bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of the Effect of Synapses: the Significance of the Dendritic Diameter in Impulse Propagation
Authors: Wolf E. , Birinyi A. , Székely G. 
Published: April 2006

AbstractThe effectiveness of synapses at various sites of the dendritic tree was studied using a segmental cable model with a program developed by Hines (Int. J. Biomed. Comput., 24, 55–68, 1989). The model rendered possible a high‐fidelity simulation of the dendritic geometry of a frog motoneuron described in the accompanying paper (Birinyi et al., Eur. J. Neurosci., 1003–1012, 1992). The model was used in the passive membrane mode and the synaptic activity was simulated with current injections into large and small diameter dendrites at proximal and distal locations. Synaptic efficiency was defined by the charge transfer ratio expressed as the proportion of the injected current which appeared at the soma. The charge transfer ratio was determined with uniform and non‐uniform distribution of specific membrane resistance over the soma–dendrite surface while the diameter of selected dendrite segments changed. The best charge transfer ratio was found with the largest dendrite membrane resistance, and the maximum efficiency of synaptic activity appeared at the original size of the dendrite segment stimulated. The amount of current that flowed in the proximal and distal directions from the segment stimulated depended on the diameter of that segment. The increase in diameter of proximal dendrites increased synaptic efficiency on distal dendrites, whereas the reverse caused a decline in synaptic efficiency on proximal dendrites. In addition to the diameter of dendrites, the arborization pattern also played a significant role in this mechanism. It is concluded that the cellulipetal increase in dendrite diameter greatly increases synaptic efficiency.
Altered Topography in the Geniculo‐cortical Projection of the Golden Hamster Following Neonatal Monocular Enucleation
Authors: Trevelyan A. J. , Thompson I. D. 
Published: April 2006

AbstractThe consequence of neonatal eye removal on the adult organization of the geniculo‐cortical pathway was studied anatomically in hamsters. Separate discrete injections of rhodamine‐ and green‐fluorescent latex microspheres were made into the primary visual cortex of adult hamsters. The distribution of labelling in the dorsal lateral geniculate nucleus (dLGN) of normal animals was compared with that seen in animals monocularly enucleated at birth. In the normal animals, as expected, the projection has a precise topographic order. This is also true of the projection contralateral to the remaining eye in the enucleated animals. However, on the side ipsilateral to the remaining eye, the visual cortex appears to receive two convergent projections from the deafferented dLGN, one mirroring the other. A single injection made in very lateral cortex labels cells in two discrete regions of the dLGN. As the injection is made progressively more medial, the two patches of labelled cells converge. Eventually, the two patches are no longer discrete so that injections into central area 17 produce just one, extended patch of labelling. These results suggest that the altered retinal input to the dLGN may affect the subsequent development of ordered geniculo‐cortical projections.
Cells Expressing mRNA for Neurotrophins and their Receptors During Embryonic Rat Development
Authors: Ernfors Patrik , Merlio Jean‐Phillipe , Persson Håkan 
Published: April 2006

Abstract In situ hybridization analysis of cells expressing messenger RNAs (mRNAs) for the neurotrophins nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF) and neurotrophin‐3 (NT‐3) and their high‐affinity receptors (trk, trkB and trkC) in the rat embryo revealed a complex but specific expression pattern for each of these mRNAs. For all mRNAs a developmentally regulated expression was seen in many different tissues. BDNF and NT‐3 mRNAs were expressed in the sensory epithelia of the cochlea and vestibule macula of the sacculus and utricle, and both trkB and trkC mRNA were expressed in the spiral and vestibule ganglia innervating these sensory structures. NGF and NT‐3 mRNA were found in the iris, innervated by the sympathetic neurons of the superior cervical ganglion and sensory neurons from the trigeminal ganglion, which expressed both trk and trkC mRNAs. Both NGF and NT‐3 mRNAs were also expressed in other target fields of the trigeminal ganglion, the epithelium of the whisker follicles (NT‐3 mRNA) and in the epithelium of the nose, tongue and jaw. NT‐3 mRNA was found in the cerebellar external granule layer and trkC mRNA in the Purkinje layer of the cerebellar primordia. These sites of synthesis are consistent with a target‐derived neurotrophic interaction for NGF, BDNF and NT‐3. However, in some cases mRNAs for both the neurotrophins and their high‐affinity receptors were detected in the same tissue, including the dorsal root, geniculate, superior, jugular, petrose and nodose ganglia, as well as in the hippocampus, frontal cortical plate and pineal recess, implying a local mode of action. Combined, these data suggest a broad function for the neurotrophins and their receptors in supporting neural innervation during embryonic development. The results also identify several novel neuronal systems that are likely to depend on the neurotrophins in vivo.
Widespread Distribution of Synaptophysin, a Synaptic Vesicle Glycoprotein, in Growing Neurites and Growth Cones
Authors: Phelan Pauline , Gordon‐Weeks Phillip R. 
Published: April 2006

