005

Investigation of the morphology of ganglion cells in the cat retina has shown that a remarkable reduction in the number of dendritic spines and branches occurs during development of the alpha and beta cell classes. To learn whether dendritic remodelling represents a generalized mechanism of mammalian retinal ganglion cell development, we have examined the morphology of ganglion cells in the retina of the developing rat. The present study has concentrated on type II cells, which retain a great number of dendritic spines and branches in the adult and comprise a large proportion of the population of rat retinal ganglion cells. To reveal fine dendritic and axonal processes, Lucifer yellow was injected intracellularly in living retinae maintained in vitro. Size and complexity of the dendritic trees were found to increase rapidly during an intial stage of development lasting from late fetal life until approximately postnatal day 12 (P12). Dendrites and axons of immature ganglion cells expressed several transient morphological features comprising an excessive number of dendritic branches and spine‐like processes, and short, delicate axonal sidebranches. The following developmental stage was characterized by a remarkable decrease in the morphological complexity of retinal ganglion cells and a slowed growth of their dendritic fields. The number of dendritic branches and spines of types I and II retinal ganglion cells declined after P12 to reach a mature level by the end of the first postnatal month. Thus, even cells that retain a highly complex dendritic tree into the adult state undergo extensive remodelling. These results suggest that regressive modifications at the level of the dendritic field constitute a generalized mechanism of maturation in mammalian retinal ganglion cells. © 1993 Wiley‐Liss, Inc.
Postnatal development and localization of an N‐acetylgalactosamine containing glycoconjugate associated with nonpyramidal neurons in cat visual cortex
Authors: Schweizer Michaela , Streit Wolfgang J. , Müller Christian M.
Published: January 2005

We have analyzed the appearance of N‐acetylgalactosamine containing glycogonjugates by staining sections of fixed cat visual cortex with the lectins from Vicia villosa (VVA) and Glycine max (SBA) conjugated to fluorescent labels, horseradish peroxidase, or biotin. The appearance of lectin staining during postnatal development followed an inside‐out gradient starting in the deep cortical layers at the fourth postnatal week, successively including more of the superficial layers during the first three postnatal months until labelled cells were present throughout layers II–VI at the seventh postnatal month. Staining was associated with the soma and proximal dendrites of bipolar and multipolar nonpyramidal neurons. Outside layer IV large neurons with basket cell and neurogliaform morphology predominated, whereas small multipolar cells were stained in layer IV. High power observation revealed a lattice‐like staining on neuronal surfaces. In the cortical white matter staining was found at the nodes of Ranvier.

The ultrastructural localization of lectin binding sites was assessed by a pre‐embedding histochemical procedure with biotinylated lectin visualized with HRP‐conjugated avidin and diaminobenzidine as the chromogen. The reaction product was found exclusively in close association with synaptic terminals on somata and proximal dendrites of nonpyramidal neurons. There was no preference with respect to the morphology of the synaptic structure, i.e., symmetric synapses with ovoid or asymmetric synapses with round vesicles. In the vicinity of synaptic contacts the staining was associated with membranes of astrocytic processes ensheathing the synapses. In the cortical white matter astrocytic processes running along myelinated axons were strongly labelled at the nodes of Ranvier.

Comparison of Western blots from 4‐week‐old and adult cat cortex membranes revealed one lectin‐positive protein band with an apparent molecular weight of about 24 kD in conjunction with the histochemical expression of perisynaptic staining in the adult tissue.