AbstractSynaptophysin, a 38‐kD glycoprotein, is one of the most abundant of the integral membrane proteins of small synaptic vesicles. The protein is widely distributed at synapses throughout the nervous system, where it is believed to be involved in the exocytosis of stored neurotransmitter. We show here that synaptophysin is also widely expressed in growing neurites and growth cones both in vitro and in vivo. In dissociated rat cerebral cortical cultures anti‐synaptophysin antiserum (G‐95) stains growth cones punctately as soon as they emerge from the cell body. In early cultures all neurites are immunoreactive. Later, synaptophysin is redistributed to become concentrated in axonal varicosities. In developing rat embryos, synaptophysin is expressed in the growing axons of, for instance, the spinal commissural interneurons and the parallel fibres of the cerebellar granule cells long before these neurons have established synaptic connections. These observations suggest that synaptic vesicle proteins like synaptophysin are functionally important in neuronal development.
Noradrenergic, but not Adrenergic Chromaffin Cells in the Adrenal Gland Express Neuromodulin (GAP‐43)
Authors: Grant Nancy J. , König Fabienne , Deloulme Jean‐Christophe , Aunis Dominique , Langley Keith 
Published: April 2006

AbstractNeuroendocrine chromaffin cells of the adrenal gland express certain molecular markers either transiently during development or permanently. In the present study, the expression of neuromodulin (GAP‐43), a neuronal protein often associated with neurite outgrowth, was examined in adult adrenals. Neuromodulin was detected by Western blot analysis in extracts of both rat adrenals and cultured bovine chromaffin cells, and was localized in situ in a subpopulation of chromaffin cells, as well as in nerve fibres and Schwann cells. The use of anti‐tyrosine hydroxylase or anti‐phenylethanolamine N‐methyltransferase antibodies in combination with anti‐neuromodulin antibodies in double immunofluorescent labelling of cryostat sections of rat glands demonstrated that neuromodulin is expressed by noradrenergic, and not by adrenergic chromaffin cells. The results provide further evidence that neuromodulin is not limited to neurons; it is also expressed in a subpopulation of neuroendocrine chromaffin cells. Neuromodulin may play a role in the development of the adrenal medulla or in the specific regulation of noradrenalin secretion from chromaffin cells.
Sodium and Calcium Currents in Glial Cells of the Mouse Corpus Callosum Slice
Authors: Berger Thomas , Schnitzer Jutta , Orkand Paula M. , Kettenmann Helmut 
Published: April 2006

AbstractWe studied Na+ and Ca2+ currents in glial cells during the development of the corpus callosum in situ. Glioblasts and oligodendrocytes from frontal brain slices of postnatal day (P) 3 to P18 mice were identified based on morphological and ultrastructural features after characterization of the currents with the patch‐clamp technique. Slices from P3‐P8 mice contained predominantly glioblasts with immature morphological features. These cells showed Na+ and Ca2+ currents, but the population with these currents decreased between P3 and P8. Na+ currents were blocked in Na+‐free bathing solution and in the presence of tetrodotoxin, Ca2+ currents were only observed when a high concentration of extracellular Ba2+ was present. The cells from the corpus callosum of P10 – P18 mice predominantly had morphological features of oligodendrocytes. In these cells, which in some cases were shown to form myelin, neither Na+ nor Ca2+ currents were detected. To compare these in situ results with those from the electrophysiologically and immunocytochemically well‐characterized cultured glial cells, we determined the expression pattern of stage‐specific antigens in the corpus callosum in situ. The first O4 antigen‐positive glial precursors were observed at P1, the earliest stage examined. The oligodendrocytic antigens O7 and O10 appeared at P6 and P14, respectively, and prominent labelling with the corresponding markers was seen at P12 and P18, respectively. Despite the existence of numerous mature, O10‐positive oligodendrocytes at P18, which expressed Ca2+ channels in vitro, we failed to detect Ca2+ currents in situ at this stage.
Heterogeneous Expression Patterns of Mammalian Potassium Channel Genes in Developing and Adult Rat Brain
Authors: Kues Wilfried A. , Wunder Frank 
Published: April 2006

AbstractVoltage‐gated K+ channels in the mammalian brain are functionally heterogeneous. Mechanisms which may underlie heterogeneity are the expression of multiple K+ channel subunit genes, alternative splicing and the formation of heteromultimers from different subunits. To examine the molecular basis of regional and cell‐specific K+ channel expression in rat brain in situ hybridization techniques were used. The transcript distribution patterns of 11 cloned mammalian K+ channel genes encoding both slow‐ and fast‐inactivating K+ channels from four different gene families were examined at different stages of development. The results show that each subunit‐specific messenger RNA (mRNA) is independently expressed and is characterized by an individual expression pattern. In the hippocampal formation transcripts of RCK2, RCK3, RCK4, RCK5, Raw3 and rat Shal genes are heterogeneously expressed and regulated during postnatal development. RCK1, Raw1, Raw2 and DRK1 mRNAs, on the other hand, are present in the hippocampus throughout postnatal life. The expression patterns of the 11 genes partially overlap, suggesting the formation of different heteromultimeric K+ channel complexes.
Light and Electron Microscopic Localization of the Neutral Metalloendopeptidase EC 3.4.24.16 in the Mesencephalon of the Rat
Authors: Woulfe John , Checler Frederic , Beaudet Alain 
Published: April 2006

AbstractThe topographic and cellular distribution of the neurotensin‐hydrolysing neutral metalloendopeptidase 24.16 (EC 3.4.24.16) was examined by light and electron microscopic immunohistochemistry in adult rat mesencephalon. Light microscopic immunoradioautography revealed a ubiquitous distribution of the enzyme throughout the midbrain with a relative enrichment of grey matter areas including the substantia nigra, ventral tegmental area, interfascicular nucleus, interpeduncular nucleus, rostral and caudal linear raphe nuclei, central grey and superficial grey of the superior colliculus. Peroxidase‐antiperoxidase immunocytochemistry revealed two distinct cellular patterns of immunostaining: (1) weakly labelled neuronal perikarya more or less uniformly distributed throughout the grey matter, and (2) intensely immunoreactive glial cells heterogeneously distributed across the mesencephalon. Areas exhibiting dense concentrations of endopeptidase 24.16‐containing glial cells corresponded to those displaying enhanced immunoreactivity in immunoradioautographs, suggesting that a major proportion of brain endopeptidase 24.16 is associated with glia. Electron microscopic examination of the substantia nigra and ventral tegmental area confirmed the association of the enzyme with a subpopulation of neurons and allowed identification of labelled glial cells as protoplasmic astrocytes. In neurons, endopeptidase 24.16 immunoreactivity was distributed heterogeneously within the cytoplasm of perikarya, dendrites and axons. Reaction product was also characteristically associated with restricted zones of the plasma membrane and underlying neuroplasm. In astrocytes, endopeptidase 24.16 immunostaining was densely and uniformly distributed throughout the cytoplasm of cell bodies and processes. Many of these processes were in direct contact with endopeptidase 24.16‐immunopositive neuronal elements. The present results demonstrate that within the midbrain, endopeptidase 24.16 is both intracytoplasmic and membrane‐associated in neurons and predominantly intracytoplasmic in glia. The presence of a large number of immunostained elements within areas of the midbrain known to display high levels of neurotensin and/or neurotensin receptors, together with the demonstrated catabolic activity of the enzyme on neurotensin in vitro, is consistent with a role of endopeptidase 24.16 in the functional inactivation of endogenous neurotensin in this region of the brain.
Effects of P‐Aminophenyl Dichloroarsine on Reduced High‐affinity [3H]Nicotine Binding Sites from Chick Brain: A Covalent, Yet Reversible, Agent for Neuronal Nicotinic Receptors
Authors: Pike Ashley , Loring Ralph H. 
Published: April 2006