It is concluded that the employed lectins selectively visualize distal astroglial processes ensheathing synapses on a subpopulation of cortical interneurons and nodes of Ranvier. On the basis of the developmental appearance and localization we consider and discuss the possibility that the N‐acetylgalactosamine containing glycoconjugate is involved in the stabilization of synaptic contacts on GABA‐ergic interneurons. © 1993 Wiley‐Liss, Inc.
Acetylcholinesterase staining differentiates functionally distinct auditory pathways in the barn owl
Authors: Adolphs R.
Published: January 2005

The aim of this study was to examine how the functional specialization of the barn owl's auditory brainstem might correlate with histochemical compartmentalizaiton. The barn owl uses interaural intensity and time differences to encode, respectively, the vertical and azimuthal positions of sound sources in space. These two auditory cues are processed in parallel ascending pathways that separate from each other at the level of the cochlear nuclei. Sections through the auditory brainstem were stained for acetylcholinesterase (AChE) to examine whether nuclei that process different auditory cues stain differentially for this enzyme. Of the two cochlear nuclei, angularis showed more intense staining than nucleus magnocellularis. Nucleus angularis projects to all of the nuclei and subdivisions of nuclei that belong to the intensity processing pathway. Acetylcholinesterase stained all regions that contain terminal fields of nucleus angularis and thus provided discrimination between the time and intensity pathways. Moreover, staining patterns with acetylcholinesterase were complementary to those prevously reported with an anti‐calbindin antibody, which stains terminal fields of nucleus laminaris, and thus stains all the nuclei and subdivisions of nuclei that belong to the time pathway. Some of the gross staining patterns observed with AChE were similar to those reported with antibodies to glutamate decarboxylase. However, AChE is a more convenient and definitive marker in discriminating between these pathways than is calbindin or glutamate decarboxylase. Acetylcholinesterase staining of the intensity pathway in the owl may be related to encoding of sound intensity by spike rate over large dynamic ranges. © 1993 Wiley‐Liss, Inc.
Differential regulation of substance P and somatostatin in martinotti cells of the developing cat visual cortex
Authors: Wahle Petra
Published: January 2005

In order to determine their morphological development and ontogenetic fate, Martinotti neurons immunoreactive for substance P and somatostatin have been analysed in the cat visual cortex. Martinotti neurons are located in layers V and VI. They are multipolar to bitufted, and most dendrites remain in layers V and VI. Their typical feature is the ascending axon, which emerges from an apical dendrite or from the upper pole of the soma. A number of collaterals branch off in layer V, forming a local terminal plexus. The axon then branches into 2–8 collaterals, which ascend as a bundle to layers III and II, where a second terminal plexus is formed. Some collaterals ascend to layer I where they adopt a horizontal course. Horizontal collaterals in the terminal layers V, III, II, and in layer I may reach up to 400 μm in length.

Martinotti neurons begin to differentiate perinatally. The quantitative analysis reveals that the initial time course of differentiation of Martinotti cells is very similar in material stained for substance P and for somatostatin. Double immunofluorescence then confirms that the two peptides are colocalized in Martinotti cells of layers V and VI during the early postnatal period. Further, substance P is colocalized with GABA.

Substance P expression in Martinotti cells can be observed only in the immature visual cortex. After postnatal day 15, the Martinotti neuron system becomes less and less detectable by substance P immunoreactivity. It declines to virtually undetectable levels after the third postnatal month. The adult visual cortex is almost devoid of substance P‐immunoreactive cell bodies, processes and axon terminals. In situ hybridization confirms this finding, revealing beta‐preprotachykinin mRNA‐expressing cell bodies in layers V and IV at postnatal day (P)6 and P12, but not in the adult cortex. This suggests a downregulation of the substance P expression at the transcriptional level.

In contrast, somatostatin‐immunoreactive Martinotti cells, most of which have coexpressed substance P during early postnatal life, can still be observed in the adult cortex. Thus, the Martinotti neurons constitute a persisting cell type, although many individual neurons of this type disappear during the second postnatal month by degeneration and cell death.