AbstractNeuronal nicotinic acetylcholine receptor (nAChR) α‐subunits contain a conserved disulphide that is essential for function. Here, we have examined the effects of sulphydryl redox reagents on [3H]nicotine binding to chick brain nAChR immunoisolated with the monoclonal antibody mAb35. The disulphide reducing agent, dithiothreitol (DTT), inhibited [3H]nicotine binding [50% inhibitory concentration (IC50) = 146 μM] but this effect was reversed (93±1.5%) by subsequent reoxidation with 1 mM dithio‐bis(nitrobenzoic acid) (DTNB). The trivalent arsenical, p‐aminophenyl dichloroarsine (APA), which reacts with pairs of spatially close sulphydryls, was a potent inhibitor of reoxidation by DTNB (IC50= 35 nM). However, application of the ‘anti‐arsenical’, 2,3‐dimercaptopropane sulphonic acid (DMPS), restored agonist binding after APA treatment (50% effective concentration = 120 μM). Paradoxically, DMPS was also found to be a potent oxidizing agent of these receptors. Affinity alkylation of reduced nAChRs with bromoacetylcholine (BAC; 100 μM) irreversibly blocked nicotine binding (>90%). We propose (but have not proven) that APA interacts with the cysteines homologous to Cys192–193 in Torpedo AChRs, since APA pretreatment of reduced neuronal receptors protected against irreversible BAC alkylation, as shown by subsequent reversal of DMPS (2 mM; 20 min). This study illustrates the potent and reversible nature of the arsenical's covalent interaction with an isolated nAChR and suggests that modified arsenicals could be useful nAChR probes.
MAP2 Isoforms in Developing Cat Cerebral Cortex and Corpus Callosum
Authors: Riederer Beat M. , Innocenti Giorgio M. 
Published: April 2006

AbstractThe microtubule‐associated protein MAP2 was studied in the developing cat visual cortex and corpus callosum. Biochemically, no MAP2a was detectable in either structure during the first postnatal month; adult cortex revealed small amounts of MAP2a. MAP2b was abundant in cortical tissue during the first postnatal month and decreased in concentration towards adulthood; it was barely detectable in corpus callosum at all ages. MAP2c was present in cortex and corpus callosum at birth; in cortex it consisted of three proteins of similar molecular weights between 65 and 70 kD. The two larger, phosphorylated forms disappeared after postnatal day 28, the smaller form after day 39. In corpus callosum, MAP2c changed from a phosphorylated to an unphosphorylated variant during the first postnatal month and then disappeared. Immunocytochemical experiments revealed MAP2 in cell bodies and dendrites of neurons in all cortical layers, from birth onwards. In corpus callosum, in the first month after birth, a little MAP2, possibly MAP2c, was detectable in axons. The present data indicate that MAP2 isoforms differ in their cellular distribution, temporal appearance and structural association, and that their composition undergoes profound changes during the period of axonal stabilization and dendritic maturation.
Bulbectomy Enhances Neurogenesis and Cell Turnover of Primary Olfactory Neurons But Does Not Abolish Carnosine Expression
Authors: Biffo Stefano , Pognetto Marco Sassoè , di Cantogno Ludovica Verdun , Perroteau Isabelle , Fasolo Aldo 
Published: April 2006

AbstractPrimary olfactory neurons located in the olfactory neuroepithelium project to the ipsilateral olfactory bulb and undergo a continuous process of neurogenesis and differentiation. We describe, in the adult rat, the kinetics of proliferation, differentiation and survival of primary olfactory neurons either in the presence or absence of their target, the olfactory bulb. The experimental design included unilateral bulbectomy, coupled with a single bromodeoxyuridine pulse 35 days after surgery. The rate of proliferation and survival of olfactory neurons was then examined by immunohistochemistry for bromodeoxyuridine, and the differentiation status by in situ hybridization for calmodulin messenger RNA in immature and mature olfactory neurons and immunohistochemistry for the dipeptide carnosine in mature olfactory neurons. We show that primary olfactory neurons can synthesize carnosine in the absence of the olfactory bulb. However, the number of carnosine‐immunopositive neurons in the absence of their target is dramatically reduced to less than one‐fourth, whereas the number of olfactory neurons expressing calmodulin messenger RNA is only slightly reduced. The numeric reduction of camosine‐positive neurons in the target‐deprived neuroepithelium is correlated with a dramatic reduction in the survival rate of olfactory neurons, since newly generated olfactory neurons are completely lost 35 days after the bromodeoxyuridine pulse. In contrast, in the normal olfactory neuroepithelium almost one‐third of newly generated olfactory neurons survive 35 days after the bromodeoxyuridine pulse. On the whole, these data indicate that most of the primary olfactory neurons have a short lifespan but that once they have connected with the olfactory bulb they may persist longer, and suggest that throughout adulthood olfactory neurons are overproduced, differentiate independently from their target, and then undergo a process of target‐induced neuronal selection.
Activity in the Precentral Motor Areas After Presentation of Targets for Delayed Reaching Movements Varies with the Initial Arm Position
Authors: Bauswein Erhard , Fromm Christoph 
Published: April 2006

AbstractWe studied single unit activity in the primary motor and premotor cortex during preparation for unrestrained arm movements that the monkey made to a right or left visual target. ‘Set‐related’ activity occurring during an instructed delay period could not only vary with the target location, but also with the initial arm posture which was changed via a motor‐driven forearm support between two positions. Modulation with arm displacement of some cells was contingent upon prior instruction, i.e. it occurred only if a target for the upcoming movement was presented, and for the majority of neurons it was different from the effects caused by the same passive arm shift when being applied before the visual instruction cue. Furthermore, responses to presentation of the same target were found to depend on the starting position of the hand. These findings suggest that both kinaesthetic and visual information interact in motor cortical cells in an appropriate manner for elaborating the movement trajectory.
Development of Light‐activated Pupilloconstriction in Rats as Mediated by Normal and Transplanted Retinae
Authors: Radel J. D. , Das S. , Lund R. D. 
Published: April 2006

AbstractThe relationship between the development of the pupilloconstriction response to changes in light levels and retinal maturation was studied in normal rats and rats that had received intracranial retinal transplants at birth. A pupillary response to light was first observed between postnatal days 7 and 9 in normal rats, and was typically of small amplitude and sluggish. By the time the eyelids first open, 2 weeks after birth, the pupillary response had improved to near adult levels. The inception of the pupillary response correlates with the first appearance of conventional synaptic contacts in the inner and outer plexiform layers of the retina, while improved responses correlate with maturation of photoreceptor outer segments and formation of synaptic ribbons in the inner plexiform layer. When embryonic retinae were transplanted to intracranial locations in newborn hosts and the transplants later illuminated as the host matured, the onset of a pupillary response to transplant illumination was delayed in proportion to the developmental disparity between the transplant and the host. The pattern of anatomical development in transplanted retinae was also similar, but delayed in time, compared to normal retinae. This indicates that the limiting factors for expression of light‐activated pupilloconstriction exist within the retina, rather than being intrinsic to the central nuclei or to the output pathway subserving the response.
Left Unilateral Inferior Pedunculotomy Prevents Neuronal Death During Postnatal Development of the Remaining Left Inferior Olivary Complex in the Rat
Authors: Armengol J. A. , López‐Román A. 
Published: April 2006

AbstractNeuronal death in the inferior olivary complex (IOC) was studied in control and unilaterally pedunculotomized newborn rats, from postnatal day 1 (P1) to P30, in order to test whether the approximately two‐fold increase in available specific targets (i.e. Purkinje cells) that is theoretically provided by sectioning one inferior cerebellar peduncle to the developing climbing fibres of the remaining IOC could prevent the loss of inferior olivary neurons taking place during the first 2 weeks of postnatal life in the rat. Numerical estimation of the number of inferior olivary neurons in control and experimental rats showed that (i) in pedunculotomized rats, the number of inferior olivary neurons of the remaining inferior olivary complex was always greater than that encountered in control rats, (ii) the consistent decrease in the number of inferior olivary neurons observed in control animals between P2 and P8 was absent in cell counts of the pedunculotomized rats, and (iii) the increase in olivary cell number following the phase of cell decrease was also absent in pedunculotomized rats. It is concluded that the increase of available Purkinje cells during early postnatal development of the olivocerebellar projection prevents neuronal death in the remaining inferior olivary complex following pedunculotomy.