In summary, while somatostatin is permanently expressed in Martinotti neurons in the cat visual cortex, substance P peptide and mRNA are transiently expressed during an early postnatal period, and apparently are downregulated later in development. © 1993 Wiley‐Liss, Inc.
Embryonic development of rat sympathetic preganglionic neurons: Possible migratory substrates
Authors: Phelps Patricia E. , Barber Robert P. , Vaughn James E.
Published: January 2005

Spinal somatic and autonomic (sympathetic preganglionic) motor neurons are generated synchronously and, subsequently, migrate from the ventricular zone together to form a common primitive motor column. However, these two subsets of motor neurons ultimately express several phenotypic differences, including somal size, peripheral targets, and spinal cord locations. While somatic motor neurons remain ventrally, autonomic motor neurons (AMNs) move both dorsally and medially between embryonic days 14 and 18, when they approximate their final locations in spinal cord. The goal of the present investigation was to determine the potential guidance substrates available to AMNs during these movements. The dorsal translocation was studied in developing upper thoracic spinal cord, because, at this level, the majority of AMNs are located dorsolaterally. Sections were double‐labeled by ChAT (choline acetyltransferase) and SNAP/TAG‐1 (stage‐specific neurite associated protein/transiently expressed axonal surface glycoprotein) immunocytochemistry to visualize motor neurons and the axons of early forming circumferential interneurons, respectively. Results showed that during the developmental stage when AMNs translocated dorsally, SNAP/TAG‐1 immunoreactive lateral circumferential axons were physically located along the borders of the AMN region, as well as among its constituent cells. These findings indicate that lateral circumferential axons, as well as the SNAP/TAG‐1 molecules contained upon their surfaces, are in the correct spatial and temporal position to serve as guidance substrates for AMNs. The medial translocation was studied in developing lower thoracic‐upper lumbar spinal cord, because, at this level, more than half of the AMNs are medially located. Sections were double‐labeled by ChAT and vimentin immunocytochemistry to visualize motor neurons and radial glial fibers, respectively. Observations on consecutive developmental days of the medial traslocation revealed that AMNs were aligned with parallel arrays of radial glial fibers. Thus, the glial processes could serve as guides for the AMN medial movement. Future experimental analyses will examine whether circumferential axons and redial glial fibers are in fact functioning as migratory guides during AMN development, and, if so, whether specific surface molecules on these guides trigger the subsequent differentiation of AMNs.
Distribution of cerebellothalamic and nigrothalamic projections in the dog: A double anterograde tracing study
Authors: Sakai Sharleen T. , Patton Kathleen
Published: January 2005

The distribution of nigrothalamic and cerebellothalamic projections was investigated in the dog by a double labeling strategy combining the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) and tritiated amino acids. Following tritiated amino acid injections into the substantia nigra pars reticulata (SNr) and WGA‐HRP injections into the contralateral cerebellar nuclei, we found that the nigrothalamic and cerebellothalamic afferents distribute to three main targets: the central portion of the ventral anterior nucleus (VA) and the ventral lateral nucleus (VL), the internal medullary lamina (IML) region, which includes the paralaminar VA, the mediodorsal nucleus (MD) and the central lateral nucleus (CL), and finally the ventromedial nucleus (VM). We observed three distribution patterns of labeled fibers: (a) Dense single label was observed in the central portion of VA following the SNr injections and in VL following the cerebellar nuclei injections. (b) A complementary pattern consisting of alternating foci of nigral and cerebellar label was found in the IML region. This pattern was also observed in the caudal intralaminar nuclei where cerebellar label predominated in the centrum medianum (CM), while the parafascicular nucleus (Pf) primarily contained nigral label. (c) An overlapping pattern of autoradiographic and WGA‐HRP label was found in the lateral half of the VM. Overall, the distribution of nigrothalamic and cerebellothalamic projections was widespread throughout much of rostrocaudal thalamus. However, the pattern of projections varied along a continuum from lateral to medial thalamus. In lateral thalamus, nigral and cerebellar projections distributed to separate nuclei while in medial thalamus, the projection pattern changed to focal and complementary in the IML and overlapping in VM. Taken together, these thalamic projections may constitute crucial links in different functional channels involved in alerting and orienting mechanisms associated with motor behavior. Our findings also suggest that the organization of motor thalamic afferents in the dog shares similarities with the segregated and parallel circuitry characteristic of primates as well as with the overlapping and converging circuits of rodents and other carnivores.
Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: Immunohistochemical and retrograde tract tracing studies
Authors: Tillet Yves , Batailler Martine , Thibault Jean
Published: January 2005

The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine‐β‐hydroxylase, phenylethanolamine N‐methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons.

Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro‐lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4).

In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.
Intrinsic GABAergic neurons in the rat central extended amygdala
Authors: Sun Ning , Cassell Martin D.
Published: January 2005

The present study examined the distribution, morphology, and connections of gamma‐aminobutyric acid‐immunoreactive (GABA‐IR) neuros in the three principal components of the central extended amygdala: the central amygdaloid nucleus, the bed nucleus of the stria terminalis (BNST) and the sublenticular substantia innominata. In the central nucleus, large numbers of GABA‐IR neurons were identified in the lateral, lateral capsular, and ventral subdivisions, though in the medial subdivision, GABA‐IR neurons were only present at very caudal levels. Combined immunocytochemistry‐Golgi impregnation revealed that GABA‐IR neurons in the lateral central nucleus were medium‐sized spiny neurons that were morphologically similar to GABAergic neurons in the striatum. Injections of horseradish peroxidase into the bed nucleus of the stria terminalis labeled a major proportion of the GABA‐IR neurons in the central nucleus. In the bed nucleus, the majority of GABA‐IR neurons were located in the anterolateral subdivision, ventral part of the posterolateral subdivision and the parastrial subdivision. GABA‐IR neurons in the anterolateral bed nucleus were of the typical mediumsized spiny type. Injections of horseradish peroxidase into the central nucleus labeled a few GABA‐IR neurons in the posterior part of the anterolateral bed nucleus. GABA‐IR neurons were identified in the sublenticular substantia innominata and medial shell of the nucleus accumbens and contributed to the continuum of GABA‐IR extending from the central nucleus to the bed nucleus. Injections of horseradish peroxidase (HRP) into the central nucleus, but not the BNST, labeled a few GABA‐IR neurons in the substantia innominata. The data point to GABA‐IR neurons being a characteristic feature of the central extended amygdala and that GABA‐IR neurons participate in the long intrinsic connections linking the major components of this structure. Since lesions of the stria terminalis and basolateral amygdaloid nucleus failed to deplete GABA‐IR terminals in the central nucleus, the role of GABA in local and short intrinsic connections in the central extended amygdala is discussed. Further, physiological findings implicating the intrinsic GABAergic system of the central extended amygdala in the tonic inhibition of brainstem efferents are reviewed.
Reorganization of the chick basilar papilla after acoustic trauma
Authors: Raphael Yehoash
Published: January 2005

The auditory epithelium in birds and mammals consists of a postmitotic population of hair cells and supporting cells. Unlike mammals, birds can regenerate their auditory epithelia after trauma. Recent evidence indicates that supporting cells undergo mitosis after acoustic trauma, suggesting that supporting cells may transdifferentiate into hair cells. The goals of this study were to (1) characterize the responses of hair cells and supporting cells to acoustic trauma, and (2) determine whether hair cell loss is a prerequisite for generation of new hair cells. Chicks were exposed to an octave‐band noise and their inner ears assayed with fluorescence or scanning electron microscopy. In one area of the basilar papilla, defined as the center of the lesion, extensive hair cell degeneration occurred. Expanded supporting cells obliterated degenerating hair cells and invaded spaces normally occupied by hair cells. Aggregates of DNA were found within the basilar papilla, suggesting that hair cell death and disintegration may occur within the epithelium. The epithelial sheet appeared structurally confluent at all times examined. Supporting cells exhibited altered apical contour in distal regions of the basilar papilla, where hair cell damage was mild or inconspicuous. Four days after noise exposure, newly generated hair cells were found in the center of the lesion and in the distal areas, where no hair cell loss could be detected. The results suggest that supporting cells may play an important role in maintenance and repair of the traumatized basilar papilla and raise the possibility that production of new hair cells is not dependent on hair cell loss in the immediate vicinity.
The fate of cryopreserved nerve isografts and allografts in normal and immunosuppressed rats
Authors: Zalewski Andrew A. , Fahy Gregory M. , Azzam Nabil A. , Azzam Rita N.
Published: January 2005

Donor Schwann cells, perineurial cells, and vasculature are known to survive in grafts of peripheral nerve. In the present study, we attempted to cryopreserve nerve to determine whether these cellular components of nerve would survive after transplantation and support host axonal regeneration through the graft. Four‐centimeter lengths of peroneal nerves were removed from inbred adult American Cancer Institute (ACI) rats and placed into vials that contained a cryoprotective mixture of dimethyl sulfoxide and formamide (DF) at room temperature. Each vial with nerves in DF was cooled at a rate of 1–1.5°C/minute down to –40°C at which point the vials were plunged into liquid nitrogen at –196°C. After 5 weeks of storage, the nerves were thawed and DF removed. Some of the cryopreserved‐thawed ACI nerves were transplanted as isografts into the legs of ACI rats. Other ACI nerves were used as allografts and inserted into immunologically normal Fischer (FR) rats that were untreated or were immunosuppressed with the drug Cyclosporin A (Cy‐A). At surgery, only one end of the nerve graft was joined to the cut proximal end of the peroneal nerve of the host. The cellular elements of ACI grafts were present at 5 weeks in grafts removed from ACI rats and FR rats treated with Cy‐A. Non‐immunosuppressed FR rats rejected ACI nerves as did FR rats in whom Cy‐A was stopped after 5 weeks of treatment. All surviving ACI grafts underwent Wallerian degeneration and consisted of columns of Schwann cells, which in their proximal portion were associated with regenerating host axons. The donor perineurial sheath and vasculature were also present in surviving grafts. ACI isografts only were examined 20 weeks postoperatively. All normal tissue components survived in these older grafts and contained regenerated and myelinated host axons throughout their 4 cm lengths. These results demonstrated that the cellular elements of nerve can be cryopreserved, and after transplantation, survive and function. Because nerves survived after prolonged cryopreservation, it seems feasible to establish a nerve bank from which grafts can be withdrawn to repair gaps in injured nerves. However, cryopreserved nerves used as allografts remain immunogenic and require immunosuppression for their survival. Published in 1993 by Wiley‐Liss, Inc.
Pigment‐dispersing hormone‐like peptide in the nervous system of the flies Phormia and Drosophila: Immunocytochemistry and partial characterization
Authors: Nässel Dick R. , Shiga Sakiko , Mohrherr Carl J. , Rao K. Ranga
Published: January 2005

β‐pigment‐dispersing hormone (β‐PDH) isolated from the fiddler crab (Rao et al., '85) is a member of an octadecapeptide family of neuropeptides common to arthropods. Whereas earlier studies of these peptides in insects were limited to orthopterans, this investigation focuses on dipteran flies. Extracts of heads from the blowfly Phormia terraenovae were assessed in a fiddler crab bioassay for PDH activity. Immunocytochemistry, dose‐response curves, gel filtration chromatography and reversed‐phase HPLC, combined with bioassay and enzymelinked immunosorbent assay (ELISA), indicate the presence of PDH‐like peptide in the blowfly. Immunocytochemical mapping of PDH‐like immunoreactive (PDHLI) neuroans was performed for the entire nervous systems of Phormia and the fruitfly Drosophila with a β‐PDH antiserum. In the cephalic ganglion (brain, optic lobe and subesophageal ganglion) PDHLI cell bodies could be detected (34 in Phormia and 16 in Drosophila). In both species, each hemisphere contains 8 PDHLI cell bodies in the optic lobes. These innervate the optic lobe neuropils bilaterally. In Phormia, another set of 8 cell bodies are located in each of the lateral neurosecretory cell groups in the superior protocerebrum. These neurons send axons to the corpora cardiaca‐hypocerebral ganglion complex and to portions of the foregut. In contrast, only the optic lobe neurons display immunoreactivity in Drosophila. Except for the optic lobes, PDHLI processes are distributed only in nonglomerular neuropils of the brain of both species. In the fused thoracico‐abdominal ganglia of Phormia, 28 PDHLI cell bodies were found (only six were found in Drosophila). In both species, six abdominal PDHLI neurons are efferents with axons innervating the hindgut. We also found that some of the PDHLI neurons in the Phormia brain and abdominal ganglion contain colocalized FMRFamide‐like immunoreactivity. Since the flies studied here do not display hormonally controlled, fast pigment migrations, the PDH‐like peptide may have a role as neurotransmitter or neuromodulator in the central nervous system, especially in the visual system, and a regulatory role in the stomatogastric system and the hindgut. © 1993 Wiley‐Liss, Inc.
Projections of physiologically characterized spherical bushy cell axons from the cochlear nucleus of the cat: Evidence for delay lines to the medial superior olive
Authors: Smith Philip H. , Joris Philip X. , Yin Tom C. T.
Published: January 2005

Bushy cells in the anteroventral cochlear nucleus (AVCN) receive their principal excitatory input from the auditory nerve and are the primary source of excitatory input to more centrally located brainstem auditory nuclei. Despite this pivotal position in the auditory pathway, details of the basic physiological information being carried by axons of these cells and their projections to more central auditory nuclei have not been fully explored.

In an attempt to clarify these details, we have physiologically characterized and anatomically labeled individual axons of the spherical bushy cell (SBC) class of the cat AVCN. The characteristic frequencies (CFs) of our injected SBC population are low, all less than 12 kHz and primarily (83%) less than 3 kHz, while their spontaneous activity is comparatively high (mean of 59 spikes/sec). In response to short tone bursts at CF, low CF (< 1 kHz) SBC units can phase‐lock better than auditory nerve fibers. SBCs with CFs above 1 kHz have primary‐like responses at all stimulus levels and can show robust phase‐locking to an off‐CF, 500 Hz tone. When compared with our previously reported population of labeled globular bushy cells (GBC; Smith et al., 1991, J. Comp. Neurol. 304:387–407), some similarities and differences are apparent in both physiological response properties and axonal projection pattern. GBCs show no low frequency bias in CFs, have lower spontaneous rates, and the high CF units exhibit a primary‐like‐with‐notch response at high stimulus levels as a consequence of a very well timed onset component. Low CF, GBC short tone responses are indistinguishable from those of SBCs. Anatomically, the axons of SBCs cross the midline in the dorsal component of the trapezoid body and typically innervate the medial superior olive (MSO) on both sides, the ipsilateral lateral superior olive (LSO), and the contralateral ventral nucleus of the lateral lemniscus (VNLL). The projections to the contralateral, but not the ipsilateral MSO, show a rostral to caudal delay line configuration, similar to the scheme first proposed by Jeffress (1948, J. Comp. Neurol. 41:35–39). The form of this delay line is consistent with the topographic map of interaural time delays reported by Yin and Chan (1990, J. Comp. Neurol. 64:465–488.). Projections to the ipsilateral LSO often take an indirect route. In contrast, GBC axons travel in the ventral component of the trapezoid body, never innervate the MSO, rarely innervate the ipsilateral LSO, and always innervate the contralateral medial nucleus of the trapezoid body. The terminal specializations of both SBC and GBC axons contain round vesicles. © 1993 Wiley‐Liss, Inc.
Midbrain dopaminergic neurons (nuclei A8, A9, and A10): Three‐dimensional reconstruction in the rat
Authors: German Dwight C. , Manaye Kebreten F.
Published: January 2005

The dopaminergic neurons in the midbrain of the rat are located in three cell groups: nucleus A8 cells in the retrourbal field, nucleus A9 cells in the substantia nigra, and nucleus A10 cells in the ventral tegmental area and related nuclei. The purpose of the present study was to map and quantify the midbrain dopaminergic neurons in two and three dimensions in the rat brain, using immunohistochemical staining and computer imaging techniques. The cells were identified with an antibody against tyrosine hydroxylase, and counted in six midbrain nuclei: the retrorubral field, substantia nigra pars compacta, substantia nigra pars reticulata, central linear nucleus, ventral tegmental area, and interfascicular nucleus. Outlines were traced around the perimeters of the coronal tissue sections, and the locations of all immunoreactive ventral midbrain cells were mapped. On one side of the brain there are approximately 1,300 nucleus A8 cells, 10,500 nucleus A9 cells, and 10,200 nucleus A10 cells. The 2‐ and 3‐dimensional reconstructions illustrate the region‐specific density of dopaminergic neurons throughout the midbrain cell complex, and provide a visual appreciation of the location and distribution of the three dopaminergic cell groups in relation to their position in the midbrain. Information about the number and location of midbrain dopaminergic neurons will be useful in conjunction with future studies that characterize these cells more specifically, for example, in terms of their co‐transmitters, and afferent and efferent projections. © 1993 Wiley‐Liss, Inc.
Medial cortex of the lizard Gekko gecko: A hodological study with emphasis on regional specialization
Authors: Hoogland Piet V. , Vermeulen‐Vanderzee Eefke
Published: January 2005

There is increasing evidence that the archicortex in mammals and reptiles is not a homogeneous structure. However, little is known about the regional specialization of this cortical area in reptiles. Therefore, the efferent connections of the medial cortex of the lizard Gekko gecko were studied with the anterograde tracer Phaseolus vulgaris‐leucoagglutinin. The small‐celled part of the medial cortex (Cxms) projects to various parts of the septum in a topological way: the rostral part projects to the anterior septal nucleus, whereas the caudal part projects to the lateral septal nucleus and the nucleus septi impar. In addition, Cxms projects to the large‐celled part of the medial cortex (Cxml). Axons that originate from the dorsal part of Cxms terminate at the proximal parts of the apical and basal dendrites of the neurons of Cxml caudal to the injection site. In contrast, fibers originating from the ventral part terminate on more distal parts of the dendrites of neurons of Cxml rostral to the injection site. Other projections from Cxms to the dorsal cortex (Cxd) and the external amygdaloid nucleus were found.

The Cxml projects bilaterally to Cxms. These projections terminate in the superficial and deep plexiform layers. In addition, projections to the cell plate of Unger, Cxd, and to the lateral septal nucleus were found.

It appears, on the basis of the efferent connections, that Cxms can be divided into a rostral and caudal part, while hodological differences also exist between the dorsal and ventral parts of Cxms. The results of the present study do not suggest a subdivision of Cxml. The regional variations of the medial cortex in the lizard Gekko gecko differ from the regional variations described in other reptilian species. © 1993 Wiley‐Liss, Inc.
Noradrenaline in the brain of the south african clawed frog Xenopus laevis: A study with antibodies against noradrenaline and dopamine‐β‐hydroxylase
Authors: González Agustín , Smeets Wilhelmus J. A. J.
Published: January 2005

To obtain insight into the noradrenergic system of amphibians, the distribution of noradrenaline was studied immunohistochemically with antibodies against noradrenaline (NA) and dopamine‐β‐hydroxylase (DBH) in the brain of the South African clawed frog Xenopus laevis. Noradrenaline‐containing cell bodies are found in the hypothalamic periventricular organ, the isthmic region, and in an area ventral and medial to the solitary tract. Noradrenaline‐immunoreactive (NAi) fibers are widely, but not uniformly, distributed throughout the brain and spinal cord. In the telencephalon, dense plexuses of NAi fibers are present dorsomedial to the nucleus accumbens, in the nucleus of the diagonal band, the dorsolateral part of the striatum, the medial amygdala, and in an area that encompasses the lateral forebrain bundle. In the diencephalon, dense plexuses are found ventrolateral to the periventricular organ, in the posterior tubercle, and in the intermediate lobe of the hypophysis. Compared to the forebrain, the brainstem and spinal cord are less densely innervated by NAi fibers.

The distribution of DBHi cell bodies and fibers resembles the pattern revealed with the NA antibodies. An exception is formed by the liquor contacting cells of the hypothalamic periventricular organ, which are immunonegative for the DBH antiserum. It is suggested that these cells accumulate rather than metabolize catecholamines. The present study, combined with the results of a previous report in Xenopus on the distribution of dopamine (González, Tuinhof, Smeets, '93, Anat. Embryol. 187:193–201) offers the opportunity to differentiate between the two catecholamines. For example, it is now shown that both dopaminergic and noradrenergic fibers innervate the intermediate lobe of the hypophysis and that, therefore, both catecholamines are likely involved in background adaptation. © 1993 Wiley‐Liss, Inc.
Protein kinase C‐delta in rat brain: Association with sensory neuronal hierarchies
Authors: Garcia Meredith M. , Cusick Catherine G. , Harlan Richard E.
Published: January 2005

Originally characterized as the calcium‐ and phospholipid‐dependent protein kinases, the protein kinases C include at least eight separate isoforms, some of which are calciumindependent and all of which are highly enriched in brain. Of the calcium‐independent isoforms, the delta subspecies of protein kinase C has the most restricted complement of lipid activators and substrate specificity, suggesting that it may have a unique role in cell signalling pathways. Using immunocytochemistry, we report that the distribution of protein kinase C‐δ immunoreactivity in rat brain is also restricted, being present in all sensory systems. Moreover, it is found in alternating hierarchies of sensory pathways: in all sensory systems except auditory, it is found in first‐ and third‐order neurons, while in the auditory system, it is found in second‐ and fourth‐order neurons. Thalamocortical systems are intensely immunoreactive, including barrel fields of the rat parietal cortex. Outside of sensory systems, protein kinase C‐δ is present in cerebellum within longitudinal stripes in Purkinje neurons, and in the caudateputamen, it appears to be associated with the striosome (patch) compartment. In contrast to all other protein kinase C isoforms, protein kinase C‐δ is absent from hippocampus. These findings suggest that protein kinase C‐δ may have a unique role in signal transduction in the central nervous system (CNS), especially in sensory systems. © 1993 Wiley‐Liss, Inc.
Degenerate hearing and sound localization in naked mole rats (Heterocephalus glaber), with an overview of central auditory structures
Authors: Heffner Rickye S. , Heffner Henry E.
Published: January 2005

Behavioral tests of absolute sensitivity and sound localization in African naked mole rats show that, despite their communal social structure and large vocal repertoire, their hearing has degenerated much like that of other subterranean species. First, their ability to detect sound is limited, with their maximum sensitivity being only 35 dB (occurring at 4 kHz). Second, their high‐frequency hearing is severely limited, with their hearing range (at 60 dB sound pressure level [SPL]) extending from 65 Hz to only 12.8 kHz. Third, determination of the effect of duration on noise thresholds indicates that, compared with other animals, mole rats require a sound to be present for a much longer duration before reaching asymptotic threshold. Finally, they are unable consistently to localize sounds shorter than 400 ms and cannot accurately localize sounds of longer duration, raising the possibility that they are unable to use binaural locus cues. Thus, it seems that the essentially one‐dimensional burrow system of a subterranean habitat produces severe changes in hearing comparable to the changes in vision that result from the absence of light. To explore the relation between vision and sound‐localization acuity, retinal ganglion cell densities were determined. The results indicate that naked mole rats have a broad area of best (albeit poor) vision, with maximum acuity estimated at 44 cycles/degree. That mammals with wide fields of best vision have poorer sound‐localization acuity than those with narrower fields is consistent with the thesis that a major function of sound localization is to direct the gaze to the source of a sound. However, the fact that subterranean mammals have little use for vision in a lightless environment suggests that they represent an extreme case in this relationship and may explain the fact that, unlike surface‐dwelling mammals, they have virtually lost the ability to localize brief sounds. Finally, despite their very limited auditory abilities, the major brainstem auditory nuclei, although relatively small, appear to be present. © 1993 Wiley‐Liss, Inc.